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

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Date:	Thu, 13 Mar 2014 11:00:34 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Simo Sorce <ssorce@...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, 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.

Thanks
Vivek
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