Fix CVE-2017-7375:

https://bugzilla.gnome.org/show_bug.cgi?id=780691 (not yet public)
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7375
https://security-tracker.debian.org/tracker/CVE-2017-7375

Patch copied from upstream source repository:

https://git.gnome.org/browse/libxml2/commit/?id=90ccb58242866b0ba3edbef8fe44214a101c2b3e

From 90ccb58242866b0ba3edbef8fe44214a101c2b3e Mon Sep 17 00:00:00 2001
From: Neel Mehta <nmehta@google.com>
Date: Fri, 7 Apr 2017 17:43:02 +0200
Subject: [PATCH] Prevent unwanted external entity reference

For https://bugzilla.gnome.org/show_bug.cgi?id=780691

* parser.c: add a specific check to avoid PE reference
---
 parser.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/parser.c b/parser.c
index 609a2703..c2c812de 100644
--- a/parser.c
+++ b/parser.c
@@ -8123,6 +8123,15 @@ xmlParsePEReference(xmlParserCtxtPtr ctxt)
 	    if (xmlPushInput(ctxt, input) < 0)
 		return;
 	} else {
+	    if ((entity->etype == XML_EXTERNAL_PARAMETER_ENTITY) &&
+	        ((ctxt->options & XML_PARSE_NOENT) == 0) &&
+		((ctxt->options & XML_PARSE_DTDVALID) == 0) &&
+		((ctxt->options & XML_PARSE_DTDLOAD) == 0) &&
+		((ctxt->options & XML_PARSE_DTDATTR) == 0) &&
+		(ctxt->replaceEntities == 0) &&
+		(ctxt->validate == 0))
+		return;
+
 	    /*
 	     * TODO !!!
 	     * handle the extra spaces added before and after
-- 
2.14.1

