Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751972AbbDIVZQ (ORCPT ); Thu, 9 Apr 2015 17:25:16 -0400 Received: from mail-ig0-f182.google.com ([209.85.213.182]:36442 "EHLO mail-ig0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751177AbbDIVZM (ORCPT ); Thu, 9 Apr 2015 17:25:12 -0400 Message-ID: <5526EE36.7050303@kernel.dk> Date: Thu, 09 Apr 2015 15:25:10 -0600 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Linus Torvalds , Jan Engelhardt CC: "Rafael J. Wysocki" , Linux Kernel Mailing List Subject: Re: NULL deref around blkmq in =?windows-1252?Q?v4=2E0-rc1=96rc7?= References:

In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2796 Lines: 75 On 04/09/2015 03:12 PM, Linus Torvalds wrote: > On Thu, Apr 9, 2015 at 11:24 AM, Jan Engelhardt wrote: >> >> It's fairly consistent (reproducible?). Only 1 in 15 or so (have not kept track >> really) attempts does it not die. >> >> With frame pointers: >> [] scsi_queue_rq+0x2e8/0x3d2 >> [] __blk_mq_run_hw_queue+0x19b/0x2a2 >> [] ? blk_mq_merge_queue_io+0x75/0x147 >> [] ? __xfs_get_blocks+0x2f9/0x2f9 [xfs] >> [] blk_mq_run_hw_queue+0x4f/0x99 >> [] blk_sq_make_request+0x163/0x170 > > Ok, good. > > So the cmd comes from > > struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req); > > which in turn is just > > return (void *) rq + sizeof(*rq); > > which in turn is written by some crazy monkey on crack. That's some > shit code. Why the hell you'd write it that way, when the natural > thing to do would be just > > return rq + 1; > > without the sizeof, and without the cast. > > The particular crazy monkey on crack is Jens Axboe, in commit 320ae51feed5c. > > Jens, really. This code is shit. That's a bit rough on a single line of code like that, don't you think? But yes, rq + 1 is identical and cleaner... > That ->sense_buffer thing is supposed to be initialized by the > blk_mq_ops.init_request() function, which is called - if it exists = > when the array of requests ('->rqs[]') is initialized. > > And that code too looks like crap. It seems to be very clever, trying > to allocaet big contiguous chunks of RAM for the requests, but then > the initialization sequence is questionable as hell. It takes that > nonzeroed allocation, and zeroes a few fields randomly. The rest will > contain whatever garbage data they used to. > > Does this entirely untested patch make any difference? > > And Jens, this all really looks very fishy. When I look at these kinds > of core functions, and find just *stupid* code like this, it makes me > unhappy. Not sure why it isn't all zeroed, definitely the saner thing to do at init time. So patch looks fine, should be applied regardless of whether or not it fixes this issue. But it's _always_ been like that, so it's not a change in behavior. It is fragile, so perhaps some SCSI change modified alloc behavior and it's not causing and issue. And if this is mpt, we recently ran into some list corruption issues due to a bug in the driver. It hit on reboot, but it was scan related, so could be a boot issue as well. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/