Re: [PATCH net 0/6] net/ncsi: harden packet parsing against malformed BMC replies

Paul Fertser
2026-04-22T16:44:32Z

Hello Michael,

On Wed, Apr 22, 2026 at 12:03:36PM -0400, Michael Bommarito wrote:
> NC-SI treats the management controller as privileged, but the Linux
...
> The threat model here is a compromised BMC or management-channel MITM
> on the NC-SI link.

The subject of the cover letter and the quoted fragment suggest that
you have a wrong impression of where NC-SI links exist and what they
carry, let me try to clarify.

On motherboards with BMC (the management controller) there often is a
way for the BMC (dedicated SoC these days) to talk to the
host-controlled NIC via NC-SI which is basically RMII (normally used
to talk to Ethernet PHY but here it's used to talk to a whole big NIC)
on hardware level plus special kind of frames sent in-band for
(partial) control and monitoring of the NIC. And regular frames are
transmitted over the same set of signals, there's no dedicated channel
for any kind of management inside NC-SI.

The code your patches modify always runs only on the BMC itself, the
packets parsed are generated by a NIC directly.

So if anything, the threat model here is compromised NIC
firmware. MITMing sounds unlikely as that would require tricky
hardware modifications and if you can do that it's easier to put a
modified NIC instead.

The idea to not trust anything coming from a NIC too much is good in
general but please take the correct context into account when
reasoning about the patches.