[SOLVED] RE: [External] - Re: Issues getting Kerberos to work with realmd and Active Directory

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[SOLVED] RE: [External] - Re: Issues getting Kerberos to work with realmd and Active Directory

Wesley Taylor
Thank you all for your responses. Fortunately for me, just running klist and
picking the UPN form got me past this issue, but if I run into any issues in
the future I will employ those other solutions. I appreciate the help!

-Wes


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-----Original Message-----
From: Simo Sorce <[hidden email]>
Sent: Thursday, July 30, 2020 12:33 PM
To: Wesley Taylor <[hidden email]>; [hidden email]
Subject: [External] - Re: Issues getting Kerberos to work with realmd and
Active Directory

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Wesley,
when joining hosts to AD a computer account is created and a UPN and SPNs are
set on it.
Unlike MIT kerberos in AD heavy use of aliases is employed so each host have a
"host password/key" that is shared with all the aliases created.
Most notably there are the UPN, generally of the form computername$@REALM and
the SPNs which are a large number of service/fqdn@REALM principal names.

The important part here is that while you can get tickets for any of those
names (the KDC has many canonicalization rules that will also match in a
case-insensitive way) when you ask for a TGT (the kinit
operation) AD normally will accept a request only if the UPN form is used as
the client principal and will refuse other forms (even though the key is the
same).

realmd has an option to specify what to set the UPN to to change the default
AD behavior. (See the --user-principal option in realm.8 manpage). You can use
it to control what to use at join time, then you should be able to use exactly
that name to kinit from the generated keytan.

HTH,
Simo.

On Thu, 2020-07-30 at 17:00 +0000, Wesley Taylor wrote:

> Hi All,
>
> I am trying to get HTCondor with Kerberos authentication (
> https://usg02.safelinks.protection.office365.us/?url=https%3A%2F%2Fhtc
> ondor.readthedocs.io%2Fen%2Fstable%2Fadmin-manual%2Fsecurity.html%3Fhi
> ghlight%3DKerberos%23kerberos-authentication&amp;data=02%7C01%7C%7Cbb5
> bd43850e34b17771508d834b70953%7Cfae7a2aedf1d444e91bebabb0900b9c2%7C0%7
> C0%7C637317308723651795&amp;sdata=uYxqJbuTqP8JbYm8Qx4oZjyGKhI1hTVWkAYH
> IKooivI%3D&amp;reserved=0
> ) to work on some linux machines I have which I joined to Windows
> Active Directory with realmd. HTCondor tries to authenticate with the
> machine principal, but I am having a hard time figuring out what that
> is. When I run 'klist -k' I see a bunch of entries from
> /etc/krb5.keytab along the lines of host/fqdn@REALM. However, when I
> run 'kinit -k' I get "kinit: Client $(hostname) not found in Kerberos
> database".
>
> I then interrogated the realm with adcli, using 'adcli testjoin --
> verbose' and it outputs the computer account name as
> HOST/HOSTNAME@REALM. When I run 'kinit -k HOST/HOSTNAME@REALM' I get
> back the error "kinit: Keytab contains no suitible keys for
> HOST/HOSTNAME@REALM".
>
> I am confused because when I run 'adcli update --verbose' it says it
> updated the keytab at /etc/krb5.keytab and outputs the same account
> name (which I am assuming is the principal for the computer) as adcli
> testjoin. I am really scratching my head about this, what am I doing
> wrong here?
>
> Thanks,
> Wes
>
>
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--
Simo Sorce
RHEL Crypto Team
Red Hat, Inc




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