Free libxml2/libxslt resources in a safer order.

Mark Simonetti reported that libxslt sometimes crashes for him, and that
swapping xslt_process's object-freeing calls around to do them in reverse
order of creation seemed to fix it.  I've not reproduced the crash, but
valgrind clearly shows a reference to already-freed memory, which is
consistent with the idea that shutdown of the xsltTransformContext is
trying to reference the already-freed stylesheet or input document.
With this patch, valgrind is no longer unhappy.

I have an inquiry in to see if this is a libxslt bug or if we're just
abusing the library; but even if it's a library bug, we'd want to adjust
our code so it doesn't fail with unpatched libraries.

Back-patch to all supported branches, because we've been doing this in
the wrong(?) order for a long time.

diff --git a/contrib/xml2/xslt_proc.c b/contrib/xml2/xslt_proc.c
index 9f1378733228ff98bf58c3daaf9b3435f9c1df32..343924e99177efb41aa30862fd8a8bd16cc42128 100644 (file)
--- a/contrib/xml2/xslt_proc.c
+++ b/contrib/xml2/xslt_proc.c
@@ -146,16 +146,16 @@ xslt_process(PG_FUNCTION_ARGS)
    }
    PG_CATCH();
    {
-       if (stylesheet != NULL)
-           xsltFreeStylesheet(stylesheet);
        if (restree != NULL)
            xmlFreeDoc(restree);
-       if (doctree != NULL)
-           xmlFreeDoc(doctree);
-       if (xslt_sec_prefs != NULL)
-           xsltFreeSecurityPrefs(xslt_sec_prefs);
        if (xslt_ctxt != NULL)
            xsltFreeTransformContext(xslt_ctxt);
+       if (xslt_sec_prefs != NULL)
+           xsltFreeSecurityPrefs(xslt_sec_prefs);
+       if (stylesheet != NULL)
+           xsltFreeStylesheet(stylesheet);
+       if (doctree != NULL)
+           xmlFreeDoc(doctree);
        xsltCleanupGlobals();
 
        pg_xml_done(xmlerrcxt, true);
@@ -164,11 +164,11 @@ xslt_process(PG_FUNCTION_ARGS)
    }
    PG_END_TRY();
 
-   xsltFreeStylesheet(stylesheet);
    xmlFreeDoc(restree);
-   xmlFreeDoc(doctree);
-   xsltFreeSecurityPrefs(xslt_sec_prefs);
    xsltFreeTransformContext(xslt_ctxt);
+   xsltFreeSecurityPrefs(xslt_sec_prefs);
+   xsltFreeStylesheet(stylesheet);
+   xmlFreeDoc(doctree);
    xsltCleanupGlobals();
 
    pg_xml_done(xmlerrcxt, false);