Hi,

thanks for the great explanation....

regards

Steven Jones

Technical Specialist - Linux RHCE

Victoria University, Wellington, NZ

0064 4 463 6272

________________________________________
From: Alexander Bokovoy [aboko...@redhat.com]
Sent: Friday, 24 February 2012 11:01 a.m.
To: Steven Jones
Cc: freeipa-users@redhat.com
Subject: Re: [Freeipa-users] samba & IPA

On Tue, 21 Feb 2012, Steven Jones wrote:

> Hi,
>
> Any good docs on making samba / smbclient / clients work with ipa?
> not having much luck with google....
The stack of protocols that Samba is implementing disassociates
authentication and actual connection to the shares. First you
authenticate and once authenticated, you can connect to any share
within the server. At this point there might be per-share limitations
put on but authentication step is done already.

As part of authentication, Samba may enforce PAM accounting
restrictions if 'obey pam restriction' option is set in the
configuration file. This would give you a way to enforce HBAC rules
per user connected to the server -- make sure your smbd PAM config is
using sssd for accounting purposes and then SSSD would do checks over
HBAC rules with 'smbd' service.

However, this would only limit access to the host globally as it
happens during authentication phase, not later, when actual connection
to the share would be done.

In order to limit per-share connection, Samba has 'valid users' and
'allow hosts' options. These specify lists of users and hosts
correspondingly. Unfortunately, the way it is implemented in Samba,
these lists are taken directly from the configuration source, thus no
way to dynamically change them other than playing with configuration
files.

One could do configuration file tuning per connected host, for
example, or per user, using 'include = /path/to/config' and Samba
configuration macros. This would still not give you dynamic
configuration though.

One could also do a 'preexec script' hook that is run before
connection to a share is made. This approach allows you to implement a
simple PAM-enabled tool that could be spawned from Samba at connection
to share time and use SSSD HBAC tests (on PAM account) plus something
additional to perform per-share restriction (see below why).

All other methods would require modifying Samba to change
'allow_access()' function API and implementation. This is not planned
at the moment -- neither from FreeIPA nor from Samba Team side. There
are also considerable performance requirements to this particular
function.

However, even if anything like that is performed, we have one specific
issue that HBAC rules do not allow to differentiate between service
and its (optional) sub-services. You can think about shares as
sub-services of a service 'smbd' but HBAC in FreeIPA doesn't allow to
specify those. Ideally, ipaHBACService object class could be extended
to include sub-services but handling those in UI would become a
nightmare -- after all, you'll need to have as much ipaHBACService
objects as number of servers x number of shares. Something better
needs to be created.

--
/ Alexander Bokovoy

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