From 011af4de71f54743e650746c9ab7db80d1636800 Mon Sep 17 00:00:00 2001
From: Mark Andrews <marka@isc.org>
Date: Fri, 22 Nov 2019 12:55:03 +1100
Subject: [PATCH] Lock dispatch manager buffer_lock before accessing buffers;
 Only test buffers for UDP dispatches.

---
 lib/dns/dispatch.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/dns/dispatch.c b/lib/dns/dispatch.c
index 6cd2fd7fe3..2e534d26c3 100644
--- a/lib/dns/dispatch.c
+++ b/lib/dns/dispatch.c
@@ -1500,8 +1500,14 @@ startrecv(dns_dispatch_t *disp, dispsocket_t *dispsock) {
 	if (disp->recv_pending != 0 && dispsock == NULL)
 		return (ISC_R_SUCCESS);
 
-	if (disp->mgr->buffers >= disp->mgr->maxbuffers)
-		return (ISC_R_NOMEMORY);
+	if (disp->socktype == isc_sockettype_udp) {
+		LOCK(&disp->mgr->buffer_lock);
+		if (disp->mgr->buffers >= disp->mgr->maxbuffers) {
+			UNLOCK(&disp->mgr->buffer_lock);
+			return (ISC_R_NOMEMORY);
+		}
+		UNLOCK(&disp->mgr->buffer_lock);
+	}
 
 	if ((disp->attributes & DNS_DISPATCHATTR_EXCLUSIVE) != 0 &&
 	    dispsock == NULL)