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Date: Tue, 13 Dec 2011 01:58:40 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
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
Message-ID: <20111212215840.GS2199@moon>
References: <20111212200642.836001668@openvz.org>
 <20111212201715.244414996@openvz.org>
 <4EE676F2.1020204@gmail.com>
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On Mon, Dec 12, 2011 at 04:49:38PM -0500, KOSAKI Motohiro wrote:
> 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.

Except brk() call I don't see where it might be extremelly
dangerous at moment but indeed it might become very dangerous
once code grows. Still if evil minded person got CAP_SYS_ADMIN
these prctls are least thing one should carry about.

> 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?
> 

It's not a problem to introduce CAP_CHECKPOINT_RESTORE, but
would it be accepted? I mean, are we fine with new capability
introduction? If yes -- I'll add new one and rebase the patch.

	Cyrill