Linux Ethernet Bridging - Dec 2010 - [Bridge] [PATCH] net: bridge: check the length of skb after nf_bridge_maybe_copy_header()

Since nf_bridge_maybe_copy_header() may change the length of skb,
we should check the length of skb after it to handle the ppoe skbs.

Signed-off-by: Changli Gao <xiaosuo at gmail.com>
---
 net/bridge/br_forward.c |   16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index 2bd11ec..ee64287 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -41,17 +41,13 @@ static inline unsigned packet_length(const struct sk_buff
*skb)
 
 int br_dev_queue_push_xmit(struct sk_buff *skb)
 {
-	/* drop mtu oversized packets except gso */
-	if (packet_length(skb) > skb->dev->mtu && !skb_is_gso(skb))
+	/* ip_fragment doesn't copy the MAC header */
+	if (nf_bridge_maybe_copy_header(skb) ||
+	    (packet_length(skb) > skb->dev->mtu && !skb_is_gso(skb)))
{
 		kfree_skb(skb);
-	else {
-		/* ip_fragment doesn't copy the MAC header */
-		if (nf_bridge_maybe_copy_header(skb))
-			kfree_skb(skb);
-		else {
-			skb_push(skb, ETH_HLEN);
-			dev_queue_xmit(skb);
-		}
+	} else {
+		skb_push(skb, ETH_HLEN);
+		dev_queue_xmit(skb);
 	}
 
 	return 0;

From: Changli Gao <xiaosuo at gmail.com>
Date: Sat, 25 Dec 2010 21:41:30 +0800
> Since nf_bridge_maybe_copy_header() may change the length of skb,
> we should check the length of skb after it to handle the ppoe skbs.
> 
> Signed-off-by: Changli Gao <xiaosuo at gmail.com>
This is really strange.

packet_length() subtracts VLAN_HLEN from the value it returns, so the
correct fix seems to be to make this function handle the PPPOE case
too.

Otherwise I suspect you have many other functions to fix as well.

I'm not applying this patch.

On Sat, Jan 1, 2011 at 3:10 AM, David Miller <davem at davemloft.net>
wrote:
> From: Changli Gao <xiaosuo at gmail.com>
> Date: Sat, 25 Dec 2010 21:41:30 +0800
>
>> Since nf_bridge_maybe_copy_header() may change the length of skb,
>> we should check the length of skb after it to handle the ppoe skbs.
>>
>> Signed-off-by: Changli Gao <xiaosuo at gmail.com>
>
> This is really strange.
>
> packet_length() subtracts VLAN_HLEN from the value it returns, so the
> correct fix seems to be to make this function handle the PPPOE case
> too.
>
It is correct. The actual MTU of 802.1q frame is 4 bytes larger. For
example, the MTU of ethernet is normally 1500, however the actual MTU
of the 802.1Q is 1504.

Please see this patch:
http://git.kernel.org/?p=linux/kernel/git/davem/net-next-2.6.git;a=commitdiff;h=c893b8066c7bf6156e4d760e5acaf4c148e37190;hp=3c0fef0b7d36e5f8d3ea3731a8228102274e3c23
> Otherwise I suspect you have many other functions to fix as well.
>
> I'm not applying this patch.
>


-- 
Regards,
Changli Gao(xiaosuo at gmail.com)