From: Chris Lalancette <clalance@redhat.com>
Subject: [RHEL5 PATCH]: Compute checksum properly in netpoll_send_udp
Date: Wed, 08 Nov 2006 00:09:18 -0500
Bugzilla: 214542
Message-Id: <4551667E.7040300@redhat.com>
Changelog: Compute checksum properly in netpoll_send_udp


All,
    While looking at some netconsole captures the other day, I noticed that 
    all packets between the netconsole client and netconsole server had a 
    zero UDP checksum.  This is because netconsole makes a call to 
    netpoll_send_udp, which just sets the checksum to 0.  While technically 
    allowed by the protocol, having no checksum is generally considered a 
    bad thing.  The attached patch fixes this by simply computing the 
    checksum before sending it out.  This fixes BZ 214542.  This patch is 
    currently upstream in David Miller's network tree.  Please ACK.

Thanks,
Chris Lalancette

--- linux-2.6.18.noarch/net/core/netpoll.c.orig	2006-11-07 20:11:48.622089003 -0500
+++ linux-2.6.18.noarch/net/core/netpoll.c	2006-11-07 20:12:14.243963859 -0500
@@ -340,6 +340,12 @@ void netpoll_send_udp(struct netpoll *np
 	udph->dest = htons(np->remote_port);
 	udph->len = htons(udp_len);
 	udph->check = 0;
+	udph->check = csum_tcpudp_magic(htonl(np->local_ip),
+					htonl(np->remote_ip),
+					udp_len, IPPROTO_UDP,
+					csum_partial((unsigned char *)udph, udp_len, 0));
+	if (udph->check == 0)
+		udph->check = -1;
 
 	iph = (struct iphdr *)skb_push(skb, sizeof(*iph));