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

From: Toshiaki Makita <[email-masked]>
Date: Mon, 06 Jan 2014 00:02:27 +0900

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()...

Thanks,
Toshiaki Makita