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From Todd Lipcon <t...@cloudera.com>
Subject Re: kudu 1.4 kerberos
Date Tue, 17 Oct 2017 04:57:48 GMT
On Mon, Oct 16, 2017 at 2:29 PM, Matteo Durighetto <m.durighetto@miriade.it>
wrote:

> Hello Todd,
>                    thank you very much for the answer. I think I have
> found something interesting.
>
> Kudu is doing the ACL list with the sAMAccountName or CN  as it writes in
> the logs:
>
>  "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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