Re: net/sctp: list double add warning in sctp_endpoint_add_asoc

[Andrey Konovalov]

On Wed, Apr 5, 2017 at 2:44 PM, Marcelo Ricardo Leitner
<marcelo.leitner@xxxxxxxxx> wrote:
> On Wed, Apr 05, 2017 at 06:48:45PM +0800, Xin Long wrote:
>> On Wed, Apr 5, 2017 at 5:14 AM, Marcelo Ricardo Leitner
>> <marcelo.leitner@xxxxxxxxx> wrote:
>> > On Wed, Apr 05, 2017 at 01:29:19AM +0800, Xin Long wrote:
>> >> On Tue, Apr 4, 2017 at 9:28 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>> >> > Hi,
>> >> >
>> >> > I've got the following error report while fuzzing the kernel with syzkaller.
>> >> >
>> >> > On commit a71c9a1c779f2499fb2afc0553e543f18aff6edf (4.11-rc5).
>> >> >
>> >> > A reproducer and .config are attached.
>> >> The script is pretty hard to reproduce the issue in my env.
>> >
>> > I didn't try running it but I also found the reproducer very complicated
>> > to follow. Do you have any plans on having some PoC optimizer, so we can
>> > have a more readable code?
>> > strace is handy for filtering the noise, yes, but sometimes it doesn't
>> > cut it.
>> I got the script now:
>> 1. create sk
>> 2. set sk->sndbuf = x
>> 3. sendmsg with size s1 (s1 < x)
>> 4. sendmsg with size s2 (s1+s2 > x)
>> 5. sendmsg with size s3 (wspace < 0), wait sndbuf, schedule out.
>> 6. listen sk (abnormal operation on sctp client)
>> 7. accept sk.
>>
>> In step 6, sk->sk_state = listening, then step 7 could get the first asoc
>> from ep->asoc_list and alloc a new sk2, attach the asoc to sk2.
>>
>> after a while, sendmsg schedule in, but asoc->sk is sk2, !=sk.
>> the same issue we fix for peeloff on commit dfcb9f4f99f1 ("sctp: deny
>> peeloff operation on asocs with threads sleeping on it") happens.
>
> Yes. That explains why the asoc isn't dead by when sendmsg comes back,
> and avoid that dead check.
>
>>
>> But we should not fix it by the same way as for peeloff. the real reason
>> causes this issue is on step 6, it should disallow listen on the established sk.
>
> Agreed.
>
>>
>> The following fix should work for this, just similar with what
>> inet_listen() did.
>>
>> @@ -7174,6 +7175,9 @@ int sctp_inet_listen(struct socket *sock, int backlog)
>>         if (sock->state != SS_UNCONNECTED)
>>                 goto out;
>>
>> +       if (!sctp_sstate(sk, LISTENING) && !sctp_sstate(sk,CLOSED))
>> +               goto out;
>> +

This fixes the report.

Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

Thanks!

>>
>> what do you think ?
>
> Yes, agreed.
> Thanks!
>
>   Marcelo