Add file permission check on config.

main.py

@@ -39,6 +39,8 @@ class BaseConfig(dict):
             if self.file == '-':
                 config = yaml.load(sys.stdin, Loader=Loader)
             else:
+                if os.stat(self.file).st_mode & 0o777 & ~0o600:
+                    raise Exception('refusing to load insecure configuration file, file must have permission 0o600')
                 with open(self.file) as fp:
                     config = yaml.load(fp, Loader=Loader)
             if config is None: