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Message-Id: <20250918162133.111922-11-chia-yu.chang@nokia-bell-labs.com>
Date: Thu, 18 Sep 2025 18:21:29 +0200
From: chia-yu.chang@...ia-bell-labs.com
To: pabeni@...hat.com,
edumazet@...gle.com,
linux-doc@...r.kernel.org,
corbet@....net,
horms@...nel.org,
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vidhi_goel@...le.com
Cc: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
Subject: [PATCH v2 net-next 10/14] tcp: accecn: unset ECT if receive or send ACE=0 in AccECN negotiaion
From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
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@...ia-bell-labs.com>
---
include/net/tcp_ecn.h | 4 +++-
net/ipv4/tcp_input.c | 2 ++
net/ipv4/tcp_minisocks.c | 33 +++++++++++++++++++++++----------
net/ipv4/tcp_output.c | 8 +++++---
4 files changed, 33 insertions(+), 14 deletions(-)
diff --git a/include/net/tcp_ecn.h b/include/net/tcp_ecn.h
index f01cac9d39c9..2256d2efa5ec 100644
--- a/include/net/tcp_ecn.h
+++ b/include/net/tcp_ecn.h
@@ -642,7 +642,8 @@ 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(struct sock *sk, const struct request_sock *req,
+ struct tcphdr *th)
{
if (req->num_retrans < 1 || req->num_timeout < 1) {
if (tcp_rsk(req)->accecn_ok)
@@ -653,6 +654,7 @@ tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
th->ae = 0;
th->cwr = 0;
th->ece = 0;
+ tcp_accecn_fail_mode_set(tcp_sk(sk), TCP_ACCECN_ACE_FAIL_SEND);
}
}
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index beb23dd34c5a..752251268cbe 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6190,6 +6190,8 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
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 1fade94813c6..ecead2b771fd 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -751,16 +751,29 @@ 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 += reqsk_timeout(req, TCP_RTO_MAX);
- 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) {
+ u8 fail_mode = TCP_ACCECN_ACE_FAIL_RECV;
+
+ tcp_accecn_fail_mode_set(tcp_sk(sk),
+ fail_mode);
+ }
+ }
+ if (!tcp_rtx_synack(sk, req)) {
+ unsigned long expires = jiffies;
+
+ expires += reqsk_timeout(req, TCP_RTO_MAX);
+ 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 d4aae5dc2201..df07b76ba84f 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -334,11 +334,13 @@ static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
return;
ecn_ect_1 = tp->ecn_flags & TCP_ECN_ECT_1;
- if (ecn_ect_1 && !tcp_accecn_ace_fail_recv(tp))
+ if (ecn_ect_1 && !tcp_accecn_ace_fail_recv(tp) &&
+ !tcp_accecn_ace_fail_send(tp))
__INET_ECN_xmit(sk, true);
if (tcp_ecn_mode_accecn(tp)) {
- if (!ecn_ect_1 && !tcp_accecn_ace_fail_recv(tp))
+ if (!ecn_ect_1 && !tcp_accecn_ace_fail_recv(tp) &&
+ !tcp_accecn_ace_fail_send(tp))
INET_ECN_xmit(sk);
tcp_accecn_set_ace(tp, skb, th);
skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ACCECN;
@@ -3990,7 +3992,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
memset(th, 0, sizeof(struct tcphdr));
th->syn = 1;
th->ack = 1;
- tcp_ecn_make_synack(req, th);
+ tcp_ecn_make_synack((struct sock *)sk, req, th);
th->source = htons(ireq->ir_num);
th->dest = ireq->ir_rmt_port;
skb->mark = ireq->ir_mark;
--
2.34.1
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