linux-kernel - Re: [PATCH V3 1/2] audit: stop an old auditd being starved out by a new auditd

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Date:	Tue, 22 Dec 2015 10:46:08 -0500
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Steve Grubb <sgrubb@...hat.com>
Cc:	Paul Moore <pmoore@...hat.com>, linux-audit@...hat.com,
	linux-kernel@...r.kernel.org, eparis@...hat.com,
	v.rathor@...il.com, ctcard@...mail.com
Subject: Re: [PATCH V3 1/2] audit: stop an old auditd being starved out by a
 new auditd

On 15/12/22, Steve Grubb wrote:
> On Tuesday, December 22, 2015 09:24:56 AM Paul Moore wrote:
> > On Tuesday, December 22, 2015 04:03:06 AM 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.
> > > 
> > > If no message to auditd has been attempted since auditd died unnaturally
> > > or got killed, audit_pid will still indicate it is alive.  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.
> > > An -ECONNREFUSED almost certainly means it disappeared and can be
> > > replaced.  Other errors are not so straightforward and may indicate
> > > transient problems that will resolve themselves and the old auditd will
> > > recover.  Yet others will likely need manual intervention for which a
> > > new auditd will not solve the problem.
> > > 
> > > Send a new message type (AUDIT_REPLACE) to the old auditd containing a
> > > u32 with the PID of the new auditd.  If the audit replace message
> > > succeeds (or doesn't fail with certainty), fail to register the new
> > > auditd and return an error (-EEXIST).
> > > 
> > > This is expected to make the patch preventing an old auditd orphaning a
> > > new auditd redundant.
> > > 
> > > V3: Switch audit message type from 1000 to 1300 block.
> > > 
> > > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > > ---
> > > 
> > >  include/uapi/linux/audit.h |    1 +
> > >  kernel/audit.c             |   16 +++++++++++++++-
> > >  2 files changed, 16 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > > index 843540c..d820aa9 100644
> > > --- a/include/uapi/linux/audit.h
> > > +++ b/include/uapi/linux/audit.h
> > > @@ -110,6 +110,7 @@
> > > 
> > >  #define AUDIT_SECCOMP		1326	/* Secure Computing event */
> > >  #define AUDIT_PROCTITLE		1327	/* Proctitle emit event */
> > >  #define AUDIT_FEATURE_CHANGE	1328	/* audit log listing feature changes
> > 
> > */
> > 
> > > +#define AUDIT_REPLACE		1329	/* Replace auditd if this packet...
> > 
> > Steve, are you okay with this record number?
> 
> Yes. Just wondering what to do with the event.

There's a u32 in it with the pid of the process trying to hijack/replace
the one the kernel thinks still exists, so it is worth recording that
information, I think, if the old auditd actually receives this message.

> -Steve

- 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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