The level 4 protocol is part of the UDP and TCP calculations.
nfq_checksum_tcpudp_ipv4() was using IPPROTO_TCP in this calculation,
which gave the wrong answer for UDP.
---
src/extra/checksum.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/extra/checksum.c b/src/extra/checksum.c
index f367f75..3ef288f 100644
--- a/src/extra/checksum.c
+++ b/src/extra/checksum.c
@@ -46,7 +46,7 @@ uint16_t nfq_checksum_tcpudp_ipv4(struct iphdr *iph)
sum += (iph->saddr) & 0xFFFF;
sum += (iph->daddr >> 16) & 0xFFFF;
sum += (iph->daddr) & 0xFFFF;
- sum += htons(IPPROTO_TCP);
+ sum += htons(iph->protocol);
sum += htons(len);
return nfq_checksum(sum, (uint16_t *)payload, len);
--
2.14.5
