Comment 0 for bug 1218107

We discussed DBus APIs in relation to application confinement in various places and decided that services that require DBus mediation, click packaging and apparmor should all agree on how to derive an application-specific DBus path. The concept of the APP_ID is central to click, the SDK, application lifecycle, apparmor and DBus services that applications use. The APP_ID is of the form:
$pkgname_$appname_$version

and this is derived from the click manifest. Eg:
  com.ubuntu.dropping-letters_dropping-letters_0.1.2.2

Application lifecycle will export the APP_ID to the environment. The click-apparmor hook creates the @{APP_ID_DBUS} variable in apparmor policy for use in dbus rules. click-apparmor uses nih_dbus_path() from libnih-dbus to generate the @{APP_ID_DBUS}. Eg, for com.ubuntu.dropping-letters_dropping-letters_0.1.2.2, we would have:
  @{APP_ID_DBUS}="com_2eubuntu_2edropping_2dletters_5fdropping_2dletters_5f0_2e1_2e2_2e2"

This allows us to have rules like this in apparmor policy:
  dbus (send)
      bus=session
      path="/com/canonical/hud/applications/@{APP_ID_DBUS}",

However, the HUD is generating a different value for its path, as seen in this dbus apparmor denial:
dbus[3390]: apparmor="DENIED" operation="dbus_method_call" bus="session" name=":1.641" path="/com/canonical/hud/applications/com_ubuntu_dropping_letters_dropping_letters_0_1_2_2" interface="org.freedesktop.DBus.Properties" member="GetAll" mask="send" pid=23875 profile="com.ubuntu.dropping-letters_dropping-letters_0.1.2.2" peer_pid=22913 peer_profile="unconfined"

Please adjust the hud to use libnih-dbus. Attached is a test C program to demonstrate how to do this.