Make gdk_event_apply_filters safe against changes in filter list

An event filter may add or remove filters itself. This patch does
two things to address this case. The first is to take a temporary
reference to the filter while it is being used. The second is
to wait until after the filter function is run before determining
the next node in the list to process. This guards against
changes to the next node. It also does not run functions
that have been marked as removed. Though I'm not sure if this
case can arise.

https://bugzilla.gnome.org/show_bug.cgi?id=635380

Backport of 323df2b2800383832ed3c2e43626f2c6821c33ec to
the gtk-2-24 branch by Wolfgang Ulbrich.

5 files changed, 122 insertions, 43 deletions

diff --git a/gdk/gdkinternals.h b/gdk/gdkinternals.h
index 0bd803f..97a1daa 100644
--- a/gdk/gdkinternals.h
+++ b/gdk/gdkinternals.h
@@ -59,9 +59,15 @@ struct _GdkColorInfo
   guint ref_count;
 };
 
+typedef enum {
+  GDK_EVENT_FILTER_REMOVED = 1 << 0
+} GdkEventFilterFlags;
+
 struct _GdkEventFilter {
   GdkFilterFunc function;
   gpointer data;
+  GdkEventFilterFlags flags;
+  guint ref_count;
 };
 
 struct _GdkClientFilter {
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 45fee34..29c878f 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -2545,13 +2545,18 @@ gdk_window_add_filter (GdkWindow     *window,
     {
       filter = (GdkEventFilter *)tmp_list->data;
       if ((filter->function == function) && (filter->data == data))
-	return;
+        {
+          filter->ref_count++;
+          return;
+        }
       tmp_list = tmp_list->next;
     }
 
   filter = g_new (GdkEventFilter, 1);
   filter->function = function;
   filter->data = data;
+  filter->ref_count = 1;
+  filter->flags = 0;
 
   if (private)
     private->filters = g_list_append (private->filters, filter);
@@ -2593,16 +2598,21 @@ gdk_window_remove_filter (GdkWindow     *window,
       tmp_list = tmp_list->next;
 
       if ((filter->function == function) && (filter->data == data))
-	{
-	  if (private)
-	    private->filters = g_list_remove_link (private->filters, node);
-	  else
-	    _gdk_default_filters = g_list_remove_link (_gdk_default_filters, node);
-	  g_list_free_1 (node);
-	  g_free (filter);
+        {
+          filter->flags |= GDK_EVENT_FILTER_REMOVED;
+          filter->ref_count--;
+          if (filter->ref_count != 0)
+            return;
 
-	  return;
-	}
+          if (private)
+            private->filters = g_list_remove_link (private->filters, node);
+          else
+            _gdk_default_filters = g_list_remove_link (_gdk_default_filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+
+          return;
+        }
     }
 }
 
diff --git a/gdk/quartz/gdkevents-quartz.c b/gdk/quartz/gdkevents-quartz.c
index 9e57edd..f199298 100644
--- a/gdk/quartz/gdkevents-quartz.c
+++ b/gdk/quartz/gdkevents-quartz.c
@@ -253,21 +253,42 @@ append_event (GdkEvent *event,
 static gint
 gdk_event_apply_filters (NSEvent *nsevent,
 			 GdkEvent *event,
-			 GList *filters)
+			 GList **filters)
 {
   GList *tmp_list;
   GdkFilterReturn result;
   
-  tmp_list = filters;
+  tmp_list = *filters;
 
   while (tmp_list)
     {
       GdkEventFilter *filter = (GdkEventFilter*) tmp_list->data;
-      
-      tmp_list = tmp_list->next;
+      GList *node;
+
+      if ((filter->flags & GDK_EVENT_FILTER_REMOVED) != 0)
+        {
+          tmp_list = tmp_list->next;
+          continue;
+        }
+
+      filter->ref_count++;
       result = filter->function (nsevent, event, filter->data);
-      if (result !=  GDK_FILTER_CONTINUE)
-	return result;
+
+      /* get the next node after running the function since the
+         function may add or remove a next node */
+      node = tmp_list;
+      tmp_list = tmp_list->next;
+
+      filter->ref_count--;
+      if (filter->ref_count == 0)
+        {
+          *filters = g_list_remove_link (*filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+        }
+
+      if (result != GDK_FILTER_CONTINUE)
+        return result;
     }
 
   return GDK_FILTER_CONTINUE;
@@ -1319,7 +1340,7 @@ gdk_event_translate (GdkEvent *event,
       /* Apply global filters */
       GdkFilterReturn result;
 
-      result = gdk_event_apply_filters (nsevent, event, _gdk_default_filters);
+      result = gdk_event_apply_filters (nsevent, event, &_gdk_default_filters);
       if (result != GDK_FILTER_CONTINUE)
         {
           return_val = (result == GDK_FILTER_TRANSLATE) ? TRUE : FALSE;
@@ -1390,19 +1411,19 @@ gdk_event_translate (GdkEvent *event,
       GdkFilterReturn result;
 
       if (filter_private->filters)
-	{
-	  g_object_ref (window);
+        {
+          g_object_ref (window);
 
-	  result = gdk_event_apply_filters (nsevent, event, filter_private->filters);
+          result = gdk_event_apply_filters (nsevent, event, &filter_private->filters);
 
-	  g_object_unref (window);
+          g_object_unref (window);
 
-	  if (result != GDK_FILTER_CONTINUE)
-	    {
-	      return_val = (result == GDK_FILTER_TRANSLATE) ? TRUE : FALSE;
-	      goto done;
-	    }
-	}
+          if (result != GDK_FILTER_CONTINUE)
+            {
+              return_val = (result == GDK_FILTER_TRANSLATE) ? TRUE : FALSE;
+              goto done;
+            }
+        }
     }
 
   /* If the app is not active leave the event to AppKit so the window gets
diff --git a/gdk/win32/gdkevents-win32.c b/gdk/win32/gdkevents-win32.c
index 8b345cb..c853e1e 100644
--- a/gdk/win32/gdkevents-win32.c
+++ b/gdk/win32/gdkevents-win32.c
@@ -1069,7 +1069,7 @@ fill_key_event_string (GdkEvent *event)
 static GdkFilterReturn
 apply_event_filters (GdkWindow  *window,
 		     MSG        *msg,
-		     GList      *filters)
+		     GList      **filters)
 {
   GdkFilterReturn result = GDK_FILTER_CONTINUE;
   GdkEvent *event;
@@ -1087,15 +1087,36 @@ apply_event_filters (GdkWindow  *window,
    */
   node = _gdk_event_queue_append (_gdk_display, event);
   
-  tmp_list = filters;
+  tmp_list = *filters;
   while (tmp_list)
     {
       GdkEventFilter *filter = (GdkEventFilter *) tmp_list->data;
-      
-      tmp_list = tmp_list->next;
+      GList *node;
+
+      if ((filter->flags & GDK_EVENT_FILTER_REMOVED) != 0)
+        {
+          tmp_list = tmp_list->next;
+          continue;
+        }
+
+      filter->ref_count++;
       result = filter->function (msg, event, filter->data);
-      if (result !=  GDK_FILTER_CONTINUE)
-	break;
+
+      /* get the next node after running the function since the
+         function may add or remove a next node */
+      node = tmp_list;
+      tmp_list = tmp_list->next;
+
+      filter->ref_count--;
+      if (filter->ref_count == 0)
+        {
+          *filters = g_list_remove_link (*filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+        }
+
+      if (result != GDK_FILTER_CONTINUE)
+        break;
     }
 
   if (result == GDK_FILTER_CONTINUE || result == GDK_FILTER_REMOVE)
@@ -2075,7 +2096,7 @@ gdk_event_translate (MSG  *msg,
     {
       /* Apply global filters */
 
-      GdkFilterReturn result = apply_event_filters (NULL, msg, _gdk_default_filters);
+      GdkFilterReturn result = apply_event_filters (NULL, msg, &_gdk_default_filters);
       
       /* If result is GDK_FILTER_CONTINUE, we continue as if nothing
        * happened. If it is GDK_FILTER_REMOVE or GDK_FILTER_TRANSLATE,
@@ -2121,7 +2142,7 @@ gdk_event_translate (MSG  *msg,
     {
       /* Apply per-window filters */
 
-      GdkFilterReturn result = apply_event_filters (window, msg, ((GdkWindowObject *) window)->filters);
+      GdkFilterReturn result = apply_event_filters (window, msg, &((GdkWindowObject *) window)->filters);
 
       if (result == GDK_FILTER_REMOVE || result == GDK_FILTER_TRANSLATE)
 	{
diff --git a/gdk/x11/gdkevents-x11.c b/gdk/x11/gdkevents-x11.c
index b96e9f5..8de98c5 100644
--- a/gdk/x11/gdkevents-x11.c
+++ b/gdk/x11/gdkevents-x11.c
@@ -96,7 +96,7 @@ struct _GdkEventTypeX11
 
 static gint	 gdk_event_apply_filters (XEvent   *xevent,
 					  GdkEvent *event,
-					  GList    *filters);
+					  GList    **filters);
 static gboolean	 gdk_event_translate	 (GdkDisplay *display,
 					  GdkEvent   *event, 
 					  XEvent     *xevent,
@@ -341,21 +341,42 @@ gdk_event_get_graphics_expose (GdkWindow *window)
 static gint
 gdk_event_apply_filters (XEvent *xevent,
 			 GdkEvent *event,
-			 GList *filters)
+			 GList **filters)
 {
   GList *tmp_list;
   GdkFilterReturn result;
   
-  tmp_list = filters;
+  tmp_list = *filters;
   
   while (tmp_list)
     {
       GdkEventFilter *filter = (GdkEventFilter*) tmp_list->data;
+      GList *node;
       
-      tmp_list = tmp_list->next;
+      if ((filter->flags & GDK_EVENT_FILTER_REMOVED) != 0)
+        {
+          tmp_list = tmp_list->next;
+          continue;
+        }
+
+      filter->ref_count++;
       result = filter->function (xevent, event, filter->data);
-      if (result !=  GDK_FILTER_CONTINUE)
-	return result;
+
+      /* get the next node after running the function since the
+         function may add or remove a next node */
+      node = tmp_list;
+      tmp_list = tmp_list->next;
+
+      filter->ref_count--;
+      if (filter->ref_count == 0)
+        {
+          *filters = g_list_remove_link (*filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+        }
+
+      if (result != GDK_FILTER_CONTINUE)
+        return result;
     }
   
   return GDK_FILTER_CONTINUE;
@@ -944,7 +965,7 @@ gdk_event_translate (GdkDisplay *display,
       /* Apply global filters */
       GdkFilterReturn result;
       result = gdk_event_apply_filters (xevent, event,
-                                        _gdk_default_filters);
+                                        &_gdk_default_filters);
       
       if (result != GDK_FILTER_CONTINUE)
         {
@@ -1050,7 +1071,7 @@ gdk_event_translate (GdkDisplay *display,
 	  g_object_ref (filter_window);
 	  
 	  result = gdk_event_apply_filters (xevent, event,
-					    filter_private->filters);
+					    &filter_private->filters);
 	  
 	  g_object_unref (filter_window);