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

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Message-ID: <20110704154405.GA9544@redhat.com>
Date:	Mon, 4 Jul 2011 17:44:05 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Vasiliy Kulikov <segoon@...nwall.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 07/04, Vasiliy Kulikov wrote:
>
> 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.

No, afaics it can't happen in do_exit() until we call exit_notify().
Otherwise, for example, any dying child will OOPS in do_notify_parent().
Or please look at exit_sem()->sem_lock_check(tsk->nsproxy->ipc_ns).

Oleg.

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