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

[Eric Dumazet]

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.