## Grid Engine Kerberos/DCE Security Modules Overview

see Customer Info

## How the security modules work

see Customer Info

## DCE version differences

This section is obsolete and is only included for historical reasons. A Grid Engine / DCE integration now uses the security modules compiled with the Kerberos GSSAPI rather than using the DCE GSSAPI library. There were too many problems with the DCE GSSAPI library and forwarding of DCE credentials. Some of the problems are explained below. For additional information on Grid Engine using DCE, see Running Kerberos binaries in a DCE environment at the bottom of this page.

The DCE GSSAPI library forwards credentials but the forwarded credentials apparently cannot be inherited by child programs. I found the following comment in the DCE source code which explains this.

> dce/src/src/security/client/login/sec_login.c, line 1295 of 2643

> /* * DCE 1.0 restriction - can't do a set context if the context was
> * marked sec_login_credentials_private. Note that this means
> * such a context can only be used as an explicit context in user
> * space applications. It cannot be used to make authenticated
> * kernel calls, because these rely on the default context. */

This is in the sec_login_set_context DCE library function which allows the user to set up a new default network credentials. (Maybe this is why DCE does not provide rlogin type of utilities which automatically forward your credentials.) However, I was able to work around this problem by using a "hack" to clear the "private" flag in the forwarded credential. Once the "private" flag is cleared, the forwarded credential can be made the user's default credential which causes the credential to be written to the user's credential cache. I plan on investigating to find out if there is a way to create a non-private credential without resorting to hacking the code.

DCE uses the KRB5CCNAME environment variable to specify the location of the credentials cache file name. However, unlike Kerberos, the DCE library determines the location of the credentials cache and sets the KRB5CCNAME environment variable on your behalf when the credentials are created. Under Kerberos, the user or application can specify the location of the credentials cache by setting the KRB5CCNAME environment variable and the Kerberos library routines will simply use it.
Grid Engine initially sets the KRB5CCNAME environment variable based on the job ID before calling the get_cred, put_cred, and delete_cred programs.
For Kerberos, this works fine. The Kerberos GSSAPI routines just use the KRB5CCNAME environment variable.
When DCE sets a credential as the default credentials, it chooses a file location for the credentials cache and overwrites the current setting of the KRB5CCNAME environment variable. In order to allow Grid Engine to refer to the credentials cache by a "handle" that it creates, the put_cred program creates a soft link from the Grid Engine provided credentials cache to the DCE provided credentials cache. This allows Grid Engine to refer to the credentials cache based on the handle that it created.

Another strange thing about DCE is that when the user's credentials are forwarded, the default Kerberos principal for the user is "sge", not his user name. The list of Kerberos service tickets remains the same as the user's original credentials. I'm not sure why this is or if it is a problem.

For some reason, get_cred always fails on notos. Specifically, it fails with the error message "Can't enable delegation in gss_init_sec_ctx (141290bd)". This is a normal gss_init_sec_context call requesting a delegated credential. It works fine on euros. I haven't yet figured out the difference. I think there is probably a configuration problem. I haven't been able to test this lately because I haven't been able to login to notos.

Once, while testing, I got an error that said the delegated token had expired. This made me think that there may be a special expiration time on a delegated token. I looked at the DCE source code and it appeared that the token got the expiration time of the credentials from which it was derived. I will probably have to test this by putting some queues on hold for a long period of time.

DCE requires the use of shepherd "starter" program to create the credentials because only descendants of this process can use the credentials.

## Building the binaries for distribution with Grid Engine

To make dependencies:
% aimk gss_depend
To compile the security binaries for Kerberos or DCE:
Make sure KRB_HOME is set correctly in aimk.site or aimk.private.
% aimk -only-core -gss gss_all

To compile k5dcelogin for DCE:
% aimk -only-core -dce k5dcelogin

To clean:
% aimk -gss gss_clean

## DCE / Kerberos Configuration

see Customer Info

## Instructions for spool directories in DFS

see Customer Info

## Turning off security

see Customer Info

## Running Kerberos binaries in a DCE environment

After having many problems with the DCE delegation code (see above) and learning a little more about how DCE uses Kerberos internally, I decided the best way to run in a DCE environment is to use the Kerberos security modules. The only addition that has to be made for a DCE environment is that the k5dcelogin command must be used as a shepherd wrapper to convert the Kerberos TGT to the user's DCE credentials before executing the shepherd process. This method works quite well. It uses the stable, robust Kerberos code for forwarding the TGT and then on the execution host, it changes the Kerberos TGT into the DCE credentials. See the Customer Info file for additional information.

Copyright 2001 Sun Microsystems, Inc. All rights reserved.