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

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Message-ID: <CAGXu5j+ZU_wrqeEYE7GCE6ArFo8z4AO=OW7mOSn0-fp1E9B6+Q@mail.gmail.com>
Date:	Tue, 2 Oct 2012 22:15:14 -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 Tue, Oct 2, 2012 at 10:12 PM, David Rientjes <rientjes@...gle.com> wrote:
> On Tue, 2 Oct 2012, Kees Cook wrote:
>
>> In the paranoid case of sysctl kernel.kptr_restrict=2, mask the kernel
>> virtual addresses in /proc/vmallocinfo too.
>>
>> Reported-by: Brad Spengler <spender@...ecurity.net>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>
> /proc/vmallocinfo is S_IRUSR, not S_IRUGO, so exactly what are you trying
> to protect?

Trying to block the root user from seeing virtual memory addresses
(mode 2 of kptr_restrict).

Documentation/sysctl/kernel.txt:
"This toggle indicates whether restrictions are placed on
exposing kernel addresses via /proc and other interfaces.  When
kptr_restrict is set to (0), there are no restrictions.  When
kptr_restrict is set to (1), the default, kernel pointers
printed using the %pK format specifier will be replaced with 0's
unless the user has CAP_SYSLOG.  When kptr_restrict is set to
(2), kernel pointers printed using %pK will be replaced with 0's
regardless of privileges."

Even though it's S_IRUSR, it still needs %pK for the paranoid case.

-Kees

-- 
Kees Cook
Chrome OS Security
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