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 struct dentry *nfs_get_root(struct super_block *sb, struct nfs_fh *mntfh, 68 const char *devname) 69 { 70 struct nfs_server *server = NFS_SB(sb); 71 struct nfs_fsinfo fsinfo; 72 struct dentry *ret; 73 struct inode *inode; 74 void *name = kstrdup(devname, GFP_KERNEL); 75 int error; 76 77 if (!name) 78 return ERR_PTR(-ENOMEM); 79 80 /* get the actual root for this mount */ 81 fsinfo.fattr = nfs_alloc_fattr(); 82 if (fsinfo.fattr == NULL) { 83 kfree(name); 84 return ERR_PTR(-ENOMEM); 85 } 86 87 error = server->nfs_client->rpc_ops->getroot(server, mntfh, &fsinfo); 88 if (error < 0) { 89 dprintk("nfs_get_root: getattr error = %d\n", -error); 90 ret = ERR_PTR(error); 91 goto out; 92 } 93 94 inode = nfs_fhget(sb, mntfh, fsinfo.fattr, NULL); 95 if (IS_ERR(inode)) { 96 dprintk("nfs_get_root: get root inode failed\n"); 97 ret = ERR_CAST(inode); 98 goto out; 99 } 100 101 error = nfs_superblock_set_dummy_root(sb, inode); 102 if (error != 0) { 103 ret = ERR_PTR(error); 104 goto out; 105 } 106 107 /* root dentries normally start off anonymous and get spliced in later 108 * if the dentry tree reaches them; however if the dentry already 109 * exists, we'll pick it up at this point and use it as the root 110 */ 111 ret = d_obtain_root(inode); 112 if (IS_ERR(ret)) { 113 dprintk("nfs_get_root: get root dentry failed\n"); 114 goto out; 115 } 116 117 security_d_instantiate(ret, inode); 118 spin_lock(&ret->d_lock); 119 if (IS_ROOT(ret) && !ret->d_fsdata && 120 !(ret->d_flags & DCACHE_NFSFS_RENAMED)) { 121 ret->d_fsdata = name; 122 name = NULL; 123 } 124 spin_unlock(&ret->d_lock); 125 out: 126 kfree(name); 127 nfs_free_fattr(fsinfo.fattr); 128 return ret; 129 } 130