improvement(client): catch exceptions for unexpecte arguments in Fire…

…wallClient._signal_receiver()

Add a try-except around dbus_to_python(). Otherwise unexpected arguments
of a D-Bus signal will raise an exception for @handle_exceptions
decorator. When talking D-Bus, we should not treat the other peer as
trusted, even if it's the firewalld daemon.

On the other hand, move cb_args.extend(cb[1]) out of the try-except.
This really is not supposed to fail.

src/firewall/client.py

@@ -3470,11 +3470,17 @@ def _signal_receiver(self, *dbus_args, member=None, interface=None, path=None):
             return
 
         # call back with dbus_args converted to python types ...
-        cb_args = [dbus_to_python(arg) for arg in dbus_args]
         try:
-            if cb[1]:
-                # add call data
-                cb_args.extend(cb[1])
+            cb_args = [dbus_to_python(arg) for arg in dbus_args]
+        except TypeError:
+            # Unexpected D-Bus type in the argument? Seems the D-Bus API
+            # is unexpected. Silently ignore.
+            return
+
+        if cb[1]:
+            # add call data
+            cb_args.extend(cb[1])
+        try:
             # call back
             cb[0](*cb_args)
         except Exception as msg: