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

From: Eric Dumazet
Date: Thu Feb 09 2017 - 23:27:20 EST

On Thu, Feb 9, 2017 at 7:33 PM, Sowmini Varadhan
<sowmini.varadhan@xxxxxxxxxx> wrote:
> On (02/09/17 19:19), 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...
> I'm not sure I follow- aiui the panic was in acceessing the
> sk_receive_queue.lock in a socket that had been closed earlier. I think
> the assumption is that rcu_read_lock_bh in __dev_queue_xmit (and
> rcu_read_lock in dev_queue_xmit_nit?) should make sure that the nit
> packet delivery can be done safely, and the synchronize_net in
> packet_release() makes sure that the Tx paths are quiesced before freeing
> the socket. What is the race-hole here? Does it have to do with the
> _bh and softirq context, somehow?

We have probably a dozen of bugs to fix in af_packet.c

The race in fanout_add() is one ot theml.

I do not believe Anoob Soman sent his fixes btw ...

( Look for this thread :