Subject: Re: [PATCH] netfilter: TCPMSS: fix dropped packets when MSS option is unaligned

From: Florian Westphal <[email-masked]>
Date: Mon, 25 May 2026 23:28:25 +0200

Kacper Kokot <[email-masked]> wrote:
> Padding TCP options with NOPs is optional, so it is legal to send an
> MSS option that is not aligned to a word boundary and therefore not
> aligned for checksum calculation. The current TCPMSS target is not
> robust to this: when the MSS option is unaligned it produces an
> invalid checksum, and the packet is dropped.

Is this an actual, real world bug?  This code is 20+ years old, all that
this hints at is that they are always aligned in reality?

(Not disputing theoretical problem).