From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7965FC433FF for ; Wed, 14 Aug 2019 11:14:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5B939214C6 for ; Wed, 14 Aug 2019 11:14:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727264AbfHNLOL (ORCPT ); Wed, 14 Aug 2019 07:14:11 -0400 Received: from mx2.suse.de ([195.135.220.15]:35574 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726265AbfHNLOL (ORCPT ); Wed, 14 Aug 2019 07:14:11 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id F260DACEC; Wed, 14 Aug 2019 11:14:09 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id ED2691E4200; Wed, 14 Aug 2019 13:14:08 +0200 (CEST) Date: Wed, 14 Aug 2019 13:14:08 +0200 From: Jan Kara To: "zhangyi (F)" Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, jack@suse.cz, adilger.kernel@dilger.ca Subject: Re: [PATCH v3] ext4: fix potential use after free in system zone via remount with noblock_validity Message-ID: <20190814111408.GC26273@quack2.suse.cz> References: <1565701547-146508-1-git-send-email-yi.zhang@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1565701547-146508-1-git-send-email-yi.zhang@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Tue 13-08-19 21:05:47, zhangyi (F) wrote: > Remount process will release system zone which was allocated before if > "noblock_validity" is specified. If we mount an ext4 file system to two > mountpoints with default mount options, and then remount one of them > with "noblock_validity", it may trigger a use after free problem when > someone accessing the other one. > > # mount /dev/sda foo > # mount /dev/sda bar > > User access mountpoint "foo" | Remount mountpoint "bar" > | > ext4_map_blocks() | ext4_remount() > check_block_validity() | ext4_setup_system_zone() > ext4_data_block_valid() | ext4_release_system_zone() > | free system_blks rb nodes > access system_blks rb nodes | > trigger use after free | > > This problem can also be reproduced by one mountpint, At the same time, > add_system_zone() can get called during remount as well so there can be > racing ext4_data_block_valid() reading the rbtree at the same time. > > This patch add RCU to protect system zone from releasing or building > when doing a remount which inverse current "noblock_validity" mount > option. It assign the rbtree after the whole tree was complete and > do actual freeing after rcu grace period, avoid any intermediate state. > > Signed-off-by: zhangyi (F) > --- > Changes since v2: > - Remove seqlock, and assign the whole rbtree when finished assembling. > - Fix the sparse warning. Thanks for the patch! It looks great to me. Just one nit below and with that applied feel free to add: Reviewed-by: Jan Kara > int ext4_setup_system_zone(struct super_block *sb) ... > /* Called when the filesystem is unmounted */ > void ext4_release_system_zone(struct super_block *sb) Can you perhaps add a comment before ext4_setup_system_zone() and ext4_release_system_zone() explaining that these two functions are called under sb->s_umount semaphore protection which also serializes updates of sb->system_blks pointer? Thanks! Honza -- Jan Kara SUSE Labs, CR