- Fix #3736: Fix 0 TTL domains stuck on SERVFAIL unless manually

flushed with serve-expired on.


git-svn-id: file:///svn/unbound/trunk@4582 be551aaa-1e26-0410-a405-d3ace91eadb9

doc/Changelog

@@ -1,5 +1,7 @@
 13 March 2018: Wouter
 	- Fix typo in documentation.
+	- Fix #3736: Fix 0 TTL domains stuck on SERVFAIL unless manually
+	  flushed with serve-expired on.
 
 12 March 2018: Wouter
 	- Added documentation for aggressive-nsec: yes.

services/cache/dns.c

@@ -108,6 +108,48 @@ store_rrsets(struct module_env* env, struct reply_info* rep, time_t now,
         }
 }
 
+/** delete message from message cache */
+static void
+msg_cache_remove(struct module_env* env, uint8_t* qname, size_t qnamelen, 
+	uint16_t qtype, uint16_t qclass, uint16_t flags)
+{
+	struct query_info k;
+	hashvalue_type h;
+
+	k.qname = qname;
+	k.qname_len = qnamelen;
+	k.qtype = qtype;
+	k.qclass = qclass;
+	k.local_alias = NULL;
+	h = query_info_hash(&k, flags);
+	slabhash_remove(env->msg_cache, h, &k);
+}
+
+/** remove servfail msg cache entry */
+static void
+msg_del_servfail(struct module_env* env, struct query_info* qinfo,
+	uint32_t flags)
+{
+	struct msgreply_entry* e;
+	/* see if the entry is servfail, and then remove it, so that
+	 * lookups move from the cacheresponse stage to the recursionresponse
+	 * stage */
+	e = msg_cache_lookup(env, qinfo->qname, qinfo->qname_len,
+		qinfo->qtype, qinfo->qclass, flags, *env->now, 0);
+	if(!e) return;
+	/* we don't check for the ttl here, also expired servfail entries
+	 * are removed.  If the user uses serve-expired, they would still be
+	 * used to answer from cache */
+	if(FLAGS_GET_RCODE(((struct reply_info*)e->entry.data)->flags)
+		!= LDNS_RCODE_SERVFAIL) {
+		lock_rw_unlock(&e->entry.lock);
+		return;
+	}
+	lock_rw_unlock(&e->entry.lock);
+	msg_cache_remove(env, qinfo->qname, qinfo->qname_len, qinfo->qtype,
+		qinfo->qclass, flags);
+}
+
 void 
 dns_cache_store_msg(struct module_env* env, struct query_info* qinfo,
 	hashvalue_type hash, struct reply_info* rep, time_t leeway, int pside,
@@ -132,6 +174,12 @@ dns_cache_store_msg(struct module_env* env, struct query_info* qinfo,
 		 * which could be useful for delegation information */
 		verbose(VERB_ALGO, "TTL 0: dropped msg from cache");
 		free(rep);
+		/* if the message is SERVFAIL in cache, remove that SERVFAIL,
+		 * so that the TTL 0 response can be returned for future
+		 * responses (i.e. don't get answered by the servfail from
+		 * cache, but instead go to recursion to get this TTL0
+		 * response). */
+		msg_del_servfail(env, qinfo, flags);
 		return;
 	}