If a person who has become junub before fajr, thinks he has enough time for ghusl and starts the ghusl.
However, before finishing the ghusl, the fajr time has begun, and he has still not completed his ghusl. Is his fast in order and will there be any kazaa or kaffara?

If there was such short time, tayammum was necessary not Ghusl

Qadha and kaffara would be due if he was able to find out the masala which is already published online and in the books