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tcp: When we have an out-of-order FIN we do want to strip off the FIN bit.
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Authored by rrs on May 27 2021, 12:12 PM.

Details

Summary

The last set of commits fixed both a panic (in rack) and an ACK-war (in freebsd and bbr).
However there was a missing case, i.e. where we get an out-of-order FIN by itself.
In such a case we don't want to leave the FIN bit set, otherwise we will do the
wrong thing and ack the FIN incorrectly. Instead we need to go through the
tcp_reasm() code and that way the FIN will be stripped and all will be well.

Test Plan

We can use the tcp-test-suite with reorder_5F4321.pkt to test this case.

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