[PATCH] libata: array underflow in ata_find_dev()

[PATCH] libata: array underflow in ata_find_dev()

[Dan Carpenter]

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>

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index d462c5a3a7ef..44ba292f2cd7 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -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];
 	}
 

Re: [PATCH] libata: array underflow in ata_find_dev()

[Tejun Heo]

Hello,

On Wed, Jul 19, 2017 at 01:06:41PM +0300, Dan Carpenter wrote:
> 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>

I'm impressed that the static checker caught this.  Thanks a lot for
the fix, and lol at the code. :) Applied to libata/for-4.13-fixes w/
stable cc'd.

Thanks!

-- 
tejun