[libxml2] Do not fetch external parameter entities

[Daniel Veillard <veillard src gnome org>]

commit 9cd1c3cfbd32655d60572c0a413e017260c854df
Author: Daniel Veillard <veillard redhat com>
Date:   Tue Apr 22 15:30:56 2014 +0800

    Do not fetch external parameter entities
    
    Unless explicitely asked for when validating or replacing entities
    with their value. Problem pointed out by Daniel Berrange <berrange redhat com>

 parser.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)
---
diff --git a/parser.c b/parser.c
index 9347ac9..c0dea05 100644
--- a/parser.c
+++ b/parser.c
@@ -2598,6 +2598,20 @@ xmlParserHandlePEReference(xmlParserCtxtPtr ctxt) {
                    xmlCharEncoding enc;
 
                    /*
+                    * Note: external parsed entities will not be loaded, it is
+                    * not required for a non-validating parser, unless the
+                    * option of validating, or substituting entities were
+                    * given. Doing so is far more secure as the parser will
+                    * only process data coming from the document entity by
+                    * default.
+                    */
+                    if ((entity->etype == XML_EXTERNAL_PARAMETER_ENTITY) &&
+                       ((ctxt->options & XML_PARSE_NOENT) == 0) &&
+                       ((ctxt->options & XML_PARSE_DTDVALID) == 0) &&
+                       (ctxt->validate == 0))
+                       return;
+
+                   /*
                     * handle the extra spaces added before and after
                     * c.f. http://www.w3.org/TR/REC-xml#as-PE
                     * this is done independently.