Hello,
I was reading some tcpdump's of netdump traffic today, and I realized
that all of the packets that go from the crashing machine to the netdump server
have a zero checksum. Looking at the code, it looks like netconsole/netdump
use the function netpoll_send_udp to send out the packets. However, in
netdump_send_udp, the checksum is set to 0, and never seems to be computed. Is
this intentional, or just an oversight? I would think that we would always
want to compute the UDP checksum, but there might be something I am
overlooking. Incidentally, it seems like the only user of netpoll_send_udp is
netconsole (and netdump in RedHat kernels).
Assuming that this is just an oversight, attached is a simple patch to
compute the UDP checksum in netpoll_send_udp.
Signed-off-by: Chris Lalancette <[EMAIL PROTECTED]>
--- linux-2.6/net/core/netpoll.c.orig 2006-11-06 18:16:58.000000000 -0500
+++ linux-2.6/net/core/netpoll.c 2006-11-06 18:31:20.000000000 -0500
@@ -356,6 +356,10 @@ void netpoll_send_udp(struct netpoll *np
put_unaligned(htonl(np->remote_ip), &(iph->daddr));
iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
+ udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr, udp_len,
+ IPPROTO_UDP,
+ csum_partial((unsigned char *)udph, udp_len, 0));
+
eth = (struct ethhdr *) skb_push(skb, ETH_HLEN);
skb->mac.raw = skb->data;
skb->protocol = eth->h_proto = htons(ETH_P_IP);
