My friend is a student at IIT Patna and shared his side of the story about city life there. Unlike the general misconception, Patna is rather a safe city.
He visited the city frequently to buy basic things and never did he feel unsafe or comfortable during the 4 years of his stay.
The campus of IIT Patna spreads across a massive 500 acres and is beautifully designed. The campus is still in its development phase but not to the extent that it will hamper your college life experience in any way. Students can be seen roaming around and indulging in sports such as table tennis and cricket.
As for the CS department, IIT Patna is very dynamic and has many clubs that will keep you motivated and interested in the field. I would certainly recommend you to go to IIT Patna and experience the bliss of college life.