Backport patch to fix CVE-2018-5743.

Ref:
https://security-tracker.debian.org/tracker/CVE-2018-5743

CVE: CVE-2018-5743
Upstream-Status: Backport [https://gitlab.isc.org/isc-projects/bind9/commit/ec2d50d]

Signed-off-by: Kai Kang <kai.kang@windriver.com>

From ec2d50da8d81814640e28593d912f4b96c7efece Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Witold=20Kr=C4=99cicki?= <wpk@isc.org>
Date: Thu, 3 Jan 2019 14:17:43 +0100
Subject: [PATCH 1/6] fix enforcement of tcp-clients (v1)

tcp-clients settings could be exceeded in some cases by
creating more and more active TCP clients that are over
the set quota limit, which in the end could lead to a
DoS attack by e.g. exhaustion of file descriptors.

If TCP client we're closing went over the quota (so it's
not attached to a quota) mark it as mortal - so that it
will be destroyed and not set up to listen for new
connections - unless it's the last client for a specific
interface.

(cherry picked from commit f97131d21b97381cef72b971b157345c1f9b4115)
(cherry picked from commit 9689ffc485df8f971f0ad81ab8ab1f5389493776)
---
 bin/named/client.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/bin/named/client.c b/bin/named/client.c
index d482da7121..0739dd48af 100644
--- a/bin/named/client.c
+++ b/bin/named/client.c
@@ -421,8 +421,19 @@ exit_check(ns_client_t *client) {
 			isc_socket_detach(&client->tcpsocket);
 		}
 
-		if (client->tcpquota != NULL)
+		if (client->tcpquota != NULL) {
 			isc_quota_detach(&client->tcpquota);
+		} else {
+			/*
+			 * We went over quota with this client, we don't
+			 * want to restart listening unless this is the
+			 * last client on this interface, which is
+			 * checked later.
+			 */
+			if (TCP_CLIENT(client)) {
+				client->mortal = true;
+			}
+		}
 
 		if (client->timerset) {
 			(void)isc_timer_reset(client->timer,
-- 
2.20.1