[Pkg-utopia-maintainers] Bug#923046: flatpak segfaults in live-build hook

[Simon McVittie]

On Sat, 23 Feb 2019 at 16:23:20 +0100, Ronny Standtke wrote:
> Unfortunately, calling flatpak in a live-build hook fails with
> some dbus and polkit error messages and then flatpak segfaults
> ...
> (flatpak remote-add:9603): GLib-GIO-CRITICAL **:
> g_dbus_connection_register_object: assertion 'G_IS_DBUS_CONNECTION
> (connection)' failed
> 
> ** (flatpak remote-add:9603): CRITICAL **:
> polkit_authority_register_authentication_agent_with_options_sync:
> assertion 'POLKIT_IS_AUTHORITY (authority)' failed
> 
> Segmentation fault

These live-build hooks appear to be running in an environment where
you don't have a D-Bus system bus (dbus-daemon --system, provided
by the systemd system unit dbus.service or the LSB init script
/etc/init.d/dbus). I don't know whether live-build can provide a system
bus or other system services while the live system is being built.

Installing Flatpak apps and runtimes system-wide normally requires the
system bus and won't work without it. It shouldn't crash, and it's a
bug that it crashes, but you can't assume that it will *work* either -
when the crash has been fixed, the most likely result is that it will
still fail, but with a better error message.

It might be possible to install system-wide without D-Bus by
running flatpak(1) as root (uid 0), which would give the flatpak
process the necessary privileges to write to /var/lib/flatpak
directly, without needing to communicate with the system helper
/usr/libexec/flatpak-system-helper over D-Bus.

Alternatively, if the live image has an ordinary user, you should be able
to run `flatpak install --user` as that user, which will install apps
into the user's ~/.local/share/flatpak instead of into /var/lib/flatpak.
This might require a D-Bus session bus (dbus-run-session) but shouldn't
require a system bus.

> I tried prefixing the call to flatpak with dbus-run-session, but it
> still fails.

dbus-run-session provides a D-Bus session bus for the current user,
which is not the same as the D-Bus system bus (even if the current
user is root or messagebus). If something needs the system bus, then
dbus-run-session won't help, and that isn't a bug.

    smcv