HID: multitouch: Fix fields from pen report ID being interpreted for multitouch

Fields like HID_DG_CONTACTCOUNT are outside of the physical collection,
but within the application collection and report ID.  Make sure to catch
those fields that are not part of the mt_report_id and return 0 so they
can be processed with the pen.  Otherwise, the wrong HID_DG_CONTACTCOUNT
will be applied to cc_index and result in dereferencing a null pointer in
mt_touch_report.

Signed-off-by: Brent Adam <brentadam@smarttech.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 6a9b05b328a9d40e06b09ed8f8c6e6010669374b..7c811252c1cefebb2418944a7f391117a8a92b6d 100644 (file)
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -778,9 +778,16 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
        /*
         * some egalax touchscreens have "application == HID_DG_TOUCHSCREEN"
         * for the stylus.
+        * The check for mt_report_id ensures we don't process
+        * HID_DG_CONTACTCOUNT from the pen report as it is outside the physical
+        * collection, but within the report ID.
         */
        if (field->physical == HID_DG_STYLUS)
                return 0;
+       else if ((field->physical == 0) &&
+                (field->report->id != td->mt_report_id) &&
+                (td->mt_report_id != -1))
+               return 0;
 
        if (field->application == HID_DG_TOUCHSCREEN ||
            field->application == HID_DG_TOUCHPAD)