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

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Date:	Wed, 09 Sep 2015 16:50:48 -0400
From:	Paul Moore <pmoore@...hat.com>
To:	Richard Guy Briggs <rgb@...hat.com>
Cc:	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	sgrubb@...hat.com, eparis@...hat.com, v.rathor@...il.com,
	ctcard@...mail.com
Subject: Re: [PATCH V1] audit: add warning that an old auditd may be starved out by a new auditd

On Monday, September 07, 2015 12:58:18 PM Richard Guy Briggs wrote:
> On 15/09/07, Richard Guy Briggs wrote:
> > Nothing prevents a new auditd starting up and replacing a valid
> > audit_pid when an old auditd is still running, effectively starving out
> > the old auditd since audit_pid no longer points to the old valid auditd.
> > 
> > There isn't an easy way to detect if an old auditd is still running on
> > the existing audit_pid other than attempting to send a message to see if
> > it fails.  If no message to auditd has been attempted since auditd died
> > unnaturally or got killed, audit_pid will still indicate it is alive.
> > 
> > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> 
> Ok, self-nack on this one for a couple of problems...
> netlink_getsockbyportid() is static to af_netlink.c and "pid" should be
> task_tgid_vnr(current).  Otherwise, any opinions on this approach?
> 
> > ---
> > Note: Would it be too bold to actually block the registration of a new
> > auditd if the netlink_getsockbyportid() call succeeded?  Would other
> > checks be appropriate?

Hmm.  It seems like we should prevent the registration of a new auditd if we 
already have an auditd instance connected, although as you say, that isn't the 
easiest thing to do.

How painful would it be to return -EAGAIN to the new auditd while sending some 
sort of keep-alive/ping/etc. message to the old daemon to check its status?

-- 
paul moore
security @ redhat

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