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

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Message-ID: <20101110082516.GB3341@elte.hu>
Date:	Wed, 10 Nov 2010 09:25:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Dan Rosenberg <drosenberg@...curity.com>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	kees.cook@...onical.com, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] Restrict unprivileged access to kernel syslog


* Dan Rosenberg <drosenberg@...curity.com> 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: Ingo Molnar <mingo@...e.hu>

Linus, Andrew, any objections against pushing this trivial control flag upstream out 
of band, after a bit of testing? It's not like it can break anything, and the flag 
is very useful to distros.

Thanks,

	Ingo
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