netdev - Re: use-after-free in sctp_do

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Date:	Tue, 8 Dec 2015 18:30:51 +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 9:52 PM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> Em 07-12-2015 18:37, Vlad Yasevich escreveu:
>>
>> On 12/07/2015 02:50 PM, Marcelo Ricardo Leitner wrote:
>>>
>>> On Mon, Dec 07, 2015 at 02:33:52PM -0500, Vlad Yasevich wrote:
>>>>
>>>> On 12/07/2015 01:52 PM, Marcelo Ricardo Leitner wrote:
>>>>>
>>>>> Vlad, I reviewed the places on which it returns SCTP_DISPOSITION_ABORT,
>>>>> and if I didn't miss something in there all of them either issue
>>>>> SCTP_CMD_ASSOC_FAILED or SCTP_CMD_INIT_FAILED before returning it, thus
>>>>> delaying DELETE_TCB and with that the asoc free.
>>>>
>>>>
>>>> They delay it from the perspective of the command interpreter since the
>>>> command
>>>> to delete the TCB happens a little later, but status code  is checked
>>>> after all
>>>> commands are processed and command processing doesn't change it.  So the
>>>> 'status'
>>>> code would still be SCTP_DISPOSITION_ABORT after DELETE_TCB command was
>>>> processed.
>>>> So, I think we may still have an use-after-free issue here.
>>>
>>>
>>> Gotcha! That's pretty much it then. From that point of view now, there
>>> shouldn't be a case that it returns _ABORT without freeing the asoc in
>>> the same loop. (more below)
>>>
>>>>> There is one place,
>>>>> though, that may not do it that way, it's sctp_sf_abort_violation(),
>>>>> but
>>>>> then that code only runs if asoc is already NULL by then.
>>>>
>>>>
>>>> I don't believe so.  The violation state function can run with a
>>>> non-NULL association
>>>> if we are encountering protocol violations after the association is
>>>> established.
>>>
>>>
>>> Yup, that's correct. I just tried to reference one case on which it
>>> would return _ABORT without issuing any of those _FAILEDs before doing
>>> so (meaning the association could still be valid) but that in that case,
>>> the asoc was already NULL.
>>
>>
>> I think it is possible to hit the 'discard:' tag in that function while
>> still
>> having a valid association.  That happens when ABORT chunk is required to
>> be
>> authenticated.  This that case, instead of generating an ABORT and
>> terminating the
>> current association, we just drop the packet, but still report an _ABORT
>> disposition code.
>>
>> This probably need to change if we are going to catch the _ABORT
>> disposition and
>> clear the asoc pointer.
>
>
> Oups. Nice one. I'll switch it to SCTP_DISPOSITION_DISCARD if it hits that
> if() then. Thanks Vlad.


So I am waiting for a new patch, right?
Can you please combine all changes into a single patch (as far as I
understand the previous one must be applied on top of the first one)?
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