tcp: NAT IPv4-mapped IPv6 addresses like IPv4 addresses

passt usually doesn't NAT, but it does do so for the remapping of the
gateway address to refer to the host.  Currently we perform this NAT with
slightly different rules on both IPv4 addresses and IPv6 addresses, but not
on IPv4-mapped IPv6 addresses.  This means we won't correctly handle the
case of an IPv4 connection over an IPv6 socket, which is possible on Linux
(and probably other platforms).

Refactor tcp_conn_from_sock() to perform the NAT after converting either
address family into an inany_addr, so IPv4 and and IPv4-mapped addresses
have the same representation.

With two new helpers this lets us remove the IPv4 and IPv6 specific paths
from tcp_conn_from_sock().

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

1 files changed, 31 insertions, 36 deletions

diff --git a/tcp.c b/tcp.c
index 7d5ac6c..59c1a93 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2725,6 +2725,34 @@ static void tcp_connect_finish(struct ctx *c, struct tcp_tap_conn *conn)
 }
 
 /**
+ * tcp_snat_inbound() - Translate source address for inbound data if needed
+ * @c:		Execution context
+ * @addr:	Source address of inbound packet/connection
+ */
+static void tcp_snat_inbound(const struct ctx *c, union inany_addr *addr)
+{
+	struct in_addr *addr4 = inany_v4(addr);
+
+	if (addr4) {
+		if (IN4_IS_ADDR_LOOPBACK(addr4) ||
+		    IN4_IS_ADDR_UNSPECIFIED(addr4) ||
+		    IN4_ARE_ADDR_EQUAL(addr4, &c->ip4.addr_seen))
+			*addr4 = c->ip4.gw;
+	} else {
+		struct in6_addr *addr6 = &addr->a6;
+
+		if (IN6_IS_ADDR_LOOPBACK(addr6) ||
+		    IN6_ARE_ADDR_EQUAL(addr6, &c->ip6.addr_seen) ||
+		    IN6_ARE_ADDR_EQUAL(addr6, &c->ip6.addr)) {
+			if (IN6_IS_ADDR_LINKLOCAL(&c->ip6.gw))
+				*addr6 = c->ip6.gw;
+			else
+				*addr6 = c->ip6.addr_ll;
+		}
+	}
+}
+
+/**
  * tcp_tap_conn_from_sock() - Initialize state for non-spliced connection
  * @c:		Execution context
  * @ref:	epoll reference of listening socket
@@ -2744,43 +2772,10 @@ static void tcp_tap_conn_from_sock(struct ctx *c, union epoll_ref ref,
 	conn->ws_to_tap = conn->ws_from_tap = 0;
 	conn_event(c, conn, SOCK_ACCEPTED);
 
-	if (sa->sa_family == AF_INET6) {
-		struct sockaddr_in6 sa6;
-
-		memcpy(&sa6, sa, sizeof(sa6));
+	inany_from_sockaddr(&conn->addr, &conn->sock_port, sa);
+	conn->tap_port = ref.r.p.tcp.tcp.index;
 
-		if (IN6_IS_ADDR_LOOPBACK(&sa6.sin6_addr) ||
-		    IN6_ARE_ADDR_EQUAL(&sa6.sin6_addr, &c->ip6.addr_seen) ||
-		    IN6_ARE_ADDR_EQUAL(&sa6.sin6_addr, &c->ip6.addr)) {
-			struct in6_addr *src;
-
-			if (IN6_IS_ADDR_LINKLOCAL(&c->ip6.gw))
-				src = &c->ip6.gw;
-			else
-				src = &c->ip6.addr_ll;
-
-			memcpy(&sa6.sin6_addr, src, sizeof(*src));
-		}
-
-		inany_from_af(&conn->addr, AF_INET6, &sa6.sin6_addr);
-
-		conn->sock_port = ntohs(sa6.sin6_port);
-		conn->tap_port = ref.r.p.tcp.tcp.index;
-	} else {
-		struct sockaddr_in sa4;
-
-		memcpy(&sa4, sa, sizeof(sa4));
-
-		if (IN4_IS_ADDR_LOOPBACK(&sa4.sin_addr) ||
-		    IN4_IS_ADDR_UNSPECIFIED(&sa4.sin_addr) ||
-		    IN4_ARE_ADDR_EQUAL(&sa4.sin_addr, &c->ip4.addr_seen))
-			sa4.sin_addr = c->ip4.gw;
-
-		inany_from_af(&conn->addr, AF_INET, &sa4.sin_addr);
-
-		conn->sock_port = ntohs(sa4.sin_port);
-		conn->tap_port = ref.r.p.tcp.tcp.index;
-	}
+	tcp_snat_inbound(c, &conn->addr);
 
 	tcp_seq_init(c, conn, now);
 	tcp_hash_insert(c, conn);