linux-kernel - Re: [PATCH tip/core/urgent] rcu: protect fork-time cgroup access

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1269939034.5109.511.camel@twins>
Date:	Tue, 30 Mar 2010 10:50:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Paul Menage <menage@...gle.com>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, abogani@...ware.it
Subject: Re: [PATCH tip/core/urgent] rcu: protect fork-time cgroup access

On Mon, 2010-03-29 at 15:43 -0700, Paul Menage wrote:
> On Mon, Mar 29, 2010 at 2:15 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > Add an rcu_read_lock() / rcu_read_unlock() pair to protect a fork-time
> > cgroup access.  This seems likely to be a false positive.
> >
> > Located by: Alessio Igor Bogani <abogani@...ware.it>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >
> >  sched.c |    2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index 9ab3cd7..d4bb5e0 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -2621,7 +2621,9 @@ void sched_fork(struct task_struct *p, int clone_flags)
> >        if (p->sched_class->task_fork)
> >                p->sched_class->task_fork(p);
> >
> > +       rcu_read_lock();
> >        set_task_cpu(p, cpu);
> > +       rcu_read_unlock();
> 
> I think you're right that this is a false positive - it would only be
> a problem if it were possible for the task to be moved to a different
> cgroup, and I think that shouldn't be the case at this point in the
> fork path since the new process isn't visible on the tasklist yet,
> right?

Well the thing is, this fork time invocation of
set_task_cpu()->set_task_rq() is in no way special, there's multiple
places like that.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/