Re: [xml] stack corruption (2.5.4)

[Daniel Veillard <veillard redhat com>]

On Wed, Apr 30, 2003 at 04:02:27PM +0100, Gary Pennington sun com wrote:
> On Wed, Apr 30, 2003 at 03:55:43PM +0100, Gary Pennington sun com wrote:
> > Ok, we've got a reproducible test case and I have some information.
> >
> > If we apply the patch you sent out, then the stack corruption problem
> > disappears but we get a core dump when the document is freed.
> >
> > This problem is caused by the following line in the patch:
> >
> >     ret->doc = NULL;
> >
> > This will set the external subset of the document to have a null pointer.
> >
> > In xmlUnlinkNode(), the following line causes the SIGSEGV:
> >
> >     if (cur->type == XML_DTD_NODE) {
> >     xmlDocPtr doc;
> >     doc = cur->doc;
> >     if (doc->intSubset == (xmlDtdPtr) cur)
> >             doc->intSubset = NULL;
> >      if (doc->extSubset == (xmlDtdPtr) cur) <== SIGSEGV HERE
>
> Oops, I of course meant SIGSEGV on the above line.

  Okay, that's a libxml2 bug too. It get a pointer and dereference it
without checking it first against NULL, that part should really be:

    if (cur->type == XML_DTD_NODE) {
        xmlDocPtr doc;
        doc = cur->doc;
        if (doc != NULL) {
            if (doc->intSubset == (xmlDtdPtr) cur)
                doc->intSubset = NULL;
            if (doc->extSubset == (xmlDtdPtr) cur)
                doc->extSubset = NULL;
        }
    }

  thanks for spotting this out.

Daniel

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