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

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Date:	Wed, 12 Mar 2014 21:17:56 -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 14:19 -0700, Andy Lutomirski wrote:
> On Wed, Mar 12, 2014 at 2:16 PM, Simo Sorce <ssorce@...hat.com> wrote:
> > 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.
> 
> You mean the same proven crappy solution?
> 
> >
> > Connection time is all we do and can care about.
> 
> You have not answered why.

We are going to disclose information to the peer based on policy that
depends on the cgroup the peer is part of. All we care for is who opened
the connection, if the peer wants to pass on that information after it
has obtained it there is nothing we can do, so connection time is all we
really care about.

Simo.

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