Is it okay for a supervisor to require students to seek permission before publishing?
If you are including your supervisors name, or anyone else's name, you should notify them first and allow them to review the paper before sending it to the publisher. 

If you are just wanting to publish under your name alone, it depends. Are you publishing findings from data that belongs to your advisor (or anyone else's data)? Typically any data collected by you that was paid for by your funding agency belongs to the principal investigator, which is usually your advisor. You should ask for their permission before you publish findings from his or her data. 

This applies to abstract submissions as well.