[PATCH 3.2 172/185] HID: multitouch: validate indexes details

Ben Hutchings
2013-12-29T02:08:44Z

From: Benjamin Tissoires <benjamin.tissoires@redhat.com>

commit 8821f5dc187bdf16cfb32ef5aa8c3035273fa79a upstream.

When working on report indexes, always validate that they are in bounds.
Without this, a HID device could report a malicious feature report that
could trick the driver into a heap overflow:

[ 634.885003] usb 1-1: New USB device found, idVendor=0596, idProduct=0500
...
[ 676.469629] BUG kmalloc-192 (Tainted: G W ): Redzone overwritten

Note that we need to change the indexes from s8 to s16 as they can
be between -1 and 255.

CVE-2013-2897

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
[bwh: Backported to 3.2: mt_device::{cc,cc_value,inputmode}_index do not
exist and the corresponding indices do not need to be validated.
mt_device::maxcontact_report_id does not exist either. So all we need
to do is to widen mt_device::inputmode.]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -66,7 +66,7 @@ struct mt_device {
unsigned last_field_index; /* last field index of the report */
unsigned last_slot_field; /* the last field of a slot */
int last_mt_collection; /* last known mt-related collection */
- __s8 inputmode; /* InputMode HID feature, -1 if non-existent */
+ __s16 inputmode; /* InputMode HID feature, -1 if non-existent */
__u8 num_received; /* how many contacts we received */
__u8 num_expected; /* expected last contact index */
__u8 maxcontacts;