router: advertise removed addresses as invalid in 3 consecutive RAs

On prefix removal, router advertisement daemon is supposed to send
advertise with an invalid PI entry (see RFC 7084 L-13).

Signed-off-by: Alin Nastac <alin.nastac@gmail.com>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>

4 files changed, 123 insertions, 25 deletions

diff --git a/src/config.c b/src/config.c
index 71b786c..31893d1 100644
--- a/src/config.c
+++ b/src/config.c
@@ -248,6 +248,7 @@ static void close_interface(struct interface *iface)
 	clean_interface(iface);
 	free(iface->addr4);
 	free(iface->addr6);
+	free(iface->invalid_addr6);
 	free(iface->ifname);
 	free(iface);
 }
diff --git a/src/netlink.c b/src/netlink.c
index 39f6245..63a0f8b 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -205,10 +205,66 @@ static void refresh_iface_addr6(int ifindex)
 			change = len != (ssize_t)iface->addr6_len;
 			for (ssize_t i = 0; !change && i < len; ++i) {
 				if (!IN6_ARE_ADDR_EQUAL(&addr[i].addr.in6, &iface->addr6[i].addr.in6) ||
+				    addr[i].prefix != iface->addr6[i].prefix ||
 				    (addr[i].preferred > (uint32_t)now) != (iface->addr6[i].preferred > (uint32_t)now) ||
 				    addr[i].valid < iface->addr6[i].valid || addr[i].preferred < iface->addr6[i].preferred)
 					change = true;
 			}
+
+			if (change) {
+				/*
+				 * Keep track on removed prefixes, so we could advertise them as invalid
+				 * for at least a couple of times.
+				 *
+				 * RFC7084 § 4.3 :
+				 *    L-13:  If the delegated prefix changes, i.e., the current prefix is
+				 *           replaced with a new prefix without any overlapping time
+				 *           period, then the IPv6 CE router MUST immediately advertise the
+				 *           old prefix with a Preferred Lifetime of zero and a Valid
+				 *           Lifetime of either a) zero or b) the lower of the current
+				 *           Valid Lifetime and two hours (which must be decremented in
+				 *           real time) in a Router Advertisement message as described in
+				 *           Section 5.5.3, (e) of [RFC4862].
+				 */
+
+				for (size_t i = 0; i < iface->addr6_len; ++i) {
+					bool removed = true;
+
+					if (iface->addr6[i].valid <= (uint32_t)now)
+						continue;
+
+					for (ssize_t j = 0; removed && j < len; ++j) {
+						size_t plen = min(addr[j].prefix, iface->addr6[i].prefix);
+
+						if (odhcpd_bmemcmp(&addr[j].addr.in6, &iface->addr6[i].addr.in6, plen) == 0)
+							removed = false;
+					}
+
+					for (size_t j = 0; removed && j < iface->invalid_addr6_len; ++j) {
+						size_t plen = min(iface->invalid_addr6[j].prefix, iface->addr6[i].prefix);
+
+						if (odhcpd_bmemcmp(&iface->invalid_addr6[j].addr.in6, &iface->addr6[i].addr.in6, plen) == 0)
+							removed = false;
+					}
+
+					if (removed) {
+						size_t pos = iface->invalid_addr6_len;
+						struct odhcpd_ipaddr *new_invalid_addr6 = realloc(iface->invalid_addr6,
+								sizeof(*iface->invalid_addr6) * (pos + 1));
+
+						if (!new_invalid_addr6)
+							break;
+
+						iface->invalid_addr6 = new_invalid_addr6;
+						iface->invalid_addr6_len++;
+						memcpy(&iface->invalid_addr6[pos], &iface->addr6[i], sizeof(*iface->invalid_addr6));
+						iface->invalid_addr6[pos].valid = iface->invalid_addr6[pos].preferred = (uint32_t)now;
+
+						if (iface->invalid_addr6[pos].prefix < 64)
+							iface->invalid_addr6[pos].prefix = 64;
+					}
+				}
+			}
 		}
 
 		iface->addr6 = addr;
diff --git a/src/odhcpd.h b/src/odhcpd.h
index ff7e105..88c8c79 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -26,6 +26,9 @@
 #include <libubox/ustream.h>
 #include <libubox/vlist.h>
 
+#define min(a, b) (((a) < (b)) ? (a) : (b))
+#define max(a, b) (((a) > (b)) ? (a) : (b))
+
 // RFC 6106 defines this router advertisement option
 #define ND_OPT_ROUTE_INFO 24
 #define ND_OPT_RECURSIVE_DNS 25
@@ -118,11 +121,16 @@ struct odhcpd_ipaddr {
 	uint32_t preferred;
 	uint32_t valid;
 
-	/* ipv6 only */
-	uint8_t dprefix;
+	union {
+		/* ipv6 only */
+		struct {
+			uint8_t dprefix;
+			uint8_t invalid_advertisements;
+		};
 
-	/* ipv4 only */
-	struct in_addr broadcast;
+		/* ipv4 only */
+		struct in_addr broadcast;
+	};
 };
 
 enum odhcpd_mode {
@@ -232,6 +240,8 @@ struct interface {
 	// IPv6 runtime data
 	struct odhcpd_ipaddr *addr6;
 	size_t addr6_len;
+	struct odhcpd_ipaddr *invalid_addr6;
+	size_t invalid_addr6_len;
 
 	// RA runtime data
 	struct odhcpd_event router_event;
diff --git a/src/router.c b/src/router.c
index 541c023..949cbe7 100644
--- a/src/router.c
+++ b/src/router.c
@@ -441,7 +441,7 @@ static int send_router_advert(struct interface *iface, const struct in6_addr *fr
 	struct iovec iov[IOV_RA_TOTAL];
 	struct sockaddr_in6 dest;
 	size_t dns_sz = 0, search_sz = 0, pfxs_cnt = 0, routes_cnt = 0;
-	ssize_t addr_cnt = 0;
+	ssize_t valid_addr_cnt = 0, invalid_addr_cnt = 0;
 	uint32_t minvalid = UINT32_MAX, maxival, lifetime;
 	int msecs, mtu = iface->ra_mtu, hlim = iface->ra_hoplimit;
 	bool default_route = false;
@@ -485,33 +485,61 @@ static int send_router_advert(struct interface *iface, const struct in6_addr *fr
 	iov[IOV_RA_ADV].iov_base = (char *)&adv;
 	iov[IOV_RA_ADV].iov_len = sizeof(adv);
 
-	/* If not shutdown */
-	if (iface->timer_rs.cb) {
-		size_t size = sizeof(*addrs) * iface->addr6_len;
+	valid_addr_cnt = (iface->timer_rs.cb /* if not shutdown */ ? iface->addr6_len : 0);
+	invalid_addr_cnt = iface->invalid_addr6_len;
 
-		addrs = alloca(size);
-		memcpy(addrs, iface->addr6, size);
+	if (valid_addr_cnt + invalid_addr_cnt) {
+		addrs = alloca(sizeof(*addrs) * (valid_addr_cnt + invalid_addr_cnt));
 
-		addr_cnt = iface->addr6_len;
+		if (valid_addr_cnt) {
+			memcpy(addrs, iface->addr6, sizeof(*addrs) * valid_addr_cnt);
 
-		/* Check default route */
-		if (iface->default_router) {
-			default_route = true;
+			/* Check default route */
+			if (iface->default_router) {
+				default_route = true;
 
-			if (iface->default_router > 1)
-				valid_prefix = true;
-		} else if (parse_routes(addrs, addr_cnt))
-			default_route = true;
+				if (iface->default_router > 1)
+					valid_prefix = true;
+			} else if (parse_routes(addrs, valid_addr_cnt))
+				default_route = true;
+		}
+
+		if (invalid_addr_cnt) {
+			size_t i = 0;
+
+			memcpy(&addrs[valid_addr_cnt], iface->invalid_addr6, sizeof(*addrs) * invalid_addr_cnt);
+
+			/* Remove invalid prefixes that were advertised 3 times */
+			while (i < iface->invalid_addr6_len) {
+				if (++iface->invalid_addr6[i].invalid_advertisements >= 3) {
+					if (i + 1 < iface->invalid_addr6_len)
+						memmove(&iface->invalid_addr6[i], &iface->invalid_addr6[i + 1], sizeof(*addrs) * (iface->invalid_addr6_len - i - 1));
+
+					iface->invalid_addr6_len--;
+
+					if (iface->invalid_addr6_len) {
+						struct odhcpd_ipaddr *new_invalid_addr6 = realloc(iface->invalid_addr6, sizeof(*addrs) * iface->invalid_addr6_len);
+
+						if (new_invalid_addr6)
+							iface->invalid_addr6 = new_invalid_addr6;
+					} else {
+						free(iface->invalid_addr6);
+						iface->invalid_addr6 = NULL;
+					}
+				} else
+					++i;
+			}
+		}
 	}
 
 	/* Construct Prefix Information options */
-	for (ssize_t i = 0; i < addr_cnt; ++i) {
+	for (ssize_t i = 0; i < valid_addr_cnt + invalid_addr_cnt; ++i) {
 		struct odhcpd_ipaddr *addr = &addrs[i];
 		struct nd_opt_prefix_info *p = NULL;
 		uint32_t preferred = 0;
 		uint32_t valid = 0;
 
-		if (addr->prefix > 96 || addr->valid <= (uint32_t)now) {
+		if (addr->prefix > 96 || (i < valid_addr_cnt && addr->valid <= (uint32_t)now)) {
 			syslog(LOG_INFO, "Address %s (prefix %d, valid %u) not suitable as RA prefix on %s",
 				inet_ntop(AF_INET6, &addr->addr.in6, buf, sizeof(buf)), addr->prefix,
 				addr->valid, iface->name);
@@ -554,14 +582,17 @@ static int send_router_advert(struct interface *iface, const struct in6_addr *fr
 				preferred = iface->preferred_lifetime;
 		}
 
-		valid = TIME_LEFT(addr->valid, now);
-		if (iface->ra_useleasetime && valid > iface->dhcp_leasetime)
-			valid = iface->dhcp_leasetime;
+		if (addr->valid > (uint32_t)now) {
+			valid = TIME_LEFT(addr->valid, now);
+
+			if (iface->ra_useleasetime && valid > iface->dhcp_leasetime)
+				valid = iface->dhcp_leasetime;
+		}
 
 		if (minvalid > valid)
 			minvalid = valid;
 
-		if (!IN6_IS_ADDR_ULA(&addr->addr.in6) || iface->default_router)
+		if ((!IN6_IS_ADDR_ULA(&addr->addr.in6) || iface->default_router) && valid)
 			valid_prefix = true;
 
 		odhcpd_bmemcpy(&p->nd_opt_pi_prefix, &addr->addr.in6,
@@ -667,7 +698,7 @@ static int send_router_advert(struct interface *iface, const struct in6_addr *fr
 	 *           WAN interface.
 	 */
 
-	for (ssize_t i = 0; i < addr_cnt; ++i) {
+	for (ssize_t i = 0; i < valid_addr_cnt; ++i) {
 		struct odhcpd_ipaddr *addr = &addrs[i];
 		struct nd_opt_route_info *tmp;
 		uint32_t valid;