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

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Message-ID: <20071218003955.GA27048@sergelap.austin.ibm.com>
Date:	Mon, 17 Dec 2007 18:39:55 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linux Containers <containers@...ts.osdl.org>
Subject: Re: [patch 1/2] [RFC] Simple tamper-proof device filesystem.

Quoting Tetsuo Handa (penguin-kernel@...ove.sakura.ne.jp):
> Hello.
> 
> Serge E. Hallyn wrote:
> > CAP_MKNOD will be removed from its capability
> I think it is not enough because the root can rename/unlink device files
> (mv /dev/sda1 /dev/tmp; mv /dev/sda2 /dev/sda1; mv /dev/tmp /dev/sda2).

Sure but that doesn't bother us :)

The admin in the container has his own /dev directory and can do what he
likes with the devices he's allowed to have.  He just shouldn't have
access to others.  If he wants to rename /dev/sda1 to /dev/sda5 that's
his choice.

> > To use your approach, i guess we would have to use selinux (or tomoyo)
> > to enforce that devices may only be created under /dev?
> Everyone can use this filesystem alone.

Sure but it is worthless alone.

No?

What will keep the container admin from doing 'mknod /root/hda1 b 3 1'?

> But use with MAC (or whatever access control mechanisms that prevent
> attackers from unmounting/overlaying this filesystem) is recomennded.

-serge
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