Recursive sandboxes: Extending systrace to empower applications

Abstract

The systrace system-call interposition mechanism has become a popular method for containing untrusted code through program-specific policies enforced by user-level daemons. We describe our extensions to systrace that allow sandboxed processes to further limit their children processes by issuing dynamically constructed policies. We discuss our extensions to the systrace daemon and the OpenBSD kernel, as well as a simple API for constructing simple policies. We present two separate implementations of our scheme, and compare their performance with the base systrace system. We show how our extensions can be used by processes such as ftpd, sendmail, and sshd. © 2004 by Springer Science+Business Media Dordrecht.