HID: multitouch: validate indexes details

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

Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-multitouch.c

@@ -101,9 +101,9 @@ struct mt_device {
 	unsigned last_slot_field;	/* the last field of a slot */
 	unsigned mt_report_id;	/* the report ID of the multitouch device */
 	unsigned pen_report_id;	/* the report ID of the pen device */
-	__s8 inputmode;		/* InputMode HID feature, -1 if non-existent */
-	__s8 inputmode_index;	/* InputMode HID feature index in the report */
-	__s8 maxcontact_report_id;	/* Maximum Contact Number HID feature,
+	__s16 inputmode;	/* InputMode HID feature, -1 if non-existent */
+	__s16 inputmode_index;	/* InputMode HID feature index in the report */
+	__s16 maxcontact_report_id;	/* Maximum Contact Number HID feature,
 				   -1 if non-existent */
 	__u8 num_received;	/* how many contacts we received */
 	__u8 num_expected;	/* expected last contact index */
@@ -312,20 +312,18 @@ static void mt_feature_mapping(struct hid_device *hdev,
 		struct hid_field *field, struct hid_usage *usage)
 {
 	struct mt_device *td = hid_get_drvdata(hdev);
-	int i;
 
 	switch (usage->hid) {
 	case HID_DG_INPUTMODE:
-		td->inputmode = field->report->id;
-		td->inputmode_index = 0; /* has to be updated below */
-
-		for (i=0; i < field->maxusage; i++) {
-			if (field->usage[i].hid == usage->hid) {
-				td->inputmode_index = i;
-				break;
-			}
+		/* Ignore if value index is out of bounds. */
+		if (usage->usage_index >= field->report_count) {
+			dev_err(&hdev->dev, "HID_DG_INPUTMODE out of range\n");
+			break;
 		}
 
+		td->inputmode = field->report->id;
+		td->inputmode_index = usage->usage_index;
+
 		break;
 	case HID_DG_CONTACTMAX:
 		td->maxcontact_report_id = field->report->id;
@@ -511,6 +509,10 @@ static int mt_touch_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 			mt_store_field(usage, td, hi);
 			return 1;
 		case HID_DG_CONTACTCOUNT:
+			/* Ignore if indexes are out of bounds. */
+			if (field->index >= field->report->maxfield ||
+			    usage->usage_index >= field->report_count)
+				return 1;
 			td->cc_index = field->index;
 			td->cc_value_index = usage->usage_index;
 			return 1;