I travelled last year on China Eastern with transit at Shanghai and Kunming. Visa was not required. We do need to go through their immigration. They stamped "Stay Permit" valid for 24 hours on our passports during entry at Shanghai. And we need to submit Departure Card when we depart Kunming. During the transit, I suggest to stay well inside the airport and don't even step anywhere near the Airport gates. Sometimes the officers stop and ask questions such as where are you going. I would suggest to wait close to your Check-in counters. If you plan to go out of airport or transit is more than 24 hours, then you need to apply for visa beforehand.