[gdm] manager: don't record wtmp entries when user unknown

[Ray Strode <halfline src gnome org>]

commit b5fb83e5d1cc70685ddcf88a66b3f29a9857d7b9
Author: Ray Strode <rstrode redhat com>
Date:   Tue Oct 10 12:49:10 2017 -0400

    manager: don't record wtmp entries when user unknown
    
    Right now we end up writing wtmp entries for the login screen
    user into /var/log/wtmp, but with a funky username of "(unknown)".
    
    The login screen session shouldn't get a wtmp entry, and we
    shouldn't ever add wtmp entries for sessions we don't know the username
    for.
    
    This commit fixes that.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=788784

 daemon/gdm-manager.c        |    5 +++++
 daemon/gdm-session-record.c |   15 +--------------
 2 files changed, 6 insertions(+), 14 deletions(-)
---
diff --git a/daemon/gdm-manager.c b/daemon/gdm-manager.c
index 256b644..c3293d9 100644
--- a/daemon/gdm-manager.c
+++ b/daemon/gdm-manager.c
@@ -677,6 +677,11 @@ add_session_record (GdmManager    *manager,
         display_device = NULL;
 
         username = gdm_session_get_username (session);
+
+        if (username == NULL) {
+                goto out;
+        }
+
         g_object_get (G_OBJECT (session),
                       "display-name", &display_name,
                       "display-hostname", &hostname,
diff --git a/daemon/gdm-session-record.c b/daemon/gdm-session-record.c
index 32933ef..487f100 100644
--- a/daemon/gdm-session-record.c
+++ b/daemon/gdm-session-record.c
@@ -61,21 +61,8 @@
 
 static void
 record_set_username (UTMP       *u,
-                     const char *user_name)
+                     const char *username)
 {
-        const char *username;
-
-        /*
-         * It is possible that PAM failed before it mapped the user
-         * input into a valid username, so we fallback to try using
-         * "(unknown)"
-         */
-        if (user_name != NULL) {
-                username = user_name;
-        } else {
-                username = "(unknown)";
-        }
-
 #if defined(HAVE_UT_UT_USER)
         strncpy (u->ut_user,
                  username,