[lwip-devel] [bug #34636] FIN_WAIT_2 - Incorrect shutdown of TCP pcb

[Kieran Mansley]

Follow-up Comment #2, bug #34636 (project lwip):

I agree with Simon.  Simply removing the FIN_WAIT_2 state will just create
more problems than it solves.

The timeout from FIN_WAIT_2 is important to avoid a denial of service attack
from the other end, where it could deliberately fail to send a FIN and keep
the connection open forever.

I'd like to understand better what Linux does in this situation...

I can see it has a similar (but three minute) timeout as a result of close
being called:
http://lxr.linux.no/#linux+v3.1/net/ipv4/tcp.c#L1997

I think the problem in lwIP is that we are starting the timeout while the app
still has a handle on the socket (i.e. after a shutdown) but we should wait
until they have called close.

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