linux-kernel - Re: [RFC] cgroups: implement device whitelist lsm (v2)

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Message-ID: <6599ad830803140218v3d9ca478ve41516a9ea627eb@mail.gmail.com>
Date:	Fri, 14 Mar 2008 02:18:10 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org, "Greg KH" <greg@...ah.com>,
	"Stephen Smalley" <sds@...ch.ncsc.mil>,
	"Casey Schaufler" <casey@...aufler-ca.com>,
	"Pavel Emelianov" <xemul@...nvz.org>
Subject: Re: [RFC] cgroups: implement device whitelist lsm (v2)

On Wed, Mar 12, 2008 at 8:27 PM, Serge E. Hallyn <serue@...ibm.com> wrote:
> Implement a cgroup using the LSM interface to enforce mknod and open
>  on device files.
>
>  This implements a simple device access whitelist.  A whitelist entry
>  has 4 fields.  'type' is a (all), c (char), or b (block).  'all' means it
>  applies to all types, all major numbers, and all minor numbers.  Major and
>  minor are obvious.  Access is a composition of r (read), w (write), and
>  m (mknod).
>
>  The root devcgroup starts with rwm to 'all'.  A child devcg gets a copy
>  of the parent.  Admins can then add and remove devices to the whitelist.
>  Once CAP_HOST_ADMIN is introduced it will be needed to add entries as
>  well or remove entries from another cgroup, though just CAP_SYS_ADMIN
>  will suffice to remove entries for your own group.
>
>  An entry is added by doing "echo <type> <maj> <min> <access>" > devcg.allow,
>  for instance:
>
>         echo b 7 0 mrw > /cgroups/1/devcg.allow
>
>  An entry is removed by doing likewise into devcg.deny.  Since this is a
>  pure whitelist, not acls, you can only remove entries which exist in the
>  whitelist.  You must explicitly
>
>         echo a 0 0 mrw > /cgroups/1/devcg.deny
>
>  to remove the "allow all" entry which is automatically inherited from
>  the root cgroup.

In keeping with the naming convention for control groups, "devices"
would be better than "devcg".

Paul
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