From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754752AbeEWSCC (ORCPT ); Wed, 23 May 2018 14:02:02 -0400 Received: from sandeen.net ([63.231.237.45]:56092 "EHLO sandeen.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750771AbeEWSCB (ORCPT ); Wed, 23 May 2018 14:02:01 -0400 Subject: Re: INFO: task hung in xlog_grant_head_check To: Eric Biggers , "Darrick J. Wong" Cc: Dave Chinner , Brian Foster , syzbot , linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, syzkaller-bugs@googlegroups.com References: <000000000000457b2d056cbb0044@google.com> <20180522123107.GC3751@bfoster.bfoster> <20180522222620.GW23861@dastard> <20180522225208.GB658@sol.localdomain> <20180523074425.GM14384@magnolia> <20180523162015.GA3684@sol.localdomain> From: Eric Sandeen Message-ID: Date: Wed, 23 May 2018 13:01:59 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180523162015.GA3684@sol.localdomain> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/23/18 11:20 AM, Eric Biggers wrote: > Hi Darrick, ... > Now, if you *really* don't want syzbot to report XFS bugs as you believe XFS > contains known unfixable bugs or for other reasons, you can formally ask Dmitry > to remove CONFIG_XFS_FS from the syzbot config. But of course that doesn't make > the bugs go away, it just makes the bug reports go away; you'll have to fix them > eventually anyway, one way or another. I'd revise that to "have to fix /some/ of them anyway." What I'm personally hung up on are the bugs where the "exploit" involves merely mounting a crafted filesystem that in reality would never (until the heat death of the universe) corrupt itself into that state on its own; it's the "malicious image" case, which is quite different than exposing fundamental bugs like the SB_BORN race or or the user-exploitable ext4 flaw you mentioned in your reply. Those are more insidious and/or things which can be hit by real users in real life. I don't know if I can win the "malicious images aren't a critical security threat" battle, but I do think they are at least a different class of flaws, because as Dave said, mount is supposed to be a privileged operation. In a perfect world we'd fix them anyway, but I don't know that our resource pool can keep up with your google-scale bot and still make progress in other critical areas. Anyway, the upshot is that we're probably just not going to care much about V4 filesystem oops-or-hang-on-mount bugs. Those problems are solved (largely) with V5 filesystem format. Maybe I /will/ propose a system-wide tunable to disallow V4 for those who are worried about such things. To Darrick's points about more collaboration, I still wish that our requests for more traditional fs fuzzer reporting (i.e. a filesystem image) weren't met with such resistance.Tailoring your bug reports to the needs of the developer community you're interacting with seems like a pretty reasonable thing to do. As an aside, I wonder how much coverage of the V5 format code syzkaller /has/ achieved; that would be another useful datapoint google could provide - if syzkaller is in fact traversing the V5 codepaths and isn't turning anything up, that'd be pretty useful to know. Thanks, -Eric