cli: deny removing values of nmcli-unchangable properties

nmc_setting_reset_property() function checks whether we allow changing the property
(set_func != NULL) and if so, the property value is reset to default.

cli/src/connections.c

@@ -5318,8 +5318,13 @@ property_edit_submenu (NmCli *nmc,
 					g_clear_error (&tmp_err);
 				}
 				g_free (option);
-			} else
+			} else {
-				nmc_property_set_default_value (curr_setting, prop_name);
+				if (!nmc_setting_reset_property (curr_setting, prop_name, &tmp_err)) {
+					printf (_("Error: failed to remove value of '%s': %s\n"), prop_name,
+					        tmp_err->message);
+					g_clear_error (&tmp_err);
+				}
+			}
 			break;
 
 		case NMC_EDITOR_SUB_CMD_DESCRIBE:
@@ -5775,6 +5780,7 @@ editor_menu_main (NmCli *nmc, NMConnection *connection, const char *connection_t
 			/* Remove setting from connection, or delete value of a property */
 			if (!cmd_arg) {
 				if (menu_ctx.level == 1) {
+					GError *tmp_err = NULL;
 					const char *prop_name;
 
 					prop_name = ask_check_property (cmd_arg,
@@ -5784,7 +5790,11 @@ editor_menu_main (NmCli *nmc, NMConnection *connection, const char *connection_t
 						break;
 
 					/* Delete property value */
-					nmc_property_set_default_value (menu_ctx.curr_setting, prop_name);
+					if (!nmc_setting_reset_property (menu_ctx.curr_setting, prop_name, &tmp_err)) {
+						printf (_("Error: failed to remove value of '%s': %s\n"), prop_name,
+						        tmp_err->message);
+						g_clear_error (&tmp_err);
+					}
 				} else
 					printf (_("Error: no argument given; valid are [%s]\n"), valid_settings_str);
 			} else {
@@ -5821,7 +5831,11 @@ editor_menu_main (NmCli *nmc, NMConnection *connection, const char *connection_t
 					char *prop_name = is_property_valid (ss, cmd_arg_p, &tmp_err);
 					if (prop_name) {
 						/* Delete property value */
-						nmc_property_set_default_value (ss, prop_name);
+						if (!nmc_setting_reset_property (ss, prop_name, &tmp_err)) {
+							printf (_("Error: failed to remove value of '%s': %s\n"), prop_name,
+							        tmp_err->message);
+							g_clear_error (&tmp_err);
+						}
 					} else {
 						/* If the string is not a property, try it as a setting */
 						NMSetting *s_tmp;

cli/src/settings.c

@@ -4769,6 +4769,32 @@ nmc_property_set_default_value (NMSetting *setting, const char *prop)
 	}
 }
 
+/*
+ * Generic function for reseting (single value) properties.
+ *
+ * The function resets the property value to the default one. It respects
+ * nmcli restrictions for changing properties. So if 'set_func' is NULL,
+ * reseting the value is denied.
+ *
+ * Returns: TRUE on success; FALSE on failure and sets error
+ */
+gboolean
+nmc_setting_reset_property (NMSetting *setting, const char *prop, GError **error)
+{
+	const NmcPropertyFuncs *item;
+
+	g_return_val_if_fail (NM_IS_SETTING (setting), FALSE);
+	g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
+
+	item = nmc_properties_find (nm_setting_get_name (setting), prop);
+	if (item && item->set_func) {
+		nmc_property_set_default_value (setting, prop);
+		return TRUE;
+	}
+	g_set_error_literal (error, 1, 0, _("the property can't be changed"));
+	return FALSE;
+}
+
 /*
  * Generic function for removing items for collection-type properties.
  *

cli/src/settings.h

@@ -66,6 +66,9 @@ gboolean    nmc_setting_set_property (NMSetting *setting,
                                       const char *prop,
                                       const char *val,
                                       GError **error);
+gboolean    nmc_setting_reset_property (NMSetting *setting,
+                                        const char *prop,
+                                        GError **error);
 gboolean    nmc_setting_remove_property_option (NMSetting *setting,
                                                 const char *prop,
                                                 const char *option,