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Taken from
http://svn.apache.org/viewvc/apr/apr/trunk/xml/apr_xml.c?r1=757729&r2=781403&view=patch
--- srclib/apr-util/xml/apr_xml.c 2009/03/24 11:12:27 757729
+++ srclib/apr-util/xml/apr_xml.c 2009/06/03 14:26:19 781403
@@ -347,6 +347,25 @@
return APR_SUCCESS;
}
+#if XML_MAJOR_VERSION > 1
+/* Stop the parser if an entity declaration is hit. */
+static void entity_declaration(void *userData, const XML_Char *entityName,
+ int is_parameter_entity, const XML_Char *value,
+ int value_length, const XML_Char *base,
+ const XML_Char *systemId, const XML_Char *publicId,
+ const XML_Char *notationName)
+{
+ apr_xml_parser *parser = userData;
+
+ XML_StopParser(parser->xp, XML_FALSE);
+}
+#else
+/* A noop default_handler. */
+static void default_handler(void *userData, const XML_Char *s, int len)
+{
+}
+#endif
+
APU_DECLARE(apr_xml_parser *) apr_xml_parser_create(apr_pool_t *pool)
{
apr_xml_parser *parser = apr_pcalloc(pool, sizeof(*parser));
@@ -372,6 +391,19 @@
XML_SetElementHandler(parser->xp, start_handler, end_handler);
XML_SetCharacterDataHandler(parser->xp, cdata_handler);
+ /* Prevent the "billion laughs" attack against expat by disabling
+ * internal entity expansion. With 2.x, forcibly stop the parser
+ * if an entity is declared - this is safer and a more obvious
+ * failure mode. With older versions, installing a noop
+ * DefaultHandler means that internal entities will be expanded as
+ * the empty string, which is also sufficient to prevent the
+ * attack. */
+#if XML_MAJOR_VERSION > 1
+ XML_SetEntityDeclHandler(parser->xp, entity_declaration);
+#else
+ XML_SetDefaultHandler(parser->xp, default_handler);
+#endif
+
return parser;
}
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