Pretty simple to fix, from Andi Kleen:
--- linux-work/net/ipv4/icmp.c-o	Tue Jan 15 11:05:17 2002
+++ linux-work/net/ipv4/icmp.c	Sun Jan 20 23:31:29 2002
@@ -495,7 +495,7 @@
         icmp_param.data.icmph.checksum=0;
         icmp_param.csum=0;
         icmp_param.skb=skb_in;
-	icmp_param.offset=skb_in->nh.raw - skb_in->data;
+	icmp_param.offset=skb_in->data - skb_in->nh.raw;
         icmp_out_count(icmp_param.data.icmph.type);
         icmp_socket->sk->protinfo.af_inet.tos = tos;
         ipc.addr = iph->saddr;
--- linux-work/net/ipv6/icmp.c-o	Thu Sep 20 23:12:56 2001
+++ linux-work/net/ipv6/icmp.c	Sun Jan 20 23:40:03 2002
@@ -361,7 +361,7 @@
         msg.icmph.icmp6_pointer = htonl(info);
 
         msg.skb = skb;
-	msg.offset = skb->nh.raw - skb->data;
+	msg.offset = skb->data - skb->nh.raw; 
         msg.csum = 0;
         msg.daddr = &hdr->saddr;