Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.unix.programmer
Subject: Re: rdist/setreuid
Message-ID: <6921@auspex.auspex.com>
Date: 30 Mar 91 23:43:40 GMT
References: <13726@arctic.nprdc.navy.mil>
Organization: Auspex Systems, Santa Clara
Lines: 16

>We ran into a problem while trying to port rdist from 4.3bsd to sysVr3.
>rdist uses setreuid to switch back and forth between root and the user,
>but sysVr3 (and even sysVr4 apparently) only has setuid; ie, once
>you're the user, there's no going back to root.  Are we overlooking
>something?  It's particularly surprising that sysVr4 also seems to
>have this limitation.

S5R4 may have, as an undocumented feature, a "seteuid()" call that, even
if you're root, sets *only* the effective UID and leaves the
saved-set-user ID alone.  I think the next POSIX 1003.1 supplement will
mandate "seteuid()", so it shouldn't remain undocumented forever....

(S5R4 apparently has a "setreuid()" call in the BSD compatibility
library; whether any particular vendor supplies that library is up to
them.  I don't know how complete it is, and I think it's implemented, in
part, atop "seteuid()"....)