linux-kernel - Re: [PATCH v3] sysctl: control functionality of /proc/pid/mem

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Date:	Tue, 31 Jan 2012 11:26:29 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Borislav Petkov <bp@...en8.de>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Dan Ballard <dan@...dstab.net>, Jiri Kosina <jkosina@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>,
	Stephen Wilson <wilsons@...rt.ca>,
	David Rientjes <rientjes@...gle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eric Paris <eparis@...hat.com>,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>,
	linux-doc@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Colin Walters <walters@...bum.org>
Subject: Re: [PATCH v3] sysctl: control functionality of /proc/pid/mem

On Wed, Jan 25, 2012 at 3:30 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Mon, 23 Jan 2012 13:21:15 -0800
> Kees Cook <keescook@...omium.org> wrote:
>> Add the "proc_pid_mem" sysctl to control whether or not /proc/pid/mem is
>> allowed to work: 0: disabled, 1: read only, 2: read/write (default).
>
> I agree with Colin on this (he stole my line!).
>
> Overall, the patch looks really hacky and random.  I felt the same way
> as Vasily: it's easy to see how a significant number of similar (and
> hacky and random) patches could be added, resulting in a regrettable
> mess.
>
> Is there some better designed, more organized way of approaching all of
> this?  Random ideas:
>
> - A parallel /procfs-perms filesystem.  You write a number into
>  /procfs-perms/stat to affect access to /proc/stat (although why the
>  heck not just run `chmod /proc/stat'?) It's unclear how to handle
>  /proc/pid/.  Perhaps literally have a /procfs-perms/pid/ directory.

This seems like too much overhead to me.

> - Make tasks inherit their /proc/pid/* permissions across fork, do a
>  chmod /proc/1/whatever in initscripts.

This is actually pretty interesting. I think as long as it only
allowed the _reduction_ of access. I don't want a process to open up
access, just restrict it further. It does make me wonder what the
side-effects would be, though. Dropping user r/w perms to things for
non-DAC_OVERRIDE processes would be ... weird.

-Kees

-- 
Kees Cook
ChromeOS Security
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