<28 at van-bc.UUCP>

[iv at hal6000.UUCP]

/* Written 10:24 am  Oct 10, 1989 by van-bc!skl in comp.unix.xenix */
|  ------------------- "setuid() in Xenix 2.3.2" -------------------
|
|  Could some setuid() or Xenix expert please help?

|  I [ . . . ] need to imitate the seteuid() calls in the code with setuid()'s,
|  since Xenix doesn't have seteuid().
|
|  What I need:
|
|	 - Start with euid(root).
|	 - ...
|	 - Switch to euid(arbitrary_uid).
|	 - ...
|	 - Revert back to euid(root).
|	 - ...

Your basic problem is that setuid() will act differently depending on
whether you are root or not.  Here's more-or-less how System V setuid()
works:

	if (effective-uid != 0 && (requested-uid == real-uid 
	                           || requested-uid == remembered-set_uid))
	{
		effective-uid = requested-uid;
	}
	else if (effective-uid == 0) {
		real-uid = requested-uid;
		effective-uid = requested-uid;
		remembered-uid = requested-uid;		/* Bye-bye privs! */
	} else
		return (EPERM);

So, though XENIX would accomodate you if you were using just two UIDs,
the fact you wish to be many users via root spells doom for this
technique.  The only way to do what you wish here is to fork
sub-processes, setuid(user) there and exit when done with that user.
(I know, I know, oooh, ick!)

|  Thank you very much for your help.
|  -- 
|  Samuel Lam     <skl at wimsey.bc.ca> or {uunet,ubc-cs}!wimsey.bc.ca!skl

Oh, did I help?  :-)
----
IV  (aka John Elliott IV)	 Domain: iv at hal6000.Tandy.COM
Tandy Systems Software		   UUCP: ...!texbell!letni!hal6000!iv
900 Two Tandy Center		     or: ...!decvax!microsoft!trsvax!hal6000!iv
Fort Worth, TX 76102		  Phone: 817/390-2701; 9:30am-6:00pm CST, M-F

[This information was provided by an individual and is  not  nor  should
 be  construed  as  being  provided by Radio Shack or Tandy Corporation.
 Radio Shack and/or Tandy Corporation have no obligation to support  the
 information  provided.   I don't think they even know what UNIX is any-
 more anyway ("Is that like DOS 4.0?"). *sigh* The author will, however, 
 cheerfully accept mail.]