netdev - Re: use-after-free in sctp_do

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Date:	Mon, 7 Dec 2015 12:26:09 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	Marcelo Ricardo Leitner <marcelo.leitner@...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 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?
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