From f0265b8fa691c41975e395dfd58dc41699adb902 Mon Sep 17 00:00:00 2001
From: Mark Andrews <marka@isc.org>
Date: Wed, 24 Mar 2021 10:58:09 +1100
Subject: [PATCH] Make whether to follow additional data records generic

Adds dns_rdatatype_followadditional() and
DNS_RDATATYPEATTR_FOLLOWADDITIONAL
---
 lib/dns/include/dns/rdata.h | 17 +++++++++++++++++
 lib/dns/rdata.c             |  9 +++++++++
 lib/dns/rdata/in_1/srv_33.c |  2 +-
 lib/ns/query.c              | 19 ++++---------------
 4 files changed, 31 insertions(+), 16 deletions(-)

diff --git a/lib/dns/include/dns/rdata.h b/lib/dns/include/dns/rdata.h
index 359f69d674..476ef5f9c7 100644
--- a/lib/dns/include/dns/rdata.h
+++ b/lib/dns/include/dns/rdata.h
@@ -695,6 +695,21 @@ dns_rdatatype_atcname(dns_rdatatype_t type);
  *
  */
 
+bool
+dns_rdatatype_followadditional(dns_rdatatype_t type);
+/*%<
+ * Return true if adding a record of type 'type' to the ADDITIONAL section
+ * of a message can itself trigger the addition of still more data to the
+ * additional section.
+ *
+ * (For example: adding SRV to the ADDITIONAL section may trigger
+ * the addition of address records associated with that SRV.)
+ *
+ * Requires:
+ * \li	'type' is a valid rdata type.
+ *
+ */
+
 unsigned int
 dns_rdatatype_attributes(dns_rdatatype_t rdtype);
 /*%<
@@ -729,6 +744,8 @@ dns_rdatatype_attributes(dns_rdatatype_t rdtype);
 #define DNS_RDATATYPEATTR_ATPARENT 0x00000200U
 /*% Can exist along side a CNAME */
 #define DNS_RDATATYPEATTR_ATCNAME 0x00000400U
+/*% Follow additional */
+#define DNS_RDATATYPEATTR_FOLLOWADDITIONAL 0x00000800U
 
 dns_rdatatype_t
 dns_rdata_covers(dns_rdata_t *rdata);
diff --git a/lib/dns/rdata.c b/lib/dns/rdata.c
index 6fb7bc3d22..c8d684a38c 100644
--- a/lib/dns/rdata.c
+++ b/lib/dns/rdata.c
@@ -2131,6 +2131,15 @@ dns_rdatatype_atparent(dns_rdatatype_t type) {
 	return (false);
 }
 
+bool
+dns_rdatatype_followadditional(dns_rdatatype_t type) {
+	if ((dns_rdatatype_attributes(type) &
+	     DNS_RDATATYPEATTR_FOLLOWADDITIONAL) != 0) {
+		return (true);
+	}
+	return (false);
+}
+
 bool
 dns_rdataclass_ismeta(dns_rdataclass_t rdclass) {
 	if (rdclass == dns_rdataclass_reserved0 ||
diff --git a/lib/dns/rdata/in_1/srv_33.c b/lib/dns/rdata/in_1/srv_33.c
index 268c0e9385..80dd1d637c 100644
--- a/lib/dns/rdata/in_1/srv_33.c
+++ b/lib/dns/rdata/in_1/srv_33.c
@@ -14,7 +14,7 @@
 #ifndef RDATA_IN_1_SRV_33_C
 #define RDATA_IN_1_SRV_33_C
 
-#define RRTYPE_SRV_ATTRIBUTES (0)
+#define RRTYPE_SRV_ATTRIBUTES (DNS_RDATATYPEATTR_FOLLOWADDITIONAL)
 
 static inline isc_result_t
 fromtext_in_srv(ARGS_FROMTEXT) {
diff --git a/lib/ns/query.c b/lib/ns/query.c
index a9b1cd9dbb..81ff6abfe7 100644
--- a/lib/ns/query.c
+++ b/lib/ns/query.c
@@ -2041,22 +2041,11 @@ addname:
 	fname = NULL;
 
 	/*
-	 * In a few cases, we want to add additional data for additional
-	 * data.  It's simpler to just deal with special cases here than
-	 * to try to create a general purpose mechanism and allow the
-	 * rdata implementations to do it themselves.
-	 *
-	 * This involves recursion, but the depth is limited.  The
-	 * most complex case is adding a SRV rdataset, which involves
-	 * recursing to add address records, which in turn can cause
-	 * recursion to add KEYs.
+	 * In some cases, a record that has been added as additional
+	 * data may *also* trigger the addition of additional data.
+	 * This cannot go more than MAX_RESTARTS levels deep.
 	 */
-	if (type == dns_rdatatype_srv && trdataset != NULL) {
-		/*
-		 * If we're adding SRV records to the additional data
-		 * section, it's helpful if we add the SRV additional data
-		 * as well.
-		 */
+	if (trdataset != NULL && dns_rdatatype_followadditional(type)) {
 		eresult = dns_rdataset_additionaldata(
 			trdataset, query_additional_cb, qctx);
 	}