linux-kernel - Re: [PATCH v3] Restrict unprivileged access to kernel syslog

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Message-ID: <20110102090541.GL32469@atrey.karlin.mff.cuni.cz>
Date:	Sun, 2 Jan 2011 10:05:41 +0100
From:	Pavel Machek <pavel@....cz>
To:	Dan Rosenberg <drosenberg@...curity.com>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	mingo@...e.hu, kees.cook@...onical.com, akpm@...ux-foundation.org,
	security@...nel.org
Subject: Re: [PATCH v3] Restrict unprivileged access to kernel syslog

Hi!

> 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.

Ok, this is very very ugly.

You essentially create a bit to control what other bit does. Clean
solution would be CAP_SYS_DMESG, and make sure that is given to
processes by default...

...and that would be actually very good thing -- on cellphones, you
want some users without ability to connect to network, so you could
introduce CAP_NETWORK etc...

								Pavel
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