auditd on nonexistent files

[Steve Grubb]

On Mon, 14 Sep 2015 16:01:17 +0000
Davíð Steinn Geirsson <dsg at sensa.is> wrote:

> Hi all,
> 
> What is the best practice for using auditd for file integrity
> monitoring?
> 
> From the documentation, I have this, which works fine:
> -a always,exit -F dir=/bin -F perm=wa
> 
> However, it seems that if I have a rule on a nonexistent directory,
> auditd will fail to add the rule (I assume because it's adding a watch
> on an inode or something like that?), but it will also just stop
> reading audit.rules and not add any subsequent rules.
> 
> This is bad in an environment where we have to have FIM for critical
> application files, but where another team may be maintaining some of
> the apps and therefore might remove some watched directories,
> especially as their mishaps may impact auditing for other parts of
> the system.
> 
> 
> Can something be done to get better behaviour here?
> 
> I see two ways it could be better
> 1) (the ideal case) auditd will add rules even for nonexistent
> directories, and when they are created will add a watch for them. If a
> directory is removed and another created with the same name, auditd
> will add a watch on the new directory.

Which kernel are you using? I want to think this was fixed in kernels
around 2.6.36 or later. This original problem was that the audit
watches are based on inotify which needs an inode. If there's no inode,
you can't place the watch.


> 2) auditd still cannot add watches to nonexistent directories, but a
> failed rule add from audit.rules will become a warning rather than an
> error so subsequent watches still get added.

Check into adding -i or -c near the top of your rules.

-Steve


> I suspect 1) is not possible, but can I get auditd to behave like in
> 2)?
> 
> Best regards,
> Davíð
>