The official line was that photography of railways in the Eastern Bloc was forbidden. Full stop. But there were a number of exceptions to that rule. The Austrian railway publisher and writer Josef Slezak was one such. He appears to have made a number of trips to the Soviet Union looking at and engaging in some limited photography of railways, with apparent offical approval.
Whether he made a useful contact during the Soviet occupation of Vienna can only be speculated at. But this book, which contains a lot of information about Soviet railways on a physical, economic and technical basis, can only have been produced with a degree of co-operation from the authorities. As such, it is a useful source, as most Western books on Soviet railways concentrate on the locomotives for the most part.