sd-radv: if lifetime < SD_RADV_DEFAULT_MAX_TIMEOUT_USEC, adjust timeout (#13491)

The RFC states that lifetime (AdvDefaultLifetime) must be at least
MaxRtrAdvInterval (which more or less corresponds to SD_RADV_DEFAULT_MAX_TIMEOUT_USEC
in systemd).

To fulfill this limit, virtually lower MaxRtrAdvInterval and MinRtrAdvInterval
accordingly.

Also check that min is not lower than 3s and max is not lower than 4s.

(cherry picked from commit ef90b6a4fb9509f61b9b917bbe4db7343afe1853)
(cherry picked from commit d4cd0e9d3242f85141d835dd5a78d880b47a0817)

Gbp-Pq: Name sd-radv-if-lifetime-SD_RADV_DEFAULT_MAX_TIMEOUT_USEC-adju.patch

diff --git a/src/libsystemd-network/sd-radv.c b/src/libsystemd-network/sd-radv.c
index 185b55e1c56ca35754fa1d1f16cb27f24399e2b6..0844462070e97ede069884a2f2d80eb88a4476d2 100644 (file)
--- a/src/libsystemd-network/sd-radv.c
+++ b/src/libsystemd-network/sd-radv.c
@@ -269,6 +269,10 @@ static int radv_recv(sd_event_source *s, int fd, uint32_t revents, void *userdat
 static usec_t radv_compute_timeout(usec_t min, usec_t max) {
         assert_return(min <= max, SD_RADV_DEFAULT_MIN_TIMEOUT_USEC);
 
+        /* RFC 4861: min must be no less than 3s, max must be no less than 4s */
+        min = MAX(min, 3*USEC_PER_SEC);
+        max = MAX(max, 4*USEC_PER_SEC);
+
         return min + (random_u32() % (max - min));
 }
 
@@ -298,6 +302,13 @@ static int radv_timeout(sd_event_source *s, uint64_t usec, void *userdata) {
                 min_timeout = SD_RADV_MAX_INITIAL_RTR_ADVERT_INTERVAL_USEC / 3;
         }
 
+        /* RFC 4861, Section 6.2.1, lifetime must be at least MaxRtrAdvInterval,
+           so lower the interval here */
+        if (ra->lifetime > 0 && (ra->lifetime * USEC_PER_SEC) < max_timeout) {
+                max_timeout = ra->lifetime * USEC_PER_SEC;
+                min_timeout = max_timeout / 3;
+        }
+
         timeout = radv_compute_timeout(min_timeout, max_timeout);
 
         log_radv("Next Router Advertisement in %s",