ixfr: Format checking + removed redundant test

- If the IXFR response contains no records or the first record is
  not SOA, consider it malformed and fail the transfer.
- AXFR-style IXFR both master side and slave side are checked in
  one test, removed the other.

src/knot/nameserver/ixfr.c

@@ -667,11 +667,27 @@ int ixfr_query(knot_pkt_t *pkt, struct query_data *qdata)
 	return ret;
 }
 
+static int check_format(knot_pkt_t *pkt)
+{
+	const knot_pktsection_t *answer = knot_pkt_section(pkt, KNOT_ANSWER);
+
+	if (answer->count >= 1 && answer->rr[0].type == KNOT_RRTYPE_SOA) {
+		return KNOT_EOK;
+	} else {
+		return KNOT_EMALF;
+	}
+}
+
 int ixfr_process_answer(knot_pkt_t *pkt, struct answer_data *adata)
 {
 	if (pkt == NULL || adata == NULL) {
 		return KNOT_NS_PROC_FAIL;
 	}
+
+	if (check_format(pkt) != KNOT_EOK) {
+		IXFRIN_LOG(LOG_WARNING, "malformed response");
+		return KNOT_NS_PROC_FAIL;
+	}
 	
 	if (adata->ext == NULL) {
 		/* Check for AXFR-style IXFR. */
@@ -697,8 +713,7 @@ int ixfr_process_answer(knot_pkt_t *pkt, struct answer_data *adata)
 		NS_NEED_TSIG_SIGNED(&adata->param->tsig_ctx, 0);
 		if (!zone_transfer_needed(adata->param->zone, pkt)) {
 			if (knot_pkt_section(pkt, KNOT_ANSWER)->count > 1) {
-				IXFRIN_LOG(LOG_WARNING, "malformed IXFR response"
-				           " (old data), ignoring");
+				IXFRIN_LOG(LOG_WARNING, "old data, ignoring");
 			} else {
 				/* Single-SOA answer. */
 				IXFRIN_LOG(LOG_INFO, "zone is up-to-date");

tests-extra/tests/ixfr/axfr_style_slave/test.py → tests-extra/tests/ixfr/axfr_style/test.py

@@ -22,7 +22,7 @@ master.update_zonefile(zone, version=1)
 master.reload()
 master.zone_wait(zone, serial)
 
-# check that master really sends AXFR-style IXFR
+# check that master properly sends AXFR-style IXFR
 t.check_axfr_style_ixfr(master, "xfr", serial)
 
 serial = slave.zone_wait(zone, serial)
@@ -45,7 +45,7 @@ master.reload()
 master.zone_wait(zone, serial)
 slave.zone_wait(zone, serial)
 
-# check that master really sends AXFR-style IXFR
+# check that master properly sends AXFR-style IXFR again
 t.check_axfr_style_ixfr(master, "xfr", serial)
 
 t.xfr_diff(master, slave, zone)

tests-extra/tests/ixfr/axfr_style_master/data/example.com.zone

-$ORIGIN example.com.
-$TTL 3600
-
-@	SOA	dns1 hostmaster 2010111201 10800 3600 1209600 7200
-	NS	dns1
-	NS	dns2
-	MX	10 mail
-
-dns1	A	192.0.2.1
-	AAAA	2001:DB8::1
-
-dns2	A	192.0.2.2
-	AAAA	2001:DB8::2
-
-mail	A	192.0.2.3
-	AAAA	2001:DB8::3

tests-extra/tests/ixfr/axfr_style_master/data/example.com.zone.1

-$ORIGIN example.com.
-$TTL 3600
-
-@	SOA	dns1 hostmaster 2010111202 10800 3600 1209600 7200
-	NS	dns1
-	NS	dns2
-	MX	10 mail
-
-dns1	A	192.0.2.1
-	AAAA	2001:DB8::1
-
-dns2	A	192.0.2.2
-	AAAA	2001:DB8::2
-
-mail	A	192.0.2.3
-	AAAA	2001:DB8::3

tests-extra/tests/ixfr/axfr_style_master/test.py

-#!/usr/bin/env python3
-
-'''Test for fallback IXFR->AXFR with Knot master'''
-
-from dnstest.test import Test
-
-t = Test()
-
-knot = t.server("knot")
-zone = t.zone("example.com.", storage=".")
-
-t.link(zone, knot, ixfr=False)
-
-t.start()
-
-# Wait for AXFR to slave server.
-serial_init = knot.zone_wait(zone)
-
-# 2nd version of the zone, differing only in serial, so that there is quite
-# a difference between AXFR and IXFR
-knot.update_zonefile(zone, 1)
-knot.reload()
-
-# Check if IXFR gives answer in the format of AXFR
-t.check_axfr_style_ixfr(knot, "example.com.", serial_init)
-
-t.end()