linux-kernel - Re: + prctl-pr_set_mm-introduce-pr_set_mm_map-operation-v3.patch added to -mm tree

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Date:	Sat, 23 Aug 2014 15:30:01 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Andrew Vagin <avagin@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Julien Tinnes <jln@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: + prctl-pr_set_mm-introduce-pr_set_mm_map-operation-v3.patch
	added to -mm tree

forgot to mention,

On 08/23, Oleg Nesterov wrote:
>
> On 08/23, Cyrill Gorcunov wrote:
>
> > Looks like I need
> > to use cred_guard_mutex instead of task_lock here, no?
>
> Please don't. First of all, it can't help because proc_pid_auxv() doesn't hold
> this lock. It does mm_access() which drops this lock after return. And to remind,
> we are going to remove mm_access/lock_trace from sys_read() paths in proc.

Besides, it can't help anyway. cred_guard_mutex is per-process (not per-thread),
suppose that a vfork()'ed child does prctl() while another thread reads the
parent's /proc/pid/auxv.

Cyrill, I am sorry, but I am starting to think that this patch should be
dropped and replaced by another version. Or do you think it would be better
to send the fixes on top?

Oleg.

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