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Message-ID: <20110704152636.GA21350@albatros>
Date: Mon, 4 Jul 2011 19:26:36 +0400
From: Vasiliy Kulikov <segoon@...nwall.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: akpm@...ux-foundation.org, Serge Hallyn <serge.hallyn@...onical.com>,
daniel.lezcano@...e.fr, ebiederm@...ssion.com, mingo@...e.hu,
rdunlap@...otime.net, tj@...nel.org,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] shm: handle separate PID namespaces case
On Mon, Jul 04, 2011 at 17:05 +0200, Oleg Nesterov wrote:
> On 07/04, Vasiliy Kulikov wrote:
> >
> > @@ -239,7 +239,23 @@ static int shm_try_destroy_current(int id, void *p, void *data)
> > if (IS_ERR(shp))
> > return 0;
> >
> > - if (shp->shm_cprid != task_tgid_vnr(current)) {
> > + if (shp->shm_creator != current) {
> > + shm_unlock(shp);
> > + return 0;
>
> I know absolutely nothing about ipc/, so probably I am wrong. But do
> we really need shm_lock()
It is needed to protect against parallel reads. To read one may just
hold shm_lock, but to write both shm_lock and rw_mutex are needed.
> (which also another idr_find)
Yes, this is a waste of time, actually. Directly locking
->shm_perm->lock is what is needed here and in shm_try_destroy_orphaned().
Thanks for looking into this!
--
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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