twm deadlocks the server

[Antoine Martin]

On 14/07/17 07:49, Aaron Plattner wrote:
> 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.
Indeed it is - thanks for the reminder.
Killing twm is the only option at that point.

AFAICT, the only way we can solve this problem in xpra is to use virtual
input devices instead of XTest.

Cheers
Antoine