The current version of the Russian Constitution declares the priority of Russian law over international law. Putin made a request to the State Duma to use the army outside of Russia in the interests of Russia and the Duma said yes, and the Council of Federations also approved this. All the formalities have been met, in principle Putin is acting within the legal framework of Russia, so the answer to your question is yes.

I would formulate the question differently in the current realities: Can anyone stop Putin to tell Ukraine what they can and cannot do in their country?