bypass-lan: Compare interface for unchanged policies

In case a subnet is moved from one interface to another the policies can
remain as is but the route has to change.  This currently doesn't happen
automatically and there is no option to update the policy or route so
removing and reinstalling the policies is the only option.

Fixes #2820.

Author: tobiasbrunner

src/libcharon/plugins/bypass_lan/bypass_lan_listener.c

@@ -64,6 +64,7 @@ typedef struct {
 	private_bypass_lan_listener_t *listener;
 	host_t *net;
 	uint8_t mask;
+	char *iface;
 	child_cfg_t *cfg;
 } bypass_policy_t;
 
@@ -85,6 +86,7 @@ static void bypass_policy_destroy(bypass_policy_t *this)
 		ts->destroy(ts);
 	}
 	this->net->destroy(this->net);
+	free(this->iface);
 	free(this);
 }
 
@@ -126,6 +128,7 @@ static job_requeue_t update_bypass(private_bypass_lan_listener_t *this)
 	enumerator_t *enumerator;
 	hashtable_t *seen;
 	bypass_policy_t *found, *lookup;
+	traffic_selector_t *ts;
 	host_t *net;
 	uint8_t mask;
 	char *iface;
@@ -146,6 +149,7 @@ static job_requeue_t update_bypass(private_bypass_lan_listener_t *this)
 		INIT(lookup,
 			.net = net->clone(net),
 			.mask = mask,
+			.iface = strdupnull(iface),
 		);
 		found = seen->put(seen, lookup, lookup);
 		if (found)
@@ -160,7 +164,6 @@ static job_requeue_t update_bypass(private_bypass_lan_listener_t *this)
 				.mode = MODE_PASS,
 			};
 			child_cfg_t *cfg;
-			traffic_selector_t *ts;
 			char name[128];
 
 			ts = traffic_selector_create_from_subnet(net->clone(net), mask,
@@ -176,6 +179,7 @@ static job_requeue_t update_bypass(private_bypass_lan_listener_t *this)
 			INIT(found,
 				.net = net->clone(net),
 				.mask = mask,
+				.iface = strdupnull(iface),
 				.cfg = cfg,
 			);
 			this->policies->put(this->policies, found, found);
@@ -186,11 +190,29 @@ static job_requeue_t update_bypass(private_bypass_lan_listener_t *this)
 	enumerator = this->policies->create_enumerator(this->policies);
 	while (enumerator->enumerate(enumerator, NULL, &lookup))
 	{
-		if (!seen->get(seen, lookup))
+		found = seen->get(seen, lookup);
+		if (!found)
 		{
 			this->policies->remove_at(this->policies, enumerator);
 			bypass_policy_destroy(lookup);
 		}
+		else if (!streq(lookup->iface, found->iface))
+		{	/* if the subnet is on multiple interfaces, we only get the last
+			 * one (hopefully, they are enumerated in a consistent order) */
+			ts = traffic_selector_create_from_subnet(
+												lookup->net->clone(lookup->net),
+												lookup->mask, 0, 0, 65535);
+			DBG1(DBG_IKE, "interface change for bypass policy for %R (from %s "
+				 "to %s)", ts, lookup->iface, found->iface);
+			ts->destroy(ts);
+			free(lookup->iface);
+			lookup->iface = strdupnull(found->iface);
+			/* there is currently no API to update shunts, so we remove and
+			 * reinstall it to update the route */
+			charon->shunts->uninstall(charon->shunts, "bypass-lan",
+									  lookup->cfg->get_name(lookup->cfg));
+			charon->shunts->install(charon->shunts, "bypass-lan", lookup->cfg);
+		}
 	}
 	enumerator->destroy(enumerator);
 	this->mutex->unlock(this->mutex);