Pvc. That's a tough one to do without removing either a piece of the ceiling downstairs or part of the floor around the flange. The ceiling will cost less to repair than the floor will. This is in order to repair it correctly. There are some repair methods available but I'm not a big fan of just patching it up. There's a couple of steel flanges that can be screwed into the floor and they sit on top of the existing flange. Something you can find at any home depot.