dhcpv6: restart DHCPv6 on receipt of RA containing a new prefix

When the upstream DHCPv6 server does not provide IA_NA or IA_PD options, odhcp6c
enters into stateless mode, which will not be exited from until SIGUSR2 signal
is received.

This change enforces DHCPv6 restart on receipt of a RA that:
  a) advertises the presence of DHCPv6 server on the network, containing
  either M or O flags
  b) has a PI (prefix information) option that contains a new prefix

thus allowing the switch to DHCPv6 stateful mode when RA PI options suggest that
the upstream DHCPv6 server now manages a new prefix.

Restart is useful even when DHCPv6 client is already in stateful mode, so the
DHCPv6 server will be able to refresh the client's IA_NA and IA_PD options
before renewal timeout is triggered, hence avoiding the usage of potentially
deprecated addresses.

Signed-off-by: Alin Nastac <alin.nastac@gmail.com>
Signed-off-by: Paul Donald <newtwen+github@gmail.com>
Link: https://github.com/openwrt/odhcp6c/pull/119
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

4 files changed, 46 insertions, 4 deletions

diff --git a/src/dhcpv6.c b/src/dhcpv6.c
index 68c04f4..49ed052 100644
--- a/src/dhcpv6.c
+++ b/src/dhcpv6.c
@@ -1661,10 +1661,19 @@ static unsigned int dhcpv6_parse_ia(void *opt, void *end, int *ret)
 
 	// Update address IA
 	dhcpv6_for_each_option(&ia_hdr[1], end, otype, olen, odata) {
-		struct odhcp6c_entry entry = {IN6ADDR_ANY_INIT, 0, 0,
-				IN6ADDR_ANY_INIT, 0, 0, 0, 0, 0, 0};
-
-		entry.iaid = ia_hdr->iaid;
+		struct odhcp6c_entry entry = {
+			.router = IN6ADDR_ANY_INIT,
+			.auxlen = 0,
+			.length = 0,
+			.ra_flags = 0,
+			.target = IN6ADDR_ANY_INIT,
+			.priority = 0,
+			.valid = 0,
+			.preferred = 0,
+			.t1 = 0,
+			.t2 = 0,
+			.iaid = ia_hdr->iaid,
+		};
 
 		switch (otype) {
 		case DHCPV6_OPT_IA_PREFIX: {
diff --git a/src/odhcp6c.c b/src/odhcp6c.c
index 7b1a387..43ec72f 100644
--- a/src/odhcp6c.c
+++ b/src/odhcp6c.c
@@ -20,6 +20,7 @@
 #include <limits.h>
 #include <linux/if_addr.h>
 #include <net/if.h>
+#include <netinet/icmp6.h>
 #include <poll.h>
 #include <resolv.h>
 #include <signal.h>
@@ -834,16 +835,43 @@ static uint8_t* odhcp6c_resize_state(enum odhcp6c_state state, ssize_t len)
 	return n;
 }
 
+static bool odhcp6c_server_advertised()
+{
+	size_t len;
+	uint8_t *start = odhcp6c_get_state(STATE_RA_ROUTE, &len);
+
+	for (struct odhcp6c_entry *c = (struct odhcp6c_entry*)start;
+			(uint8_t*)c < &start[len] &&
+			(uint8_t*)odhcp6c_next_entry(c) <= &start[len];
+			c = odhcp6c_next_entry(c)) {
+		// Only default route entries have flags
+		if (c->length != 0 || IN6_IS_ADDR_UNSPECIFIED(&c->router))
+			continue;
+
+		if (c->ra_flags & (ND_RA_FLAG_MANAGED | ND_RA_FLAG_OTHER))
+			return true;
+	}
+
+	return false;
+}
+
 bool odhcp6c_signal_process(void)
 {
 	while (signal_io) {
 		signal_io = false;
 
+		size_t old_ra_prefix_size = state_len[STATE_RA_PREFIX];
 		bool ra_updated = ra_process();
 
 		if (ra_link_up()) {
 			signal_usr2 = true;
 			ra = false;
+		} else if (old_ra_prefix_size != state_len[STATE_RA_PREFIX] &&
+				odhcp6c_server_advertised()) {
+			// Restart DHCPv6 transaction when router advertisement flags
+			// show presence of a DHCPv6 server and new prefixes were
+			// added to STATE_RA_PREFIX state
+			signal_usr2 = true;
 		}
 
 		if (ra_updated && (bound || config_dhcp->allow_slaac_only >= 0)) {
@@ -953,6 +981,8 @@ bool odhcp6c_update_entry(enum odhcp6c_state state, struct odhcp6c_entry *new,
 			return false;
 
 		x->valid = new->valid;
+		x->ra_flags = new->ra_flags;
+		x->priority = new->priority;
 		x->preferred = new->preferred;
 		x->t1 = new->t1;
 		x->t2 = new->t2;
diff --git a/src/odhcp6c.h b/src/odhcp6c.h
index b229412..410da1e 100644
--- a/src/odhcp6c.h
+++ b/src/odhcp6c.h
@@ -481,6 +481,7 @@ struct odhcp6c_entry {
 	struct in6_addr router;
 	uint8_t auxlen;
 	uint8_t length;
+	uint8_t ra_flags;
 	struct in6_addr target;
 	int16_t priority;
 	uint32_t valid;
diff --git a/src/ra.c b/src/ra.c
index ca9e691..b1011be 100644
--- a/src/ra.c
+++ b/src/ra.c
@@ -430,6 +430,7 @@ bool ra_process(void)
 		entry->target = any;
 		entry->length = 0;
 		entry->router = from.sin6_addr;
+		entry->ra_flags = adv->nd_ra_flags_reserved & (ND_RA_FLAG_MANAGED | ND_RA_FLAG_OTHER);
 		entry->priority = pref_to_priority(adv->nd_ra_flags_reserved);
 		if (entry->priority < 0)
 			entry->priority = pref_to_priority(0);
@@ -438,6 +439,7 @@ bool ra_process(void)
 		entry->preferred = entry->valid;
 		changed |= odhcp6c_update_entry(STATE_RA_ROUTE, entry,
 						ra_holdoff_interval);
+		entry->ra_flags = 0; // other STATE_RA_* entries don't have flags
 
 		// Parse hop limit
 		changed |= ra_set_hoplimit(adv->nd_ra_curhoplimit);