linux-kernel - Re: [dm-devel] [PATCH 1/1] dm: add message command to disallow device open

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Date:   Tue, 2 Aug 2022 21:23:08 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Daniil Lunev <dlunev@...omium.org>
Cc:     Zdenek Kabelac <zdenek.kabelac@...il.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Mike Snitzer <snitzer@...nel.org>,
        linux-kernel@...r.kernel.org, dm-devel@...hat.com,
        Mikulas Patocka <mpatocka@...hat.com>,
        Alasdair Kergon <agk@...hat.com>
Subject: Re: [dm-devel] [PATCH 1/1] dm: add message command to disallow
 device open

On Wed, Aug 03, 2022 at 02:12:26PM +1000, Daniil Lunev wrote:
> Hello all
> To signal boost here. What can we do to advance the discussion on this
> topic? Can we move forward with the approach or are there any
> alternative suggestions how the desired behaviour can be achieved?
> Thanks,
> --Daniil
> 
> On Tue, Jul 19, 2022 at 9:42 AM Daniil Lunev <dlunev@...omium.org> wrote:
> >
> > We understand that if someone acquires root it is a game over. The intent of
> > this mechanism is to reduce the attack surface. The exposure might be a
> > certain system daemon that is exploited into accessing a wrong node in
> > the filesystem. And exposing modifiable system memory is a pathway for
> > further escalation and leaks of secrets. This is a defense in depth mechanism,
> > that is intended to make attackers' lives harder even if they find an
> > exploitable
> > vulnerability.
> > We understand that in regular situations people may not want the behaviour,
> > that is why the mechanism is controlled via a side channel - if a message is
> > never sent - the behaviour is not altered.
> > --Daniil

This seems like an access control policy, which the Linux kernel already has a
lot of mechanisms for.  Chrome OS already uses SELinux.  Couldn't this be solved
by giving the device node an SELinux label that no one has permission to open?

- Eric