cdrom: fix improper type cast, which can leat to information leak.

There is another cast from unsigned long to int which causes
a bounds check to fail with specially crafted input. The value is
then used as an index in the slot array in cdrom_slot_status().

This issue is similar to CVE-2018-16658 and CVE-2018-10940.

Signed-off-by: Young_X <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
(cherry picked from commit e4f3aa2)

Orabug: 28906151
CVE: CVE-2018-18710

Reviewed-by: Darren Kenny <[email protected]>
Signed-off-by: Allen Pais <[email protected]>

Author: Yoha-test

drivers/cdrom/cdrom.c

@@ -2441,7 +2441,7 @@ static int cdrom_ioctl_select_disc(struct cdrom_device_info *cdi,
 		return -ENOSYS;
 
 	if (arg != CDSL_CURRENT && arg != CDSL_NONE) {
-		if ((int)arg >= cdi->capacity)
+		if (arg >= cdi->capacity)
 			return -EINVAL;
 	}