samba - Mar 2021 - Understanding ID mapping between a campus AD and a local LDAP

I'll try to describe our situation as completely as possible:

- Our campus runs active directory. It contains an entry for every campus
identity / account, as you'd expect.

- Our (research computing / unixy) group runs an LDAP server (389 Directory
Server) that has the same usernames as are in the campus active directory, but
potentially different uidNumbers.

- We have data in multiple shared file systems within our (research computing /
unixy) environment. We are trying to make some of this data available via SMB.

- Our Samba server is joined to our campus AD, and we are trying to map the
identities in the campus AD to the identities in our internal LDAP by matching
up usernames.

- So if I log into Samba (e.g., with macOS Finder) with my AD credentials, I
want it to see my name is "username" in AD, authenticate, then look up
"username" in our internal LDAP (either via LDAP using idmap_rfc2307,
or via NSS using idmap_nss) to find what my UID number is in the Unix
environment, ignoring what AD says my UID number should be.

If this is not what Samba idmap is for (or, at least, what idmap_rfc2307 or
idmap_nss is for), then I do not understand what Samba idmap is for.

I very much appreciate your response. I'm hoping to understand better.
Thanks for your help.

~jonathon

________________________________________
From: samba <samba-bounces at lists.samba.org> on behalf of Rowland penny
via samba <samba at lists.samba.org>
Sent: Tuesday, March 23, 2021 9:00 AM
To: samba at lists.samba.org
Subject: Re: [Samba] Understanding ID mapping between a campus AD and a local
LDAP

On 23/03/2021 14:43, Jonathon A Anderson via samba
wrote:
> We?re trying to get ID mapping set up between a campus AD and our internal
LDAP. I?ve tried both idmap_rfc2307 and idmap_nss backends; but if my LDAP
uidNumber doesn?t match my AD uidNumber, mapping doesn?t appear to work. This
surprises me because the _names_ match (AD sAMAccountName and LDAP uid (name)),
and I thought that the whole point of idmap was to translate an AD username into
a UNIX uidNumber. What am I misunderstanding or doing wrong?
>
> For example, when using idmap_nss, I see that it?s trying to call getpwuid
with my AD uidNumber, rather than with my LDAP uidNumber.
>
> I feel like I?m missing something fundamental about how idmap works and
what it?s for if it?s trying to look up a local identity by the AD uidNumber
rather than by the LDAP uidNumber or uid (name).
>
> Thanks for you attention and advice.
>
> ~jonathon
>
It sounds like you are trying to map users & groups from two places at
once, if this is the case, I don't think it is ever going to work.

what do you use the ldap for ?

Rowland



--
To unsubscribe from this list go to the following URL and read the
instructions:  https://lists.samba.org/mailman/options/samba

On 23/03/2021 16:50, Jonathon A Anderson wrote:
> I'll try to describe our situation as completely as possible:
>
> - Our campus runs active directory. It contains an entry for every campus
identity / account, as you'd expect.
>
> - Our (research computing / unixy) group runs an LDAP server (389 Directory
Server) that has the same usernames as are in the campus active directory, but
potentially different uidNumbers.
>
> - We have data in multiple shared file systems within our (research
computing / unixy) environment. We are trying to make some of this data
available via SMB.
>
> - Our Samba server is joined to our campus AD, and we are trying to map the
identities in the campus AD to the identities in our internal LDAP by matching
up usernames.
>
> - So if I log into Samba (e.g., with macOS Finder) with my AD credentials,
I want it to see my name is "username" in AD, authenticate, then look
up "username" in our internal LDAP (either via LDAP using
idmap_rfc2307, or via NSS using idmap_nss) to find what my UID number is in the
Unix environment, ignoring what AD says my UID number should be.
>
> If this is not what Samba idmap is for (or, at least, what idmap_rfc2307 or
idmap_nss is for), then I do not understand what Samba idmap is for.

Are you using the 389 Directory Server just for authentication ? Using 
exactly the same users & groups that are in AD ?

If so, then probably the best way out of this is to join all your Unix 
machines to your AD and use the winbind 'rid' backend on all of them, 
Unfortunately you will get new Unix ID's, but I think this will happen 
with whatever method you end up using. The big benefit to using AD, you 
will be able to turn off the 389 Directory server and then have only one 
point of management.

If you are using the 389 Directory Server for more than authentication 
(mailserver for instance), then it would be a bit more difficult, but 
the above should still work.

Rowland