tcp, udp: Don't pre-fill IPv4 destination address in headers

Because packets sent on the tap interface will always be going to the
guest/namespace, we more-or-less know what address they'll be going to.  So
we pre-fill this destination address in our header buffers for IPv4.  We
can't do the same for IPv6 because we could need either the global or
link-local address for the guest.  In future we're going to want more
flexibility for the destination address, so this pre-filling will get in
the way.

Change the flow so we always fill in the IPv4 destination address for each
packet, rather than prefilling it from proto_update_l2_buf().  In fact for
TCP we already redundantly filled the destination for each packet anyway.

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

8 files changed, 15 insertions, 32 deletions

diff --git a/passt.c b/passt.c
index ca0acc6..8ddd9b3 100644
--- a/passt.c
+++ b/passt.c
@@ -117,13 +117,11 @@ static void timer_init(struct ctx *c, const struct timespec *now)
  * proto_update_l2_buf() - Update scatter-gather L2 buffers in protocol handlers
  * @eth_d:	Ethernet destination address, NULL if unchanged
  * @eth_s:	Ethernet source address, NULL if unchanged
- * @ip_da:	Pointer to IPv4 destination address, NULL if unchanged
  */
-void proto_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s,
-			 const struct in_addr *ip_da)
+void proto_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s)
 {
-	tcp_update_l2_buf(eth_d, eth_s, ip_da);
-	udp_update_l2_buf(eth_d, eth_s, ip_da);
+	tcp_update_l2_buf(eth_d, eth_s);
+	udp_update_l2_buf(eth_d, eth_s);
 }
 
 /**
@@ -247,7 +245,7 @@ int main(int argc, char **argv)
 	if (!c.no_icmp)
 		icmp_init();
 
-	proto_update_l2_buf(c.mac_guest, c.mac, &c.ip4.addr);
+	proto_update_l2_buf(c.mac_guest, c.mac);
 
 	if (c.ifi4 && !c.no_dhcp)
 		dhcp_init();
diff --git a/passt.h b/passt.h
index 0500ff0..282bd1a 100644
--- a/passt.h
+++ b/passt.h
@@ -303,7 +303,7 @@ struct ctx {
 	int low_rmem;
 };
 
-void proto_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s,
-			 const struct in_addr *ip_da);
+void proto_update_l2_buf(const unsigned char *eth_d,
+			 const unsigned char *eth_s);
 
 #endif /* PASST_H */
diff --git a/pasta.c b/pasta.c
index dbe8e8c..9bc26d5 100644
--- a/pasta.c
+++ b/pasta.c
@@ -353,7 +353,7 @@ void pasta_ns_conf(struct ctx *c)
 		}
 	}
 
-	proto_update_l2_buf(c->mac_guest, NULL, NULL);
+	proto_update_l2_buf(c->mac_guest, NULL);
 }
 
 /**
diff --git a/tap.c b/tap.c
index 4ed63f1..ee79be0 100644
--- a/tap.c
+++ b/tap.c
@@ -625,10 +625,8 @@ resume:
 
 		l4_len = l3_len - hlen;
 
-		if (iph->saddr && c->ip4.addr_seen.s_addr != iph->saddr) {
+		if (iph->saddr && c->ip4.addr_seen.s_addr != iph->saddr)
 			c->ip4.addr_seen.s_addr = iph->saddr;
-			proto_update_l2_buf(NULL, NULL, &c->ip4.addr_seen);
-		}
 
 		l4h = packet_get(in, i, sizeof(*eh) + hlen, l4_len, NULL);
 		if (!l4h)
@@ -969,7 +967,7 @@ redo:
 
 		if (memcmp(c->mac_guest, eh->h_source, ETH_ALEN)) {
 			memcpy(c->mac_guest, eh->h_source, ETH_ALEN);
-			proto_update_l2_buf(c->mac_guest, NULL, NULL);
+			proto_update_l2_buf(c->mac_guest, NULL);
 		}
 
 		switch (ntohs(eh->h_proto)) {
@@ -1030,7 +1028,7 @@ restart:
 
 		if (memcmp(c->mac_guest, eh->h_source, ETH_ALEN)) {
 			memcpy(c->mac_guest, eh->h_source, ETH_ALEN);
-			proto_update_l2_buf(c->mac_guest, NULL, NULL);
+			proto_update_l2_buf(c->mac_guest, NULL);
 		}
 
 		switch (ntohs(eh->h_proto)) {
diff --git a/tcp.c b/tcp.c
index c52ea2b..87f443a 100644
--- a/tcp.c
+++ b/tcp.c
@@ -997,10 +997,8 @@ static void tcp_update_check_tcp6(struct tcp6_l2_buf_t *buf)
  * tcp_update_l2_buf() - Update L2 buffers with Ethernet and IPv4 addresses
  * @eth_d:	Ethernet destination address, NULL if unchanged
  * @eth_s:	Ethernet source address, NULL if unchanged
- * @ip_da:	Pointer to IPv4 destination address, NULL if unchanged
  */
-void tcp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s,
-		       const struct in_addr *ip_da)
+void tcp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s)
 {
 	int i;
 
@@ -1014,10 +1012,6 @@ void tcp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s,
 		tap_update_mac(&b6->taph, eth_d, eth_s);
 		tap_update_mac(&b4f->taph, eth_d, eth_s);
 		tap_update_mac(&b6f->taph, eth_d, eth_s);
-
-		if (ip_da) {
-			b4f->iph.daddr = b4->iph.daddr = ip_da->s_addr;
-		}
 	}
 }
 
diff --git a/tcp.h b/tcp.h
index 3454d9a..1608d58 100644
--- a/tcp.h
+++ b/tcp.h
@@ -26,8 +26,7 @@ void tcp_timer(struct ctx *c, const struct timespec *ts);
 void tcp_defer_handler(struct ctx *c);
 
 void tcp_sock_set_bufsize(const struct ctx *c, int s);
-void tcp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s,
-		       const struct in_addr *ip_da);
+void tcp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s);
 
 /**
  * union tcp_epoll_ref - epoll reference portion for TCP connections
diff --git a/udp.c b/udp.c
index 6bb515a..f4ed660 100644
--- a/udp.c
+++ b/udp.c
@@ -276,10 +276,8 @@ static void udp_update_check4(struct udp4_l2_buf_t *buf)
  * udp_update_l2_buf() - Update L2 buffers with Ethernet and IPv4 addresses
  * @eth_d:	Ethernet destination address, NULL if unchanged
  * @eth_s:	Ethernet source address, NULL if unchanged
- * @ip_da:	Pointer to IPv4 destination address, NULL if unchanged
  */
-void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s,
-		       const struct in_addr *ip_da)
+void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s)
 {
 	int i;
 
@@ -289,10 +287,6 @@ void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s,
 
 		tap_update_mac(&b4->taph, eth_d, eth_s);
 		tap_update_mac(&b6->taph, eth_d, eth_s);
-
-		if (ip_da) {
-			b4->iph.daddr = ip_da->s_addr;
-		}
 	}
 }
 
@@ -578,6 +572,7 @@ static size_t udp_update_hdr4(const struct ctx *c, int n, in_port_t dstport,
 	ip_len = udp4_l2_mh_sock[n].msg_len + sizeof(b->iph) + sizeof(b->uh);
 
 	b->iph.tot_len = htons(ip_len);
+	b->iph.daddr = c->ip4.addr_seen.s_addr;
 
 	src_port = ntohs(b->s_in.sin_port);
 
diff --git a/udp.h b/udp.h
index f9d4459..f553de2 100644
--- a/udp.h
+++ b/udp.h
@@ -16,8 +16,7 @@ int udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 		  const void *addr, const char *ifname, in_port_t port);
 int udp_init(struct ctx *c);
 void udp_timer(struct ctx *c, const struct timespec *ts);
-void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s,
-		       const struct in_addr *ip_da);
+void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s);
 
 /**
  * union udp_epoll_ref - epoll reference portion for TCP connections