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

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Date:	Sun, 02 Jan 2011 11:08:55 -0500
From:	Dan Rosenberg <drosenberg@...curity.com>
To:	Pavel Machek <pavel@....cz>
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

On Sun, 2011-01-02 at 10:05 +0100, Pavel Machek wrote:
> 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

The CONFIG was added on suggestion that it would make it easier for
distributions to enable this behavior by default.  The patch was
modified to use CAP_SYSLOG, which seems in line with what you want.  

Thanks,
Dan

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