Reject Will messages that attempt to publish to $CONTROL/.

ChangeLog.txt

@@ -1,3 +1,6 @@
+Security:
+- Broker will reject Will messages that attempt to publish to $CONTROL/.
+
 Broker:
 - Fix $SYS messages being expired after 60 seconds and hence unchanged values
   disappearing.

src/handle_connect.c

@@ -375,6 +375,10 @@ static int will__read(struct mosquitto *context, const char *client_id, struct m
 		will_struct->msg.topic = will_topic_mount;
 	}
 
+	if(!strncmp(will_struct->msg.topic, "$CONTROL/", strlen("$CONTROL/"))){
+		rc = MOSQ_ERR_ACL_DENIED;
+		goto error_cleanup;
+	}
 	rc = mosquitto_pub_topic_check(will_struct->msg.topic);
 	if(rc) goto error_cleanup;
 

test/broker/07-will-control.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+
+# Test whether a client setting a will with $CONTROL in is denied
+
+from mosq_test_helper import *
+
+
+def do_test(start_broker, proto_ver):
+    rc = 1
+    mid = 1
+    connect_packet = mosq_test.gen_connect("will", will_topic="$CONTROL/dynamic-security/v1", will_payload=b"will-message", proto_ver=proto_ver)
+
+    port = mosq_test.get_port()
+    if start_broker:
+        broker = mosq_test.start_broker(filename=os.path.basename(__file__), port=port)
+
+    try:
+        sock = mosq_test.client_connect_only(port=port)
+        sock.send(connect_packet)
+        d = sock.recv(1)
+        if d == b"":
+            rc = 0
+
+        sock.close()
+    except mosq_test.TestError:
+        pass
+    except Exception as e:
+        print(e)
+    finally:
+        if start_broker:
+            broker.terminate()
+            broker.wait()
+            (stdo, stde) = broker.communicate()
+            if rc:
+                print(stde.decode('utf-8'))
+                exit(rc)
+        else:
+            return rc
+
+
+def all_tests(start_broker=False):
+    rc = do_test(start_broker, proto_ver=4)
+    if rc:
+        return rc;
+    rc = do_test(start_broker, proto_ver=5)
+    if rc:
+        return rc;
+    return 0
+
+if __name__ == '__main__':
+    all_tests(True)

test/broker/Makefile

@@ -125,6 +125,7 @@ msg_sequence_test:
 	./06-bridge-reconnect-local-out.py
 
 07 :
+	./07-will-control.py
 	./07-will-delay-invalid-573191.py
 	./07-will-delay-reconnect.py
 	./07-will-delay-recover.py

test/broker/test.py

@@ -101,6 +101,7 @@ tests = [
     (3, './06-bridge-per-listener-settings.py'),
     (2, './06-bridge-reconnect-local-out.py'),
 
+    (1, './07-will-control.py'),
     (1, './07-will-delay-invalid-573191.py'),
     (1, './07-will-delay-reconnect.py'),
     (1, './07-will-delay-recover.py'),