cachefiles: add consistency check for copen/cread

In the Linux kernel, the following vulnerability has been resolved: cachefiles: add consistency check for copen/cread This prevents malicious processes from completing random copen/cread requests and crashing the system. Added checks are listed below: * Generic, copen can only complete open requests, and cread can only complete read requests. * For copen, ondemand_id must not be 0, because this indicates that the request has not been read by the daemon. * For cread, the object corresponding to fd and req should be the same.