netdev - Re: use-after-free in sctp_do

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Date:	Fri, 4 Dec 2015 19:34:28 -0200
From:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Vlad Yasevich <vyasevich@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	syzkaller <syzkaller@...glegroups.com>,
	linux-sctp@...r.kernel.org, Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: use-after-free in sctp_do_sm

On Fri, Dec 04, 2015 at 09:25:35PM +0100, Dmitry Vyukov wrote:
> On Fri, Dec 4, 2015 at 6:48 PM, Marcelo Ricardo Leitner
> <marcelo.leitner@...il.com> wrote:
> > Hi Dmitry,
> >
> > Can you please test this patch?
> > I'll re-post with proper subject if it works.
> 
> Still happening with the same stacks.

Then there may be another one, I'm afraid.

I'm using the testapp you shared in the first email, with that debug line
enabled and added a new one:
+       pr_debug("%p %d\n", asoc, asoc ? asoc->state : 0);
        debug_post_sfx();
(should have used %x, but ok)

Also enabled slub_debug=PUZ, and I get:

without the patch:
[   87.873640] sctp: ffff8800b71533d8 1
[   87.873647] sctp: sctp_do_sm[post-sfx]: error:0,
asoc:ffff8800b71533d8[STATE_CLOSED]
[   87.873739] sctp: ffff8800b71533d8 1
[   87.873742] sctp: sctp_do_sm[post-sfx]: error:0,
asoc:ffff8800b71533d8[STATE_CLOSED]
[   87.875149] sctp: ffff8800b71533d8 1802201963
[   87.875238] sctp: sctp_do_sm[post-sfx]: error:0,
asoc:ffff8800b71533d8[STATE_CLOSED]

1802201963 = 0x6b6b6b6b, poison

with the patch:
[   81.071265] sctp: ffff880137571148 1
[   81.071273] sctp: sctp_do_sm[post-sfx]: error:0,
asoc:ffff880137571148[STATE_CLOSED]
[   81.071372] sctp: ffff880137571148 1
[   81.071375] sctp: sctp_do_sm[post-sfx]: error:0,
asoc:ffff880137571148[STATE_CLOSED]
[   81.072423] sctp:           (null) 0
[   81.072427] sctp: sctp_do_sm[post-sfx]: error:0, asoc:
(null)[STATE_CLOSED]

This one, at least, is gone with this patch.

  Marcelo

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