The Soviet Union was NOT socialist, regardless of what they called themselves. Nor were they true communists. The same reason why the Democratic People's Republic of Korea is not democratic, a republic, nor does it belong to the people. The same reason the People's Republic of China is neither a republic nor does it belong to the people. The same reason the United States of America is no longer United.
Too many people see the global political spectrum through American filters. True socialism is on the left side of that spectrum, basically one step further left than democratic socialism, which is what most American liberals are whether they realize it or not. Very few Americans are *true* socialists. So yes, socialism is a type of government based on the philosophy of liberalism.