Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752437AbdLSTaX (ORCPT ); Tue, 19 Dec 2017 14:30:23 -0500 Received: from scorn.kernelslacker.org ([45.56.101.199]:48506 "EHLO scorn.kernelslacker.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751291AbdLSTaW (ORCPT ); Tue, 19 Dec 2017 14:30:22 -0500 Date: Tue, 19 Dec 2017 14:30:20 -0500 From: Dave Jones To: "Eric W. Biederman" Cc: Linus Torvalds , Al Viro , Linux Kernel Subject: Re: proc_flush_task oops Message-ID: <20171219193020.GA9237@codemonkey.org.uk> Mail-Followup-To: Dave Jones , "Eric W. Biederman" , Linus Torvalds , Al Viro , Linux Kernel References: <20171218214438.GA32728@codemonkey.org.uk> <20171218221541.GP21978@ZenIV.linux.org.uk> <20171218231013.GA9481@codemonkey.org.uk> <20171219033926.GA26981@codemonkey.org.uk> <87lghy7eul.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87lghy7eul.fsf@xmission.com> User-Agent: Mutt/1.9.2 (2017-12-15) X-Spam-Note: SpamAssassin invocation failed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1396 Lines: 34 On Tue, Dec 19, 2017 at 12:27:30PM -0600, Eric W. Biederman wrote: > Dave Jones writes: > > > On Mon, Dec 18, 2017 at 03:50:52PM -0800, Linus Torvalds wrote: > > > > > But I don't see what would have changed in this area recently. > > > > > > Do you end up saving the seeds that cause crashes? Is this > > > reproducible? (Other than seeing it twoce, of course) > > > > Only clue so far, is every time I'm able to trigger it, the last thing > > the child process that triggers it did, was an execveat. > > Is there any chance the excveat might be called from a child thread? If trinity choose one of the exec syscalls, it forks off an extra child to do it in, on the off-chance that it succeeds, and we never return. https://github.com/kernelslacker/trinity/blob/master/syscall.c#L139 > That switching pids between tasks of a process during exec can get a > little bit tricky. > > > Telling it to just fuzz execveat doesn't instantly trigger it, so it > > must be a combination of some other syscall. I'll leave a script running > > overnight to see if I can binary search the other syscalls in > > combination with it. > > Could we have a buggy syscall that is stomping something? Not totally impossible I guess, though I would expect that would manifest in additional random failures, whereas this seems remarkably consistent. Dave