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

From: Kees Cook
Date: Wed Nov 10 2010 - 11:32:59 EST


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@xxxxxxxxxxxxx>
> CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> CC: Ingo Molnar <mingo@xxxxxxx>
> CC: Kees Cook <kees.cook@xxxxxxxxxxxxx>
> CC: stable <stable@xxxxxxxxxx>

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

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

--
Kees Cook
Ubuntu Security Team
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/