Follow along this post and you'll end up with one case in the wild all by yourself on your own machine: https://theinvisiblethings.blogspot.com/2011/04/linux-securi...
Xace was designed to address the mess that is Xsecurity and using the SELinux sandbox for GUI apps, except Xace barely works for mitigating exploits well on the desktop; it's so finicky that Dan Walsh himself concluded that XACE does not work and instead opted to use nested X servers (!!): http://people.fedoraproject.org/~dwalsh/SELinux/Presentation...