diff options
| author | Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com> | 2026-01-31 23:25:09 +0100 |
|---|---|---|
| committer | Paolo Abeni <pabeni@redhat.com> | 2026-02-03 15:13:24 +0100 |
| commit | f326f1f17f3772dae4b37360c639ed6b76fe6354 (patch) | |
| tree | f5630d5f39ee666b78b7e111ab0e6449be1ffaf4 /include | |
| parent | f1eaea5585e4d193e007d671f0916f4371c72c0b (diff) | |
tcp: accecn: retransmit SYN/ACK without AccECN option or non-AccECN SYN/ACK
For Accurate ECN, the first SYN/ACK sent by the TCP server shall set
the ACE flag (Table 1 of RFC9768) and the AccECN option to complete the
capability negotiation. However, if the TCP server needs to retransmit
such a SYN/ACK (for example, because it did not receive an ACK
acknowledging its SYN/ACK, or received a second SYN requesting AccECN
support), the TCP server retransmits the SYN/ACK without the AccECN
option. This is because the SYN/ACK may be lost due to congestion, or a
middlebox may block the AccECN option. Furthermore, if this retransmission
also times out, to expedite connection establishment, the TCP server
should retransmit the SYN/ACK with (AE,CWR,ECE) = (0,0,0) and without the
AccECN option, while maintaining AccECN feedback mode.
This complies with Section 3.2.3.2.2 of the AccECN spec RFC9768.
Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260131222515.8485-10-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/net/tcp_ecn.h | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h index a709fb1756eb..796c613b5ef3 100644 --- a/include/net/tcp_ecn.h +++ b/include/net/tcp_ecn.h @@ -649,12 +649,22 @@ static inline void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb) } static inline void -tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th) +tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th, + enum tcp_synack_type synack_type) { - if (tcp_rsk(req)->accecn_ok) - tcp_accecn_echo_syn_ect(th, tcp_rsk(req)->syn_ect_rcv); - else if (inet_rsk(req)->ecn_ok) - th->ece = 1; + /* Accurate ECN shall retransmit SYN/ACK with ACE=0 if the + * previously retransmitted SYN/ACK also times out. + */ + if (!req->num_timeout || synack_type != TCP_SYNACK_RETRANS) { + if (tcp_rsk(req)->accecn_ok) + tcp_accecn_echo_syn_ect(th, tcp_rsk(req)->syn_ect_rcv); + else if (inet_rsk(req)->ecn_ok) + th->ece = 1; + } else if (tcp_rsk(req)->accecn_ok) { + th->ae = 0; + th->cwr = 0; + th->ece = 0; + } } static inline bool tcp_accecn_option_beacon_check(const struct sock *sk) |