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

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Date:	Wed, 10 Nov 2010 07:26:38 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Dan Rosenberg <drosenberg@...curity.com>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	kees.cook@...onical.com
Subject: Re: [PATCH v2] Restrict unprivileged access to kernel syslog

On Wed, 10 Nov 2010 09:25:16 +0100 Ingo Molnar <mingo@...e.hu> wrote:

> 
> * 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.
> 

OK by me, apart from ...

a) I'd question the need for the config option.  Are distros really
   so lame that they can't trust themselves to poke a number into
   procfs at boot time?

b) we have "dmesg_restrict" and "CONFIG_RESTRICT_DMESG".  Less
   dyslexia, please.
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