If the leak has been fixed and dried out then the ceiling needs to be painted with 1 or 2 coats of stain block first to prevent the water stain from bleeding through the finished surface. You can then put a couple of coats of a good quality paint suitable for bathrooms on top of this.
Do not use an undercoat instead of the stain blocker if you go for the cheap method your ceiling will flash i.e.; you will notice two different shadow of white and they will not integrate together. The water based finish ceiling paint will not adhere cohesively to the oil based undercoat.
Sometimes moisture can still "seat" in the walls and ceiling especially if there is some insulation between you and neighbours level. Solution for some time is to get humidifier to take wet from the room and paint area with the stain block paint.