Bypassing audit's file watches

[Michael C Thompson]

Michael C Thompson wrote:
> Timothy R. Chavez wrote:
>> On Fri, 2006-07-07 at 10:58 -0400, Steve wrote:
>>> I have found that I can modify files that are being watched and audit 
>>> not catch it (ie. no events are dispatched).  When monitoring a file 
>>> for all system calls, I can:
>>>
>>> echo "" > /file/to/watch
>>>
>>> or
>>>
>>> cat some_file > /file/to/watch
>>>
>>> without generating audit events.  I assume this has to do with how 
>>> the kernel handles re-direction.  Is it possible to catch these 
>>> modifications?
>>>
>>> Thanks,
>>> Steve
>>
>> What are your rules?  You should catch these on open()
>> of /file/to/watch, right?
>>
>> -tim
> 
> I am seeing this as well with the .42 kernel and audit-1.2.4-1. Not sure 
> when this might have broken, but its broke now.
> 
> It seems if you set a watch on /file/to (to use your example above), 
> then you are getting the opens that bash does, although the PATH record 
> shows the item as "/file/to/watch".
> 
> So watching the parent directory will audit redirect shell magic, but 
> watching the target of that redirection will not audit that same magic.
> 
> Mike

Oh, and it turns out if the action fails, then the watch on the target 
of redirection will get audited. So if you echo "123" > 
not_writable_file, and you have a watch on 'not_writable_file', you will 
see an audit record, but if the write is successful, then you don't see it.

Mike