Ignore SECURITY DEFINER and SET attributes for a PL's call handler.

tglsfdc · tglsfdc · commit b53c7c3bc696 · 2012-05-30T23:28:16.000-04:00
It's not very sensible to set such attributes on a handler function; but if one were to do so, fmgr.c went into infinite recursion because it would call fmgr_security_definer instead of the handler function proper. There is no way for fmgr_security_definer to know that it ought to call the handler and not the original function referenced by the FmgrInfo's fn_oid, so it tries to do the latter, causing the whole process to start over again. Ordinarily such misconfiguration of a procedural language's handler could be written off as superuser error. However, because we allow non-superuser database owners to create procedural languages and the handler for such a language becomes owned by the database owner, it is possible for a database owner to crash the backend, which ideally shouldn't be possible without superuser privileges. In 9.2 and up we will adjust things so that the handler functions are always owned by superusers, but in existing branches this is a minor security fix. Problem noted by Noah Misch (after several of us had failed to detect it :-(). This is CVE-2012-2655.
diff --git a/src/backend/utils/fmgr/fmgr.c b/src/backend/utils/fmgr/fmgr.c
@@ -153,7 +153,7 @@ fmgr_lookupByName(const char *name)
 void
 fmgr_info(Oid functionId, FmgrInfo *finfo)
 {
-	fmgr_info_cxt(functionId, finfo, CurrentMemoryContext);
+	fmgr_info_cxt_security(functionId, finfo, CurrentMemoryContext, false);
 }
 
 /*
@@ -168,7 +168,7 @@ fmgr_info_cxt(Oid functionId, FmgrInfo *finfo, MemoryContext mcxt)
 
 /*
  * This one does the actual work.  ignore_security is ordinarily false
- * but is set to true by fmgr_security_definer to avoid recursion.
+ * but is set to true when we need to avoid recursion.
  */
 static void
 fmgr_info_cxt_security(Oid functionId, FmgrInfo *finfo, MemoryContext mcxt,
@@ -218,7 +218,7 @@ fmgr_info_cxt_security(Oid functionId, FmgrInfo *finfo, MemoryContext mcxt,
 	/*
 	 * If it has prosecdef set, or non-null proconfig, use
 	 * fmgr_security_definer call handler --- unless we are being called again
-	 * by fmgr_security_definer.
+	 * by fmgr_security_definer or fmgr_info_other_lang.
 	 *
 	 * When using fmgr_security_definer, function stats tracking is always
 	 * disabled at the outer level, and instead we set the flag properly in
@@ -399,7 +399,13 @@ fmgr_info_other_lang(Oid functionId, FmgrInfo *finfo, HeapTuple procedureTuple)
 		elog(ERROR, "cache lookup failed for language %u", language);
 	languageStruct = (Form_pg_language) GETSTRUCT(languageTuple);
 
-	fmgr_info(languageStruct->lanplcallfoid, &plfinfo);
+	/*
+	 * Look up the language's call handler function, ignoring any attributes
+	 * that would normally cause insertion of fmgr_security_definer.  We
+	 * need to get back a bare pointer to the actual C-language function.
+	 */
+	fmgr_info_cxt_security(languageStruct->lanplcallfoid, &plfinfo,
+						   CurrentMemoryContext, true);
 	finfo->fn_addr = plfinfo.fn_addr;
 
 	/*
