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Application-only Access: Implementing the Strategy

IBM i (OS/400, i5/OS)
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A PC attached to your AS/400 sits on a desk, seemingly inert, looking innocent. However, when you stop to think about what someone using that PC could be capable of, you might start to see the PC as a wolf in sheep's clothing. You may see that PC as the representation of a gaping and ragged hole in the security of the data on your AS/400.

In a previous article, I described that the commonly used methods of securing data are no longer robust enough to protect the data on your AS/400 in a network environment. Tools like ODBC, FTP, and Client Access (also known as PC Support) provide many ways to get at your data. It is difficult, if not impossible, to control access from PCs by limiting options on a menu. A new methodology is needed, and that's where this article comes in.

While working with clients to strengthen their systems' security, I recognized the problem and developed a new strategy called application-only access. Application-only uses the AS/400 security features of security level 30 and above to restrict access to production data outside of an application. This article will give the details of application-only access and tell you about some of the problems you may encounter along the way.

Application-only access is a security strategy that does not give users access to production data except when they use production applications. The application users should not have a group profile that would give them access to the production data.

This prevents modification and disclosure of the data outside of the production applications, but the users do need to access the data within the production applications. Users are given an initial program that adopts the needed access for the production libraries. The adopted authority of the entry program allows users access from within the application where the operations a user can perform are controlled. However, the users have no access outside of the application, such as with PC file transfer, remote commands, or FTP.

Applications sometimes give the interactive users menu options that cause the submission of batch jobs. The submitted batch programs also need to adopt authority. Only the entry programs for batch processes need to adopt authority. However, finding the starting point for all batch jobs may not be a simple task.

When it is not possible to determine all of the entry programs for batch processes, the solution is to change all of the production system's programs to adopt authority. Changing all programs to adopt authority allows the submitted jobs to adopt the needed access to production data. However, when possible, I recommend that only the batch entry programs adopt authority.

A security officer can use the Change Program (CHGPGM) command to change programs that are observable to adopt authority without recompilation of the programs. Programs with their observability removed must be recompiled. If you use vendor-supplied programs that have observability removed, you won't be able to implement this strategy without your software supplier's cooperation.

My first attempt to implement application-only access was to use library security. The data files and programs in the library had *PUBLIC access, but the production libraries in which the data and programs resided had a public access of *EXCLUDE. To access the data, the programs would adopt the library owner's authority to the production libraries. Library security strategy is easy to implement, which is why I chose this alternative first.

Library security works well for interactive users. When interactive users enter the application, an entry program adopts the access of the production data library owner and adds the production libraries to the library list. This allows the users to access the production data libraries.

However, when an interactive user selects a menu option that submits a batch job, the submitted batch jobs do not inherit the adopted authority from the interactive job. The submitted batch job fails to start because the batch job is not authorized to the production libraries.

The production libraries are on the library list for the submitted job because the default for the Submit Job (SBMJOB) command is to use the library list from the interactive job to start the batch job. However, the batch job has no mechanism to adopt the authority to these production libraries. Because the batch jobs fail, some strategy other than library security is required to protect production data.

If interactive users of applications do not submit jobs, and all batch jobs are started by the system operators, the problem with batch jobs not starting can be eliminated. Library security alone would be sufficient. The initial library list for the batch jobs submitted by the operators would not have the production libraries. Then, an entry program could adopt the needed access to add production libraries to the library list. Even in this scenario, there is a possibility that future applications will allow users to submit production batch jobs, so I recommend a more flexible strategy than library security.

The problem with limiting access to production libraries was that the batch jobs failed before they were allowed to adopt access. If the *PUBLIC access to the production libraries is *USE, the batch jobs will start. After the batch jobs start, entry programs in the batch job can adopt the needed authority for the files.

Since *PUBLIC has *USE access to the libraries, there needs to be some way to prevent the user from accessing the production data files. Preventing disclosure and modification of production data requires that the *PUBLIC access to all production data files be *EXCLUDE.

You will also want to restrict which users can run the application programs so the programs will also have *PUBLIC authority of *EXCLUDE. So that users are allowed to run the programs, the group profile GRPAPP01 is granted *USE access to the programs. (Only the entry program needs to be authorized to GRPAPP01, as the other programs can be accessed through adopted authority.)

Changing the authority of all production objects sounds like a major project, but it is not difficult. The Grant Object Authority (GRTOBJAUT) command has a generic option that can be used to change the authority of all objects in a library in one operation.

I recommend using authorization lists to protect the production data files (for more information on authorization lists, see "Authorization Lists to the Rescue," MC, May 1993). Authorization lists have the advantage of allowing changes to security even while the files are open. The only challenge will be finding a time when the files in the library are not in use to first add the authorization lists.

The implementation of application-only access is shown in 1. The user profile PRDOWN01 has no password and is the owner of all production programs, files, and libraries. The entry programs will adopt the access of PRDOWN01 to allow users access to production objects.

The implementation of application-only access is shown in Figure 1. The user profile PRDOWN01 has no password and is the owner of all production programs, files, and libraries. The entry programs will adopt the access of PRDOWN01 to allow users access to production objects.

When a user in GRPAPP01 selects menu option 1, an entry program from the PGMLIB is called. This program adopts the ownership of PRDOWN01, which gives the user access to the production data. The entry program is a shell program that calls the actual application function. In the case of purchased software, you may not be able to control the program that is submitted, so every program in the application is changed to adopt the ownership of the production owner (PRDOWN01).

Frequently, installations supplement the reports available from production applications by using Query, ODBC, or some report generation tools. Since users have no access to the data, there needs to be some way for them to produce these reports. One alternative is to give the users *USE access to the data. This would allow the users to copy production data, though. If the copying of production data must be controlled, the users cannot be given *USE access to the data.

The users still need to be able to run queries to produce reports. This is accomplished by adopting the query user profile (QRYUSR01) while the users are running Query.

QRYUSR01 has no password and is the owner of the entry program and query definitions. When the user selects menu option 2, as shown in 1, the entry program in QRYLIB is called. This adopts the access of QRYUSR01. The access of QRYUSR01 to production files is *USE, which allows read-only access. This prevents the Query user from modifying production data.

QRYUSR01 has no password and is the owner of the entry program and query definitions. When the user selects menu option 2, as shown in Figure 1, the entry program in QRYLIB is called. This adopts the access of QRYUSR01. The access of QRYUSR01 to production files is *USE, which allows read-only access. This prevents the Query user from modifying production data.

The libraries PGMLIB and DATALIB are given *PUBLIC access of *USE so submitted jobs will start. Unless the users are running menu option 1 or 2, they have no access to the data files or programs.

The authorities granted to QRYUSR01 can be either private authorities or access granted using an authorization list. I recommend using V3R1's new support for Primary Group Profile (PGP) authority. Use of PGP authority for QRYUSR01 will improve performance over the private authorities or authorization lists. If you have not installed V3R1, use private authorities. ("V3R1 Security Enhancements," MC, January 1995 described the details of PGP authority. This article also had a sample program that converts the private authorities for a user such as QRYUSR01 into PGP authority.)

The application-only access strategy uses the following techniques:

o Objects are owned by a production owner user profile.

o The production owner user profile is not a group profile for users.

o The "entry" programs into production applications will adopt the production owner user profile. This gives application users the access needed to perform their daily tasks only while running the production application.

o Users are limited to menus and prevented from command line access. The user profile specifies LMTCPB(*YES) so users cannot enter commands. Application-only access does not allow users to access data outside the application. Users are prevented from using the command line as extra protection in case the user gets to a display that might allow users to access the command line. It also prevents the user from entering a command that isn't dependent on adopted authority, such as PWRDWNSYS. (Note that PWRDWNSYS does require *JOBCTL authority.)

o Users are assigned a group profile that will authorize them to use the production application programs.

o Reports using production data can be produced by Query by giving a QRYUSR user profile *USE access to production data files.

Using this technique, you'll be able to protect your AS/400's data and keep your site more secure from PCs and other systems in your network. So you don't need to think of the humble little PC as the big bad wolf anymore. I highly recommend you use this technique at your site.

Wayne O. Evans is an AS/400 security consultant and a frequent speaker on security topics. During his 27 years with IBM Corporation, he was involved with AS/400 security design issues. The application-only access method was developed after he recognized that the implementation of security at several of his clients' installations allowed users excessive access to production data. He can be reached by E-mail at This email address is being protected from spambots. You need JavaScript enabled to view it..

Application-only Access: Implementing the Strategy

Figure 1: Application-only Access Overview



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