linux-kernel - Re: [PATCH] mm: use %pK for /proc/vmallocinfo

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Message-ID: <CAGXu5jKAYYd5MxF4QmUxuFtAx2V8j3GMtmcA5v6ShGHAQZQh7Q@mail.gmail.com>
Date:	Wed, 3 Oct 2012 11:39:27 -0700
From:	Kees Cook <keescook@...omium.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Joe Perches <joe@...ches.com>,
	Kautuk Consul <consul.kautuk@...il.com>, linux-mm@...ck.org,
	Brad Spengler <spender@...ecurity.net>
Subject: Re: [PATCH] mm: use %pK for /proc/vmallocinfo

On Wed, Oct 3, 2012 at 11:02 AM, David Rientjes <rientjes@...gle.com> wrote:
> On Wed, 3 Oct 2012, Kees Cook wrote:
>
>> > So root does echo 0 > /proc/sys/kernel/kptr_restrict first.  Again: what
>> > are you trying to protect?
>>
>> Only CAP_SYS_ADMIN can change the setting. This is, for example, for
>> containers, or other situations where a uid 0 process lacking
>> CAP_SYS_ADMIN cannot see virtual addresses. It's a very paranoid case,
>> yes, but it's part of how this feature was designed. Think of it as
>> supporting the recent uid 0 vs ring 0 boundary. :)
>>
>
> The intention of /proc/vmallocinfo being S_IRUSR is obviously to only
> allow root to read this information to begin with, so if root lacks
> CAP_SYS_ADMIN then it seems the best fix would be to return an empty file
> on read()?  Or give permission to everybody to read it but only return a
> positive count when they have CAP_SYS_ADMIN?
>
> There's no need to make this so convoluted that you need to have the right
> combination of uid, kptr_restrict, CAP_SYS_ADMIN, and CAP_SYSLOG to get
> anything valuable out of this file, though.

Well, the existing mechanism is using %pK. I see no reason to add
additional complexity.

-Kees

-- 
Kees Cook
Chrome OS Security
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