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 2f24b39bcc0043f0bdcba98023327359dc584a0a..bfe28dea4db2e4204b3ff7f8e0a04971dca492a0 100644 (file)
--- a/contrib/xml2/xslt_proc.c
+++ b/contrib/xml2/xslt_proc.c
@@ -150,16 +150,16 @@ 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);
@@ -168,11 +168,11 @@ 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);