This patch was derived from a source code patch provided by ISC to

resolve ISC ticket RT #43779. [9.6-ESV-R11-S10]

--- old/./CHANGES	Thu Jan 12 00:28:22 2017

+++ new/./CHANGES	Thu Jan 12 00:28:22 2017

@@ -1,5 +1,9 @@

 	--- 9.6-ESV-R11-S10 released ---

+4530.	[bug]		Change 4489 broke the handling of CNAME -> DNAME

+			in responses resulting in SERVFAIL being returned.

+			[RT #43779]

+

 4517.	[security]	Named could mishandle authority sections that were

 			missing RRSIGs triggering an assertion failure.

 			(CVE-2016-9444) [RT #43632]

--- old/bin/tests/system/dname/ns2/example.db	Thu Jan 12 00:28:22 2017

+++ new/bin/tests/system/dname/ns2/example.db	Thu Jan 12 00:28:22 2017

@@ -29,4 +29,6 @@

 short-dname		DNAME	short

 a.longlonglonglonglonglonglonglonglonglonglonglonglong	A 10.0.0.2

 long-dname		DNAME	longlonglonglonglonglonglonglonglonglonglonglonglong

-;

+cname			CNAME	a.cnamedname

+cnamedname		DNAME	target

+a.target		A	10.0.0.3

--- old/bin/tests/system/dname/tests.sh	Thu Jan 12 00:28:22 2017

+++ new/bin/tests/system/dname/tests.sh	Thu Jan 12 00:28:22 2017

@@ -63,6 +63,24 @@

 if [ $ret != 0 ]; then echo "I:failed"; fi

 status=`expr $status + $ret`

+echo "I:checking cname to dname from authoritative"

+ret=0

+$DIG cname.example @10.53.0.2 a -p 5300 > dig.out.ns2.cname

+grep "status: NOERROR" dig.out.ns2.cname > /dev/null || ret=1

+if [ $ret != 0 ]; then echo "I:failed"; fi

+status=`expr $status + $ret`

+

+echo "I:checking cname to dname from recursive"

+ret=0

+$DIG cname.example @10.53.0.4 a -p 5300 > dig.out.ns4.cname

+grep "status: NOERROR" dig.out.ns4.cname > /dev/null || ret=1

+grep '^cname.example.' dig.out.ns4.cname > /dev/null || ret=1

+grep '^cnamedname.example.' dig.out.ns4.cname > /dev/null || ret=1

+grep '^a.cnamedname.example.' dig.out.ns4.cname > /dev/null || ret=1

+grep '^a.target.example.' dig.out.ns4.cname > /dev/null || ret=1

+if [ $ret != 0 ]; then echo "I:failed"; fi

+status=`expr $status + $ret`

+

 echo "I:exit status: $status"

 exit $status

--- old/lib/dns/resolver.c	Thu Jan 12 00:28:23 2017

+++ new/lib/dns/resolver.c	Thu Jan 12 00:28:23 2017

@@ -5776,7 +5776,7 @@

 answer_response(fetchctx_t *fctx) {

 	isc_result_t result;

 	dns_message_t *message;

-	dns_name_t *name, *dname = NULL, *qname, *dqname, tname, *ns_name;

+	dns_name_t *name, *dname = NULL, *qname, tname, *ns_name;

 	dns_name_t *cname = NULL;

 	dns_rdataset_t *rdataset, *ns_rdataset;

 	isc_boolean_t done, external, chaining, aa, found, want_chaining;

@@ -5784,7 +5784,7 @@

 	isc_boolean_t wanted_chaining;

 	unsigned int aflag;

 	dns_rdatatype_t type;

-	dns_fixedname_t fdname, fqname, fqdname;

+	dns_fixedname_t fdname, fqname;

 	FCTXTRACE("answer_response");

@@ -5807,12 +5807,11 @@

 		aa = ISC_TRUE;

 	else

 		aa = ISC_FALSE;

-	dqname = qname = &fctx->name;

+	qname = &fctx->name;

 	type = fctx->type;

-	dns_fixedname_init(&fqdname);

 	result = dns_message_firstname(message, DNS_SECTION_ANSWER);

 	while (!done && result == ISC_R_SUCCESS) {

-		dns_namereln_t namereln, dnamereln;

+		dns_namereln_t namereln;

 		int order;

 		unsigned int nlabels;

@@ -5821,8 +5820,6 @@

 		dns_message_currentname(message, DNS_SECTION_ANSWER, &name);

 		external = ISC_TF(!dns_name_issubdomain(name, &fctx->domain));

 		namereln = dns_name_fullcompare(qname, name, &order, &nlabels);

-		dnamereln = dns_name_fullcompare(dqname, name, &order,

-						     &nlabels);

 		if (namereln == dns_namereln_equal) {

 			wanted_chaining = ISC_FALSE;

 			for (rdataset = ISC_LIST_HEAD(name->list);

@@ -6074,11 +6071,24 @@

 					return (DNS_R_FORMERR);

 				}

-				if (dnamereln != dns_namereln_subdomain) {

+				/*

+				 * If DNAME + synthetic CNAME then the

+				 * namereln is dns_namereln_subdomain.

+				 *

+				 * If synthetic CNAME + DNAME then the

+				 * namereln is dns_namereln_commonancestor

+				 * and the number of label must match the

+				 * DNAME.  This order is not RFC compliant.

+				 */

+

+				if (namereln != dns_namereln_subdomain &&

+				    (namereln != dns_namereln_commonancestor ||

+				     nlabels != dns_name_countlabels(name)))

+				{

 					char qbuf[DNS_NAME_FORMATSIZE];

 					char obuf[DNS_NAME_FORMATSIZE];

-					dns_name_format(dqname, qbuf,

+					dns_name_format(qname, qbuf,

 							sizeof(qbuf));

 					dns_name_format(name, obuf,

 							sizeof(obuf));

@@ -6097,7 +6107,7 @@

 					want_chaining = ISC_TRUE;

 					POST(want_chaining);

 					aflag = DNS_RDATASETATTR_ANSWER;

-					result = dname_target(rdataset, dqname,

+					result = dname_target(rdataset, qname,

 							      nlabels, &fdname);

 					if (result == ISC_R_NOSPACE) {

 						/*

@@ -6113,8 +6123,6 @@

 						dnameset = rdataset;

 					dname = dns_fixedname_name(&fdname);

-					dqname = dns_fixedname_name(&fqdname);

-					dns_name_copy(dname, dqname, NULL);

 				} else {

 					/*

 					 * We've found a signature that

@@ -6261,7 +6269,8 @@

 						rdataset->trust =

 						    dns_trust_additional;

-					if (rdataset->type == dns_rdatatype_ns) {

+					if (rdataset->type == dns_rdatatype_ns)

+					{

 						ns_name = name;

 						ns_rdataset = rdataset;

 					}