How to change default file permission of log files in /var/log/logstash/

I want to change the default file permission of logstash's log files as 600, currently it is 644.
In logstash.yml file I found only the file path and log level related information but I didn't get any file permission related info.
so can any one suggest how to change it?

You may be able to adjust it in the log4j2 configuration. See here.