Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!purdue!haven!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.unix.questions
Subject: Re: doing setreuid with setuid in modern sysv
Message-ID: <11955@smoke.BRL.MIL>
Date: 16 Jan 90 04:22:31 GMT
References: <90Jan14.130354est.2125@neat.cs.toronto.edu>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 9

In article <90Jan14.130354est.2125@neat.cs.toronto.edu> rayan@cs.toronto.edu (Rayan Zachariassen) writes:
>Could someone set me straight on this please?  How does one flip back and
>forth between uid 0 and uid != 0 in a process started by uid 0 on a modern
>System V ?

Make the binary owned by UID 0 and turn on its set-UID bit.
Then when executed by somebody whose UID is non-zero,
setuid() can be used to toggle between the initial EUID of
0 and the invoker's UID.