They aren't in a position to bite the hand that is humiliating and controlling trump.
Putin has calculated the costs, and he has set his course. He doesn't care about iran except to the extent that he can use it to increase his leverage in the region. He certainly doesn't want a strong and independent iran. He has enough ethnic troubles at home without having to worry about a foreign power fanning the flames.
No unintended consequences yet. And none likely.
He wants instability in the region. He wants trump to remain in office. He wants to increase his grip on the region.
Iran is in a tight spot. They can't let this go unanswered for domestic reasons. They can't let it escalate to all out war. They would surely lose an all out war, at least from an internal stability standpoint if not flat out losing territory. They could end up like syria, with a patchwork of foreign powers and rebel groups controlling territory.
But what can they do? Sink ships? Shoot down aircraft? IED's? Terror strikes? Cyber attacks?
They might find allies for a cyber war. Trump has slashed funding for cyber defense. North Korea, Russia, China, etc, might be willing to help under cover of proxies. That could really hurt. And troops wouldn't be triggered.
Plus, trump is an idiot and since he has shredded the nsc and other agency intelligence networks, he is as much in the dark over what the response will be as we are.