From 4024081feb87fb11ac7bd36d8c397ccdd81ed302 Mon Sep 17 00:00:00 2001 From: Chia-Yu Chang Date: Sat, 31 Jan 2026 23:25:10 +0100 Subject: [PATCH] tcp: accecn: unset ECT if receive or send ACE=0 in AccECN negotiaion Based on specification: https://tools.ietf.org/id/draft-ietf-tcpm-accurate-ecn-28.txt Based on Section 3.1.5 of AccECN spec (RFC9768), a TCP Server in AccECN mode MUST NOT set ECT on any packet for the rest of the connection, if it has received or sent at least one valid SYN or Acceptable SYN/ACK with (AE,CWR,ECE) = (0,0,0) during the handshake. In addition, a host in AccECN mode that is feeding back the IP-ECN field on a SYN or SYN/ACK MUST feed back the IP-ECN field on the latest valid SYN or acceptable SYN/ACK to arrive. Signed-off-by: Chia-Yu Chang Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260131222515.8485-11-chia-yu.chang@nokia-bell-labs.com Signed-off-by: Paolo Abeni --- net/ipv4/inet_connection_sock.c | 3 +++ net/ipv4/tcp_input.c | 2 ++ net/ipv4/tcp_minisocks.c | 36 ++++++++++++++++++++++++--------- net/ipv4/tcp_output.c | 5 ++++- net/ipv4/tcp_timer.c | 3 +++ 5 files changed, 38 insertions(+), 11 deletions(-) diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c index 13372d2cbed53..018e8ffc07176 100644 --- a/net/ipv4/inet_connection_sock.c +++ b/net/ipv4/inet_connection_sock.c @@ -20,6 +20,7 @@ #include #include #include +#include #include #include @@ -1103,6 +1104,8 @@ static void reqsk_timer_handler(struct timer_list *t) (!resend || !tcp_rtx_synack(sk_listener, req) || inet_rsk(req)->acked)) { + if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok) + tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND; if (req->num_timeout++ == 0) atomic_dec(&queue->young); mod_timer(&req->rsk_timer, jiffies + tcp_reqsk_timeout(req)); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 59dafcb45c168..988d161e9918c 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -6469,6 +6469,8 @@ step1: if (th->syn) { if (tcp_ecn_mode_accecn(tp)) { accecn_reflector = true; + tp->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & + INET_ECN_MASK; if (tp->rx_opt.accecn && tp->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) { u8 saw_opt = tcp_accecn_option_init(skb, tp->rx_opt.accecn); diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 9776c921d1bb4..ec128865f5c02 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -481,6 +481,10 @@ static void tcp_ecn_openreq_child(struct sock *sk, tp->syn_ect_snt = treq->syn_ect_snt; tcp_accecn_third_ack(sk, skb, treq->syn_ect_snt); tp->saw_accecn_opt = treq->saw_accecn_opt; + if (treq->accecn_fail_mode & TCP_ACCECN_ACE_FAIL_SEND) + tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_SEND); + if (treq->accecn_fail_mode & TCP_ACCECN_ACE_FAIL_RECV) + tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_RECV); tp->prev_ecnfield = treq->syn_ect_rcv; tp->accecn_opt_demand = 1; tcp_ecn_received_counters_payload(sk, skb); @@ -749,16 +753,28 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, */ if (!tcp_oow_rate_limited(sock_net(sk), skb, LINUX_MIB_TCPACKSKIPPEDSYNRECV, - &tcp_rsk(req)->last_oow_ack_time) && - - !tcp_rtx_synack(sk, req)) { - unsigned long expires = jiffies; - - expires += tcp_reqsk_timeout(req); - if (!fastopen) - mod_timer_pending(&req->rsk_timer, expires); - else - req->rsk_timer.expires = expires; + &tcp_rsk(req)->last_oow_ack_time)) { + if (tcp_rsk(req)->accecn_ok) { + u8 ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & + INET_ECN_MASK; + + tcp_rsk(req)->syn_ect_rcv = ect_rcv; + if (tcp_accecn_ace(tcp_hdr(skb)) == 0x0) + tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_RECV; + } + if (!tcp_rtx_synack(sk, req)) { + unsigned long expires = jiffies; + + if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok) + tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND; + + expires += tcp_reqsk_timeout(req); + if (!fastopen) + mod_timer_pending(&req->rsk_timer, + expires); + else + req->rsk_timer.expires = expires; + } } return NULL; } diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 22728daed436a..2b356fdbf2ca3 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -334,8 +334,11 @@ static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb, return; if (tcp_ecn_mode_accecn(tp)) { - if (!tcp_accecn_ace_fail_recv(tp)) + if (!tcp_accecn_ace_fail_recv(tp) && + !tcp_accecn_ace_fail_send(tp)) INET_ECN_xmit(sk); + else + INET_ECN_dontxmit(sk); tcp_accecn_set_ace(tp, skb, th); skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ACCECN; } else { diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 160080c9021d0..5a14a53a3c9ef 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -22,6 +22,7 @@ #include #include #include +#include #include static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk) @@ -479,6 +480,8 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req) * it's not good to give up too easily. */ tcp_rtx_synack(sk, req); + if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok) + tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND; req->num_timeout++; tcp_update_rto_stats(sk); if (!tp->retrans_stamp) -- 2.47.3