Re: [PATCH] ratelimit printk messages from the audit system

[Paul Moore <paul.moore@hp.com>]

On Thursday 24 January 2008 1:01:12 pm Eric Paris wrote:
> On Thu, 2008-01-24 at 12:52 -0500, Paul Moore wrote:
> > On Wednesday 23 January 2008 5:06:53 pm Linda Knippers wrote:
> > > Eric Paris wrote:
> > > > On Wed, 2008-01-23 at 16:05 -0500, Linda Knippers wrote:
> > > >> This is unrelated to your patch but I think it would be nice
> > > >> if audit_lost represented the number of audit messages lost
> > > >> since the last time the message came out or the last time an
> > > >> audit record came out. Today its a cumulative count since the
> > > >> system was booted.  Is it too much overhead to zero it?
> > > >
> > > > Shouldn't be too much overhead, we are already on a
> > > > slow/unlikely path. What's the benefit though?  Just don't want
> > > > to have to do a subtraction?
> > >
> > > Well that, plus if the system is up for a long time (which we
> > > hope) and the message is infrequent (which we also hope), then it
> > > could take me a while to find the previous message in order to do
> > > the subtraction.
> > >
> > > > If we are dropping the 'we lost some messages' message 0'ing
> > > > the counter at that time would be a bad idea, certainly not
> > > > unsolvable, but I don't see what it buys us.
> > >
> > > I wouldn't want to lose the message, just make it more useful. 
> > > And if we zero it we don't have to worry about it wrapping.  As
> > > it is now, its really just the count since the last time it
> > > wrapped.
> >
> > I like Linda's idea of zero'ing the lost message counter once we
> > are able to start sending messages again for all the reasons listed
> > above. I haven't looked at the audit message sending code, but we
> > are only talking about adding an extra conditional in the common
> > case and in the worst case a conditional and an assignment. 
> > Granted they are atomic ops, but everyone keeps telling me that
> > atomic ops are pretty quick on almost all of the platforms that
> > Linux supports ...
>
> Delivery of audit lost messages is through printk/syslog.  Assuming
> we can assure it gets out of printk when we reset the counter we
> can't assure that it made it to syslog.  That means we could lose
> that message and have no record of it at all, nor any chance that in
> the future it would get recorded that it was lost either.

That sort of begs the question - why do we even bother printing the 
audit record lost message?

 :)

> I wouldn't NAK such a patch, but at the same time don't anyone expect
> me to write it   :)

<mumbling>
... everytime I open my mouth I end up with more work ...
</mumbling>

-- 
paul moore
linux security @ hp