From 4eff09c6b1e524b0efc393ee948b5c4cdf16ccb8 Mon Sep 17 00:00:00 2001
From: Mark Andrews <marka@isc.org>
Date: Wed, 3 Feb 2021 11:10:20 +1100
Subject: [PATCH] Check SOA owner names in zone transfers

An IXFR containing SOA records with owner names different than the
transferred zone's origin can result in named serving a version of that
zone without an SOA record at the apex.  This causes a RUNTIME_CHECK
assertion failure the next time such a zone is refreshed.  Fix by
immediately rejecting a zone transfer (either an incremental or
non-incremental one) upon detecting an SOA record not placed at the apex
of the transferred zone.
---
 lib/dns/xfrin.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lib/dns/xfrin.c b/lib/dns/xfrin.c
index 3a3f407289..0ba82e4974 100644
--- a/lib/dns/xfrin.c
+++ b/lib/dns/xfrin.c
@@ -477,6 +477,20 @@ xfr_rr(dns_xfrin_ctx_t *xfr, dns_name_t *name, uint32_t ttl,
 	    dns_rdatatype_ismeta(rdata->type))
 		FAIL(DNS_R_FORMERR);
 
+	/*
+	 * Immediately reject the entire transfer if the RR that is currently
+	 * being processed is an SOA record that is not placed at the zone
+	 * apex.
+	 */
+	if (rdata->type == dns_rdatatype_soa &&
+	    !dns_name_equal(&xfr->name, name)) {
+		char namebuf[DNS_NAME_FORMATSIZE];
+		dns_name_format(name, namebuf, sizeof(namebuf));
+		xfrin_log(xfr, ISC_LOG_DEBUG(3), "SOA name mismatch: '%s'",
+			  namebuf);
+		FAIL(DNS_R_NOTZONETOP);
+	}
+
  redo:
 	switch (xfr->state) {
 	case XFRST_SOAQUERY:
-- 
2.26.3