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 */
nfs_superblock_set_dummy_root(struct super_block * sb,struct inode * inode)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 */
nfs_get_root(struct super_block * s,struct fs_context * fc)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);
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();
84 if (fsinfo.fattr == NULL)
85 goto out_name;
86
87 fsinfo.fattr->label = nfs4_label_alloc(server, GFP_KERNEL);
88 if (IS_ERR(fsinfo.fattr->label))
89 goto out_fattr;
90 error = server->nfs_client->rpc_ops->getroot(server, ctx->mntfh, &fsinfo);
91 if (error < 0) {
92 dprintk("nfs_get_root: getattr error = %d\n", -error);
93 nfs_errorf(fc, "NFS: Couldn't getattr on root");
94 goto out_label;
95 }
96
97 inode = nfs_fhget(s, ctx->mntfh, fsinfo.fattr, NULL);
98 if (IS_ERR(inode)) {
99 dprintk("nfs_get_root: get root inode failed\n");
100 error = PTR_ERR(inode);
101 nfs_errorf(fc, "NFS: Couldn't get root inode");
102 goto out_label;
103 }
104
105 error = nfs_superblock_set_dummy_root(s, inode);
106 if (error != 0)
107 goto out_label;
108
109 /* root dentries normally start off anonymous and get spliced in later
110 * if the dentry tree reaches them; however if the dentry already
111 * exists, we'll pick it up at this point and use it as the root
112 */
113 root = d_obtain_root(inode);
114 if (IS_ERR(root)) {
115 dprintk("nfs_get_root: get root dentry failed\n");
116 error = PTR_ERR(root);
117 nfs_errorf(fc, "NFS: Couldn't get root dentry");
118 goto out_label;
119 }
120
121 security_d_instantiate(root, inode);
122 spin_lock(&root->d_lock);
123 if (IS_ROOT(root) && !root->d_fsdata &&
124 !(root->d_flags & DCACHE_NFSFS_RENAMED)) {
125 root->d_fsdata = name;
126 name = NULL;
127 }
128 spin_unlock(&root->d_lock);
129 fc->root = root;
130 if (NFS_SB(s)->caps & NFS_CAP_SECURITY_LABEL)
131 kflags |= SECURITY_LSM_NATIVE_LABELS;
132 if (ctx->clone_data.sb) {
133 if (d_inode(fc->root)->i_fop != &nfs_dir_operations) {
134 error = -ESTALE;
135 goto error_splat_root;
136 }
137 /* clone lsm security options from the parent to the new sb */
138 error = security_sb_clone_mnt_opts(ctx->clone_data.sb,
139 s, kflags, &kflags_out);
140 } else {
141 error = security_sb_set_mnt_opts(s, fc->security,
142 kflags, &kflags_out);
143 }
144 if (error)
145 goto error_splat_root;
146 if (NFS_SB(s)->caps & NFS_CAP_SECURITY_LABEL &&
147 !(kflags_out & SECURITY_LSM_NATIVE_LABELS))
148 NFS_SB(s)->caps &= ~NFS_CAP_SECURITY_LABEL;
149
150 nfs_setsecurity(inode, fsinfo.fattr, fsinfo.fattr->label);
151 error = 0;
152
153 out_label:
154 nfs4_label_free(fsinfo.fattr->label);
155 out_fattr:
156 nfs_free_fattr(fsinfo.fattr);
157 out_name:
158 kfree(name);
159 out:
160 return error;
161 error_splat_root:
162 dput(fc->root);
163 fc->root = NULL;
164 goto out_label;
165 }
166