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