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tcp: accecn: unset ECT if receive or send ACE=0 in AccECN negotiaion

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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 <chia-yu.chang@nokia-bell-labs.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260131222515.8485-11-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Chia-Yu Chang 2026-01-31 23:25:10 +01:00 • committed by Paolo Abeni
parent f326f1f17f
commit 4024081feb
5 changed files with 36 additions and 9 deletions
Download patch file Download diff file Expand all files Collapse all files

3
net/ipv4/inet_connection_sock.c
View file

@ -20,6 +20,7 @@
#include <net/tcp_states.h>
#include <net/xfrm.h>
#include <net/tcp.h>
#include <net/tcp_ecn.h>
#include <net/sock_reuseport.h>
#include <net/addrconf.h>
@ -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));

2
net/ipv4/tcp_input.c
View file

@ -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);

32
net/ipv4/tcp_minisocks.c
View file

@ -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_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_rtx_synack(sk, req)) {
unsigned long expires = jiffies;
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;
expires += tcp_reqsk_timeout(req);
if (!fastopen)
mod_timer_pending(&req->rsk_timer, expires);
else
req->rsk_timer.expires = expires;
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;
}

5
net/ipv4/tcp_output.c
View file

@ -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 {

3
net/ipv4/tcp_timer.c
View file

@ -22,6 +22,7 @@
#include <linux/module.h>
#include <linux/gfp.h>
#include <net/tcp.h>
#include <net/tcp_ecn.h>
#include <net/rstreason.h>
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)