It varies from place to place. Rebels are only occupying buildings in Donetsk and Luhansk Oblasts. Generally control increases with the Ukrainian proportion of the population. Russia could help matters by not exploiting the situation for geopolitical advantage. For a start they should rule out military intervention and remove their menacing army from the Ukrainian border. And they could tell their propaganda channels to dampen down the sabre-rattling which appears to be about building a case for intervention.
A poll in April found only 15.4% of people in Eastern Ukraine support leaving Ukraine and 65% support a unitary Ukraine i.e. not federalisation.