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

From: Vlad Yasevich <[email-masked]>
Date: Mon, 06 Jan 2014 11:02:34 -0500

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 <[email-masked]>
>> CC: Toshiaki Makita <[email-masked]>
>> Signed-off-by: Vlad Yasevich <[email-masked]>
>> ---
> ...
>> 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.

-vlad

> Thanks,
> Toshiaki Makita