netdev - Re: [PATCH v2] bridge: Fix crash with vlan filtering and tcpdump

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Date:	Thu, 23 Jan 2014 21:38:31 +0900
From:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:	Vlad Yasevich <vyasevic@...hat.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH v2] bridge: Fix crash with vlan filtering and tcpdump

On Wed, 2014-01-22 at 13:24 -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 Oops 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 <makita.toshiaki@....ntt.co.jp>
> CC: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
> Signed-off-by: Vlad Yasevich <vyasevic@...hat.com>
> ---
> Changes since v1:
>   - Do not use a BUG or BUG_ON as it is possible to trigger the
>     false BUG condition when thrashing the vlan_enable toggle.
>     Instead just drop the skb.

Maybe that frame went through should_deliver() while vlan_filtering was
disabled?
I hope it doesn't affect other codes in an adverse way...

> 
>  net/bridge/br_input.c | 11 ++++++-----
>  net/bridge/br_vlan.c  | 14 ++++++++++++++
>  2 files changed, 20 insertions(+), 5 deletions(-)
> 
...
> diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
> index af5ebd1..abc841c 100644
> --- a/net/bridge/br_vlan.c
> +++ b/net/bridge/br_vlan.c
> @@ -144,6 +144,20 @@ struct sk_buff *br_handle_vlan(struct net_bridge *br,
>  	if (!br->vlan_enabled)
>  		goto out;
>  
> +	/* Vlan filter table must be configured 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;
> +		else {
> +			kfree_skb_list(skb);

Why is this not kfree_skb() but kfree_skb_list()?
I haven't seen kfree_skb_list() in the bridge code.

Thanks,
Toshiaki Makita

> +			return NULL;
> +		}
> +	}
> +
>  	/* At this point, we know that the frame was filtered and contains
>  	 * a valid vlan id.  If the vlan id is set in the untagged bitmap,
>  	 * send untagged; otherwise, send taged.


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