HID: wacom: Fix sibling detection regression

Commit 345857b ("HID: wacom: generic: Add support for sensor offsets") included
a change to the operation and location of the call to 'wacom_add_shared_data'
in 'wacom_parse_and_register'. The modifications included moving it higher up
so that it would occur before the call to 'wacom_retrieve_hid_descriptor'. This
was done to prevent a crash that would have occured when the report containing
tablet offsets was fed into the driver with 'wacom_hid_report_raw_event'
(specifically: the various 'wacom_wac_*_report' functions were written with the
assumption that they would only be called once tablet setup had completed;
'wacom_wac_pen_report' in particular dereferences 'shared' which wasn't yet
allocated).

Moving the call to 'wacom_add_shared_data' effectively prevented the crash but
also broke the sibiling detection code which assumes that the HID descriptor
has been read and the various device_type flags set.

To fix this situation, we restore the original 'wacom_add_shared_data'
operation and location and instead implement an alternative change that can
also prevent the crash. Specifically, we notice that the report functions
mentioned above expect to be called only for input reports.  By adding a check,
we can prevent feature reports (such as the offset report) from
causing trouble.

Fixes: 345857b ("HID: wacom: generic: Add support for sensor offsets")
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Tested-by: Ping Cheng <pingc@wacom.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_sys.c

@@ -740,6 +740,11 @@ static int wacom_add_shared_data(struct hid_device *hdev)
 		return retval;
 	}
 
+	if (wacom_wac->features.device_type & WACOM_DEVICETYPE_TOUCH)
+		wacom_wac->shared->touch = hdev;
+	else if (wacom_wac->features.device_type & WACOM_DEVICETYPE_PEN)
+		wacom_wac->shared->pen = hdev;
+
 out:
 	mutex_unlock(&wacom_udev_list_lock);
 	return retval;
@@ -2036,10 +2041,6 @@ static int wacom_parse_and_register(struct wacom *wacom, bool wireless)
 	if (error)
 		goto fail;
 
-	error = wacom_add_shared_data(hdev);
-	if (error)
-		goto fail;
-
 	/*
 	 * Bamboo Pad has a generic hid handling for the Pen, and we switch it
 	 * into debug mode for the touch part.
@@ -2080,10 +2081,9 @@ static int wacom_parse_and_register(struct wacom *wacom, bool wireless)
 
 	wacom_update_name(wacom, wireless ? " (WL)" : "");
 
-	if (wacom_wac->features.device_type & WACOM_DEVICETYPE_TOUCH)
-		wacom_wac->shared->touch = hdev;
-	else if (wacom_wac->features.device_type & WACOM_DEVICETYPE_PEN)
-		wacom_wac->shared->pen = hdev;
+	error = wacom_add_shared_data(hdev);
+	if (error)
+		goto fail;
 
 	if (!(features->device_type & WACOM_DEVICETYPE_WL_MONITOR) &&
 	     (features->quirks & WACOM_QUIRK_BATTERY)) {

drivers/hid/wacom_wac.c

@@ -2187,6 +2187,16 @@ void wacom_wac_report(struct hid_device *hdev, struct hid_report *report)
 
 	wacom_report_events(hdev, report);
 
+	/*
+	 * Non-input reports may be sent prior to the device being
+	 * completely initialized. Since only their events need
+	 * to be processed, exit after 'wacom_report_events' has
+	 * been called to prevent potential crashes in the report-
+	 * processing functions.
+	 */
+	if (report->type != HID_INPUT_REPORT)
+		return;
+
 	if (WACOM_PAD_FIELD(field)) {
 		wacom_wac_pad_battery_report(hdev, report);
 		if (wacom->wacom_wac.pad_input)