[PATCH 02/16] tcp, udp: Don't precompute port remappings in epoll references

[David Gibson <david@gibson.dropbear.id.au>]

The epoll references for both TCP listening sockets and UDP sockets
includes a port number.  This gives the destination port that traffic to
that socket will be sent to on the other side.  That will usually be the
same as the socket's bound port, but might not if the -t, -u, -T or -U
options are given with different original and forwarded port numbers.

As we move towards a more flexible forwarding model for passt, it's going
to become possible for that destination port to vary depending on more
things (for example the source or destination address).  So, it will no
longer make sense to have a fixed value for a listening socket.

Change to simpler semantics where this field in the reference gives the
bound port of the socket.  We apply the translations to the correct
destination port later on, when we're actually forwarding.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c        |  8 ++++----
 tcp.h        |  2 +-
 tcp_splice.c |  4 ++++
 udp.c        | 14 ++++++++------
 4 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/tcp.c b/tcp.c
index fdf56713..cd833728 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2676,7 +2676,7 @@ static void tcp_tap_conn_from_sock(struct ctx *c,
 	conn_event(c, conn, SOCK_ACCEPTED);
 
 	inany_from_sockaddr(&conn->faddr, &conn->fport, sa);
-	conn->eport = ref.port;
+	conn->eport = ref.port + c->tcp.fwd_in.delta[ref.port];
 
 	tcp_snat_inbound(c, &conn->faddr);
 
@@ -2861,7 +2861,7 @@ static int tcp_sock_init_af(const struct ctx *c, sa_family_t af, in_port_t port,
 			    const void *addr, const char *ifname)
 {
 	union tcp_listen_epoll_ref tref = {
-		.port = port + c->tcp.fwd_in.delta[port],
+		.port = port,
 		.pif = PIF_HOST,
 	};
 	int s;
@@ -2923,7 +2923,7 @@ int tcp_sock_init(const struct ctx *c, sa_family_t af, const void *addr,
 static void tcp_ns_sock_init4(const struct ctx *c, in_port_t port)
 {
 	union tcp_listen_epoll_ref tref = {
-		.port = port + c->tcp.fwd_out.delta[port],
+		.port = port,
 		.pif = PIF_SPLICE,
 	};
 	struct in_addr loopback = IN4ADDR_LOOPBACK_INIT;
@@ -2949,7 +2949,7 @@ static void tcp_ns_sock_init4(const struct ctx *c, in_port_t port)
 static void tcp_ns_sock_init6(const struct ctx *c, in_port_t port)
 {
 	union tcp_listen_epoll_ref tref = {
-		.port = port + c->tcp.fwd_out.delta[port],
+		.port = port,
 		.pif = PIF_SPLICE,
 	};
 	int s;
diff --git a/tcp.h b/tcp.h
index 875006ed..5e6756d4 100644
--- a/tcp.h
+++ b/tcp.h
@@ -37,7 +37,7 @@ union tcp_epoll_ref {
 
 /**
  * union tcp_listen_epoll_ref - epoll reference portion for TCP listening
- * @port:	Port number we're forwarding *to* (listening port plus delta)
+ * @port:	Bound port number of the socket
  * @pif:	pif in which the socket is listening
  * @u32:	Opaque u32 value of reference
  */
diff --git a/tcp_splice.c b/tcp_splice.c
index cc9745e8..b8d64eba 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -401,6 +401,8 @@ static int tcp_splice_new(const struct ctx *c, struct tcp_splice_conn *conn,
 		int *p = CONN_V6(conn) ? init_sock_pool6 : init_sock_pool4;
 		sa_family_t af = CONN_V6(conn) ? AF_INET6 : AF_INET;
 
+		port += c->tcp.fwd_out.delta[port];
+
 		s = tcp_conn_pool_sock(p);
 		if (s < 0)
 			s = tcp_conn_new_sock(c, af);
@@ -409,6 +411,8 @@ static int tcp_splice_new(const struct ctx *c, struct tcp_splice_conn *conn,
 
 		ASSERT(pif == PIF_HOST);
 
+		port += c->tcp.fwd_in.delta[port];
+
 		/* If pool is empty, refill it first */
 		if (p[TCP_SOCK_POOL_SIZE-1] < 0)
 			NS_CALL(tcp_sock_refill_ns, c);
diff --git a/udp.c b/udp.c
index c839e269..02cb7889 100644
--- a/udp.c
+++ b/udp.c
@@ -762,6 +762,11 @@ void udp_sock_handler(const struct ctx *c, union epoll_ref ref, uint32_t events,
 	if (c->no_udp || !(events & EPOLLIN))
 		return;
 
+	if (ref.udp.pif == PIF_SPLICE)
+		dstport += c->udp.fwd_out.f.delta[dstport];
+	else if (ref.udp.pif == PIF_HOST)
+		dstport += c->udp.fwd_in.f.delta[dstport];
+
 	if (v6) {
 		mmh_recv = udp6_l2_mh_sock;
 		udp6_localname.sin6_port = htons(dstport);
@@ -989,16 +994,13 @@ int udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 		  const void *addr, const char *ifname, in_port_t port)
 {
 	union udp_epoll_ref uref = { .splice = (c->mode == MODE_PASTA),
-				     .orig = true };
+				     .orig = true, .port = port };
 	int s, r4 = FD_REF_MAX + 1, r6 = FD_REF_MAX + 1;
 
-	if (ns) {
+	if (ns)
 		uref.pif = PIF_SPLICE;
-		uref.port = (in_port_t)(port + c->udp.fwd_out.f.delta[port]);
-	} else {
+	else
 		uref.pif = PIF_HOST;
-		uref.port = (in_port_t)(port + c->udp.fwd_in.f.delta[port]);
-	}
 
 	if ((af == AF_INET || af == AF_UNSPEC) && c->ifi4) {
 		uref.v6 = 0;
-- 
@@ -762,6 +762,11 @@ void udp_sock_handler(const struct ctx *c, union epoll_ref ref, uint32_t events,
 	if (c->no_udp || !(events & EPOLLIN))
 		return;
 
+	if (ref.udp.pif == PIF_SPLICE)
+		dstport += c->udp.fwd_out.f.delta[dstport];
+	else if (ref.udp.pif == PIF_HOST)
+		dstport += c->udp.fwd_in.f.delta[dstport];
+
 	if (v6) {
 		mmh_recv = udp6_l2_mh_sock;
 		udp6_localname.sin6_port = htons(dstport);
@@ -989,16 +994,13 @@ int udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 		  const void *addr, const char *ifname, in_port_t port)
 {
 	union udp_epoll_ref uref = { .splice = (c->mode == MODE_PASTA),
-				     .orig = true };
+				     .orig = true, .port = port };
 	int s, r4 = FD_REF_MAX + 1, r6 = FD_REF_MAX + 1;
 
-	if (ns) {
+	if (ns)
 		uref.pif = PIF_SPLICE;
-		uref.port = (in_port_t)(port + c->udp.fwd_out.f.delta[port]);
-	} else {
+	else
 		uref.pif = PIF_HOST;
-		uref.port = (in_port_t)(port + c->udp.fwd_in.f.delta[port]);
-	}
 
 	if ((af == AF_INET || af == AF_UNSPEC) && c->ifi4) {
 		uref.v6 = 0;
-- 
2.43.0