odhcp6c: apply draft-ietf-6man-slaac-renum-11 lifetime rules

Instead of applying the complicated ruleset from RFC 4862,
just use the new address information as described in the draft
draft-ietf-6man-slaac-renum-11.

Signed-off-by: Jonas Lochmann <git@inkompetenz.org>
Link: https://github.com/openwrt/odhcp6c/pull/114
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

4 files changed, 24 insertions, 58 deletions

diff --git a/src/dhcpv6.c b/src/dhcpv6.c
index 7f73699..872f169 100644
--- a/src/dhcpv6.c
+++ b/src/dhcpv6.c
@@ -1742,7 +1742,7 @@ static unsigned int dhcpv6_parse_ia(void *opt, void *end, int *ret)
 			}
 
 			if (update_state) {
-				if (odhcp6c_update_entry(STATE_IA_PD, &entry, 0, 0))
+				if (odhcp6c_update_entry(STATE_IA_PD, &entry, 0))
 					updated_IAs++;
 
 				syslog(LOG_INFO, "%s/%d preferred %d valid %d",
@@ -1797,7 +1797,7 @@ static unsigned int dhcpv6_parse_ia(void *opt, void *end, int *ret)
 			}
 
 			if (update_state) {
-				if (odhcp6c_update_entry(STATE_IA_NA, &entry, 0, 0))
+				if (odhcp6c_update_entry(STATE_IA_NA, &entry, 0))
 					updated_IAs++;
 
 				syslog(LOG_INFO, "%s preferred %d valid %d",
diff --git a/src/odhcp6c.c b/src/odhcp6c.c
index 8b880e3..7b1a387 100644
--- a/src/odhcp6c.c
+++ b/src/odhcp6c.c
@@ -939,64 +939,20 @@ static struct odhcp6c_entry* odhcp6c_find_entry(enum odhcp6c_state state, const
 }
 
 bool odhcp6c_update_entry(enum odhcp6c_state state, struct odhcp6c_entry *new,
-		uint32_t safe, unsigned int holdoff_interval)
+		unsigned int holdoff_interval)
 {
 	struct odhcp6c_entry *x = odhcp6c_find_entry(state, new);
-	uint32_t new_valid;
-
-	/*
-	 * "safe" refers to https://www.rfc-editor.org/rfc/rfc4862#section-5.5.3
-	 * section e; it is either the two hours in seconds or zero when (e)
-	 * does not apply.
-	 *
-	 * The base condition for applying safe is that there is already a
-	 * matching prefix (and safe itself must be set).
-	 */
-	if (safe && x) {
-		if (new->valid > safe || new->valid > x->valid) {
-			/*
-			 * 1: If the received Valid Lifetime is greater than 2 hours or
-			 * greater than RemainingLifetime, set the valid lifetime of the
-			 * corresponding address to the advertised Valid Lifetime.
-			 */
-			new_valid = new->valid;
-		} else if (x->valid <= safe) {
-			/*
-			 * 2: If RemainingLifetime is less than or equal
-			 * to 2 hours, ignore the Prefix Information option with
-			 * regards to the valid lifetime, unless the Router
-			 * Advertisement from which this option was obtained has
-			 * been authenticated (e.g., via Secure Neighbor
-			 * Discovery [RFC3971]).  If the Router Advertisement
-			 * was authenticated, the valid lifetime of the
-			 * corresponding address should be set to the Valid
-			 * Lifetime in the received option.
-			 *
-			 * Since authenticated advertisements aren't supported we
-			 * always keep the old value.
-			 */
-			new_valid = x->valid;
-		} else {
-			/*
-			 * 3: Otherwise, reset the valid lifetime of the corresponding
-			 * address to 2 hours.
-			 */
-			new_valid = safe;
-		}
-	} else {
-		new_valid = new->valid;
-	}
 
 	if (x) {
-		if (holdoff_interval && new_valid >= x->valid &&
-				new_valid != UINT32_MAX &&
-				new_valid - x->valid < holdoff_interval &&
+		if (holdoff_interval && new->valid >= x->valid &&
+				new->valid != UINT32_MAX &&
+				new->valid - x->valid < holdoff_interval &&
 				new->preferred >= x->preferred &&
 				new->preferred != UINT32_MAX &&
 				new->preferred - x->preferred < holdoff_interval)
 			return false;
 
-		x->valid = new_valid;
+		x->valid = new->valid;
 		x->preferred = new->preferred;
 		x->t1 = new->t1;
 		x->t2 = new->t2;
diff --git a/src/odhcp6c.h b/src/odhcp6c.h
index 42c645d..b229412 100644
--- a/src/odhcp6c.h
+++ b/src/odhcp6c.h
@@ -576,7 +576,7 @@ void* odhcp6c_get_state(enum odhcp6c_state state, size_t *len);
 
 // Entry manipulation
 bool odhcp6c_update_entry(enum odhcp6c_state state, struct odhcp6c_entry *new,
-				uint32_t safe, unsigned int holdoff_interval);
+				unsigned int holdoff_interval);
 
 void odhcp6c_expire(bool expire_ia_pd);
 uint32_t odhcp6c_elapsed(void);
diff --git a/src/ra.c b/src/ra.c
index dcc5fd6..ca9e691 100644
--- a/src/ra.c
+++ b/src/ra.c
@@ -437,7 +437,7 @@ bool ra_process(void)
 		entry->valid = router_valid;
 		entry->preferred = entry->valid;
 		changed |= odhcp6c_update_entry(STATE_RA_ROUTE, entry,
-						0, ra_holdoff_interval);
+						ra_holdoff_interval);
 
 		// Parse hop limit
 		changed |= ra_set_hoplimit(adv->nd_ra_curhoplimit);
@@ -478,8 +478,18 @@ bool ra_process(void)
 
 				if (entry->priority > 0)
 					changed |= odhcp6c_update_entry(STATE_RA_ROUTE, entry,
-									0, ra_holdoff_interval);
+									ra_holdoff_interval);
 			} else if (opt->type == ND_OPT_PREFIX_INFORMATION && opt->len == 4) {
+				/*
+				 * We implement draft-ietf-6man-slaac-renum-11 here:
+				 * https://datatracker.ietf.org/doc/html/draft-ietf-6man-slaac-renum-11#section-5.4
+				 *
+				 * This removes the two hour magic and instead just uses the new
+				 * data. If the lifetime is zero, then the prefix is removed.
+				 *
+				 * An entry with lifetime zero is added. odhcp6c_expire will remove
+				 * it again. odhcp6c_expire is called at the end of this function.
+				 */
 				struct nd_opt_prefix_info *pinfo = (struct nd_opt_prefix_info*)opt;
 				entry->router = any;
 				entry->target = pinfo->nd_opt_pi_prefix;
@@ -497,7 +507,7 @@ bool ra_process(void)
 				if ((pinfo->nd_opt_pi_flags_reserved & ND_OPT_PI_FLAG_ONLINK) &&
 				    !ptp_link)
 					changed |= odhcp6c_update_entry(STATE_RA_ROUTE, entry,
-									7200, ra_holdoff_interval);
+									ra_holdoff_interval);
 
 				if (!(pinfo->nd_opt_pi_flags_reserved & ND_OPT_PI_FLAG_AUTO) ||
 						pinfo->nd_opt_pi_prefix_len != 64)
@@ -507,7 +517,7 @@ bool ra_process(void)
 				entry->target.s6_addr32[3] = lladdr.s6_addr32[3];
 
 				changed |= odhcp6c_update_entry(STATE_RA_PREFIX, entry,
-								7200, ra_holdoff_interval);
+								ra_holdoff_interval);
 			} else if (opt->type == ND_OPT_RECURSIVE_DNS && opt->len > 2) {
 				entry->router = from.sin6_addr;
 				entry->priority = 0;
@@ -520,7 +530,7 @@ bool ra_process(void)
 					memcpy(&entry->target, &opt->data[6 + i * sizeof(entry->target)],
 							sizeof(entry->target));
 					changed |= odhcp6c_update_entry(STATE_RA_DNS, entry,
-									0, ra_holdoff_interval);
+									ra_holdoff_interval);
 				}
 			} else if (opt->type == ND_OPT_DNSSL && opt->len > 1) {
 				uint32_t *valid = (uint32_t*)&opt->data[2];
@@ -542,7 +552,7 @@ bool ra_process(void)
 						continue;
 
 					changed |= odhcp6c_update_entry(STATE_RA_SEARCH, entry,
-									0, ra_holdoff_interval);
+									ra_holdoff_interval);
 					entry->auxlen = 0;
 				}
 			}