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sys/netinet: handle IPv4 PMTU Discovery
Needs ReviewPublic

Authored by wma on Jul 2 2021, 4:37 AM.

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Reviewers
mw
imp
np
tuexen
Summary

On input ICMP handler is updating tcp_hostcache with the PMTU value.
On output calculate MTU based on the route/interface and hostcache.

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wma requested review of this revision.Jul 2 2021, 4:37 AM

SCTP and TCP do a similar handling, but only after performing some checks (port numbers and vtag in case of SCTP, port numbers and sequence number in case of TCP) to make it non-trivial for an off-path attacker to generate an ICMP message, which will be accepted and the corresponding MTU will be cached.

How is such an check done in this context?

Good point. I removed all *input processing and left only *output check, which might be worth to have it in one place as we don't update mtu here anyway. Also pushed some changes to UDP ctlinput to match https://reviews.freebsd.org/D30992