Add csum_udp4() helper for calculating UDP over IPv4 checksums

At least two places in passt fill in UDP over IPv4 checksums, although
since UDP checksums are optional with IPv4 that just amounts to storing
a 0 (in tap_ip_send()) or leaving a 0 from an earlier initialization (in
dhcp()).  For consistency, add a helper for this "calculation".

Just for the heck of it, add the option (compile time disabled for now) to
calculate real UDP checksums.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/tap.c b/tap.c
index 9c197cb..58fc1de 100644
--- a/tap.c
+++ b/tap.c
@@ -145,7 +145,7 @@ void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
 		} else if (iph->protocol == IPPROTO_UDP) {
 			struct udphdr *uh = (struct udphdr *)(iph + 1);
 
-			uh->check = 0;
+			csum_udp4(uh, iph->saddr, iph->daddr, uh + 1, len - sizeof(*uh));
 		} else if (iph->protocol == IPPROTO_ICMP) {
 			struct icmphdr *ih = (struct icmphdr *)(iph + 1);
 			csum_icmp4(ih, ih + 1, len - sizeof(*ih));