1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* getroot.c: get the root dentry for an NFS mount
3 *
4 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8 #include <linux/module.h>
9 #include <linux/init.h>
10
11 #include <linux/time.h>
12 #include <linux/kernel.h>
13 #include <linux/mm.h>
14 #include <linux/string.h>
15 #include <linux/stat.h>
16 #include <linux/errno.h>
17 #include <linux/unistd.h>
18 #include <linux/sunrpc/clnt.h>
19 #include <linux/sunrpc/stats.h>
20 #include <linux/nfs_fs.h>
21 #include <linux/nfs_mount.h>
22 #include <linux/lockd/bind.h>
23 #include <linux/seq_file.h>
24 #include <linux/mount.h>
25 #include <linux/vfs.h>
26 #include <linux/namei.h>
27 #include <linux/security.h>
28
29 #include <linux/uaccess.h>
30
31 #include "internal.h"
32
33 #define NFSDBG_FACILITY NFSDBG_CLIENT
34
35 /*
36 * Set the superblock root dentry.
37 * Note that this function frees the inode in case of error.
38 */
39 static int nfs_superblock_set_dummy_root(struct super_block *sb, struct inode *inode)
40 {
41 /* The mntroot acts as the dummy root dentry for this superblock */
42 if (sb->s_root == NULL) {
43 sb->s_root = d_make_root(inode);
44 if (sb->s_root == NULL)
45 return -ENOMEM;
46 ihold(inode);
47 /*
48 * Ensure that this dentry is invisible to d_find_alias().
49 * Otherwise, it may be spliced into the tree by
50 * d_splice_alias if a parent directory from the same
51 * filesystem gets mounted at a later time.
52 * This again causes shrink_dcache_for_umount_subtree() to
53 * Oops, since the test for IS_ROOT() will fail.
54 */
55 spin_lock(&d_inode(sb->s_root)->i_lock);
56 spin_lock(&sb->s_root->d_lock);
57 hlist_del_init(&sb->s_root->d_u.d_alias);
58 spin_unlock(&sb->s_root->d_lock);
59 spin_unlock(&d_inode(sb->s_root)->i_lock);
60 }
61 return 0;
62 }
63
64 /*
65 * get an NFS2/NFS3 root dentry from the root filehandle
66 */
67 int nfs_get_root(struct super_block *s, struct fs_context *fc)
68 {
69 struct nfs_fs_context *ctx = nfs_fc2context(fc);
70 struct nfs_server *server = NFS_SB(s), *clone_server;
71 struct nfs_fsinfo fsinfo;
72 struct dentry *root;
73 struct inode *inode;
74 char *name;
75 int error = -ENOMEM;
76 unsigned long kflags = 0, kflags_out = 0;
77
78 name = kstrdup(fc->source, GFP_KERNEL);
79 if (!name)
80 goto out;
81
82 /* get the actual root for this mount */
83 fsinfo.fattr = nfs_alloc_fattr_with_label(server);
84 if (fsinfo.fattr == NULL)
85 goto out_name;
86
87 error = server->nfs_client->rpc_ops->getroot(server, ctx->mntfh, &fsinfo);
88 if (error < 0) {
89 dprintk("nfs_get_root: getattr error = %d\n", -error);
90 nfs_errorf(fc, "NFS: Couldn't getattr on root");
91 goto out_fattr;
92 }
93
94 inode = nfs_fhget(s, ctx->mntfh, fsinfo.fattr);
95 if (IS_ERR(inode)) {
96 dprintk("nfs_get_root: get root inode failed\n");
97 error = PTR_ERR(inode);
98 nfs_errorf(fc, "NFS: Couldn't get root inode");
99 goto out_fattr;
100 }
101
102 error = nfs_superblock_set_dummy_root(s, inode);
103 if (error != 0)
104 goto out_fattr;
105
106 /* root dentries normally start off anonymous and get spliced in later
107 * if the dentry tree reaches them; however if the dentry already
108 * exists, we'll pick it up at this point and use it as the root
109 */
110 root = d_obtain_root(inode);
111 if (IS_ERR(root)) {
112 dprintk("nfs_get_root: get root dentry failed\n");
113 error = PTR_ERR(root);
114 nfs_errorf(fc, "NFS: Couldn't get root dentry");
115 goto out_fattr;
116 }
117
118 security_d_instantiate(root, inode);
119 spin_lock(&root->d_lock);
120 if (IS_ROOT(root) && !root->d_fsdata &&
121 !(root->d_flags & DCACHE_NFSFS_RENAMED)) {
122 root->d_fsdata = name;
123 name = NULL;
124 }
125 spin_unlock(&root->d_lock);
126 fc->root = root;
127 if (server->caps & NFS_CAP_SECURITY_LABEL)
128 kflags |= SECURITY_LSM_NATIVE_LABELS;
129 if (ctx->clone_data.sb) {
130 if (d_inode(fc->root)->i_fop != &nfs_dir_operations) {
131 error = -ESTALE;
132 goto error_splat_root;
133 }
134 /* clone lsm security options from the parent to the new sb */
135 error = security_sb_clone_mnt_opts(ctx->clone_data.sb,
136 s, kflags, &kflags_out);
137 if (error)
138 goto error_splat_root;
139 clone_server = NFS_SB(ctx->clone_data.sb);
140 server->has_sec_mnt_opts = clone_server->has_sec_mnt_opts;
141 } else {
142 error = security_sb_set_mnt_opts(s, fc->security,
143 kflags, &kflags_out);
144 }
145 if (error)
146 goto error_splat_root;
147 if (server->caps & NFS_CAP_SECURITY_LABEL &&
148 !(kflags_out & SECURITY_LSM_NATIVE_LABELS))
149 server->caps &= ~NFS_CAP_SECURITY_LABEL;
150
151 nfs_setsecurity(inode, fsinfo.fattr);
152 error = 0;
153
154 out_fattr:
155 nfs_free_fattr(fsinfo.fattr);
156 out_name:
157 kfree(name);
158 out:
159 return error;
160 error_splat_root:
161 dput(fc->root);
162 fc->root = NULL;
163 goto out_fattr;
164 }
165
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