Kernel Stack info leak at exportObjectToClient function

bug details:

macOS<=10.14.3 && iOS < 12.2

There is a bug at Function exportObjectToClient in IOKit class, which can lead to leak 4 bytes of kernel stack info. exportObjectToClient just like its name which make an arbitrary OSObject available to the client task.It’s a basic function, many other kernel function use it .

IOReturn IOUserClient::exportObjectToClient(task_t task, OSObject *obj, io_object_t *clientObj)

{ mach_port_name_t name; name = IOMachPort::makeSendRightForTask( task, obj, IKOT_IOKIT_OBJECT ); *(mach_port_name_t *)clientObj = name; // (1). force the type convert to mach_port_name_t if (obj) obj->release(); return kIOReturnSuccess; }

We know io_object_t length is 8 bytes and at (1) which was force convert to mach_port_name_t(4 bytes) ,so lead to the high 4 bytes not inital