ubifs: Rectify space budget for ubifs_xrename()

There is no space budget for ubifs_xrename(). It may let
make_reservation() return with -ENOSPC, which could turn
ubifs to read-only mode in do_writepage() process.
Fix it by adding space budget for ubifs_xrename().

Fetch a reproducer in [Link].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216569
Fixes: 9ec64962 ("ubifs: Implement RENAME_EXCHANGE")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/dir.c

@@ -1576,6 +1576,10 @@ static int ubifs_xrename(struct inode *old_dir, struct dentry *old_dentry,
 		return err;
 	}
 
+	err = ubifs_budget_space(c, &req);
+	if (err)
+		goto out;
+
 	lock_4_inodes(old_dir, new_dir, NULL, NULL);
 
 	time = current_time(old_dir);
@@ -1601,6 +1605,7 @@ static int ubifs_xrename(struct inode *old_dir, struct dentry *old_dentry,
 	unlock_4_inodes(old_dir, new_dir, NULL, NULL);
 	ubifs_release_budget(c, &req);
 
+out:
 	fscrypt_free_filename(&fst_nm);
 	fscrypt_free_filename(&snd_nm);
 	return err;