4 files changed, 8 insertions, 6 deletions

diff --git a/checksum.c b/checksum.c
index a5a506c..b330e1e 100644
--- a/checksum.c
+++ b/checksum.c
@@ -116,7 +116,7 @@ uint16_t csum_fold(uint32_t sum)
 
 /**
  * csum_ip4_header() - Calculate IPv4 header checksum
- * @tot_len:	IPv4 payload length (data + IP header, network order)
+ * @tot_len:	IPv4 packet length (data + IP header, host order)
  * @protocol:	Protocol number
  * @saddr:	IPv4 source address
  * @daddr:	IPv4 destination address
@@ -128,7 +128,7 @@ uint16_t csum_ip4_header(uint16_t tot_len, uint8_t protocol,
 {
 	uint32_t sum = L2_BUF_IP4_PSUM(protocol);
 
-	sum += tot_len;
+	sum += htons(tot_len);
 	sum += (saddr.s_addr >> 16) & 0xffff;
 	sum += saddr.s_addr & 0xffff;
 	sum += (daddr.s_addr >> 16) & 0xffff;
diff --git a/tap.c b/tap.c
index d0ef6b5..230566b 100644
--- a/tap.c
+++ b/tap.c
@@ -149,17 +149,19 @@ static void *tap_push_l2h(const struct ctx *c, void *buf, uint16_t proto)
 static void *tap_push_ip4h(struct iphdr *ip4h, struct in_addr src,
 			   struct in_addr dst, size_t len, uint8_t proto)
 {
+	uint16_t tot_len = len + sizeof(*ip4h);
+
 	ip4h->version = 4;
 	ip4h->ihl = sizeof(struct iphdr) / 4;
 	ip4h->tos = 0;
-	ip4h->tot_len = htons(len + sizeof(*ip4h));
+	ip4h->tot_len = htons(tot_len);
 	ip4h->id = 0;
 	ip4h->frag_off = 0;
 	ip4h->ttl = 255;
 	ip4h->protocol = proto;
 	ip4h->saddr = src.s_addr;
 	ip4h->daddr = dst.s_addr;
-	ip4h->check = csum_ip4_header(ip4h->tot_len, proto, src, dst);
+	ip4h->check = csum_ip4_header(tot_len, proto, src, dst);
 	return ip4h + 1;
 }
 
diff --git a/tcp.c b/tcp.c
index 24f99cd..3ba3aa4 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1359,7 +1359,7 @@ static size_t tcp_fill_headers4(const struct ctx *c,
 	iph->daddr = c->ip4.addr_seen.s_addr;
 
 	iph->check = check ? *check :
-			     csum_ip4_header(iph->tot_len, IPPROTO_TCP,
+			     csum_ip4_header(ip_len, IPPROTO_TCP,
 					     *a4, c->ip4.addr_seen);
 
 	tcp_fill_header(th, conn, seq);
diff --git a/udp.c b/udp.c
index 4bf9059..09f9813 100644
--- a/udp.c
+++ b/udp.c
@@ -605,7 +605,7 @@ static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *b,
 	b->iph.tot_len = htons(ip_len);
 	b->iph.daddr = c->ip4.addr_seen.s_addr;
 	b->iph.saddr = src.s_addr;
-	b->iph.check = csum_ip4_header(b->iph.tot_len, IPPROTO_UDP,
+	b->iph.check = csum_ip4_header(ip_len, IPPROTO_UDP,
 				       src, c->ip4.addr_seen);
 
 	b->uh.source = b->s_in.sin_port;