Fix `max_connections` option not being correctly counted.

ChangeLog.txt

@@ -5,6 +5,7 @@ Broker:
 - Fix possible out of bounds memory reads when reading a corrupt/crafted
   configuration file. Unless your configuration file is writable by untrusted
   users this is not a risk. Closes #567213.
+- Fix `max_connections` option not being correctly counted.
 
 Clients:
 - mosquitto_sub and mosquitto_rr now open stdout in binary mode on Windows

lib/net_mosq.c

@@ -250,6 +250,7 @@ int net__socket_close(struct mosquitto *mosq)
 #ifdef WITH_BROKER
 	if(mosq->listener){
 		mosq->listener->client_count--;
+		mosq->listener = NULL;
 	}
 #endif
 

test/broker/01-connect-max-connections.py

@@ -0,0 +1,79 @@
+#!/usr/bin/env python3
+
+# Test whether max_connections works with repeated connections
+
+from mosq_test_helper import *
+
+def write_config(filename, port):
+    with open(filename, 'w') as f:
+        f.write("listener %d\n" % (port))
+        f.write("allow_anonymous true\n")
+        f.write("max_connections 10\n")
+
+def do_test():
+    rc = 1
+
+    connect_packets_ok = []
+    connack_packets_ok = []
+    for i in range(0, 10):
+        connect_packets_ok.append(mosq_test.gen_connect("max-conn-%d"%i, proto_ver=5))
+        connack_packets_ok.append(mosq_test.gen_connack(rc=0, proto_ver=5))
+
+    connect_packet_bad = mosq_test.gen_connect("max-conn-bad", proto_ver=5)
+    connack_packet_bad = b""
+
+    port = mosq_test.get_port()
+    conf_file = os.path.basename(__file__).replace('.py', '.conf')
+    write_config(conf_file, port)
+    broker = mosq_test.start_broker(filename=os.path.basename(__file__), use_conf=True, port=port)
+
+    socks = []
+    try:
+        # Open all allowed connections, a limit of 10
+        for i in range(0, 10):
+            socks.append(mosq_test.do_client_connect(connect_packets_ok[i], connack_packets_ok[i], port=port))
+
+        # Try to open an 11th connection
+        try:
+            sock_bad = mosq_test.do_client_connect(connect_packet_bad, connack_packet_bad, port=port)
+        except ConnectionResetError:
+            # Expected behaviour
+            pass
+
+        # Close all allowed connections
+        for i in range(0, 10):
+            socks[i].close()
+
+        ## Now repeat - check it works as before
+
+        # Open all allowed connections, a limit of 10
+        for i in range(0, 10):
+            socks.append(mosq_test.do_client_connect(connect_packets_ok[i], connack_packets_ok[i], port=port))
+
+        # Try to open an 11th connection
+        try:
+            sock_bad = mosq_test.do_client_connect(connect_packet_bad, connack_packet_bad, port=port)
+        except ConnectionResetError:
+            # Expected behaviour
+            pass
+
+        # Close all allowed connections
+        for i in range(0, 10):
+            socks[i].close()
+
+        rc = 0
+    except mosq_test.TestError:
+        pass
+    except Exception as err:
+        print(err)
+    finally:
+        os.remove(conf_file)
+        broker.terminate()
+        broker.wait()
+        (stdo, stde) = broker.communicate()
+        if rc:
+            print(stde.decode('utf-8'))
+            exit(rc)
+
+do_test()
+exit(0)

test/broker/Makefile

@@ -30,6 +30,7 @@ test : test-compile 01 02 03 04 05 06 07 08 09 10 11 12 13 14
 	./01-connect-invalid-id-utf8.py
 	./01-connect-invalid-protonum.py
 	./01-connect-invalid-reserved.py
+	./01-connect-max-connections.py
 	./01-connect-success.py
 	./01-connect-uname-invalid-utf8.py
 	./01-connect-uname-no-flag.py

test/broker/test.py

@@ -15,6 +15,7 @@ tests = [
     (1, './01-connect-invalid-id-utf8.py'),
     (1, './01-connect-invalid-protonum.py'),
     (1, './01-connect-invalid-reserved.py'),
+    (1, './01-connect-max-connections.py'),
     (1, './01-connect-success.py'),
     (1, './01-connect-uname-invalid-utf8.py'),
     (1, './01-connect-uname-no-flag.py'),