btrfs: Check name_len before in btrfs_del_root_ref

btrfs_del_root_ref calls btrfs_search_slot and reads name from root_ref.
Call btrfs_is_name_len_valid before memcmp.
Signed-off-by: NSu Yue <suy.fnst@cn.fujitsu.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/root-tree.c

@@ -390,6 +390,13 @@ int btrfs_del_root_ref(struct btrfs_trans_handle *trans,
 		WARN_ON(btrfs_root_ref_dirid(leaf, ref) != dirid);
 		WARN_ON(btrfs_root_ref_name_len(leaf, ref) != name_len);
 		ptr = (unsigned long)(ref + 1);
+		ret = btrfs_is_name_len_valid(leaf, path->slots[0], ptr,
+					      name_len);
+		if (!ret) {
+			err = -EIO;
+			goto out;
+		}
+
 		WARN_ON(memcmp_extent_buffer(leaf, name, ptr, name_len));
 		*sequence = btrfs_root_ref_sequence(leaf, ref);