The answer is no, you don't need permission, but you do incur a legal and ethical risk whenever you do research, and as such, the more you can do to strengthen the legal and ethical arguments in your defense, the better.
IRBs are simply a way to say "I had an independent group of ethical and legal authority review my research and they thought it was ok".
IRBs are simply a way to say "I had an independent group of ethical and legal authority review my research and they thought it was ok".