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

[Kees Cook <kees.cook@canonical.com>]

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@vsecurity.com>
> CC: Linus Torvalds <torvalds@linux-foundation.org>
> CC: Ingo Molnar <mingo@elte.hu>
> CC: Kees Cook <kees.cook@canonical.com>
> CC: stable <stable@kernel.org>

Acked-by: Kees Cook <kees.cook@canonical.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