audit.rules being really processed sequentially?

audit.rules being really processed sequentially?

[Ede Wolf]

Hello,


In my pursuit of taming auditd in that it only logs what has explicitly 
been defined and nothing more, I've thought of a set of catch all rules 
at the end. As the rules file is supposedly being processed 
sequentially, i.e. first hit matches, this ought to work. But it doesn't.

Having a very simple rules file as an example:

-D
-e 1

-a exit,always -F arch=b64 -S execve -F path=/bin/vi -k EDIT_FILE

-a always,exclude -F msgtype=EXECVE
-a always,exclude -F msgtype=FD_PAIR
-a always,exclude -F msgtype=FS_RELABEL
...

(continue this for every messagetype from this link:

  https://access.redhat.com/articles/4409591#audit-record-types-2)

As easily to be guessed, my expectation would be, the invokation of vi 
by anyone would get logged, as that rules comes first, but really 
nothing else, as it is being discaded by the catchall rules.

Surprisingly however, in reality, nothing gets logged at all, not even 
the invocation of vi.

Now, removing those catchall rules at the end does log the calling of 
vi, but of course also all other stuff I neither  have defined nor want 
to be written out.

So, if the audit.rules file really is being processed sequentally, what 
am I missing in my approach?


Thanks very much for any insight.


Ede

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Re: audit.rules being really processed sequentially?

[Steve Grubb]

On Thursday, September 2, 2021 11:54:12 AM EDT Ede Wolf wrote:
> In my pursuit of taming auditd in that it only logs what has explicitly
> been defined and nothing more, I've thought of a set of catch all rules
> at the end. As the rules file is supposedly being processed
> sequentially, i.e. first hit matches, this ought to work. But it doesn't.
> 
> Having a very simple rules file as an example:
> 
> -D
> -e 1
> 
> -a exit,always -F arch=b64 -S execve -F path=/bin/vi -k EDIT_FILE
> 
> -a always,exclude -F msgtype=EXECVE
> -a always,exclude -F msgtype=FD_PAIR
> -a always,exclude -F msgtype=FS_RELABEL
> ...
> 
> (continue this for every messagetype from this link:
> 
>   https://access.redhat.com/articles/4409591#audit-record-types-2)
> 
> As easily to be guessed, my expectation would be, the invokation of vi
> by anyone would get logged, as that rules comes first, but really
> nothing else, as it is being discaded by the catchall rules.
> 
> Surprisingly however, in reality, nothing gets logged at all, not even
> the invocation of vi.
> 
> Now, removing those catchall rules at the end does log the calling of
> vi, but of course also all other stuff I neither  have defined nor want
> to be written out.
> 
> So, if the audit.rules file really is being processed sequentally, what
> am I missing in my approach?

It might be useful to look at slide 15 of this:

http://people.redhat.com/sgrubb/audit/audit_ids_2011.pdf

The output of the rule matching engine gets fed to the exclude filter for a 
second look. The exclude filter then drops objectionable records. In your 
case, it its told to drop everything.

Audit records in the 1300 block are related to rules. You need to let all of 
them through.

-Steve


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Re: audit.rules being really processed sequentially?

[Ede Wolf]

Thanks very much for your help and heads up, even though of course bad news.

Ede

Am 02.09.21 um 18:21 schrieb Steve Grubb:
> On Thursday, September 2, 2021 11:54:12 AM EDT Ede Wolf wrote:
>> In my pursuit of taming auditd in that it only logs what has explicitly
>> been defined and nothing more, I've thought of a set of catch all rules
>> at the end. As the rules file is supposedly being processed
>> sequentially, i.e. first hit matches, this ought to work. But it doesn't.
>>
>> Having a very simple rules file as an example:
>>
>> -D
>> -e 1
>>
>> -a exit,always -F arch=b64 -S execve -F path=/bin/vi -k EDIT_FILE
>>
>> -a always,exclude -F msgtype=EXECVE
>> -a always,exclude -F msgtype=FD_PAIR
>> -a always,exclude -F msgtype=FS_RELABEL
>> ...
>>
>> (continue this for every messagetype from this link:
>>
>>    https://access.redhat.com/articles/4409591#audit-record-types-2)
>>
>> As easily to be guessed, my expectation would be, the invokation of vi
>> by anyone would get logged, as that rules comes first, but really
>> nothing else, as it is being discaded by the catchall rules.
>>
>> Surprisingly however, in reality, nothing gets logged at all, not even
>> the invocation of vi.
>>
>> Now, removing those catchall rules at the end does log the calling of
>> vi, but of course also all other stuff I neither  have defined nor want
>> to be written out.
>>
>> So, if the audit.rules file really is being processed sequentally, what
>> am I missing in my approach?
> 
> It might be useful to look at slide 15 of this:
> 
> http://people.redhat.com/sgrubb/audit/audit_ids_2011.pdf
> 
> The output of the rule matching engine gets fed to the exclude filter for a
> second look. The exclude filter then drops objectionable records. In your
> case, it its told to drop everything.
> 
> Audit records in the 1300 block are related to rules. You need to let all of
> them through.
> 
> -Steve
> 
> 

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