From: Vlad Yasevich <vyasevich@gmail.com>
Date: Mon, 14 Dec 2015 14:25:54 +0000
Subject: Re: use-after-free in sctp_do_sm
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To: David Laight <David.Laight@ACULAB.COM>, Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>, Dmitry Vyukov <dvyukov@google.com>
Cc: netdev <netdev@vger.kernel.org>, Eric Dumazet <eric.dumazet@gmail.com>, syzkaller <syzkaller@googlegroups.com>, "linux-sctp@vger.kernel.org" <linux-sctp@vger.kernel.org>, Kostya Serebryany <kcc@google.com>, Alexander Potapenko <glider@google.com>, Sasha Levin <sasha.levin@oracle.com>

On 12/14/2015 04:50 AM, David Laight wrote:
> From: Vlad Yasevich
>> Sent: 11 December 2015 18:38
> ...
>>> Found a similar place in abort primitive handling like in this last
>>> patch update, it's probably the issue you're still triggering.
>>>
>>> Also found another place that may lead to this use after free, in case
>>> we receive a packet with a chunk that has no data.
>>>
>>> Oh my.. :)
>>
>> Yes.  This is what I was worried about...  Anything that triggers
>> a DELTE_TCB command has to return a code that we can trap.
>>
>> The other way is to do what Dmitri suggested, but even there, we
>> need to be very careful.
> 
> I'm always wary of anything that queues actions up for later processing.
> It is far too easy (as found here) to end up processing actions
> in invalid states, or to process actions in 'unusual' orders when
> specific events happen close together.
> 
> I wonder how much fallout there'd be from getting the sctp code
> to immediately action things, instead of queuing the actions for later.
> It would certainly remove a lot of the unusual combinations of events.
> 

We've bandied this idea around for a while, but no one has had the time
to tackle this.  This would be rather time-consuming task, but in the end
might be a good idea.

-vlad

> 	David
> 
>