[apparmor] May a GUI program be manipulated via a display server socket?

[me at beroal.in.ua]

Hi. Suppose that a program M (malicious) tries to open a URL in a web 
browser V (victim). In a typical AppArmor profile for M, V is executed 
with the `Px` mode, for example:

```
/usr/lib/firefox/firefox Px,
```

Can M give V an environment variable (`WAYLAND_DISPLAY` for Wayland or 
`DISPLAY` for X11) which tells V to execute user input from a Unix 
socket which M controls? If yes, then M can do something on websites 
under the name of a user. In other words, V isn't isolated after all.

I'm worried because this situation is quite common. Many programs are 
expected to open a URL, and many jobs are controlled via a web browser 
nowadays.