diff -ur kernel-2.6.28.orig/net/ipv4/netfilter/iphb.c kernel-2.6.28/net/ipv4/netfilter/iphb.c
--- kernel-2.6.28.orig/net/ipv4/netfilter/iphb.c	2010-01-19 06:32:06.000000000 +0100
+++ kernel-2.6.28/net/ipv4/netfilter/iphb.c	2010-01-29 19:32:34.000000000 +0100
@@ -276,6 +276,11 @@
 	tsk = tcp_sk(skb->sk);
 	tcp = tcp_hdr(skb);
 
+	if (! tcp || ! tsk) {
+		flush_keepalives(1);
+		return NF_ACCEPT;	
+	}
+
 	len -= hlen;           /* ip4/6 header len     */
 	len -= tcp->doff << 2; /* tcp header + options */