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[2001:470:26:54b:226:9eff:fe70:80c2]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7b9ee9b5254sm69514347b3.41.2026.04.22.09.44.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Apr 2026 09:44:31 -0700 (PDT) Received: from home.paul.comp (home.paul.comp [IPv6:0:0:0:0:0:0:0:1]) by home.paul.comp (8.15.2/8.15.2/Debian-22+deb11u3) with ESMTP id 63MGiRaZ018350; Wed, 22 Apr 2026 19:44:28 +0300 Received: (from paul@localhost) by home.paul.comp (8.15.2/8.15.2/Submit) id 63MGiPLn018349; Wed, 22 Apr 2026 19:44:25 +0300 Date: Wed, 22 Apr 2026 19:44:25 +0300 From: Paul Fertser To: Michael Bommarito Cc: Samuel Mendoza-Jonas , netdev@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , linux-kernel@vger.kernel.org Subject: Re: [PATCH net 0/6] net/ncsi: harden packet parsing against malformed BMC replies Message-ID: References: <20260422160342.1975093-1-michael.bommarito@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260422160342.1975093-1-michael.bommarito@gmail.com> 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.