1st release of an LSA authentication package

Igor Peshansky pechtcha@cs.nyu.edu
Mon Nov 27 15:02:00 GMT 2006


On Mon, 27 Nov 2006, Corinna Vinschen wrote:

> Finally, after mulling over the idea to write an LSA authentication
> package for over 5 years and after 5 years of idly complaining about
> Microsoft's documention, I now managed to create an LSA authentication
> package to support our setuid implementation.
>
> I've checked the code in a couple of minutes ago.  This new LSA
> authentication code has been tested on Windows 2000, XP, XP 64 bit,
> 2003 R2 64 bit and Vista RC2.
>
> This LSA authentication package is supposed to replace the subauth stuff
> entirely.  For now I have only disabled subauthentication, but I intend
> to throw the code away at one point.
>
> So, what are the advantages of having an LSA authentication package?
>
> - The returned user token is matching the needs of all underlying OSes,
>   especially the new concepts in Vista.
>
> - A real logon session gets created.  Native calls to LookupAccountSid
>   will return the correct domain\user combination (See the output of a
>   native whoami.exe).
>
> - The user token is an interactive token, not a network token as
>   returned by subauthentication.
>
> - The authentication package DLL can simply sit in /bin.  The
>   installation and registration of the authentication package only
>   requires to tweak a registry key and rebooting.
>
> - This package comes complete with an installation script called
>   /bin/cyglsa-config.
>
> - Using LSA authentication allows services like sshd to run under the
>   SYSTEM account again.  Using NtCreateToken requires SeCreateTokenPrivilege
>   and starting with Windows 2003, services running under the SYSTEM
>   account don't have this privilege anymore.  So it was necessary to add
>   special user accounts like sshd_server.  LSA authentication only
>   requires the SeTcbPrivilege, which SYSTEM is running with by default.
>
> - Under Vista, the user token contains everything necessary to support
>   mandatory integrity control.  It was *not* enough just to add a MIC
>   SID to the group list and call NtCreateToken.  The underlying mechanism
>   is a bit more complicated.  So, in the long run, the NtCreateToken
>   method should only be a fallback to support NT 4.  All other systems
>   are better off with LSA authentication.

Thanks, Corinna!  All of this sounds really cool, but...

> [snip]
> Anything else?
>
> - Yes.  LSA authentication packages are loaded by LSASS.EXE at boot
>   time.  Consequentially it's impossible to replace the DLL without
>   rebooting the machine.  Which means, everybody having registered the
>   Cygwin LSA auth package will always have to reboot after installing a
>   new Cygwin DLL version.  However, the cyglsa DLL is bound to the
>   Cygwin version it's shipped with, so LSA authentication will fail
>   until the machine has been rebooted.

This is making me quite uncomfortable.  I really don't want to have to
reboot every time I update Cygwin (especially since there is no easy way
to detect from setup.exe that a reboot is needed if all Cygwin processes
are stopped).  Would it be enough to just restart the "Net Logon" service?
Can this be done in the lsa/cygwin postinstall script?

I'll investigate the above when I can get my machine into a rebootable
state...  Makes me wish I were running VMware...
	Igor
-- 
				http://cs.nyu.edu/~pechtcha/
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