Re: [nfsv4] [Labeled-nfs] New MAC label support Internet Draft posted to IETF website

[Stephen Smalley <sds@tycho.nsa.gov>]

On Mon, 2009-03-30 at 11:30 -0700, Jarrett Lu wrote:
> On 03/30/09 10:37, Stephen Smalley wrote: 
> > On Fri, 2009-03-27 at 11:56 -0700, Jarrett Lu wrote:
> >   
> > > Nicolas Williams wrote:
> > >     
> > > > On Fri, Mar 27, 2009 at 10:03:35AM -0700, Jarrett Lu wrote:
> > > >   
> > > >       
> > > > > I agree with your statements on TE vs. MLS/BLP. The problem we try to 
> > > > > solve is whether a DOI field + an opaque string is sufficient to solve 
> > > > > the interoperability problem. My opinion is that it's insufficient as it 
> > > > > doesn't take the "how to interpret MAC attribute agreement among all 
> > > > > communicating peers" into account. The current proposal seems to assume 
> > > > > when a node sees a DOI value of 5, it knows how to interpret the opaque 
> > > > > field. This may not be true. In MLS, one also needs to know which agreed 
> > > > > upon label encoding file to use in order to interpret label in the 
> > > > > opaque filed. I believe the same is true for TE -- one needs to know the 
> > > > > security policy being used in order to correctly interpret security 
> > > > > context string in the opaque field. DOI + opaque field doesn't say which 
> > > > > label encoding scheme or which security policy.
> > > > >     
> > > > >         
> > > > What would you add or remove on the wire to solve this problem?  My
> > > > guess: a registry of per-DOI rules, like CALIPSO does.  I don't think a
> > > > registry of DOI rules is strictly necessary for NFS (though I can see
> > > > how it helps in the case of IP), but I certainly don't object.
> > > >   
> > > >       
> > > I don't yet see a good way to solve this problem using bits on the wire. 
> > > The agreement on what label encodings or security policy to use seems 
> > > better solved in an out of band manner. For example, on a (secure) 
> > > website, you can say "download this label encoding file or configure 
> > > your MAC system with this policy and use DOI number 5. Then we can talk".
> > > 
> > > BTW, CALIPSO with IP module has the same issue. While the spec talks a 
> > > lot about how a CALIPSO  system should behave, CALIPSO can't tell its 
> > > peers to use a particular label encoding. That's done outside CALIPSO.
> > > 
> > > I believe it's still worthwhile to request adding a DOI + an opaque 
> > > field in NFSv4 protocol. The spec should be clear that other 
> > > arrangements need to be made before interoperability can take place.
> > > 
> > > Once we decouple DOI from how the opaque field should be interpreted, 
> > > it's possible for NFSv4 to use CALIPSO DOI. For example, DOD can reserve 
> > > DOI 1000 through 1005. It can then decide that 1000 is only used by MLS 
> > > systems with a particular label encoding; and 1004 is for TE systems 
> > > configured with a particular secular security policy. As long as all 
> > > systems using these DOIs agreeing to that, they can communicate with 
> > > each other. But the agreement happens outside NFSv4 protocol itself. I 
> > > understand this is different from the public internet where all you need 
> > > is an IP address to communicate. But this is how MAC systems are used, I 
> > > believe.
> > >     
> > 
> > I'm not sure if this conflicts with what you are saying, but the DOI
> > should merely identify the (externally) agreed-upon network label space
> > for the data to be shared between the communicating systems.  That label
> > space shouldn't need to be identical to the native/host label spaces of
> > any of the individual systems; they just need to have a way of mapping
> > between their host label spaces and the network label space identified
> > by the DOI in a manner that preserves their security goals.  The two
> > systems shouldn't necessarily have to share a label encodings file or
> > security policy configuration in order to communicate using a given DOI.
> > 
> >   
> 
> As Casey and others pointed out, a lot more information about a
> communicating peer is needed in order to be able to translate a label
> and other security attributes.

Yes, but the DOI is all that NFSv4 needs to convey in order to identify
that (external) information (i.e. the DOI is the key/identifier by which
the receiving system looks up the right set of translation/mapping
functions for dealing with the network label space associated with the
DOI, where the translation/mapping functions are configured via
information established OOB to NFSv4 itself).  Defining precisely how
that external information gets populated is IMHO out of scope for
NFSv4. 

>  People have tried this in 90's. Apparently the solution is no longer
> in use today. Maybe we can do something better 15 years later. The
> first step is to figure out how much information is needed and then
> look into how to get this info across securely. GSS_SEC may be able to
> help us. To make NFSv4 work, only TCP is needed. So peer information
> is needed per session vs. per packet, I believe. Evidently, there is
> more work to do in figuring this all out.
> 
> A process related question: Should we move the "design" related
> discussion to a smaller alias? I assume most people don't care about
> the details and prefer not see this in their email inbox. I set up a
> mail alias, doi-discuss@opensolaris.org, a few months ago for a
> similar discussion. If people think that's a good way to go, I can
> provide more info.

Seems like it just becomes one more list that people have to follow to
get the whole picture for labeled NFS.

-- 
Stephen Smalley
National Security Agency


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