[PATCH 3.16 033/294] libata: array underflow in ata_find_dev()

From: Ben Hutchings
Date: Mon Nov 06 2017 - 19:17:32 EST


3.16.50-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

commit 59a5e266c3f5c1567508888dd61a45b86daed0fa upstream.

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@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
drivers/ata/libata-scsi.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -2796,10 +2796,12 @@ static unsigned int atapi_xlat(struct at
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];
}