Undermining XGrabKeyboard

Octavio Alvarez alvarezp at alvarezp.ods.org
Tue Mar 4 08:27:24 PST 2008

On Tue, 2008-03-04 at 17:16 +0100, Sebastian wrote:
> even a non-setuid application can make a core grab requesting all input
> with a XGrabKeyboard(d,w,True,GrabModeSync,GrabModeSync,CurrentTime).
> If it fails to propagate this input unconsciously or maliciously, this
> results in a non-responding desktop where I can not intervene even with
> the Ctrl+Alt+Backspace or the virtual terminal combos. (Running on a
> i386 Linux) 
> As I can't remote login into the machine this means the machine is
> effectivly hung at this point (even if it's not in a technically sense).

In xorg.conf:

Section "ServerFlags"
  Option "AllowDeactivateGrabs" "On"
  Option "AllowClosedownGrabs" "On"

This should allow you to release grabs with Ctrl+Alt+* and Ctrl+Alt+/.


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