I live in an apartment building. Each house has a bathroom with a concrete floor covered in tiles. In the corner of the floor is a drain with its pipe going all the way through. However, I have noticed water leaking into my roof space from the upstairs neighbor's bathroom. The leak seems to be through the join between the drain pipe and the concrete.
What is the best way to seal this floor so that the water will stop leaking through?
Edit: Added a view of the pipe from above as people are clearly miss understanding the situation.