Re: net/sctp: use-after-free in __sctp_connect

[Andrey Konovalov]

On Wed, Nov 2, 2016 at 11:42 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
> On Wed, Oct 19, 2016 at 6:57 PM, Marcelo Ricardo Leitner
> <marcelo.leitner@xxxxxxxxx> wrote:
>> On Wed, Oct 19, 2016 at 02:25:24PM +0200, Andrey Konovalov wrote:
>>> Hi,
>>>
>>> I've got the following error report while running the syzkaller fuzzer:
>>>
>>> ==================================================================
>>> BUG: KASAN: use-after-free in __sctp_connect+0xabe/0xbf0 at addr
>>> ffff88006b1dc610
>>
>> Seems this is the same that Dmitry Vyukov had reported back in Jan 13th.
>> So far I couldn't identify the reason.
>> "Good" to know it's still there, thanks for reporting it.

Hi Marcelo,

So I've looked at the code.
As far as I understand, the problem is a race condition between
setsockopt(SCTP_SOCKOPT_CONNECTX) and shutdown on an sctp socket.
setsockopt() calls sctp_wait_for_connect(), which exits the for loop
on the sk->sk_shutdown & RCV_SHUTDOWN if clause, and then frees asoc
with sctp_association_put() and returns err = 0.
Then __sctp_connect() checks that err == 0 and reads asoc->assoc_id
from the freed asoc.