Bug 104939

Summary: Tablet tools without ABS_Z cause a crash when updating rotation
Product: Wayland Reporter: Peter Hutterer <peter.hutterer>
Component: libinputAssignee: Wayland bug list <wayland-bugs>
Status: RESOLVED FIXED QA Contact:
Severity: normal    
Priority: medium CC: peter.hutterer
Version: unspecified   
Hardware: Other   
OS: All   
Whiteboard:
i915 platform: i915 features:
Bug Depends on:    
Bug Blocks: 104911    

Description Peter Hutterer 2018-02-04 23:26:23 UTC 
This affects tablets that are not listed in libwacom, specifically, tablets where libwacom does not provide the stylus axis information.

On tablet init, we check the event codes. A tablet may have ABS_Z and thus have rotation. Or it has BTN_TOOL_MOUSE + ABS_TILT_X/Y and thus have rotation. On init, all axes are marked as 'changed' to ensure we send the data in the first event. For non-libwacom tablets, the tool has the same bits set as the tablet provides, so if mouse+tilt is there, we have rotation on all tools. But the code itself relies on ABS_Z for rotation on all the styli (except mouse/lense).

In the case of Aiptek tablets we do have mouse+tilt but we *don't* have ABS_Z. If the first tool that comes into proximity is *not* the mouse/lens tool [1], we try to update the rotation by accessing ABS_Z. This leads to a null-pointer dereference in tablet_update_artpen_rotation() on the very first event.

See https://bugzilla.redhat.com/show_bug.cgi?id=1535755.

It doesn't matter that the tool never sends the actual events - because all axes are marked as 'changed' on proximity in, we always access the axis on the first event and crash.

[1] see also Bug 104911
Comment 2 Peter Hutterer 2018-02-07 01:47:25 UTC 
And for extra fun, the series starting here:
https://lists.freedesktop.org/archives/wayland-devel/2018-February/036853.html
Comment 3 Peter Hutterer 2018-02-09 02:28:46 UTC 
commit cbb4ec1e3e76b64ec53c25036976e0374aaf41de
Author: Peter Hutterer <peter.hutterer@who-t.net>
Date:   Mon Feb 5 09:11:42 2018 +1000

    tablet: don't set rotation on a tool if we don't have ABS_Z

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