vrrp: Ensure VRRPv3 advert interval strictly <= 40.95 seconds

If an advert interval of 40.958 seconds was configured, it was being
round up to 40.96 after the check that the advert interval was less than
40.96. The consequence of this was that adverts were being sent at
40.96 second intervals, but worse, the advert interval in the VRRP
packet was set to 0.

This commit now ensures that after the rounding the advert interval is
<= 40.95 seconds.

Signed-off-by: Quentin Armitage <[email protected]>

Author: pqarmitage

keepalived/vrrp/vrrp.c

@@ -1852,10 +1852,8 @@ vrrp_state_leave_fault(vrrp_t * vrrp)
 		vrrp->state = vrrp->wantstate;
 		send_instance_notifies(vrrp);
 
-		if (vrrp->state == VRRP_STATE_BACK) {
+		if (vrrp->state == VRRP_STATE_BACK)
 			vrrp->preempt_time.tv_sec = 0;
-			vrrp->master_adver_int = vrrp->adver_int;
-		}
 	}
 
 	/* Set the down timer */
@@ -3346,8 +3344,11 @@ vrrp_complete_instance(vrrp_t * vrrp)
 			vrrp->adver_int = vrrp->adver_int + (TIMER_CENTI_HZ / 2);
 			vrrp->adver_int -= vrrp->adver_int % TIMER_CENTI_HZ;
 
+			/* Ensure don't round outside [0.01,40.95] */
 			if (vrrp->adver_int == 0)
 				vrrp->adver_int = TIMER_CENTI_HZ;
+			else if (vrrp->adver_int == (1<<12) * TIMER_CENTI_HZ)
+				vrrp->adver_int = ((1<<12) - 1) * TIMER_CENTI_HZ;
 		}
 	}
 	vrrp->master_adver_int = vrrp->adver_int;