machined: reject invalid class types when registering machines

Follow-up for fbe550738d

src/machine/machine-varlink.c

@@ -155,6 +155,9 @@ int vl_method_register(sd_varlink *link, sd_json_variant *parameters, sd_varlink
         if (r != 0)
                 return r;
 
+        if (!IN_SET(machine->class, MACHINE_CONTAINER, MACHINE_VM))
+                return sd_varlink_error_invalid_parameter_name(link, "class");
+
         if (manager->runtime_scope != RUNTIME_SCOPE_USER) {
                 r = varlink_verify_polkit_async(
                                 link,

src/machine/machined-dbus.c

@@ -433,7 +433,7 @@ static int method_create_or_register_machine(
                 c = _MACHINE_CLASS_INVALID;
         else {
                 c = machine_class_from_string(class);
-                if (c < 0)
+                if (c < 0 || !IN_SET(c, MACHINE_CONTAINER, MACHINE_VM))
                         return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid machine class parameter");
         }
 
@@ -608,7 +608,7 @@ static int method_create_or_register_machine_ex(
                 c = _MACHINE_CLASS_INVALID;
         else {
                 c = machine_class_from_string(class);
-                if (c < 0)
+                if (c < 0 || !IN_SET(c, MACHINE_CONTAINER, MACHINE_VM))
                         return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid machine class parameter");
         }