Is castling legal regarding rooks passing over attacked squares? I was playing a game of chess and I was playing black. I had a rook on b2. I had control of the b1 square. My opponent white did not have any pawns in the second  rank. My opponent; white castled queenside. Is it illegal for his rook to pass the b1 square considering his rook passed the b1 square I had control of. Wouldn't it make this castle move illegal on white's part?
It is still possible to castle if the rook passes through squares that are attacked(under control by opponent's rook e.g. as you say), it's only in the case of the king that such scenario prohibits you from castling.

Have a look at the post Cleveland has suggested in the comments.

Here's an example anyway: 

[Title "O-O-O"]
[StartFlipped "0"]
[fen "2bk2nr/p1p2ppp/2p5/2p5/2P1P3/2N5/Pr3PPP/R3KB1R w KQkq - 0 1"]

1.O-O-O+