linux-kernel - Re: [PATCH] for account_group_exec_runtime(), make sure ->signal can't be freed under rq->lock

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]

Date:	Tue, 11 Nov 2008 13:58:44 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frank Mayhar <fmayhar@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>, adobriyan@...il.com,
	Doug Chapman <doug.chapman@...com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] for account_group_exec_runtime(), make sure ->signal
	can't be freed under rq->lock

On 11/11, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@...hat.com> wrote:
>
> > The patch is ugly, but I don't see the better fix for now. Needs the
> > review from Peter/Ingo.
>
> this is indeed too ugly,

Agreed. It was "unless we find another fix for 2.6.28".

> Regarding this teardown bug. Stupid question: why cannot the signal
> structure live as long as the last user is around? It's a tiny amount
> of RAM.

Well, release_task()->__exit_signal() clears/frees ->signal exactly
because it doesn't (must not) have users any longer. And we have the
code which checks ->signal != NULL to know if the task was already
released or not.

Now scheduler wants to play with ->signal. We can change the code so
that we don't actually free it until the task does the last schedule.
Say, we can free it __from put_task_struct(). But this means we need
another counter in signal_struct (signal_struct->count can't work).
And, until we change the code which checks ->signal != NULL, we need
another pointer in task_struct.

Perhaps this makes sense regardless of this bug, but I don't think
this is 2.6.28 material anyway.

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/