Sunday, March 31, 2019

A Case Study: Implementing a Db2 for z/OS Implicit Trusted Connection

I've been interested in the role and trusted context features of Db2 for z/OS for a long time (I posted a two-part blog entry on the topic back in 2011). Theory is nice, but what about practice? Recently, I had an opportunity to assist a DBA in implementing implicit trusted connection functionality in his Db2 for z/OS environment (more on the implicit part in a moment). Today I'll share some of what the DBA and I learned through that endeavor.

First, the backstory: the DBA's organization wanted to tighten Db2 for z/OS data security by preventing unauthorized utilization of the authentication credentials used by an application to connect to a Db2 system. The kind of application we're talking about here is one that accesses a Db2 for z/OS server through a TCP/IP link via the IBM Data Server Driver (or its predecessor, Db2 Connect). In requesting a connection to a Db2 system, the application provides an authorization ID and an associated password (assuming authentication using an ID and a password, versus an ID and a certificate). Often, the ID and password in question are known by several of the application's developers. What is to keep someone from using the application's authorization credentials to connect to the Db2 system from, say, a laptop PC, thereby gaining access to data that should be accessible only through the application?

Enter roles and trusted contexts. These Db2 features work together to shut down the potential security exposure just described. How does this work? First of all, any Db2 privileges needed by the application (e.g., the SELECT privilege on table T1) are NOT granted to the application's Db2 authorization ID. Those privileges are instead granted to a Db2 role, which I'll call APP1ROLE. Next, a Db2 trusted context is created to specify the circumstances under which the Db2 privileges granted to the role can be used by an application. If the trusted context is named TRCON1, and if the application authenticates to the Db2 system using authorization ID APP1ID and the application runs on the two application servers at IP addresses and, the Db2 DDL statement defining the trusted context might look something like this:


Here's what the above DDL statement is essentially saying: "The Db2 privileges granted to role APP1ROLE can be used ONLY by the application that connects to Db2 using authorization ID APP1ID, and ONLY when that application connects to this Db2 system from either IP address or IP address" Following creation of the role and trusted context, suppose that someone who know's the application's authentication credentials uses them to connect to the Db2 system from a laptop PC. Assuming a successful connection from the laptop PC, is that an "Uh-oh" situation? No. Why not? Because no Db2 privileges have been granted to the application's authorization ID (connecting to a Db2 for z/OS system doesn't get you anywhere if you can't do anything after connecting). But what about the privileges granted to role APP1ROLE, which we've associated with the application's authorization ID? Those privileges are not available to the person who used the application's credentials to connect to the Db2 system from a laptop PC because the laptop's IP address is not one of the two specified in the definition of the trusted context (those being the addresses of the two application servers on which the application runs). What has been accomplished through the creation of the role and trusted context is a vast reduction in what security people sometimes call the "threat area": instead of worrying about the application's credentials being misused from any IP address, we just need to secure the two IP addresses referenced in the trusted context definition (in other words, we need to ensure that an individual cannot make an unauthorized connection to the Db2 system from the two application servers on which the application of interest runs).

Back to my DBA friend. His first attempt at successful use of a Db2 role and trusted context didn't work: the SELECT privilege on table T1 was granted to a role but not to authorization ID APP1ID (using the example ID previously referenced), and an attempt to execute SELECT COL1 FROM T1 by way of a trusted context, using ID APP1ID, failed with a Db2 "ID not authorized to perform this action" error code. We decided to check to make sure that the IP address used in defining the trusted context was the right one. To help with that verification, we 1) turned auto-commit off on the tool being used by the developer who was helping us with the test, and 2) granted SELECT ON T1 to APP1ID. Why did we do these two things? So that we could see the IP address of the developer's Db2 thread in Db2 -DISPLAY THREAD command output (granting SELECT ON T1 to APP1ID ensured that the thread information wouldn't disappear due to the aforementioned authorization error, and making sure that a commit wasn't issued after the successful SELECT similarly preserved the thread's information, which would have disappeared when the thread went into a disconnected state following a commit).

After we'd taken those two actions to keep the developer's thread in a connected state following the SELECT FROM T1, we had the developer try again. Sure enough, we saw information about the developer's still-connected Db2 thread in -DISPLAY THREAD(*) DETAIL output, but the client IP address information was missing. That information was absent because -DISPLAY THREAD(*) DETAIL was an overly-generic form of the command -DISPLAY THREAD. When we switched to the form -DISPLAY THREAD(*) LOCATION(*) DETAIL, which tells Db2 that you only want to see information about DDF threads, we got additional DDF-related information in the command, including the client IP address associated with the developer's transaction (that address is in the V445 section of the command's output). The client address we saw was the one used in the definition of the trusted context, so why didn't the trusted context work for us? Because in this case the developer's connection to the Db2 system was through a Db2 Connect "gateway" server (versus a direct connection from the client via the IBM Data Server Driver), and in that case the client IP address that Db2 "sees" is the address of the Db2 Connect gateway server, not the address of the client that is "upstream" from the Db2 Connect gateway server.

OK, so we addressed that problem by re-defining the trusted context, this time using the IP address of the Db2 Connect gateway server. Well, not exactly. We actually re-defined the trusted context by specifying the domain name of the Db2 Connect gateway server, instead of its IP address. That can certainly be done in a CREATE (or ALTER) TRUSTED CONTEXT statement, and such a specification can be useful when (as was the case for my DBA friend's organization) the IP address of the Db2 Connect gateway server used by an application can change from time to time (if the application server references the Db2 Connect gateway server's domain name, a change in the gateway server's IP address does not require a client-side change - the domain name is simply mapped to the new gateway server's IP address versus the address of the old gateway server). We tried again with the redefined trusted context AND IT STILL DIDN'T WORK. ARRGGGHHH. What was going on? Further investigation revealed the problem: the domain name we were given by a network administration colleague of the DBA was actually associated with a pair of IP addresses (corresponding to a pair of Db2 Connect gateway servers), and for a domain name specification in the ATTRIBUTES part of a CREATE (or ALTER) TRUSTED CONTEXT statement to work properly, it has to be associated with a single IP address.

Once again, the DBA re-defined the trusted context, this time using two domain names as address attributes, with each domain name being specific to the one IP address of one of the two Db2 Connect gateway servers in a cluster. He revoked SELECT ON T1 from the APP1ID authorization ID, and had the developer try again with a SELECT from T1 using APP1ID, AND IT WORKED!! The successful execution of the SELECT from T1 showed that the privilege granted to the role APP1ROLE was being used, and indeed we saw in the output of a -DISPLAY THREAD(*) LOCATION(*) DETAIL command that the developer's thread was using the established trusted context (that information is in the V485 section of the command's output).

Now, about the "implicit" nature of the trusted connection, referenced way up at the top of this blog entry (and in the entry's title): I wanted to make sure to emphasize the implicit nature of the trusted connection used in this example, because so much of the documentation on Db2 for z/OS trusted contexts pertains to explicit trusted connections. What's the difference? Well, in the latter case a client application explicitly requests a trusted connection to the Db2 server, whereas in the former case the connection is just a "regular" connection from the client application's perspective, and it becomes a trusted connection because a trusted context matching the application's authorization ID and IP address (or domain name or whatever other attribute is specified) has been defined on the Db2 side. If you can get a trusted connection to a Db2 server (one that enables use of the Db2 privileges granted to a role associated with the trusted connection) without having to explicitly request such a connection, why would you go the explicit route? You'd go that route if you needed functionality that is ONLY available for explicit trusted connections. An example of that functionality: an application, having requested and obtained an explicit trusted connection to a Db2 for z/OS server, can then tell Db2 that it is "switching" use of the explicit trusted connection from its ID (the ID the application used to connect to the Db2 server) to the ID of an end user of the application. That switching from one ID to another (and the associated flowing by the application of an actual end-user's ID to the Db2 server system) is one of the things that has to happen if you want to make use of (for example) the enterprise identity mapping capability provided by RACF (whereby an individual's "network" ID can be mapped to a RACF ID). Note that a trusted context defined for the purpose of supporting explicit trusted connection functionality would likely include the WITH USE FOR clause in the CREATE TRUSTED CONTEXT statement - that clause can be used to reference end-user IDs passed to Db2 by an application. In the situation I've described in this blog entry, the DBA did not require explicit trusted connection functionality, so setting up implicit trusted connection capability was appropriate.

I hope that the information I've provided here will be useful to you if you want to utilize implicit trusted connection functionality in your Db2 for z/OS environment.


  1. I wish CIDR notation could be used. We have connections from cloud environments and I have to put 255 ip addresses in the trusted context definition due to the way the cloud applications use ip addresses.

    1. Understood - that would indeed make life easier in such cases. You might consider submitting that as a Db2 for z/OS enhancement idea, via the IBM Db2 for z/OS ideas portal at This is one of the primary mechanisms through which the Db2 for z/OS development team hears "the voice of the customer."