tcp: Fix ACK sequence on FIN to tap

If we reach end-of-file on a socket (or get EPOLLRDHUP / EPOLLHUP) and
send a FIN segment to the guest / container acknowledging a sequence
number that's behind what we received so far, we won't have any
further trigger to send an updated ACK segment, as we are now
switching the epoll socket monitoring to edge-triggered mode.

To avoid this situation, in tcp_update_seqack_wnd(), we set the next
acknowledgement sequence to the current observed sequence, regardless
of what was acknowledged socket-side.

However, we don't necessarily call tcp_update_seqack_wnd() before
sending the FIN segment, which might potentially lead to a situation,
not observed in practice, where we unnecessarily cause a
retransmission at some point after our FIN segment.

Avoid that by setting the ACK sequence to whatever we received from
the container / guest, before sending a FIN segment and switching to
EPOLLET.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

0 files changed, 0 insertions, 0 deletions