linux-kernel - Re: [PATCH V1] audit: add warning that an old auditd may be starved out by a new auditd

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Message-ID: <20150917113539.GA6873@madcap2.tricolour.ca>
Date:	Thu, 17 Sep 2015 07:35:39 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Paul Moore <paul@...l-moore.com>
Cc:	v.rathor@...il.com, linux-kernel@...r.kernel.org,
	linux-audit@...hat.com
Subject: Re: [PATCH V1] audit: add warning that an old auditd may be starved
 out by a new auditd

On 15/09/16, Paul Moore wrote:
> On Wed, Sep 16, 2015 at 6:24 AM, Richard Guy Briggs <rgb@...hat.com> wrote:
> > On 15/09/14, Paul Moore wrote:
> >> On Sunday, September 13, 2015 12:08:19 PM Richard Guy Briggs wrote:
> >> > On 15/09/11, Paul Moore wrote:
> >> > > Although I suppose if nothing else we could send a record indicating
> >> > > that another auditd attempted to replace it ... if we can send it
> >> > > great, drop the new request and be glad we audited it, if we can't
> >> > > send it, reset the auditd tracking.
> >> >
> >> > This is actually a good idea.
> >>
> >> This would go well with your last patch to try harder on netlink send
> >> failures.
> >
> > Re-looking at the AUDIT_STATUS_PID case, I'm noticing we only
> > audit_log_config_change() on success.  At the moment, auditd userspace
> > doesn't know about this new AUDIT_PING netlink message type I'm adding
> > for testing the health of the existing audit, so it will just be dropped
> > by existing auditd.  I think it makes sense to add
> > audit_log_config_change() on both the orphaning and starving cases
> > indicating the result=0 so that there is a record.  Arguably the
> > orphaning case can never happen again since the starving fix will
> > prevent a newer auditd from running.
> 
> Just so I'm clear, the "starving" case is when a new auditd tries to
> evict a perfectly good auditd?

Not evict so much as trample.  It just stomps on the existing audit_pid
reference and the old one isn't aware (unless it sends a status request
and checks the PID value) that it has been supplanted.

> Otherwise, I think adding a result/success field to the
> AUDIT_CONFIG_CHANGE record makes sense as long as it doesn't break
> Steve's parsing code (I don't think it will, although it may simply
> ignore it, which is okay).

It is already there, but never used for anything but success.  I'm
proposing to add code to actually report the failures too.

> paul moore

- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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