[BRIDGE] netfilter: memory corruption fix

The bridge-netfilter code will overwrite memory if there is not
headroom in the skb to save the header.  This first showed up when
using Xen with sky2 driver that doesn't allocate the extra space.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index 6ccd32b..864fbbc 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -40,11 +40,15 @@
 	else {
 #ifdef CONFIG_BRIDGE_NETFILTER
 		/* ip_refrag calls ip_fragment, doesn't copy the MAC header. */
-		nf_bridge_maybe_copy_header(skb);
+		if (nf_bridge_maybe_copy_header(skb))
+			kfree_skb(skb);
+		else
 #endif
-		skb_push(skb, ETH_HLEN);
+		{
+			skb_push(skb, ETH_HLEN);
 
-		dev_queue_xmit(skb);
+			dev_queue_xmit(skb);
+		}
 	}
 
 	return 0;