Consider non-stale data when in serve-stale mode

With 'stale-answer-enable yes;' and 'stale-answer-client-timeout off;',
consider the following situation:

A CNAME record and its target record are in the cache, then the CNAME
record expires, but the target record is still valid.

When a new query for the CNAME record arrives, and the query fails,
the stale record is used, and then the query "restarts" to follow
the CNAME target. The problem is that the query's multiple stale
options (like DNS_DBFIND_STALEOK) are not reset, so 'query_lookup()'
treats the restarted query as a lookup following a failed lookup,
and returns a SERVFAIL answer when there is no stale data found in the
cache, even if there is valid non-stale data there available.

With this change, query_lookup() now considers non-stale data in the
cache in the first place, and returns it if it is available.

(cherry picked from commit 91a1a8efc5bca44ff3aa6861c31759449ea65ecd)

diff --git a/lib/dns/include/dns/rdataset.h b/lib/dns/include/dns/rdataset.h
index ac2329fb7d978e814d9d90b84e4a84cf316d0b37..de3f638f895fc777d24f63e81b97676df4b178eb 100644 (file)
--- a/lib/dns/include/dns/rdataset.h
+++ b/lib/dns/include/dns/rdataset.h
@@ -157,6 +157,11 @@ struct dns_rdataset {
  *
  * \def DNS_RDATASETATTR_LOADORDER
  *     Output the RRset in load order.
+ *
+ * \def DNS_RDATASETATTR_STALE_ADDED
+ *     Set on rdatasets that were added during a stale-answer-client-timeout
+ *     lookup. In other words, the RRset was added during a lookup of stale
+ *     data and does not necessarily mean that the rdataset itself is stale.
  */
 
 #define DNS_RDATASETATTR_NONE        0x00000000 /*%< No ordering. */

diff --git a/lib/ns/query.c b/lib/ns/query.c
index 308fc019532f2d7c7e6061123f8b2e88cee2cdb5..81ade5282b7cb7c764434e15fe9229b690a30f5e 100644 (file)
--- a/lib/ns/query.c
+++ b/lib/ns/query.c
@@ -5761,6 +5761,7 @@ query_lookup(query_ctx_t *qctx) {
        dns_ttl_t stale_refresh = 0;
        bool dbfind_stale = false;
        bool stale_timeout = false;
+       bool answer_found = false;
        bool stale_found = false;
        bool stale_refresh_window = false;
 
@@ -5867,6 +5868,14 @@ query_lookup(query_ctx_t *qctx) {
         */
        stale_timeout = ((dboptions & DNS_DBFIND_STALETIMEOUT) != 0);
 
+       if (dns_rdataset_isassociated(qctx->rdataset) &&
+           dns_rdataset_count(qctx->rdataset) > 0 && !STALE(qctx->rdataset))
+       {
+               /* Found non-stale usable rdataset. */
+               answer_found = true;
+               goto gotanswer;
+       }
+
        if (dbfind_stale || stale_refresh_window || stale_timeout) {
                dns_name_format(qctx->client->query.qname, namebuf,
                                sizeof(namebuf));
@@ -5973,7 +5982,8 @@ query_lookup(query_ctx_t *qctx) {
                }
        }
 
-       if (stale_timeout && stale_found) {
+gotanswer:
+       if (stale_timeout && (answer_found || stale_found)) {
                /*
                 * Mark RRsets that we are adding to the client message on a
                 * lookup during 'stale-answer-client-timeout', so we can