[gdm/benzea/fix-multiple-greeter-sessions: 2/2] session: Always use separate session bus for greeter sessions

[Benjamin Berg <bberg src gnome org>]

commit c1b863a9b977afd7f3ec52281b6958e382f2a532
Author: Benjamin Berg <bberg redhat com>
Date:   Thu Apr 16 15:17:56 2020 +0200

    session: Always use separate session bus for greeter sessions
    
    This is a workaround for the fact that we currently need to run multiple
    greeter sessions in multi-seat environments that use the same user. We
    should not be doing this in the first place. Doing this effectively
    prevents GNOME from using a systemd startup, which would cause relevant
    processes to be outside of the session scope preventing lookups of the
    logind session from the PID.
    
    Instead, we really should be running each of the greeter session as a
    separate (dynamic) user. But lacking that, this workaround should get
    multi-seat support up and running again for the time being.
    
    See: #526

 NEWS                 |  3 +++
 daemon/gdm-session.c | 26 ++++++++++++++++++--------
 2 files changed, 21 insertions(+), 8 deletions(-)
---
diff --git a/NEWS b/NEWS
index eba83b06..0ec0c08f 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,6 @@
+- Always use separate session bus for greeter sessions
+  This runs dbus-run-session, so the binary needs to be available
+
 ==============
 Version 3.34.1
 ==============
diff --git a/daemon/gdm-session.c b/daemon/gdm-session.c
index 4e303e70..ca7d98f1 100644
--- a/daemon/gdm-session.c
+++ b/daemon/gdm-session.c
@@ -2900,23 +2900,33 @@ gdm_session_start_session (GdmSession *self,
 
                 g_free (command);
         } else {
+                /* FIXME:
+                 * Always use a separate DBus bus for each greeter session.
+                 * Firstly, this means that if we run multiple greeter session
+                 * (which we really should not do, but have to currently), then
+                 * each one will get its own DBus session bus.
+                 * But, we also explicitly do this for seat0, because that way
+                 * it cannot make use of systemd to run the GNOME session. This
+                 * prevents the session lookup logic from getting confused.
+                 * This has a similar effect as passing --builtin to gnome-session.
+                 *
+                 * We really should not be doing this. But the fix is to use
+                 * separate dynamically created users and that requires some
+                 * major refactorings.
+                 */
                 if (run_launcher) {
                         if (is_x11) {
-                                program = g_strdup_printf (LIBEXECDIR "/gdm-x-session %s\"%s\"",
+                                program = g_strdup_printf (LIBEXECDIR "/gdm-x-session %s\"dbus-run-session 
-- %s\"",
                                                            register_session ? "--register-session " : "",
                                                            self->selected_program);
                         } else {
-                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session %s\"%s\"",
+                                program = g_strdup_printf (LIBEXECDIR "/gdm-wayland-session 
%s\"dbus-run-session -- %s\"",
                                                            register_session ? "--register-session " : "",
                                                            self->selected_program);
                         }
                 } else {
-                        if (g_strcmp0 (self->display_seat_id, "seat0") != 0) {
-                                program = g_strdup_printf ("dbus-run-session -- %s",
-                                                           self->selected_program);
-                        } else {
-                                program = g_strdup (self->selected_program);
-                        }
+                        program = g_strdup_printf ("dbus-run-session -- %s",
+                                                   self->selected_program);
                 }
         }