twm deadlocks the server

[Aaron Plattner]

On 07/03/2017 10:41 PM, Antoine Martin wrote:
> Hi,
> 
> I've just come across this easy DoS with twm and
> X.Org X Server 1.19.3 from Fedora 26.
> 
> Steps:
> /usr/libexec/Xorg -noreset -novtswitch -config /etc/xpra/xorg.conf :10&
> #verify we can access the display:
> DISPLAY=:10 xprop -root
> #start xterm so we have a window, then twm:
> DISPLAY=:10 xterm&
> DISPLAY=:10 twm&
> #now click on the title bar of the xterm:
> DISPLAY=:10 xdotool mousemove 90 10 mousedown 1
> #and now the X11 server is inaccessible:
> DISPLAY=:10 xprop -root

Isn't this just twm grabbing the server? If you can connect to the 
server to launch twm, you can also just call XGrabServer() and not let go.

> Cheers
> Antoine
> 
> PS: the xorg.conf to use for the dummy driver can be found here:
> http://xpra.org/trac/browser/xpra/tags/v2.0.x/src/etc/xpra/xorg.conf