HID: wacom: Avoid using stale array indicies to read contact count

If we ever see a touch report with contact count data we initialize
several variables used to read the contact count in the pre-report
phase. These variables are never reset if we process a report which
doesn't contain a contact count, however. This can cause the pre-
report function to trigger a read of arbitrary memory (e.g. NULL
if we're lucky) and potentially crash the driver.

This commit restores resetting of the variables back to default
"none" values that were used prior to the commit mentioned
below.

Link: https://github.com/linuxwacom/input-wacom/issues/276
Fixes: 003f50ab673c (HID: wacom: Update last_slot_field during pre_report phase)
CC: stable@vger.kernel.org
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index 92b52b1de526ba58d1e93f7f3910e758e31dc19f..a7176fc0635dd2b7aa0fd7977938f8feb9b6a2ec 100644 (file)
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -2682,6 +2682,10 @@ static void wacom_wac_finger_pre_report(struct hid_device *hdev,
 
        hid_data->confidence = true;
 
+       hid_data->cc_report = 0;
+       hid_data->cc_index = -1;
+       hid_data->cc_value_index = -1;
+
        for (i = 0; i < report->maxfield; i++) {
                struct hid_field *field = report->field[i];
                int j;