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 */
39static 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 */
67int 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
154out_fattr:
155	nfs_free_fattr(fsinfo.fattr);
156out_name:
157	kfree(name);
158out:
159	return error;
160error_splat_root:
161	dput(fc->root);
162	fc->root = NULL;
163	goto out_fattr;
164}
165