IPv6 SLAAC: Honor small PIO Valid Lifetimes

This commit implements Section 4.2 of
<https://tools.ietf.org/html/draft-gont-6man-slaac-renum-05>, to improve the
reaction of IPv6 SLAAC to renumbering events.

Namely:

* It honors PIO Valid Lifetimes < 2 hours, deviating from item "e)"
  (pp. 19-20) of Section 5.5.3 of RFC4862.

[thaller@redhat.com: squash commits and adjust unit test]

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/454

2 files changed, 18 insertions, 26 deletions

diff --git a/src/ndisc/nm-ndisc.c b/src/ndisc/nm-ndisc.c
index 5e556084e8..bb3a92b05d 100644
--- a/src/ndisc/nm-ndisc.c
+++ b/src/ndisc/nm-ndisc.c
@@ -442,8 +442,15 @@ nm_ndisc_add_address (NMNDisc *ndisc,
 	}
 
 	if (existing) {
+		/* A Valid Lifetime of 0 eliminates the corresponding address(es). This deviates
+		 * from RFC4862 Section 5.5.3, item e), as recommended in IETF draft draft-gont-6man-slaac-renum.
+		 */
+		if (new->lifetime == 0) {
+			g_array_remove_index (rdata->addresses, i);
+			return TRUE;
+		}
+
 		if (from_ra) {
-			const gint32 NM_NDISC_PREFIX_LFT_MIN = 7200; /* seconds, RFC4862 5.5.3.e */
 			gint64 old_expiry_lifetime, old_expiry_preferred;
 
 			old_expiry_lifetime = get_expiry (existing);
@@ -452,25 +459,16 @@ nm_ndisc_add_address (NMNDisc *ndisc,
 			if (new->lifetime == NM_NDISC_INFINITY)
 				existing->lifetime = NM_NDISC_INFINITY;
 			else {
-				gint64 new_lifetime, remaining_lifetime;
+				gint64 new_lifetime;
 
-				/* see RFC4862 5.5.3.e */
-				if (existing->lifetime == NM_NDISC_INFINITY)
-					remaining_lifetime = G_MAXINT64;
-				else
-					remaining_lifetime = ((gint64) existing->timestamp) + ((gint64) existing->lifetime) - ((gint64) now_s);
+				/* Honor small valid lifetimes, as discussed in
+				 * draft-gont-6man-slaac-renum, to allow for more timelier
+				 * reaction to renumbering events. This deviates from
+				 * RFC4862 Section 5.5.3, item e).
+				 */
 				new_lifetime = ((gint64) new->timestamp) + ((gint64) new->lifetime) - ((gint64) now_s);
-
-				if (   new_lifetime > (gint64) NM_NDISC_PREFIX_LFT_MIN
-				    || new_lifetime > remaining_lifetime) {
-					existing->timestamp = now_s;
-					existing->lifetime = CLAMP (new_lifetime, (gint64) 0, (gint64) (G_MAXUINT32 - 1));
-				} else if (remaining_lifetime <= (gint64) NM_NDISC_PREFIX_LFT_MIN) {
-					/* keep the current lifetime. */
-				} else {
-					existing->timestamp = now_s;
-					existing->lifetime = NM_NDISC_PREFIX_LFT_MIN;
-				}
+				existing->timestamp = now_s;
+				existing->lifetime = CLAMP (new_lifetime, (gint64) 0, (gint64) (G_MAXUINT32 - 1));
 			}
 
 			if (new->preferred == NM_NDISC_INFINITY) {
@@ -487,11 +485,6 @@ nm_ndisc_add_address (NMNDisc *ndisc,
 			       || old_expiry_preferred != get_expiry_preferred (existing);
 		}
 
-		if (new->lifetime == 0) {
-			g_array_remove_index (rdata->addresses, i);
-			return TRUE;
-		}
-
 		if (   get_expiry (existing) == get_expiry (new)
 		    && get_expiry_preferred (existing) == get_expiry_preferred (new))
 			return FALSE;
diff --git a/src/ndisc/tests/test-ndisc-fake.c b/src/ndisc/tests/test-ndisc-fake.c
index 91fe9802d7..7a5eea012d 100644
--- a/src/ndisc/tests/test-ndisc-fake.c
+++ b/src/ndisc/tests/test-ndisc-fake.c
@@ -217,9 +217,8 @@ test_everything_changed (NMNDisc *ndisc, const NMNDiscData *rdata, guint changed
 
 		g_assert_cmpint (rdata->gateways_n, ==, 1);
 		match_gateway (rdata, 0, "fe80::2", data->timestamp1, 10, NM_ICMPV6_ROUTER_PREF_MEDIUM);
-		g_assert_cmpint (rdata->addresses_n, ==, 2);
-		match_address (rdata, 0, "2001:db8:a:a::1", data->timestamp1, 10, 0);
-		match_address (rdata, 1, "2001:db8:a:b::1", data->timestamp1, 10, 10);
+		g_assert_cmpint (rdata->addresses_n, ==, 1);
+		match_address (rdata, 0, "2001:db8:a:b::1", data->timestamp1, 10, 10);
 		g_assert_cmpint (rdata->routes_n, ==, 1);
 		match_route (rdata, 0, "2001:db8:a:b::", 64, "fe80::2", data->timestamp1, 10, 10);
 		g_assert_cmpint (rdata->dns_servers_n, ==, 1);