LXR linux/fs/nfs/getroot.c

   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();
  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 (server->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                if (error)
 141                        goto error_splat_root;
 142                clone_server = NFS_SB(ctx->clone_data.sb);
 143                server->has_sec_mnt_opts = clone_server->has_sec_mnt_opts;
 144        } else {
 145                error = security_sb_set_mnt_opts(s, fc->security,
 146                                                        kflags, &kflags_out);
 147        }
 148        if (error)
 149                goto error_splat_root;
 150        if (server->caps & NFS_CAP_SECURITY_LABEL &&
 151                !(kflags_out & SECURITY_LSM_NATIVE_LABELS))
 152                server->caps &= ~NFS_CAP_SECURITY_LABEL;
 153
 154        nfs_setsecurity(inode, fsinfo.fattr, fsinfo.fattr->label);
 155        error = 0;
 156
 157out_label:
 158        nfs4_label_free(fsinfo.fattr->label);
 159out_fattr:
 160        nfs_free_fattr(fsinfo.fattr);
 161out_name:
 162        kfree(name);
 163out:
 164        return error;
 165error_splat_root:
 166        dput(fc->root);
 167        fc->root = NULL;
 168        goto out_label;
 169}
 170