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@@ -1184,6 +1184,16 @@ impl<'a> TcpSocket<'a> {
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self.abort();
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return Err(Error::Dropped)
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}
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+ // SYN|ACK in the SYN-SENT state must have the exact ACK number.
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+ (State::SynSent, &TcpRepr {
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+ control: TcpControl::Syn, ack_number: Some(ack_number), ..
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+ }) => {
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+ if ack_number != self.local_seq_no + 1 {
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+ net_debug!("{}:{}:{}: unacceptable SYN|ACK in response to initial SYN",
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+ self.meta.handle, self.local_endpoint, self.remote_endpoint);
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+ return Err(Error::Dropped)
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+ }
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+ }
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// Every acknowledgement must be for transmitted but unacknowledged data.
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(_, &TcpRepr { ack_number: Some(ack_number), .. }) => {
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let unacknowledged = self.tx_buffer.len() + control_len;
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@@ -2738,6 +2748,29 @@ mod test {
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sanity!(s, socket_established());
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}
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+ #[test]
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+ fn test_syn_sent_syn_ack_not_incremented() {
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+ let mut s = socket_syn_sent();
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+ recv!(s, [TcpRepr {
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+ control: TcpControl::Syn,
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+ seq_number: LOCAL_SEQ,
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+ ack_number: None,
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+ max_seg_size: Some(BASE_MSS),
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+ window_scale: Some(0),
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+ sack_permitted: true,
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+ ..RECV_TEMPL
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+ }]);
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+ send!(s, TcpRepr {
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+ control: TcpControl::Syn,
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+ seq_number: REMOTE_SEQ,
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+ ack_number: Some(LOCAL_SEQ), // WRONG
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+ max_seg_size: Some(BASE_MSS - 80),
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+ window_scale: Some(0),
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+ ..SEND_TEMPL
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+ }, Err(Error::Dropped));
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+ assert_eq!(s.state, State::SynSent);
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+ }
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+
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#[test]
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fn test_syn_sent_rst() {
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let mut s = socket_syn_sent();
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