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libata: array underflow in ata_find_dev()

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My static checker complains that "devno" can be negative, meaning that
we read before the start of the loop.  I've looked at the code, and I
think the warning is right.  This come from /proc so it's root only or
it would be quite a quite a serious bug.  The call tree looks like this:

proc_scsi_write() <- gets id and channel from simple_strtoul()
-> scsi_add_single_device() <- calls shost->transportt->user_scan()
   -> ata_scsi_user_scan()
      -> ata_find_dev()

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # all versions at this point
This commit is contained in:
Dan Carpenter 2017-07-19 13:06:41 +03:00 committed by Tejun Heo
parent 6ac1d1532c
commit 59a5e266c3
1 changed files with 4 additions and 2 deletions
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6
drivers/ata/libata-scsi.c
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@ -3030,10 +3030,12 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc)
static struct ata_device *ata_find_dev(struct ata_port *ap, int devno)
{
if (!sata_pmp_attached(ap)) {
if (likely(devno < ata_link_max_devices(&ap->link)))
if (likely(devno >= 0 &&
devno < ata_link_max_devices(&ap->link)))
return &ap->link.device[devno];
} else {
if (likely(devno < ap->nr_pmp_links))
if (likely(devno >= 0 &&
devno < ap->nr_pmp_links))
return &ap->pmp_link[devno].device[0];
}