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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5C443C25B08 for ; Wed, 10 Aug 2022 07:20:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230483AbiHJHU5 (ORCPT ); Wed, 10 Aug 2022 03:20:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229969AbiHJHUz (ORCPT ); Wed, 10 Aug 2022 03:20:55 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9518CF5C; Wed, 10 Aug 2022 00:20:52 -0700 (PDT) Received: from dggpeml500021.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4M2h9J3grLzfYwv; Wed, 10 Aug 2022 15:17:56 +0800 (CST) Received: from [10.174.177.174] (10.174.177.174) by dggpeml500021.china.huawei.com (7.185.36.21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 10 Aug 2022 15:20:49 +0800 Message-ID: Date: Wed, 10 Aug 2022 15:20:48 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [PATCH] ext4: fix null-ptr-deref in ext4_write_info To: Lukas Czerner CC: , , , , , , , , , , Baokun Li References: <20220805123947.565152-1-libaokun1@huawei.com> <20220805130726.a3otpkbrjv3ijumd@fedora> From: Baokun Li In-Reply-To: <20220805130726.a3otpkbrjv3ijumd@fedora> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.174] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpeml500021.china.huawei.com (7.185.36.21) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2022/8/5 21:07, Lukas Czerner 写道: > On Fri, Aug 05, 2022 at 08:39:47PM +0800, Baokun Li wrote: >> I caught a null-ptr-deref bug as follows: >> ================================================================== >> KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f] >> CPU: 1 PID: 1589 Comm: umount Not tainted 5.10.0-02219-dirty #339 >> RIP: 0010:ext4_write_info+0x53/0x1b0 >> [...] >> Call Trace: >> dquot_writeback_dquots+0x341/0x9a0 >> ext4_sync_fs+0x19e/0x800 >> __sync_filesystem+0x83/0x100 >> sync_filesystem+0x89/0xf0 >> generic_shutdown_super+0x79/0x3e0 >> kill_block_super+0xa1/0x110 >> deactivate_locked_super+0xac/0x130 >> deactivate_super+0xb6/0xd0 >> cleanup_mnt+0x289/0x400 >> __cleanup_mnt+0x16/0x20 >> task_work_run+0x11c/0x1c0 >> exit_to_user_mode_prepare+0x203/0x210 >> syscall_exit_to_user_mode+0x5b/0x3a0 >> do_syscall_64+0x59/0x70 >> entry_SYSCALL_64_after_hwframe+0x44/0xa9 >> ================================================================== >> >> Above issue may happen as follows: >> ------------------------------------- >> exit_to_user_mode_prepare >> task_work_run >> __cleanup_mnt >> cleanup_mnt >> deactivate_super >> deactivate_locked_super >> kill_block_super >> generic_shutdown_super >> shrink_dcache_for_umount >> dentry = sb->s_root >> sb->s_root = NULL <--- Here set NULL >> sync_filesystem >> __sync_filesystem >> sb->s_op->sync_fs > ext4_sync_fs >> dquot_writeback_dquots >> sb->dq_op->write_info > ext4_write_info >> ext4_journal_start(d_inode(sb->s_root), EXT4_HT_QUOTA, 2) >> d_inode(sb->s_root) >> s_root->d_inode <--- Null pointer dereference >> >> To solve this problem, we use ext4_journal_start_sb directly >> to avoid s_root being used. > Are we syncing the file system after the superblock shutdown and getting > away with it? This does not look good. Do you have a reproducer? > > Thanks! > -Lukas Hi, Lukas! This problem is triggered by a pressure test when I reproduce another problem. So I didn't have the reproducer. I looked at the error stack code and found that it seems there is something wrong. Moreover, it's really weird to write code like "ext4_journal_start(d_inode(sb->s_root), ...)". >> Signed-off-by: Baokun Li >> --- >> fs/ext4/super.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/ext4/super.c b/fs/ext4/super.c >> index 9a66abcca1a8..0ce4565422f6 100644 >> --- a/fs/ext4/super.c >> +++ b/fs/ext4/super.c >> @@ -6653,7 +6653,7 @@ static int ext4_write_info(struct super_block *sb, int type) >> handle_t *handle; >> >> /* Data block + inode block */ >> - handle = ext4_journal_start(d_inode(sb->s_root), EXT4_HT_QUOTA, 2); >> + handle = ext4_journal_start_sb(sb, EXT4_HT_QUOTA, 2); >> if (IS_ERR(handle)) >> return PTR_ERR(handle); >> ret = dquot_commit_info(sb, type); >> -- >> 2.31.1 >> > . Thanks! -- With Best Regards, Baokun Li