// SPDX-License-Identifier: GPL-2.0-or-later
/* getroot.c: get the root dentry for an NFS mount
 *
 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/module.h>
#include <linux/init.h>

#include <linux/time.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/unistd.h>
#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/stats.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>
#include <linux/lockd/bind.h>
#include <linux/seq_file.h>
#include <linux/mount.h>
#include <linux/vfs.h>
#include <linux/namei.h>
#include <linux/security.h>

#include <linux/uaccess.h>

#include "internal.h"

#define NFSDBG_FACILITY         NFSDBG_CLIENT

/*
 * Set the superblock root dentry.
 * Note that this function frees the inode in case of error.
 */
static int nfs_superblock_set_dummy_root(struct super_block *sb, struct inode *inode)
{
        /* The mntroot acts as the dummy root dentry for this superblock */
        if (sb->s_root == NULL) {
                sb->s_root = d_make_root(inode);
                if (sb->s_root == NULL)
                        return -ENOMEM;
                ihold(inode);
                /*
                 * Ensure that this dentry is invisible to d_find_alias().
                 * Otherwise, it may be spliced into the tree by
                 * d_splice_alias if a parent directory from the same
                 * filesystem gets mounted at a later time.
                 * This again causes shrink_dcache_for_umount_subtree() to
                 * Oops, since the test for IS_ROOT() will fail.
                 */
                spin_lock(&d_inode(sb->s_root)->i_lock);
                spin_lock(&sb->s_root->d_lock);
                hlist_del_init(&sb->s_root->d_u.d_alias);
                spin_unlock(&sb->s_root->d_lock);
                spin_unlock(&d_inode(sb->s_root)->i_lock);
        }
        return 0;
}

/*
 * get a root dentry from the root filehandle
 */
int nfs_get_root(struct super_block *s, struct fs_context *fc)
{
        struct nfs_fs_context *ctx = nfs_fc2context(fc);
        struct nfs_server *server = NFS_SB(s), *clone_server;
        struct nfs_fsinfo fsinfo;
        struct dentry *root;
        struct inode *inode;
        char *name;
        int error = -ENOMEM;
        unsigned long kflags = 0, kflags_out = 0;

        name = kstrdup(fc->source, GFP_KERNEL);
        if (!name)
                goto out;

        /* get the actual root for this mount */
        fsinfo.fattr = nfs_alloc_fattr_with_label(server);
        if (fsinfo.fattr == NULL)
                goto out_name;

        error = server->nfs_client->rpc_ops->getroot(server, ctx->mntfh, &fsinfo);
        if (error < 0) {
                dprintk("nfs_get_root: getattr error = %d\n", -error);
                nfs_errorf(fc, "NFS: Couldn't getattr on root");
                goto out_fattr;
        }

        inode = nfs_fhget(s, ctx->mntfh, fsinfo.fattr);
        if (IS_ERR(inode)) {
                dprintk("nfs_get_root: get root inode failed\n");
                error = PTR_ERR(inode);
                nfs_errorf(fc, "NFS: Couldn't get root inode");
                goto out_fattr;
        }

        error = nfs_superblock_set_dummy_root(s, inode);
        if (error != 0)
                goto out_fattr;

        /* root dentries normally start off anonymous and get spliced in later
         * if the dentry tree reaches them; however if the dentry already
         * exists, we'll pick it up at this point and use it as the root
         */
        root = d_obtain_root(inode);
        if (IS_ERR(root)) {
                dprintk("nfs_get_root: get root dentry failed\n");
                error = PTR_ERR(root);
                nfs_errorf(fc, "NFS: Couldn't get root dentry");
                goto out_fattr;
        }

        security_d_instantiate(root, inode);
        spin_lock(&root->d_lock);
        if (IS_ROOT(root) && !root->d_fsdata &&
            !(root->d_flags & DCACHE_NFSFS_RENAMED)) {
                root->d_fsdata = name;
                name = NULL;
        }
        spin_unlock(&root->d_lock);
        fc->root = root;
        if (server->caps & NFS_CAP_SECURITY_LABEL)
                kflags |= SECURITY_LSM_NATIVE_LABELS;
        if (ctx->clone_data.sb) {
                if (d_inode(fc->root)->i_fop != &nfs_dir_operations) {
                        error = -ESTALE;
                        goto error_splat_root;
                }
                /* clone lsm security options from the parent to the new sb */
                error = security_sb_clone_mnt_opts(ctx->clone_data.sb,
                                                   s, kflags, &kflags_out);
                if (error)
                        goto error_splat_root;
                clone_server = NFS_SB(ctx->clone_data.sb);
                server->has_sec_mnt_opts = clone_server->has_sec_mnt_opts;
        } else {
                error = security_sb_set_mnt_opts(s, fc->security,
                                                        kflags, &kflags_out);
        }
        if (error)
                goto error_splat_root;
        if (server->caps & NFS_CAP_SECURITY_LABEL &&
                !(kflags_out & SECURITY_LSM_NATIVE_LABELS))
                server->caps &= ~NFS_CAP_SECURITY_LABEL;

        nfs_setsecurity(inode, fsinfo.fattr);
        error = 0;

out_fattr:
        nfs_free_fattr(fsinfo.fattr);
out_name:
        kfree(name);
out:
        return error;
error_splat_root:
        dput(fc->root);
        fc->root = NULL;
        goto out_fattr;
}