[PATCH 6/8] tcp: Track guest-side correspondent address

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

Currently the only address we explicitly track in the TCP connection
structure is the tap side forwarding address - that is the remote address
from the guest's point of view.  The tap side correspondent address - the
local address from the guest's point of view - is assumed to always be one
of the handful of guest addresses we track as addr_seen (one each for IPv4,
IPv6 global and IPv6 link-local).

We want to generalize our forwarding model to allow the guest to have
multiple addresses.  As a start on this, track the tap-side correspondent
address in the connection structure, only using one of the addr_seen
variables when we start a new connection.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c      | 37 +++++++++++++++++--------------------
 tcp_conn.h |  2 ++
 2 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/tcp.c b/tcp.c
index ac7ae60..6c4d71e 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1449,7 +1449,7 @@ do {									\
 		ip_len = plen + sizeof(struct iphdr) + sizeof(struct tcphdr);
 		b->iph.tot_len = htons(ip_len);
 		b->iph.saddr = a4->s_addr;
-		b->iph.daddr = c->ip4.addr_seen.s_addr;
+		b->iph.daddr = inany_v4(&conn->caddr)->s_addr;
 
 		if (check)
 			b->iph.check = *check;
@@ -1468,10 +1468,7 @@ do {									\
 
 		b->ip6h.payload_len = htons(plen + sizeof(struct tcphdr));
 		b->ip6h.saddr = conn->faddr.a6;
-		if (IN6_IS_ADDR_LINKLOCAL(&b->ip6h.saddr))
-			b->ip6h.daddr = c->ip6.addr_ll_seen;
-		else
-			b->ip6h.daddr = c->ip6.addr_seen;
+		b->ip6h.daddr = conn->caddr.a6;
 
 		memset(b->ip6h.flow_lbl, 0, 3);
 
@@ -1820,13 +1817,12 @@ static void tcp_clamp_window(const struct ctx *c, struct tcp_tap_conn *conn,
 /**
  * tcp_seq_init() - Calculate initial sequence number according to RFC 6528
  * @c:		Execution context
- * @conn:	TCP connection, with faddr, fport and cport populated
+ * @conn:	TCP connection, with faddr, fport, caddr, cport populated
  * @now:	Current timestamp
  */
 static void tcp_seq_init(const struct ctx *c, struct tcp_tap_conn *conn,
 			 const struct timespec *now)
 {
-	union inany_addr aany;
 	struct {
 		union inany_addr src;
 		in_port_t srcport;
@@ -1835,16 +1831,11 @@ static void tcp_seq_init(const struct ctx *c, struct tcp_tap_conn *conn,
 	} __attribute__((__packed__)) in = {
 		.src = conn->faddr,
 		.srcport = conn->cport,
+		.dst = conn->caddr,
 		.dstport = conn->fport,
 	};
 	uint32_t ns, seq = 0;
 
-	if (CONN_V4(conn))
-		inany_from_af(&aany, AF_INET, &c->ip4.addr);
-	else
-		inany_from_af(&aany, AF_INET6, &c->ip6.addr);
-	in.dst = aany;
-
 	seq = siphash_36b((uint8_t *)&in, c->tcp.hash_secret);
 
 	/* 32ns ticks, overflows 32 bits every 137s */
@@ -2011,8 +2002,6 @@ static void tcp_conn_from_tap(struct ctx *c,
 	socklen_t sl;
 	int s, mss;
 
-	(void)saddr;
-
 	if (c->tcp.conn_count >= TCP_MAX_CONNS)
 		return;
 
@@ -2061,6 +2050,9 @@ static void tcp_conn_from_tap(struct ctx *c,
 		conn->wnd_from_tap = 1;
 
 	inany_from_af(&conn->faddr, af, daddr);
+	inany_from_af(&conn->caddr, af, saddr);
+	conn->fport = ntohs(th->dest);
+	conn->cport = ntohs(th->source);
 
 	if (af == AF_INET) {
 		sa = (struct sockaddr *)&addr4;
@@ -2070,9 +2062,6 @@ static void tcp_conn_from_tap(struct ctx *c,
 		sl = sizeof(addr6);
 	}
 
-	conn->fport = ntohs(th->dest);
-	conn->cport = ntohs(th->source);
-
 	conn->seq_init_from_tap = ntohl(th->seq);
 	conn->seq_from_tap = conn->seq_init_from_tap + 1;
 	conn->seq_ack_to_tap = conn->seq_from_tap;
@@ -2731,10 +2720,18 @@ static void tcp_tap_conn_from_sock(struct ctx *c, union epoll_ref ref,
 	conn_event(c, conn, SOCK_ACCEPTED);
 
 	inany_from_sockaddr(&conn->faddr, &conn->fport, sa);
-	conn->cport = ref.r.p.tcp.tcp.index;
-
 	tcp_snat_inbound(c, &conn->faddr);
 
+	if (CONN_V4(conn)) {
+		inany_from_af(&conn->caddr, AF_INET, &c->ip4.addr_seen);
+	} else {
+		if (IN6_IS_ADDR_LINKLOCAL(&conn->faddr.a6))
+			conn->caddr.a6 = c->ip6.addr_ll_seen;
+		else
+			conn->caddr.a6 = c->ip6.addr_seen;
+	}
+	conn->cport = ref.r.p.tcp.tcp.index;
+
 	tcp_seq_init(c, conn, now);
 	tcp_hash_insert(c, conn);
 
diff --git a/tcp_conn.h b/tcp_conn.h
index ba2a1ef..9151c18 100644
--- a/tcp_conn.h
+++ b/tcp_conn.h
@@ -35,6 +35,7 @@ extern const char *tcp_common_flag_str[];
  * @ws_to_tap:		Window scaling factor advertised to tap/guest
  * @sndbuf:		Sending buffer in kernel, rounded to 2 ^ SNDBUF_BITS
  * @seq_dup_ack_approx:	Last duplicate ACK number sent to tap
+ * @caddr:		Guest side correspondent address (guest's local address)
  * @faddr:		Guest side forwarding address (guest's remote address)
  * @cport:		Guest side correspondent port (guest's local port)
  * @fport:		Guest side forwarding port (guest's remote port)
@@ -105,6 +106,7 @@ struct tcp_tap_conn {
 	uint8_t		seq_dup_ack_approx;
 
 
+	union inany_addr caddr;
 	union inany_addr faddr;
 	in_port_t	cport;
 	in_port_t	fport;
-- 
@@ -35,6 +35,7 @@ extern const char *tcp_common_flag_str[];
  * @ws_to_tap:		Window scaling factor advertised to tap/guest
  * @sndbuf:		Sending buffer in kernel, rounded to 2 ^ SNDBUF_BITS
  * @seq_dup_ack_approx:	Last duplicate ACK number sent to tap
+ * @caddr:		Guest side correspondent address (guest's local address)
  * @faddr:		Guest side forwarding address (guest's remote address)
  * @cport:		Guest side correspondent port (guest's local port)
  * @fport:		Guest side forwarding port (guest's remote port)
@@ -105,6 +106,7 @@ struct tcp_tap_conn {
 	uint8_t		seq_dup_ack_approx;
 
 
+	union inany_addr caddr;
 	union inany_addr faddr;
 	in_port_t	cport;
 	in_port_t	fport;
-- 
2.41.0