Fix resolution of unusual ip6.arpa names

Before this commit, BIND was unable to resolve ip6.arpa names like
the one reported in issue #1847 when using query minimization.

As reported in the issue, an attempt to resolve a name like
'rec-test-dom-158937817846788.test123.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.3.4.3.5.4.0.8.2.6.0.1.0.0.2.ip6.arpa'
using default settings would fail.

The reason was that query minimization algorithm in 'fctx_minimize_qname'
would divide any ip6.arpa names in increasing number of labels,
7,11, ... up to 35, thus limiting the destination name (minimized) to a number
of 35 labels.

In case the last query minimization attempt (with 35 labels) would fail with
NXDOMAIN, BIND would attempt the query mininimization again with the exact
same QNAME, limited on the 35 labels, and that in turn would fail again.

This fix avoids this fail loop by considering the extra labels that may appear
in the leftmost part of an ip6.arpa name, those after the IPv6 part.

diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
index df43b0a09a6144502837d936af425edd4320ed53..612dab1501381f75c6e575698a49755f81b4d5b1 100644 (file)
--- a/lib/dns/resolver.c
+++ b/lib/dns/resolver.c
@@ -10646,8 +10646,10 @@ fctx_minimize_qname(fetchctx_t *fctx) {
                        fctx->qmin_labels = 17;
                } else if (fctx->qmin_labels < 19) {
                        fctx->qmin_labels = 19;
-               } else if (fctx->qmin_labels > 19) {
+               } else if (fctx->qmin_labels < 35) {
                        fctx->qmin_labels = 35;
+               } else {
+                       fctx->qmin_labels = nlabels;
                }
        } else if (fctx->qmin_labels > DNS_QMIN_MAXLABELS) {
                fctx->qmin_labels = DNS_MAX_LABELS + 1;