linux-kernel - Re: [RFC] ipc: introduce shm_rmid

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Date:	Mon, 4 Jul 2011 19:36:44 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	kernel-hardening@...ts.openwall.com,
	Randy Dunlap <rdunlap@...otime.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>,
	Daniel Lezcano <daniel.lezcano@...e.fr>,
	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [RFC] ipc: introduce shm_rmid_forced sysctl

On Mon, Jul 04, 2011 at 17:08 +0200, Oleg Nesterov wrote:
> On 06/22, Vasiliy Kulikov wrote:
> >
> > +void exit_shm(struct task_struct *task)
> > +{
> > +	struct nsproxy *nsp = task->nsproxy;
> > +	struct ipc_namespace *ns;
> > +
> > +	if (!nsp)
> > +		return;
> > +	ns = nsp->ipc_ns;
> > +	if (!ns || !ns->shm_rmid_forced)
> 
> This looks confusing, imho. How it is possible that ->nsproxy or
> ->ipc_ns is NULL?

I spotted the same checking logic in other places.  I don't know whether
it is redundant, I guess it can happen when the namespace is dying.
Probably it cannot happed inside of task do_exit(), only for extern
observers.


> > +		return;
> > +
> > +	/* Destroy all already created segments, but not mapped yet */
> > +	down_write(&shm_ids(ns).rw_mutex);
> > +	idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_current, ns);
> >  	up_write(&shm_ids(ns).rw_mutex);
> 
> Again, I do not pretend I understand ipc/, but it seems we can check
> ns->ipc_ids[].in_use != 0 before the slow path, no?

Looks like you're right.  Given it is do_exit(), the boost is
significant.

I'll send the patch for this thing and the locking part.


Thank you!

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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