From a19b51ad9e446948ba60c359641f6c4c14fec1da Mon Sep 17 00:00:00 2001
From: Michal Srb <msrb@suse.com>
Date: Fri, 26 Jan 2018 10:49:18 +0100
Subject: [PATCH] Add runtime option to disable starting X server as user

If the environmental variable GDM_DISABLE_USER_DISPLAY_SERVER is defined, the
X server will be started under root. The same way as if gdm was built with
--disable-user-display-server option.

This allows system to run X server under root if and only-if necessary.
Index: gdm-45.0.1/daemon/gdm-local-display-factory.c
===================================================================
--- gdm-45.0.1.orig/daemon/gdm-local-display-factory.c
+++ gdm-45.0.1/daemon/gdm-local-display-factory.c
@@ -384,6 +384,7 @@ gdm_local_display_factory_create_transie
         preferred_display_server = get_preferred_display_server (factory);
 
 #ifdef ENABLE_USER_DISPLAY_SERVER
+        if (getenv ("GDM_DISABLE_USER_DISPLAY_SERVER") == NULL ) {
         if (g_strcmp0 (preferred_display_server, "wayland") == 0 ||
             g_strcmp0 (preferred_display_server, "xorg") == 0) {
                 g_auto(GStrv) session_types = NULL;
@@ -405,8 +406,9 @@ gdm_local_display_factory_create_transie
                               NULL);
                 is_initial = TRUE;
         }
+        }
 #endif
-        if (g_strcmp0 (preferred_display_server, "legacy-xorg") == 0) {
+	//if (g_strcmp0 (preferred_display_server, "legacy-xorg") == 0) {
                 if (display == NULL) {
                         guint32 num;
 
@@ -414,7 +416,7 @@ gdm_local_display_factory_create_transie
 
                         display = gdm_legacy_display_new (num);
                 }
-        }
+	//}
 
         if (display == NULL) {
                 g_set_error_literal (error,
@@ -928,6 +930,7 @@ ensure_display_for_seat (GdmLocalDisplay
         g_debug ("GdmLocalDisplayFactory: Adding display on seat %s", seat_id);
 
 #ifdef ENABLE_USER_DISPLAY_SERVER
+        if (getenv ("GDM_DISABLE_USER_DISPLAY_SERVER") == NULL ) {
         if (g_strcmp0 (preferred_display_server, "wayland") == 0 ||
             g_strcmp0 (preferred_display_server, "xorg") == 0) {
                 display = gdm_local_display_new ();
@@ -936,6 +939,7 @@ ensure_display_for_seat (GdmLocalDisplay
                               "supported-session-types", session_types,
                               NULL);
         }
+        }
 #endif
 
         if (display == NULL) {
@@ -1252,6 +1256,10 @@ on_vt_changed (GIOChannel    *source,
         g_debug ("GdmLocalDisplayFactory: VT changed from %u to %u",
                  previous_vt, factory->active_vt);
 
+        if (getenv ("GDM_DISABLE_USER_DISPLAY_SERVER") != NULL) {
+                return G_SOURCE_CONTINUE;
+        }
+
         store = gdm_display_factory_get_display_store (GDM_DISPLAY_FACTORY (factory));
 
         /* if the old VT was running a wayland login screen kill it
@@ -1393,6 +1401,7 @@ gdm_local_display_factory_start_monitor
 #endif
 
 #if defined(ENABLE_USER_DISPLAY_SERVER)
+        if (getenv ("GDM_DISABLE_USER_DISPLAY_SERVER") == NULL ) {
         io_channel = g_io_channel_new_file ("/sys/class/tty/tty0/active", "r", NULL);
 
         if (io_channel != NULL) {
@@ -1403,6 +1412,7 @@ gdm_local_display_factory_start_monitor
                                         on_vt_changed,
                                         factory);
         }
+        }
 #endif
 }
 
Index: gdm-45.0.1/daemon/gdm-manager.c
===================================================================
--- gdm-45.0.1.orig/daemon/gdm-manager.c
+++ gdm-45.0.1/daemon/gdm-manager.c
@@ -1355,6 +1355,8 @@ set_up_automatic_login_session (GdmManag
                       "supported-session-types", supported_session_types,
                       NULL);
 
+        if (getenv ("GDM_DISABLE_USER_DISPLAY_SERVER") != NULL)
+                manager->did_automatic_login = TRUE;
         g_debug ("GdmManager: Starting automatic login conversation");
         gdm_session_start_conversation (session, "gdm-autologin");
 }
Index: gdm-45.0.1/daemon/gdm-server.c
===================================================================
--- gdm-45.0.1.orig/daemon/gdm-server.c
+++ gdm-45.0.1/daemon/gdm-server.c
@@ -238,9 +238,9 @@ gdm_server_init_command (GdmServer *serv
         /* For systemd, we don't have a log file but instead log to stdout,
            so set it to the xserver's built-in default verbosity */
         if (debug)
-            verbosity = "7 -logfile /dev/null";
+            verbosity = "7";
         else
-            verbosity = "3 -logfile /dev/null";
+            verbosity = "3";
 #endif
 
         if (g_access (SYSTEMD_X_SERVER, X_OK) < 0) {
@@ -749,7 +749,7 @@ gdm_server_start (GdmServer *server)
         g_return_val_if_fail (GDM_IS_SERVER (server), FALSE);
 
         /* Hardcode the VT for the initial X server, but nothing else */
-        if (server->is_initial) {
+        if (server->is_initial && g_strcmp0 (server->display_name, ":0") == 0) {
                 vtarg = "vt" G_STRINGIFY (GDM_INITIAL_VT);
         }
 
Index: gdm-45.0.1/daemon/gdm-session.c
===================================================================
--- gdm-45.0.1.orig/daemon/gdm-session.c
+++ gdm-45.0.1/daemon/gdm-session.c
@@ -3436,6 +3436,7 @@ gdm_session_get_display_mode (GdmSession
         }
 
 #ifdef ENABLE_USER_DISPLAY_SERVER
+        if (getenv ("GDM_DISABLE_USER_DISPLAY_SERVER") == NULL ) {
         /* All other cases (wayland login screen, X login screen,
          * wayland user session, X user session) use the NEW_VT
          * display mode.  That display mode means that GDM allocates
@@ -3458,7 +3459,8 @@ gdm_session_get_display_mode (GdmSession
          *   are paused when handed out.
          */
         return GDM_SESSION_DISPLAY_MODE_NEW_VT;
-#else
+//#else
+        } else {
 
 #ifdef ENABLE_WAYLAND_SUPPORT
         /* Wayland sessions are for now assumed to run in a
@@ -3469,6 +3471,7 @@ gdm_session_get_display_mode (GdmSession
         }
 #endif
         return GDM_SESSION_DISPLAY_MODE_REUSE_VT;
+        }
 #endif
 }