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From: Luis Chamberlain <mcgrof@kernel.org>
To: Eric Sandeen <sandeen@sandeen.net>
Cc: axboe@kernel.dk, viro@zeniv.linux.org.uk,
	gregkh@linuxfoundation.org, rostedt@goodmis.org,
	mingo@redhat.com, jack@suse.cz, ming.lei@redhat.com,
	nstange@suse.de, mhocko@suse.com, linux-block@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Bart Van Assche <bvanassche@acm.org>,
	Omar Sandoval <osandov@fb.com>, Hannes Reinecke <hare@suse.com>,
	Michal Hocko <mhocko@kernel.org>,
	syzbot+603294af2d01acfdd6da@syzkaller.appspotmail.com
Subject: Re: [RFC 2/3] blktrace: fix debugfs use after free
Date: Thu, 2 Apr 2020 16:14:04 +0000	[thread overview]
Message-ID: <20200402161404.GD11244@42.do-not-panic.com> (raw)
In-Reply-To: <9a6576cf-b89d-d1af-2d74-652878cb78c8@sandeen.net>

On Wed, Apr 01, 2020 at 08:57:42PM -0500, Eric Sandeen wrote:
> On 4/1/20 7:00 PM, Luis Chamberlain wrote:
> > On commit 6ac93117ab00 ("blktrace: use existing disk debugfs directory")
> > Omar fixed the original blktrace code for multiqueue use. 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:
> 
> Weird, I swear I tested that and didn't hit it, but ...

The real issue was also the dangling block device, a loop device proves
easy to test that. I'll note that another way to test this as well would
be to have a virtual machine with a block devices that goes in and out
via whatever virsh shenanigans to make a block device appear / disappear.

> > This issue can be reproduced with break-blktrace [2] using:
> > 
> >   break-blktrace -c 10 -d
> 
> + -s, right?

Yeap, sorry about that.

> > This patch fixes this issue. Note that there is also another
> > respective UAF but from the ioctl path [3], this should also fix
> > that issue.
> > 
> > This patch then also contends the severity of CVE-2019-19770 as
> > this issue is only possible using root to shoot yourself in the
> > foot by also misuing blktrace.
> > 
> > [0] https://bugzilla.kernel.org/show_bug.cgi?id=205713
> > [1] https://nvd.nist.gov/vuln/detail/CVE-2019-19770
> > [2] https://github.com/mcgrof/break-blktrace
> 
> I verified that this does reproduce the exact same KASAN splat on
> kernel 4.19.83 as reported in the original bug, thanks!

I just codified what Nicolai suspected, we should thank him :)

  Luis

  reply	other threads:[~2020-04-02 16:14 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-01 23:59 [RFC 0/3] block: address blktrace use-after-free Luis Chamberlain
2020-04-02  0:00 ` [RFC 1/3] block: move main block debugfs initialization to its own file Luis Chamberlain
2020-04-05  3:12   ` Bart Van Assche
2020-04-06 14:23     ` Luis Chamberlain
2020-04-02  0:00 ` [RFC 2/3] blktrace: fix debugfs use after free Luis Chamberlain
2020-04-02  1:57   ` Eric Sandeen
2020-04-02 16:14     ` Luis Chamberlain [this message]
2020-04-05  3:39   ` Bart Van Assche
2020-04-06  1:27     ` Eric Sandeen
2020-04-06  4:25       ` Bart Van Assche
2020-04-06  9:18         ` Nicolai Stange
2020-04-06 15:19           ` Luis Chamberlain
2020-04-07  8:15             ` Luis Chamberlain
2020-04-06 14:29         ` Eric Sandeen
2020-04-07  8:09           ` Luis Chamberlain
2020-04-06 15:14     ` Luis Chamberlain
2020-04-02  0:00 ` [RFC 3/3] block: avoid deferral of blk_release_queue() work Luis Chamberlain
2020-04-02  3:39   ` Bart Van Assche
2020-04-02 14:49     ` Nicolai Stange
2020-04-06  9:11       ` Nicolai Stange
2020-04-09 18:11       ` Luis Chamberlain
2020-04-02  7:44 ` [RFC 0/3] block: address blktrace use-after-free Greg KH
2020-04-03  8:19 ` Ming Lei
2020-04-03 14:06   ` Luis Chamberlain
2020-04-03 14:13   ` Bart Van Assche
2020-04-03 19:49     ` Luis Chamberlain
2020-04-07  2:47   ` yukuai (C)
2020-04-07 19:00     ` Luis Chamberlain
2020-04-09 20:59       ` Luis Chamberlain

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