Re: [xml] C14N issue with digital signature due to pointer comparison

How do you manipulate the XML tree? If you are using "official" LibXML2
function then I believe this code should work just fine unless there is
a bug in the strings dictionary.


On 3/12/14, 10:28 AM, Frank Gross wrote:

  I'm getting some trouble to verify a XML signature because the
xmlC14NProcessNamespacesAxis() function does a xmlNsPtr pointer
comparison to decide whether a sub node belongs to the same default
namespace as an ancestor. But if the sub node has been manipulated by
program (in my case) to point to another xmlNsPtr with same values, the
canonicalization process breaks. Wouldn't it be better to check the
namespace href values instead as in following patch ?

diff --git a/lib-xmlsoft-libxml2/src/c14n.c
index 9c3cad2..f73e709 100644
--- a/lib-xmlsoft-libxml2/src/c14n.c
+++ b/lib-xmlsoft-libxml2/src/c14n.c
@@ -623,7 +623,7 @@ xmlC14NProcessNamespacesAxis(xmlC14NCtxPtr ctx,
xmlNodePtr cur, int visible)
     for(ns = n->nsDef; ns != NULL; ns = ns->next) {
         tmp = xmlSearchNs(cur->doc, cur, ns->prefix);

-        if((tmp == ns) && !xmlC14NIsXmlNs(ns) && xmlC14NIsVisible(ctx,
ns, cur)) {
+        if((xmlStrEqual(tmp->href,ns->href)) &&
(xmlStrEqual(tmp->prefix,ns->prefix)) && !xmlC14NIsXmlNs(ns) &&
xmlC14NIsVisible(ctx, ns, cur)) {
         already_rendered = xmlC14NVisibleNsStackFind(ctx->ns_rendered,
         if(visible) {
                 xmlC14NVisibleNsStackAdd(ctx->ns_rendered, ns, cur);


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