[gdm] wayland-session: don't start new session with stale session env vars

[Ray Strode <halfline src gnome org>]

commit 3d2aa559a4a7decc8b6568de6b41cf9f94170613
Author: Ray Strode <rstrode redhat com>
Date:   Wed Sep 21 15:38:02 2016 -0400

    wayland-session: don't start new session with stale session env vars
    
    commit 448134d3cdbc54e5359ea33d387993b0defdaefa changed gdm to
    import the session from systemd --user.
    
    Unfortunately, it broke log in after log out. The problem is, certain
    session specific environment variables from the previous session
    were getting leaked into the new session.
    
    This commit wipes the ones causing the most problems on the GDM side,
    but gnome-session should also probably purge them from the systemd
    --user environment when it exits.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=771786

 daemon/gdm-wayland-session.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/daemon/gdm-wayland-session.c b/daemon/gdm-wayland-session.c
index 503c398..8b0e56a 100644
--- a/daemon/gdm-wayland-session.c
+++ b/daemon/gdm-wayland-session.c
@@ -318,6 +318,13 @@ spawn_session (State        *state,
         if (state->bus_address != NULL) {
                 g_subprocess_launcher_setenv (launcher, "DBUS_SESSION_BUS_ADDRESS", state->bus_address, 
TRUE);
         }
+
+        /* Don't allow session specific environment variables from earlier sessions to leak through */
+        g_subprocess_launcher_unsetenv (launcher, "DISPLAY");
+        g_subprocess_launcher_unsetenv (launcher, "XAUTHORITY");
+        g_subprocess_launcher_unsetenv (launcher, "WAYLAND_DISPLAY");
+        g_subprocess_launcher_unsetenv (launcher, "WAYLAND_SOCKET");
+
         subprocess = g_subprocess_launcher_spawnv (launcher,
                                                    (const char * const *) argv,
                                                    &error);