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From Matteo Durighetto <m.durighe...@miriade.it>
Subject Re: kudu 1.4 kerberos
Date Tue, 17 Oct 2017 07:46:34 GMT
Hello Todd,
                   because our systems are join in AD Domain with red hat
SSSD, this system map the principal bypassing krb5.conf
and map every principal to an univocal sAMAccount, the sAMAccount is a
unique attribute of the entry of an AD record ( https://blogs.msdn.microsoft
ributes-in-active-directory/ ), so its not possible to have the same
sAMAccount for different kudu principals

By  default SSSD  introduce in krb5.conf this entry :

includedir /var/lib/sss/pubconf/krb5.include.d/

And with this entry it include the :

cat /var/lib/sss/pubconf/krb5.include.d/localauth_plugin
 localauth = {
  module = sssd:/usr/lib64/sssd/modules/sssd_krb5_localauth_plugin.so

So the auth_to_local krb5 api return the sAMAccount, instead of "kudu" for
a principal like kudu/<hostname>@domain

I created a new krb5.conf withtout "includedir
and used that variable in KUDU env advanced setting and now it's work.

So for a new enviroment there a set of possible solutions  :
1) create a new /etc/krb5_onlykudu.conf and set KRB5_CONFIG=/etc/krb5_
2) modify  /etc/krb5.conf and remove the entry "includedir
3) if there is the entry  "includedir /var/lib/sss/pubconf/krb5.include.d/"
in  /etc/krb5.conf , remove the file "/var/lib/sss/pubconf/krb5.

Thank you very much for your support

Kind Regards

Matteo Durighetto

 "Logged in from keytab as kudu/<host>@REALM (short username
>> <sAMAccountName> )"
>> I begin to think that the problem is between sssd with plugin
>> sssd_krb5_localauth_plugin.so
>> so for every principal kudu/<host>@REALM kudu maps to  <sAMAccountName>,
>> so seems impossible to have the all  kudu/<host>@REALM mapped to the same
>> "kudu"
>> as suggested "So, basically, it's critical that the username that the
>> master determines for itself (from this function)
>> matches the username that it has determined for the tablet servers when
>> they authenticate
>>  (what you pasted as 'abcdefgh1234' above)."
> Interesting. What is the sAMAccountName in this case? Wouldn't all of the
> 'kudu' have the same account name?
>> The strange thing is that with hadoop I have the correct mapping (
>> probably because I have no rule, so
>> it switch to default rule )
>> hadoop org.apache.hadoop.security.HadoopKerberosName  kudu/<host>@REALM
>>  ==> kudu
> This makes sense since Hadoop uses its own auth_to_local configuration
> defined in its core-site.xml rather than relying on the system krb5
> library. Kudu, being implemented in C++, uses the system krb5 API to do
> mapping, and hence picks upthe sssd localauth plugin as you found.
> As a temporary workaround, one thing you could try is to duplicate your
> krb5.conf and make a new one like krb5.kudu.conf. In this file remove the
> localauth plugin and any auth_to_local mappings that are causing trouble.
> You can then start the kudu servers with KRB5_CONFIG=/path/to/krb5.kudu.conf
> . I believe this will ensure that the local-auth mapping performs as you'd
> like.
> Given your setup, do you think we should provide an advanced option to
> override the system-configured localauth mapping and instead just use the
> "simple" mapping of using the short principal name? Generally we'd prefer
> to have as simple a configuration as possible but if your configuration is
> relatively commonplace it seems we might want an easier workaround than
> duplicating krb5.conf.
> -Todd
>> 2017-10-13 1:32 GMT+02:00 Todd Lipcon <todd@cloudera.com>:
>>> Hey Matteo,
>>> Looks like you did quite a bit of digging in the code! Responses inline
>>> below.
>>> On Wed, Oct 11, 2017 at 1:24 PM, Matteo Durighetto <
>>> m.durighetto@miriade.it> wrote:
>>>> Hello,
>>>>            I have a strange behaviour with Kudu 1.4 and kerberos.
>>>> I enabled kerberos on kudu, I have the principal correctly in the OU of
>>>> an AD, but
>>>> at startup I got a lot of errors on method TSHeartbeat between tablet
>>>> server and
>>>> master server as unauthorized. There's no firewall between nodes.
>>> right, "unauthorized" indicates that the connection was made fine, but
>>> the individual RPC call was determined to not be allowed for the identity
>>> presented on the other side of the connection.
>>>> W1011 <time>   server_base.cc:316] Unauthorized access attempt
>>>> to method kudu.master.MasterService.TSHeartbeat
>>>> from {username='abcdefgh1234', principal='kudu/HOSTNAME@DOMAIN.XYZ'}
>>>> at <IP>:37360
>>>> the "abcdefgh1234" it's an example of the the string created by the
>>>> cloudera manager during the enable kerberos.
>>> This output indicates that it successfully authenticated via Kerberos as
>>> the principal listed above. That's good news and means you don't need to
>>> worry about rdns, etc (if you had issues with that it would have had
>>> trouble finding a service ticket or authenticating the connection). This
>>> means you got past the "authentication" step and having problems at the
>>> "authorization" step.
>>>> The other services (hdfs and so on ) are under kerberos without problem
>>>> and there is the rdns at true in the /etc/krb5.conf (  KUDU-2032 ).
>>>> As I understand the problem is something about the 3° level of
>>>> authorization between master servers and tablet servers.
>>> Right.
>>>> ... <snipped>
>>>> So I think the problem, as I say before, could be
>>>> in  ContainsKey(users_, username);  :
>>>> bool SimpleAcl::UserAllowed(const string& username) {
>>>>   return ContainsKey(users_, "*") || ContainsKey(users_, username);
>>>> }
>>>> At this point It's not clear for me how Kudu build the array/key list
>>>> users for daemon service ( it's not as super users or user ACL an external
>>>> parameter).
>>> Exactly. The users here for the 'service' ACL are set in
>>> ServerBase::InitAcls():
>>>   boost::optional<string> keytab_user = security::GetLoggedInUsernameF
>>> romKeytab();
>>>   if (keytab_user) {
>>>     // If we're logged in from a keytab, then everyone should be, and we
>>> expect them
>>>     // to use the same mapped username.
>>>     service_user = *keytab_user;
>>>   } else {
>>>     // If we aren't logged in from a keytab, then just assume that the
>>> services
>>>     // will be running as the same Unix user as we are.
>>>     RETURN_NOT_OK_PREPEND(GetLoggedInUser(&service_user),
>>>                           "could not deterine local username");
>>>   }
>>> Since you're using Kerberos, the top branch here would apply -- it's
>>> calling GetLoggedInUsernameFromKeytab() from init.cc.
>>> You can see what username the server is getting by looking for a log
>>> message at startup like "Logged in from keytab as kudu/<host>@REALM (short
>>> username <XYZ>)". Here 'XYZ' is the username that ends up in the service
>>> ACL.
>>> So, basically, it's critical that the username that the master
>>> determines for itself (from this function) matches the username that it has
>>> determined for the tablet servers when they authenticate (what you pasted
>>> as 'abcdefgh1234' above).
>>> That brings us to the next question: how do we convert from a principal
>>> like kudu/<HOST>@REALM to a short "username"? The answer there is the
>>> function 'MapPrincipalToLocalName' again from security/init.cc. This
>>> function delegates the mapping to the krb5 library itself using the
>>> krb5_aname_to_localname() API. The results of this API can vary depending
>>> on the kerberos configuration, but in typical configurations it's
>>> determined by the 'auth_to_local' configuration in your krb5.conf. See the
>>> corresponding section in the docs here:
>>> https://web.mit.edu/kerberos/krb5-1.12/doc/admin/conf_files/
>>> krb5_conf.html
>>> My guess is that your host has been configured such that when the master
>>> maps its own principal, it's getting a different result than when it maps
>>> the principal being used by the tservers.
>>> Hope that gets you on the right track.
>>> Thanks
>>> -Todd
>>> --
>>> Todd Lipcon
>>> Software Engineer, Cloudera
> --
> Todd Lipcon
> Software Engineer, Cloudera

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