From: Luis Chamberlain <mcgrof@kernel.org>
To: Eric Sandeen <sandeen@sandeen.net>
Cc: axboe@kernel.dk, viro@zeniv.linux.org.uk, bvanassche@acm.org,
gregkh@linuxfoundation.org, rostedt@goodmis.org,
mingo@redhat.com, jack@suse.cz, ming.lei@redhat.com,
nstange@suse.de, akpm@linux-foundation.org, mhocko@suse.com,
yukuai3@huawei.com, linux-block@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Omar Sandoval <osandov@fb.com>,
Hannes Reinecke <hare@suse.com>, Michal Hocko <mhocko@kernel.org>,
syzbot+603294af2d01acfdd6da@syzkaller.appspotmail.com
Subject: Re: [PATCH 2/5] blktrace: fix debugfs use after free
Date: Thu, 16 Apr 2020 01:20:42 +0000 [thread overview]
Message-ID: <20200416012042.GD11244@42.do-not-panic.com> (raw)
In-Reply-To: <924950e6-e016-25b2-4ee1-b5ea9f752c12@sandeen.net>
On Wed, Apr 15, 2020 at 08:02:04PM -0500, Eric Sandeen wrote:
>
>
> On 4/15/20 7:56 PM, Luis Chamberlain wrote:
> > On Wed, Apr 15, 2020 at 12:38:26PM -0500, Eric Sandeen wrote:
> >> On 4/13/20 11:18 PM, Luis Chamberlain wrote:
> >>> On commit 6ac93117ab00 ("blktrace: use existing disk debugfs directory")
> >>> merged on v4.12 Omar fixed the original blktrace code for request-based
> >>> drivers (multiqueue). This however left in place a possible crash, if you
> >>> happen to abuse blktrace in a way it was not intended.
> >>>
> >>> Namely, if you loop adding a device, setup the blktrace with BLKTRACESETUP,
> >>> forget to BLKTRACETEARDOWN, and then just remove the device you end up
> >>> with a panic:
> >>
> >> I think this patch makes this all cleaner anyway, but - without the apparent
> >> loop bug mentioned by Bart which allows removal of the loop device while blktrace
> >> is active (if I read that right), can this still happen?
> >
> > I have not tested that, but some modifications of the break-blktrace
> > program could enable us to test that
>
> FWIW, I modified it to modprobe & rmmod scsi_debug instead of the loop ioctls,
> and the module can't be unloaded after the blktrace is started since it's busy.
>
> Not sure that's equivalent tho.
Given what Bart mentioned about sd_open, that might be the saving grace
for blocking async behaviour on scsi. If it only refcounted the
request_queue as the loop driver it would have been exposed to the
same bug.
> > however I don't think the race
> > would be possible after patch 3/5 "blktrace: refcount the request_queue
> > during ioctl" is merged, as removal then a pending blktrace would
> > refcount the request_queue and the removal would have to wait until
> > the refcount is decremeneted, until after the blktrace ioctl.
>
> I'm out of my depth in the block layer, not sure who's supposed to take
> refs on what. ;)
I'm new to all this code, only been a few weeks looking into it, but am
trying to do my best ot make sense of it. So the above is what I can
tell would be needed.
Luis
next prev parent reply other threads:[~2020-04-16 1:21 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 4:18 [PATCH 0/5] blktrace: fix use after free Luis Chamberlain
2020-04-14 4:18 ` [PATCH 1/5] block: move main block debugfs initialization to its own file Luis Chamberlain
2020-04-14 7:35 ` Greg KH
2020-04-15 2:44 ` Bart Van Assche
2020-04-14 4:18 ` [PATCH 2/5] blktrace: fix debugfs use after free Luis Chamberlain
2020-04-14 7:37 ` Greg KH
2020-04-14 15:38 ` Christoph Hellwig
2020-04-15 2:46 ` Bart Van Assche
2020-04-15 17:38 ` Eric Sandeen
2020-04-15 21:48 ` Bart Van Assche
2020-04-16 0:56 ` Luis Chamberlain
2020-04-16 1:02 ` Eric Sandeen
2020-04-16 1:20 ` Luis Chamberlain [this message]
2020-04-16 2:10 ` Ming Lei
2020-04-16 5:25 ` Luis Chamberlain
2020-04-16 5:47 ` Ming Lei
2020-04-16 6:09 ` Ming Lei
2020-04-16 6:22 ` Luis Chamberlain
2020-04-16 6:20 ` Luis Chamberlain
2020-04-16 6:28 ` Ming Lei
2020-04-17 4:09 ` Luis Chamberlain
2020-04-14 4:19 ` [PATCH 3/5] blktrace: refcount the request_queue during ioctl Luis Chamberlain
2020-04-14 15:40 ` Christoph Hellwig
2020-04-15 6:16 ` Luis Chamberlain
2020-04-15 7:14 ` Christoph Hellwig
2020-04-15 12:34 ` Luis Chamberlain
2020-04-15 12:39 ` Christoph Hellwig
2020-04-15 13:25 ` Luis Chamberlain
2020-04-15 14:18 ` Bart Van Assche
2020-04-16 1:12 ` Luis Chamberlain
2020-04-16 3:43 ` Bart Van Assche
2020-04-16 5:29 ` Luis Chamberlain
2020-04-15 14:45 ` Bart Van Assche
2020-04-16 1:17 ` Luis Chamberlain
2020-04-16 2:31 ` Ming Lei
2020-04-16 5:36 ` Luis Chamberlain
2020-04-14 4:19 ` [PATCH 4/5] mm/swapfile: refcount block and queue before using blkcg_schedule_throttle() Luis Chamberlain
2020-04-14 15:44 ` Christoph Hellwig
2020-04-15 5:42 ` Luis Chamberlain
2020-04-15 7:27 ` Christoph Hellwig
2020-04-15 7:34 ` Christoph Hellwig
2020-04-15 13:19 ` Luis Chamberlain
2020-04-16 6:10 ` Christoph Hellwig
2020-04-16 6:22 ` Ming Lei
2020-04-16 6:25 ` Luis Chamberlain
2020-04-16 6:34 ` Ming Lei
2020-04-14 4:19 ` [PATCH 5/5] block: revert back to synchronous request_queue removal Luis Chamberlain
2020-04-14 15:47 ` Christoph Hellwig
2020-04-14 20:58 ` Luis Chamberlain
2020-04-15 6:46 ` Christoph Hellwig
2020-04-15 13:20 ` Luis Chamberlain
2020-04-16 2:36 ` Ming Lei
2020-04-14 7:38 ` [PATCH 0/5] blktrace: fix use after free Greg KH
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