TOMOYO Linux Cross Reference
Linux/fs/namespace.c

   // SPDX-License-Identifier: GPL-2.0-only
   /*
    *  linux/fs/namespace.c
    *
    * (C) Copyright Al Viro 2000, 2001
    *
    * Based on code from fs/super.c, copyright Linus Torvalds and others.
    * Heavily rewritten.
    */
  
  #include <linux/syscalls.h>
  #include <linux/export.h>
  #include <linux/capability.h>
  #include <linux/mnt_namespace.h>
  #include <linux/user_namespace.h>
  #include <linux/namei.h>
  #include <linux/security.h>
  #include <linux/cred.h>
  #include <linux/idr.h>
  #include <linux/init.h>         /* init_rootfs */
  #include <linux/fs_struct.h>    /* get_fs_root et.al. */
  #include <linux/fsnotify.h>     /* fsnotify_vfsmount_delete */
  #include <linux/file.h>
  #include <linux/uaccess.h>
  #include <linux/proc_ns.h>
  #include <linux/magic.h>
  #include <linux/memblock.h>
  #include <linux/proc_fs.h>
  #include <linux/task_work.h>
  #include <linux/sched/task.h>
  #include <uapi/linux/mount.h>
  #include <linux/fs_context.h>
  #include <linux/shmem_fs.h>
  #include <linux/mnt_idmapping.h>
  #include <linux/nospec.h>
  
  #include "pnode.h"
  #include "internal.h"
  
  /* Maximum number of mounts in a mount namespace */
  static unsigned int sysctl_mount_max __read_mostly = 100000;
  
  static unsigned int m_hash_mask __ro_after_init;
  static unsigned int m_hash_shift __ro_after_init;
  static unsigned int mp_hash_mask __ro_after_init;
  static unsigned int mp_hash_shift __ro_after_init;
  
  static __initdata unsigned long mhash_entries;
  static int __init set_mhash_entries(char *str)
  {
          if (!str)
                  return 0;
          mhash_entries = simple_strtoul(str, &str, 0);
          return 1;
  }
  __setup("mhash_entries=", set_mhash_entries);
  
  static __initdata unsigned long mphash_entries;
  static int __init set_mphash_entries(char *str)
  {
          if (!str)
                  return 0;
          mphash_entries = simple_strtoul(str, &str, 0);
          return 1;
  }
  __setup("mphash_entries=", set_mphash_entries);
  
  static u64 event;
  static DEFINE_IDA(mnt_id_ida);
  static DEFINE_IDA(mnt_group_ida);
  
  /* Don't allow confusion with old 32bit mount ID */
  #define MNT_UNIQUE_ID_OFFSET (1ULL << 31)
  static atomic64_t mnt_id_ctr = ATOMIC64_INIT(MNT_UNIQUE_ID_OFFSET);
  
  static struct hlist_head *mount_hashtable __ro_after_init;
  static struct hlist_head *mountpoint_hashtable __ro_after_init;
  static struct kmem_cache *mnt_cache __ro_after_init;
  static DECLARE_RWSEM(namespace_sem);
  static HLIST_HEAD(unmounted);   /* protected by namespace_sem */
  static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
  static DEFINE_RWLOCK(mnt_ns_tree_lock);
  static struct rb_root mnt_ns_tree = RB_ROOT; /* protected by mnt_ns_tree_lock */
  
  struct mount_kattr {
          unsigned int attr_set;
          unsigned int attr_clr;
          unsigned int propagation;
          unsigned int lookup_flags;
          bool recurse;
          struct user_namespace *mnt_userns;
          struct mnt_idmap *mnt_idmap;
  };
  
  /* /sys/fs */
  struct kobject *fs_kobj __ro_after_init;
  EXPORT_SYMBOL_GPL(fs_kobj);
  
  /*
  * vfsmount lock may be taken for read to prevent changes to the
  * vfsmount hash, ie. during mountpoint lookups or walking back
  * up the tree.
  *
  * It should be taken for write in all cases where the vfsmount
  * tree or hash is modified or when a vfsmount structure is modified.
  */
 __cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
 
 static int mnt_ns_cmp(u64 seq, const struct mnt_namespace *ns)
 {
         u64 seq_b = ns->seq;
 
         if (seq < seq_b)
                 return -1;
         if (seq > seq_b)
                 return 1;
         return 0;
 }
 
 static inline struct mnt_namespace *node_to_mnt_ns(const struct rb_node *node)
 {
         if (!node)
                 return NULL;
         return rb_entry(node, struct mnt_namespace, mnt_ns_tree_node);
 }
 
 static bool mnt_ns_less(struct rb_node *a, const struct rb_node *b)
 {
         struct mnt_namespace *ns_a = node_to_mnt_ns(a);
         struct mnt_namespace *ns_b = node_to_mnt_ns(b);
         u64 seq_a = ns_a->seq;
 
         return mnt_ns_cmp(seq_a, ns_b) < 0;
 }
 
 static void mnt_ns_tree_add(struct mnt_namespace *ns)
 {
         guard(write_lock)(&mnt_ns_tree_lock);
         rb_add(&ns->mnt_ns_tree_node, &mnt_ns_tree, mnt_ns_less);
 }
 
 static void mnt_ns_release(struct mnt_namespace *ns)
 {
         lockdep_assert_not_held(&mnt_ns_tree_lock);
 
         /* keep alive for {list,stat}mount() */
         if (refcount_dec_and_test(&ns->passive)) {
                 put_user_ns(ns->user_ns);
                 kfree(ns);
         }
 }
 DEFINE_FREE(mnt_ns_release, struct mnt_namespace *, if (_T) mnt_ns_release(_T))
 
 static void mnt_ns_tree_remove(struct mnt_namespace *ns)
 {
         /* remove from global mount namespace list */
         if (!is_anon_ns(ns)) {
                 guard(write_lock)(&mnt_ns_tree_lock);
                 rb_erase(&ns->mnt_ns_tree_node, &mnt_ns_tree);
         }
 
         mnt_ns_release(ns);
 }
 
 /*
  * Returns the mount namespace which either has the specified id, or has the
  * next smallest id afer the specified one.
  */
 static struct mnt_namespace *mnt_ns_find_id_at(u64 mnt_ns_id)
 {
         struct rb_node *node = mnt_ns_tree.rb_node;
         struct mnt_namespace *ret = NULL;
 
         lockdep_assert_held(&mnt_ns_tree_lock);
 
         while (node) {
                 struct mnt_namespace *n = node_to_mnt_ns(node);
 
                 if (mnt_ns_id <= n->seq) {
                         ret = node_to_mnt_ns(node);
                         if (mnt_ns_id == n->seq)
                                 break;
                         node = node->rb_left;
                 } else {
                         node = node->rb_right;
                 }
         }
         return ret;
 }
 
 /*
  * Lookup a mount namespace by id and take a passive reference count. Taking a
  * passive reference means the mount namespace can be emptied if e.g., the last
  * task holding an active reference exits. To access the mounts of the
  * namespace the @namespace_sem must first be acquired. If the namespace has
  * already shut down before acquiring @namespace_sem, {list,stat}mount() will
  * see that the mount rbtree of the namespace is empty.
  */
 static struct mnt_namespace *lookup_mnt_ns(u64 mnt_ns_id)
 {
        struct mnt_namespace *ns;
 
        guard(read_lock)(&mnt_ns_tree_lock);
        ns = mnt_ns_find_id_at(mnt_ns_id);
        if (!ns || ns->seq != mnt_ns_id)
                return NULL;
 
        refcount_inc(&ns->passive);
        return ns;
 }
 
 static inline void lock_mount_hash(void)
 {
         write_seqlock(&mount_lock);
 }
 
 static inline void unlock_mount_hash(void)
 {
         write_sequnlock(&mount_lock);
 }
 
 static inline struct hlist_head *m_hash(struct vfsmount *mnt, struct dentry *dentry)
 {
         unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
         tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
         tmp = tmp + (tmp >> m_hash_shift);
         return &mount_hashtable[tmp & m_hash_mask];
 }
 
 static inline struct hlist_head *mp_hash(struct dentry *dentry)
 {
         unsigned long tmp = ((unsigned long)dentry / L1_CACHE_BYTES);
         tmp = tmp + (tmp >> mp_hash_shift);
         return &mountpoint_hashtable[tmp & mp_hash_mask];
 }
 
 static int mnt_alloc_id(struct mount *mnt)
 {
         int res = ida_alloc(&mnt_id_ida, GFP_KERNEL);
 
         if (res < 0)
                 return res;
         mnt->mnt_id = res;
         mnt->mnt_id_unique = atomic64_inc_return(&mnt_id_ctr);
         return 0;
 }
 
 static void mnt_free_id(struct mount *mnt)
 {
         ida_free(&mnt_id_ida, mnt->mnt_id);
 }
 
 /*
  * Allocate a new peer group ID
  */
 static int mnt_alloc_group_id(struct mount *mnt)
 {
         int res = ida_alloc_min(&mnt_group_ida, 1, GFP_KERNEL);
 
         if (res < 0)
                 return res;
         mnt->mnt_group_id = res;
         return 0;
 }
 
 /*
  * Release a peer group ID
  */
 void mnt_release_group_id(struct mount *mnt)
 {
         ida_free(&mnt_group_ida, mnt->mnt_group_id);
         mnt->mnt_group_id = 0;
 }
 
 /*
  * vfsmount lock must be held for read
  */
 static inline void mnt_add_count(struct mount *mnt, int n)
 {
 #ifdef CONFIG_SMP
         this_cpu_add(mnt->mnt_pcp->mnt_count, n);
 #else
         preempt_disable();
         mnt->mnt_count += n;
         preempt_enable();
 #endif
 }
 
 /*
  * vfsmount lock must be held for write
  */
 int mnt_get_count(struct mount *mnt)
 {
 #ifdef CONFIG_SMP
         int count = 0;
         int cpu;
 
         for_each_possible_cpu(cpu) {
                 count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
         }
 
         return count;
 #else
         return mnt->mnt_count;
 #endif
 }
 
 static struct mount *alloc_vfsmnt(const char *name)
 {
         struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
         if (mnt) {
                 int err;
 
                 err = mnt_alloc_id(mnt);
                 if (err)
                         goto out_free_cache;
 
                 if (name) {
                         mnt->mnt_devname = kstrdup_const(name,
                                                          GFP_KERNEL_ACCOUNT);
                         if (!mnt->mnt_devname)
                                 goto out_free_id;
                 }
 
 #ifdef CONFIG_SMP
                 mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
                 if (!mnt->mnt_pcp)
                         goto out_free_devname;
 
                 this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
 #else
                 mnt->mnt_count = 1;
                 mnt->mnt_writers = 0;
 #endif
 
                 INIT_HLIST_NODE(&mnt->mnt_hash);
                 INIT_LIST_HEAD(&mnt->mnt_child);
                 INIT_LIST_HEAD(&mnt->mnt_mounts);
                 INIT_LIST_HEAD(&mnt->mnt_list);
                 INIT_LIST_HEAD(&mnt->mnt_expire);
                 INIT_LIST_HEAD(&mnt->mnt_share);
                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
                 INIT_LIST_HEAD(&mnt->mnt_slave);
                 INIT_HLIST_NODE(&mnt->mnt_mp_list);
                 INIT_LIST_HEAD(&mnt->mnt_umounting);
                 INIT_HLIST_HEAD(&mnt->mnt_stuck_children);
                 mnt->mnt.mnt_idmap = &nop_mnt_idmap;
         }
         return mnt;
 
 #ifdef CONFIG_SMP
 out_free_devname:
         kfree_const(mnt->mnt_devname);
 #endif
 out_free_id:
         mnt_free_id(mnt);
 out_free_cache:
         kmem_cache_free(mnt_cache, mnt);
         return NULL;
 }
 
 /*
  * Most r/o checks on a fs are for operations that take
  * discrete amounts of time, like a write() or unlink().
  * We must keep track of when those operations start
  * (for permission checks) and when they end, so that
  * we can determine when writes are able to occur to
  * a filesystem.
  */
 /*
  * __mnt_is_readonly: check whether a mount is read-only
  * @mnt: the mount to check for its write status
  *
  * This shouldn't be used directly ouside of the VFS.
  * It does not guarantee that the filesystem will stay
  * r/w, just that it is right *now*.  This can not and
  * should not be used in place of IS_RDONLY(inode).
  * mnt_want/drop_write() will _keep_ the filesystem
  * r/w.
  */
 bool __mnt_is_readonly(struct vfsmount *mnt)
 {
         return (mnt->mnt_flags & MNT_READONLY) || sb_rdonly(mnt->mnt_sb);
 }
 EXPORT_SYMBOL_GPL(__mnt_is_readonly);
 
 static inline void mnt_inc_writers(struct mount *mnt)
 {
 #ifdef CONFIG_SMP
         this_cpu_inc(mnt->mnt_pcp->mnt_writers);
 #else
         mnt->mnt_writers++;
 #endif
 }
 
 static inline void mnt_dec_writers(struct mount *mnt)
 {
 #ifdef CONFIG_SMP
         this_cpu_dec(mnt->mnt_pcp->mnt_writers);
 #else
         mnt->mnt_writers--;
 #endif
 }
 
 static unsigned int mnt_get_writers(struct mount *mnt)
 {
 #ifdef CONFIG_SMP
         unsigned int count = 0;
         int cpu;
 
         for_each_possible_cpu(cpu) {
                 count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
         }
 
         return count;
 #else
         return mnt->mnt_writers;
 #endif
 }
 
 static int mnt_is_readonly(struct vfsmount *mnt)
 {
         if (READ_ONCE(mnt->mnt_sb->s_readonly_remount))
                 return 1;
         /*
          * The barrier pairs with the barrier in sb_start_ro_state_change()
          * making sure if we don't see s_readonly_remount set yet, we also will
          * not see any superblock / mount flag changes done by remount.
          * It also pairs with the barrier in sb_end_ro_state_change()
          * assuring that if we see s_readonly_remount already cleared, we will
          * see the values of superblock / mount flags updated by remount.
          */
         smp_rmb();
         return __mnt_is_readonly(mnt);
 }
 
 /*
  * Most r/o & frozen checks on a fs are for operations that take discrete
  * amounts of time, like a write() or unlink().  We must keep track of when
  * those operations start (for permission checks) and when they end, so that we
  * can determine when writes are able to occur to a filesystem.
  */
 /**
  * mnt_get_write_access - get write access to a mount without freeze protection
  * @m: the mount on which to take a write
  *
  * This tells the low-level filesystem that a write is about to be performed to
  * it, and makes sure that writes are allowed (mnt it read-write) before
  * returning success. This operation does not protect against filesystem being
  * frozen. When the write operation is finished, mnt_put_write_access() must be
  * called. This is effectively a refcount.
  */
 int mnt_get_write_access(struct vfsmount *m)
 {
         struct mount *mnt = real_mount(m);
         int ret = 0;
 
         preempt_disable();
         mnt_inc_writers(mnt);
         /*
          * The store to mnt_inc_writers must be visible before we pass
          * MNT_WRITE_HOLD loop below, so that the slowpath can see our
          * incremented count after it has set MNT_WRITE_HOLD.
          */
         smp_mb();
         might_lock(&mount_lock.lock);
         while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD) {
                 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
                         cpu_relax();
                 } else {
                         /*
                          * This prevents priority inversion, if the task
                          * setting MNT_WRITE_HOLD got preempted on a remote
                          * CPU, and it prevents life lock if the task setting
                          * MNT_WRITE_HOLD has a lower priority and is bound to
                          * the same CPU as the task that is spinning here.
                          */
                         preempt_enable();
                         lock_mount_hash();
                         unlock_mount_hash();
                         preempt_disable();
                 }
         }
         /*
          * The barrier pairs with the barrier sb_start_ro_state_change() making
          * sure that if we see MNT_WRITE_HOLD cleared, we will also see
          * s_readonly_remount set (or even SB_RDONLY / MNT_READONLY flags) in
          * mnt_is_readonly() and bail in case we are racing with remount
          * read-only.
          */
         smp_rmb();
         if (mnt_is_readonly(m)) {
                 mnt_dec_writers(mnt);
                 ret = -EROFS;
         }
         preempt_enable();
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(mnt_get_write_access);
 
 /**
  * mnt_want_write - get write access to a mount
  * @m: the mount on which to take a write
  *
  * This tells the low-level filesystem that a write is about to be performed to
  * it, and makes sure that writes are allowed (mount is read-write, filesystem
  * is not frozen) before returning success.  When the write operation is
  * finished, mnt_drop_write() must be called.  This is effectively a refcount.
  */
 int mnt_want_write(struct vfsmount *m)
 {
         int ret;
 
         sb_start_write(m->mnt_sb);
         ret = mnt_get_write_access(m);
         if (ret)
                 sb_end_write(m->mnt_sb);
         return ret;
 }
 EXPORT_SYMBOL_GPL(mnt_want_write);
 
 /**
  * mnt_get_write_access_file - get write access to a file's mount
  * @file: the file who's mount on which to take a write
  *
  * This is like mnt_get_write_access, but if @file is already open for write it
  * skips incrementing mnt_writers (since the open file already has a reference)
  * and instead only does the check for emergency r/o remounts.  This must be
  * paired with mnt_put_write_access_file.
  */
 int mnt_get_write_access_file(struct file *file)
 {
         if (file->f_mode & FMODE_WRITER) {
                 /*
                  * Superblock may have become readonly while there are still
                  * writable fd's, e.g. due to a fs error with errors=remount-ro
                  */
                 if (__mnt_is_readonly(file->f_path.mnt))
                         return -EROFS;
                 return 0;
         }
         return mnt_get_write_access(file->f_path.mnt);
 }
 
 /**
  * mnt_want_write_file - get write access to a file's mount
  * @file: the file who's mount on which to take a write
  *
  * This is like mnt_want_write, but if the file is already open for writing it
  * skips incrementing mnt_writers (since the open file already has a reference)
  * and instead only does the freeze protection and the check for emergency r/o
  * remounts.  This must be paired with mnt_drop_write_file.
  */
 int mnt_want_write_file(struct file *file)
 {
         int ret;
 
         sb_start_write(file_inode(file)->i_sb);
         ret = mnt_get_write_access_file(file);
         if (ret)
                 sb_end_write(file_inode(file)->i_sb);
         return ret;
 }
 EXPORT_SYMBOL_GPL(mnt_want_write_file);
 
 /**
  * mnt_put_write_access - give up write access to a mount
  * @mnt: the mount on which to give up write access
  *
  * Tells the low-level filesystem that we are done
  * performing writes to it.  Must be matched with
  * mnt_get_write_access() call above.
  */
 void mnt_put_write_access(struct vfsmount *mnt)
 {
         preempt_disable();
         mnt_dec_writers(real_mount(mnt));
         preempt_enable();
 }
 EXPORT_SYMBOL_GPL(mnt_put_write_access);
 
 /**
  * mnt_drop_write - give up write access to a mount
  * @mnt: the mount on which to give up write access
  *
  * Tells the low-level filesystem that we are done performing writes to it and
  * also allows filesystem to be frozen again.  Must be matched with
  * mnt_want_write() call above.
  */
 void mnt_drop_write(struct vfsmount *mnt)
 {
         mnt_put_write_access(mnt);
         sb_end_write(mnt->mnt_sb);
 }
 EXPORT_SYMBOL_GPL(mnt_drop_write);
 
 void mnt_put_write_access_file(struct file *file)
 {
         if (!(file->f_mode & FMODE_WRITER))
                 mnt_put_write_access(file->f_path.mnt);
 }
 
 void mnt_drop_write_file(struct file *file)
 {
         mnt_put_write_access_file(file);
         sb_end_write(file_inode(file)->i_sb);
 }
 EXPORT_SYMBOL(mnt_drop_write_file);
 
 /**
  * mnt_hold_writers - prevent write access to the given mount
  * @mnt: mnt to prevent write access to
  *
  * Prevents write access to @mnt if there are no active writers for @mnt.
  * This function needs to be called and return successfully before changing
  * properties of @mnt that need to remain stable for callers with write access
  * to @mnt.
  *
  * After this functions has been called successfully callers must pair it with
  * a call to mnt_unhold_writers() in order to stop preventing write access to
  * @mnt.
  *
  * Context: This function expects lock_mount_hash() to be held serializing
  *          setting MNT_WRITE_HOLD.
  * Return: On success 0 is returned.
  *         On error, -EBUSY is returned.
  */
 static inline int mnt_hold_writers(struct mount *mnt)
 {
         mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
         /*
          * After storing MNT_WRITE_HOLD, we'll read the counters. This store
          * should be visible before we do.
          */
         smp_mb();
 
         /*
          * With writers on hold, if this value is zero, then there are
          * definitely no active writers (although held writers may subsequently
          * increment the count, they'll have to wait, and decrement it after
          * seeing MNT_READONLY).
          *
          * It is OK to have counter incremented on one CPU and decremented on
          * another: the sum will add up correctly. The danger would be when we
          * sum up each counter, if we read a counter before it is incremented,
          * but then read another CPU's count which it has been subsequently
          * decremented from -- we would see more decrements than we should.
          * MNT_WRITE_HOLD protects against this scenario, because
          * mnt_want_write first increments count, then smp_mb, then spins on
          * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
          * we're counting up here.
          */
         if (mnt_get_writers(mnt) > 0)
                 return -EBUSY;
 
         return 0;
 }
 
 /**
  * mnt_unhold_writers - stop preventing write access to the given mount
  * @mnt: mnt to stop preventing write access to
  *
  * Stop preventing write access to @mnt allowing callers to gain write access
  * to @mnt again.
  *
  * This function can only be called after a successful call to
  * mnt_hold_writers().
  *
  * Context: This function expects lock_mount_hash() to be held.
  */
 static inline void mnt_unhold_writers(struct mount *mnt)
 {
         /*
          * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
          * that become unheld will see MNT_READONLY.
          */
         smp_wmb();
         mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
 }
 
 static int mnt_make_readonly(struct mount *mnt)
 {
         int ret;
 
         ret = mnt_hold_writers(mnt);
         if (!ret)
                 mnt->mnt.mnt_flags |= MNT_READONLY;
         mnt_unhold_writers(mnt);
         return ret;
 }
 
 int sb_prepare_remount_readonly(struct super_block *sb)
 {
         struct mount *mnt;
         int err = 0;
 
         /* Racy optimization.  Recheck the counter under MNT_WRITE_HOLD */
         if (atomic_long_read(&sb->s_remove_count))
                 return -EBUSY;
 
         lock_mount_hash();
         list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
                 if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
                         err = mnt_hold_writers(mnt);
                         if (err)
                                 break;
                 }
         }
         if (!err && atomic_long_read(&sb->s_remove_count))
                 err = -EBUSY;
 
         if (!err)
                 sb_start_ro_state_change(sb);
         list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
                 if (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
                         mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
         }
         unlock_mount_hash();
 
         return err;
 }
 
 static void free_vfsmnt(struct mount *mnt)
 {
         mnt_idmap_put(mnt_idmap(&mnt->mnt));
         kfree_const(mnt->mnt_devname);
 #ifdef CONFIG_SMP
         free_percpu(mnt->mnt_pcp);
 #endif
         kmem_cache_free(mnt_cache, mnt);
 }
 
 static void delayed_free_vfsmnt(struct rcu_head *head)
 {
         free_vfsmnt(container_of(head, struct mount, mnt_rcu));
 }
 
 /* call under rcu_read_lock */
 int __legitimize_mnt(struct vfsmount *bastard, unsigned seq)
 {
         struct mount *mnt;
         if (read_seqretry(&mount_lock, seq))
                 return 1;
         if (bastard == NULL)
                 return 0;
         mnt = real_mount(bastard);
         mnt_add_count(mnt, 1);
         smp_mb();                       // see mntput_no_expire()
         if (likely(!read_seqretry(&mount_lock, seq)))
                 return 0;
         if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
                 mnt_add_count(mnt, -1);
                 return 1;
         }
         lock_mount_hash();
         if (unlikely(bastard->mnt_flags & MNT_DOOMED)) {
                 mnt_add_count(mnt, -1);
                 unlock_mount_hash();
                 return 1;
         }
         unlock_mount_hash();
         /* caller will mntput() */
         return -1;
 }
 
 /* call under rcu_read_lock */
 static bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
 {
         int res = __legitimize_mnt(bastard, seq);
         if (likely(!res))
                 return true;
         if (unlikely(res < 0)) {
                 rcu_read_unlock();
                 mntput(bastard);
                 rcu_read_lock();
         }
         return false;
 }
 
 /**
  * __lookup_mnt - find first child mount
  * @mnt:        parent mount
  * @dentry:     mountpoint
  *
  * If @mnt has a child mount @c mounted @dentry find and return it.
  *
  * Note that the child mount @c need not be unique. There are cases
  * where shadow mounts are created. For example, during mount
  * propagation when a source mount @mnt whose root got overmounted by a
  * mount @o after path lookup but before @namespace_sem could be
  * acquired gets copied and propagated. So @mnt gets copied including
  * @o. When @mnt is propagated to a destination mount @d that already
  * has another mount @n mounted at the same mountpoint then the source
  * mount @mnt will be tucked beneath @n, i.e., @n will be mounted on
  * @mnt and @mnt mounted on @d. Now both @n and @o are mounted at @mnt
  * on @dentry.
  *
  * Return: The first child of @mnt mounted @dentry or NULL.
  */
 struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
 {
         struct hlist_head *head = m_hash(mnt, dentry);
         struct mount *p;
 
         hlist_for_each_entry_rcu(p, head, mnt_hash)
                 if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
                         return p;
         return NULL;
 }
 
 /*
  * lookup_mnt - Return the first child mount mounted at path
  *
  * "First" means first mounted chronologically.  If you create the
  * following mounts:
  *
  * mount /dev/sda1 /mnt
  * mount /dev/sda2 /mnt
  * mount /dev/sda3 /mnt
  *
  * Then lookup_mnt() on the base /mnt dentry in the root mount will
  * return successively the root dentry and vfsmount of /dev/sda1, then
  * /dev/sda2, then /dev/sda3, then NULL.
  *
  * lookup_mnt takes a reference to the found vfsmount.
  */
 struct vfsmount *lookup_mnt(const struct path *path)
 {
         struct mount *child_mnt;
         struct vfsmount *m;
         unsigned seq;
 
         rcu_read_lock();
         do {
                 seq = read_seqbegin(&mount_lock);
                 child_mnt = __lookup_mnt(path->mnt, path->dentry);
                 m = child_mnt ? &child_mnt->mnt : NULL;
         } while (!legitimize_mnt(m, seq));
         rcu_read_unlock();
         return m;
 }
 
 /*
  * __is_local_mountpoint - Test to see if dentry is a mountpoint in the
  *                         current mount namespace.
  *
  * The common case is dentries are not mountpoints at all and that
  * test is handled inline.  For the slow case when we are actually
  * dealing with a mountpoint of some kind, walk through all of the
  * mounts in the current mount namespace and test to see if the dentry
  * is a mountpoint.
  *
  * The mount_hashtable is not usable in the context because we
  * need to identify all mounts that may be in the current mount
  * namespace not just a mount that happens to have some specified
  * parent mount.
  */
 bool __is_local_mountpoint(struct dentry *dentry)
 {
         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
         struct mount *mnt, *n;
         bool is_covered = false;
 
         down_read(&namespace_sem);
         rbtree_postorder_for_each_entry_safe(mnt, n, &ns->mounts, mnt_node) {
                 is_covered = (mnt->mnt_mountpoint == dentry);
                 if (is_covered)
                         break;
         }
         up_read(&namespace_sem);
 
         return is_covered;
 }
 
 static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
 {
         struct hlist_head *chain = mp_hash(dentry);
         struct mountpoint *mp;
 
         hlist_for_each_entry(mp, chain, m_hash) {
                 if (mp->m_dentry == dentry) {
                         mp->m_count++;
                         return mp;
                 }
         }
         return NULL;
 }
 
 static struct mountpoint *get_mountpoint(struct dentry *dentry)
 {
         struct mountpoint *mp, *new = NULL;
         int ret;
 
         if (d_mountpoint(dentry)) {
                 /* might be worth a WARN_ON() */
                 if (d_unlinked(dentry))
                         return ERR_PTR(-ENOENT);
 mountpoint:
                 read_seqlock_excl(&mount_lock);
                 mp = lookup_mountpoint(dentry);
                 read_sequnlock_excl(&mount_lock);
                 if (mp)
                         goto done;
         }
 
         if (!new)
                 new = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
         if (!new)
                 return ERR_PTR(-ENOMEM);
 
 
         /* Exactly one processes may set d_mounted */
         ret = d_set_mounted(dentry);
 
         /* Someone else set d_mounted? */
         if (ret == -EBUSY)
                 goto mountpoint;
 
         /* The dentry is not available as a mountpoint? */
         mp = ERR_PTR(ret);
         if (ret)
                 goto done;
 
         /* Add the new mountpoint to the hash table */
         read_seqlock_excl(&mount_lock);
         new->m_dentry = dget(dentry);
         new->m_count = 1;
         hlist_add_head(&new->m_hash, mp_hash(dentry));
         INIT_HLIST_HEAD(&new->m_list);
         read_sequnlock_excl(&mount_lock);
 
         mp = new;
         new = NULL;
 done:
         kfree(new);
         return mp;
 }
 
 /*
  * vfsmount lock must be held.  Additionally, the caller is responsible
  * for serializing calls for given disposal list.
  */
 static void __put_mountpoint(struct mountpoint *mp, struct list_head *list)
 {
         if (!--mp->m_count) {
                 struct dentry *dentry = mp->m_dentry;
                 BUG_ON(!hlist_empty(&mp->m_list));
                 spin_lock(&dentry->d_lock);
                 dentry->d_flags &= ~DCACHE_MOUNTED;
                 spin_unlock(&dentry->d_lock);
                 dput_to_list(dentry, list);
                 hlist_del(&mp->m_hash);
                 kfree(mp);
         }
 }
 
 /* called with namespace_lock and vfsmount lock */
 static void put_mountpoint(struct mountpoint *mp)
 {
         __put_mountpoint(mp, &ex_mountpoints);
 }
 
 static inline int check_mnt(struct mount *mnt)
 {
         return mnt->mnt_ns == current->nsproxy->mnt_ns;
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void touch_mnt_namespace(struct mnt_namespace *ns)
 {
         if (ns) {
                 ns->event = ++event;
                 wake_up_interruptible(&ns->poll);
         }
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void __touch_mnt_namespace(struct mnt_namespace *ns)
 {
         if (ns && ns->event != event) {
                 ns->event = event;
                 wake_up_interruptible(&ns->poll);
         }
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static struct mountpoint *unhash_mnt(struct mount *mnt)
 {
         struct mountpoint *mp;
         mnt->mnt_parent = mnt;
         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
         list_del_init(&mnt->mnt_child);
         hlist_del_init_rcu(&mnt->mnt_hash);
         hlist_del_init(&mnt->mnt_mp_list);
         mp = mnt->mnt_mp;
         mnt->mnt_mp = NULL;
         return mp;
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void umount_mnt(struct mount *mnt)
 {
         put_mountpoint(unhash_mnt(mnt));
 }
 
 /*
  * vfsmount lock must be held for write
  */
 void mnt_set_mountpoint(struct mount *mnt,
                         struct mountpoint *mp,
                         struct mount *child_mnt)
 {
         mp->m_count++;
         mnt_add_count(mnt, 1);  /* essentially, that's mntget */
         child_mnt->mnt_mountpoint = mp->m_dentry;
         child_mnt->mnt_parent = mnt;
         child_mnt->mnt_mp = mp;
         hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
 }
 
 /**
  * mnt_set_mountpoint_beneath - mount a mount beneath another one
  *
  * @new_parent: the source mount
  * @top_mnt:    the mount beneath which @new_parent is mounted
  * @new_mp:     the new mountpoint of @top_mnt on @new_parent
  *
  * Remove @top_mnt from its current mountpoint @top_mnt->mnt_mp and
  * parent @top_mnt->mnt_parent and mount it on top of @new_parent at
  * @new_mp. And mount @new_parent on the old parent and old
  * mountpoint of @top_mnt.
  *
  * Context: This function expects namespace_lock() and lock_mount_hash()
  *          to have been acquired in that order.
  */
 static void mnt_set_mountpoint_beneath(struct mount *new_parent,
                                        struct mount *top_mnt,
                                        struct mountpoint *new_mp)
 {
         struct mount *old_top_parent = top_mnt->mnt_parent;
         struct mountpoint *old_top_mp = top_mnt->mnt_mp;
 
         mnt_set_mountpoint(old_top_parent, old_top_mp, new_parent);
         mnt_change_mountpoint(new_parent, new_mp, top_mnt);
 }
 
 
 static void __attach_mnt(struct mount *mnt, struct mount *parent)
 {
         hlist_add_head_rcu(&mnt->mnt_hash,
                            m_hash(&parent->mnt, mnt->mnt_mountpoint));
         list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 }
 
 /**
  * attach_mnt - mount a mount, attach to @mount_hashtable and parent's
  *              list of child mounts
  * @parent:  the parent
  * @mnt:     the new mount
  * @mp:      the new mountpoint
  * @beneath: whether to mount @mnt beneath or on top of @parent
  *
  * If @beneath is false, mount @mnt at @mp on @parent. Then attach @mnt
  * to @parent's child mount list and to @mount_hashtable.
  *
  * If @beneath is true, remove @mnt from its current parent and
  * mountpoint and mount it on @mp on @parent, and mount @parent on the
  * old parent and old mountpoint of @mnt. Finally, attach @parent to
  * @mnt_hashtable and @parent->mnt_parent->mnt_mounts.
  *
  * Note, when __attach_mnt() is called @mnt->mnt_parent already points
  * to the correct parent.
  *
  * Context: This function expects namespace_lock() and lock_mount_hash()
  *          to have been acquired in that order.
  */
 static void attach_mnt(struct mount *mnt, struct mount *parent,
                        struct mountpoint *mp, bool beneath)
 {
         if (beneath)
                 mnt_set_mountpoint_beneath(mnt, parent, mp);
         else
                 mnt_set_mountpoint(parent, mp, mnt);
         /*
          * Note, @mnt->mnt_parent has to be used. If @mnt was mounted
          * beneath @parent then @mnt will need to be attached to
          * @parent's old parent, not @parent. IOW, @mnt->mnt_parent
          * isn't the same mount as @parent.
          */
         __attach_mnt(mnt, mnt->mnt_parent);
 }
 
 void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt)
 {
         struct mountpoint *old_mp = mnt->mnt_mp;
         struct mount *old_parent = mnt->mnt_parent;
 
         list_del_init(&mnt->mnt_child);
         hlist_del_init(&mnt->mnt_mp_list);
         hlist_del_init_rcu(&mnt->mnt_hash);
 
         attach_mnt(mnt, parent, mp, false);
 
         put_mountpoint(old_mp);
         mnt_add_count(old_parent, -1);
 }
 
 static inline struct mount *node_to_mount(struct rb_node *node)
 {
         return node ? rb_entry(node, struct mount, mnt_node) : NULL;
 }
 
 static void mnt_add_to_ns(struct mnt_namespace *ns, struct mount *mnt)
 {
         struct rb_node **link = &ns->mounts.rb_node;
         struct rb_node *parent = NULL;
 
         WARN_ON(mnt->mnt.mnt_flags & MNT_ONRB);
         mnt->mnt_ns = ns;
         while (*link) {
                 parent = *link;
                 if (mnt->mnt_id_unique < node_to_mount(parent)->mnt_id_unique)
                         link = &parent->rb_left;
                 else
                         link = &parent->rb_right;
         }
         rb_link_node(&mnt->mnt_node, parent, link);
         rb_insert_color(&mnt->mnt_node, &ns->mounts);
         mnt->mnt.mnt_flags |= MNT_ONRB;
 }
 
 /*
  * vfsmount lock must be held for write
  */
 static void commit_tree(struct mount *mnt)
 {
         struct mount *parent = mnt->mnt_parent;
         struct mount *m;
         LIST_HEAD(head);
         struct mnt_namespace *n = parent->mnt_ns;
 
         BUG_ON(parent == mnt);
 
         list_add_tail(&head, &mnt->mnt_list);
         while (!list_empty(&head)) {
                 m = list_first_entry(&head, typeof(*m), mnt_list);
                 list_del(&m->mnt_list);
 
                 mnt_add_to_ns(n, m);
         }
         n->nr_mounts += n->pending_mounts;
         n->pending_mounts = 0;
 
         __attach_mnt(mnt, parent);
         touch_mnt_namespace(n);
 }
 
 static struct mount *next_mnt(struct mount *p, struct mount *root)
 {
         struct list_head *next = p->mnt_mounts.next;
         if (next == &p->mnt_mounts) {
                 while (1) {
                         if (p == root)
                                 return NULL;
                         next = p->mnt_child.next;
                         if (next != &p->mnt_parent->mnt_mounts)
                                 break;
                         p = p->mnt_parent;
                 }
         }
         return list_entry(next, struct mount, mnt_child);
 }
 
 static struct mount *skip_mnt_tree(struct mount *p)
 {
         struct list_head *prev = p->mnt_mounts.prev;
         while (prev != &p->mnt_mounts) {
                 p = list_entry(prev, struct mount, mnt_child);
                 prev = p->mnt_mounts.prev;
         }
         return p;
 }
 
 /**
  * vfs_create_mount - Create a mount for a configured superblock
  * @fc: The configuration context with the superblock attached
  *
  * Create a mount to an already configured superblock.  If necessary, the
  * caller should invoke vfs_get_tree() before calling this.
  *
  * Note that this does not attach the mount to anything.
  */
 struct vfsmount *vfs_create_mount(struct fs_context *fc)
 {
         struct mount *mnt;
 
         if (!fc->root)
                 return ERR_PTR(-EINVAL);
 
         mnt = alloc_vfsmnt(fc->source ?: "none");
         if (!mnt)
                 return ERR_PTR(-ENOMEM);
 
         if (fc->sb_flags & SB_KERNMOUNT)
                 mnt->mnt.mnt_flags = MNT_INTERNAL;
 
         atomic_inc(&fc->root->d_sb->s_active);
         mnt->mnt.mnt_sb         = fc->root->d_sb;
         mnt->mnt.mnt_root       = dget(fc->root);
         mnt->mnt_mountpoint     = mnt->mnt.mnt_root;
         mnt->mnt_parent         = mnt;
 
         lock_mount_hash();
         list_add_tail(&mnt->mnt_instance, &mnt->mnt.mnt_sb->s_mounts);
         unlock_mount_hash();
         return &mnt->mnt;
 }
 EXPORT_SYMBOL(vfs_create_mount);
 
 struct vfsmount *fc_mount(struct fs_context *fc)
 {
         int err = vfs_get_tree(fc);
         if (!err) {
                 up_write(&fc->root->d_sb->s_umount);
                 return vfs_create_mount(fc);
         }
         return ERR_PTR(err);
 }
 EXPORT_SYMBOL(fc_mount);
 
 struct vfsmount *vfs_kern_mount(struct file_system_type *type,
                                 int flags, const char *name,
                                 void *data)
 {
         struct fs_context *fc;
         struct vfsmount *mnt;
         int ret = 0;
 
         if (!type)
                 return ERR_PTR(-EINVAL);
 
         fc = fs_context_for_mount(type, flags);
         if (IS_ERR(fc))
                 return ERR_CAST(fc);
 
         if (name)
                 ret = vfs_parse_fs_string(fc, "source",
                                           name, strlen(name));
         if (!ret)
                 ret = parse_monolithic_mount_data(fc, data);
         if (!ret)
                 mnt = fc_mount(fc);
         else
                 mnt = ERR_PTR(ret);
 
         put_fs_context(fc);
         return mnt;
 }
 EXPORT_SYMBOL_GPL(vfs_kern_mount);
 
 struct vfsmount *
 vfs_submount(const struct dentry *mountpoint, struct file_system_type *type,
              const char *name, void *data)
 {
         /* Until it is worked out how to pass the user namespace
          * through from the parent mount to the submount don't support
          * unprivileged mounts with submounts.
          */
         if (mountpoint->d_sb->s_user_ns != &init_user_ns)
                 return ERR_PTR(-EPERM);
 
         return vfs_kern_mount(type, SB_SUBMOUNT, name, data);
 }
 EXPORT_SYMBOL_GPL(vfs_submount);
 
 static struct mount *clone_mnt(struct mount *old, struct dentry *root,
                                         int flag)
 {
         struct super_block *sb = old->mnt.mnt_sb;
         struct mount *mnt;
         int err;
 
         mnt = alloc_vfsmnt(old->mnt_devname);
         if (!mnt)
                 return ERR_PTR(-ENOMEM);
 
         if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
                 mnt->mnt_group_id = 0; /* not a peer of original */
         else
                 mnt->mnt_group_id = old->mnt_group_id;
 
         if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
                 err = mnt_alloc_group_id(mnt);
                 if (err)
                         goto out_free;
         }
 
         mnt->mnt.mnt_flags = old->mnt.mnt_flags;
         mnt->mnt.mnt_flags &= ~(MNT_WRITE_HOLD|MNT_MARKED|MNT_INTERNAL|MNT_ONRB);
 
         atomic_inc(&sb->s_active);
         mnt->mnt.mnt_idmap = mnt_idmap_get(mnt_idmap(&old->mnt));
 
         mnt->mnt.mnt_sb = sb;
         mnt->mnt.mnt_root = dget(root);
         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
         mnt->mnt_parent = mnt;
         lock_mount_hash();
         list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
         unlock_mount_hash();
 
         if ((flag & CL_SLAVE) ||
             ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
                 list_add(&mnt->mnt_slave, &old->mnt_slave_list);
                 mnt->mnt_master = old;
                 CLEAR_MNT_SHARED(mnt);
         } else if (!(flag & CL_PRIVATE)) {
                 if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
                         list_add(&mnt->mnt_share, &old->mnt_share);
                 if (IS_MNT_SLAVE(old))
                         list_add(&mnt->mnt_slave, &old->mnt_slave);
                 mnt->mnt_master = old->mnt_master;
         } else {
                 CLEAR_MNT_SHARED(mnt);
         }
         if (flag & CL_MAKE_SHARED)
                 set_mnt_shared(mnt);
 
         /* stick the duplicate mount on the same expiry list
          * as the original if that was on one */
         if (flag & CL_EXPIRE) {
                 if (!list_empty(&old->mnt_expire))
                         list_add(&mnt->mnt_expire, &old->mnt_expire);
         }
 
         return mnt;
 
  out_free:
         mnt_free_id(mnt);
         free_vfsmnt(mnt);
         return ERR_PTR(err);
 }
 
 static void cleanup_mnt(struct mount *mnt)
 {
         struct hlist_node *p;
         struct mount *m;
         /*
          * The warning here probably indicates that somebody messed
          * up a mnt_want/drop_write() pair.  If this happens, the
          * filesystem was probably unable to make r/w->r/o transitions.
          * The locking used to deal with mnt_count decrement provides barriers,
          * so mnt_get_writers() below is safe.
          */
         WARN_ON(mnt_get_writers(mnt));
         if (unlikely(mnt->mnt_pins.first))
                 mnt_pin_kill(mnt);
         hlist_for_each_entry_safe(m, p, &mnt->mnt_stuck_children, mnt_umount) {
                 hlist_del(&m->mnt_umount);
                 mntput(&m->mnt);
         }
         fsnotify_vfsmount_delete(&mnt->mnt);
         dput(mnt->mnt.mnt_root);
         deactivate_super(mnt->mnt.mnt_sb);
         mnt_free_id(mnt);
         call_rcu(&mnt->mnt_rcu, delayed_free_vfsmnt);
 }
 
 static void __cleanup_mnt(struct rcu_head *head)
 {
         cleanup_mnt(container_of(head, struct mount, mnt_rcu));
 }
 
 static LLIST_HEAD(delayed_mntput_list);
 static void delayed_mntput(struct work_struct *unused)
 {
         struct llist_node *node = llist_del_all(&delayed_mntput_list);
         struct mount *m, *t;
 
         llist_for_each_entry_safe(m, t, node, mnt_llist)
                 cleanup_mnt(m);
 }
 static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
 
 static void mntput_no_expire(struct mount *mnt)
 {
         LIST_HEAD(list);
         int count;
 
         rcu_read_lock();
         if (likely(READ_ONCE(mnt->mnt_ns))) {
                 /*
                  * Since we don't do lock_mount_hash() here,
                  * ->mnt_ns can change under us.  However, if it's
                  * non-NULL, then there's a reference that won't
                  * be dropped until after an RCU delay done after
                  * turning ->mnt_ns NULL.  So if we observe it
                  * non-NULL under rcu_read_lock(), the reference
                  * we are dropping is not the final one.
                  */
                 mnt_add_count(mnt, -1);
                 rcu_read_unlock();
                 return;
         }
         lock_mount_hash();
         /*
          * make sure that if __legitimize_mnt() has not seen us grab
          * mount_lock, we'll see their refcount increment here.
          */
         smp_mb();
         mnt_add_count(mnt, -1);
         count = mnt_get_count(mnt);
         if (count != 0) {
                 WARN_ON(count < 0);
                 rcu_read_unlock();
                 unlock_mount_hash();
                 return;
         }
         if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
                 rcu_read_unlock();
                 unlock_mount_hash();
                 return;
         }
         mnt->mnt.mnt_flags |= MNT_DOOMED;
         rcu_read_unlock();
 
         list_del(&mnt->mnt_instance);
 
         if (unlikely(!list_empty(&mnt->mnt_mounts))) {
                 struct mount *p, *tmp;
                 list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
                         __put_mountpoint(unhash_mnt(p), &list);
                         hlist_add_head(&p->mnt_umount, &mnt->mnt_stuck_children);
                 }
         }
         unlock_mount_hash();
         shrink_dentry_list(&list);
 
         if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
                 struct task_struct *task = current;
                 if (likely(!(task->flags & PF_KTHREAD))) {
                         init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
                         if (!task_work_add(task, &mnt->mnt_rcu, TWA_RESUME))
                                 return;
                 }
                 if (llist_add(&mnt->mnt_llist, &delayed_mntput_list))
                         schedule_delayed_work(&delayed_mntput_work, 1);
                 return;
         }
         cleanup_mnt(mnt);
 }
 
 void mntput(struct vfsmount *mnt)
 {
         if (mnt) {
                 struct mount *m = real_mount(mnt);
                 /* avoid cacheline pingpong */
                 if (unlikely(m->mnt_expiry_mark))
                         WRITE_ONCE(m->mnt_expiry_mark, 0);
                 mntput_no_expire(m);
         }
 }
 EXPORT_SYMBOL(mntput);
 
 struct vfsmount *mntget(struct vfsmount *mnt)
 {
         if (mnt)
                 mnt_add_count(real_mount(mnt), 1);
         return mnt;
 }
 EXPORT_SYMBOL(mntget);
 
 /*
  * Make a mount point inaccessible to new lookups.
  * Because there may still be current users, the caller MUST WAIT
  * for an RCU grace period before destroying the mount point.
  */
 void mnt_make_shortterm(struct vfsmount *mnt)
 {
         if (mnt)
                 real_mount(mnt)->mnt_ns = NULL;
 }
 
 /**
  * path_is_mountpoint() - Check if path is a mount in the current namespace.
  * @path: path to check
  *
  *  d_mountpoint() can only be used reliably to establish if a dentry is
  *  not mounted in any namespace and that common case is handled inline.
  *  d_mountpoint() isn't aware of the possibility there may be multiple
  *  mounts using a given dentry in a different namespace. This function
  *  checks if the passed in path is a mountpoint rather than the dentry
  *  alone.
  */
 bool path_is_mountpoint(const struct path *path)
 {
         unsigned seq;
         bool res;
 
         if (!d_mountpoint(path->dentry))
                 return false;
 
         rcu_read_lock();
         do {
                 seq = read_seqbegin(&mount_lock);
                 res = __path_is_mountpoint(path);
         } while (read_seqretry(&mount_lock, seq));
         rcu_read_unlock();
 
         return res;
 }
 EXPORT_SYMBOL(path_is_mountpoint);
 
 struct vfsmount *mnt_clone_internal(const struct path *path)
 {
         struct mount *p;
         p = clone_mnt(real_mount(path->mnt), path->dentry, CL_PRIVATE);
         if (IS_ERR(p))
                 return ERR_CAST(p);
         p->mnt.mnt_flags |= MNT_INTERNAL;
         return &p->mnt;
 }
 
 /*
  * Returns the mount which either has the specified mnt_id, or has the next
  * smallest id afer the specified one.
  */
 static struct mount *mnt_find_id_at(struct mnt_namespace *ns, u64 mnt_id)
 {
         struct rb_node *node = ns->mounts.rb_node;
         struct mount *ret = NULL;
 
         while (node) {
                 struct mount *m = node_to_mount(node);
 
                 if (mnt_id <= m->mnt_id_unique) {
                         ret = node_to_mount(node);
                         if (mnt_id == m->mnt_id_unique)
                                 break;
                         node = node->rb_left;
                 } else {
                         node = node->rb_right;
                 }
         }
         return ret;
 }
 
 /*
  * Returns the mount which either has the specified mnt_id, or has the next
  * greater id before the specified one.
  */
 static struct mount *mnt_find_id_at_reverse(struct mnt_namespace *ns, u64 mnt_id)
 {
         struct rb_node *node = ns->mounts.rb_node;
         struct mount *ret = NULL;
 
         while (node) {
                 struct mount *m = node_to_mount(node);
 
                 if (mnt_id >= m->mnt_id_unique) {
                         ret = node_to_mount(node);
                         if (mnt_id == m->mnt_id_unique)
                                 break;
                         node = node->rb_right;
                 } else {
                         node = node->rb_left;
                 }
         }
         return ret;
 }
 
 #ifdef CONFIG_PROC_FS
 
 /* iterator; we want it to have access to namespace_sem, thus here... */
 static void *m_start(struct seq_file *m, loff_t *pos)
 {
         struct proc_mounts *p = m->private;
 
         down_read(&namespace_sem);
 
         return mnt_find_id_at(p->ns, *pos);
 }
 
 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
 {
         struct mount *next = NULL, *mnt = v;
         struct rb_node *node = rb_next(&mnt->mnt_node);
 
         ++*pos;
         if (node) {
                 next = node_to_mount(node);
                 *pos = next->mnt_id_unique;
         }
         return next;
 }
 
 static void m_stop(struct seq_file *m, void *v)
 {
         up_read(&namespace_sem);
 }
 
 static int m_show(struct seq_file *m, void *v)
 {
         struct proc_mounts *p = m->private;
         struct mount *r = v;
         return p->show(m, &r->mnt);
 }
 
 const struct seq_operations mounts_op = {
         .start  = m_start,
         .next   = m_next,
         .stop   = m_stop,
         .show   = m_show,
 };
 
 #endif  /* CONFIG_PROC_FS */
 
 /**
  * may_umount_tree - check if a mount tree is busy
  * @m: root of mount tree
  *
  * This is called to check if a tree of mounts has any
  * open files, pwds, chroots or sub mounts that are
  * busy.
  */
 int may_umount_tree(struct vfsmount *m)
 {
         struct mount *mnt = real_mount(m);
         int actual_refs = 0;
         int minimum_refs = 0;
         struct mount *p;
         BUG_ON(!m);
 
         /* write lock needed for mnt_get_count */
         lock_mount_hash();
         for (p = mnt; p; p = next_mnt(p, mnt)) {
                 actual_refs += mnt_get_count(p);
                 minimum_refs += 2;
         }
         unlock_mount_hash();
 
         if (actual_refs > minimum_refs)
                 return 0;
 
         return 1;
 }
 
 EXPORT_SYMBOL(may_umount_tree);
 
 /**
  * may_umount - check if a mount point is busy
  * @mnt: root of mount
  *
  * This is called to check if a mount point has any
  * open files, pwds, chroots or sub mounts. If the
  * mount has sub mounts this will return busy
  * regardless of whether the sub mounts are busy.
  *
  * Doesn't take quota and stuff into account. IOW, in some cases it will
  * give false negatives. The main reason why it's here is that we need
  * a non-destructive way to look for easily umountable filesystems.
  */
 int may_umount(struct vfsmount *mnt)
 {
         int ret = 1;
         down_read(&namespace_sem);
         lock_mount_hash();
         if (propagate_mount_busy(real_mount(mnt), 2))
                 ret = 0;
         unlock_mount_hash();
         up_read(&namespace_sem);
         return ret;
 }
 
 EXPORT_SYMBOL(may_umount);
 
 static void namespace_unlock(void)
 {
         struct hlist_head head;
         struct hlist_node *p;
         struct mount *m;
         LIST_HEAD(list);
 
         hlist_move_list(&unmounted, &head);
         list_splice_init(&ex_mountpoints, &list);
 
         up_write(&namespace_sem);
 
         shrink_dentry_list(&list);
 
         if (likely(hlist_empty(&head)))
                 return;
 
         synchronize_rcu_expedited();
 
         hlist_for_each_entry_safe(m, p, &head, mnt_umount) {
                 hlist_del(&m->mnt_umount);
                 mntput(&m->mnt);
         }
 }
 
 static inline void namespace_lock(void)
 {
         down_write(&namespace_sem);
 }
 
 enum umount_tree_flags {
         UMOUNT_SYNC = 1,
         UMOUNT_PROPAGATE = 2,
         UMOUNT_CONNECTED = 4,
 };
 
 static bool disconnect_mount(struct mount *mnt, enum umount_tree_flags how)
 {
         /* Leaving mounts connected is only valid for lazy umounts */
         if (how & UMOUNT_SYNC)
                 return true;
 
         /* A mount without a parent has nothing to be connected to */
         if (!mnt_has_parent(mnt))
                 return true;
 
         /* Because the reference counting rules change when mounts are
          * unmounted and connected, umounted mounts may not be
          * connected to mounted mounts.
          */
         if (!(mnt->mnt_parent->mnt.mnt_flags & MNT_UMOUNT))
                 return true;
 
         /* Has it been requested that the mount remain connected? */
         if (how & UMOUNT_CONNECTED)
                 return false;
 
         /* Is the mount locked such that it needs to remain connected? */
         if (IS_MNT_LOCKED(mnt))
                 return false;
 
         /* By default disconnect the mount */
         return true;
 }
 
 /*
  * mount_lock must be held
  * namespace_sem must be held for write
  */
 static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
 {
         LIST_HEAD(tmp_list);
         struct mount *p;
 
         if (how & UMOUNT_PROPAGATE)
                 propagate_mount_unlock(mnt);
 
         /* Gather the mounts to umount */
         for (p = mnt; p; p = next_mnt(p, mnt)) {
                 p->mnt.mnt_flags |= MNT_UMOUNT;
                 if (p->mnt.mnt_flags & MNT_ONRB)
                         move_from_ns(p, &tmp_list);
                 else
                         list_move(&p->mnt_list, &tmp_list);
         }
 
         /* Hide the mounts from mnt_mounts */
         list_for_each_entry(p, &tmp_list, mnt_list) {
                 list_del_init(&p->mnt_child);
         }
 
         /* Add propogated mounts to the tmp_list */
         if (how & UMOUNT_PROPAGATE)
                 propagate_umount(&tmp_list);
 
         while (!list_empty(&tmp_list)) {
                 struct mnt_namespace *ns;
                 bool disconnect;
                 p = list_first_entry(&tmp_list, struct mount, mnt_list);
                 list_del_init(&p->mnt_expire);
                 list_del_init(&p->mnt_list);
                 ns = p->mnt_ns;
                 if (ns) {
                         ns->nr_mounts--;
                         __touch_mnt_namespace(ns);
                 }
                 p->mnt_ns = NULL;
                 if (how & UMOUNT_SYNC)
                         p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
 
                 disconnect = disconnect_mount(p, how);
                 if (mnt_has_parent(p)) {
                         mnt_add_count(p->mnt_parent, -1);
                         if (!disconnect) {
                                 /* Don't forget about p */
                                 list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
                         } else {
                                 umount_mnt(p);
                         }
                 }
                 change_mnt_propagation(p, MS_PRIVATE);
                 if (disconnect)
                         hlist_add_head(&p->mnt_umount, &unmounted);
         }
 }
 
 static void shrink_submounts(struct mount *mnt);
 
 static int do_umount_root(struct super_block *sb)
 {
         int ret = 0;
 
         down_write(&sb->s_umount);
         if (!sb_rdonly(sb)) {
                 struct fs_context *fc;
 
                 fc = fs_context_for_reconfigure(sb->s_root, SB_RDONLY,
                                                 SB_RDONLY);
                 if (IS_ERR(fc)) {
                         ret = PTR_ERR(fc);
                 } else {
                         ret = parse_monolithic_mount_data(fc, NULL);
                         if (!ret)
                                 ret = reconfigure_super(fc);
                         put_fs_context(fc);
                 }
         }
         up_write(&sb->s_umount);
         return ret;
 }
 
 static int do_umount(struct mount *mnt, int flags)
 {
         struct super_block *sb = mnt->mnt.mnt_sb;
         int retval;
 
         retval = security_sb_umount(&mnt->mnt, flags);
         if (retval)
                 return retval;
 
         /*
          * Allow userspace to request a mountpoint be expired rather than
          * unmounting unconditionally. Unmount only happens if:
          *  (1) the mark is already set (the mark is cleared by mntput())
          *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
          */
         if (flags & MNT_EXPIRE) {
                 if (&mnt->mnt == current->fs->root.mnt ||
                     flags & (MNT_FORCE | MNT_DETACH))
                         return -EINVAL;
 
                 /*
                  * probably don't strictly need the lock here if we examined
                  * all race cases, but it's a slowpath.
                  */
                 lock_mount_hash();
                 if (mnt_get_count(mnt) != 2) {
                         unlock_mount_hash();
                         return -EBUSY;
                 }
                 unlock_mount_hash();
 
                 if (!xchg(&mnt->mnt_expiry_mark, 1))
                         return -EAGAIN;
         }
 
         /*
          * If we may have to abort operations to get out of this
          * mount, and they will themselves hold resources we must
          * allow the fs to do things. In the Unix tradition of
          * 'Gee thats tricky lets do it in userspace' the umount_begin
          * might fail to complete on the first run through as other tasks
          * must return, and the like. Thats for the mount program to worry
          * about for the moment.
          */
 
         if (flags & MNT_FORCE && sb->s_op->umount_begin) {
                 sb->s_op->umount_begin(sb);
         }
 
         /*
          * No sense to grab the lock for this test, but test itself looks
          * somewhat bogus. Suggestions for better replacement?
          * Ho-hum... In principle, we might treat that as umount + switch
          * to rootfs. GC would eventually take care of the old vfsmount.
          * Actually it makes sense, especially if rootfs would contain a
          * /reboot - static binary that would close all descriptors and
          * call reboot(9). Then init(8) could umount root and exec /reboot.
          */
         if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
                 /*
                  * Special case for "unmounting" root ...
                  * we just try to remount it readonly.
                  */
                 if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
                         return -EPERM;
                 return do_umount_root(sb);
         }
 
         namespace_lock();
         lock_mount_hash();
 
         /* Recheck MNT_LOCKED with the locks held */
         retval = -EINVAL;
         if (mnt->mnt.mnt_flags & MNT_LOCKED)
                 goto out;
 
         event++;
         if (flags & MNT_DETACH) {
                 if (mnt->mnt.mnt_flags & MNT_ONRB ||
                     !list_empty(&mnt->mnt_list))
                         umount_tree(mnt, UMOUNT_PROPAGATE);
                 retval = 0;
         } else {
                 shrink_submounts(mnt);
                 retval = -EBUSY;
                 if (!propagate_mount_busy(mnt, 2)) {
                         if (mnt->mnt.mnt_flags & MNT_ONRB ||
                             !list_empty(&mnt->mnt_list))
                                 umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
                         retval = 0;
                 }
         }
 out:
         unlock_mount_hash();
         namespace_unlock();
         return retval;
 }
 
 /*
  * __detach_mounts - lazily unmount all mounts on the specified dentry
  *
  * During unlink, rmdir, and d_drop it is possible to loose the path
  * to an existing mountpoint, and wind up leaking the mount.
  * detach_mounts allows lazily unmounting those mounts instead of
  * leaking them.
  *
  * The caller may hold dentry->d_inode->i_mutex.
  */
 void __detach_mounts(struct dentry *dentry)
 {
         struct mountpoint *mp;
         struct mount *mnt;
 
         namespace_lock();
         lock_mount_hash();
         mp = lookup_mountpoint(dentry);
         if (!mp)
                 goto out_unlock;
 
         event++;
         while (!hlist_empty(&mp->m_list)) {
                 mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
                 if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
                         umount_mnt(mnt);
                         hlist_add_head(&mnt->mnt_umount, &unmounted);
                 }
                 else umount_tree(mnt, UMOUNT_CONNECTED);
         }
         put_mountpoint(mp);
 out_unlock:
         unlock_mount_hash();
         namespace_unlock();
 }
 
 /*
  * Is the caller allowed to modify his namespace?
  */
 bool may_mount(void)
 {
         return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
 }
 
 static void warn_mandlock(void)
 {
         pr_warn_once("=======================================================\n"
                      "WARNING: The mand mount option has been deprecated and\n"
                      "         and is ignored by this kernel. Remove the mand\n"
                      "         option from the mount to silence this warning.\n"
                      "=======================================================\n");
 }
 
 static int can_umount(const struct path *path, int flags)
 {
         struct mount *mnt = real_mount(path->mnt);
 
         if (!may_mount())
                 return -EPERM;
         if (!path_mounted(path))
                 return -EINVAL;
         if (!check_mnt(mnt))
                 return -EINVAL;
         if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
                 return -EINVAL;
         if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
                 return -EPERM;
         return 0;
 }
 
 // caller is responsible for flags being sane
 int path_umount(struct path *path, int flags)
 {
         struct mount *mnt = real_mount(path->mnt);
         int ret;
 
         ret = can_umount(path, flags);
         if (!ret)
                 ret = do_umount(mnt, flags);
 
         /* we mustn't call path_put() as that would clear mnt_expiry_mark */
         dput(path->dentry);
         mntput_no_expire(mnt);
         return ret;
 }
 
 static int ksys_umount(char __user *name, int flags)
 {
         int lookup_flags = LOOKUP_MOUNTPOINT;
         struct path path;
         int ret;
 
         // basic validity checks done first
         if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
                 return -EINVAL;
 
         if (!(flags & UMOUNT_NOFOLLOW))
                 lookup_flags |= LOOKUP_FOLLOW;
         ret = user_path_at(AT_FDCWD, name, lookup_flags, &path);
         if (ret)
                 return ret;
         return path_umount(&path, flags);
 }
 
 SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
 {
         return ksys_umount(name, flags);
 }
 
 #ifdef __ARCH_WANT_SYS_OLDUMOUNT
 
 /*
  *      The 2.0 compatible umount. No flags.
  */
 SYSCALL_DEFINE1(oldumount, char __user *, name)
 {
         return ksys_umount(name, 0);
 }
 
 #endif
 
 static bool is_mnt_ns_file(struct dentry *dentry)
 {
         /* Is this a proxy for a mount namespace? */
         return dentry->d_op == &ns_dentry_operations &&
                dentry->d_fsdata == &mntns_operations;
 }
 
 static struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
 {
         return container_of(ns, struct mnt_namespace, ns);
 }
 
 struct ns_common *from_mnt_ns(struct mnt_namespace *mnt)
 {
         return &mnt->ns;
 }
 
 static bool mnt_ns_loop(struct dentry *dentry)
 {
         /* Could bind mounting the mount namespace inode cause a
          * mount namespace loop?
          */
         struct mnt_namespace *mnt_ns;
         if (!is_mnt_ns_file(dentry))
                 return false;
 
         mnt_ns = to_mnt_ns(get_proc_ns(dentry->d_inode));
         return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
 }
 
 struct mount *copy_tree(struct mount *src_root, struct dentry *dentry,
                                         int flag)
 {
         struct mount *res, *src_parent, *src_root_child, *src_mnt,
                 *dst_parent, *dst_mnt;
 
         if (!(flag & CL_COPY_UNBINDABLE) && IS_MNT_UNBINDABLE(src_root))
                 return ERR_PTR(-EINVAL);
 
         if (!(flag & CL_COPY_MNT_NS_FILE) && is_mnt_ns_file(dentry))
                 return ERR_PTR(-EINVAL);
 
         res = dst_mnt = clone_mnt(src_root, dentry, flag);
         if (IS_ERR(dst_mnt))
                 return dst_mnt;
 
         src_parent = src_root;
         dst_mnt->mnt_mountpoint = src_root->mnt_mountpoint;
 
         list_for_each_entry(src_root_child, &src_root->mnt_mounts, mnt_child) {
                 if (!is_subdir(src_root_child->mnt_mountpoint, dentry))
                         continue;
 
                 for (src_mnt = src_root_child; src_mnt;
                     src_mnt = next_mnt(src_mnt, src_root_child)) {
                         if (!(flag & CL_COPY_UNBINDABLE) &&
                             IS_MNT_UNBINDABLE(src_mnt)) {
                                 if (src_mnt->mnt.mnt_flags & MNT_LOCKED) {
                                         /* Both unbindable and locked. */
                                         dst_mnt = ERR_PTR(-EPERM);
                                         goto out;
                                 } else {
                                         src_mnt = skip_mnt_tree(src_mnt);
                                         continue;
                                 }
                         }
                         if (!(flag & CL_COPY_MNT_NS_FILE) &&
                             is_mnt_ns_file(src_mnt->mnt.mnt_root)) {
                                 src_mnt = skip_mnt_tree(src_mnt);
                                 continue;
                         }
                         while (src_parent != src_mnt->mnt_parent) {
                                 src_parent = src_parent->mnt_parent;
                                 dst_mnt = dst_mnt->mnt_parent;
                         }
 
                         src_parent = src_mnt;
                         dst_parent = dst_mnt;
                         dst_mnt = clone_mnt(src_mnt, src_mnt->mnt.mnt_root, flag);
                         if (IS_ERR(dst_mnt))
                                 goto out;
                         lock_mount_hash();
                         list_add_tail(&dst_mnt->mnt_list, &res->mnt_list);
                         attach_mnt(dst_mnt, dst_parent, src_parent->mnt_mp, false);
                         unlock_mount_hash();
                 }
         }
         return res;
 
 out:
         if (res) {
                 lock_mount_hash();
                 umount_tree(res, UMOUNT_SYNC);
                 unlock_mount_hash();
         }
         return dst_mnt;
 }
 
 /* Caller should check returned pointer for errors */
 
 struct vfsmount *collect_mounts(const struct path *path)
 {
         struct mount *tree;
         namespace_lock();
         if (!check_mnt(real_mount(path->mnt)))
                 tree = ERR_PTR(-EINVAL);
         else
                 tree = copy_tree(real_mount(path->mnt), path->dentry,
                                  CL_COPY_ALL | CL_PRIVATE);
         namespace_unlock();
         if (IS_ERR(tree))
                 return ERR_CAST(tree);
         return &tree->mnt;
 }
 
 static void free_mnt_ns(struct mnt_namespace *);
 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *, bool);
 
 void dissolve_on_fput(struct vfsmount *mnt)
 {
         struct mnt_namespace *ns;
         namespace_lock();
         lock_mount_hash();
         ns = real_mount(mnt)->mnt_ns;
         if (ns) {
                 if (is_anon_ns(ns))
                         umount_tree(real_mount(mnt), UMOUNT_CONNECTED);
                 else
                         ns = NULL;
         }
         unlock_mount_hash();
         namespace_unlock();
         if (ns)
                 free_mnt_ns(ns);
 }
 
 void drop_collected_mounts(struct vfsmount *mnt)
 {
         namespace_lock();
         lock_mount_hash();
         umount_tree(real_mount(mnt), 0);
         unlock_mount_hash();
         namespace_unlock();
 }
 
 bool has_locked_children(struct mount *mnt, struct dentry *dentry)
 {
         struct mount *child;
 
         list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
                 if (!is_subdir(child->mnt_mountpoint, dentry))
                         continue;
 
                 if (child->mnt.mnt_flags & MNT_LOCKED)
                         return true;
         }
         return false;
 }
 
 /**
  * clone_private_mount - create a private clone of a path
  * @path: path to clone
  *
  * This creates a new vfsmount, which will be the clone of @path.  The new mount
  * will not be attached anywhere in the namespace and will be private (i.e.
  * changes to the originating mount won't be propagated into this).
  *
  * Release with mntput().
  */
 struct vfsmount *clone_private_mount(const struct path *path)
 {
         struct mount *old_mnt = real_mount(path->mnt);
         struct mount *new_mnt;
 
         down_read(&namespace_sem);
         if (IS_MNT_UNBINDABLE(old_mnt))
                 goto invalid;
 
         if (!check_mnt(old_mnt))
                 goto invalid;
 
         if (has_locked_children(old_mnt, path->dentry))
                 goto invalid;
 
         new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
         up_read(&namespace_sem);
 
         if (IS_ERR(new_mnt))
                 return ERR_CAST(new_mnt);
 
         /* Longterm mount to be removed by kern_unmount*() */
         new_mnt->mnt_ns = MNT_NS_INTERNAL;
 
         return &new_mnt->mnt;
 
 invalid:
         up_read(&namespace_sem);
         return ERR_PTR(-EINVAL);
 }
 EXPORT_SYMBOL_GPL(clone_private_mount);
 
 int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
                    struct vfsmount *root)
 {
         struct mount *mnt;
         int res = f(root, arg);
         if (res)
                 return res;
         list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
                 res = f(&mnt->mnt, arg);
                 if (res)
                         return res;
         }
         return 0;
 }
 
 static void lock_mnt_tree(struct mount *mnt)
 {
         struct mount *p;
 
         for (p = mnt; p; p = next_mnt(p, mnt)) {
                 int flags = p->mnt.mnt_flags;
                 /* Don't allow unprivileged users to change mount flags */
                 flags |= MNT_LOCK_ATIME;
 
                 if (flags & MNT_READONLY)
                         flags |= MNT_LOCK_READONLY;
 
                 if (flags & MNT_NODEV)
                         flags |= MNT_LOCK_NODEV;
 
                 if (flags & MNT_NOSUID)
                         flags |= MNT_LOCK_NOSUID;
 
                 if (flags & MNT_NOEXEC)
                         flags |= MNT_LOCK_NOEXEC;
                 /* Don't allow unprivileged users to reveal what is under a mount */
                 if (list_empty(&p->mnt_expire))
                         flags |= MNT_LOCKED;
                 p->mnt.mnt_flags = flags;
         }
 }
 
 static void cleanup_group_ids(struct mount *mnt, struct mount *end)
 {
         struct mount *p;
 
         for (p = mnt; p != end; p = next_mnt(p, mnt)) {
                 if (p->mnt_group_id && !IS_MNT_SHARED(p))
                         mnt_release_group_id(p);
         }
 }
 
 static int invent_group_ids(struct mount *mnt, bool recurse)
 {
         struct mount *p;
 
         for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
                 if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
                         int err = mnt_alloc_group_id(p);
                         if (err) {
                                 cleanup_group_ids(mnt, p);
                                 return err;
                         }
                 }
         }
 
         return 0;
 }
 
 int count_mounts(struct mnt_namespace *ns, struct mount *mnt)
 {
         unsigned int max = READ_ONCE(sysctl_mount_max);
         unsigned int mounts = 0;
         struct mount *p;
 
         if (ns->nr_mounts >= max)
                 return -ENOSPC;
         max -= ns->nr_mounts;
         if (ns->pending_mounts >= max)
                 return -ENOSPC;
         max -= ns->pending_mounts;
 
         for (p = mnt; p; p = next_mnt(p, mnt))
                 mounts++;
 
         if (mounts > max)
                 return -ENOSPC;
 
         ns->pending_mounts += mounts;
         return 0;
 }
 
 enum mnt_tree_flags_t {
         MNT_TREE_MOVE = BIT(0),
         MNT_TREE_BENEATH = BIT(1),
 };
 
 /**
  * attach_recursive_mnt - attach a source mount tree
  * @source_mnt: mount tree to be attached
  * @top_mnt:    mount that @source_mnt will be mounted on or mounted beneath
  * @dest_mp:    the mountpoint @source_mnt will be mounted at
  * @flags:      modify how @source_mnt is supposed to be attached
  *
  *  NOTE: in the table below explains the semantics when a source mount
  *  of a given type is attached to a destination mount of a given type.
  * ---------------------------------------------------------------------------
  * |         BIND MOUNT OPERATION                                            |
  * |**************************************************************************
  * | source-->| shared        |       private  |       slave    | unbindable |
  * | dest     |               |                |                |            |
  * |   |      |               |                |                |            |
  * |   v      |               |                |                |            |
  * |**************************************************************************
  * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
  * |          |               |                |                |            |
  * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
  * ***************************************************************************
  * A bind operation clones the source mount and mounts the clone on the
  * destination mount.
  *
  * (++)  the cloned mount is propagated to all the mounts in the propagation
  *       tree of the destination mount and the cloned mount is added to
  *       the peer group of the source mount.
  * (+)   the cloned mount is created under the destination mount and is marked
  *       as shared. The cloned mount is added to the peer group of the source
  *       mount.
  * (+++) the mount is propagated to all the mounts in the propagation tree
  *       of the destination mount and the cloned mount is made slave
  *       of the same master as that of the source mount. The cloned mount
  *       is marked as 'shared and slave'.
  * (*)   the cloned mount is made a slave of the same master as that of the
  *       source mount.
  *
  * ---------------------------------------------------------------------------
  * |                    MOVE MOUNT OPERATION                                 |
  * |**************************************************************************
  * | source-->| shared        |       private  |       slave    | unbindable |
  * | dest     |               |                |                |            |
  * |   |      |               |                |                |            |
  * |   v      |               |                |                |            |
  * |**************************************************************************
  * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
  * |          |               |                |                |            |
  * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
  * ***************************************************************************
  *
  * (+)  the mount is moved to the destination. And is then propagated to
  *      all the mounts in the propagation tree of the destination mount.
  * (+*)  the mount is moved to the destination.
  * (+++)  the mount is moved to the destination and is then propagated to
  *      all the mounts belonging to the destination mount's propagation tree.
  *      the mount is marked as 'shared and slave'.
  * (*)  the mount continues to be a slave at the new location.
  *
  * if the source mount is a tree, the operations explained above is
  * applied to each mount in the tree.
  * Must be called without spinlocks held, since this function can sleep
  * in allocations.
  *
  * Context: The function expects namespace_lock() to be held.
  * Return: If @source_mnt was successfully attached 0 is returned.
  *         Otherwise a negative error code is returned.
  */
 static int attach_recursive_mnt(struct mount *source_mnt,
                                 struct mount *top_mnt,
                                 struct mountpoint *dest_mp,
                                 enum mnt_tree_flags_t flags)
 {
         struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
         HLIST_HEAD(tree_list);
         struct mnt_namespace *ns = top_mnt->mnt_ns;
         struct mountpoint *smp;
         struct mount *child, *dest_mnt, *p;
         struct hlist_node *n;
         int err = 0;
         bool moving = flags & MNT_TREE_MOVE, beneath = flags & MNT_TREE_BENEATH;
 
         /*
          * Preallocate a mountpoint in case the new mounts need to be
          * mounted beneath mounts on the same mountpoint.
          */
         smp = get_mountpoint(source_mnt->mnt.mnt_root);
         if (IS_ERR(smp))
                 return PTR_ERR(smp);
 
         /* Is there space to add these mounts to the mount namespace? */
         if (!moving) {
                 err = count_mounts(ns, source_mnt);
                 if (err)
                         goto out;
         }
 
         if (beneath)
                 dest_mnt = top_mnt->mnt_parent;
         else
                 dest_mnt = top_mnt;
 
         if (IS_MNT_SHARED(dest_mnt)) {
                 err = invent_group_ids(source_mnt, true);
                 if (err)
                         goto out;
                 err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
         }
         lock_mount_hash();
         if (err)
                 goto out_cleanup_ids;
 
         if (IS_MNT_SHARED(dest_mnt)) {
                 for (p = source_mnt; p; p = next_mnt(p, source_mnt))
                         set_mnt_shared(p);
         }
 
         if (moving) {
                 if (beneath)
                         dest_mp = smp;
                 unhash_mnt(source_mnt);
                 attach_mnt(source_mnt, top_mnt, dest_mp, beneath);
                 touch_mnt_namespace(source_mnt->mnt_ns);
         } else {
                 if (source_mnt->mnt_ns) {
                         LIST_HEAD(head);
 
                         /* move from anon - the caller will destroy */
                         for (p = source_mnt; p; p = next_mnt(p, source_mnt))
                                 move_from_ns(p, &head);
                         list_del_init(&head);
                 }
                 if (beneath)
                         mnt_set_mountpoint_beneath(source_mnt, top_mnt, smp);
                 else
                         mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
                 commit_tree(source_mnt);
         }
 
         hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) {
                 struct mount *q;
                 hlist_del_init(&child->mnt_hash);
                 q = __lookup_mnt(&child->mnt_parent->mnt,
                                  child->mnt_mountpoint);
                 if (q)
                         mnt_change_mountpoint(child, smp, q);
                 /* Notice when we are propagating across user namespaces */
                 if (child->mnt_parent->mnt_ns->user_ns != user_ns)
                         lock_mnt_tree(child);
                 child->mnt.mnt_flags &= ~MNT_LOCKED;
                 commit_tree(child);
         }
         put_mountpoint(smp);
         unlock_mount_hash();
 
         return 0;
 
  out_cleanup_ids:
         while (!hlist_empty(&tree_list)) {
                 child = hlist_entry(tree_list.first, struct mount, mnt_hash);
                 child->mnt_parent->mnt_ns->pending_mounts = 0;
                 umount_tree(child, UMOUNT_SYNC);
         }
         unlock_mount_hash();
         cleanup_group_ids(source_mnt, NULL);
  out:
         ns->pending_mounts = 0;
 
         read_seqlock_excl(&mount_lock);
         put_mountpoint(smp);
         read_sequnlock_excl(&mount_lock);
 
         return err;
 }
 
 /**
  * do_lock_mount - lock mount and mountpoint
  * @path:    target path
  * @beneath: whether the intention is to mount beneath @path
  *
  * Follow the mount stack on @path until the top mount @mnt is found. If
  * the initial @path->{mnt,dentry} is a mountpoint lookup the first
  * mount stacked on top of it. Then simply follow @{mnt,mnt->mnt_root}
  * until nothing is stacked on top of it anymore.
  *
  * Acquire the inode_lock() on the top mount's ->mnt_root to protect
  * against concurrent removal of the new mountpoint from another mount
  * namespace.
  *
  * If @beneath is requested, acquire inode_lock() on @mnt's mountpoint
  * @mp on @mnt->mnt_parent must be acquired. This protects against a
  * concurrent unlink of @mp->mnt_dentry from another mount namespace
  * where @mnt doesn't have a child mount mounted @mp. A concurrent
  * removal of @mnt->mnt_root doesn't matter as nothing will be mounted
  * on top of it for @beneath.
  *
  * In addition, @beneath needs to make sure that @mnt hasn't been
  * unmounted or moved from its current mountpoint in between dropping
  * @mount_lock and acquiring @namespace_sem. For the !@beneath case @mnt
  * being unmounted would be detected later by e.g., calling
  * check_mnt(mnt) in the function it's called from. For the @beneath
  * case however, it's useful to detect it directly in do_lock_mount().
  * If @mnt hasn't been unmounted then @mnt->mnt_mountpoint still points
  * to @mnt->mnt_mp->m_dentry. But if @mnt has been unmounted it will
  * point to @mnt->mnt_root and @mnt->mnt_mp will be NULL.
  *
  * Return: Either the target mountpoint on the top mount or the top
  *         mount's mountpoint.
  */
 static struct mountpoint *do_lock_mount(struct path *path, bool beneath)
 {
         struct vfsmount *mnt = path->mnt;
         struct dentry *dentry;
         struct mountpoint *mp = ERR_PTR(-ENOENT);
 
         for (;;) {
                 struct mount *m;
 
                 if (beneath) {
                         m = real_mount(mnt);
                         read_seqlock_excl(&mount_lock);
                         dentry = dget(m->mnt_mountpoint);
                         read_sequnlock_excl(&mount_lock);
                 } else {
                         dentry = path->dentry;
                 }
 
                 inode_lock(dentry->d_inode);
                 if (unlikely(cant_mount(dentry))) {
                         inode_unlock(dentry->d_inode);
                         goto out;
                 }
 
                 namespace_lock();
 
                 if (beneath && (!is_mounted(mnt) || m->mnt_mountpoint != dentry)) {
                         namespace_unlock();
                         inode_unlock(dentry->d_inode);
                         goto out;
                 }
 
                 mnt = lookup_mnt(path);
                 if (likely(!mnt))
                         break;
 
                 namespace_unlock();
                 inode_unlock(dentry->d_inode);
                 if (beneath)
                         dput(dentry);
                 path_put(path);
                 path->mnt = mnt;
                 path->dentry = dget(mnt->mnt_root);
         }
 
         mp = get_mountpoint(dentry);
         if (IS_ERR(mp)) {
                 namespace_unlock();
                 inode_unlock(dentry->d_inode);
         }
 
 out:
         if (beneath)
                 dput(dentry);
 
         return mp;
 }
 
 static inline struct mountpoint *lock_mount(struct path *path)
 {
         return do_lock_mount(path, false);
 }
 
 static void unlock_mount(struct mountpoint *where)
 {
         struct dentry *dentry = where->m_dentry;
 
         read_seqlock_excl(&mount_lock);
         put_mountpoint(where);
         read_sequnlock_excl(&mount_lock);
 
         namespace_unlock();
         inode_unlock(dentry->d_inode);
 }
 
 static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
 {
         if (mnt->mnt.mnt_sb->s_flags & SB_NOUSER)
                 return -EINVAL;
 
         if (d_is_dir(mp->m_dentry) !=
               d_is_dir(mnt->mnt.mnt_root))
                 return -ENOTDIR;
 
         return attach_recursive_mnt(mnt, p, mp, 0);
 }
 
 /*
  * Sanity check the flags to change_mnt_propagation.
  */
 
 static int flags_to_propagation_type(int ms_flags)
 {
         int type = ms_flags & ~(MS_REC | MS_SILENT);
 
         /* Fail if any non-propagation flags are set */
         if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
                 return 0;
         /* Only one propagation flag should be set */
         if (!is_power_of_2(type))
                 return 0;
         return type;
 }
 
 /*
  * recursively change the type of the mountpoint.
  */
 static int do_change_type(struct path *path, int ms_flags)
 {
         struct mount *m;
         struct mount *mnt = real_mount(path->mnt);
         int recurse = ms_flags & MS_REC;
         int type;
         int err = 0;
 
         if (!path_mounted(path))
                 return -EINVAL;
 
         type = flags_to_propagation_type(ms_flags);
         if (!type)
                 return -EINVAL;
 
         namespace_lock();
         if (type == MS_SHARED) {
                 err = invent_group_ids(mnt, recurse);
                 if (err)
                         goto out_unlock;
         }
 
         lock_mount_hash();
         for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
                 change_mnt_propagation(m, type);
         unlock_mount_hash();
 
  out_unlock:
         namespace_unlock();
         return err;
 }
 
 static struct mount *__do_loopback(struct path *old_path, int recurse)
 {
         struct mount *mnt = ERR_PTR(-EINVAL), *old = real_mount(old_path->mnt);
 
         if (IS_MNT_UNBINDABLE(old))
                 return mnt;
 
         if (!check_mnt(old) && old_path->dentry->d_op != &ns_dentry_operations)
                 return mnt;
 
         if (!recurse && has_locked_children(old, old_path->dentry))
                 return mnt;
 
         if (recurse)
                 mnt = copy_tree(old, old_path->dentry, CL_COPY_MNT_NS_FILE);
         else
                 mnt = clone_mnt(old, old_path->dentry, 0);
 
         if (!IS_ERR(mnt))
                 mnt->mnt.mnt_flags &= ~MNT_LOCKED;
 
         return mnt;
 }
 
 /*
  * do loopback mount.
  */
 static int do_loopback(struct path *path, const char *old_name,
                                 int recurse)
 {
         struct path old_path;
         struct mount *mnt = NULL, *parent;
         struct mountpoint *mp;
         int err;
         if (!old_name || !*old_name)
                 return -EINVAL;
         err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
         if (err)
                 return err;
 
         err = -EINVAL;
         if (mnt_ns_loop(old_path.dentry))
                 goto out;
 
         mp = lock_mount(path);
         if (IS_ERR(mp)) {
                 err = PTR_ERR(mp);
                 goto out;
         }
 
         parent = real_mount(path->mnt);
         if (!check_mnt(parent))
                 goto out2;
 
         mnt = __do_loopback(&old_path, recurse);
         if (IS_ERR(mnt)) {
                 err = PTR_ERR(mnt);
                 goto out2;
         }
 
         err = graft_tree(mnt, parent, mp);
         if (err) {
                 lock_mount_hash();
                 umount_tree(mnt, UMOUNT_SYNC);
                 unlock_mount_hash();
         }
 out2:
         unlock_mount(mp);
 out:
         path_put(&old_path);
         return err;
 }
 
 static struct file *open_detached_copy(struct path *path, bool recursive)
 {
         struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
         struct mnt_namespace *ns = alloc_mnt_ns(user_ns, true);
         struct mount *mnt, *p;
         struct file *file;
 
         if (IS_ERR(ns))
                 return ERR_CAST(ns);
 
         namespace_lock();
         mnt = __do_loopback(path, recursive);
         if (IS_ERR(mnt)) {
                 namespace_unlock();
                 free_mnt_ns(ns);
                 return ERR_CAST(mnt);
         }
 
         lock_mount_hash();
         for (p = mnt; p; p = next_mnt(p, mnt)) {
                 mnt_add_to_ns(ns, p);
                 ns->nr_mounts++;
         }
         ns->root = mnt;
         mntget(&mnt->mnt);
         unlock_mount_hash();
         namespace_unlock();
 
         mntput(path->mnt);
         path->mnt = &mnt->mnt;
         file = dentry_open(path, O_PATH, current_cred());
         if (IS_ERR(file))
                 dissolve_on_fput(path->mnt);
         else
                 file->f_mode |= FMODE_NEED_UNMOUNT;
         return file;
 }
 
 SYSCALL_DEFINE3(open_tree, int, dfd, const char __user *, filename, unsigned, flags)
 {
         struct file *file;
         struct path path;
         int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
         bool detached = flags & OPEN_TREE_CLONE;
         int error;
         int fd;
 
         BUILD_BUG_ON(OPEN_TREE_CLOEXEC != O_CLOEXEC);
 
         if (flags & ~(AT_EMPTY_PATH | AT_NO_AUTOMOUNT | AT_RECURSIVE |
                       AT_SYMLINK_NOFOLLOW | OPEN_TREE_CLONE |
                       OPEN_TREE_CLOEXEC))
                 return -EINVAL;
 
         if ((flags & (AT_RECURSIVE | OPEN_TREE_CLONE)) == AT_RECURSIVE)
                 return -EINVAL;
 
         if (flags & AT_NO_AUTOMOUNT)
                 lookup_flags &= ~LOOKUP_AUTOMOUNT;
         if (flags & AT_SYMLINK_NOFOLLOW)
                 lookup_flags &= ~LOOKUP_FOLLOW;
         if (flags & AT_EMPTY_PATH)
                 lookup_flags |= LOOKUP_EMPTY;
 
         if (detached && !may_mount())
                 return -EPERM;
 
         fd = get_unused_fd_flags(flags & O_CLOEXEC);
         if (fd < 0)
                 return fd;
 
         error = user_path_at(dfd, filename, lookup_flags, &path);
         if (unlikely(error)) {
                 file = ERR_PTR(error);
         } else {
                 if (detached)
                         file = open_detached_copy(&path, flags & AT_RECURSIVE);
                 else
                         file = dentry_open(&path, O_PATH, current_cred());
                 path_put(&path);
         }
         if (IS_ERR(file)) {
                 put_unused_fd(fd);
                 return PTR_ERR(file);
         }
         fd_install(fd, file);
         return fd;
 }
 
 /*
  * Don't allow locked mount flags to be cleared.
  *
  * No locks need to be held here while testing the various MNT_LOCK
  * flags because those flags can never be cleared once they are set.
  */
 static bool can_change_locked_flags(struct mount *mnt, unsigned int mnt_flags)
 {
         unsigned int fl = mnt->mnt.mnt_flags;
 
         if ((fl & MNT_LOCK_READONLY) &&
             !(mnt_flags & MNT_READONLY))
                 return false;
 
         if ((fl & MNT_LOCK_NODEV) &&
             !(mnt_flags & MNT_NODEV))
                 return false;
 
         if ((fl & MNT_LOCK_NOSUID) &&
             !(mnt_flags & MNT_NOSUID))
                 return false;
 
         if ((fl & MNT_LOCK_NOEXEC) &&
             !(mnt_flags & MNT_NOEXEC))
                 return false;
 
         if ((fl & MNT_LOCK_ATIME) &&
             ((fl & MNT_ATIME_MASK) != (mnt_flags & MNT_ATIME_MASK)))
                 return false;
 
         return true;
 }
 
 static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags)
 {
         bool readonly_request = (mnt_flags & MNT_READONLY);
 
         if (readonly_request == __mnt_is_readonly(&mnt->mnt))
                 return 0;
 
         if (readonly_request)
                 return mnt_make_readonly(mnt);
 
         mnt->mnt.mnt_flags &= ~MNT_READONLY;
         return 0;
 }
 
 static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags)
 {
         mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
         mnt->mnt.mnt_flags = mnt_flags;
         touch_mnt_namespace(mnt->mnt_ns);
 }
 
 static void mnt_warn_timestamp_expiry(struct path *mountpoint, struct vfsmount *mnt)
 {
         struct super_block *sb = mnt->mnt_sb;
 
         if (!__mnt_is_readonly(mnt) &&
            (!(sb->s_iflags & SB_I_TS_EXPIRY_WARNED)) &&
            (ktime_get_real_seconds() + TIME_UPTIME_SEC_MAX > sb->s_time_max)) {
                 char *buf, *mntpath;
 
                 buf = (char *)__get_free_page(GFP_KERNEL);
                 if (buf)
                         mntpath = d_path(mountpoint, buf, PAGE_SIZE);
                 else
                         mntpath = ERR_PTR(-ENOMEM);
                 if (IS_ERR(mntpath))
                         mntpath = "(unknown)";
 
                 pr_warn("%s filesystem being %s at %s supports timestamps until %ptTd (0x%llx)\n",
                         sb->s_type->name,
                         is_mounted(mnt) ? "remounted" : "mounted",
                         mntpath, &sb->s_time_max,
                         (unsigned long long)sb->s_time_max);
 
                 sb->s_iflags |= SB_I_TS_EXPIRY_WARNED;
                 if (buf)
                         free_page((unsigned long)buf);
         }
 }
 
 /*
  * Handle reconfiguration of the mountpoint only without alteration of the
  * superblock it refers to.  This is triggered by specifying MS_REMOUNT|MS_BIND
  * to mount(2).
  */
 static int do_reconfigure_mnt(struct path *path, unsigned int mnt_flags)
 {
         struct super_block *sb = path->mnt->mnt_sb;
         struct mount *mnt = real_mount(path->mnt);
         int ret;
 
         if (!check_mnt(mnt))
                 return -EINVAL;
 
         if (!path_mounted(path))
                 return -EINVAL;
 
         if (!can_change_locked_flags(mnt, mnt_flags))
                 return -EPERM;
 
         /*
          * We're only checking whether the superblock is read-only not
          * changing it, so only take down_read(&sb->s_umount).
          */
         down_read(&sb->s_umount);
         lock_mount_hash();
         ret = change_mount_ro_state(mnt, mnt_flags);
         if (ret == 0)
                 set_mount_attributes(mnt, mnt_flags);
         unlock_mount_hash();
         up_read(&sb->s_umount);
 
         mnt_warn_timestamp_expiry(path, &mnt->mnt);
 
         return ret;
 }
 
 /*
  * change filesystem flags. dir should be a physical root of filesystem.
  * If you've mounted a non-root directory somewhere and want to do remount
  * on it - tough luck.
  */
 static int do_remount(struct path *path, int ms_flags, int sb_flags,
                       int mnt_flags, void *data)
 {
         int err;
         struct super_block *sb = path->mnt->mnt_sb;
         struct mount *mnt = real_mount(path->mnt);
         struct fs_context *fc;
 
         if (!check_mnt(mnt))
                 return -EINVAL;
 
         if (!path_mounted(path))
                 return -EINVAL;
 
         if (!can_change_locked_flags(mnt, mnt_flags))
                 return -EPERM;
 
         fc = fs_context_for_reconfigure(path->dentry, sb_flags, MS_RMT_MASK);
         if (IS_ERR(fc))
                 return PTR_ERR(fc);
 
         /*
          * Indicate to the filesystem that the remount request is coming
          * from the legacy mount system call.
          */
         fc->oldapi = true;
 
         err = parse_monolithic_mount_data(fc, data);
         if (!err) {
                 down_write(&sb->s_umount);
                 err = -EPERM;
                 if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
                         err = reconfigure_super(fc);
                         if (!err) {
                                 lock_mount_hash();
                                 set_mount_attributes(mnt, mnt_flags);
                                 unlock_mount_hash();
                         }
                 }
                 up_write(&sb->s_umount);
         }
 
         mnt_warn_timestamp_expiry(path, &mnt->mnt);
 
         put_fs_context(fc);
         return err;
 }
 
 static inline int tree_contains_unbindable(struct mount *mnt)
 {
         struct mount *p;
         for (p = mnt; p; p = next_mnt(p, mnt)) {
                 if (IS_MNT_UNBINDABLE(p))
                         return 1;
         }
         return 0;
 }
 
 /*
  * Check that there aren't references to earlier/same mount namespaces in the
  * specified subtree.  Such references can act as pins for mount namespaces
  * that aren't checked by the mount-cycle checking code, thereby allowing
  * cycles to be made.
  */
 static bool check_for_nsfs_mounts(struct mount *subtree)
 {
         struct mount *p;
         bool ret = false;
 
         lock_mount_hash();
         for (p = subtree; p; p = next_mnt(p, subtree))
                 if (mnt_ns_loop(p->mnt.mnt_root))
                         goto out;
 
         ret = true;
 out:
         unlock_mount_hash();
         return ret;
 }
 
 static int do_set_group(struct path *from_path, struct path *to_path)
 {
         struct mount *from, *to;
         int err;
 
         from = real_mount(from_path->mnt);
         to = real_mount(to_path->mnt);
 
         namespace_lock();
 
         err = -EINVAL;
         /* To and From must be mounted */
         if (!is_mounted(&from->mnt))
                 goto out;
         if (!is_mounted(&to->mnt))
                 goto out;
 
         err = -EPERM;
         /* We should be allowed to modify mount namespaces of both mounts */
         if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN))
                 goto out;
         if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN))
                 goto out;
 
         err = -EINVAL;
         /* To and From paths should be mount roots */
         if (!path_mounted(from_path))
                 goto out;
         if (!path_mounted(to_path))
                 goto out;
 
         /* Setting sharing groups is only allowed across same superblock */
         if (from->mnt.mnt_sb != to->mnt.mnt_sb)
                 goto out;
 
         /* From mount root should be wider than To mount root */
         if (!is_subdir(to->mnt.mnt_root, from->mnt.mnt_root))
                 goto out;
 
         /* From mount should not have locked children in place of To's root */
         if (has_locked_children(from, to->mnt.mnt_root))
                 goto out;
 
         /* Setting sharing groups is only allowed on private mounts */
         if (IS_MNT_SHARED(to) || IS_MNT_SLAVE(to))
                 goto out;
 
         /* From should not be private */
         if (!IS_MNT_SHARED(from) && !IS_MNT_SLAVE(from))
                 goto out;
 
         if (IS_MNT_SLAVE(from)) {
                 struct mount *m = from->mnt_master;
 
                 list_add(&to->mnt_slave, &m->mnt_slave_list);
                 to->mnt_master = m;
         }
 
         if (IS_MNT_SHARED(from)) {
                 to->mnt_group_id = from->mnt_group_id;
                 list_add(&to->mnt_share, &from->mnt_share);
                 lock_mount_hash();
                 set_mnt_shared(to);
                 unlock_mount_hash();
         }
 
         err = 0;
 out:
         namespace_unlock();
         return err;
 }
 
 /**
  * path_overmounted - check if path is overmounted
  * @path: path to check
  *
  * Check if path is overmounted, i.e., if there's a mount on top of
  * @path->mnt with @path->dentry as mountpoint.
  *
  * Context: This function expects namespace_lock() to be held.
  * Return: If path is overmounted true is returned, false if not.
  */
 static inline bool path_overmounted(const struct path *path)
 {
         rcu_read_lock();
         if (unlikely(__lookup_mnt(path->mnt, path->dentry))) {
                 rcu_read_unlock();
                 return true;
         }
         rcu_read_unlock();
         return false;
 }
 
 /**
  * can_move_mount_beneath - check that we can mount beneath the top mount
  * @from: mount to mount beneath
  * @to:   mount under which to mount
  * @mp:   mountpoint of @to
  *
  * - Make sure that @to->dentry is actually the root of a mount under
  *   which we can mount another mount.
  * - Make sure that nothing can be mounted beneath the caller's current
  *   root or the rootfs of the namespace.
  * - Make sure that the caller can unmount the topmost mount ensuring
  *   that the caller could reveal the underlying mountpoint.
  * - Ensure that nothing has been mounted on top of @from before we
  *   grabbed @namespace_sem to avoid creating pointless shadow mounts.
  * - Prevent mounting beneath a mount if the propagation relationship
  *   between the source mount, parent mount, and top mount would lead to
  *   nonsensical mount trees.
  *
  * Context: This function expects namespace_lock() to be held.
  * Return: On success 0, and on error a negative error code is returned.
  */
 static int can_move_mount_beneath(const struct path *from,
                                   const struct path *to,
                                   const struct mountpoint *mp)
 {
         struct mount *mnt_from = real_mount(from->mnt),
                      *mnt_to = real_mount(to->mnt),
                      *parent_mnt_to = mnt_to->mnt_parent;
 
         if (!mnt_has_parent(mnt_to))
                 return -EINVAL;
 
         if (!path_mounted(to))
                 return -EINVAL;
 
         if (IS_MNT_LOCKED(mnt_to))
                 return -EINVAL;
 
         /* Avoid creating shadow mounts during mount propagation. */
         if (path_overmounted(from))
                 return -EINVAL;
 
         /*
          * Mounting beneath the rootfs only makes sense when the
          * semantics of pivot_root(".", ".") are used.
          */
         if (&mnt_to->mnt == current->fs->root.mnt)
                 return -EINVAL;
         if (parent_mnt_to == current->nsproxy->mnt_ns->root)
                 return -EINVAL;
 
         for (struct mount *p = mnt_from; mnt_has_parent(p); p = p->mnt_parent)
                 if (p == mnt_to)
                         return -EINVAL;
 
         /*
          * If the parent mount propagates to the child mount this would
          * mean mounting @mnt_from on @mnt_to->mnt_parent and then
          * propagating a copy @c of @mnt_from on top of @mnt_to. This
          * defeats the whole purpose of mounting beneath another mount.
          */
         if (propagation_would_overmount(parent_mnt_to, mnt_to, mp))
                 return -EINVAL;
 
         /*
          * If @mnt_to->mnt_parent propagates to @mnt_from this would
          * mean propagating a copy @c of @mnt_from on top of @mnt_from.
          * Afterwards @mnt_from would be mounted on top of
          * @mnt_to->mnt_parent and @mnt_to would be unmounted from
          * @mnt->mnt_parent and remounted on @mnt_from. But since @c is
          * already mounted on @mnt_from, @mnt_to would ultimately be
          * remounted on top of @c. Afterwards, @mnt_from would be
          * covered by a copy @c of @mnt_from and @c would be covered by
          * @mnt_from itself. This defeats the whole purpose of mounting
          * @mnt_from beneath @mnt_to.
          */
         if (propagation_would_overmount(parent_mnt_to, mnt_from, mp))
                 return -EINVAL;
 
         return 0;
 }
 
 static int do_move_mount(struct path *old_path, struct path *new_path,
                          bool beneath)
 {
         struct mnt_namespace *ns;
         struct mount *p;
         struct mount *old;
         struct mount *parent;
         struct mountpoint *mp, *old_mp;
         int err;
         bool attached;
         enum mnt_tree_flags_t flags = 0;
 
         mp = do_lock_mount(new_path, beneath);
         if (IS_ERR(mp))
                 return PTR_ERR(mp);
 
         old = real_mount(old_path->mnt);
         p = real_mount(new_path->mnt);
         parent = old->mnt_parent;
         attached = mnt_has_parent(old);
         if (attached)
                 flags |= MNT_TREE_MOVE;
         old_mp = old->mnt_mp;
         ns = old->mnt_ns;
 
         err = -EINVAL;
         /* The mountpoint must be in our namespace. */
         if (!check_mnt(p))
                 goto out;
 
         /* The thing moved must be mounted... */
         if (!is_mounted(&old->mnt))
                 goto out;
 
         /* ... and either ours or the root of anon namespace */
         if (!(attached ? check_mnt(old) : is_anon_ns(ns)))
                 goto out;
 
         if (old->mnt.mnt_flags & MNT_LOCKED)
                 goto out;
 
         if (!path_mounted(old_path))
                 goto out;
 
         if (d_is_dir(new_path->dentry) !=
             d_is_dir(old_path->dentry))
                 goto out;
         /*
          * Don't move a mount residing in a shared parent.
          */
         if (attached && IS_MNT_SHARED(parent))
                 goto out;
 
         if (beneath) {
                 err = can_move_mount_beneath(old_path, new_path, mp);
                 if (err)
                         goto out;
 
                 err = -EINVAL;
                 p = p->mnt_parent;
                 flags |= MNT_TREE_BENEATH;
         }
 
         /*
          * Don't move a mount tree containing unbindable mounts to a destination
          * mount which is shared.
          */
         if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
                 goto out;
         err = -ELOOP;
         if (!check_for_nsfs_mounts(old))
                 goto out;
         for (; mnt_has_parent(p); p = p->mnt_parent)
                 if (p == old)
                         goto out;
 
         err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp, flags);
         if (err)
                 goto out;
 
         /* if the mount is moved, it should no longer be expire
          * automatically */
         list_del_init(&old->mnt_expire);
         if (attached)
                 put_mountpoint(old_mp);
 out:
         unlock_mount(mp);
         if (!err) {
                 if (attached)
                         mntput_no_expire(parent);
                 else
                         free_mnt_ns(ns);
         }
         return err;
 }
 
 static int do_move_mount_old(struct path *path, const char *old_name)
 {
         struct path old_path;
         int err;
 
         if (!old_name || !*old_name)
                 return -EINVAL;
 
         err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
         if (err)
                 return err;
 
         err = do_move_mount(&old_path, path, false);
         path_put(&old_path);
         return err;
 }
 
 /*
  * add a mount into a namespace's mount tree
  */
 static int do_add_mount(struct mount *newmnt, struct mountpoint *mp,
                         const struct path *path, int mnt_flags)
 {
         struct mount *parent = real_mount(path->mnt);
 
         mnt_flags &= ~MNT_INTERNAL_FLAGS;
 
         if (unlikely(!check_mnt(parent))) {
                 /* that's acceptable only for automounts done in private ns */
                 if (!(mnt_flags & MNT_SHRINKABLE))
                         return -EINVAL;
                 /* ... and for those we'd better have mountpoint still alive */
                 if (!parent->mnt_ns)
                         return -EINVAL;
         }
 
         /* Refuse the same filesystem on the same mount point */
         if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb && path_mounted(path))
                 return -EBUSY;
 
         if (d_is_symlink(newmnt->mnt.mnt_root))
                 return -EINVAL;
 
         newmnt->mnt.mnt_flags = mnt_flags;
         return graft_tree(newmnt, parent, mp);
 }
 
 static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags);
 
 /*
  * Create a new mount using a superblock configuration and request it
  * be added to the namespace tree.
  */
 static int do_new_mount_fc(struct fs_context *fc, struct path *mountpoint,
                            unsigned int mnt_flags)
 {
         struct vfsmount *mnt;
         struct mountpoint *mp;
         struct super_block *sb = fc->root->d_sb;
         int error;
 
         error = security_sb_kern_mount(sb);
         if (!error && mount_too_revealing(sb, &mnt_flags))
                 error = -EPERM;
 
         if (unlikely(error)) {
                 fc_drop_locked(fc);
                 return error;
         }
 
         up_write(&sb->s_umount);
 
         mnt = vfs_create_mount(fc);
         if (IS_ERR(mnt))
                 return PTR_ERR(mnt);
 
         mnt_warn_timestamp_expiry(mountpoint, mnt);
 
         mp = lock_mount(mountpoint);
         if (IS_ERR(mp)) {
                 mntput(mnt);
                 return PTR_ERR(mp);
         }
         error = do_add_mount(real_mount(mnt), mp, mountpoint, mnt_flags);
         unlock_mount(mp);
         if (error < 0)
                 mntput(mnt);
         return error;
 }
 
 /*
  * create a new mount for userspace and request it to be added into the
  * namespace's tree
  */
 static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
                         int mnt_flags, const char *name, void *data)
 {
         struct file_system_type *type;
         struct fs_context *fc;
         const char *subtype = NULL;
         int err = 0;
 
         if (!fstype)
                 return -EINVAL;
 
         type = get_fs_type(fstype);
         if (!type)
                 return -ENODEV;
 
         if (type->fs_flags & FS_HAS_SUBTYPE) {
                 subtype = strchr(fstype, '.');
                 if (subtype) {
                         subtype++;
                         if (!*subtype) {
                                 put_filesystem(type);
                                 return -EINVAL;
                         }
                 }
         }
 
         fc = fs_context_for_mount(type, sb_flags);
         put_filesystem(type);
         if (IS_ERR(fc))
                 return PTR_ERR(fc);
 
         /*
          * Indicate to the filesystem that the mount request is coming
          * from the legacy mount system call.
          */
         fc->oldapi = true;
 
         if (subtype)
                 err = vfs_parse_fs_string(fc, "subtype",
                                           subtype, strlen(subtype));
         if (!err && name)
                 err = vfs_parse_fs_string(fc, "source", name, strlen(name));
         if (!err)
                 err = parse_monolithic_mount_data(fc, data);
         if (!err && !mount_capable(fc))
                 err = -EPERM;
         if (!err)
                 err = vfs_get_tree(fc);
         if (!err)
                 err = do_new_mount_fc(fc, path, mnt_flags);
 
         put_fs_context(fc);
         return err;
 }
 
 int finish_automount(struct vfsmount *m, const struct path *path)
 {
         struct dentry *dentry = path->dentry;
         struct mountpoint *mp;
         struct mount *mnt;
         int err;
 
         if (!m)
                 return 0;
         if (IS_ERR(m))
                 return PTR_ERR(m);
 
         mnt = real_mount(m);
         /* The new mount record should have at least 2 refs to prevent it being
          * expired before we get a chance to add it
          */
         BUG_ON(mnt_get_count(mnt) < 2);
 
         if (m->mnt_sb == path->mnt->mnt_sb &&
             m->mnt_root == dentry) {
                 err = -ELOOP;
                 goto discard;
         }
 
         /*
          * we don't want to use lock_mount() - in this case finding something
          * that overmounts our mountpoint to be means "quitely drop what we've
          * got", not "try to mount it on top".
          */
         inode_lock(dentry->d_inode);
         namespace_lock();
         if (unlikely(cant_mount(dentry))) {
                 err = -ENOENT;
                 goto discard_locked;
         }
         if (path_overmounted(path)) {
                 err = 0;
                 goto discard_locked;
         }
         mp = get_mountpoint(dentry);
         if (IS_ERR(mp)) {
                 err = PTR_ERR(mp);
                 goto discard_locked;
         }
 
         err = do_add_mount(mnt, mp, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
         unlock_mount(mp);
         if (unlikely(err))
                 goto discard;
         mntput(m);
         return 0;
 
 discard_locked:
         namespace_unlock();
         inode_unlock(dentry->d_inode);
 discard:
         /* remove m from any expiration list it may be on */
         if (!list_empty(&mnt->mnt_expire)) {
                 namespace_lock();
                 list_del_init(&mnt->mnt_expire);
                 namespace_unlock();
         }
         mntput(m);
         mntput(m);
         return err;
 }
 
 /**
  * mnt_set_expiry - Put a mount on an expiration list
  * @mnt: The mount to list.
  * @expiry_list: The list to add the mount to.
  */
 void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
 {
         namespace_lock();
 
         list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
 
         namespace_unlock();
 }
 EXPORT_SYMBOL(mnt_set_expiry);
 
 /*
  * process a list of expirable mountpoints with the intent of discarding any
  * mountpoints that aren't in use and haven't been touched since last we came
  * here
  */
 void mark_mounts_for_expiry(struct list_head *mounts)
 {
         struct mount *mnt, *next;
         LIST_HEAD(graveyard);
 
         if (list_empty(mounts))
                 return;
 
         namespace_lock();
         lock_mount_hash();
 
         /* extract from the expiration list every vfsmount that matches the
          * following criteria:
          * - only referenced by its parent vfsmount
          * - still marked for expiry (marked on the last call here; marks are
          *   cleared by mntput())
          */
         list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
                 if (!xchg(&mnt->mnt_expiry_mark, 1) ||
                         propagate_mount_busy(mnt, 1))
                         continue;
                 list_move(&mnt->mnt_expire, &graveyard);
         }
         while (!list_empty(&graveyard)) {
                 mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
                 touch_mnt_namespace(mnt->mnt_ns);
                 umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
         }
         unlock_mount_hash();
         namespace_unlock();
 }
 
 EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
 
 /*
  * Ripoff of 'select_parent()'
  *
  * search the list of submounts for a given mountpoint, and move any
  * shrinkable submounts to the 'graveyard' list.
  */
 static int select_submounts(struct mount *parent, struct list_head *graveyard)
 {
         struct mount *this_parent = parent;
         struct list_head *next;
         int found = 0;
 
 repeat:
         next = this_parent->mnt_mounts.next;
 resume:
         while (next != &this_parent->mnt_mounts) {
                 struct list_head *tmp = next;
                 struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
 
                 next = tmp->next;
                 if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
                         continue;
                 /*
                  * Descend a level if the d_mounts list is non-empty.
                  */
                 if (!list_empty(&mnt->mnt_mounts)) {
                         this_parent = mnt;
                         goto repeat;
                 }
 
                 if (!propagate_mount_busy(mnt, 1)) {
                         list_move_tail(&mnt->mnt_expire, graveyard);
                         found++;
                 }
         }
         /*
          * All done at this level ... ascend and resume the search
          */
         if (this_parent != parent) {
                 next = this_parent->mnt_child.next;
                 this_parent = this_parent->mnt_parent;
                 goto resume;
         }
         return found;
 }
 
 /*
  * process a list of expirable mountpoints with the intent of discarding any
  * submounts of a specific parent mountpoint
  *
  * mount_lock must be held for write
  */
 static void shrink_submounts(struct mount *mnt)
 {
         LIST_HEAD(graveyard);
         struct mount *m;
 
         /* extract submounts of 'mountpoint' from the expiration list */
         while (select_submounts(mnt, &graveyard)) {
                 while (!list_empty(&graveyard)) {
                         m = list_first_entry(&graveyard, struct mount,
                                                 mnt_expire);
                         touch_mnt_namespace(m->mnt_ns);
                         umount_tree(m, UMOUNT_PROPAGATE|UMOUNT_SYNC);
                 }
         }
 }
 
 static void *copy_mount_options(const void __user * data)
 {
         char *copy;
         unsigned left, offset;
 
         if (!data)
                 return NULL;
 
         copy = kmalloc(PAGE_SIZE, GFP_KERNEL);
         if (!copy)
                 return ERR_PTR(-ENOMEM);
 
         left = copy_from_user(copy, data, PAGE_SIZE);
 
         /*
          * Not all architectures have an exact copy_from_user(). Resort to
          * byte at a time.
          */
         offset = PAGE_SIZE - left;
         while (left) {
                 char c;
                 if (get_user(c, (const char __user *)data + offset))
                         break;
                 copy[offset] = c;
                 left--;
                 offset++;
         }
 
         if (left == PAGE_SIZE) {
                 kfree(copy);
                 return ERR_PTR(-EFAULT);
         }
 
         return copy;
 }
 
 static char *copy_mount_string(const void __user *data)
 {
         return data ? strndup_user(data, PATH_MAX) : NULL;
 }
 
 /*
  * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
  * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
  *
  * data is a (void *) that can point to any structure up to
  * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
  * information (or be NULL).
  *
  * Pre-0.97 versions of mount() didn't have a flags word.
  * When the flags word was introduced its top half was required
  * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
  * Therefore, if this magic number is present, it carries no information
  * and must be discarded.
  */
 int path_mount(const char *dev_name, struct path *path,
                 const char *type_page, unsigned long flags, void *data_page)
 {
         unsigned int mnt_flags = 0, sb_flags;
         int ret;
 
         /* Discard magic */
         if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
                 flags &= ~MS_MGC_MSK;
 
         /* Basic sanity checks */
         if (data_page)
                 ((char *)data_page)[PAGE_SIZE - 1] = 0;
 
         if (flags & MS_NOUSER)
                 return -EINVAL;
 
         ret = security_sb_mount(dev_name, path, type_page, flags, data_page);
         if (ret)
                 return ret;
         if (!may_mount())
                 return -EPERM;
         if (flags & SB_MANDLOCK)
                 warn_mandlock();
 
         /* Default to relatime unless overriden */
         if (!(flags & MS_NOATIME))
                 mnt_flags |= MNT_RELATIME;
 
         /* Separate the per-mountpoint flags */
         if (flags & MS_NOSUID)
                 mnt_flags |= MNT_NOSUID;
         if (flags & MS_NODEV)
                 mnt_flags |= MNT_NODEV;
         if (flags & MS_NOEXEC)
                 mnt_flags |= MNT_NOEXEC;
         if (flags & MS_NOATIME)
                 mnt_flags |= MNT_NOATIME;
         if (flags & MS_NODIRATIME)
                 mnt_flags |= MNT_NODIRATIME;
         if (flags & MS_STRICTATIME)
                 mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
         if (flags & MS_RDONLY)
                 mnt_flags |= MNT_READONLY;
         if (flags & MS_NOSYMFOLLOW)
                 mnt_flags |= MNT_NOSYMFOLLOW;
 
         /* The default atime for remount is preservation */
         if ((flags & MS_REMOUNT) &&
             ((flags & (MS_NOATIME | MS_NODIRATIME | MS_RELATIME |
                        MS_STRICTATIME)) == 0)) {
                 mnt_flags &= ~MNT_ATIME_MASK;
                 mnt_flags |= path->mnt->mnt_flags & MNT_ATIME_MASK;
         }
 
         sb_flags = flags & (SB_RDONLY |
                             SB_SYNCHRONOUS |
                             SB_MANDLOCK |
                             SB_DIRSYNC |
                             SB_SILENT |
                             SB_POSIXACL |
                             SB_LAZYTIME |
                             SB_I_VERSION);
 
         if ((flags & (MS_REMOUNT | MS_BIND)) == (MS_REMOUNT | MS_BIND))
                 return do_reconfigure_mnt(path, mnt_flags);
         if (flags & MS_REMOUNT)
                 return do_remount(path, flags, sb_flags, mnt_flags, data_page);
         if (flags & MS_BIND)
                 return do_loopback(path, dev_name, flags & MS_REC);
         if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
                 return do_change_type(path, flags);
         if (flags & MS_MOVE)
                 return do_move_mount_old(path, dev_name);
 
         return do_new_mount(path, type_page, sb_flags, mnt_flags, dev_name,
                             data_page);
 }
 
 long do_mount(const char *dev_name, const char __user *dir_name,
                 const char *type_page, unsigned long flags, void *data_page)
 {
         struct path path;
         int ret;
 
         ret = user_path_at(AT_FDCWD, dir_name, LOOKUP_FOLLOW, &path);
         if (ret)
                 return ret;
         ret = path_mount(dev_name, &path, type_page, flags, data_page);
         path_put(&path);
         return ret;
 }
 
 static struct ucounts *inc_mnt_namespaces(struct user_namespace *ns)
 {
         return inc_ucount(ns, current_euid(), UCOUNT_MNT_NAMESPACES);
 }
 
 static void dec_mnt_namespaces(struct ucounts *ucounts)
 {
         dec_ucount(ucounts, UCOUNT_MNT_NAMESPACES);
 }
 
 static void free_mnt_ns(struct mnt_namespace *ns)
 {
         if (!is_anon_ns(ns))
                 ns_free_inum(&ns->ns);
         dec_mnt_namespaces(ns->ucounts);
         mnt_ns_tree_remove(ns);
 }
 
 /*
  * Assign a sequence number so we can detect when we attempt to bind
  * mount a reference to an older mount namespace into the current
  * mount namespace, preventing reference counting loops.  A 64bit
  * number incrementing at 10Ghz will take 12,427 years to wrap which
  * is effectively never, so we can ignore the possibility.
  */
 static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
 
 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool anon)
 {
         struct mnt_namespace *new_ns;
         struct ucounts *ucounts;
         int ret;
 
         ucounts = inc_mnt_namespaces(user_ns);
         if (!ucounts)
                 return ERR_PTR(-ENOSPC);
 
         new_ns = kzalloc(sizeof(struct mnt_namespace), GFP_KERNEL_ACCOUNT);
         if (!new_ns) {
                 dec_mnt_namespaces(ucounts);
                 return ERR_PTR(-ENOMEM);
         }
         if (!anon) {
                 ret = ns_alloc_inum(&new_ns->ns);
                 if (ret) {
                         kfree(new_ns);
                         dec_mnt_namespaces(ucounts);
                         return ERR_PTR(ret);
                 }
         }
         new_ns->ns.ops = &mntns_operations;
         if (!anon)
                 new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
         refcount_set(&new_ns->ns.count, 1);
         refcount_set(&new_ns->passive, 1);
         new_ns->mounts = RB_ROOT;
         RB_CLEAR_NODE(&new_ns->mnt_ns_tree_node);
         init_waitqueue_head(&new_ns->poll);
         new_ns->user_ns = get_user_ns(user_ns);
         new_ns->ucounts = ucounts;
         return new_ns;
 }
 
 __latent_entropy
 struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
                 struct user_namespace *user_ns, struct fs_struct *new_fs)
 {
         struct mnt_namespace *new_ns;
         struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
         struct mount *p, *q;
         struct mount *old;
         struct mount *new;
         int copy_flags;
 
         BUG_ON(!ns);
 
         if (likely(!(flags & CLONE_NEWNS))) {
                 get_mnt_ns(ns);
                 return ns;
         }
 
         old = ns->root;
 
         new_ns = alloc_mnt_ns(user_ns, false);
         if (IS_ERR(new_ns))
                 return new_ns;
 
         namespace_lock();
         /* First pass: copy the tree topology */
         copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
         if (user_ns != ns->user_ns)
                 copy_flags |= CL_SHARED_TO_SLAVE;
         new = copy_tree(old, old->mnt.mnt_root, copy_flags);
         if (IS_ERR(new)) {
                 namespace_unlock();
                 free_mnt_ns(new_ns);
                 return ERR_CAST(new);
         }
         if (user_ns != ns->user_ns) {
                 lock_mount_hash();
                 lock_mnt_tree(new);
                 unlock_mount_hash();
         }
         new_ns->root = new;
 
         /*
          * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
          * as belonging to new namespace.  We have already acquired a private
          * fs_struct, so tsk->fs->lock is not needed.
          */
         p = old;
         q = new;
         while (p) {
                 mnt_add_to_ns(new_ns, q);
                 new_ns->nr_mounts++;
                 if (new_fs) {
                         if (&p->mnt == new_fs->root.mnt) {
                                 new_fs->root.mnt = mntget(&q->mnt);
                                 rootmnt = &p->mnt;
                         }
                         if (&p->mnt == new_fs->pwd.mnt) {
                                 new_fs->pwd.mnt = mntget(&q->mnt);
                                 pwdmnt = &p->mnt;
                         }
                 }
                 p = next_mnt(p, old);
                 q = next_mnt(q, new);
                 if (!q)
                         break;
                 // an mntns binding we'd skipped?
                 while (p->mnt.mnt_root != q->mnt.mnt_root)
                         p = next_mnt(skip_mnt_tree(p), old);
         }
         mnt_ns_tree_add(new_ns);
         namespace_unlock();
 
         if (rootmnt)
                 mntput(rootmnt);
         if (pwdmnt)
                 mntput(pwdmnt);
 
         return new_ns;
 }
 
 struct dentry *mount_subtree(struct vfsmount *m, const char *name)
 {
         struct mount *mnt = real_mount(m);
         struct mnt_namespace *ns;
         struct super_block *s;
         struct path path;
         int err;
 
         ns = alloc_mnt_ns(&init_user_ns, true);
         if (IS_ERR(ns)) {
                 mntput(m);
                 return ERR_CAST(ns);
         }
         ns->root = mnt;
         ns->nr_mounts++;
         mnt_add_to_ns(ns, mnt);
 
         err = vfs_path_lookup(m->mnt_root, m,
                         name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
 
         put_mnt_ns(ns);
 
         if (err)
                 return ERR_PTR(err);
 
         /* trade a vfsmount reference for active sb one */
         s = path.mnt->mnt_sb;
         atomic_inc(&s->s_active);
         mntput(path.mnt);
         /* lock the sucker */
         down_write(&s->s_umount);
         /* ... and return the root of (sub)tree on it */
         return path.dentry;
 }
 EXPORT_SYMBOL(mount_subtree);
 
 SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
                 char __user *, type, unsigned long, flags, void __user *, data)
 {
         int ret;
         char *kernel_type;
         char *kernel_dev;
         void *options;
 
         kernel_type = copy_mount_string(type);
         ret = PTR_ERR(kernel_type);
         if (IS_ERR(kernel_type))
                 goto out_type;
 
         kernel_dev = copy_mount_string(dev_name);
         ret = PTR_ERR(kernel_dev);
         if (IS_ERR(kernel_dev))
                 goto out_dev;
 
         options = copy_mount_options(data);
         ret = PTR_ERR(options);
         if (IS_ERR(options))
                 goto out_data;
 
         ret = do_mount(kernel_dev, dir_name, kernel_type, flags, options);
 
         kfree(options);
 out_data:
         kfree(kernel_dev);
 out_dev:
         kfree(kernel_type);
 out_type:
         return ret;
 }
 
 #define FSMOUNT_VALID_FLAGS                                                    \
         (MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOSUID | MOUNT_ATTR_NODEV |            \
          MOUNT_ATTR_NOEXEC | MOUNT_ATTR__ATIME | MOUNT_ATTR_NODIRATIME |       \
          MOUNT_ATTR_NOSYMFOLLOW)
 
 #define MOUNT_SETATTR_VALID_FLAGS (FSMOUNT_VALID_FLAGS | MOUNT_ATTR_IDMAP)
 
 #define MOUNT_SETATTR_PROPAGATION_FLAGS \
         (MS_UNBINDABLE | MS_PRIVATE | MS_SLAVE | MS_SHARED)
 
 static unsigned int attr_flags_to_mnt_flags(u64 attr_flags)
 {
         unsigned int mnt_flags = 0;
 
         if (attr_flags & MOUNT_ATTR_RDONLY)
                 mnt_flags |= MNT_READONLY;
         if (attr_flags & MOUNT_ATTR_NOSUID)
                 mnt_flags |= MNT_NOSUID;
         if (attr_flags & MOUNT_ATTR_NODEV)
                 mnt_flags |= MNT_NODEV;
         if (attr_flags & MOUNT_ATTR_NOEXEC)
                 mnt_flags |= MNT_NOEXEC;
         if (attr_flags & MOUNT_ATTR_NODIRATIME)
                 mnt_flags |= MNT_NODIRATIME;
         if (attr_flags & MOUNT_ATTR_NOSYMFOLLOW)
                 mnt_flags |= MNT_NOSYMFOLLOW;
 
         return mnt_flags;
 }
 
 /*
  * Create a kernel mount representation for a new, prepared superblock
  * (specified by fs_fd) and attach to an open_tree-like file descriptor.
  */
 SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
                 unsigned int, attr_flags)
 {
         struct mnt_namespace *ns;
         struct fs_context *fc;
         struct file *file;
         struct path newmount;
         struct mount *mnt;
         struct fd f;
         unsigned int mnt_flags = 0;
         long ret;
 
         if (!may_mount())
                 return -EPERM;
 
         if ((flags & ~(FSMOUNT_CLOEXEC)) != 0)
                 return -EINVAL;
 
         if (attr_flags & ~FSMOUNT_VALID_FLAGS)
                 return -EINVAL;
 
         mnt_flags = attr_flags_to_mnt_flags(attr_flags);
 
         switch (attr_flags & MOUNT_ATTR__ATIME) {
         case MOUNT_ATTR_STRICTATIME:
                 break;
         case MOUNT_ATTR_NOATIME:
                 mnt_flags |= MNT_NOATIME;
                 break;
         case MOUNT_ATTR_RELATIME:
                 mnt_flags |= MNT_RELATIME;
                 break;
         default:
                 return -EINVAL;
         }
 
         f = fdget(fs_fd);
         if (!f.file)
                 return -EBADF;
 
         ret = -EINVAL;
         if (f.file->f_op != &fscontext_fops)
                 goto err_fsfd;
 
         fc = f.file->private_data;
 
         ret = mutex_lock_interruptible(&fc->uapi_mutex);
         if (ret < 0)
                 goto err_fsfd;
 
         /* There must be a valid superblock or we can't mount it */
         ret = -EINVAL;
         if (!fc->root)
                 goto err_unlock;
 
         ret = -EPERM;
         if (mount_too_revealing(fc->root->d_sb, &mnt_flags)) {
                 pr_warn("VFS: Mount too revealing\n");
                 goto err_unlock;
         }
 
         ret = -EBUSY;
         if (fc->phase != FS_CONTEXT_AWAITING_MOUNT)
                 goto err_unlock;
 
         if (fc->sb_flags & SB_MANDLOCK)
                 warn_mandlock();
 
         newmount.mnt = vfs_create_mount(fc);
         if (IS_ERR(newmount.mnt)) {
                 ret = PTR_ERR(newmount.mnt);
                 goto err_unlock;
         }
         newmount.dentry = dget(fc->root);
         newmount.mnt->mnt_flags = mnt_flags;
 
         /* We've done the mount bit - now move the file context into more or
          * less the same state as if we'd done an fspick().  We don't want to
          * do any memory allocation or anything like that at this point as we
          * don't want to have to handle any errors incurred.
          */
         vfs_clean_context(fc);
 
         ns = alloc_mnt_ns(current->nsproxy->mnt_ns->user_ns, true);
         if (IS_ERR(ns)) {
                 ret = PTR_ERR(ns);
                 goto err_path;
         }
         mnt = real_mount(newmount.mnt);
         ns->root = mnt;
         ns->nr_mounts = 1;
         mnt_add_to_ns(ns, mnt);
         mntget(newmount.mnt);
 
         /* Attach to an apparent O_PATH fd with a note that we need to unmount
          * it, not just simply put it.
          */
         file = dentry_open(&newmount, O_PATH, fc->cred);
         if (IS_ERR(file)) {
                 dissolve_on_fput(newmount.mnt);
                 ret = PTR_ERR(file);
                 goto err_path;
         }
         file->f_mode |= FMODE_NEED_UNMOUNT;
 
         ret = get_unused_fd_flags((flags & FSMOUNT_CLOEXEC) ? O_CLOEXEC : 0);
         if (ret >= 0)
                 fd_install(ret, file);
         else
                 fput(file);
 
 err_path:
         path_put(&newmount);
 err_unlock:
         mutex_unlock(&fc->uapi_mutex);
 err_fsfd:
         fdput(f);
         return ret;
 }
 
 /*
  * Move a mount from one place to another.  In combination with
  * fsopen()/fsmount() this is used to install a new mount and in combination
  * with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be used to copy
  * a mount subtree.
  *
  * Note the flags value is a combination of MOVE_MOUNT_* flags.
  */
 SYSCALL_DEFINE5(move_mount,
                 int, from_dfd, const char __user *, from_pathname,
                 int, to_dfd, const char __user *, to_pathname,
                 unsigned int, flags)
 {
         struct path from_path, to_path;
         unsigned int lflags;
         int ret = 0;
 
         if (!may_mount())
                 return -EPERM;
 
         if (flags & ~MOVE_MOUNT__MASK)
                 return -EINVAL;
 
         if ((flags & (MOVE_MOUNT_BENEATH | MOVE_MOUNT_SET_GROUP)) ==
             (MOVE_MOUNT_BENEATH | MOVE_MOUNT_SET_GROUP))
                 return -EINVAL;
 
         /* If someone gives a pathname, they aren't permitted to move
          * from an fd that requires unmount as we can't get at the flag
          * to clear it afterwards.
          */
         lflags = 0;
         if (flags & MOVE_MOUNT_F_SYMLINKS)      lflags |= LOOKUP_FOLLOW;
         if (flags & MOVE_MOUNT_F_AUTOMOUNTS)    lflags |= LOOKUP_AUTOMOUNT;
         if (flags & MOVE_MOUNT_F_EMPTY_PATH)    lflags |= LOOKUP_EMPTY;
 
         ret = user_path_at(from_dfd, from_pathname, lflags, &from_path);
         if (ret < 0)
                 return ret;
 
         lflags = 0;
         if (flags & MOVE_MOUNT_T_SYMLINKS)      lflags |= LOOKUP_FOLLOW;
         if (flags & MOVE_MOUNT_T_AUTOMOUNTS)    lflags |= LOOKUP_AUTOMOUNT;
         if (flags & MOVE_MOUNT_T_EMPTY_PATH)    lflags |= LOOKUP_EMPTY;
 
         ret = user_path_at(to_dfd, to_pathname, lflags, &to_path);
         if (ret < 0)
                 goto out_from;
 
         ret = security_move_mount(&from_path, &to_path);
         if (ret < 0)
                 goto out_to;
 
         if (flags & MOVE_MOUNT_SET_GROUP)
                 ret = do_set_group(&from_path, &to_path);
         else
                 ret = do_move_mount(&from_path, &to_path,
                                     (flags & MOVE_MOUNT_BENEATH));
 
 out_to:
         path_put(&to_path);
 out_from:
         path_put(&from_path);
         return ret;
 }
 
 /*
  * Return true if path is reachable from root
  *
  * namespace_sem or mount_lock is held
  */
 bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
                          const struct path *root)
 {
         while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
                 dentry = mnt->mnt_mountpoint;
                 mnt = mnt->mnt_parent;
         }
         return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
 }
 
 bool path_is_under(const struct path *path1, const struct path *path2)
 {
         bool res;
         read_seqlock_excl(&mount_lock);
         res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
         read_sequnlock_excl(&mount_lock);
         return res;
 }
 EXPORT_SYMBOL(path_is_under);
 
 /*
  * pivot_root Semantics:
  * Moves the root file system of the current process to the directory put_old,
  * makes new_root as the new root file system of the current process, and sets
  * root/cwd of all processes which had them on the current root to new_root.
  *
  * Restrictions:
  * The new_root and put_old must be directories, and  must not be on the
  * same file  system as the current process root. The put_old  must  be
  * underneath new_root,  i.e. adding a non-zero number of /.. to the string
  * pointed to by put_old must yield the same directory as new_root. No other
  * file system may be mounted on put_old. After all, new_root is a mountpoint.
  *
  * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
  * See Documentation/filesystems/ramfs-rootfs-initramfs.rst for alternatives
  * in this situation.
  *
  * Notes:
  *  - we don't move root/cwd if they are not at the root (reason: if something
  *    cared enough to change them, it's probably wrong to force them elsewhere)
  *  - it's okay to pick a root that isn't the root of a file system, e.g.
  *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
  *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
  *    first.
  */
 SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
                 const char __user *, put_old)
 {
         struct path new, old, root;
         struct mount *new_mnt, *root_mnt, *old_mnt, *root_parent, *ex_parent;
         struct mountpoint *old_mp, *root_mp;
         int error;
 
         if (!may_mount())
                 return -EPERM;
 
         error = user_path_at(AT_FDCWD, new_root,
                              LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &new);
         if (error)
                 goto out0;
 
         error = user_path_at(AT_FDCWD, put_old,
                              LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old);
         if (error)
                 goto out1;
 
         error = security_sb_pivotroot(&old, &new);
         if (error)
                 goto out2;
 
         get_fs_root(current->fs, &root);
         old_mp = lock_mount(&old);
         error = PTR_ERR(old_mp);
         if (IS_ERR(old_mp))
                 goto out3;
 
         error = -EINVAL;
         new_mnt = real_mount(new.mnt);
         root_mnt = real_mount(root.mnt);
         old_mnt = real_mount(old.mnt);
         ex_parent = new_mnt->mnt_parent;
         root_parent = root_mnt->mnt_parent;
         if (IS_MNT_SHARED(old_mnt) ||
                 IS_MNT_SHARED(ex_parent) ||
                 IS_MNT_SHARED(root_parent))
                 goto out4;
         if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
                 goto out4;
         if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
                 goto out4;
         error = -ENOENT;
         if (d_unlinked(new.dentry))
                 goto out4;
         error = -EBUSY;
         if (new_mnt == root_mnt || old_mnt == root_mnt)
                 goto out4; /* loop, on the same file system  */
         error = -EINVAL;
         if (!path_mounted(&root))
                 goto out4; /* not a mountpoint */
         if (!mnt_has_parent(root_mnt))
                 goto out4; /* not attached */
         if (!path_mounted(&new))
                 goto out4; /* not a mountpoint */
         if (!mnt_has_parent(new_mnt))
                 goto out4; /* not attached */
         /* make sure we can reach put_old from new_root */
         if (!is_path_reachable(old_mnt, old.dentry, &new))
                 goto out4;
         /* make certain new is below the root */
         if (!is_path_reachable(new_mnt, new.dentry, &root))
                 goto out4;
         lock_mount_hash();
         umount_mnt(new_mnt);
         root_mp = unhash_mnt(root_mnt);  /* we'll need its mountpoint */
         if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
                 new_mnt->mnt.mnt_flags |= MNT_LOCKED;
                 root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
         }
         /* mount old root on put_old */
         attach_mnt(root_mnt, old_mnt, old_mp, false);
         /* mount new_root on / */
         attach_mnt(new_mnt, root_parent, root_mp, false);
         mnt_add_count(root_parent, -1);
         touch_mnt_namespace(current->nsproxy->mnt_ns);
         /* A moved mount should not expire automatically */
         list_del_init(&new_mnt->mnt_expire);
         put_mountpoint(root_mp);
         unlock_mount_hash();
         chroot_fs_refs(&root, &new);
         error = 0;
 out4:
         unlock_mount(old_mp);
         if (!error)
                 mntput_no_expire(ex_parent);
 out3:
         path_put(&root);
 out2:
         path_put(&old);
 out1:
         path_put(&new);
 out0:
         return error;
 }
 
 static unsigned int recalc_flags(struct mount_kattr *kattr, struct mount *mnt)
 {
         unsigned int flags = mnt->mnt.mnt_flags;
 
         /*  flags to clear */
         flags &= ~kattr->attr_clr;
         /* flags to raise */
         flags |= kattr->attr_set;
 
         return flags;
 }
 
 static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
 {
         struct vfsmount *m = &mnt->mnt;
         struct user_namespace *fs_userns = m->mnt_sb->s_user_ns;
 
         if (!kattr->mnt_idmap)
                 return 0;
 
         /*
          * Creating an idmapped mount with the filesystem wide idmapping
          * doesn't make sense so block that. We don't allow mushy semantics.
          */
         if (kattr->mnt_userns == m->mnt_sb->s_user_ns)
                 return -EINVAL;
 
         /*
          * Once a mount has been idmapped we don't allow it to change its
          * mapping. It makes things simpler and callers can just create
          * another bind-mount they can idmap if they want to.
          */
         if (is_idmapped_mnt(m))
                 return -EPERM;
 
         /* The underlying filesystem doesn't support idmapped mounts yet. */
         if (!(m->mnt_sb->s_type->fs_flags & FS_ALLOW_IDMAP))
                 return -EINVAL;
 
         /* We're not controlling the superblock. */
         if (!ns_capable(fs_userns, CAP_SYS_ADMIN))
                 return -EPERM;
 
         /* Mount has already been visible in the filesystem hierarchy. */
         if (!is_anon_ns(mnt->mnt_ns))
                 return -EINVAL;
 
         return 0;
 }
 
 /**
  * mnt_allow_writers() - check whether the attribute change allows writers
  * @kattr: the new mount attributes
  * @mnt: the mount to which @kattr will be applied
  *
  * Check whether thew new mount attributes in @kattr allow concurrent writers.
  *
  * Return: true if writers need to be held, false if not
  */
 static inline bool mnt_allow_writers(const struct mount_kattr *kattr,
                                      const struct mount *mnt)
 {
         return (!(kattr->attr_set & MNT_READONLY) ||
                 (mnt->mnt.mnt_flags & MNT_READONLY)) &&
                !kattr->mnt_idmap;
 }
 
 static int mount_setattr_prepare(struct mount_kattr *kattr, struct mount *mnt)
 {
         struct mount *m;
         int err;
 
         for (m = mnt; m; m = next_mnt(m, mnt)) {
                 if (!can_change_locked_flags(m, recalc_flags(kattr, m))) {
                         err = -EPERM;
                         break;
                 }
 
                 err = can_idmap_mount(kattr, m);
                 if (err)
                         break;
 
                 if (!mnt_allow_writers(kattr, m)) {
                         err = mnt_hold_writers(m);
                         if (err)
                                 break;
                 }
 
                 if (!kattr->recurse)
                         return 0;
         }
 
         if (err) {
                 struct mount *p;
 
                 /*
                  * If we had to call mnt_hold_writers() MNT_WRITE_HOLD will
                  * be set in @mnt_flags. The loop unsets MNT_WRITE_HOLD for all
                  * mounts and needs to take care to include the first mount.
                  */
                 for (p = mnt; p; p = next_mnt(p, mnt)) {
                         /* If we had to hold writers unblock them. */
                         if (p->mnt.mnt_flags & MNT_WRITE_HOLD)
                                 mnt_unhold_writers(p);
 
                         /*
                          * We're done once the first mount we changed got
                          * MNT_WRITE_HOLD unset.
                          */
                         if (p == m)
                                 break;
                 }
         }
         return err;
 }
 
 static void do_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
 {
         if (!kattr->mnt_idmap)
                 return;
 
         /*
          * Pairs with smp_load_acquire() in mnt_idmap().
          *
          * Since we only allow a mount to change the idmapping once and
          * verified this in can_idmap_mount() we know that the mount has
          * @nop_mnt_idmap attached to it. So there's no need to drop any
          * references.
          */
         smp_store_release(&mnt->mnt.mnt_idmap, mnt_idmap_get(kattr->mnt_idmap));
 }
 
 static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt)
 {
         struct mount *m;
 
         for (m = mnt; m; m = next_mnt(m, mnt)) {
                 unsigned int flags;
 
                 do_idmap_mount(kattr, m);
                 flags = recalc_flags(kattr, m);
                 WRITE_ONCE(m->mnt.mnt_flags, flags);
 
                 /* If we had to hold writers unblock them. */
                 if (m->mnt.mnt_flags & MNT_WRITE_HOLD)
                         mnt_unhold_writers(m);
 
                 if (kattr->propagation)
                         change_mnt_propagation(m, kattr->propagation);
                 if (!kattr->recurse)
                         break;
         }
         touch_mnt_namespace(mnt->mnt_ns);
 }
 
 static int do_mount_setattr(struct path *path, struct mount_kattr *kattr)
 {
         struct mount *mnt = real_mount(path->mnt);
         int err = 0;
 
         if (!path_mounted(path))
                 return -EINVAL;
 
         if (kattr->mnt_userns) {
                 struct mnt_idmap *mnt_idmap;
 
                 mnt_idmap = alloc_mnt_idmap(kattr->mnt_userns);
                 if (IS_ERR(mnt_idmap))
                         return PTR_ERR(mnt_idmap);
                 kattr->mnt_idmap = mnt_idmap;
         }
 
         if (kattr->propagation) {
                 /*
                  * Only take namespace_lock() if we're actually changing
                  * propagation.
                  */
                 namespace_lock();
                 if (kattr->propagation == MS_SHARED) {
                         err = invent_group_ids(mnt, kattr->recurse);
                         if (err) {
                                 namespace_unlock();
                                 return err;
                         }
                 }
         }
 
         err = -EINVAL;
         lock_mount_hash();
 
         /* Ensure that this isn't anything purely vfs internal. */
         if (!is_mounted(&mnt->mnt))
                 goto out;
 
         /*
          * If this is an attached mount make sure it's located in the callers
          * mount namespace. If it's not don't let the caller interact with it.
          *
          * If this mount doesn't have a parent it's most often simply a
          * detached mount with an anonymous mount namespace. IOW, something
          * that's simply not attached yet. But there are apparently also users
          * that do change mount properties on the rootfs itself. That obviously
          * neither has a parent nor is it a detached mount so we cannot
          * unconditionally check for detached mounts.
          */
         if ((mnt_has_parent(mnt) || !is_anon_ns(mnt->mnt_ns)) && !check_mnt(mnt))
                 goto out;
 
         /*
          * First, we get the mount tree in a shape where we can change mount
          * properties without failure. If we succeeded to do so we commit all
          * changes and if we failed we clean up.
          */
         err = mount_setattr_prepare(kattr, mnt);
         if (!err)
                 mount_setattr_commit(kattr, mnt);
 
 out:
         unlock_mount_hash();
 
         if (kattr->propagation) {
                 if (err)
                         cleanup_group_ids(mnt, NULL);
                 namespace_unlock();
         }
 
         return err;
 }
 
 static int build_mount_idmapped(const struct mount_attr *attr, size_t usize,
                                 struct mount_kattr *kattr, unsigned int flags)
 {
         int err = 0;
         struct ns_common *ns;
         struct user_namespace *mnt_userns;
         struct fd f;
 
         if (!((attr->attr_set | attr->attr_clr) & MOUNT_ATTR_IDMAP))
                 return 0;
 
         /*
          * We currently do not support clearing an idmapped mount. If this ever
          * is a use-case we can revisit this but for now let's keep it simple
          * and not allow it.
          */
         if (attr->attr_clr & MOUNT_ATTR_IDMAP)
                 return -EINVAL;
 
         if (attr->userns_fd > INT_MAX)
                 return -EINVAL;
 
         f = fdget(attr->userns_fd);
         if (!f.file)
                 return -EBADF;
 
         if (!proc_ns_file(f.file)) {
                 err = -EINVAL;
                 goto out_fput;
         }
 
         ns = get_proc_ns(file_inode(f.file));
         if (ns->ops->type != CLONE_NEWUSER) {
                 err = -EINVAL;
                 goto out_fput;
         }
 
         /*
          * The initial idmapping cannot be used to create an idmapped
          * mount. We use the initial idmapping as an indicator of a mount
          * that is not idmapped. It can simply be passed into helpers that
          * are aware of idmapped mounts as a convenient shortcut. A user
          * can just create a dedicated identity mapping to achieve the same
          * result.
          */
         mnt_userns = container_of(ns, struct user_namespace, ns);
         if (mnt_userns == &init_user_ns) {
                 err = -EPERM;
                 goto out_fput;
         }
 
         /* We're not controlling the target namespace. */
         if (!ns_capable(mnt_userns, CAP_SYS_ADMIN)) {
                 err = -EPERM;
                 goto out_fput;
         }
 
         kattr->mnt_userns = get_user_ns(mnt_userns);
 
 out_fput:
         fdput(f);
         return err;
 }
 
 static int build_mount_kattr(const struct mount_attr *attr, size_t usize,
                              struct mount_kattr *kattr, unsigned int flags)
 {
         unsigned int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
 
         if (flags & AT_NO_AUTOMOUNT)
                 lookup_flags &= ~LOOKUP_AUTOMOUNT;
         if (flags & AT_SYMLINK_NOFOLLOW)
                 lookup_flags &= ~LOOKUP_FOLLOW;
         if (flags & AT_EMPTY_PATH)
                 lookup_flags |= LOOKUP_EMPTY;
 
         *kattr = (struct mount_kattr) {
                 .lookup_flags   = lookup_flags,
                 .recurse        = !!(flags & AT_RECURSIVE),
         };
 
         if (attr->propagation & ~MOUNT_SETATTR_PROPAGATION_FLAGS)
                 return -EINVAL;
         if (hweight32(attr->propagation & MOUNT_SETATTR_PROPAGATION_FLAGS) > 1)
                 return -EINVAL;
         kattr->propagation = attr->propagation;
 
         if ((attr->attr_set | attr->attr_clr) & ~MOUNT_SETATTR_VALID_FLAGS)
                 return -EINVAL;
 
         kattr->attr_set = attr_flags_to_mnt_flags(attr->attr_set);
         kattr->attr_clr = attr_flags_to_mnt_flags(attr->attr_clr);
 
         /*
          * Since the MOUNT_ATTR_<atime> values are an enum, not a bitmap,
          * users wanting to transition to a different atime setting cannot
          * simply specify the atime setting in @attr_set, but must also
          * specify MOUNT_ATTR__ATIME in the @attr_clr field.
          * So ensure that MOUNT_ATTR__ATIME can't be partially set in
          * @attr_clr and that @attr_set can't have any atime bits set if
          * MOUNT_ATTR__ATIME isn't set in @attr_clr.
          */
         if (attr->attr_clr & MOUNT_ATTR__ATIME) {
                 if ((attr->attr_clr & MOUNT_ATTR__ATIME) != MOUNT_ATTR__ATIME)
                         return -EINVAL;
 
                 /*
                  * Clear all previous time settings as they are mutually
                  * exclusive.
                  */
                 kattr->attr_clr |= MNT_RELATIME | MNT_NOATIME;
                 switch (attr->attr_set & MOUNT_ATTR__ATIME) {
                 case MOUNT_ATTR_RELATIME:
                         kattr->attr_set |= MNT_RELATIME;
                         break;
                 case MOUNT_ATTR_NOATIME:
                         kattr->attr_set |= MNT_NOATIME;
                         break;
                 case MOUNT_ATTR_STRICTATIME:
                         break;
                 default:
                         return -EINVAL;
                 }
         } else {
                 if (attr->attr_set & MOUNT_ATTR__ATIME)
                         return -EINVAL;
         }
 
         return build_mount_idmapped(attr, usize, kattr, flags);
 }
 
 static void finish_mount_kattr(struct mount_kattr *kattr)
 {
         put_user_ns(kattr->mnt_userns);
         kattr->mnt_userns = NULL;
 
         if (kattr->mnt_idmap)
                 mnt_idmap_put(kattr->mnt_idmap);
 }
 
 SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path,
                 unsigned int, flags, struct mount_attr __user *, uattr,
                 size_t, usize)
 {
         int err;
         struct path target;
         struct mount_attr attr;
         struct mount_kattr kattr;
 
         BUILD_BUG_ON(sizeof(struct mount_attr) != MOUNT_ATTR_SIZE_VER0);
 
         if (flags & ~(AT_EMPTY_PATH |
                       AT_RECURSIVE |
                       AT_SYMLINK_NOFOLLOW |
                       AT_NO_AUTOMOUNT))
                 return -EINVAL;
 
         if (unlikely(usize > PAGE_SIZE))
                 return -E2BIG;
         if (unlikely(usize < MOUNT_ATTR_SIZE_VER0))
                 return -EINVAL;
 
         if (!may_mount())
                 return -EPERM;
 
         err = copy_struct_from_user(&attr, sizeof(attr), uattr, usize);
         if (err)
                 return err;
 
         /* Don't bother walking through the mounts if this is a nop. */
         if (attr.attr_set == 0 &&
             attr.attr_clr == 0 &&
             attr.propagation == 0)
                 return 0;
 
         err = build_mount_kattr(&attr, usize, &kattr, flags);
         if (err)
                 return err;
 
         err = user_path_at(dfd, path, kattr.lookup_flags, &target);
         if (!err) {
                 err = do_mount_setattr(&target, &kattr);
                 path_put(&target);
         }
         finish_mount_kattr(&kattr);
         return err;
 }
 
 int show_path(struct seq_file *m, struct dentry *root)
 {
         if (root->d_sb->s_op->show_path)
                 return root->d_sb->s_op->show_path(m, root);
 
         seq_dentry(m, root, " \t\n\\");
         return 0;
 }
 
 static struct vfsmount *lookup_mnt_in_ns(u64 id, struct mnt_namespace *ns)
 {
         struct mount *mnt = mnt_find_id_at(ns, id);
 
         if (!mnt || mnt->mnt_id_unique != id)
                 return NULL;
 
         return &mnt->mnt;
 }
 
 struct kstatmount {
         struct statmount __user *buf;
         size_t bufsize;
         struct vfsmount *mnt;
         u64 mask;
         struct path root;
         struct statmount sm;
         struct seq_file seq;
 };
 
 static u64 mnt_to_attr_flags(struct vfsmount *mnt)
 {
         unsigned int mnt_flags = READ_ONCE(mnt->mnt_flags);
         u64 attr_flags = 0;
 
         if (mnt_flags & MNT_READONLY)
                 attr_flags |= MOUNT_ATTR_RDONLY;
         if (mnt_flags & MNT_NOSUID)
                 attr_flags |= MOUNT_ATTR_NOSUID;
         if (mnt_flags & MNT_NODEV)
                 attr_flags |= MOUNT_ATTR_NODEV;
         if (mnt_flags & MNT_NOEXEC)
                 attr_flags |= MOUNT_ATTR_NOEXEC;
         if (mnt_flags & MNT_NODIRATIME)
                 attr_flags |= MOUNT_ATTR_NODIRATIME;
         if (mnt_flags & MNT_NOSYMFOLLOW)
                 attr_flags |= MOUNT_ATTR_NOSYMFOLLOW;
 
         if (mnt_flags & MNT_NOATIME)
                 attr_flags |= MOUNT_ATTR_NOATIME;
         else if (mnt_flags & MNT_RELATIME)
                 attr_flags |= MOUNT_ATTR_RELATIME;
         else
                 attr_flags |= MOUNT_ATTR_STRICTATIME;
 
         if (is_idmapped_mnt(mnt))
                 attr_flags |= MOUNT_ATTR_IDMAP;
 
         return attr_flags;
 }
 
 static u64 mnt_to_propagation_flags(struct mount *m)
 {
         u64 propagation = 0;
 
         if (IS_MNT_SHARED(m))
                 propagation |= MS_SHARED;
         if (IS_MNT_SLAVE(m))
                 propagation |= MS_SLAVE;
         if (IS_MNT_UNBINDABLE(m))
                 propagation |= MS_UNBINDABLE;
         if (!propagation)
                 propagation |= MS_PRIVATE;
 
         return propagation;
 }
 
 static void statmount_sb_basic(struct kstatmount *s)
 {
         struct super_block *sb = s->mnt->mnt_sb;
 
         s->sm.mask |= STATMOUNT_SB_BASIC;
         s->sm.sb_dev_major = MAJOR(sb->s_dev);
         s->sm.sb_dev_minor = MINOR(sb->s_dev);
         s->sm.sb_magic = sb->s_magic;
         s->sm.sb_flags = sb->s_flags & (SB_RDONLY|SB_SYNCHRONOUS|SB_DIRSYNC|SB_LAZYTIME);
 }
 
 static void statmount_mnt_basic(struct kstatmount *s)
 {
         struct mount *m = real_mount(s->mnt);
 
         s->sm.mask |= STATMOUNT_MNT_BASIC;
         s->sm.mnt_id = m->mnt_id_unique;
         s->sm.mnt_parent_id = m->mnt_parent->mnt_id_unique;
         s->sm.mnt_id_old = m->mnt_id;
         s->sm.mnt_parent_id_old = m->mnt_parent->mnt_id;
         s->sm.mnt_attr = mnt_to_attr_flags(&m->mnt);
         s->sm.mnt_propagation = mnt_to_propagation_flags(m);
         s->sm.mnt_peer_group = IS_MNT_SHARED(m) ? m->mnt_group_id : 0;
         s->sm.mnt_master = IS_MNT_SLAVE(m) ? m->mnt_master->mnt_group_id : 0;
 }
 
 static void statmount_propagate_from(struct kstatmount *s)
 {
         struct mount *m = real_mount(s->mnt);
 
         s->sm.mask |= STATMOUNT_PROPAGATE_FROM;
         if (IS_MNT_SLAVE(m))
                 s->sm.propagate_from = get_dominating_id(m, &current->fs->root);
 }
 
 static int statmount_mnt_root(struct kstatmount *s, struct seq_file *seq)
 {
         int ret;
         size_t start = seq->count;
 
         ret = show_path(seq, s->mnt->mnt_root);
         if (ret)
                 return ret;
 
         if (unlikely(seq_has_overflowed(seq)))
                 return -EAGAIN;
 
         /*
          * Unescape the result. It would be better if supplied string was not
          * escaped in the first place, but that's a pretty invasive change.
          */
         seq->buf[seq->count] = '\0';
         seq->count = start;
         seq_commit(seq, string_unescape_inplace(seq->buf + start, UNESCAPE_OCTAL));
         return 0;
 }
 
 static int statmount_mnt_point(struct kstatmount *s, struct seq_file *seq)
 {
         struct vfsmount *mnt = s->mnt;
         struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
         int err;
 
         err = seq_path_root(seq, &mnt_path, &s->root, "");
         return err == SEQ_SKIP ? 0 : err;
 }
 
 static int statmount_fs_type(struct kstatmount *s, struct seq_file *seq)
 {
         struct super_block *sb = s->mnt->mnt_sb;
 
         seq_puts(seq, sb->s_type->name);
         return 0;
 }
 
 static void statmount_mnt_ns_id(struct kstatmount *s, struct mnt_namespace *ns)
 {
         s->sm.mask |= STATMOUNT_MNT_NS_ID;
         s->sm.mnt_ns_id = ns->seq;
 }
 
 static int statmount_mnt_opts(struct kstatmount *s, struct seq_file *seq)
 {
         struct vfsmount *mnt = s->mnt;
         struct super_block *sb = mnt->mnt_sb;
         int err;
 
         if (sb->s_op->show_options) {
                 size_t start = seq->count;
 
                 err = sb->s_op->show_options(seq, mnt->mnt_root);
                 if (err)
                         return err;
 
                 if (unlikely(seq_has_overflowed(seq)))
                         return -EAGAIN;
 
                 if (seq->count == start)
                         return 0;
 
                 /* skip leading comma */
                 memmove(seq->buf + start, seq->buf + start + 1,
                         seq->count - start - 1);
                 seq->count--;
         }
 
         return 0;
 }
 
 static int statmount_string(struct kstatmount *s, u64 flag)
 {
         int ret;
         size_t kbufsize;
         struct seq_file *seq = &s->seq;
         struct statmount *sm = &s->sm;
 
         switch (flag) {
         case STATMOUNT_FS_TYPE:
                 sm->fs_type = seq->count;
                 ret = statmount_fs_type(s, seq);
                 break;
         case STATMOUNT_MNT_ROOT:
                 sm->mnt_root = seq->count;
                 ret = statmount_mnt_root(s, seq);
                 break;
         case STATMOUNT_MNT_POINT:
                 sm->mnt_point = seq->count;
                 ret = statmount_mnt_point(s, seq);
                 break;
         case STATMOUNT_MNT_OPTS:
                 sm->mnt_opts = seq->count;
                 ret = statmount_mnt_opts(s, seq);
                 break;
         default:
                 WARN_ON_ONCE(true);
                 return -EINVAL;
         }
 
         if (unlikely(check_add_overflow(sizeof(*sm), seq->count, &kbufsize)))
                 return -EOVERFLOW;
         if (kbufsize >= s->bufsize)
                 return -EOVERFLOW;
 
         /* signal a retry */
         if (unlikely(seq_has_overflowed(seq)))
                 return -EAGAIN;
 
         if (ret)
                 return ret;
 
         seq->buf[seq->count++] = '\0';
         sm->mask |= flag;
         return 0;
 }
 
 static int copy_statmount_to_user(struct kstatmount *s)
 {
         struct statmount *sm = &s->sm;
         struct seq_file *seq = &s->seq;
         char __user *str = ((char __user *)s->buf) + sizeof(*sm);
         size_t copysize = min_t(size_t, s->bufsize, sizeof(*sm));
 
         if (seq->count && copy_to_user(str, seq->buf, seq->count))
                 return -EFAULT;
 
         /* Return the number of bytes copied to the buffer */
         sm->size = copysize + seq->count;
         if (copy_to_user(s->buf, sm, copysize))
                 return -EFAULT;
 
         return 0;
 }
 
 static struct mount *listmnt_next(struct mount *curr, bool reverse)
 {
         struct rb_node *node;
 
         if (reverse)
                 node = rb_prev(&curr->mnt_node);
         else
                 node = rb_next(&curr->mnt_node);
 
         return node_to_mount(node);
 }
 
 static int grab_requested_root(struct mnt_namespace *ns, struct path *root)
 {
         struct mount *first, *child;
 
         rwsem_assert_held(&namespace_sem);
 
         /* We're looking at our own ns, just use get_fs_root. */
         if (ns == current->nsproxy->mnt_ns) {
                 get_fs_root(current->fs, root);
                 return 0;
         }
 
         /*
          * We have to find the first mount in our ns and use that, however it
          * may not exist, so handle that properly.
          */
         if (RB_EMPTY_ROOT(&ns->mounts))
                 return -ENOENT;
 
         first = child = ns->root;
         for (;;) {
                 child = listmnt_next(child, false);
                 if (!child)
                         return -ENOENT;
                 if (child->mnt_parent == first)
                         break;
         }
 
         root->mnt = mntget(&child->mnt);
         root->dentry = dget(root->mnt->mnt_root);
         return 0;
 }
 
 static int do_statmount(struct kstatmount *s, u64 mnt_id, u64 mnt_ns_id,
                         struct mnt_namespace *ns)
 {
         struct path root __free(path_put) = {};
         struct mount *m;
         int err;
 
         /* Has the namespace already been emptied? */
         if (mnt_ns_id && RB_EMPTY_ROOT(&ns->mounts))
                 return -ENOENT;
 
         s->mnt = lookup_mnt_in_ns(mnt_id, ns);
         if (!s->mnt)
                 return -ENOENT;
 
         err = grab_requested_root(ns, &root);
         if (err)
                 return err;
 
         /*
          * Don't trigger audit denials. We just want to determine what
          * mounts to show users.
          */
         m = real_mount(s->mnt);
         if (!is_path_reachable(m, m->mnt.mnt_root, &root) &&
             !ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
                 return -EPERM;
 
         err = security_sb_statfs(s->mnt->mnt_root);
         if (err)
                 return err;
 
         s->root = root;
         if (s->mask & STATMOUNT_SB_BASIC)
                 statmount_sb_basic(s);
 
         if (s->mask & STATMOUNT_MNT_BASIC)
                 statmount_mnt_basic(s);
 
         if (s->mask & STATMOUNT_PROPAGATE_FROM)
                 statmount_propagate_from(s);
 
         if (s->mask & STATMOUNT_FS_TYPE)
                 err = statmount_string(s, STATMOUNT_FS_TYPE);
 
         if (!err && s->mask & STATMOUNT_MNT_ROOT)
                 err = statmount_string(s, STATMOUNT_MNT_ROOT);
 
         if (!err && s->mask & STATMOUNT_MNT_POINT)
                 err = statmount_string(s, STATMOUNT_MNT_POINT);
 
         if (!err && s->mask & STATMOUNT_MNT_OPTS)
                 err = statmount_string(s, STATMOUNT_MNT_OPTS);
 
         if (!err && s->mask & STATMOUNT_MNT_NS_ID)
                 statmount_mnt_ns_id(s, ns);
 
         if (err)
                 return err;
 
         return 0;
 }
 
 static inline bool retry_statmount(const long ret, size_t *seq_size)
 {
         if (likely(ret != -EAGAIN))
                 return false;
         if (unlikely(check_mul_overflow(*seq_size, 2, seq_size)))
                 return false;
         if (unlikely(*seq_size > MAX_RW_COUNT))
                 return false;
         return true;
 }
 
 #define STATMOUNT_STRING_REQ (STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT | \
                               STATMOUNT_FS_TYPE | STATMOUNT_MNT_OPTS)
 
 static int prepare_kstatmount(struct kstatmount *ks, struct mnt_id_req *kreq,
                               struct statmount __user *buf, size_t bufsize,
                               size_t seq_size)
 {
         if (!access_ok(buf, bufsize))
                 return -EFAULT;
 
         memset(ks, 0, sizeof(*ks));
         ks->mask = kreq->param;
         ks->buf = buf;
         ks->bufsize = bufsize;
 
         if (ks->mask & STATMOUNT_STRING_REQ) {
                 if (bufsize == sizeof(ks->sm))
                         return -EOVERFLOW;
 
                 ks->seq.buf = kvmalloc(seq_size, GFP_KERNEL_ACCOUNT);
                 if (!ks->seq.buf)
                         return -ENOMEM;
 
                 ks->seq.size = seq_size;
         }
 
         return 0;
 }
 
 static int copy_mnt_id_req(const struct mnt_id_req __user *req,
                            struct mnt_id_req *kreq)
 {
         int ret;
         size_t usize;
 
         BUILD_BUG_ON(sizeof(struct mnt_id_req) != MNT_ID_REQ_SIZE_VER1);
 
         ret = get_user(usize, &req->size);
         if (ret)
                 return -EFAULT;
         if (unlikely(usize > PAGE_SIZE))
                 return -E2BIG;
         if (unlikely(usize < MNT_ID_REQ_SIZE_VER0))
                 return -EINVAL;
         memset(kreq, 0, sizeof(*kreq));
         ret = copy_struct_from_user(kreq, sizeof(*kreq), req, usize);
         if (ret)
                 return ret;
         if (kreq->spare != 0)
                 return -EINVAL;
         /* The first valid unique mount id is MNT_UNIQUE_ID_OFFSET + 1. */
         if (kreq->mnt_id <= MNT_UNIQUE_ID_OFFSET)
                 return -EINVAL;
         return 0;
 }
 
 /*
  * If the user requested a specific mount namespace id, look that up and return
  * that, or if not simply grab a passive reference on our mount namespace and
  * return that.
  */
 static struct mnt_namespace *grab_requested_mnt_ns(u64 mnt_ns_id)
 {
         if (mnt_ns_id)
                 return lookup_mnt_ns(mnt_ns_id);
         refcount_inc(&current->nsproxy->mnt_ns->passive);
         return current->nsproxy->mnt_ns;
 }
 
 SYSCALL_DEFINE4(statmount, const struct mnt_id_req __user *, req,
                 struct statmount __user *, buf, size_t, bufsize,
                 unsigned int, flags)
 {
         struct mnt_namespace *ns __free(mnt_ns_release) = NULL;
         struct kstatmount *ks __free(kfree) = NULL;
         struct mnt_id_req kreq;
         /* We currently support retrieval of 3 strings. */
         size_t seq_size = 3 * PATH_MAX;
         int ret;
 
         if (flags)
                 return -EINVAL;
 
         ret = copy_mnt_id_req(req, &kreq);
         if (ret)
                 return ret;
 
         ns = grab_requested_mnt_ns(kreq.mnt_ns_id);
         if (!ns)
                 return -ENOENT;
 
         if (kreq.mnt_ns_id && (ns != current->nsproxy->mnt_ns) &&
             !ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
                 return -ENOENT;
 
         ks = kmalloc(sizeof(*ks), GFP_KERNEL_ACCOUNT);
         if (!ks)
                 return -ENOMEM;
 
 retry:
         ret = prepare_kstatmount(ks, &kreq, buf, bufsize, seq_size);
         if (ret)
                 return ret;
 
         scoped_guard(rwsem_read, &namespace_sem)
                 ret = do_statmount(ks, kreq.mnt_id, kreq.mnt_ns_id, ns);
 
         if (!ret)
                 ret = copy_statmount_to_user(ks);
         kvfree(ks->seq.buf);
         if (retry_statmount(ret, &seq_size))
                 goto retry;
         return ret;
 }
 
 static ssize_t do_listmount(struct mnt_namespace *ns, u64 mnt_parent_id,
                             u64 last_mnt_id, u64 *mnt_ids, size_t nr_mnt_ids,
                             bool reverse)
 {
         struct path root __free(path_put) = {};
         struct path orig;
         struct mount *r, *first;
         ssize_t ret;
 
         rwsem_assert_held(&namespace_sem);
 
         ret = grab_requested_root(ns, &root);
         if (ret)
                 return ret;
 
         if (mnt_parent_id == LSMT_ROOT) {
                 orig = root;
         } else {
                 orig.mnt = lookup_mnt_in_ns(mnt_parent_id, ns);
                 if (!orig.mnt)
                         return -ENOENT;
                 orig.dentry = orig.mnt->mnt_root;
         }
 
         /*
          * Don't trigger audit denials. We just want to determine what
          * mounts to show users.
          */
         if (!is_path_reachable(real_mount(orig.mnt), orig.dentry, &root) &&
             !ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
                 return -EPERM;
 
         ret = security_sb_statfs(orig.dentry);
         if (ret)
                 return ret;
 
         if (!last_mnt_id) {
                 if (reverse)
                         first = node_to_mount(rb_last(&ns->mounts));
                 else
                         first = node_to_mount(rb_first(&ns->mounts));
         } else {
                 if (reverse)
                         first = mnt_find_id_at_reverse(ns, last_mnt_id - 1);
                 else
                         first = mnt_find_id_at(ns, last_mnt_id + 1);
         }
 
         for (ret = 0, r = first; r && nr_mnt_ids; r = listmnt_next(r, reverse)) {
                 if (r->mnt_id_unique == mnt_parent_id)
                         continue;
                 if (!is_path_reachable(r, r->mnt.mnt_root, &orig))
                         continue;
                 *mnt_ids = r->mnt_id_unique;
                 mnt_ids++;
                 nr_mnt_ids--;
                 ret++;
         }
         return ret;
 }
 
 SYSCALL_DEFINE4(listmount, const struct mnt_id_req __user *, req,
                 u64 __user *, mnt_ids, size_t, nr_mnt_ids, unsigned int, flags)
 {
         u64 *kmnt_ids __free(kvfree) = NULL;
         const size_t maxcount = 1000000;
         struct mnt_namespace *ns __free(mnt_ns_release) = NULL;
         struct mnt_id_req kreq;
         u64 last_mnt_id;
         ssize_t ret;
 
         if (flags & ~LISTMOUNT_REVERSE)
                 return -EINVAL;
 
         /*
          * If the mount namespace really has more than 1 million mounts the
          * caller must iterate over the mount namespace (and reconsider their
          * system design...).
          */
         if (unlikely(nr_mnt_ids > maxcount))
                 return -EOVERFLOW;
 
         if (!access_ok(mnt_ids, nr_mnt_ids * sizeof(*mnt_ids)))
                 return -EFAULT;
 
         ret = copy_mnt_id_req(req, &kreq);
         if (ret)
                 return ret;
 
         last_mnt_id = kreq.param;
         /* The first valid unique mount id is MNT_UNIQUE_ID_OFFSET + 1. */
         if (last_mnt_id != 0 && last_mnt_id <= MNT_UNIQUE_ID_OFFSET)
                 return -EINVAL;
 
         kmnt_ids = kvmalloc_array(nr_mnt_ids, sizeof(*kmnt_ids),
                                   GFP_KERNEL_ACCOUNT);
         if (!kmnt_ids)
                 return -ENOMEM;
 
         ns = grab_requested_mnt_ns(kreq.mnt_ns_id);
         if (!ns)
                 return -ENOENT;
 
         if (kreq.mnt_ns_id && (ns != current->nsproxy->mnt_ns) &&
             !ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
                 return -ENOENT;
 
         scoped_guard(rwsem_read, &namespace_sem)
                 ret = do_listmount(ns, kreq.mnt_id, last_mnt_id, kmnt_ids,
                                    nr_mnt_ids, (flags & LISTMOUNT_REVERSE));
         if (ret <= 0)
                 return ret;
 
         if (copy_to_user(mnt_ids, kmnt_ids, ret * sizeof(*mnt_ids)))
                 return -EFAULT;
 
         return ret;
 }
 
 static void __init init_mount_tree(void)
 {
         struct vfsmount *mnt;
         struct mount *m;
         struct mnt_namespace *ns;
         struct path root;
 
         mnt = vfs_kern_mount(&rootfs_fs_type, 0, "rootfs", NULL);
         if (IS_ERR(mnt))
                 panic("Can't create rootfs");
 
         ns = alloc_mnt_ns(&init_user_ns, false);
         if (IS_ERR(ns))
                 panic("Can't allocate initial namespace");
         m = real_mount(mnt);
         ns->root = m;
         ns->nr_mounts = 1;
         mnt_add_to_ns(ns, m);
         init_task.nsproxy->mnt_ns = ns;
         get_mnt_ns(ns);
 
         root.mnt = mnt;
         root.dentry = mnt->mnt_root;
         mnt->mnt_flags |= MNT_LOCKED;
 
         set_fs_pwd(current->fs, &root);
         set_fs_root(current->fs, &root);
 
         mnt_ns_tree_add(ns);
 }
 
 void __init mnt_init(void)
 {
         int err;
 
         mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
 
         mount_hashtable = alloc_large_system_hash("Mount-cache",
                                 sizeof(struct hlist_head),
                                 mhash_entries, 19,
                                 HASH_ZERO,
                                 &m_hash_shift, &m_hash_mask, 0, 0);
         mountpoint_hashtable = alloc_large_system_hash("Mountpoint-cache",
                                 sizeof(struct hlist_head),
                                 mphash_entries, 19,
                                 HASH_ZERO,
                                 &mp_hash_shift, &mp_hash_mask, 0, 0);
 
         if (!mount_hashtable || !mountpoint_hashtable)
                 panic("Failed to allocate mount hash table\n");
 
         kernfs_init();
 
         err = sysfs_init();
         if (err)
                 printk(KERN_WARNING "%s: sysfs_init error: %d\n",
                         __func__, err);
         fs_kobj = kobject_create_and_add("fs", NULL);
         if (!fs_kobj)
                 printk(KERN_WARNING "%s: kobj create error\n", __func__);
         shmem_init();
         init_rootfs();
         init_mount_tree();
 }
 
 void put_mnt_ns(struct mnt_namespace *ns)
 {
         if (!refcount_dec_and_test(&ns->ns.count))
                 return;
         drop_collected_mounts(&ns->root->mnt);
         free_mnt_ns(ns);
 }
 
 struct vfsmount *kern_mount(struct file_system_type *type)
 {
         struct vfsmount *mnt;
         mnt = vfs_kern_mount(type, SB_KERNMOUNT, type->name, NULL);
         if (!IS_ERR(mnt)) {
                 /*
                  * it is a longterm mount, don't release mnt until
                  * we unmount before file sys is unregistered
                 */
                 real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
         }
         return mnt;
 }
 EXPORT_SYMBOL_GPL(kern_mount);
 
 void kern_unmount(struct vfsmount *mnt)
 {
         /* release long term mount so mount point can be released */
         if (!IS_ERR(mnt)) {
                 mnt_make_shortterm(mnt);
                 synchronize_rcu();      /* yecchhh... */
                 mntput(mnt);
         }
 }
 EXPORT_SYMBOL(kern_unmount);
 
 void kern_unmount_array(struct vfsmount *mnt[], unsigned int num)
 {
         unsigned int i;
 
         for (i = 0; i < num; i++)
                 mnt_make_shortterm(mnt[i]);
         synchronize_rcu_expedited();
         for (i = 0; i < num; i++)
                 mntput(mnt[i]);
 }
 EXPORT_SYMBOL(kern_unmount_array);
 
 bool our_mnt(struct vfsmount *mnt)
 {
         return check_mnt(real_mount(mnt));
 }
 
 bool current_chrooted(void)
 {
         /* Does the current process have a non-standard root */
         struct path ns_root;
         struct path fs_root;
         bool chrooted;
 
         /* Find the namespace root */
         ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
         ns_root.dentry = ns_root.mnt->mnt_root;
         path_get(&ns_root);
         while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
                 ;
 
         get_fs_root(current->fs, &fs_root);
 
         chrooted = !path_equal(&fs_root, &ns_root);
 
         path_put(&fs_root);
         path_put(&ns_root);
 
         return chrooted;
 }
 
 static bool mnt_already_visible(struct mnt_namespace *ns,
                                 const struct super_block *sb,
                                 int *new_mnt_flags)
 {
         int new_flags = *new_mnt_flags;
         struct mount *mnt, *n;
         bool visible = false;
 
         down_read(&namespace_sem);
         rbtree_postorder_for_each_entry_safe(mnt, n, &ns->mounts, mnt_node) {
                 struct mount *child;
                 int mnt_flags;
 
                 if (mnt->mnt.mnt_sb->s_type != sb->s_type)
                         continue;
 
                 /* This mount is not fully visible if it's root directory
                  * is not the root directory of the filesystem.
                  */
                 if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
                         continue;
 
                 /* A local view of the mount flags */
                 mnt_flags = mnt->mnt.mnt_flags;
 
                 /* Don't miss readonly hidden in the superblock flags */
                 if (sb_rdonly(mnt->mnt.mnt_sb))
                         mnt_flags |= MNT_LOCK_READONLY;
 
                 /* Verify the mount flags are equal to or more permissive
                  * than the proposed new mount.
                  */
                 if ((mnt_flags & MNT_LOCK_READONLY) &&
                     !(new_flags & MNT_READONLY))
                         continue;
                 if ((mnt_flags & MNT_LOCK_ATIME) &&
                     ((mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
                         continue;
 
                 /* This mount is not fully visible if there are any
                  * locked child mounts that cover anything except for
                  * empty directories.
                  */
                 list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
                         struct inode *inode = child->mnt_mountpoint->d_inode;
                         /* Only worry about locked mounts */
                         if (!(child->mnt.mnt_flags & MNT_LOCKED))
                                 continue;
                         /* Is the directory permanetly empty? */
                         if (!is_empty_dir_inode(inode))
                                 goto next;
                 }
                 /* Preserve the locked attributes */
                 *new_mnt_flags |= mnt_flags & (MNT_LOCK_READONLY | \
                                                MNT_LOCK_ATIME);
                 visible = true;
                 goto found;
         next:   ;
         }
 found:
         up_read(&namespace_sem);
         return visible;
 }
 
 static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags)
 {
         const unsigned long required_iflags = SB_I_NOEXEC | SB_I_NODEV;
         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
         unsigned long s_iflags;
 
         if (ns->user_ns == &init_user_ns)
                 return false;
 
         /* Can this filesystem be too revealing? */
         s_iflags = sb->s_iflags;
         if (!(s_iflags & SB_I_USERNS_VISIBLE))
                 return false;
 
         if ((s_iflags & required_iflags) != required_iflags) {
                 WARN_ONCE(1, "Expected s_iflags to contain 0x%lx\n",
                           required_iflags);
                 return true;
         }
 
         return !mnt_already_visible(ns, sb, new_mnt_flags);
 }
 
 bool mnt_may_suid(struct vfsmount *mnt)
 {
         /*
          * Foreign mounts (accessed via fchdir or through /proc
          * symlinks) are always treated as if they are nosuid.  This
          * prevents namespaces from trusting potentially unsafe
          * suid/sgid bits, file caps, or security labels that originate
          * in other namespaces.
          */
         return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) &&
                current_in_userns(mnt->mnt_sb->s_user_ns);
 }
 
 static struct ns_common *mntns_get(struct task_struct *task)
 {
         struct ns_common *ns = NULL;
         struct nsproxy *nsproxy;
 
         task_lock(task);
         nsproxy = task->nsproxy;
         if (nsproxy) {
                 ns = &nsproxy->mnt_ns->ns;
                 get_mnt_ns(to_mnt_ns(ns));
         }
         task_unlock(task);
 
         return ns;
 }
 
 static void mntns_put(struct ns_common *ns)
 {
         put_mnt_ns(to_mnt_ns(ns));
 }
 
 static int mntns_install(struct nsset *nsset, struct ns_common *ns)
 {
         struct nsproxy *nsproxy = nsset->nsproxy;
         struct fs_struct *fs = nsset->fs;
         struct mnt_namespace *mnt_ns = to_mnt_ns(ns), *old_mnt_ns;
         struct user_namespace *user_ns = nsset->cred->user_ns;
         struct path root;
         int err;
 
         if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
             !ns_capable(user_ns, CAP_SYS_CHROOT) ||
             !ns_capable(user_ns, CAP_SYS_ADMIN))
                 return -EPERM;
 
         if (is_anon_ns(mnt_ns))
                 return -EINVAL;
 
         if (fs->users != 1)
                 return -EINVAL;
 
         get_mnt_ns(mnt_ns);
         old_mnt_ns = nsproxy->mnt_ns;
         nsproxy->mnt_ns = mnt_ns;
 
         /* Find the root */
         err = vfs_path_lookup(mnt_ns->root->mnt.mnt_root, &mnt_ns->root->mnt,
                                 "/", LOOKUP_DOWN, &root);
         if (err) {
                 /* revert to old namespace */
                 nsproxy->mnt_ns = old_mnt_ns;
                 put_mnt_ns(mnt_ns);
                 return err;
         }
 
         put_mnt_ns(old_mnt_ns);
 
         /* Update the pwd and root */
         set_fs_pwd(fs, &root);
         set_fs_root(fs, &root);
 
         path_put(&root);
         return 0;
 }
 
 static struct user_namespace *mntns_owner(struct ns_common *ns)
 {
         return to_mnt_ns(ns)->user_ns;
 }
 
 const struct proc_ns_operations mntns_operations = {
         .name           = "mnt",
         .type           = CLONE_NEWNS,
         .get            = mntns_get,
         .put            = mntns_put,
         .install        = mntns_install,
         .owner          = mntns_owner,
 };
 
 #ifdef CONFIG_SYSCTL
 static struct ctl_table fs_namespace_sysctls[] = {
         {
                 .procname       = "mount-max",
                 .data           = &sysctl_mount_max,
                 .maxlen         = sizeof(unsigned int),
                 .mode           = 0644,
                 .proc_handler   = proc_dointvec_minmax,
                 .extra1         = SYSCTL_ONE,
         },
 };
 
 static int __init init_fs_namespace_sysctls(void)
 {
         register_sysctl_init("fs", fs_namespace_sysctls);
         return 0;
 }
 fs_initcall(init_fs_namespace_sysctls);
 
 #endif /* CONFIG_SYSCTL */