Subject: RE: [rddp] comments on draft-black-rdma-concerns-00.txt

From: Caitlin Bestler <[email-masked]>
Date: Thu, 1 Aug 2002 12:10:42 -0500

On 7/31/02, H.K. Jerry Chu wrote:

>>
>>If connection scope is chosen, then an attacker must both
>>"hijack the TCP connection" and guess the correct STag.
>
>What you said is true only if the connection scope is
>enforced by the DDP-capable NICs before data is placed.
>This almost requires TOE in NICs, which is a difficult
>hoop to jump, both technically and economically.
>

As previously discussed, a packet that has been previosly
acked MUST NOT be placed.

Knowing that state requires identifying the connection. With
transports designed for RDMA, such as InfiniBand, this is
exceedingly simple. For an IB reliable connection a
connectino Queue Pair fully identifies the connection.

For IP transports the  connection must be identied by the
header, presumably using the same techniques used by
masquerading and/or virtualizing routers.

Given that the connection must be identified, that means
that the Protection Zone has been identified (PZ is the DAT
Collaborative generic term for the class of protection
mechansims that InfiniBand Protecion Domain's are an
instance of).

Within the scope of a NIC, the STag could be a key value.
The Protection Zone would then be an attribute that is
checked. Or the Protection Zone AND the STag could be key
value, in which case only its existence is checked.

The two approaches are not distinquishable to a compliant
external peer. The STag is valid for the purpose it was
distributed. Whether a different buffer advertisement that
happens to have the same value refers to the same memory is
not relevant to the external peer.

If local interfaces allowed easy cloning of new Protection
Zones for new connections then mimimizing the risk of
inadvertant or deliberate STag abuse is easy. It can be
easily implemented on a per-NIC basis with no impact on the
wire protocol.

I prefer to leave the mapping of STags to local resource
unspecified. But I would argue that anything that is
specified should be compatible with this solution.

Caitlin Bestler
http://www.asomi.com/CaitlinBestler.html

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