From: Witold Kręcicki <wpk@isc.org>
Date: Thu, 21 May 2020 09:18:53 +0000 (+0200)
Subject: Fix assertion failure during startup when the server is under load.
X-Git-Tag: v9.17.3~22^2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b4f3fafcffad55e64ec8958691db41a417320bb0;p=thirdparty%2Fbind9.git

Fix assertion failure during startup when the server is under load.

When we're coming back from recursion fetch_callback does not accept
DNS_R_NXDOMAIN as an rcode - query_gotanswer calls query_nxdomain in
which an assertion fails on qctx->is_zone. Yet, under some
circumstances, qname minimization will return an DNS_R_NXDOMAIN - when
root zone mirror is not yet loaded. The fix changes the DNS_R_NXDOMAIN
answer to DNS_R_SERVFAIL.
---

diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
index 5a1f0c9f06a..8aa78191e87 100644
--- a/lib/dns/resolver.c
+++ b/lib/dns/resolver.c
@@ -4397,6 +4397,15 @@ resume_qmin(isc_task_t *task, isc_event_t *event) {
 				      fctx->now, findoptions, true, true,
 				      &fctx->nameservers, NULL);
 
+	/*
+	 * DNS_R_NXDOMAIN here means we have not loaded the root zone mirror
+	 * yet - but DNS_R_NXDOMAIN is not a valid return value when doing
+	 * recursion, we need to patch it.
+	 */
+	if (result == DNS_R_NXDOMAIN) {
+		result = DNS_R_SERVFAIL;
+	}
+
 	if (result != ISC_R_SUCCESS) {
 		fctx_done(fctx, result, __LINE__);
 		goto cleanup;