[2433] catch an invalid case where NS name is CNAME.

src/lib/dns/tests/zone_checker_unittest.cc

@@ -186,14 +186,33 @@ TEST_F(ZoneCheckerTest, checkNSData) {
     expected_warns_.push_back("zone example.com/IN: NS has no address");
     checkIssues();
 
+    // If there's a CNAME at the name instead, it's an error.
+    RRsetPtr cname(new RRset(ns_name, zclass_, RRType::CNAME(), RRTTL(60)));
+    cname->addRdata(generic::CNAME("cname.example.com"));
+    rrsets_->addRRset(cname);
+    EXPECT_FALSE(checkZone(zname_, zclass_, *rrsets_, callbacks_));
+    expected_errors_.push_back("zone example.com/IN: NS 'ns.example.com' is "
+                               "a CNAME (illegal per RFC2181)");
+    checkIssues();
+
     // It doesn't have to be A.  An AAAA is enough.
+    rrsets_->removeRRset(ns_name, zclass_, RRType::CNAME());
     RRsetPtr aaaa(new RRset(ns_name, zclass_, RRType::AAAA(), RRTTL(60)));
     aaaa->addRdata(in::AAAA("2001:db8::1"));
     rrsets_->addRRset(aaaa);
     EXPECT_TRUE(checkZone(zname_, zclass_, *rrsets_, callbacks_));
     checkIssues();
 
-    // Or it doesn't matter if the NS name is "out of bailiwick".
+    // Coexisting CNAME makes it error (CNAME with other record is itself
+    // invalid, but it's a different issue in this context)
+    rrsets_->addRRset(cname);
+    EXPECT_FALSE(checkZone(zname_, zclass_, *rrsets_, callbacks_));
+    expected_errors_.push_back("zone example.com/IN: NS 'ns.example.com' is "
+                               "a CNAME (illegal per RFC2181)");
+    checkIssues();
+
+    // It doesn't matter if the NS name is "out of bailiwick".
+    rrsets_->removeRRset(ns_name, zclass_, RRType::CNAME());
     rrsets_->removeRRset(zname_, zclass_, RRType::NS());
     ns_.reset(new RRset(zname_, zclass_, RRType::NS(), RRTTL(60)));
     ns_->addRdata(generic::NS("ns.example.org"));

src/lib/dns/zone_checker.cc

@@ -161,6 +161,12 @@ checkNSNames(const Name& zone_name, const RRClass& zone_class,
                 assert(false);
             }
         }
+        if (zone_rrsets.find(ns_name, RRType::CNAME(), zone_class) != NULL) {
+            callbacks.error("zone " + zoneText(zone_name, zone_class) +
+                            ": NS '" + ns_name.toText(true) + "' is a CNAME " +
+                            "(illegal per RFC2181)");
+            continue;
+        }
         if (zone_rrsets.find(ns_name, RRType::A(), zone_class) == NULL &&
             zone_rrsets.find(ns_name, RRType::AAAA(), zone_class) == NULL) {
             callbacks.warn("zone " + zoneText(zone_name, zone_class) +