Bug#807878: gnome: Gnome freezes when root windows are open on user screen.

[Laurent Bigonville]

On Sun, 13 Dec 2015 22:28:41 -0300 Edilson Azevedo <edilsona6 at aim.com> 
wrote:
 > Package: gnome
 > Version: 1:3.14+3
 > Severity: critical
 > Justification: causes serious data loss
 >
 > *** Scenario ***
 >
 > Non-classic gnome logged as a regular user and some root windows 
open. e.g.
 > synaptic, nautilus-as-root, root-terminal, etc.
 >
 > *** Causing the problem ***
 >
 > Hitting the upper left corner of the screen with mouse cursor - or - 
clicking
 > over Activities.
 >
 > *** Problem ***
 >
 > Screen freezes (no usual shrink) cursor moves. No reaction to clicks.
 >
 > *** Observation ***
 >
 > top, running on a <ctrl><alt><F1-6> text window shows 
gnome-settings-daemon
 > busy (50%).
 >
 > Logs like syslog, messages, etc. get huge filled with several 
messages like
 > below:
 >
 > <<< gnome-session[1367]: (gnome-settings-daemon:1434): dconf-CRITICAL **:
 > unable to create file '/run/user/1000/dconf/user': Access denied. 
dconf will
 > not work properly. >>>
 >
 > ls -l /run/user/1000/dconf/user --> -rw------- 1 root root 2 Dec 13 21:42
 > /run/user/1000/dconf/user !!!
 > rebooting:
 > ls -l /run/user/1000/dconf/user --> -rw------- 1 user user 2 Dec 13 21:54
 > /run/user/1000/dconf/user
 >
 > *** My conclusion ***
 >
 > For some reason the owner of the file referred above turns from user 
to root.
 > >From this moment on gnome system is desperately trying to access it 
as user,
 > overloading the machine, filling logs with same message, and no escape.
 >
 > *** My comments ***
 >
 > 1) As I don't know which part of software is responsible for
 > /run/user/1000/dconf/user writing and creation I blame gnome.
 > 2) It can be harmful to the system because when one doesn't what to 
do, he/she
 > will press reset button and get corrupted files.
 > 3) A workaround for the crash is to hit <ctrl><alt><F1-6> and 
<ctrl><alt><del>.
 > 4) By now, when I need work as root, I hit <ctrl><alt><F1-6> and 
startx. Some
 > say it might lead to safety problems ...
 >
 > Thanks for your patience, anyway, I believe solution is closer.

Well you should never start a X session as root, as you mentioned, this 
has security implications.

Can you still reproduce this now?

Are you using systemd as PID 1? If I'm not wrong, /run/user/<UID> is 
created by logind. What is loginctl and loginctl show-session 
<session-number> showing you?

Cheers,

Laurent Bigonville