From: Mark Andrews <marka@isc.org>
Date: Mon, 1 Mar 2021 05:46:07 +0000 (+1100)
Subject: Handle DNAME lookup via itself
X-Git-Tag: v9.17.12~3^2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1c3d8191bb1dde2522b946c66785fbfad1dde061;p=thirdparty%2Fbind9.git

Handle DNAME lookup via itself

When answering a query, named should never attempt to add the same RRset
to the ANSWER section more than once.  However, such a situation may
arise when chasing DNAME records: one of the DNAME records placed in the
ANSWER section may turn out to be the final answer to a client query,
but there is no way to know that in advance.  Tweak the relevant INSIST
assertion in query_respond() so that it handles this case properly.
qctx->rdataset is freed later anyway, so there is no need to clean it up
in query_respond().
---

diff --git a/lib/ns/query.c b/lib/ns/query.c
index 79110122866..65d582f4cff 100644
--- a/lib/ns/query.c
+++ b/lib/ns/query.c
@@ -8176,10 +8176,16 @@ query_respond(query_ctx_t *qctx) {
 	query_addnoqnameproof(qctx);
 
 	/*
-	 * We shouldn't ever fail to add 'rdataset'
-	 * because it's already in the answer.
-	 */
-	INSIST(qctx->rdataset == NULL);
+	 * 'qctx->rdataset' will only be non-NULL here if the ANSWER section of
+	 * the message to be sent to the client already contains an RRset with
+	 * the same owner name and the same type as 'qctx->rdataset'.  This
+	 * should never happen, with one exception: when chasing DNAME records,
+	 * one of the DNAME records placed in the ANSWER section may turn out
+	 * to be the final answer to the client's query, but we have no way of
+	 * knowing that until now.  In such a case, 'qctx->rdataset' will be
+	 * freed later, so we do not need to free it here.
+	 */
+	INSIST(qctx->rdataset == NULL || qctx->qtype == dns_rdatatype_dname);
 
 	query_addauth(qctx);