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Date: Mon, 12 Dec 2011 17:24:56 -0500
From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
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To: Cyrill Gorcunov <gorcunov@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
References: <20111212200642.836001668@openvz.org> <20111212201715.244414996@openvz.org> <4EE676F2.1020204@gmail.com> <20111212215840.GS2199@moon>
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(12/12/11 4:58 PM), Cyrill Gorcunov wrote:
> 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.

I'm sorry, I misunderstood your code. Your code only allow to change
their own process attribute. So, it's enough harmless. Please ignore
my last mail.



>> 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.