Allow to skip data dir permission checks by config

Enables installation on services that don't allow/support permission
changes.

Signed-off-by: Arthur Schiwon <blizzz@arthur-schiwon.de>

config/config.sample.php

@@ -645,6 +645,18 @@ $CONFIG = array(
  */
 'check_for_working_htaccess' => true,
 
+/**
+ * In rare setups (e.g. on Openshift or docker on windows) the permissions check
+ * might block the installation while the underlying system offers no means to
+ * "correct" the permissions. In this case, set the value to false.
+ *
+ * In regular cases, if issues with permissions are encountered they should be
+ * adjusted accordingly. Changing the flag is discouraged.
+ *
+ * Defaults to ``true``
+ */
+'check_data_directory_permissions' => true,
+
 /**
  * In certain environments it is desired to have a read-only configuration file.
  * When this switch is set to ``true`` Nextcloud will not verify whether the

lib/private/legacy/util.php

@@ -959,8 +959,11 @@ class OC_Util {
 	 * @return array arrays with error messages and hints
 	 */
 	public static function checkDataDirectoryPermissions($dataDirectory) {
+		if(\OC::$server->getConfig()->getSystemValue('check_data_directory_permissions', true) === false) {
+			return  [];
+		}
 		$l = \OC::$server->getL10N('lib');
-		$errors = array();
+		$errors = [];
 		$permissionsModHint = $l->t('Please change the permissions to 0770 so that the directory'
 			. ' cannot be listed by other users.');
 		$perms = substr(decoct(@fileperms($dataDirectory)), -3);