Packet Size Mismatches

[Patrick Venture]

Per the maximum response size patch
(https://gerrit.openbmc-project.xyz/15743), the goal is to know how
many bytes can be returned by the channel.  This can vary by channel,
per the comments, and other related changes.  However, presently,
we're seeing a memory corruption over kcs which has a limit of 256.
So, we're copying way too much data onto the response.  The code
itself has no idea how many bytes it can send.

https://github.com/openbmc/phosphor-host-ipmid/blob/master/ipmid.cpp#L409
is a 64-byte buffer, but the ipmi message could ask for data beyond
that, and leads to a blind memcpy situation.

If I'm reading that patchset (not yet merged) correctly
(https://gerrit.openbmc-project.xyz/16285) it lets the IPMI client
request channel information to know the maximum it can request.
However, what lets the code running ask that question?  How does my
library know it's responding to a legal request?  Or is the idea that
with the reworking that's underway it'll only be able to provide legal
responses automatically for the channel on which the request came?

(Also, unrelated, but at some point is the goal still to have one
daemon handle all ipmi traffic, including network ipmi traffic, via a
bridge similar to kcsbridge and btbridge?)

Patrick