[Date Prev][Date Next] [Chronological] [Thread] [Top]

Re: SASL pass-through autentication with a ldap-backend KDC

Howard Chu a écrit :
Guillaume Rousse wrote:
Hello list.

Reading http://www.openldap.org/doc/admin24/security.html#SASL password
storage scheme, I understand autentication can be delegated to an
external mechanisme. Such as, for instance, a kerberos server. In this
case, it is advised to prevent changing passwords in the directory.

That part of the doc appears to be wrong. slapd will call SASL's setpass function to change a SASL password, so there's no reason to prevent changing passwords via LDAP.
I guess it is just a phrasing issue, and the doc means 'take care users don't inadvertly rewrite their password attribute with a true password instead of keeping this pointer'.

Also, the {KERBEROS} delegation scheme has been removed, only SASL delegation is supported.

What happens if the autentication provider is an heimdal server, using
OpenLDAP as its backend, and smbkrb5 overlay to keep ldap, samba and
kerberos password synced ? Does pass-through still work ?

When using the smbk5pwd overlay in such a configuration, there is no pass-through. The Kerberos credentials reside in slapd and slapd validates the authentication directly.
Only if you use the {SMBKRB5} redirection, or even if you use a {SASL} one ?

I know smbkrb5 has a special {smbkrb5} password storage scheme for
redirecting autentication against kerberos password internally, not
relying on a external SASL process. But it's only usable if smbkrb5
overlay is available (some of our slaves servers are centos-based, and
don't have this overlay, but still need to autenticate users).

You can always obtain the source tree that was used to build your distro and compile the overlay yourself.
Out of my control, unfortunatly (otherwise, those servers wouldn't use centOs at all :P). Anyway, it doesn't really hurt, it will just make those servers from a specific department unable to autenticate users from other department, not their own ones.

And the
trick of setting password-hash directive in slapd.conf to {smbkrb5} to
prevent overwriting of userPassword attribute on PasswordChange
operation with a normal value has the drawback than even pure ldap
administrative accounts (syncrepl, for instance) get redirected to
kerberos password for autentication, whereas only our users have
principals currently.

The password_hash setting in slapd.conf is only a default. You can explicitly set any hash type on any account.
Yes, if you use an normal attribute change operation. I don't think there is a way to use an extended password change operation, and bypass this value. Anyway, it doesn't matter very much either, only sysadmins are suposed to take care of administrative accounts.

Let's to summarize what's I'm understanding so far.

First, you have to use either password_hash or ACLs to prevent users to rewrite password attribute with a standard password. Using password_hash is only possible with smbkrb5 overlay, because it uses a fixed {SMBKRB5} pattern, whereas {SASL} storage scheme change with any user

Second, {SMBKRB5} is an optimisation only possible with smbkrb5 overlay, whereas {SASL} is more generical, but also more expensives, as external calls are needed.

Am I correct ?
Guillaume Rousse
Moyens Informatiques - INRIA Futurs
Tel: 01 69 35 69 62