Re: net/packet: use-after-free in packet_rcv_fanout

[Cong Wang]

On Fri, Feb 10, 2017 at 10:02 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> On Fri, 2017-02-10 at 09:59 -0800, Eric Dumazet wrote:
>> On Fri, 2017-02-10 at 09:49 -0800, Cong Wang wrote:
>> > On Thu, Feb 9, 2017 at 7:23 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>> > > On Thu, 2017-02-09 at 19:19 -0800, Eric Dumazet wrote:
>> > >
>> > >> More likely the bug is in fanout_add(), with a buggy sequence in error
>> > >> case, and not correct locking.
>> > >>
>> > >> kfree(po->rollover);
>> > >> po->rollover = NULL;
>> > >>
>> > >> Two cpus entering fanout_add() (using the same af_packet socket,
>> > >> syzkaller courtesy...) might both see po->fanout being NULL.
>> > >>
>> > >> Then they grab the mutex.  Too late...
>> > >
>> > > Patch could be :
>> > >
>> >
>> > For me, clearly the data structure that use-after-free'd is struct sock
>> > rather than struct packet_rollover.
>>
>> Fine. But your patch makes absolutely no sense.
>
> At least, Anoob patch is making a step into the right direction ;)
>
> https://patchwork.ozlabs.org/patch/726532/
>

Yeah, but still looks like a different one with the one Dmitry reported.