thats what Rubenstein said yesterday. "the investigation is limited and anything beyond Russia hacking needs his approval".

Actually I don't think this is what Rosenstein said. I think there is a distinction between crimes that are uncovered organically and crimes which are tangential and thus would require an investigation to start. Rosenstein emphasized no "fishing expeditions" and he didn't define Mueller's scope.

For example, if say, Paul Manafort confessed he colluded with Russia in this election AND confessed that he is guilty of money laundering. Mueller could prosecute both. There would be no need to move the money laundering to a different investigation. This is did not come about as part of a fishing expedition, it was a crime confessed to during the investigation.

Here's how LawNewz reported it

Deputy Attorney General Rod Rosenstein said on Sunday that Special Counsel Robert Mueller can investigate whatever crime he uncovers as part of the Russia probe. The thing is, Mueller has to check in with him first.

“The special counsel is subject to the rules and regulations of the Department of Justice and we don’t engage in fishing expeditions,” he told Fox News host Chris Wallace. “Bob Mueller understands and I understand the specific scope of the investigation, and so no, it’s not a fishing expedition.”

He said that Mueller needs to ask for permission before expanding the probe beyond its initial scope if investigators discover a crime outside the parameters.

“If it’s something outside that scope, he needs to come to the Acting Attorney General–at this time, me–for permission to expand his investigation,” he told Fox News host Chris Wallace.

Rosenstein did not specify in detail what that scope was.

So I think Rosenstein was being very careful with his words.