conf, fwd: Split notion of gateway/router from guest-visible host address

The @gw fields in the ip4_ctx and ip6_ctx give the (host's) default
gateway.  We use this for two quite distinct things: advertising the
gateway that the guest should use (via DHCP, NDP and/or --config-net)
and for a limited form of NAT.  So that the guest can access services
on the host, we map the gateway address within the guest to the
loopback address on the host.

Using the gateway address for this isn't necessarily the best choice
for this purpose, certainly not for all circumstances.  So, start off
by splitting the notion of these into two different values: @guest_gw
which is the gateway address the guest should use and @nat_host_loopback,
which is the guest visible address to remap to the host's loopback.

Usually nat_host_loopback will have the same value as guest_gw.  However
when --no-map-gw is specified we leave them unspecified instead.  This
means when we use nat_host_loopback, we don't need to separately check
c->no_map_gw to see if it's relevant.

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

1 files changed, 33 insertions, 28 deletions

diff --git a/conf.c b/conf.c
index 7eec313..d4a3e9c 100644
--- a/conf.c
+++ b/conf.c
@@ -410,12 +410,12 @@ static void add_dns_resolv(struct ctx *c, const char *nameserver,
 		 * redirect
 		 */
 		if (IN4_IS_ADDR_LOOPBACK(&ns4)) {
-			if (c->no_map_gw)
+			if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.map_host_loopback))
 				return;
 
-			ns4 = c->ip4.gw;
+			ns4 = c->ip4.map_host_loopback;
 			if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_match))
-				c->ip4.dns_match = c->ip4.gw;
+				c->ip4.dns_match = c->ip4.map_host_loopback;
 		}
 
 		*idx4 += add_dns4(c, &ns4, *idx4);
@@ -429,13 +429,13 @@ static void add_dns_resolv(struct ctx *c, const char *nameserver,
 		 * redirect
 		 */
 		if (IN6_IS_ADDR_LOOPBACK(&ns6)) {
-			if (c->no_map_gw)
+			if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_host_loopback))
 				return;
 
-			ns6 = c->ip6.gw;
+			ns6 = c->ip6.map_host_loopback;
 
 			if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_match))
-				c->ip6.dns_match = c->ip6.gw;
+				c->ip6.dns_match = c->ip6.map_host_loopback;
 		}
 
 		*idx6 += add_dns6(c, &ns6, *idx6);
@@ -625,8 +625,9 @@ static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
 		return 0;
 	}
 
-	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->gw)) {
-		int rc = nl_route_get_def(nl_sock, ifi, AF_INET, &ip4->gw);
+	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->guest_gw)) {
+		int rc = nl_route_get_def(nl_sock, ifi, AF_INET,
+					  &ip4->guest_gw);
 		if (rc < 0) {
 			err("Couldn't discover IPv4 gateway address: %s",
 			    strerror(-rc));
@@ -658,7 +659,7 @@ static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
 
 	ip4->addr_seen = ip4->addr;
 
-	ip4->our_tap_addr = ip4->gw;
+	ip4->our_tap_addr = ip4->guest_gw;
 
 	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr))
 		return 0;
@@ -686,8 +687,8 @@ static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
 		return 0;
 	}
 
-	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->gw)) {
-		rc = nl_route_get_def(nl_sock, ifi, AF_INET6, &ip6->gw);
+	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->guest_gw)) {
+		rc = nl_route_get_def(nl_sock, ifi, AF_INET6, &ip6->guest_gw);
 		if (rc < 0) {
 			err("Couldn't discover IPv6 gateway address: %s",
 			    strerror(-rc));
@@ -705,8 +706,8 @@ static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
 
 	ip6->addr_seen = ip6->addr;
 
-	if (IN6_IS_ADDR_LINKLOCAL(&ip6->gw))
-		ip6->our_tap_ll = ip6->gw;
+	if (IN6_IS_ADDR_LINKLOCAL(&ip6->guest_gw))
+		ip6->our_tap_ll = ip6->guest_gw;
 
 	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->addr) ||
 	    IN6_IS_ADDR_UNSPECIFIED(&ip6->our_tap_ll))
@@ -969,7 +970,8 @@ static void conf_print(const struct ctx *c)
 			info("    mask: %s",
 			     inet_ntop(AF_INET, &mask,        buf4, sizeof(buf4)));
 			info("    router: %s",
-			     inet_ntop(AF_INET, &c->ip4.gw,   buf4, sizeof(buf4)));
+			     inet_ntop(AF_INET, &c->ip4.guest_gw,
+				       buf4, sizeof(buf4)));
 		}
 
 		for (i = 0; !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns[i]); i++) {
@@ -999,7 +1001,7 @@ static void conf_print(const struct ctx *c)
 		info("    assign: %s",
 		     inet_ntop(AF_INET6, &c->ip6.addr, buf6, sizeof(buf6)));
 		info("    router: %s",
-		     inet_ntop(AF_INET6, &c->ip6.gw,   buf6, sizeof(buf6)));
+		     inet_ntop(AF_INET6, &c->ip6.guest_gw, buf6, sizeof(buf6)));
 		info("    our link-local: %s",
 		     inet_ntop(AF_INET6, &c->ip6.our_tap_ll,
 			       buf6, sizeof(buf6)));
@@ -1173,7 +1175,7 @@ fail:
  */
 void conf(struct ctx *c, int argc, char **argv)
 {
-	int netns_only = 0;
+	int netns_only = 0, no_map_gw = 0;
 	const struct option options[] = {
 		{"debug",	no_argument,		NULL,		'd' },
 		{"quiet",	no_argument,		NULL,		'q' },
@@ -1202,7 +1204,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		{"no-dhcpv6",	no_argument,		&c->no_dhcpv6,	1 },
 		{"no-ndp",	no_argument,		&c->no_ndp,	1 },
 		{"no-ra",	no_argument,		&c->no_ra,	1 },
-		{"no-map-gw",	no_argument,		&c->no_map_gw,	1 },
+		{"no-map-gw",	no_argument,		&no_map_gw,	1 },
 		{"ipv4-only",	no_argument,		NULL,		'4' },
 		{"ipv6-only",	no_argument,		NULL,		'6' },
 		{"one-off",	no_argument,		NULL,		'1' },
@@ -1503,18 +1505,18 @@ void conf(struct ctx *c, int argc, char **argv)
 			parse_mac(c->our_tap_mac, optarg);
 			break;
 		case 'g':
-			if (inet_pton(AF_INET6, optarg, &c->ip6.gw)     &&
-			    !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.gw)	&&
-			    !IN6_IS_ADDR_LOOPBACK(&c->ip6.gw)) {
+			if (inet_pton(AF_INET6, optarg, &c->ip6.guest_gw) &&
+			    !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.guest_gw)	&&
+			    !IN6_IS_ADDR_LOOPBACK(&c->ip6.guest_gw)) {
 				if (c->mode == MODE_PASTA)
 					c->ip6.no_copy_routes = true;
 				break;
 			}
 
-			if (inet_pton(AF_INET, optarg, &c->ip4.gw)	&&
-			    !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.gw)	&&
-			    !IN4_IS_ADDR_BROADCAST(&c->ip4.gw)		&&
-			    !IN4_IS_ADDR_LOOPBACK(&c->ip4.gw)) {
+			if (inet_pton(AF_INET, optarg, &c->ip4.guest_gw) &&
+			    !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.guest_gw)	&&
+			    !IN4_IS_ADDR_BROADCAST(&c->ip4.guest_gw)	&&
+			    !IN4_IS_ADDR_LOOPBACK(&c->ip4.guest_gw)) {
 				if (c->mode == MODE_PASTA)
 					c->ip4.no_copy_routes = true;
 				break;
@@ -1637,11 +1639,14 @@ void conf(struct ctx *c, int argc, char **argv)
 	    (*c->ip6.ifname_out && !c->ifi6))
 		die("External interface not usable");
 
-	if (c->ifi4 && IN4_IS_ADDR_UNSPECIFIED(&c->ip4.gw))
-		c->no_map_gw = c->no_dhcp = 1;
+	if (c->ifi4 && !no_map_gw)
+		c->ip4.map_host_loopback = c->ip4.guest_gw;
 
-	if (c->ifi6 && IN6_IS_ADDR_UNSPECIFIED(&c->ip6.gw))
-		c->no_map_gw = 1;
+	if (c->ifi6 && !no_map_gw)
+		c->ip6.map_host_loopback = c->ip6.guest_gw;
+
+	if (c->ifi4 && IN4_IS_ADDR_UNSPECIFIED(&c->ip4.guest_gw))
+		c->no_dhcp = 1;
 
 	/* Inbound port options & DNS can be parsed now (after IPv4/IPv6
 	 * settings)