Path: utzoo!mnetor!uunet!husc6!rutgers!clyde!watmath!gamiddleton
From: gamiddleton@watmath.waterloo.edu (Guy Middleton)
Newsgroups: comp.unix.wizards
Subject: Re: setreuid() functionality in sysV
Message-ID: <16600@watmath.waterloo.edu>
Date: 28 Jan 88 21:25:17 GMT
References: <1988Jan19.192854.3411@jarvis.csri.toronto.edu> <172@hudson.acc.virginia.edu> <1962@munnari.oz>
Reply-To: gamiddleton@watmath.waterloo.edu (Guy Middleton)
Organization: University of Waterloo [MFCF/ICR]
Lines: 33

In article <1962@munnari.oz> kre@munnari.oz (Robert Elz) writes:
> The Sys V developers at AT&T saw the need (correctly) for this facility,
> (that is, real and effective uid switching) .. its been added to unix
> ever since Waterloo (and probably others) did it in V6.
> 
> However, they seem to have a real phobia about adding anything new,
> so rather than add a new system call, which could have worked sanely,
> without annoying limitations, they just added the internal, hidden,
> saved set_user value, and allowed the old setuid() sys call to use
> that whenever it wanted.

As a point of information, here is the way it worked at Waterloo:

	Instead of two uids (real and effetive), there were three: real,
	effective, and effective-at-exec-time.  This third uid (called the
	euid) was not directly settable, and was never (well, almost never)
	examined.

	Two new syscalls were provided --

		schizo(), which would set the effective uid to either of
		the other two.

		become(), which would set the effective uid to an arbitrary
		value.  It would only work if the effective-at-exec uid was
		zero [this was the only place the euid was looked at].

	setuid() did the usual thing, except it left the euid unaffected.

We don't use this any more.  The BSD setreuid() makes it unnecessary.

 -Guy Middleton, University of Waterloo Institute for Computer Research
 gamiddleton@math.waterloo.edu, watmath!gamiddleton