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 F086FC00140 for ; Fri, 5 Aug 2022 13:07:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240864AbiHENHk (ORCPT ); Fri, 5 Aug 2022 09:07:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59816 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240879AbiHENHi (ORCPT ); Fri, 5 Aug 2022 09:07:38 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 8A2391ADB1 for ; Fri, 5 Aug 2022 06:07:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659704856; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=lUrjF/MAixi7Bh8/ayeTczijWfCC7xeP+l/HtT9IEjI=; b=NAdngT+HFeItj7jOQq5DNjA71ili0dK0PIXz28c8MSSGgrxnGlIikSZ0uIiAaNirGmF9Zp 9gWc/sFSKp23Vcc5Kn21AiKneLYirkS4s33BeYmLf5Vle3PK09P5PEZpPHb49F/Vq+vrEF vRohzHMn2lexzFYVeKVd7ogNQk+ar/Q= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-222-e5sA7g74PgCA1DfCoTzntg-1; Fri, 05 Aug 2022 09:07:31 -0400 X-MC-Unique: e5sA7g74PgCA1DfCoTzntg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id DE136381A08C; Fri, 5 Aug 2022 13:07:30 +0000 (UTC) Received: from fedora (unknown [10.40.193.205]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 352F040CFD0A; Fri, 5 Aug 2022 13:07:28 +0000 (UTC) Date: Fri, 5 Aug 2022 15:07:26 +0200 From: Lukas Czerner To: Baokun Li Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca, jack@suse.cz, ritesh.list@gmail.com, enwlinux@gmail.com, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, yebin10@huawei.com, yukuai3@huawei.com Subject: Re: [PATCH] ext4: fix null-ptr-deref in ext4_write_info Message-ID: <20220805130726.a3otpkbrjv3ijumd@fedora> References: <20220805123947.565152-1-libaokun1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220805123947.565152-1-libaokun1@huawei.com> X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org 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 > > 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 >