linux-kernel - Re: [PATCH V10] fixup! audit: add audit by children of executable path

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Date:	Mon, 10 Aug 2015 12:53:54 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Paul Moore <pmoore@...hat.com>
Cc:	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	sgrubb@...hat.com, eparis@...hat.com, peter@...3.com
Subject: Re: [PATCH V10] fixup! audit: add audit by children of executable
 path

On 15/08/10, Paul Moore wrote:
> On Saturday, August 08, 2015 10:23:48 AM Richard Guy Briggs wrote:
> > Adding "C=1 CF=-D__CHECK_ENDIAN__" to enable sparse warnings identified a
> > warning with the
> > 	[PATCH V9 3/3] audit: add audit by children of executable path
> > patch posted a couple of days ago (and just re-posted due to another fix):
> > 
> > kernel/auditsc.c:476:46: warning: dereference of noderef expression
> > kernel/auditsc.c:477:61: warning: dereference of noderef expression
> > 
> > task_struct->parent requires RCU locking for access.  This fix resolves the
> > two warnings.
> > 
> > This patch should be merged with the patch it fixes once the fix is
> > confirmed to be the correct approach since the original patch hasn't been
> > accepted yet.
> > 
> > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > ---
> > My hesitation is that the rcu lock scope is too broad.  If the loop were
> > re-structured to hold the rcu_read_lock() and call rcu_dereference() once
> > per iteration, would lock release and retake action cause more overhead?
> > 
> >  kernel/auditsc.c |    7 +++++--
> >  1 files changed, 5 insertions(+), 2 deletions(-)
> 
> I'm still not convinced that we need to merge exe child filtering patch so I'm 
> not going to apply this, or your v10 patch, at this point in time.  If you 
> want to hold on to the code in case you and/or Steve think you can convince me 
> at a later date, you might as well merge this fixup patch into the v10 patch.

I fixed the known problems and reposted it for reference and public
archive so that it wasn't buried privately in my tree.

Aside from the need for the child filtering patch, do the RCU treatments
here look reasonable?

> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index e1f0da2..3ed043d 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -473,13 +473,16 @@ static int audit_filter_rules(struct task_struct *tsk,
> > {
> >  			struct task_struct *ptsk;
> > 
> > -			for (ptsk = tsk; ptsk->parent->pid > 0;
> > -			     ptsk = find_task_by_pid_ns(ptsk->parent->pid, &init_pid_ns)) {
> > +			rcu_read_lock();
> > +			for (ptsk = tsk; rcu_dereference(ptsk->parent)->pid > 0;
> > +			     ptsk = find_task_by_pid_ns(rcu_dereference(ptsk->parent)->pid
> > +							, &init_pid_ns)) {
> >  				if (audit_exe_compare(ptsk, rule->exe)) {
> >  					++result;
> >  					break;
> >  				}
> >  			}
> > +			rcu_read_unlock();
> >  		}
> >  			break;
> >  		case AUDIT_UID:
> 
> 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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