nixos/virtualbox/hostonlyif: Fix writing to /root.

Creates unnecessary cruft in the root users home directory, which we
really don't need. Except the log, but therefore we now cat the log to
stderr and the private temporary directory is cleaned up afterwards.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
(cherry picked from commit d85fabd68c)

nixos/modules/programs/virtualbox-host.nix

@@ -97,10 +97,13 @@ in
         path = [ virtualbox ];
         serviceConfig.RemainAfterExit = true;
         serviceConfig.Type = "oneshot";
+        serviceConfig.PrivateTmp = true;
+        environment.VBOX_USER_HOME = "/tmp";
         script =
           ''
             if ! [ -e /sys/class/net/vboxnet0 ]; then
               VBoxManage hostonlyif create
+              cat /tmp/VBoxSVC.log >&2
             fi
           '';
         postStop =

nixos/tests/virtualbox.nix

@@ -348,6 +348,7 @@ in {
 
     subtest "privilege-escalation", sub {
       $machine->fail("test -e '/root/VirtualBox VMs'");
+      $machine->fail("test -e '/root/.config/VirtualBox'");
       $machine->succeed("test -e '/home/alice/VirtualBox VMs'");
     };