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, 9 Sep 2015 02:31:54 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	sgrubb@...hat.com, pmoore@...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 15/09/08, Eric Paris wrote:
> This is already going to be in the audit log, right? We're going to
> send a CONFIG_CHANGE record with old_pid == the existing auditd. I bet
> it gets delivered to the old auditd.

Actually, delivered by the new auditd is what I'm seeing...  (Tested by
running "auditd -f" to have it show up in the debug output and not in
the log file.)  I did see it once as two seperate messages, one setting
to zero and the next to the new PID, but that may have been a testing
procedure error...

(Note: Why does auditd run in a terminal with -n or -f not respond to ^C?)

> But why is this a printk(KERN_WARN) ?

Because we're still trying to figure out what is going on...  But point
taken, we already should have that information.  If it is listed as a
warning it has a better chance of getting reported.  What do you suggest
instead?


Eric, thanks for taking the time to review this...


> On Mon, 2015-09-07 at 12:48 -0400, 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>
> > ---
> > 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?
> > 
> >  kernel/audit.c |    5 +++++
> >  1 files changed, 5 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index 18cdfe2..1fa1e0d 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -872,6 +872,11 @@ static int audit_receive_msg(struct sk_buff
> > *skb, struct nlmsghdr *nlh)
> >  		if (s.mask & AUDIT_STATUS_PID) {
> >  			int new_pid = s.pid;
> >  
> > +			if (audit_pid && new_pid &&
> > +			   !IS_ERR(netlink_getsockbyportid(audit_sock, audit_nlk_portid)))
> > +				pr_warn("auditd replaced by new auditd before normal shutdown: "
> > +					"(old)audit_pid=%d (by)pid=%d new_pid=%d",
> > +					audit_pid, pid, new_pid);
> >  			if ((!new_pid) && (task_tgid_vnr(current) != audit_pid))
> >  				return -EACCES;
> >  			if (audit_enabled != AUDIT_OFF)

- 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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