[libxslt] Fix for type confusion in preprocessing attributes

[Daniel Veillard <veillard src gnome org>]

commit 7ca19df892ca22d9314e95d59ce2abdeff46b617
Author: Daniel Veillard <veillard redhat com>
Date:   Thu Oct 29 19:33:23 2015 +0800

    Fix for type confusion in preprocessing attributes
    
    CVE-2015-7995 http://www.openwall.com/lists/oss-security/2015/10/27/10
    We need to check that the parent node is an element before dereferencing
    its namespace

 libxslt/preproc.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/libxslt/preproc.c b/libxslt/preproc.c
index 0eb80a0..7f69325 100644
--- a/libxslt/preproc.c
+++ b/libxslt/preproc.c
@@ -2249,7 +2249,8 @@ xsltStylePreCompute(xsltStylesheetPtr style, xmlNodePtr inst) {
        } else if (IS_XSLT_NAME(inst, "attribute")) {
            xmlNodePtr parent = inst->parent;
 
-           if ((parent == NULL) || (parent->ns == NULL) ||
+           if ((parent == NULL) ||
+               (parent->type != XML_ELEMENT_NODE) || (parent->ns == NULL) ||
                ((parent->ns != inst->ns) &&
                 (!xmlStrEqual(parent->ns->href, inst->ns->href))) ||
                (!xmlStrEqual(parent->name, BAD_CAST "attribute-set"))) {