Re: [PATCH net] bridge: Fix crash with vlan filtering and tcpdump

[Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>]

On Mon, 2014-01-06 at 11:02 -0500, Vlad Yasevich wrote:
> On 01/05/2014 10:02 AM, Toshiaki Makita wrote:
> > On Fri, 2014-01-03 at 11:12 -0500, Vlad Yasevich wrote:
> >> When the vlan filtering is enabled on the bridge, but
> >> the filter is not configured on the bridge device itself,
> >> running tcpdump on the bridge device will result in a
> >> an Ooops with NULL pointer dereference.  The reason
> >     ^^^^^
> > Oops?
> > 
> >> is that br_pass_frame_up() will bypass the vlan
> >> check because promisc flag is set.  It will then try
> >> to get the table pointer and process the packet based
> >> on the table.  Since the table pointer is NULL, we oops.
> >> Catch this special condition in br_handle_vlan().
> >>
> >> Reported-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
> >> CC: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
> >> Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
> >> ---
> > ...
> >> diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
> >> index af5ebd1..ea0c29b 100644
> >> --- a/net/bridge/br_vlan.c
> >> +++ b/net/bridge/br_vlan.c
> >> @@ -144,6 +144,18 @@ struct sk_buff *br_handle_vlan(struct net_bridge *br,
> >>  	if (!br->vlan_enabled)
> >>  		goto out;
> >>  
> >> +	/* Vlan filter table must be configrured at this point.  The
> >> +	 * only exception is the bridge is set in promisc mode and the
> >> +	 * packet is destined for the bridge device.  In this case
> >> +	 * pass the packet as is.
> >> +	 */
> >> +	if (!pv) {
> >> +       		if ((br->dev->flags & IFF_PROMISC) && skb->dev == br->dev)
> >> +			goto out;
> > 
> > Currently this function is calling __vlan_put_tag() if port_idx==0.
> > You are going to bypass it only if br is promisc mode.
> > 
> > However it doesn't seem to lead any problem because
> > __netif_receive_skb_core() can handle hw accel vlan tag.
> > 
> > Instead, I doubt if __vlan_put_tag() is necessary in br_handle_vlan()...
> 
> I'll need to re-test, but I remember having had to add that code to make
> it work on the bridge...
> 
> Looking at it again, I agree that special handling for forwarding to the
> bridge doesn't seem to be needed.
> 

Then, I'm OK with that "goto" statement :)

One more comment:
How about using BUG_ON() instead of "if-else BUG()"?
I think it could make the code slightly more efficient and simple.

Thanks,
Toshiaki Makita