Pointer grabs causing accessibility issues! Why not deprecate them?

Peter Hutterer mailinglists at who-t.net
Wed Apr 30 20:44:35 PDT 2008

Eamon Walsh wrote:
> Francesco Fumanti wrote:
>>> Honestly I'm increasingly convinced that MPX is the best way to solve 
>>> this problem, and related problems such as separating input by security 
>>> level.
>>> Create a new virtual mouse/keyboard that no one else can see and use to 
>>> it to get the password.
>> Wikipedia just informed me that MPX stands for Multi-Pointer X Server. ;-)
>> But how does it solve the pointer grabbing issue: could an application 
>> not simply grab the events of all pointers and keyboards?
> This can be controlled through security policy or an extension.  Devices 
> are referenced by number in protocol requests and the device lookup 
> function does a permission check.  MPX has some built-in access 
> controls.  There's almost certainly work to be done but the concept of a 
> private device (that could still be seen by input helpers) seems not too 
> far-fetched.  Under this scenario the password dialog would not need to 
> perform a grab.

MPX access control is _NOT_ a security feature*. It's a GUI feature to 
avoid events being sent to specific elements.
When you have N users clicking on the same UI at the same time, it can 
be helpful to say "button X only responds to user X". MPX allows do to 
this simply, but that's about it. Events still get sent, albeit to 
different windows and/or clients.

* I don't see why it couldn't be made into one, but I'm not a security 
guy. Feel free to look at it and help me improve it.


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