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

On Thu, Feb 9, 2017 at 7:33 PM, Sowmini Varadhan
[off-list ref] wrote:

On (02/09/17 19:19), Eric Dumazet wrote:

quoted

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 : http://marc.info/?l=linux-netdev&m=148588680525648&w=2