linux-kernel - Re: [PATCH v2] Restrict unprivileged access to kernel syslog

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Date:	Wed, 10 Nov 2010 08:32:45 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	Dan Rosenberg <drosenberg@...curity.com>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	mingo@...e.hu
Subject: Re: [PATCH v2] Restrict unprivileged access to kernel syslog

On Tue, Nov 09, 2010 at 07:18:29PM -0500, Dan Rosenberg wrote:
> The kernel syslog contains debugging information that is often useful
> during exploitation of other vulnerabilities, such as kernel heap
> addresses.  Rather than futilely attempt to sanitize hundreds (or
> thousands) of printk statements and simultaneously cripple useful
> debugging functionality, it is far simpler to create an option that
> prevents unprivileged users from reading the syslog.
> 
> This patch, loosely based on grsecurity's GRKERNSEC_DMESG, creates the
> dmesg_restrict sysctl.  When set to "0", the default, no restrictions
> are enforced.  When set to "1", only users with CAP_SYS_ADMIN can read
> the kernel syslog via dmesg(8) or other mechanisms.
> 
> v2 adds CONFIG_SECURITY_RESTRICT_DMESG.  When enabled, the default
> sysctl value is set to "1".  When disabled, the default sysctl value is
> set to "0".
> 
> Signed-off-by: Dan Rosenberg <drosenberg@...curity.com>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Ingo Molnar <mingo@...e.hu>
> CC: Kees Cook <kees.cook@...onical.com>
> CC: stable <stable@...nel.org>

Acked-by: Kees Cook <kees.cook@...onical.com>

As before, this looks fine and does the right thing with regard to /proc
access to the kernel log.

-- 
Kees Cook
Ubuntu Security Team
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