From 80a43c9241d7a58e0d6c68107dfb5891a01c05ad Mon Sep 17 00:00:00 2001
From: Aram Sargsyan <aram@isc.org>
Date: Mon, 12 May 2025 13:58:38 +0000
Subject: [PATCH] Prepare a zone for shutting down when deleting it from a view

After b171cacf4f0123ba96bef6eedfc92dfb608db6b7, a zone object can
remain in the memory for a while, until garbage collection is run.
Setting the DNS_ZONEFLG_EXITING flag should prevent the zone
maintenance function from running while it's in that state.
Otherwise, a secondary zone could initiate a zone transfer after
it had been deleted.

(cherry picked from commit 874ca5ca2f1f381e434304e262ea08e77e3bdf65)
---
 lib/dns/include/dns/zone.h | 14 ++++++++++++++
 lib/dns/view.c             |  2 ++
 lib/dns/zone.c             |  9 +++++++++
 3 files changed, 25 insertions(+)

diff --git a/lib/dns/include/dns/zone.h b/lib/dns/include/dns/zone.h
index 57ff194c2b..8573c1dce5 100644
--- a/lib/dns/include/dns/zone.h
+++ b/lib/dns/include/dns/zone.h
@@ -1757,6 +1757,20 @@ dns_zone_findkeys(dns_zone_t *zone, dns_db_t *db, dns_dbversion_t *ver,
  *\li	Error
  */
 
+void
+dns_zone_prepare_shutdown(dns_zone_t *zone);
+/*%<
+ * Prepare a zone for shutdown by setting the DNS_ZONEFLG_EXITING flag even
+ * before the final reference is detached. Useful, because the zone object can
+ * be kept around with a valid reference from the zonetable until qp garbage
+ * collector runs, and we don't want, for example, zone maintenance to happen
+ * while waiting for it. Note that the zone can not be used normally again after
+ * this function is called.
+ *
+ * Requires:
+ *\li	'zone' to be a valid initialised zone.
+ */
+
 void
 dns_zonemgr_create(isc_mem_t *mctx, isc_nm_t *netmgr, dns_zonemgr_t **zmgrp);
 /*%<
diff --git a/lib/dns/view.c b/lib/dns/view.c
index a82c078a70..b5d751ad54 100644
--- a/lib/dns/view.c
+++ b/lib/dns/view.c
@@ -785,6 +785,8 @@ dns_view_delzone(dns_view_t *view, dns_zone_t *zone) {
 
 	REQUIRE(DNS_VIEW_VALID(view));
 
+	dns_zone_prepare_shutdown(zone);
+
 	rcu_read_lock();
 	zonetable = rcu_dereference(view->zonetable);
 	if (zonetable != NULL) {
diff --git a/lib/dns/zone.c b/lib/dns/zone.c
index 845902b160..c070b38810 100644
--- a/lib/dns/zone.c
+++ b/lib/dns/zone.c
@@ -6401,6 +6401,15 @@ failure:
 	return result;
 }
 
+void
+dns_zone_prepare_shutdown(dns_zone_t *zone) {
+	REQUIRE(DNS_ZONE_VALID(zone));
+
+	LOCK_ZONE(zone);
+	DNS_ZONE_SETFLAG(zone, DNS_ZONEFLG_EXITING);
+	UNLOCK_ZONE(zone);
+}
+
 /*%
  * Find DNSSEC keys used for signing zone with dnssec-policy. Load these keys
  * into 'keys'. Requires KASP to be locked.