mirror of
https://github.com/jmcorgan/fips.git
synced 2026-08-09 08:14:42 +00:00
Johnathan Corgan
7fc890b7a2
The TUN-side TCP MSS clamp consults `path_mtu_lookup` (FipsAddress- keyed) when sizing outbound TCP flows. Until now, only the reactive `MtuExceeded` handler mirrored the bottleneck MTU into that store; the proactive end-to-end `PathMtuNotification` echoed by the destination updated only `MmpSessionState.path_mtu`, leaving the TUN mirror stale. On stable long-lived paths, the proactive echo can tighten the session-canonical MTU well before any transit router fires a `MtuExceeded` for those flows (since all current traffic is already sized by the tighter session value). New TCP flows opened during that window get clamped by the discovery-time value rather than the session-canonical one, leading to PMTU-D loss until the reactive path eventually fires. Mirror the post-apply MTU into `path_mtu_lookup` whenever `apply_notification` returns true, with the same tighter-only semantics as the reactive mirror — never loosen the clamp. Gated on the bool return so spurious writes don't happen on rejected increases or no-op same-value notifications. Four new unit tests exercise the empty-lookup write, tighten- existing, keep-tighter-existing, and no-session-no-op paths, parallel to the existing reactive-mirror test trio.