kerberos error: PAC checksum type is not keyed

[Aaron Solochek]

On 11/02/2010 07:19 AM, Andrew Bartlett wrote:
> On Wed, 2010-10-27 at 15:39 +1100, Andrew Bartlett wrote:
>> On Wed, 2010-10-27 at 11:05 +1100, Andrew Bartlett wrote:
>>> On Thu, 2010-10-21 at 08:17 +1100, Andrew Bartlett wrote:
>>>> On Wed, 2010-10-20 at 10:22 -0400, Aaron Solochek wrote:
>>>>> I'm getting ever closer to having nfs4 working with the samba4 kdc.  Currently I
>>>>> seem to be blocking on the error "PAC checksum type is not keyed" which is
>>>>> generated by the kdc when nfs sends a PA-TGS-REQ for nfs/foo.bar.com.
>>>>>
>>>>> >From googling, it seemed to be related to the des-cbc-crc enctype, so I set
>>>>>
>>>>> default_tkt_enctypes = rc4-hmac des-cbc-md5
>>>>>
>>>>> in krb5.conf on both client and server.
>>>>>
>>>>>
>>>>> Then the problem changes slightly.  With that option set, the client first
>>>>> requests nfs/foo.bar.com with enctypes "rc4-hmac des-cbc-md5", and that
>>>>> succeeds, but immediately following that the client sends the exact same
>>>>> request, only this time the enctypes are back to "des-cbc-crc des-cbc-md5
>>>>> des-cbc-md4" and it fails again with PAC checksum error.
>>>>>
>>>>>
>>>>> So it seems that I have 2 bugs.
>>>>>
>>>>> 1) PAC checksum bug
>>>>>
>>>>> 2) kerberos client (libraries or nfs4?) bug that causes the second request
>>>>> ignoring the enctypes specified in krb5.conf.
>>>>>
>>>>>
>>>>> What can I do about #1?
>>>>
>>>> Someone needs to confirm what Windows does here.  The PAC security
>>>> relies on the checksum being keyed, so my gut feeling is to omit the
>>>> checksum in this case.  We need to determine if this is security issue
>>>> with Windows, or there is some other protection, or Windows omits it.
>>>> (This should not be relevant for NFSv4, which should never need to use
>>>> DES, but is important for AFS clients).
>>>
>>> I've now looked into the windows behaviour, which is documented here:
>>> http://blogs.msdn.com/b/openspecification/archive/2010/01/01/verifying-the-server-signature-in-kerberos-privilege-account-certificate.aspx
>>>
>>> The problem is that when different crypto-systems are used (Example 2),
>>> Heimdal objects because the keys involved are not the right type or
>>> length.  I'm working with upstream Heimdal to find out if we can get a
>>> better API for this, plus a way to handle the crazy windows behaviour
>>> exception noted there. 
>>
>> Attached is my patch for testing.  
> 
> A more complete and correct fix is in the autobuild queue, and should be
> available in master shortly.
> 
> Andrew Bartlett
> 

I've been trying to rebuild the debian packages with this patch for testing, but
that package has lots of build issues at the moment.  I think I'm getting close
to getting it to build, and once I do I'll report back about how it works for me.

Thank you.

-Aaron