block: cciss: fix information leak to userland

Structure IOCTL_Command_struct is copied to userland with
some padding fields at the end of the struct unitialized.
It leads to leaking of contents of kernel stack memory.
Signed-off-by: NVasiliy Kulikov <segooon@gmail.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

drivers/block/cciss.c

@@ -1184,6 +1184,7 @@ static int cciss_ioctl32_big_passthru(struct block_device *bdev, fmode_t mode,
 	int err;
 	u32 cp;
 
+	memset(&arg64, 0, sizeof(arg64));
 	err = 0;
 	err |=
 	    copy_from_user(&arg64.LUN_info, &arg32->LUN_info,