Auditing and onaudit

Compliance is one of those things you can hardly ignore as a DBA these days. Whether it’s a PCI-DSS, financial or internal best practice audit, at some point someone is going to ask you whether you are using database auditing. In my experience the auditors struggle to ask Informix specific questions but this is one that always comes up.

I guess there are three answers to this question:

  • Yes, we use database auditing.
  • No we don’t use Informix auditing but we have a third party solution somewhere else in the stack that means someone else worries about it.
  • Can we have a compensating control, please?

Rarely I find that auditors are too concerned about the detail of what you’re actually auditing. If you can log in, do some stuff and show them that this resulted in some messages in the audit log, they are usually happy. They are usually more concerned about where the logs go, who can read them and so on.

While the auditors are clearly not Informix DBAs familiar with all the auditing pneumonics, they are not daft and know they can take most of what they asked for granted next year and ask more probing questions next time.

So should you look at onaudit for your requirements? It’s been around a long time but I expect it may see a pick up in interest as more and more systems take payments in one way or another. In some ways it could do with some updates. Integration with syslog, allowing easy upload to a centralised question, is needed. There is an RFE open for this (id 58678). It’s not mine but it had six votes when I last checked and it deserves more!

Positives about onaudit include:

  • It’s free with all editions.
  • Provided you stay away from selective row auditing (I don’t cover this in this blog post) and don’t try to audit much or any of what your application does the overhead is negligible.
  • It gives you as a DBA a clearer idea of what is happening on your system.

So I think it’s certainly worthy of consideration. I know some customers prefer security solutions external to the database like Guardium but these are costly. I don’t know much about them so I shall leave that thought there.

Auditing needs to be part of a more general secure framework. If everyone at your site logs in as user informix or any shared account, the worst case being the same account as your application, it’s not going to be as useful. Applying rules by user will be difficult or impossible.

Some sites I’ve seen let DBAs do all their work as user informix. It definitely saves developing a more secure framework for DBAs to work in (this is not a good thing!) but has disadvantages. Even if you avoid shared passwords by using sudo to informix (on UNIX) having logged in as yourself, you’d need then to cross-check with the secure logs on your server to see who it was and if two people have escalated privileges at the same time it can be tricky to distinguish their actions. Ideally you need DBAs and every other real person working under their own user ids as much as possible.

To work as a DBA without access to the informix account you simply add yourself to the same group as the group owning the $INFORMIXDIR/etc folder and grant yourself dba in any databases you need to do DDL in, plus sysmaster, sysadmin, sysutils, sysha and sysuser but it still presents the following challenges which may require specific sudo type solutions:

  • Starting an instance; stopping one is no problem.
  • Running xtrace and certain oncheck commands.

Additionally as a DBA you may need root access occasionally for installations, upgrades and to use debuggers.

So before you even start there are some highly desirable prerequisites:

  • Your applications use their own account or (ideally) accounts and real users cannot run ad-hoc sessions using these.
  • Real users don’t use shared accounts (and especially not shared passwords). This means locking down the informix account.
  • DBAs practise what they preach and administer the system under their own accounts as much as possible.

Getting this far can be a struggle but even if you’re only some of the way there, you can still proceed.

The next step is consider whether to install Informix with role separation. I’m not going to discuss this at length so I’ll point to the documentation. There are no real gotchas here: it works pretty much as it says on the tin. The key idea is that it separates the DBAs from the people who decide what should be audited and who can see the audit trail. In practice I think total separation is impossible because the people deciding what should be audited need to understand the impact on the system of what they audit and the volume of data this produces. It is certainly possible to slow a system down by auditing every update.

So you’re now ready to switch on auditing? Nearly. If you monitor your system via onstat or have scripts which call onmode, ‘onmode -c [un]block’ being a specific example where care is required, you need to be aware that in all but the latest Informix releases, this includes right up to 12.10.FC5W1, as soon as you switch on auditing your onstat and onmode commands will run more slowly. This can also affect admin API command equivalents and not just the ones which are direct equivalents for onmode. The situation can get quite bad when lots of these commands run at the same time, leading to significant delays in the response from these commands.

Fortunately there are some fixes for this:

IC89645
TURNING ON THE AUDITING LEVEL 1 ADDS AN UNNECESSARY DELAY TO ONSTAT AND ONMODE COMMANDS

This has been around for a while and appeared in 11.70.FC7W1. However it is not very effective and only eliminates the delay if the volume of onstat commands being run on your system is low.

IT08812
TURNING ON THE AUDITING LEVEL 1 ADDS AN UNNECESSARY DELAY TO ONSTAT & ONMODE COMMANDS

This is completely effective and means that onstat and onmode behave identically to when auditing is switched off but it only works if you do not have any audit masks which log the use of these commands.

There are workarounds for the auditing delay such as using sysmaster equivalents for the onstat commands and performing onstat commands inside an onstat -i interactive session.

Finally you’ll want to consider setting up some audit masks. I take the following approach to this:

_require mask
This mask defines the minimum events to be audited for all users. I put everything that’s common in here.
_default mask
If an account is not assigned a specific mask, it will pick up all the events in there. To avoid having to assign masks to all real users, I don’t assign them any mask and then they automatically inherit this one (in addition to what is in the _require mask).
Other masks
For my applications and other accounts needing special treatment, I create a custom mask and assign it to the user.

Finally if you’re feeling brave switch auditing on with some commands like:

onaudit -p /path/to/audit/trail
onaudit -s 1048576 # 1 Mb files
onaudit -e 0
onaudit -l 1

Now there is just that application security model for you to tackle.

Good luck and may you sail through your audits!