linux-kernel - Re: [patch 1/2] [RFC] Simple tamper-proof device filesystem.

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Date:	Sun, 16 Dec 2007 17:52:08 +0100 (CET)
From:	"Indan Zupancic" <indan@....nu>
To:	"Tetsuo Handa" <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	david@...idnewall.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] [RFC] Simple tamper-proof device filesystem.

Hi,

On Sun, December 16, 2007 13:03, Tetsuo Handa wrote:
> Hello.
>
> David Newall wrote:
>> > You won't be able to login to the system because /sbin/mingetty
>> > fails to "chown/chmod" /dev/tty* if /dev is mounted for read-only mode.
>>
>> Good point.  So, if only root can modify files in /dev, what's the
>> problem you're fixing?  (I'm sure you tried to explain this in your
>> original post, but your reasons weren't clear to me.)
>
> In 2003, I was trying to make / partition read-only to avoid tampering system
> files.
> Use of policy based mandatory access control (such as SELinux) is
> one of ways to avoid tampering, but management of policy was a daunting task.
> So, I tried to store / partition in a read-only medium so that
> the system is free from tampering system files.
>
> When I attended at Security Stadium 2003 as a defense side,
> I was using devfs for /dev directory. The files in /dev directory
> were deleted by attckers and the administrator was unable to login.
> So I developed this filesystem so that attackers who got root privilege
> can't tamper files in /dev directory.

What prevents them from mounting tmpfs on top of /dev, bypassing your fs?

Also, if they have root there are plenty of ways to prevent an administrator
from logging in, e.g. using iptables or changing the password.

Greetings,

Indan


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