Is it permissible to agree to purchase iron at today's price, on condition that it be delivered at the same price if it rises, and at a lower price if it falls?

The transaction described is a salam contract, but it contains two prohibitions: ignorance of the term, and linking the capital of the salam to a decrease in the price of iron. Therefore, the transaction is invalid and must be annulled. To rectify it, a known term for the subject of the salam must be specified, and the capital should not be linked to the price of iron when the term is due; rather, the price must be determined from now.