Re: Audit reporting Invalid argument

[Steve Grubb <sgrubb@redhat.com>]

On Monday, May 09, 2016 01:40:58 PM Bhagwat, Shriniketan Manjunath wrote:
> I am trying to monitor multiple files using Linux audit. In order to get
> better performance, I am trying to reduce number of rules. If I specify
> more than one path field  as in below example I am getting "Invalid
> argument".
> 
> Examle1:
> # auditctl -a always,exit -F arch=x86_64 -F path=/home/secpack/test.c -F
> path=/home/secpack/test -S open Error sending add rule data request
> (Invalid argument)
>
> # auditctl -a always,exit -F arch=x86_64 -F path=/home/secpack/test.c -F
> dir=/tmp/ -S open Error sending add rule data request (Invalid argument)
> 
> However, I am able to create a single rule to monitor multiple PIDs or UIDs
> as below.
> 
> Examle2:
> # auditctl -a always,exit -F arch=x86_64 -F pid=3526 -F pid=3537
> # auditctl -a always,exit -F arch=x86_64 -F auid=0 -F auid=512 -F auid=1002

Which will produce no events due to the anding you mention below. Something 
cannot have both pid 3526 and 3537.

 
> As per the auditctl man page, Build a rule field takes up to 64 fields on a
> single command line. Each one must start with -F. Each field  equation  is 
> anded  with  each other  to  trigger  an audit record. My question is,
> 1. specify more than one path field as in example1 is valid?

Nope.

> 2. If not valid than how do I create single audit rule to monitor multiple
> files/directory?

They need to be separate rules. You can also recursively watch a directory 
with 'dir'


> 3. If valid, then why "Invalid argument" is reported?
> 4. To monitor 10 files, should 10 audit rules required?

Possibly.

> 5.  if 10 rules are required, how to I optimize the rule for performance?

The filesystem watches are very efficient. You can probably put a 100 watches on 
random files and you will not be able to see any performance hit unless they 
are actually triggered. Syscall rules on the otherhand do affect performance.


> My next question is does Linux audit support regular expressions?

No. The kernel pretty much wants things to be numbers rather than strings.

> How do I create audit rule to monitor /var/log/*.log?

-a always,exit -F dir=/var/log/audit/ -F perm=wa -F key=write-audit-log
 
-Steve


> # auditctl -a always,exit -F arch=x86_64 -F path=^/var/log/*.log$  -S open
> Error sending add rule data request (Invalid argument)
> 
> If my questions are already documented, please guide me to the
> documentation.
> 
> Regards,
> Ketan