Bug 695934

Desktop : Gnome or XFCE

If you run Xephyr directly does it work?  Are you seeing any AVC messages?

Yes Xephyr works.
Even launching directly /usr/share/sandbox/sandboxX.sh works.

Then you must be getting AVC's

I don't see any AVC in /var/log/messages.
Besides, the behavior is the same in permissive mode (setenforce 0).

In that case this is a problem of namespacing.  The $HOME and /tmp are being mounted over before the Xephyr is started.  I guess you would have to figure out the files that are being mounted over.  It could also be a bug in that NX is looking for /tmp/.X11-unix/X0 rather than using the abstract namespace.

Lets see if the nx guys have any ideas.

Could you explain this procedure in the program sandbox ?

def __copyfiles(self):
    files = self.__init_files + self.__paths
    homedir=pwd.getpwuid(os.getuid()).pw_dir
    for f in files:
         copyfile(f, homedir, self.__homedir)
         copyfile(f, "/tmp", self.__tmpdir)

Does it perform a copy of all files in homedir and /tmp to the mounted polyinstanciated folders ?
What represents the variable 'files' in the loop 'for f in files:' ?

sandbox -i and sandbox -I populate files.

For example.

sandbox -i ~/.mozilla -X -t sandbox_web_t -W metacity -w 1000x900 firefox $*

Does that mean that, unless -i is used, the mounted /tmp and homedir are empty ?

When trying under NX (with setenforce 0) :

sandbox -i ~/.mozilla -X xterm

the program aborts and displays 'File exists'. Is that normal ?

When trying :
sandbox -i /tmp/.X11-unix -X xterm
it displays :
[Errno 6] No such device or address: '/tmp/.X11-unix/X2000'

Same problem.  You would want to do 

sandbox -i NXFILES -X xterm to make this work.  What is happening I believe is some file used by NX to allow access to the remote display is not being passed.  It could be ~/.Xauthority or something like /tmp/.X11-unix directory.

What do these show?

echo $XAUTHORITY 
echo $DISPLAY

$XAUTHORITY is blank
$DISPLAY is :2000.0

Is NX only listening at /tmp/.X11-unix/X2000

and not at

@/tmp/.X11-unix/X2000

It should use that by default.

Apparently it is not a NX problem.

Indeed, the same problem occurs when I connect using ssh + XMing (Xserver under Windows).
I can launch xterm or Xephyr in a window but the command 'sandbox -X xterm' fails with the message 'Xephyr cannot open host display. Is DISPLAY set?'

Well they both have the same bug.  ssh and NX, in that they are relying on /tmp containing /tmp/.X11-unix/...

They both should be using abstract namespace like the X Server does.   Then the user can do what he wants with /tmp, including mount over it.

nx and freenx-server both have /tmp not @/tmp abstract namespace for /tmp/.X11-unix and several other nx specific bits.

One could s|/tmp/.X11-unix|@/tmp/.X11-unix|g on the source and hope for the best. Since nx/freenx are not linux specific a patch would not make it upstream.

Given that ssh is not likely to be patched, maybe there could be another solution to passing xauthority/display?

Any chance of just setting up fall backs.  This is what xlib is doing.  It tries both real and abstract namespace.

The same problem occurs using pam_namespace.so in /etc/pam.d/sshd.
Freenx does not work with a /tmp folder polyinstanciated.
It seems related to https://bugzilla.redhat.com/show_bug.cgi?id=503181.

The problem with pam_namespace.so and the polyinstanciation of /tmp is solved in adding in namespace.init :

if [ "$1" = /tmp ]; then
   mkdir -p -- "/tmp/.X11-unix"
   chmod 1777 "/tmp/.X11-unix"    
fi

The lack of the folder .X11-unix was preventing the execution of FreeNX.

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