add a disk_free_space check before writing config

Signed-off-by: Simon L <szaimen@e.mail.de>

Author: szaimen

lib/private/Config.php

@@ -290,6 +290,12 @@ private function writeData() {
 			throw new \Exception(sprintf('Could not acquire an exclusive lock on the config file %s', $this->configFilePath));
 		}
 
+		// Never write file back if disk space should be low (less than 100 KiB)
+		$df = disk_free_space($this->configDir);
+		if ($df !== false && (int)$df < 102400) {
+			throw new \Exception($this->configDir . " does not have enough space for writing the config file! Not writing it back!");
+		}
+
 		// Write the config and release the lock
 		ftruncate($filePointer, 0);
 		fwrite($filePointer, $content);