linux-kernel - Re: [PATCH 2/2] net: Implement SO

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Message-ID: <1394728389.32465.230.camel@willson.li.ssimo.org>
Date:	Thu, 13 Mar 2014 12:33:09 -0400
From:	Simo Sorce <ssorce@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"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 Thu, 2014-03-13 at 11:00 -0400, Vivek Goyal wrote:
> On Thu, Mar 13, 2014 at 10:55:34AM -0400, Simo Sorce wrote:
> 
> [..]
> > > > 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.
> > > 
> > > That's a good point. What guarantees that previous cgroup was not
> > > reassigned to a different container.
> > > 
> > > What if a process A opens the connection with sssd. Process A passes the
> > > file descriptor to a different process B in a differnt container.
> > 
> > Stop right here.
> > If the process passes the fd it is not my problem anymore.
> > The process can as well just 'proxy' all the information to another
> > process.
> > 
> > We just care to properly identify the 'original' container, we are not
> > in the business of detecting malicious behavior. That's something other
> > mechanism need to protect against (SELinux or other LSMs, normal
> > permissions, capabilities, etc...).
> > 
> > > Process A exits. Container gets removed from system and new one gets
> > > launched which uses same cgroup as old one. Now process B sends a new
> > > request and SSSD will serve it based on policy of newly launched
> > > container.
> > > 
> > > This sounds very similar to pid race where socket/connection will outlive
> > > the pid.
> > 
> > Nope, completely different.
> > 
> 
> I think you missed my point. Passing file descriptor is not the problem.
> Problem is reuse of same cgroup name for a different container while
> socket lives on. And it is same race as reuse of a pid for a different
> process.

The cgroup name should not be reused of course, if userspace does that,
it is userspace's issue. cgroup names are not a constrained namespace
like pids which force the kernel to reuse them for processes of a
different nature.

Simo.

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