netdev - Re: use-after-free in sctp_do

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Date:	Mon, 7 Dec 2015 14:20:47 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:	Vlad Yasevich <vyasevich@...il.com>,
	netdev <netdev@...r.kernel.org>,
	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 Mon, Dec 7, 2015 at 2:15 PM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> On Mon, Dec 07, 2015 at 12:26:09PM +0100, Dmitry Vyukov wrote:
>> On Sat, Dec 5, 2015 at 5:39 PM, Vlad Yasevich <vyasevich@...il.com> wrote:
>> > On 12/04/2015 04:34 PM, Marcelo Ricardo Leitner wrote:
>> >> 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
>> >>
>> >
>> > Hi Marcelo
>> >
>> > I think you also need to catch the SCTP_DISPOSITION_ABORT and update
>> > the pointer.  There are some issues there though as some functions report
>> > that code without actually destroying the association.  This happens when
>> > the ABORT chunk may be dropped.
>> >
>> > I think this might be why we still see the issue.
>>
>>
>> Marcelo,
>>
>> Is this info enough for you to cook another fix?
>
> Hi, I think so. I was really wondering how you could trigger that issue
> without the timestamp fix and Vlad's comment does shed some light on it.
>
> I'll do more tests later today, but what did you have connecting to the
> listening socket? Somehow you made that accept() call to return..

Local connect in another thread I guess.
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