It's not legal.

I asked a colleague at O'Reilly about this a few months ago, having found a Russian web site with all of the released CD bookshelves available.

Copyright law, in the US, sometimes makes an exception for educational purposes. If your teacher only wants to make the books available to his students, there might be an exception.

If that is the case, I would recommend he send a short e-mail to either Tim O'Reilly or Frank Willison, explaining the situation and asking for clarification.