Merge branch 'patch-php-sess-tmp-safe-exec' into 'stable-3.1'

Fix exec to exec_safe to make placeholder work again, #5434 #5510

See merge request ispconfig/ispconfig3!946

Author: Till Brehm

server/lib/classes/cron.d/200-logfiles.inc.php

@@ -217,7 +217,7 @@ public function onRunJob() {
 			foreach($records as $rec){
 				$tmp_path = realpath($rec['document_root'].'/tmp');
 				if($tmp_path != '' && strlen($tmp_path) > 10 && is_dir($tmp_path) && $app->system->is_user($rec['system_user'])){
-					exec("cd ?; find . -mtime +1 -name 'sess_*' | grep -v -w .no_delete | xargs rm > /dev/null 2> /dev/null", $tmp_path);
+					$app->system->exec_safe("cd ?; find . -mtime +1 -name 'sess_*' | grep -v -w .no_delete | xargs rm > /dev/null 2> /dev/null", $tmp_path);
 				}
 			}
 		}