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); 71 struct nfs_fsinfo fsinfo; 72 struct dentry *root; 73 struct inode *inode; 74 char *name; 75 int error = -ENOMEM; 76 77 name = kstrdup(fc->source, GFP_KERNEL); 78 if (!name) 79 goto out; 80 81 /* get the actual root for this mount */ 82 fsinfo.fattr = nfs_alloc_fattr(); 83 if (fsinfo.fattr == NULL) 84 goto out_name; 85 86 error = server->nfs_client->rpc_ops->getroot(server, ctx->mntfh, &fsinfo); 87 if (error < 0) { 88 dprintk("nfs_get_root: getattr error = %d\n", -error); 89 nfs_errorf(fc, "NFS: Couldn't getattr on root"); 90 goto out_fattr; 91 } 92 93 inode = nfs_fhget(s, ctx->mntfh, fsinfo.fattr, NULL); 94 if (IS_ERR(inode)) { 95 dprintk("nfs_get_root: get root inode failed\n"); 96 error = PTR_ERR(inode); 97 nfs_errorf(fc, "NFS: Couldn't get root inode"); 98 goto out_fattr; 99 } 100 101 error = nfs_superblock_set_dummy_root(s, inode); 102 if (error != 0) 103 goto out_fattr; 104 105 /* root dentries normally start off anonymous and get spliced in later 106 * if the dentry tree reaches them; however if the dentry already 107 * exists, we'll pick it up at this point and use it as the root 108 */ 109 root = d_obtain_root(inode); 110 if (IS_ERR(root)) { 111 dprintk("nfs_get_root: get root dentry failed\n"); 112 error = PTR_ERR(root); 113 nfs_errorf(fc, "NFS: Couldn't get root dentry"); 114 goto out_fattr; 115 } 116 117 security_d_instantiate(root, inode); 118 spin_lock(&root->d_lock); 119 if (IS_ROOT(root) && !root->d_fsdata && 120 !(root->d_flags & DCACHE_NFSFS_RENAMED)) { 121 root->d_fsdata = name; 122 name = NULL; 123 } 124 spin_unlock(&root->d_lock); 125 fc->root = root; 126 error = 0; 127 128 out_fattr: 129 nfs_free_fattr(fsinfo.fattr); 130 out_name: 131 kfree(name); 132 out: 133 return error; 134 } 135