I totally agree with Mike. If you've never dealt with a multi-level
security (MLS) system, let's just say they are non-trivial, and this
issue with TCP ports is only one part of the overall system. Just the
act of labeling the IP packets effectively creates multiple virtual
networks, and the place where they clash is in the MLS host. As Mike
said, those that aren't MLS aware don't have to do anything
different. But explicitly calling this out for MLS hosts, as this
draft does, seems to me to be perfectly reasonable.
-David Borman
On Oct 2, 2008, at 1:57 PM, Michael StJohns wrote:
Hi Joe -
A quick disclaimer - although I was complicit in allowing this draft
to be resurrected from 1992, I have had very little to do with it on
this cycle.
At 02:18 PM 10/2/2008, Joe Touch wrote:
First, I don't agree with this document's recommendation in section
7.3.1.
TCP's current definition of a connection is:
local IP address
remote IP address
local port
remote port
protocol (e.g., TCP)
I don't agree that treating each sensitivity level as a separate
virtual
network (Sec 3 of this ID) is the appropriate analogy. If that were
the
case, we'd need to redefine every Internet protocol to understand the
pair [address, sensitivity level] as an identifier, and that is not
realistic. Further, if we did need to do such an extension, there are
other equally (or arguably more) worthy candidates, notably VPN-ID.
The issue isn't so much the network, but how the host views it and
deals with resources that might otherwise be in multiple sensitivity
domains.
Consider a multi-level host that runs at both SECRET and TOP
SECRET. Consider that it wants to run some protocol to send and
receive data from other hosts, some multi level, some single level
SECRET and some single level TOP SECRET.
A single level process at TOP SECRET does a passive open of the port
(call it 666) and waits for connections.
A second single level process at SECRET also attempts to do a
passive open to the same port - but gets blocked because the port
resource is being held by the TOP SECRET process. The SECRET
process now has one bit of information about the TOP SECRET part of
the host. By grabbing and releasing port resources, the TS process
can signal data to processes at lower security levels.
In 1987 I used a rough analog of the old 1822 protocol using TCP
ports to build a fairly fast covert channel between two processes at
different security levels on the same host.
The fix was to virtualize TCP so that there was a complete set of
TCP ports per distinct security domain.
You could try doing this by writing the processes as multi-level,
but that means you can't use off the shelf code for things like a
mail server that only wants to handle mail of a specific security
level.
Mostly, this only applies to protocols just above IP which have
distinguishable host resources. In other words, TCP, UDP and their
ilk.
I.e., I don't think this needs to update 793 - it needs to redefine
the
Internet architecture in places like 1122, 1123, and 1812, and flow
down
through all protocols they impact to make this sort of change, and I
don't see a reason to do so solely for this issue.
Overall, I see no reason why 793's current rules aren't sufficient to
emulate the desirable separation of sensitivity levels without
extending
this to true virtualization. I.e., the current rule (in 793, sec 3.6,
paraphrased):
- match the levels proposed by both ends of the connection
where there is a mismatch, terminate the connection
I.e., I don't see how to extend TCP to support concurrent connections
with matching connection identifiers on different sensitivity levels
without rearchitecting the entire Internet. AFAICT, it's sufficient
to
allow each TCP connection to have exactly one sensitivity level, as
is
already currently required.
Not quite the point. If you have a single level process reserving a
TCP port, then the port has sensitivity level of the process. If
you have a multi-level process reserving a port then the port can
have one, some or all of the sensitivity levels of the process.
Each instantiation of a connection does have one and only one
sensitivity level.
The changes don't have to happen on the entire internet, just those
hosts and routers that are CIPSO aware AND multi-level. If the host
is CIPSO aware (or for that matter IPSO aware), but not multi-level,
it's just looking for the specific label and doesn't have to deal
with the multiple virtual network cruft.
Joe
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