Tag: SAS Configuration

SAS & IWA: Reviewing SPNs

My last post was about configuring additional Service Principal Names (SPNs) in Active Directory to support the use of Integrated Windows Authentication (IWA) in a SAS® platform installation that uses host name aliases in preference to physical host names.

When working on a SAS & IWA setup like this, I’d start by reviewing the currently registered SPNs for all of the SAS servers involved (as well as any other servers that might be accessed from a SAS server using IWA). This gives an idea of what SPNs might have already been added, which ones still need to be added, and potentially which ones might need to be removed.

This is the command I use Continue reading “SAS & IWA: Reviewing SPNs”

SAS & IWA: Host Name Aliases and SPNs

I’m quite keen on using host name aliases, rather than their physical host names, when referring to machines in SAS® platform installations. It does however mean a little extra configuration is required when using Integrated Windows Authentication. That is what this post is about: configuring Active Directory with additional Service Principal Names (SPNs) based on the aliases.

Host name aliases have several benefits over using physical host names. They can be easier to remember (e.g. sasmeta v.s. p106547). They can be easily redirected from primary environments to disaster recovery environments (e.g. sasmeta from p106547 to d106547) with no client reconfiguration requirements. They also allow host machines to be readily renamed if/when required with little or no changes to SAS configuration files, programs and/or metadata.

Whilst they have obvious benefits, Continue reading “SAS & IWA: Host Name Aliases and SPNs”

SAS & IWA: Verifying Trusted for Delegation Status

Update 26Sep2018: This post is now several years old and naturally technology and security have progressed in that time. For more up to date information regarding delegation and, in particular, the requirement for constrained delegation when working with Windows Defender Credential Guard in Windows 10 and Windows Server 2016, please see Stuart Rogers’ very useful SAS Global Forum 2018 Paper: SAS 9.4 on Microsoft Windows: Unleashing Kerberos on Apache Hadoop.

I mentioned in a previous post that host machines need to be Trusted for Delegation when a SAS® software component, such as a SAS Workspace Server, needs to make outgoing connections to secondary servers when the initial incoming connection was made using Integrated Windows Authentication (IWA).

When a server needs to be Trusted for Delegation, it takes a domain administrator to change the machine account in Active Directory. I rarely have domain admin privileges when working at customer sites so I usually can’t do this for myself. :( This post describes the method I use, as a lowly domain user, to verify that a Windows server has been configured in Active Directory as Trusted for Delegation.

The screenshot below shows an example of what the domain admin might see in the Properties dialog Delegation tab for the machine account in Active Directory (via the Active Directory Users and Computers tool (under Start > All Programs > Administrative Tools).

This machine account (P1001) is not yet trusted for delegation. The domain admin would click the radio button for “Trust this computer for delegation to any service (Kerberos only)“.

Once the domain admin has advised that the change has been applied, we can test it out from the SAS platform. What happens if the test still fails? I like to double check that the server is definitely trusted for delegation before I move on to checking other things. Everyone makes mistakes from time to time, even domain admins; maybe the wrong machine account was modified (it does happen). So to avoid wasting time later on, I like to verify this pre-requisite before moving on. I could ask the domain admin to email me a screenshot of the dialog to confirm, but they’re likely very busy people, so why not do it myself? I often don’t have access to the Active Directory Users and Computers tool so I have to find another way to verify trusted for delegation. This is where the very useful AdExplorer utility helps. It’s one of the SysInternals tools available for download from Microsoft. As the name suggests it provides an explorer interface to Active Directory so you can browse the objects and attributes.

Here’s an AdExplorer screenshot showing the same machine account (P1001) from the dialog shown earlier.

I have selected the userAccessControl attribute and can see it has the value 4128. This is not good; I’ll explain why in a moment :) Essentially it means that the machine is not trusted for delegation. What I would rather see, is the next screenshot where it has the value 528416 meaning it is trusted for delegation.

So where do these magic numbers come from, and how do we know that 528416 is trusted and 4128 is not? The userAccessControl value is a bitmap value (or bit array). There are a number of possible flags that can be set in this value which are documented in the Microsoft resource How to use the UserAccountControl flags to manipulate user account properties. The main flag of interest here is TRUSTED_FOR_DELEGATION with value 0x80000 (hex) or 524288 (decimal) which is listed in the document as:

TRUSTED_FOR_DELEGATION – When this flag is set, the service account (the user or computer account) under which a service runs is trusted for Kerberos delegation. Any such service can impersonate a client requesting the service. To enable a service for Kerberos delegation, you must set this flag on the userAccountControl property of the service account.

The (trusted) decimal value 528416 (hex 0x81020) we saw above consists of TRUSTED_FOR_DELEGATION (decimal 524288 hex 0x80000) + WORKSTATION_TRUST_ACCOUNT (decimal 4096 hex 0x1000) + PASSWD_NOTREQD (decimal 32 hex 0x0020). The (untrusted) decimal value 4128 (hex 0x1020) we saw earlier only consists of WORKSTATION_TRUST_ACCOUNT (decimal hex 0x1000) + PASSWD_NOTREQD (decimal 32 hex 0x0020). It’s missing the TRUSTED_FOR_DELEGATION value. You might see other values in your environment, including other flag values, but the important thing to check is that it includes the TRUSTED_FOR_DELEGATION value.

If you know of any other ways to verify a server’s trusted for delegation status (as a normal domain user) please let me know by leaving a comment.

For more posts in this series have a look at the IWA tag.

SAS and IWA: Two Hops

Update 26Sep2018: This post is now several years old and naturally technology and security have progressed in that time. For more up to date information regarding delegation and, in particular, the requirement for constrained delegation when working with Windows Defender Credential Guard in Windows 10 and Windows Server 2016, please see Stuart Rogers’ very useful SAS Global Forum 2018 Paper: SAS 9.4 on Microsoft Windows: Unleashing Kerberos on Apache Hadoop.

In an earlier post I mentioned that I would jot down a few notes about my experiences with SAS® software and Integrated Windows Authentication (IWA). This is the first of these posts and concerns the initial configuration. Chances are, if you knew you wanted to use IWA before you installed SAS, then it would have been discussed and implemented during the initial installation and configuration. If you decided to implement IWA after the fact then you would most likely have followed the instructions from either:

A basic SAS and IWA configuration might then look something like this. In the diagram below we have a client PC (saspc001), a dedicated metadata server machine (sasmeta) and an application server machine (sasapp). This is a homogenous environment consisting of all Windows machines in the same Windows domain. Other configurations might have multiple domains that trust each other, and now with SAS 9.3, some of the SAS servers may also be UNIX based (assuming the prerequisites are met).

In the diagram above a SAS Enterprise Guide user working on the saspc001 workstation initially connects (1) to the SAS Metadata Server on sasmeta using a connection profile with IWA enabled. When they run a project, an IWA connection (2) is then made to the SAS Object Spawner on sasapp to launch a standard SAS Workspace Server to execute the SAS code. The logical SAS Workspace Server has been configured in metadata to accept IWA connections. Both of these IWA connections involve only 1-hop from the workstation: saspc001 to sasmeta, and saspc001 to sasapp.

Problems might then arise when secondary connections need to be made from the workspace server to additional servers and access denied errors are seen in the SAS log. One example of a secondary connection includes executing code on the workspace server that reads a CSV or XML file from another file server (filesrv) using a UNC path (e.g. \\filesrv\share\file.xml). Another example might be assigning a library in the workspace server session that uses SAS/ACCESS Interface to ODBC or SAS/ACCESS Interface to OLEDB to connect to a Microsoft SQL Server database on another server (sqlsrv). These examples are shown in the diagram below as (3) and (4) respectively.

Both of these example involve IWA being used in 2-hops from the client. In the first hop (2) IWA is used to connect from saspc001 to sasapp as before. In the second hops the SAS workspace server process has to then connect and authenticate to the secondary servers: sasapp to filesrv (3), and sasapp to sqlsrv (4). It is these second hops which may fail if additional measures have not been taken:

  • Trusted for Delegation: the intermediate server (sasapp in this example – where the workspace server is running) needs to configured in Active Directory as Trusted for Delegation. This must be done by a domain admin. This configuration is mentioned in the SAS Intelligence Platform: Security Administration Guide on the Windows Privileges page for both SAS 9.2 and SAS 9.3. In a future post I’ll show the method I use as a non-domain-admin to double check this as part of the troubleshooting process.
  • Force Kerberos: you also need to ensure the Kerberos protocol is used and not NTLM. Whilst you could get all of your users to configure their SAS client connection profiles to use Kerberos, it is usually preferable to leave the clients alone and instead configure the SAS servers to only offer Kerberos and not NTLM. This is documented in the in the SAS Intelligence Platform: Security Administration Guide on the How to Force Use of Kerberos page for SAS 9.2, and the How to Configure Integrated Windows Authentication page for SAS 9.3. Things can get a bit trickier when DNS host aliases (or CNAMEs) are used in environments configured for disaster recovery. In a future post I’ll show some examples of additional Service Principal Names (SPNs) that might be required in these situations.

So if you find yourself getting access denied messages when using SAS and IWA in situations where multiple hops are involved, I hope this post gives you some ideas of things to investigate further.

For more posts in this series have a look at the IWA tag.

Dynamic Logging Reconfiguration in SAS® 9.3

One of the exciting new features in SAS 9.3 (well for me anyway) is the ability to replace or modify the logging configuration on-the-fly for a running server without needing to restart it. Previously in SAS 9.2 you could dynamically change the levels for loggers on servers (via SAS Management Console Server Manager Loggers tabs) but not modify the appender configuration. Now in SAS 9.3 you can completely change the logging configuration file and apply it without restarting the server. This is exciting because it means you can do something like add a new appender for a new custom log file for the metadata server in the middle of the day with out having to restart the entire platform of dependant services. That’s really neat!

I tried it out. I made a small change to the metadata server logconfig.xml, saved it, and then waited … watching the log file. I’d thought that maybe the servers had a watchdog thread to monitor changes to the log config file (a bit like the log4j’s configureAndWatch) but after watching and waiting for a little while nothing happened. I then checked the documentation (always a good idea) and found that you actually need to prod the server to tell it to change its logging config via proc iomoperate (also new in SAS 9.3).

This is the code I used to tell the SAS Metadata Server to reload its logging configuration file (logconfig.xml) – the one I had changed.

proc iomoperate;
connect host='sas93lnx01' port=8561 user='sasadm@saspw' password='thesecretpassword';
set log cfg="/opt/ebiedieg/Lev1/SASMeta/MetadataServer/logconfig.xml";
quit;

It worked. The metadata server immediately closed it’s current log file (SASMeta_MetadataServer_2012-01-10_sas93lnx01_1266.log) and opened a new one with a _0 suffix (SASMeta_MetadataServer_2012-01-10_sas93lnx01_1266.log_0) using the modified config. I wondered why it had added the _0 suffix? Subsequent executions increase the log file suffix (_1, _2, etc.). Perhaps it was done to delineate the old and new logging config in case someone wanted to parse the logs? If anyone knows how to make it continue to log to the same log file I’d love to know.

Of course this dynamic logging reconfiguration also means you can readily switch between normal and trace level logging config files to troubleshoot a problem and then switch back again quickly – all without a restart. Something like this:

* switch to trace log configuration;
proc iomoperate;
connect host='sas93lnx01' port=8561 user='sasadm@saspw' password='thesecretpassword';
set log cfg="/opt/ebiedieg/Lev1/SASMeta/MetadataServer/logconfig.trace.xml";
quit;

* >>> REPLICATE THE PROBLEM;
* switch back to normal log configuration;
proc iomoperate;
connect host='sas93lnx01' port=8561 user='sasadm@saspw' password='thesecretpassword';
set log cfg="/opt/ebiedieg/Lev1/SASMeta/MetadataServer/logconfig.xml";
quit;

For more info check out the following SAS documentation references: