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

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Message-ID: <20080314140031.GF8744@sergelap.austin.ibm.com>
Date:	Fri, 14 Mar 2008 09:00:31 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	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)

Quoting Paul Menage (menage@...gle.com):
> 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".

Noted, thanks.

-serge
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