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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT 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 950D5C43381 for ; Fri, 1 Mar 2019 03:31:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6579F20854 for ; Fri, 1 Mar 2019 03:31:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728342AbfCADbf (ORCPT ); Thu, 28 Feb 2019 22:31:35 -0500 Received: from mx1.redhat.com ([209.132.183.28]:59528 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726347AbfCADbf (ORCPT ); Thu, 28 Feb 2019 22:31:35 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DB64D30C2509; Fri, 1 Mar 2019 03:31:34 +0000 (UTC) Received: from treble (ovpn-121-121.rdu2.redhat.com [10.10.121.121]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1C3D6183D9; Fri, 1 Mar 2019 03:31:31 +0000 (UTC) Date: Thu, 28 Feb 2019 21:31:29 -0600 From: Josh Poimboeuf To: Andrew Morton Cc: syzbot , amir73il@gmail.com, darrick.wong@oracle.com, david@fromorbit.com, hannes@cmpxchg.org, hughd@google.com, jrdr.linux@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, willy@infradead.org, Jan Kara Subject: Re: BUG: unable to handle kernel NULL pointer dereference in __generic_file_write_iter Message-ID: <20190301033129.5tepij2g4lcbvk4s@treble> References: <0000000000001aab8b0582689e11@google.com> <20190221113624.284fe267e73752639186a563@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190221113624.284fe267e73752639186a563@linux-foundation.org> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Fri, 01 Mar 2019 03:31:35 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 21, 2019 at 11:36:24AM -0800, Andrew Morton wrote: > On Thu, 21 Feb 2019 06:52:04 -0800 syzbot wrote: > > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: 4aa9fc2a435a Revert "mm, memory_hotplug: initialize struct.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=1101382f400000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=4fceea9e2d99ac20 > > dashboard link: https://syzkaller.appspot.com/bug?extid=ca95b2b7aef9e7cbd6ab > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > Unfortunately, I don't have any reproducer for this crash yet. > > Not understanding. That seems to be saying that we got a NULL pointer > deref in __generic_file_write_iter() at > > written = generic_perform_write(file, from, iocb->ki_pos); > > which isn't possible. > > I'm not seeing recent changes in there which could have caused this. Help. FWIW, the panic happened in generic_perform_write() when it called a_ops->write_begin, which was NULL. I agree with Jann that the unwinders should handle this scenario better. -- Josh