sys/netinet: handle IPv4 PMTU Discovery
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Authored by wma on Jul 2 2021, 4:37 AM.

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melifaro

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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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rG FreeBSD src repository

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wma created this revision.Jul 2 2021, 4:37 AM

Herald added a subscriber: melifaro. · View Herald TranscriptJul 2 2021, 4:37 AM

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?

wma updated this revision to Diff 92414.Jul 19 2021, 11:16 AM

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