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net: tcp: When sending FIN, make sure it goes with ACK and proper seq

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Without change to add ACK to FIN, invalid TCP packet is generated,
where ack sequence number is non-zero. Without adjusting sequence
number as done, ACK which we send in response to peer's FIN/ACK is
not recognized by peer, and peer keeps retransmitting its FIN/ACK.

Jira: ZEP-2104

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
This commit is contained in:
Paul Sokolovsky 2017-05-04 17:41:56 +03:00 • committed by Jukka Rissanen
commit d6b93b311f
1 changed files with 13 additions and 1 deletions
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14
subsys/net/ip/tcp.c
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@ -414,7 +414,19 @@ int net_tcp_prepare_segment(struct net_tcp *tcp, u8_t flags,
if (flags & NET_TCP_FIN) {
tcp->flags |= NET_TCP_FINAL_SENT;
seq++;
/* RFC793 says about ACK bit: "Once a connection is
* established this is always sent." as teardown
* happens when connection is established, it must
* have ACK set.
*/
flags |= NET_TCP_ACK;
/* FIXME: We apparently miss increment in another
* transition of the state machine, so have to
* adjust seq no by 2 here. This is required for
* Linux to detect active close on server side, and
* to make Wireshark happy about sequence numbers.
*/
seq += 2;
if (net_tcp_get_state(tcp) == NET_TCP_ESTABLISHED ||
net_tcp_get_state(tcp) == NET_TCP_SYN_RCVD) {