Prevent access to external files/URLs via contrib/xml2's xslt_process().

libxslt offers the ability to read and write both files and URLs through
stylesheet commands, thus allowing unprivileged database users to both read
and write data with the privileges of the database server.  Disable that
through proper use of libxslt's security options.

Also, remove xslt_process()'s ability to fetch documents and stylesheets
from external files/URLs.  While this was a documented "feature", it was
long regarded as a terrible idea.  The fix for CVE-2012-3489 broke that
capability, and rather than expend effort on trying to fix it, we're just
going to summarily remove it.

While the ability to write as well as read makes this security hole
considerably worse than CVE-2012-3489, the problem is mitigated by the fact
that xslt_process() is not available unless contrib/xml2 is installed,
and the longstanding warnings about security risks from that should have
discouraged prudent DBAs from installing it in security-exposed databases.

Reported and fixed by Peter Eisentraut.

Security: CVE-2012-3488

1 files changed, 52 insertions, 18 deletions

diff --git a/contrib/xml2/xslt_proc.c b/contrib/xml2/xslt_proc.c
index a93931d2618..2f24b39bcc0 100644
--- a/contrib/xml2/xslt_proc.c
+++ b/contrib/xml2/xslt_proc.c
@@ -26,6 +26,7 @@
 
 #include <libxslt/xslt.h>
 #include <libxslt/xsltInternals.h>
+#include <libxslt/security.h>
 #include <libxslt/transform.h>
 #include <libxslt/xsltutils.h>
 #endif   /* USE_LIBXSLT */
@@ -61,7 +62,8 @@ xslt_process(PG_FUNCTION_ARGS)
 	volatile xsltStylesheetPtr stylesheet = NULL;
 	volatile xmlDocPtr doctree = NULL;
 	volatile xmlDocPtr restree = NULL;
-	volatile xmlDocPtr ssdoc = NULL;
+	volatile xsltSecurityPrefsPtr xslt_sec_prefs = NULL;
+	volatile xsltTransformContextPtr xslt_ctxt = NULL;
 	volatile int resstat = -1;
 	xmlChar    *resstr = NULL;
 	int			reslen = 0;
@@ -83,36 +85,62 @@ xslt_process(PG_FUNCTION_ARGS)
 
 	PG_TRY();
 	{
-		/* Check to see if document is a file or a literal */
+		xmlDocPtr	ssdoc;
+		bool		xslt_sec_prefs_error;
 
-		if (VARDATA(doct)[0] == '<')
-			doctree = xmlParseMemory((char *) VARDATA(doct), VARSIZE(doct) - VARHDRSZ);
-		else
-			doctree = xmlParseFile(text_to_cstring(doct));
+		/* Parse document */
+		doctree = xmlParseMemory((char *) VARDATA(doct),
+								 VARSIZE(doct) - VARHDRSZ);
 
 		if (doctree == NULL)
 			xml_ereport(xmlerrcxt, ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
 						"error parsing XML document");
 
 		/* Same for stylesheet */
-		if (VARDATA(ssheet)[0] == '<')
-		{
-			ssdoc = xmlParseMemory((char *) VARDATA(ssheet),
-								   VARSIZE(ssheet) - VARHDRSZ);
-			if (ssdoc == NULL)
-				xml_ereport(xmlerrcxt, ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
-							"error parsing stylesheet as XML document");
+		ssdoc = xmlParseMemory((char *) VARDATA(ssheet),
+							   VARSIZE(ssheet) - VARHDRSZ);
 
-			stylesheet = xsltParseStylesheetDoc(ssdoc);
-		}
-		else
-			stylesheet = xsltParseStylesheetFile((xmlChar *) text_to_cstring(ssheet));
+		if (ssdoc == NULL)
+			xml_ereport(xmlerrcxt, ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
+						"error parsing stylesheet as XML document");
+
+		/* After this call we need not free ssdoc separately */
+		stylesheet = xsltParseStylesheetDoc(ssdoc);
 
 		if (stylesheet == NULL)
 			xml_ereport(xmlerrcxt, ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
 						"failed to parse stylesheet");
 
-		restree = xsltApplyStylesheet(stylesheet, doctree, params);
+		xslt_ctxt = xsltNewTransformContext(stylesheet, doctree);
+
+		xslt_sec_prefs_error = false;
+		if ((xslt_sec_prefs = xsltNewSecurityPrefs()) == NULL)
+			xslt_sec_prefs_error = true;
+
+		if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_READ_FILE,
+								 xsltSecurityForbid) != 0)
+			xslt_sec_prefs_error = true;
+		if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_WRITE_FILE,
+								 xsltSecurityForbid) != 0)
+			xslt_sec_prefs_error = true;
+		if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_CREATE_DIRECTORY,
+								 xsltSecurityForbid) != 0)
+			xslt_sec_prefs_error = true;
+		if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_READ_NETWORK,
+								 xsltSecurityForbid) != 0)
+			xslt_sec_prefs_error = true;
+		if (xsltSetSecurityPrefs(xslt_sec_prefs, XSLT_SECPREF_WRITE_NETWORK,
+								 xsltSecurityForbid) != 0)
+			xslt_sec_prefs_error = true;
+		if (xsltSetCtxtSecurityPrefs(xslt_sec_prefs, xslt_ctxt) != 0)
+			xslt_sec_prefs_error = true;
+
+		if (xslt_sec_prefs_error)
+			ereport(ERROR,
+					(errmsg("could not set libxslt security preferences")));
+
+		restree = xsltApplyStylesheetUser(stylesheet, doctree, params,
+										  NULL, NULL, xslt_ctxt);
 
 		if (restree == NULL)
 			xml_ereport(xmlerrcxt, ERROR, ERRCODE_EXTERNAL_ROUTINE_EXCEPTION,
@@ -128,6 +156,10 @@ xslt_process(PG_FUNCTION_ARGS)
 			xmlFreeDoc(restree);
 		if (doctree != NULL)
 			xmlFreeDoc(doctree);
+		if (xslt_sec_prefs != NULL)
+			xsltFreeSecurityPrefs(xslt_sec_prefs);
+		if (xslt_ctxt != NULL)
+			xsltFreeTransformContext(xslt_ctxt);
 		xsltCleanupGlobals();
 
 		pg_xml_done(xmlerrcxt, true);
@@ -139,6 +171,8 @@ xslt_process(PG_FUNCTION_ARGS)
 	xsltFreeStylesheet(stylesheet);
 	xmlFreeDoc(restree);
 	xmlFreeDoc(doctree);
+	xsltFreeSecurityPrefs(xslt_sec_prefs);
+	xsltFreeTransformContext(xslt_ctxt);
 	xsltCleanupGlobals();
 
 	pg_xml_done(xmlerrcxt, false);