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tcp: Reply with RST to ACKs with invalid ackno in SYN_SENT. 

Should fix aramperes/onetun#17
master
Dario Nieuwenhuis 2021-10-19 03:35:57 +02:00
parent 7a89d23cf3
commit 3baa13372c
1 changed files with 114 additions and 2 deletions
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116
src/socket/tcp.rs
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@ -1354,6 +1354,30 @@ impl<'a> TcpSocket<'a> {
return Ok(Some(Self::rst_reply(ip_repr, repr)));
}
}
// ACKs in the SYN-SENT state are invalid.
(State::SynSent, TcpControl::None, Some(ack_number)) => {
// If the sequence number matches, ignore it instead of RSTing.
// I'm not sure why, I think it may be a workaround for broken TCP
// servers, or a defense against reordering. Either way, if Linux
// does it, we do too.
if ack_number == self.local_seq_no + 1 {
net_debug!(
"{}:{}:{}: expecting a SYN|ACK, received an ACK with the right ack_number, ignoring.",
self.meta.handle,
self.local_endpoint,
self.remote_endpoint
);
return Err(Error::Dropped);
}
net_debug!(
"{}:{}:{}: expecting a SYN|ACK, received an ACK with the wrong ack_number, sending RST.",
self.meta.handle,
self.local_endpoint,
self.remote_endpoint
);
return Ok(Some(Self::rst_reply(ip_repr, repr)));
}
// Anything else in the SYN-SENT state is invalid.
(State::SynSent, _, _) => {
net_debug!(
@ -3475,15 +3499,103 @@ mod test {
#[test]
fn test_syn_sent_bad_ack() {
let mut s = socket_syn_sent();
recv!(
s,
[TcpRepr {
control: TcpControl::Syn,
seq_number: LOCAL_SEQ,
ack_number: None,
max_seg_size: Some(BASE_MSS),
window_scale: Some(0),
sack_permitted: true,
..RECV_TEMPL
}]
);
send!(
s,
TcpRepr {
control: TcpControl::None,
ack_number: Some(TcpSeqNumber(1)),
control: TcpControl::None, // Unexpected
seq_number: REMOTE_SEQ,
ack_number: Some(LOCAL_SEQ + 1), // Correct
..SEND_TEMPL
},
Err(Error::Dropped)
);
// It should trigger no response and change no state
recv!(s, []);
assert_eq!(s.state, State::SynSent);
}
#[test]
fn test_syn_sent_bad_ack_seq_1() {
let mut s = socket_syn_sent();
recv!(
s,
[TcpRepr {
control: TcpControl::Syn,
seq_number: LOCAL_SEQ,
ack_number: None,
max_seg_size: Some(BASE_MSS),
window_scale: Some(0),
sack_permitted: true,
..RECV_TEMPL
}]
);
send!(
s,
TcpRepr {
control: TcpControl::None,
seq_number: REMOTE_SEQ,
ack_number: Some(LOCAL_SEQ), // WRONG
..SEND_TEMPL
},
Ok(Some(TcpRepr {
control: TcpControl::Rst,
seq_number: LOCAL_SEQ, // matching the ack_number of the unexpected ack
ack_number: None,
window_len: 0,
..RECV_TEMPL
}))
);
// It should trigger a RST, and change no state
assert_eq!(s.state, State::SynSent);
}
#[test]
fn test_syn_sent_bad_ack_seq_2() {
let mut s = socket_syn_sent();
recv!(
s,
[TcpRepr {
control: TcpControl::Syn,
seq_number: LOCAL_SEQ,
ack_number: None,
max_seg_size: Some(BASE_MSS),
window_scale: Some(0),
sack_permitted: true,
..RECV_TEMPL
}]
);
send!(
s,
TcpRepr {
control: TcpControl::None,
seq_number: REMOTE_SEQ,
ack_number: Some(LOCAL_SEQ + 123456), // WRONG
..SEND_TEMPL
},
Ok(Some(TcpRepr {
control: TcpControl::Rst,
seq_number: LOCAL_SEQ + 123456, // matching the ack_number of the unexpected ack
ack_number: None,
window_len: 0,
..RECV_TEMPL
}))
);
// It should trigger a RST, and change no state
assert_eq!(s.state, State::SynSent);
}