A method, apparatus and computer program product for performing authorization control in a cloud storage system. The method comprises: receiving an access request to a file block, wherein the file block is embedded with tag data comprising at least file block authorization information; retrieving the file block; extracting the file block authorization information from the tag data; determining whether the access request matches the file block authorization information; and performing the access request if the access request matches the file block authorization information. Effective authorization control may be performed in a cloud storage system.