From: Ondřej Surý <ondrej@isc.org>
Date: Tue, 21 Jul 2020 09:35:42 +0000 (+0200)
Subject: Expire the 0 TTL RRSet quickly rather using them for serve-stale
X-Git-Tag: v9.17.4~16^2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6ffa2ddae0bc31271492481ec50f99d68263b25b;p=thirdparty%2Fbind9.git

Expire the 0 TTL RRSet quickly rather using them for serve-stale

When a received RRSet has TTL 0, they would be preserved for
serve-stale (default `max-stale-cache` is 12 hours) rather than expiring
them quickly from the cache database.

This commit makes sure the RRSet didn't have TTL 0 before marking the
entry in the database as "stale".
---

diff --git a/lib/dns/rbtdb.c b/lib/dns/rbtdb.c
index 0e26425a301..9ca6de2ae08 100644
--- a/lib/dns/rbtdb.c
+++ b/lib/dns/rbtdb.c
@@ -1630,6 +1630,8 @@ mark_header_stale(dns_rbtdb_t *rbtdb, rdatasetheader_t *header) {
 	uint_least16_t attributes = atomic_load_acquire(&header->attributes);
 	uint_least16_t newattributes = 0;
 
+	INSIST((attributes & RDATASET_ATTR_ZEROTTL) == 0);
+
 	/*
 	 * If we are already stale there is nothing to do.
 	 */
@@ -4522,9 +4524,11 @@ check_stale_header(dns_rbtnode_t *node, rdatasetheader_t *header,
 		/*
 		 * If this data is in the stale window keep it and if
 		 * DNS_DBFIND_STALEOK is not set we tell the caller to
-		 * skip this record.
+		 * skip this record.  We skip the records with ZEROTTL
+		 * (these records should not be cached anyway).
 		 */
-		if (KEEPSTALE(search->rbtdb) && stale > search->now) {
+		if (!ZEROTTL(header) && KEEPSTALE(search->rbtdb) &&
+		    stale > search->now) {
 			mark_header_stale(search->rbtdb, header);
 			*header_prev = header;
 			return ((search->options & DNS_DBFIND_STALEOK) == 0);