Security fix for CVE-2009-2473: prevent the "billion laughs" attack

against expat:

* src/ne_xml.c (ne_xml_create) [HAVE_EXPAT]: Register entity
  decl handler.
  [HAVE_LIBXML]: Use xmlCtxtUseOptions interface.
  (entity_declaration): New function.

* test/xml.c (fail_parse): Add billion laughs test case.

* test/run.sh: Limit run-time CPU use to 120 seconds.


git-svn-id: http://svn.webdav.org/repos/projects/neon/trunk@1687 61a7d7f5-40b7-0310-9c16-bb0ea8cb1845

1 files changed, 43 insertions, 1 deletions

diff --git a/src/ne_xml.c b/src/ne_xml.c
index 7c95a2e..3870701 100644
--- a/src/ne_xml.c
+++ b/src/ne_xml.c
@@ -1,6 +1,6 @@
 /* 
    Wrapper interface to XML parser
-   Copyright (C) 1999-2007, Joe Orton <joe@manyfish.co.uk>
+   Copyright (C) 1999-2007, 2009, Joe Orton <joe@manyfish.co.uk>
 
    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
@@ -405,6 +405,28 @@ static void end_element(void *userdata, const ne_xml_char *name)
     destroy_element(elm);
 }
 
+#if defined(HAVE_EXPAT) && 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)
+{
+    ne_xml_parser *parser = userData;
+    
+    NE_DEBUG(NE_DBG_XMLPARSE, "XML: entity declaration [%s]. Failing.\n",
+             entityName);
+
+    XML_StopParser(parser->parser, XML_FALSE);
+}
+#elif defined(HAVE_EXPAT)
+/* A noop default_handler. */
+static void default_handler(void *userData, const XML_Char *s, int len)
+{
+}
+#endif
+
 /* Find a namespace definition for 'prefix' in given element, where
  * length of prefix is 'pfxlen'.  Returns the URI or NULL. */
 static const char *resolve_nspace(const struct element *elm, 
@@ -459,14 +481,34 @@ ne_xml_parser *ne_xml_create(void)
     XML_SetCharacterDataHandler(p->parser, char_data);
     XML_SetUserData(p->parser, (void *) p);
     XML_SetXmlDeclHandler(p->parser, decl_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(p->parser, entity_declaration);
 #else
+    XML_SetDefaultHandler(p->parser, default_handler);
+#endif
+
+#else /* HAVE_LIBXML */
     p->parser = xmlCreatePushParserCtxt(&sax_handler, 
 					(void *)p, NULL, 0, NULL);
     if (p->parser == NULL) {
 	abort();
     }
+#if LIBXML_VERSION < 20602
     p->parser->replaceEntities = 1;
+#else
+    /* Enable expansion of entities, and disable network access. */
+    xmlCtxtUseOptions(p->parser, XML_PARSE_NOENT | XML_PARSE_NONET);
 #endif
+
+#endif /* HAVE_LIBXML || HAVE_EXPAT */
     return p;
 }