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Date: Mon, 9 Jan 2006 16:00:22 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: 'su' no longer working?
Message-ID: <20060109150022.GE32312@calimero.vinschen.de>
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On Jan  9 09:30, Igor Peshansky wrote:
> On Mon, 9 Jan 2006, Eric Blake wrote:
> 
> > According to Igor Peshansky on 1/9/2006 6:04 AM:
> > >
> > > Right, that's pretty much what I was asking for above.  Eric, if it
> > > helps, I can look into submitting the patch later this week, though I
> > > haven't looked at the coreutils code in a while, so it might take some
> > > time to understand the specifics.
> >
> > I've already been playing some with a cygwin-specific patch.  Using the
> > tips at http://cygwin.com/cygwin-ug-net/ntsec.html#ntsec-setuid, I have
> > already gotten a working implementation that will switch user context on
> > NT machines with a password.  But I still want to get passwordless
> > switching working where possible.  The patch should apply to src/su.c
> > provided in the 5.93-2 source tarball from setup.exe, as a starting
> > point for your hacking.
> 
> Ok, thanks, I'll play around with it...
> 
> > Speaking of which, I noticed that in my attached patch (work in
> > progress), I got a failure return for PrivilegeCheck on my NT machine
> > when run as SYSTEM, even though my understanding is that on NT, SYSTEM
> > has the privileges of passwordless context switching.  Any ideas what I
> > might need to fix to make this check more robust, short of just trying a
> > setuid() to see if it will succeed without first doing the
> > cygwin_logon_user()/cygwin_set_impersonation_token() check?
> 
> Heh, what's wrong with doing that?  If setuid() fails, try it with a
> password -- I can't think of any caveats, frankly...  Corinna?

It's fine if su implements password login and trying to call set(e)uid
just to check if passwordless login might work is fine, too, but it's
a bit off my point.

My point is that Administrators don't have the permissions to do any one
of these actions by default.  You can't change user context unless you
have a service running under a privileged (SYSTEM) account, which starts
the process for you (RunAs, sshd).  The important fact here is that
users working under an Admin account expect that su just works for them,
but it doesn't.

So, whatever you do codewise, be prepared to either add descriptive
messages to su so that users read *why* su might fail for them, or
be prepared to get lots of question on this list (since nobody reads
mailing list archives anyway).


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat


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