From 792d8a74ab5af8723ecc53a6eb20d1a47ec71b11 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ond=C5=99ej=20Sur=C3=BD?= <ondrej@isc.org>
Date: Sat, 14 Mar 2026 10:10:34 +0100
Subject: [PATCH] Add invariant check for delegset in rctx_nextserver()

The get_nameservers path in rctx_nextserver() is only reachable from
rctx_referral(), which already detaches fctx->delegset.  Assert that
it is NULL rather than redundantly detaching it, since
dns_view_bestzonecut() requires *delegsetp == NULL.
---
 lib/dns/resolver.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
index 11a57ca681..25ba14bd73 100644
--- a/lib/dns/resolver.c
+++ b/lib/dns/resolver.c
@@ -9379,6 +9379,7 @@ rctx_nextserver(respctx_t *rctx, dns_message_t *message,
 		} else {
 			name = fctx->domain;
 		}
+		INSIST(fctx->delegset == NULL);
 		result = dns_view_bestzonecut(fctx->res->view, name, fname,
 					      dcname, fctx->now, findoptions,
 					      true, true, &fctx->delegset);