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riccardom
13451079c3
The data-path socket identified a sender only by its source IP and port and trusted that anything reaching the overlay address came through the tunnel. On a host-bound socket that does not hold: Linux delivers a datagram to a local overlay IP from a physical interface too (rp_filter is loose, the firewall's input rules match the tunnel interface), so a LAN-adjacent host spoofing a peer's overlay source could inject a KEM offer. A forged bootstrap offer was adopted outright, desynchronising the two PSKs until a re-bootstrap, and repeating it sustains the outage (security review of #7098, finding F-003). No traffic is disclosed, but the exchange must not accept unauthenticated input. Seal every data-path message with an HMAC keyed from the PSK the two peers share; only a peer that holds it can rotate. A reply is sealed under the key that verified the request, because the responder has already committed the new PSK when it answers. The previous PSK stays valid for verification so an offer retransmitted after that commit is still answered. Bootstraps are refused on the data path entirely: they start without a shared PSK and only signalling can carry them. A rotation between peers whose configured secrets differ is now refused at authentication, so the configured-secret test checks that instead.