On 3/31/2009 7:47 AM, Paul Moore wrote:

On Monday 30 March 2009 11:07:02 pm Casey Schaufler wrote:

Jarrett Lu wrote:

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.

Not to throw a puppy in the gears, but sophisticated handshaking and negotiation protocols are not the answer. We had TSIG session management for doing that and it is just not enough. How would you negotiate the differences between two SELinux policies?

I'm with Casey, I don't think it is worth spending a whole lot of time right now finding out how to pass information across the network in a secure manner. There are plenty of ways of to do that which are well established, interoperable and generally regarded as "secure".

I'm not reinventing another secure way to pass information. I thought kerberos gss api may be a good candidate. I also agree that sophisticated handshaking negotiation protocol or complicated security attribute mapping between various systems is not the way to go.

From my point of view the real issue is how do we translate/resolve security labels defined by DOI X to an internal, security model/policy specific label? Some have mentioned a mechanism which would serve up label encoding data whenever a new system joined the network; unfortunately, I believe this only works when you know the security policy of the system before hand (or can restrict the security policy, after all a TSOL label encodings file will do nothing for SELinux and/or Smack). While I think it is reasonable to assume a limited number of on-the-wire label encodings and DOIs I think it would be a mistake to assume a limited number of security models and or policies.

True. The first question is whether we should try to solve, or at least ease, the label interpretation / translation problem in the context of NFSv4 protocol. I don't know if we can solve it, but it seems worthwhile to explore further, to gain more understanding if nothing else. The challenge of interpreting and translating labels is that one system needs to know a lot of info about its peer. And there is no good way to describe the (sometimes subtle) difference. I think this problem may be harder on DTE systems than on MLS systems, I believe.

Ultimately I believe that the required label translation information (wire/DOI label to internal and the other way around) is going to need to be bundled with the system's security policy and distributed as a single "package". Granted this does require prior knowledge of the DOIs in use but I believe this is a much easier requirement than the opposite. From a practical point of view this isn't too far removed from the notion of sending sending label encoding data upon joining the network, the big difference is that we are sending both security policy and label encoding/DOI-translation data at the same time (in the TSOL case I suspect this would just be the label encoding data, which may mean the original poster had this in mind).

Depending how different the systems are, the "package" content will be different. Assuming we can assemble all the information required to do label translation correctly into a package, passing that around the systems seem inefficient, non-scalable, and probably outside the scope of labeled NFSv4 enhancement. So realistically, I think the DOI + opaque label is useful between very compatible systems. Given that limitation, may be the "package" is small enough and can be passed in RPC layer during authentication so that MLS can share files with like MLS systems, and same is true for DTE, fmac, smack, ....


Jarrett

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On 3/31/2009 11:58 PM, James Morris wrote:

On Tue, 31 Mar 2009, Jarrett Lu wrote:

I'm in general agreement with you on this. I am not sure to what extent the extensibility stuff makes sense, e.g. how much may be enough? I guess we need to study more use scenarios. I suspect TE systems may have more challenges in this area, just because security policies on TE systems tend to be more flexible. For example, how many things are critical in order to translate label correctly, OS version, vendor, label parser, security policy file? How likely DTE systems are configured with exact same policy files? Does it make sense that a (harmless) update to security policy file causes label translation failures from that point on?

With SELinux systems, policies do not need to be identical to be considered part of the same DOI. Generally, labels need to remain semantically equivalent (i.e. mean the same thing on each system), and the policies need to be managed within the same administrative boundary. Systems may restrict which labels they'll interpret from remote systems (similar to root_squash).

Understood. My point is that a signature on a policy file may not always be the right tool to determine whether label translation should be done. When policies are different on two systems, how does one system know labels or types are semantically equivalent or not? Are you also saying that DOI is tied to administrative boundary, and the fact that systems using the same DOI implies the label and type definitions in each policy are always semantically equivalent?


Jarrett

- James

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