There are a few interesting arguments to work through here. Official media such Pravda, Izvestia, Komsomolskaya and Pionerskaya Pravda did speak of the Polish invasion, and characteristically implicated Britain and France in the build-up to the invasion.

On September 1st, Pravda runs the story “On the Ratification of the Soviet-German Non-Aggression Pact,” a speech given by Molotov on August 31st, about a week after it was signed. This speech closely allies Poland with England and France, "because [Poland] refused the military help of the Soviet Union"

The Soviet Union invaded Poland just weeks after the German invasion, and the front page of the November 1st Pravda is the story “On the Foreign Policy of the Soviet Union.” One passage from this story is quite telling:

The attempts of the English and French governments to justify this new position by the commitments given to Poland are certainly, obviously indefensible. For the restoration of the old Poland, as all know, is not an option. Therefore, it is meaningless to continue the present war under the flag of the restoration of the former Polish state.... [Pravda 303, 1939]

The pact would receive an amendment on September 28 further dividing Central Europe, and again just before Germany would invade the Soviet Union they professed to relinquish portions of the Baltic.

However, the way these state papers talk about the German invasions, particularly of the actual underpinnings of the Molotov-Ribbentrop Pact, is characterized by a paper on the topic as:

From the perspective of [the official] account, there is nothing to say about the secret protocols of the pact since they simply did not exist: the fact that the Baltic countries became part of the USSR had nothing to do with spheres of influence or any other form of external coercion… [2]

The exact place of the Molotov-Ribbentrop pact in Soviet foreign policy is unclear;

The question can be asked whether the policies of 1939 - 1941 should be viewed as an extension of the policies of the 1930s or whether they reflected a reorientation of Soviet policy after the Munich agreement [1]

One of the more interesting things about newspapers preceding the pact is that German aggression was critically spoken of. So, before late August, Soviet media has Germany as the invader and the fascist; after, the liberator, or just the lion you can always trust to bite. England, France, and America are to blame. By summer 1941, of course, this reverses. In the interim German bombings of England are reported rather straightforwardly from what I can see.

Another paper draws from the official history of the Soviet Union by 1970 (do note, however, that the view of Stalin had radically shifted from 1953/1956 by this point) quoting that

”[I]n August 1939 Hitler’s government proposed a non-aggression pact to the Soviet Government. The Soviet Union was threatened with war on two fronts—in Europe and the Far East—and was completely isolated. The Soviet Government, therefore, agreed to make a pact of non-aggression with Germany. Subsequent events revealed that this step was the only correct one under the circumstances. By taking it the USSR was able to continue peaceful construction for nearly two years and to strengthen its defenses.” [2]

This exculpatory characterization would persist until nearly the dissolution of the Soviet Union, despite Western knowledge of the pact. Ribbentrop was executed after the Nuremberg Trials, while Molotov, who remained First Deputy under Stalin and Malenkov, was dismissed by Khrushchev in 1957.

In 1948, the United States published a collection of German documents as Nazi–Soviet Relations, 1939–1941: Documents from the Archives of The German Foreign Office that Stalin personally responded to with the brief book Falsifiers of History which again places blame on England and France for the German invasion of Poland, and now blames the United States for a variety of rather credulous crimes.

[1] Thompson, Ewa M. "Nationalist Propaganda in the Soviet Russian Press, 1939-1941." Slavic Review 50, no. 2 (1991): 385-399.

[2] Wertsch, James V. "Blank spots in collective memory: A case study of Russia." AAPSS 617, no. 1 (2008): 58-71.