From: Witold Kręcicki <wpk@isc.org>
Date: Thu, 3 Jan 2019 13:17:43 +0000 (+0100)
Subject: fix enforcement of tcp-clients (v1)
X-Git-Tag: v9.15.0~25^2~6
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=07c3365b0bc57226baedaa177ac5cb74cc013950;p=thirdparty%2Fbind9.git

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 eafcff07c25bdbe038ae1e4b6660602a080b9395)
(cherry picked from commit 9e7617cc84f465769be1a3f426f30cd516220902)
---

diff --git a/lib/ns/client.c b/lib/ns/client.c
index 12fb45f4747..6f101713afc 100644
--- a/lib/ns/client.c
+++ b/lib/ns/client.c
@@ -439,8 +439,19 @@ 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,