[mutter] window: don't set _NET_WM_FULLSCREEN_MONITORS to bogus values

[Giovanni Campagna <gcampagna src gnome org>]

commit 3aac2bf934a059a8046e297a0d755dd9193a6b30
Author: Giovanni Campagna <gcampagna src gnome org>
Date:   Sat Dec 14 14:24:27 2013 +0100

    window: don't set _NET_WM_FULLSCREEN_MONITORS to bogus values
    
    Prior to the DisplayConfig merge, we would set _NET_WM_FULLSCREEN_MONITORS
    to (unsigned)-1 when unset. After that, we would have invalid
    reads inside meta_screen_monitor_index_to_xinerama_index() (called
    with -1).
    The way I read the specification, the proper way to indicate
    that the window is back to fullscreen on all monitors is to
    remove the property, so do that.
    
    Also, add an assertion that meta_screne_monitor_index_to_xinerama_index()
    is doing the right thing.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=724258

 src/core/screen.c |    2 ++
 src/core/window.c |   46 +++++++++++++++++++++++++++++-----------------
 2 files changed, 31 insertions(+), 17 deletions(-)
---
diff --git a/src/core/screen.c b/src/core/screen.c
index 5b832a0..7b800e7 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -390,6 +390,8 @@ int
 meta_screen_monitor_index_to_xinerama_index (MetaScreen *screen,
                                              int         index)
 {
+  g_return_val_if_fail (index >= 0 && index < screen->n_monitor_infos, -1);
+
   meta_screen_ensure_xinerama_indices (screen);
 
   return screen->monitor_infos[index].xinerama_index;
diff --git a/src/core/window.c b/src/core/window.c
index c6666ba..936fa76 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -2061,23 +2061,35 @@ set_net_wm_state (MetaWindow *window)
 
   if (window->fullscreen)
     {
-      data[0] = meta_screen_monitor_index_to_xinerama_index (window->screen,
-                                                             window->fullscreen_monitors[0]);
-      data[1] = meta_screen_monitor_index_to_xinerama_index (window->screen,
-                                                             window->fullscreen_monitors[1]);
-      data[2] = meta_screen_monitor_index_to_xinerama_index (window->screen,
-                                                             window->fullscreen_monitors[2]);
-      data[3] = meta_screen_monitor_index_to_xinerama_index (window->screen,
-                                                             window->fullscreen_monitors[3]);
-
-      meta_verbose ("Setting _NET_WM_FULLSCREEN_MONITORS\n");
-      meta_error_trap_push (window->display);
-      XChangeProperty (window->display->xdisplay,
-                       window->xwindow,
-                       window->display->atom__NET_WM_FULLSCREEN_MONITORS,
-                       XA_CARDINAL, 32, PropModeReplace,
-                       (guchar*) data, 4);
-      meta_error_trap_pop (window->display);
+      if (window->fullscreen_monitors[0] >= 0)
+        {
+          data[0] = meta_screen_monitor_index_to_xinerama_index (window->screen,
+                                                                 window->fullscreen_monitors[0]);
+          data[1] = meta_screen_monitor_index_to_xinerama_index (window->screen,
+                                                                 window->fullscreen_monitors[1]);
+          data[2] = meta_screen_monitor_index_to_xinerama_index (window->screen,
+                                                                 window->fullscreen_monitors[2]);
+          data[3] = meta_screen_monitor_index_to_xinerama_index (window->screen,
+                                                                 window->fullscreen_monitors[3]);
+
+          meta_verbose ("Setting _NET_WM_FULLSCREEN_MONITORS\n");
+          meta_error_trap_push (window->display);
+          XChangeProperty (window->display->xdisplay,
+                           window->xwindow,
+                           window->display->atom__NET_WM_FULLSCREEN_MONITORS,
+                           XA_CARDINAL, 32, PropModeReplace,
+                           (guchar*) data, 4);
+          meta_error_trap_pop (window->display);
+        }
+      else
+        {
+          meta_verbose ("Clearing _NET_WM_FULLSCREEN_MONITORS\n");
+          meta_error_trap_push (window->display);
+          XDeleteProperty (window->display->xdisplay,
+                           window->xwindow,
+                           window->display->atom__NET_WM_FULLSCREEN_MONITORS);
+          meta_error_trap_pop (window->display);
+        }
     }
 }