netdev - Re: [PATCH 2/2] net: Implement SO

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Date:	Wed, 12 Mar 2014 17:16:22 -0400
From:	Simo Sorce <ssorce@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	cgroups@...r.kernel.org,
	Network Development <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>, Tejun Heo <tj@...nel.org>,
	jkaluza@...hat.com, lpoetter@...hat.com, kay@...hat.com
Subject: Re: [PATCH 2/2] net: Implement SO_PEERCGROUP

On Wed, 2014-03-12 at 14:12 -0700, Andy Lutomirski wrote:
> On Wed, Mar 12, 2014 at 2:00 PM, Andy Lutomirski <luto@...capital.net> wrote:
> > On 03/12/2014 01:46 PM, Vivek Goyal wrote:
> >> Implement SO_PEERCGROUP along the lines of SO_PEERCRED. This returns the
> >> cgroup of first mounted hierarchy of the task. For the case of client,
> >> it represents the cgroup of client at the time of opening the connection.
> >> After that client cgroup might change.
> >
> > Even if people decide that sending cgroups over a unix socket is a good
> > idea, this API has my NAK in the strongest possible sense, for whatever
> > my NAK is worth.
> >
> > IMO SO_PEERCRED is a disaster.  Calling send(2) or write(2) should
> > *never* imply the use of a credential.  A program should always have to
> > *explicitly* request use of a credential.  What you want is SCM_CGROUP.
> >
> > (I've found privilege escalations before based on this observation, and
> > I suspect I'll find them again.)
> >
> >
> > Note that I think that you really want SCM_SOMETHING_ELSE and not
> > SCM_CGROUP, but I don't know what the use case is yet.
> 
> This might not be quite as awful as I thought.  At least you're
> looking up the cgroup at connection time instead of at send time.
> 
> OTOH, this is still racy -- the socket could easily outlive the cgroup
> that created it.

I think you do not understand how this whole problem space works.

The problem is exactly the same as with SO_PEERCRED, so we are taking
the same proven solution.

Connection time is all we do and can care about.

Simo.


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