knot: master with older serial triggers error

src/knot/events/handlers/refresh.c

@@ -759,13 +759,15 @@ static int soa_query_consume(knot_layer_t *layer, knot_pkt_t *pkt)
 	uint32_t local_serial = knot_soa_serial(&data->soa->rrs);
 	uint32_t remote_serial = knot_soa_serial(&rr->rrs);
 	bool current = serial_is_current(local_serial, remote_serial);
+	bool master_uptodate = serial_is_current(remote_serial, local_serial);
 
 	REFRESH_LOG(LOG_INFO, data->zone->name, data->remote,
 	            "remote serial %u, %s", remote_serial,
-	            current ? "zone is up-to-date" : "zone is outdated");
+	            current ? (master_uptodate ? "zone is up-to-date" :
+	            "master is outdated") : "zone is outdated");
 
 	if (current) {
-		return KNOT_STATE_DONE;
+		return master_uptodate ? KNOT_STATE_DONE : KNOT_STATE_FAIL;
 	} else {
 		data->state = STATE_TRANSFER;
 		return KNOT_STATE_RESET;

tests-extra/tests/zone/older_soa/data/example.zone

+$ORIGIN example.
+$TTL 1200
+
+@ SOA ns admin 20110102 5 5 13 600
+ns AAAA ::0
+added A 1.2.3.4

tests-extra/tests/zone/older_soa/data/example.zone.1

+$ORIGIN example.
+$TTL 1200
+
+@ SOA ns admin 20110101 25 25 80 600
+ns AAAA ::0

tests-extra/tests/zone/older_soa/test.py

+#!/usr/bin/env python3
+
+'''Test of Knot behavior when master has older SOA'''
+
+from dnstest.test import Test
+
+EXPIRE_SLEEP = 13
+RESYNC_SLEEP = 5
+TEST_START_EXPECTED = 3
+
+t = Test()
+
+master = t.server("knot")
+slave = t.server("knot")
+
+# this zone has refresh = 5s, retry = 5s and expire = 13s
+zone = t.zone("example.", storage=".")
+t.link(zone, master, slave)
+
+master.disable_notify = True
+slave.disable_notify = True
+
+t.start()
+
+# initial convenience check
+
+master.zone_wait(zone)
+slave.zone_wait(zone)
+
+resp = slave.dig("added.example.", "A")
+resp.check(rcode="NOERROR", rdata="1.2.3.4")
+
+# check that slave ignored outdated master
+
+master.update_zonefile(zone, version=1)
+master.stop()
+master.start()
+t.sleep(RESYNC_SLEEP - TEST_START_EXPECTED)
+
+resp = master.dig("added.example.", "A")
+resp.check(rcode="NXDOMAIN")
+
+resp = slave.dig("added.example.", "A")
+resp.check(rcode="NOERROR", rdata="1.2.3.4")
+
+# check that slave bootstrapped older zone
+
+t.sleep(EXPIRE_SLEEP - RESYNC_SLEEP)
+
+resp = slave.dig("added.example.", "A")
+resp.check(rcode="NXDOMAIN")
+
+t.stop()