[gtk+] GtkLabelAccessible: Sanity check _get_text() input values

[Bastien Nocera <hadess src gnome org>]

commit 32825a66ac8e65bf98cafed26a339fa1f31eddd4
Author: Bastien Nocera <hadess hadess net>
Date:   Wed Mar 6 15:46:51 2013 +0100

    GtkLabelAccessible: Sanity check _get_text() input values

 gtk/a11y/gtklabelaccessible.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)
---
diff --git a/gtk/a11y/gtklabelaccessible.c b/gtk/a11y/gtklabelaccessible.c
index dc59d3c..c88b7d7 100644
--- a/gtk/a11y/gtklabelaccessible.c
+++ b/gtk/a11y/gtklabelaccessible.c
@@ -307,7 +307,21 @@ gtk_label_accessible_get_text (AtkText *atk_text,
   text = gtk_label_get_text (GTK_LABEL (widget));
 
   if (text)
-    return g_utf8_substring (text, start_pos, end_pos > -1 ? end_pos : g_utf8_strlen (text, -1));
+    {
+      guint length;
+      const gchar *start, *end;
+
+      length = g_utf8_strlen (text, -1);
+      if (end_pos < 0 || end_pos > length)
+        end_pos = length;
+      if (start_pos > length)
+        start_pos = length;
+      if (end_pos <= start_pos)
+        return g_strdup ("");
+      start = g_utf8_offset_to_pointer (text, start_pos);
+      end = g_utf8_offset_to_pointer (start, end_pos - start_pos);
+      return g_strndup (start, end - start);
+    }
 
   return NULL;
 }