Sorry to barge in straight away with a question like this, but my time is running out and I have not been able to get a straight answer out of google. I'm going through the hypotheticals for using ldap as the backend for kerberos, and I've hit a chicken and egg problem with SASL- can someone untangle my mind? IF kerberos is using ldap as a backend store for keys, users, etc, and one can set the rootdn and leave the rootpw for later entry in the database itself, and the password can use SASL auth- what happens if you use kerberos as the auth mechanism? According to the book, slapd needs to set up the access to the key from startup, and kerberos in this scenario will need ldap up to provide the key. Is ldap up enough that kerberos can provide this? Or does ldap retry or something so that this problem is overcome?

Da Rock wrote: > Sorry to barge in straight away with a question like this, but my time > is running out and I have not been able to get a straight answer out of > google. > > I'm going through the hypotheticals for using ldap as the backend for > kerberos, and I've hit a chicken and egg problem with SASL- can someone > untangle my mind? > > IF kerberos is using ldap as a backend store for keys, users, etc, and > one can set the rootdn and leave the rootpw for later entry in the > database itself, and the password can use SASL auth- what happens if you > use kerberos as the auth mechanism? > > According to the book, slapd needs to set up the access to the key from > startup, and kerberos in this scenario will need ldap up to provide the > key. Is ldap up enough that kerberos can provide this? Or does ldap > retry or something so that this problem is overcome? Which KDC are you going to use? Why do you want to use Kerberos as authc mech for the connection between the KDC and the LDAP backend server? Usually one stashes the password at the KDC which does a simple bind. There's nothing wrong with that. Also I wouldn't use the rootdn as bind-DN for the KDC. I'd rather recommend to create service accounts and define appropriate ACLs. Another possibility is to use SASL/EXTERNAL for a ldapi:/// connection (Unix domain socket) and map the Unix user to a service account for the KDC. In this case the service account does not need a password at all. But KDC and LDAP server have to run on the same machine for this to work.

We are starting to work towards implimenting this very solution. Is there any documentation you have found to be particularly helpful? Thanks -Troy

On Mar 4, 2009, at 2:30 AM, Da Rock wrote: > Sorry to barge in straight away with a question like this, but my time > is running out and I have not been able to get a straight answer out > of > google. > > I'm going through the hypotheticals for using ldap as the backend for > kerberos, and I've hit a chicken and egg problem with SASL- can > someone > untangle my mind? > > IF kerberos is using ldap as a backend store for keys, users, etc, and > one can set the rootdn and leave the rootpw for later entry in the > database itself, and the password can use SASL auth- what happens if > you > use kerberos as the auth mechanism? > > According to the book, slapd needs to set up the access to the key > from > startup, and kerberos in this scenario will need ldap up to provide > the > key. Is ldap up enough that kerberos can provide this? Or does ldap > retry or something so that this problem is overcome? > > Thoughts? > > Cheers >

Da Rock wrote: > On Wed, 2009-03-04 at 20:13 +0100, Michael Ströder wrote: >> Da Rock wrote: >>> Sorry to barge in straight away with a question like this, but my time >>> is running out and I have not been able to get a straight answer out of >>> google. >>> >>> I'm going through the hypotheticals for using ldap as the backend for >>> kerberos, and I've hit a chicken and egg problem with SASL- can someone >>> untangle my mind? >>> >>> IF kerberos is using ldap as a backend store for keys, users, etc, and >>> one can set the rootdn and leave the rootpw for later entry in the >>> database itself, and the password can use SASL auth- what happens if you >>> use kerberos as the auth mechanism? >>> >>> According to the book, slapd needs to set up the access to the key from >>> startup, and kerberos in this scenario will need ldap up to provide the >>> key. Is ldap up enough that kerberos can provide this? Or does ldap >>> retry or something so that this problem is overcome? >> Which KDC are you going to use? Why do you want to use Kerberos as authc >> mech for the connection between the KDC and the LDAP backend server? >> >> Usually one stashes the password at the KDC which does a simple bind. >> There's nothing wrong with that. Also I wouldn't use the rootdn as >> bind-DN for the KDC. I'd rather recommend to create service accounts and >> define appropriate ACLs. >> >> Another possibility is to use SASL/EXTERNAL for a ldapi:/// connection >> (Unix domain socket) and map the Unix user to a service account for the >> KDC. In this case the service account does not need a password at all. >> But KDC and LDAP server have to run on the same machine for this to work. > > I'm not sure you quite understand what I mean here- at least I'm not > sure I get your point (if you care to clarify). Although maybe my > mention of rootdn has confused the matter...? > > To be precise Heimdal offers an option to use the ldap as a backend > store for all of its data (keytabs, user profiles, etc). Obviously ACLs > need to reflect this so although ladpi:/// socket is used, one should > use ACLs that allow only the Heimdal to access the database (at least > the keys anyway). > > Openldap, in turn, offers the use of Kerberos (Heimdal in this case) to > provide authentication through SASL. In the docs it says slapd needs to > setup the key with kerberos at the start, so services need to be > registered with kerberos through kadmin. > > Now, IF Heimdal Kerberos is using ldap as its backend store and the user > info for itself is in the database, and IF ldap is using SASL for auth, > then ldap needs to register with Heimdal as a service to authenticate > Heimdal which is using ldap as its backend service (Typing it out like > this is kinda helping to clear the picture in my own mind... :) ). A > chicken and egg scenario if I ever saw one. You're missing the obvious fact that GSSAPI/Kerberos is not the only secure SASL mechanism available in this picture, and it is obviously not the one the KDC uses to talk to LDAP.

> A couple of points of interest come to mind: > > 1. Security of the ldapi socket needs to be paramount. Permission should > be as tight as can be allowed so that only access is as necessary for > use. On top of this, ACLs should only allow heimdal itself to access at > least the keys (users and passwords could be changed by other means (?) > such as secure web or script as the keys are what allows a user to do > what they want and are what could be stolen or targeted at any rate). No, security of the ldapi socket is irrelevant since the identity of the client connecting to the socket is what's actually used for the LDAP server's authentication/authorization purposes.

> 2. rootdn should not be allocated a password in the config (no matter > what form is used (slapd.conf or slapd.d/cn=config). Since rootdn can > change anything in the database on a whim, access to the details of this > should be left out of anything that an intruder could gain access to > (even though IF root on the host is compromised all hope could well be > lost anyway- keep as secure as possible) That's generally true. > 3. Obviously SASL should be used as authentication (thats why its being > setup isn't it?). Yes. But SASL != Kerberos.

On Wed, 2009-03-04 at 17:27 -0800, Howard Chu wrote: > You're missing the obvious fact that GSSAPI/Kerberos is not the only secure > SASL mechanism available in this picture, and it is obviously not the one the > KDC uses to talk to LDAP.

I'm aware that SASL GSSAPI is not the only SASL auth on offer, but I'm not sure of the latter part of your statement: do you mean that the ldap used as a backend cannot use the kdc using the ldap as the backend for authentication?

You have awoken an alternative in my mind, though. I'll just go and stick my head back in my Openldap doc under SASL for a bit- I'll probably come back with another stupid question shortly... :) >> A couple of points of interest come to mind: >> >> 1. Security of the ldapi socket needs to be paramount. Permission should >> be as tight as can be allowed so that only access is as necessary for >> use. On top of this, ACLs should only allow heimdal itself to access at >> least the keys (users and passwords could be changed by other means (?) >> such as secure web or script as the keys are what allows a user to do >> what they want and are what could be stolen or targeted at any rate).

> No, security of the ldapi socket is irrelevant since the identity of the > client connecting to the socket is what's actually used for the LDAP server's > authentication/authorization purposes.

Surely at least some form of protection from say bruteforce or other form of attack should be implemented here? Stands to reason that only users or services that need something should be allowed access to it. Why leave a hole in the wall when a door could be used to keep out the nasties?

On Thu, 2009-03-05 at 02:43 +0100, Michael Ströder wrote: > Da Rock wrote: >> I'm not sure you quite understand what I mean here- > I think I do. ;-) > > There's no reason why you shouldn't be able to do the following: > > LDAP Client > --ldap:// with SASL/GSSAPI--> slapd > --KRB5--> heimdal KDC > --ldapi:// with SASL/EXTERNAL--> slapd > > In fact the picture is a bit more complicated but I'm too tired to draw > the real one. Hope you get the idea. Actually thats very well presented- at least I get what your saying. A hiccup here is that I mean that there is no ldap client- yet. I'm talking about at startup, slapd looks to authenticate with kerberos as a service

On Wed, 2009-03-04 at 18:20 -0800, Howard Chu wrote: > There is no hole in this wall. An LDAP server is designed to securely process > requests from multiple disparate clients. If your KDC and its host machine are > secure, and the ACLs in your slapd are correct, then the issue is closed. You > cannot bruteforce SASL/EXTERNAL over ldapi://. You can only fool it if you > already have superuser access on the host system, and in that case, you were > lost already anyway.

What about pretending to be a user with access to the socket (like ldap or the kdc users)? First rule of sysadmin: don't leave open a door that doesn't need to be open- even an internal one. But if you're talking about only superuser access on the socket then you're doing this anyway... :)

On Wed, 2009-03-04 at 18:20 -0800, Howard Chu wrote: > There is no hole in this wall. An LDAP server is designed to securely process > requests from multiple disparate clients. If your KDC and its host machine are > secure, and the ACLs in your slapd are correct, then the issue is closed. You > cannot bruteforce SASL/EXTERNAL over ldapi://. You can only fool it if you > already have superuser access on the host system, and in that case, you were > lost already anyway. > What about pretending to be a user with access to the socket (like ldap or the kdc users)?

First rule of sysadmin: don't leave open a door that doesn't need to be open- even an internal one.

> You can of course choose to dedicate one LDAP server to back your KDC, but if > you're going to isolate it from any other usage in this manner, then you're no > longer getting any special benefit from using LDAP. I'm not sure exactly what I'm doing yet, but I am researching the possibilities. One possibility is user management, another is replication for other kdc's, not sure about any of these yet.