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Date: Mon, 09 Jan 2006 15:08:45 -0500
From: "Larry Hall (Cygwin)" <reply-to-list-only-lh AT cygwin DOT com>
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To: cygwin AT cygwin DOT com, cygwin AT cygwin DOT com
Subject: Re: 'su' no longer working?
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Corinna Vinschen wrote:
> 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).

This is a good point.  Perhaps this is an argument to change the name of
the "working" su to syssu or something and leave the su script as is.
Certainly if there's some useful functionality in su in certain cases, it's
a shame to mask it completely but it seems reasonable to shield ourselves
from those who would use su with expectations and with an itchy email
finger. ;-)

-- 
Larry Hall                              http://www.rfk.com
RFK Partners, Inc.                      (508) 893-9779 - RFK Office
838 Washington Street                   (508) 893-9889 - FAX
Holliston, MA 01746


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