--- libsandbox.c.orig	2003-10-13 21:26:35.000000000 +0200
+++ libsandbox.c.orig	2003-10-13 21:25:47.000000000 +0200
@@ -596,6 +596,9 @@ 
 	int result = -1;
 	char old_canonic[SB_PATH_MAX], new_canonic[SB_PATH_MAX];
 
+	if (!oldpath || !newpath || !strlen (oldpath) || !strlen (newpath))
+		return -EINVAL;
+
 	canonicalize_int(oldpath, old_canonic);
 	canonicalize_int(newpath, new_canonic);