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To: Ruslan Ermilov <ru@FreeBSD.org>
Subject: Re: cvs commit: src/usr.bin/at panic.c privs.h 
Cc: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
In-reply-to: Your message of "Tue, 04 Sep 2001 20:44:23 +0300."
		<20010904204423.D17754@sunbay.com> 
References: <20010904204423.D17754@sunbay.com>  <20010904192252.G1669@sunbay.com> <200109041615.f84GFpx76144@freefall.freebsd.org> <200109041620.f84GKZh35512@harmony.village.org> <20010904192252.G1669@sunbay.com> <200109041730.f84HUPh36129@harmony.village.org> 
Date: Tue, 04 Sep 2001 11:48:46 -0600
From: Warner Losh <imp@harmony.village.org>
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In message <20010904204423.D17754@sunbay.com> Ruslan Ermilov writes:
: On Tue, Sep 04, 2001 at 11:30:25AM -0600, Warner Losh wrote:
: > In message <20010904192252.G1669@sunbay.com> Ruslan Ermilov writes:
: > : On Tue, Sep 04, 2001 at 10:20:35AM -0600, Warner Losh wrote:
: > : > In message <200109041615.f84GFpx76144@freefall.freebsd.org> Ruslan Ermilov writes:
: > : > :   The setre[ug]id() calls are still used in the REDUCE_PERM macro (with
: > : > :   the r[ug]id arguments of -1) so that the call changes the saved user
: > : > :   and group IDs of the process to that specified.
: > : > 
: > : > Just a side note: We should not use setre* calls in the base sources.
: > : > They present problems for dropping privs since they obliterate the
: > : > saved uid.
: > : > 
: > : Exactly what was needed in this case -- to set saved IDs to the specified
: > : values.
: > 
: > setuid() does the same thing and is a less dangerous interface to use
: > is my point.
: > 
: Not in FreeBSD's implementation.  In our implementation, setuid() always sets
: real, effective, and saved IDs to the specified values (if permitted).
: Consider the case where the ``setuid root'' program run by the user ``joe''
: wants to "reduce" its privileges to ``setuid daemon'', still preserving the
: original real IDs, and allowing to switch between ``joe'' and ``daemon''.

No, in FreeBSD's implementation.  setreuid should never be used.

Use seteuid() do do the switching.  It will allow the library routines
to drop and add privs better than setreuid().

Warner

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