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

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Message-ID: <alpine.DEB.2.00.1210031051150.29765@chino.kir.corp.google.com>
Date:	Wed, 3 Oct 2012 11:02:07 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Kees Cook <keescook@...omium.org>
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, 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.
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