1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * fs/sysfs/symlink.c - operations for initializing and mounting sysfs
4 *
5 * Copyright (c) 2001-3 Patrick Mochel
6 * Copyright (c) 2007 SUSE Linux Products GmbH
7 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
8 *
9 * Please see Documentation/filesystems/sysfs.rst for more information.
10 */
11
12 #include <linux/fs.h>
13 #include <linux/magic.h>
14 #include <linux/mount.h>
15 #include <linux/init.h>
16 #include <linux/slab.h>
17 #include <linux/user_namespace.h>
18 #include <linux/fs_context.h>
19 #include <net/net_namespace.h>
20
21 #include "sysfs.h"
22
23 static struct kernfs_root *sysfs_root;
24 struct kernfs_node *sysfs_root_kn;
25
26 static int sysfs_get_tree(struct fs_context *fc)
27 {
28 struct kernfs_fs_context *kfc = fc->fs_private;
29 int ret;
30
31 ret = kernfs_get_tree(fc);
32 if (ret)
33 return ret;
34
35 if (kfc->new_sb_created)
36 fc->root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE;
37 return 0;
38 }
39
40 static void sysfs_fs_context_free(struct fs_context *fc)
41 {
42 struct kernfs_fs_context *kfc = fc->fs_private;
43
44 if (kfc->ns_tag)
45 kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag);
46 kernfs_free_fs_context(fc);
47 kfree(kfc);
48 }
49
50 static const struct fs_context_operations sysfs_fs_context_ops = {
51 .free = sysfs_fs_context_free,
52 .get_tree = sysfs_get_tree,
53 };
54
55 static int sysfs_init_fs_context(struct fs_context *fc)
56 {
57 struct kernfs_fs_context *kfc;
58 struct net *netns;
59
60 if (!(fc->sb_flags & SB_KERNMOUNT)) {
61 if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
62 return -EPERM;
63 }
64
65 kfc = kzalloc(sizeof(struct kernfs_fs_context), GFP_KERNEL);
66 if (!kfc)
67 return -ENOMEM;
68
69 kfc->ns_tag = netns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
70 kfc->root = sysfs_root;
71 kfc->magic = SYSFS_MAGIC;
72 fc->fs_private = kfc;
73 fc->ops = &sysfs_fs_context_ops;
74 if (netns) {
75 put_user_ns(fc->user_ns);
76 fc->user_ns = get_user_ns(netns->user_ns);
77 }
78 fc->global = true;
79 return 0;
80 }
81
82 static void sysfs_kill_sb(struct super_block *sb)
83 {
84 void *ns = (void *)kernfs_super_ns(sb);
85
86 kernfs_kill_sb(sb);
87 kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
88 }
89
90 static struct file_system_type sysfs_fs_type = {
91 .name = "sysfs",
92 .init_fs_context = sysfs_init_fs_context,
93 .kill_sb = sysfs_kill_sb,
94 .fs_flags = FS_USERNS_MOUNT,
95 };
96
97 int __init sysfs_init(void)
98 {
99 int err;
100
101 sysfs_root = kernfs_create_root(NULL, KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
102 NULL);
103 if (IS_ERR(sysfs_root))
104 return PTR_ERR(sysfs_root);
105
106 sysfs_root_kn = kernfs_root_to_node(sysfs_root);
107
108 err = register_filesystem(&sysfs_fs_type);
109 if (err) {
110 kernfs_destroy_root(sysfs_root);
111 return err;
112 }
113
114 return 0;
115 }
116
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