router/dhcpv6: use link-local addresses for DNS

4 files changed, 21 insertions, 32 deletions

diff --git a/src/dhcpv6.c b/src/dhcpv6.c
index c62a08f..9f91162 100644
--- a/src/dhcpv6.c
+++ b/src/dhcpv6.c
@@ -228,7 +228,7 @@ static void handle_client_request(void *addr, void *data, size_t len,
 	size_t dns_cnt = iface->dns_cnt;
 
 	if ((dns_cnt == 0) &&
-		odhcpd_get_preferred_interface_address(iface->ifindex, &dns_addr)) {
+		!odhcpd_get_linklocal_interface_address(iface->ifindex, &dns_addr)) {
 		dns_addr_ptr = &dns_addr;
 		dns_cnt = 1;
 	}
@@ -460,7 +460,7 @@ static void relay_server_response(uint8_t *data, size_t len)
 		size_t rewrite_cnt = iface->dns_cnt;
 
 		if (rewrite_cnt == 0) {
-			if (odhcpd_get_preferred_interface_address(iface->ifindex, &addr) < 1)
+			if (odhcpd_get_linklocal_interface_address(iface->ifindex, &addr))
 				return; // Unable to get interface address
 
 			rewrite = &addr;
diff --git a/src/odhcpd.c b/src/odhcpd.c
index 5774a4f..9c7f27c 100644
--- a/src/odhcpd.c
+++ b/src/odhcpd.c
@@ -254,24 +254,21 @@ ssize_t odhcpd_get_interface_addresses(int ifindex,
 	return ret;
 }
 
-int odhcpd_get_preferred_interface_address(int ifindex, struct in6_addr *addr)
+int odhcpd_get_linklocal_interface_address(int ifindex, struct in6_addr *lladdr)
 {
-	struct odhcpd_ipaddr ipaddrs[8];
-	ssize_t ip_cnt = odhcpd_get_interface_addresses(ifindex, ipaddrs, ARRAY_SIZE(ipaddrs));
-	uint32_t preferred = 0;
-	int ret = 0;
-
-	for (ssize_t i = 0; i < ip_cnt; i++) {
-		struct odhcpd_ipaddr *ipaddr = &ipaddrs[i];
-
-		if (ipaddr->preferred > preferred || !preferred) {
-			preferred = ipaddr->preferred;
-			*addr = ipaddr->addr;
-			ret = 1;
+		int status = -1;
+		struct sockaddr_in6 addr = {AF_INET6, 0, 0, ALL_IPV6_ROUTERS, ifindex};
+		socklen_t alen = sizeof(addr);
+		int sock = socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);
+
+		if (!connect(sock, (struct sockaddr*)&addr, sizeof(addr)) &&
+				!getsockname(sock, (struct sockaddr*)&addr, &alen)) {
+			*lladdr = addr.sin6_addr;
+			status = 0;
 		}
-	}
 
-	return ret;
+		close(sock);
+		return status;
 }
 
 void odhcpd_setup_route(const struct in6_addr *addr, int prefixlen,
diff --git a/src/odhcpd.h b/src/odhcpd.h
index ab24674..81f4bee 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -185,7 +185,7 @@ ssize_t odhcpd_send(int socket, struct sockaddr_in6 *dest,
 		const struct interface *iface);
 ssize_t odhcpd_get_interface_addresses(int ifindex,
 		struct odhcpd_ipaddr *addrs, size_t cnt);
-int odhcpd_get_preferred_interface_address(int ifindex, struct in6_addr *addr);
+int odhcpd_get_linklocal_interface_address(int ifindex, struct in6_addr *lladdr);
 struct interface* odhcpd_get_interface_by_name(const char *name);
 int odhcpd_get_interface_config(const char *ifname, const char *what);
 int odhcpd_get_mac(const struct interface *iface, uint8_t mac[6]);
diff --git a/src/router.c b/src/router.c
index 1ae8d1a..853b9e8 100644
--- a/src/router.c
+++ b/src/router.c
@@ -264,10 +264,11 @@ static uint64_t send_router_advert(struct interface *iface, const struct in6_add
 	// Construct Prefix Information options
 	size_t cnt = 0;
 
-	struct in6_addr dns_pref = IN6ADDR_ANY_INIT, *dns_addr = &dns_pref;
-	uint32_t dns_time = 0;
+	struct in6_addr dns_pref, *dns_addr = &dns_pref;
 	size_t dns_cnt = 1;
 
+	odhcpd_get_linklocal_interface_address(iface->ifindex, &dns_pref);
+
 	for (ssize_t i = 0; i < ipcnt; ++i) {
 		struct odhcpd_ipaddr *addr = &addrs[i];
 		if (addr->prefix > 96 || addr->valid <= (uint32_t)now)
@@ -316,12 +317,6 @@ static uint64_t send_router_advert(struct interface *iface, const struct in6_add
 			p->nd_opt_pi_preferred_time = htonl(TIME_LEFT(addr->preferred, now));
 		else if (addr->valid - now < 7200)
 			p->nd_opt_pi_valid_time = 0;
-
-
-		if (TIME_LEFT(addr->preferred, now) > dns_time) {
-			dns_time = TIME_LEFT(addr->preferred, now);
-			dns_pref = addr->addr;
-		}
 	}
 
 	if (!iface->default_router && ntohs(adv.h.nd_ra_router_lifetime) == 1) {
@@ -334,7 +329,6 @@ static uint64_t send_router_advert(struct interface *iface, const struct in6_add
 	if (iface->dns_cnt > 0) {
 		dns_addr = iface->dns;
 		dns_cnt = iface->dns_cnt;
-		dns_time = 0;
 	}
 
 	if (!dns_addr || IN6_IS_ADDR_UNSPECIFIED(dns_addr))
@@ -346,7 +340,7 @@ static uint64_t send_router_advert(struct interface *iface, const struct in6_add
 		uint8_t pad;
 		uint8_t pad2;
 		uint32_t lifetime;
-	} dns = {ND_OPT_RECURSIVE_DNS, (1 + (2 * dns_cnt)), 0, 0, htonl(dns_time)};
+	} dns = {ND_OPT_RECURSIVE_DNS, (1 + (2 * dns_cnt)), 0, 0, 0};
 
 
 
@@ -440,9 +434,7 @@ static uint64_t send_router_advert(struct interface *iface, const struct in6_add
 	minival = (maxival * 3) / 4;
 
 	search->lifetime = htonl(maxvalid / 1000);
-
-	if (!dns.lifetime)
-		dns.lifetime = search->lifetime;
+	dns.lifetime = search->lifetime;
 
 	odhcpd_urandom(&msecs, sizeof(msecs));
 	msecs = (labs(msecs) % (maxival - minival)) + minival;
@@ -569,7 +561,7 @@ static void forward_router_advertisement(uint8_t *data, size_t len)
 			size_t rewrite_cnt = iface->dns_cnt;
 
 			if (rewrite_cnt == 0) {
-				if (odhcpd_get_preferred_interface_address(iface->ifindex, &addr) < 1)
+				if (odhcpd_get_linklocal_interface_address(iface->ifindex, &addr))
 					continue; // Unable to comply
 
 				rewrite = &addr;