linux-kernel - Re: [RFC] [PATCH 2/2] cgroups: make procs file writable

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20100603144810.GB6284@redhat.com>
Date:	Thu, 3 Jun 2010 16:48:10 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ben Blum <bblum@...rew.cmu.edu>
Cc:	Paul Menage <menage@...gle.com>, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, akpm@...ux-foundation.org,
	ebiederm@...ssion.com, lizf@...fujitsu.com, matthltc@...ibm.com
Subject: Re: [RFC] [PATCH 2/2] cgroups: make procs file writable

On 06/03, Ben Blum wrote:
>
> On Wed, Jun 02, 2010 at 10:58:55PM +0200, Oleg Nesterov wrote:
> > Hmm. The usage of ->thread_group in ->can_attach() methods doesn't
> > look safe to me... but currently bool threadgroup is always false.
>
> I recall putting a rcu_read_lock() around that part and being assured
> that made it safe. But I don't remember the details. Maybe taking
> tasklist_lock is necessary?

rcu_read_lock() is not enough, see another email I sent.

Once again.

	rcu_read_lock()
	list_for_each_rcu(tsk->thread_group)

assumes that at least tsk->thread_group->next can't point to nowhere,
this is not true. This memory can go away _before_ we take rcu lock.

Oleg.

--
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/