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=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 AC476C433DB for ; Tue, 30 Mar 2021 15:03:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5F50C61953 for ; Tue, 30 Mar 2021 15:03:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230243AbhC3PCo (ORCPT ); Tue, 30 Mar 2021 11:02:44 -0400 Received: from mx2.suse.de ([195.135.220.15]:57786 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231874AbhC3PCb (ORCPT ); Tue, 30 Mar 2021 11:02:31 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7591EB30E; Tue, 30 Mar 2021 15:02:30 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id D3EF21E4353; Tue, 30 Mar 2021 17:02:29 +0200 (CEST) Date: Tue, 30 Mar 2021 17:02:29 +0200 From: Jan Kara To: Zhang Yi Cc: Jan Kara , "Theodore Y. Ts'o" , Ext4 Developers List , yangerkun , linfeilong@huawei.com Subject: Re: [BUG && Question] question of SB_ACTIVE flag in ext4_orphan_cleanup() Message-ID: <20210330150229.GC30749@quack2.suse.cz> References: <8a6864dd-7e6c-5268-2b5b-1010f99d2a1b@huawei.com> <20210322172551.GJ31783@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Mon 29-03-21 17:20:35, Zhang Yi wrote: > On 2021/3/23 1:25, Jan Kara wrote: > > Hi! > > > > On Mon 22-03-21 23:24:23, Zhang Yi wrote: > >> We find a use after free problem when CONFIG_QUOTA is enabled, the detail of > >> this problem is below. > >> > >> mount_bdev() > >> ext4_fill_super() > >> sb->s_root = d_make_root(root); > >> ext4_orphan_cleanup() > >> sb->s_flags |= SB_ACTIVE; <--- 1. mark sb active > >> ext4_orphan_get() > >> ext4_truncate() > >> ext4_block_truncate_page() > >> mark_buffer_dirty <--- 2. dirty inode > >> iput() > >> iput_final <--- 3. put into lru list > >> ext4_mark_recovery_complete <--- 4. failed and return error > >> sb->s_root = NULL; > >> deactivate_locked_super() > >> kill_block_super() > >> generic_shutdown_super() > >> <--- 5. did not evict_inodes > >> put_super() > >> __put_super() > >> <--- 6. put super block > >> > >> Because of the truncated inodes was dirty and will write them back later, it > >> will trigger use after free problem. Now the question is why we need to set > >> SB_ACTIVE bit when enable CONFIG_QUOTA below? > >> > >> #ifdef CONFIG_QUOTA > >> /* Needed for iput() to work correctly and not trash data */ > >> sb->s_flags |= SB_ACTIVE; > >> > >> This code was merged long long ago in v2.6.6, IIUC, it may not affect > >> the quota statistics it we evict inode directly in the last iput. > >> In order to slove this UAF problem, I'm not sure is there any side effect > >> if we just remove this code, or remove SB_ACTIVE and call evict_inodes() > >> in the error path of ext4_fill_super(). > >> > >> Could you give some suggestions? > > > > That's a very good question. I do remember that I've added this code back > > then because otherwise orphan cleanup was loosing updates to quota files. > > But you're right that now I don't see how that could be happening and it > > would be nice if we could get rid of this hack (and even better if it also > > fixes the problem you've found). I guess I'll just try and test this change > > with various quota configurations to see whether something still breaks or > > not. Thanks report! > > > > Thanks for taking time to look at this, is this change OK under your various > quota test cases? Yes, I did tests both with journalled quotas and with ext4 quota feature and the quota accounting was correct after orphan recovery. So just removing the SB_ACTIVE setting is fine AFAICT. Will you send a patch or should I do it? Honza -- Jan Kara SUSE Labs, CR