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

[Cong Wang]

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.