What is bug finder in codechef?
If you find a bug on the codechef website. For example that their rating system is not working properly and formula is wrong. Just an example. Anything like that if you find you will be rewarded 50-1000 laddus depending on how big the bug was.
If you find any kind of bug in CodeChef website then you can report about the bug on firstname.lastname@example.org and depending on the kind of bug you will be awarded rewards in the form of “Laddus” which you can redeem for the CodeChef goodies.