[RFC][PATCH] audit: add feature audit_lost reset

[Paul Moore]

On Wed, Dec 7, 2016 at 10:58 AM, Richard Guy Briggs <rgb at redhat.com> wrote:
> On 2016-12-07 10:53, Steve Grubb wrote:
>> On Wednesday, December 7, 2016 10:05:30 AM EST Paul Moore wrote:
>> > On Tue, Dec 6, 2016 at 10:32 PM, Richard Guy Briggs <rgb at redhat.com> wrote:
>> > > On 2016-12-06 19:17, Paul Moore wrote:
>> > >> On Tue, Dec 6, 2016 at 12:13 AM, Richard Guy Briggs <rgb at redhat.com>
>> > >> Okay, back up ... this whole mess about atomic_xchg() was always
>> > >> unrelated to my original suggestion, let's focus on my original
>> > >> comment ... don't reset the counter on a AUDIT_GET, reset it on a
>> > >> AUDIT_SET with an AUDIT_STATUS_LOST, does that make sense?
>> > >
>> > > I understood that.  It sounds like a nice simple and straightforward
>> > > method to do it but for the question of accuracy.  Please rewind to my
>> > > fundamental point: How do we get an accurate reading of the last value
>> > > of audit_lost before resetting it?
>> >
>> > Okay, I thought you were worried about a different race, which is why
>> > this discussion wasn't making much sense to me.  I understand your
>> > point, but I really dislike the API; although that's not your fault,
>> > it's really the only way to do it via AUDIT_GET.
>> >
>> > I'd much prefer we go with the cleaner AUDIT_SET approach and just not
>> > worry about the small race window.  It would only be an issue if you
>> > reset the count under heavy audit load, and why would you reset the
>> > lost value if you were under a heavy audit load?  That just doesn't
>> > make sense.
>> >
>> > I suppose we should hear from Steve on this since he was the one who
>> > has been asking for this feature, although I'm pretty sure I know what
>> > he is going to say.
>>
>> To start with, this request comes from users of the audit system. I just
>> passed along the request. The issue is that when you do auditctl -s, you get
>> the number of records lost. If you do it the next day, you have to do math to
>> see what the one day delta is. So, to make reporting easy, they want it to be
>> reset whenever they do audictl -s.
>>
>> You could also make a AUDIT_GET_RESET that gets the status and resets the
>> number atomically. Then I can add another commandline option to auditctl that
>> allows an admin to say also reset the counters. If that command line option is
>> passed, I call AUDIT_GET_RESET otherwise I call AUDIT_GET. Thought?
>
> This would be slightly simpler in kernel implementation than the method
> I proposed and would work fine, off the top of my head.

I'd prefer not to introduce another command message type for something
small like this.

Steve, do you have any objection to the AUDIT_SET based approach?
Based on what you've said above, it would seem like the potential race
condition with AUDIT_SET wouldn't be a significant issue.

-- 
paul moore
www.paul-moore.com