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From "Larry McCay (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13558) UserGroupInformation created from a Subject incorrectly tries to renew the Kerberos ticket
Date Wed, 31 Aug 2016 12:17:20 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13558?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15452079#comment-15452079
] 

Larry McCay commented on HADOOP-13558:
--------------------------------------

Hi [~tucu00]!

I agree with [~stevel@apache.org]'s point regarding the double instantiation of the realUser.
In fact, it seems to me that the setting of the loginContext and authenticationMethod get
lost when you create the second one. This really looks like a bug, if not, it needs to be
made clear as to why it is doing that.

Beyond that, the new ctor should call the existing one and override the setting of isKeytab
afterward in order to pick up any changes to the behavior of the other ctor going forward.

Tricking UGI into not renewing/reloggin by overriding this field is simple but really should
be done in an OO way instead.
UGI being what it is, this simple change is probably the safest way forward.
Let's comment this clearly in the new ctor - so when someone is stepping through and see the
keytab credential they don't see this as a bug.


> UserGroupInformation created from a Subject incorrectly tries to renew the Kerberos ticket
> ------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-13558
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13558
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: security
>    Affects Versions: 2.7.2, 2.6.4, 3.0.0-alpha2
>            Reporter: Alejandro Abdelnur
>         Attachments: HADOOP-13558.01.patch
>
>
> The UGI {{checkTGTAndReloginFromKeytab()}} method checks certain conditions and if they
are met it invokes the {{reloginFromKeytab()}}. The {{reloginFromKeytab()}} method then fails
with an {{IOException}} "loginUserFromKeyTab must be done first" because there is no keytab
associated with the UGI.
> The {{checkTGTAndReloginFromKeytab()}} method checks if there is a keytab ({{isKeytab}}
UGI instance variable) associated with the UGI, if there is one it triggers a call to {{reloginFromKeytab()}}.
The problem is that the {{keytabFile}} UGI instance variable is NULL, and that triggers the
mentioned {{IOException}}.
> The root of the problem seems to be when creating a UGI via the {{UGI.loginUserFromSubject(Subject)}}
method, this method uses the {{UserGroupInformation(Subject)}} constructor, and this constructor
does the following to determine if there is a keytab or not.
> {code}
>   this.isKeytab = KerberosUtil.hasKerberosKeyTab(subject);
> {code}
> If the {{Subject}} given had a keytab, then the UGI instance will have the {{isKeytab}}
set to TRUE.
> It sets the UGI instance as it would have a keytab because the Subject has a keytab.
This has 2 problems:
> First, it does not set the keytab file (and this, having the {{isKeytab}} set to TRUE
and the {{keytabFile}} set to NULL) is what triggers the {{IOException}} in the method {{reloginFromKeytab()}}.
> Second (and even if the first problem is fixed, this still is a problem), it assumes
that because the subject has a keytab it is up to UGI to do the relogin using the keytab.
This is incorrect if the UGI was created using the {{UGI.loginUserFromSubject(Subject)}} method.
In such case, the owner of the Subject is not the UGI, but the caller, so the caller is responsible
for renewing the Kerberos tickets and the UGI should not try to do so.



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