Re: pgxml bug (crash) in xslt_proc.c

PS, I forgot to mention that this is on a Windows system. I have not
yet tried to repeat it on Linux but I can give it a try.

Regards,
Mark.
--

On 11/10/2014 16:52, Mark Simonetti wrote:
> Hi Tom,
> I hadn't really thought of it as a security issue, it came about from
> just trying to use it normally while developing software for one of my
> clients. At first I found it hard to repeat, but I eventually found a
> query to repeat the problem 100% of the time. Unfortunately the XML I
> used to repeat it is vast and generated from lots of database data so
> it would be hard to submit that as a test case (though I can if it
> would help by capturing the XML data into a file and sending it along
> with the XSLT file). It seems to be to do with the order in which
> resources are freed:
>
> I changed this (xslt_proc.c, pgxml, postgres 9.3.5, line 167 onwards) : -
>
> xsltFreeStylesheet(stylesheet);
> xmlFreeDoc(restree);
> xmlFreeDoc(doctree);
> xsltFreeSecurityPrefs(xslt_sec_prefs);
> xsltFreeTransformContext(xslt_ctxt); <== crash here
>
> To this:
>
> xsltFreeTransformContext(xslt_ctxt);
> xsltFreeSecurityPrefs(xslt_sec_prefs);
> xsltFreeStylesheet(stylesheet);
> xmlFreeDoc(restree);
> xmlFreeDoc(doctree);
>
> No more crash.
>
> The offending part seemed to be freeing the transform "xslt_ctxt"
> context before freeing the doc "doctree". Indeed if I check the XSLT
> example with the XSLT distribution
> (http://xmlsoft.org/libxslt/downloads.html) they do free the transform
> context first.
>
> I'm guessing that when the transform context is freed, it is trying to
> free something related to the previously already freed document.
>
> I also switched the order in the "catch" segment just above (line 147
> onwards).
>
> Regards,
> Mark.
> --
>
> On 11/10/2014 16:33, Tom Lane wrote:
>> Mark Simonetti <marks(at)opalsoftware(dot)co(dot)uk> writes:
>>> I think I've found a bug in xslt_proc.c in the pgxml contrib module
>>> that
>>> I've also fixed. It is a serious bug as it crashes the entire database
>>> backend. Do I just describe it here, or is there somewhere else to
>>> report that, or is there a way for me to submit the actual bug fix?
>> If you want you can report it to pgsql-security at postgresql.org
>> instead of the regular bugs list. We'd probably only treat it as
>> a security issue if the bug seems exploitable for more than a mere
>> crash (eg, if it could lead to privilege escalation or arbitrary
>> code execution). If you're not sure about the possible consequences
>> probably best to let the -security list see it first.
>>
>> Whichever way you report it, please include your proposed fix along
>> with the bug report.
>>
>> regards, tom lane
>