[OpenAFS-devel] 1.5.1 - multiple Kerberos realm support

Jeffrey Altman jaltman@secure-endpoints.com
Sun, 07 May 2006 08:08:30 -0400


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Christopher D. Clausen wrote:
> Jeffrey Altman <jaltman@secure-endpoints.com> wrote:
>> Each realm listed in the krb.conf file is considered a local realm.
>> Authenticated principals belonging to a local realm are treated as
>> local cell usernames.  For example, if the krb.conf file contains
>> the realm names:
>>
>>  EXAMPLE.COM  AD.EXAMPLE.COM
>>
>> then the principal names user@EXAMPLE.COM and user@AD.EXAMPLE.COM will
>> both be treated as the AFSID whose name is "user".  Whereas the
>> principal name user@FOREIGN.COM will be treated as a foreign identity.
> 
> Let me see if I understand this...
> 
> Currently, ACM.UIUC.EDU (MIT realm) trusts AD.UIUC.EDU (MS Active 
> Directory.)  Our afs cell keyfile is only in ACM.UIUC.EDU.  Users in the 
> AD realm can either use gssklog to obtain tokens for acm.uiuc.edu 
> directly, or use aklog and show up as foreign.  Upgrading to 1.5.1 (or 
> newer) on the servers would allow user@AD principals to be treated as 
> local users in the acm cell?  

Correct

> I would not need to add  the 
> afs/acm.uiuc.edu princial in the AD realm?  

Correct

> Would the clients also need 
> to be upgraded to 1.5.1, or would client accesses be transparently 
> handled from older clients through the newer servers?

This is a server only change.

>>> Usernames must map directly e.g. be the same in all realms, though.
>> In addition to the krb.conf file there is also an exclusion file.
>>
>>  /usr/afs/etc/krb.excl
>>
>> This file contains a list of principal names that should not be
>> treated as a local AFS identity.  This file contains one principal
>> name per line.
>>
>>  user@AD.EXAMPLE.COM
>>  admin@AD.EXAMPLE.COM
> 
> Would principals with instances be written using Kerberos 5 syntax or 
> Kerberos IV? i.e. would I use cclausen/admin@AD.UIUC.EDU or 
> cclausen.admin@AD.UIUC.EDU to prevent an AD admin from creating a 
> principal to map to my system:administrator account?

Kerberos 5

> Is the exclusion file functionality in the 1.5.1 code?

Yes

>>>> And what exactly does "partial support" mean?
>>> It means later you'll be able to also say
>>> userA@realm1 maps to userB@realm2
>> To elaborate on this statement.  Work is being performed to extend the
>> AFS Protection database to allow multiple names to be associated with
>> the same AFSID.  Currently, I have multiple Kerberos principals from
>> realms that have exchanged cross-realm keys.  When accessing a volume
>> in cell 'a' I want to be able to access the volume with a single AFSID
>> regardless of which of the Kerberos principals I control that I am
>> using at a given time.
>>
>> When the Protection Server extensions are complete, it will be
>> possible to associate not only short names "user" with an AFSID but a
>> Kerberos 5 principal name or other name types that may be registered
>> in the future.
> 
> Ah, Excellent!
> 
> Realm trusts (in at least one direction) must exist between these realms 
> though, correct?

If a cross-realm key exchange has not been performed then you can create
afs/cell@REALM service principals in multiple realms and install all of
the keys.  As long as the kvno values are different the multiple keys
can co-exist.

Jeffrey Altman


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