From: Tanaka Akira <akr@...17n.org>
Date: 2004-05-19T23:16:07+09:00
Subject: Re: RCR: UNIX credentials

In article <1084926982.2388.130.camel@comp>,
  Guillaume Marcais <guslist@free.fr> writes:

> The Linux system provide a mechanism to send UNIX credentials as
> ancilary data (the same way as you can pass file descriptors,
> implemented in Ruby as send_io). Other UNIX implementation I believe
> offer similar mechanism.

I surveyed the feature sometime ago.
Unfortunately it is not so portable.

1. SCM_CREDS and getpeerid.

  There are 2 kind of interfaces.
  SCM_CREDS: a client must send a credential explicitly.
  getpeerid: a client doesn't need to send a credential.

2. getpeerid

  As far as I know, following system has getpeerid or similar.

  FreeBSD 4.6 (LOCAL_PEERCRED, http://www.freebsd.org/cgi/cvsweb.cgi/src/lib/libc/gen/getpeereid.3)
  OpenBSD 3.0 (http://www.openbsd.org/cgi-bin/man.cgi?query=getpeereid&sektion=2)
  Linux (socket(7): getsockopt SO_PEERCRED)
  MacOS X (http://www.hmug.org/man/3/getpeereid.html)

  DJB recommends getpeerid.
  http://cr.yp.to/docs/secureipc.html

2. SCM_CREDS

  As far as I know, following system has SCM_CREDS or similar.
  However, credential information varies on each system.

  FreeBSD 3.0 (recvmsg(2): SCM_CREDS: pid, uid, euid, gid, supp groups)
  NetBSD 1.4.0 (unix(4): LOCAL_CREDS, SCM_CREDS: uid, euid, gid, egid, supp groups: http://www.netbsd.org/Changes/changes-1.4.html)
  OpenBSD 2.5 (SCM_CREDS: uid, euid, gid, egid, supp groups)
  Linux (unix(7): SCM_CREDENTIALS: pid, uid, gid)

3. send_io/recv_io may be usable for authentication.

  See: Secure UNIX Programming FAQ
  4.4) How do I authenticate a non-parent process?
  http://www.whitefang.com/sup/secure-faq.html
-- 
Tanaka Akira