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Date: Mon, 12 Dec 2011 16:49:38 -0500
From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
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To: Cyrill Gorcunov <gorcunov@openvz.org>
CC: LKML <linux-kernel@vger.kernel.org>, Tejun Heo <tj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrew Vagin <avagin@openvz.org>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Vasiliy Kulikov <segoon@openwall.com>,
        Kees Cook <keescook@chromium.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: [patch 3/3] [PATCH] prctl: Add PR_SET_MM codes to set up mm_struct
 entires v3
References: <20111212200642.836001668@openvz.org> <20111212201715.244414996@openvz.org>
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Hi

> When we restore a task we need to set up text, data and data
> heap sizes from userspace to the values a task had at
> checkpoint time. This patch adds auxilary prctl codes for that.
> 
> While most of them have a statistical nature (their values
> are involved into calculation of /proc/<pid>/statm output)
> the start_brk and brk values are used to compute an allowed
> size of program data segment expansion. Which means an arbitrary
> changes of this values might be dangerous operation. So to restrict
> access the following requirements applied to prctl calls:
> 
>   - The process has to have CAP_SYS_ADMIN capability granted.

This is very dangerous feature and useless from regular admins.
Moreover, CAP_SYS_ADMIN has a pretty overweight meanings and
we can't disable it on practical. So, I have a question. Why
don't you make new capability for checkpoint?