If you are doing nothing wrong, you have nothing to worry about. It is being done for YOUR protection. I do hope you simply forgot the /sarcasm flag.
Legalities and rights aside, this was very foolish on the school's part. The ill will and low student morale this will cause is far beyond any good they might have thought could come from it.
If there was a clause in the contract which gave the school the right to search for contraband,this is a mute point. Waste of time arguing with that.