Re: [PATCH] can: Fix kernel panic at security_sock_rcv_skb

[Oliver Hartkopp]

Hello Eric,

On 01/14/2017 04:43 AM, Liu Shuo wrote:
> On Thu 12.Jan'17 at 17:33:38 +0100, Oliver Hartkopp wrote:
> > On 01/12/2017 02:01 PM, Eric Dumazet wrote:

> > > The main problem seems that the sockets themselves are not RCU
> > > protected.
> > >
> > > If CAN uses RCU for delivery, then sockets should be freed only after
> > > one RCU grace period.
> > >
> > > On recent kernels, following patch could help :
> >
> > Thanks Eric!
> >
> > @Liu ShuoX: Can you check if Eric's suggestion fixes the issue in your
> > setup?
> Sorry for late reply. I was OOO yesterday.
> With Eric's hint, i just found his patch that "net: add SOCK_RCU_FREE
> socket flag" in the latest kernel. With backporting this one plus Eric's
> following patch, it fixs my failure.

what would be the best approach to fix this issue - even in stable kernels?

E.g. would this change be ok for a stable as a quick fix?

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 1108079d934f..6b974c2b66ef 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -112,6 +112,7 @@ EXPORT_SYMBOL(can_ioctl);

 static void can_sock_destruct(struct sock *sk)
 {
+       synchronize_rcu();
        skb_queue_purge(&sk->sk_receive_queue);
 }

And once this arrived in the mainline tree your suggested patch could be 
applied?

In any case we should not forget to give Reported-by credits to Liu.

Best regards,
Oliver