Howard,
Howard Chu wrote:
Date: Wed, 27 Dec 2006 10:01:42 -0800
From: Jim Hogan <jimh@xxxxxxxxxxxxxxxx>
I have a brand-new Samba 3.x domain working with LDAP/FDS backend;
this is just for my small (university) department of ~350 users.
The university operates an overarching Kerberos realm. My best
possible case would be to use that Kerberos realm for
authentication/password but continue to maintain department LDAP for
actual user/group authorization/rights. If I can get everything to
use people's existing university password, that would be very sweet;
failing that, I have to give out about 300 passwords in the next
month :(
I see the FDS Kerberos Howto, and it seems to make Kerberos
integration pretty simple, but what is not clear to me is whether it
is possible to pass this Kerberos authentication through to Samba
clients. The few references I see to Samba-Kerberos integration
modify the smb.conf with direct references to kerberos realm and
keytab that would seem to result in:
Samba ----> Kerberos
_____ <---- ________
where what I think I want is more like:
Samba ----> LDAP ----> Kerberos
_____ <---- ____ <---- ________
(sorry for the awful ASCII!) where I retain "passdb backend =
ldapsam:ldap://x.x.x.x"; as the user/group store, but where LDAP
refers to Kerberos for authn/passwd.
I was going to pose this question to the Samba users list, but I
thought there might be more value to ask first whether anyone has
worked on this in a FDS context. Not to say anything bad about other
LDAP servers, but I can sometimes find it hard to map integration
discussions that use OpenLDAP examples to my situation.
So, anyone on the list running a completely integrated
Samba/FDS/Kerberos setup that references an overarching Kerberos realm?
You're confusing some of these steps.
That happens on a regular basis :( To say that I understand Kerberos
poorly would be charitable.
First of all, the direct Samba -> Kerberos route is only talking about
a very special case - an SMB client with its own TGT, getting a
service ticket from Kerberos for talking to Samba. In this case, Samba
uses Kerberos as the actual client authentication mechanism. And as
noted here:
http://www.mail-archive.com/samba@xxxxxxxxxxxxxxx/msg80208.html
this only works in Samba3 when Samba is talking to a real
ActiveDirectory server.
Yes. While my little diagram might still hold some water from a
"desired effect" basis, the more I looked at it, the more it seemed
obvious that there would need to be a client TGT, not some imagined LDAP
pass-through.
When Samba is configured to talk directly to LDAP, it only uses it as
a data store, not as an authentication mechanism. In that case, it is
expecting to find sambaNTPassword or sambaLMPassword attributes in the
LDAP store, so that it can validate the authentication itself. As
such, your Samba -> LDAP -> Kerberos picture doesn't apply.
Currently the only way to have all of these things integrated in one
place is to use the OpenLDAP server with smbk5pwd module, with Heimdal
KDC using OpenLDAP as its data store, and Samba using OpenLDAP as its
data store. I've contributed code to the Fedora project to assist them
along these same lines but it's still missing secure ldapi:// support
and a few other things, so AFAIK OpenLDAP is the only solution at the
moment.
Thanks for your contributions on all fronts. I debated OpenLDAP vs. FDS
for some time, and wound up deploying FDS in part due to admin tools and
some built-in self-service functionality.
The only way you could set things up so that authentication works as
you want is if the clients send plaintext passwords over the wire.
That's obviously a bad idea to begin with, and for recent clients (W2K
etc) it's not even an option.
If your existing Kerberos KDC is not Heimdal, and you don't have the
option of migrating to Heimdal, then I think you're out of luck.
The gent who can answer that question is on vacation, but I bet I am out
of luck :)
I know that there's preliminary support for LDAP in recent MIT
releases, but my experience with MIT Kerberos has been pretty
unsatisfactory over the years. They only recently took steps to make
their library thread-safe, and their library performance is still
several times slower than Heimdal's, making it unsuitable for busy
sites. Even if you decided to switch to using Heimdal integrated with
LDAP, you still need the NTLM keys, which you cannot derive from the
Kerberos keys, so I think you're looking at regenerating your ~300
passwords regardless.
Some of the necessary steps here seem to imply a degree of control (NTLM
Keys) over Kerberos infrastructure which I will never have. Whatever I
do WRT our university Kerberos, it will have to be as a basic,
unprivileged client. I don't know enough to contemplate whether ruuning
our own Kerberos service of some type would be of any use.
Of course, there's always the brute force approach of running a
password cracker on the KDC database to try to guess the original
plaintext. It's a self-defeating activity but I've been cajoled into
doing it in the past. (It takes a long time, you may not successfully
crack all the accounts, and succeeding only means that your users have
poorly chosen passwords that they ought to change anyway.)
I don't think any brute force is in my future ('tho you just reminded me
to try to figure out why my smb.conf minimum password length isn't
working!!)
Thanks very much for this exhaustive reply. Being restless during this
break week I posted a similar question to Samba list, but perhaps I can
reference your response there to forestall any other time-consuming
effort to reply.....
Cheers,
Jim
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