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

From: Vlad Yasevich <[email-masked]>
Date: Fri, 03 Jan 2014 12:41:01 -0500

On 01/03/2014 01:06 PM, Sergei Shtylyov wrote:
> Hello.
> 
> On 01/03/2014 07:12 PM, 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
>> 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 "configured".
> 
>> +     * 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)
> 
>    You've indented this *if* too much.

Thanks, will fix in v2.  For now, will now wait for a few more reviews.

-vlad

>> +            goto out;
>> +        else
>> +            BUG();
>> +    }
>> +
> WBR, Sergei