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tcp: accecn: AccECN option failure handling 

AccECN option may fail in various way, handle these:
- Attempt to negotiate the use of AccECN on the 1st retransmitted SYN
	- From the 2nd retransmitted SYN, stop AccECN negotiation
- Remove option from SYN/ACK rexmits to handle blackholes
- If no option arrives in SYN/ACK, assume Option is not usable
        - If an option arrives later, re-enabled
- If option is zeroed, disable AccECN option processing

This patch use existing padding bits in tcp_request_sock and
holes in tcp_sock without increasing the size.

Signed-off-by: Ilpo Järvinen <ij@kernel.org>
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/20250916082434.100722-9-chia-yu.chang@nokia-bell-labs.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Chia-Yu Chang 2025-09-16 10:24:32 +02:00 committed by Paolo Abeni
parent aa55a7dde7
commit b40671b5ee
7 changed files with 111 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/linux/tcp.h
View File

@ -173,6 +173,7 @@ struct tcp_request_sock {
u8 syn_ect_snt: 2,
syn_ect_rcv: 2,
accecn_fail_mode:4;
u8 saw_accecn_opt :2;
#ifdef CONFIG_TCP_AO
u8 ao_keyid;
u8 ao_rcv_next;
@ -407,7 +408,8 @@ struct tcp_sock {
syn_fastopen_child:1; /* created TFO passive child socket */
u8 keepalive_probes; /* num of allowed keep alive probes */
u8 accecn_fail_mode:4; /* AccECN failure handling */
u8 accecn_fail_mode:4, /* AccECN failure handling */
saw_accecn_opt:2; /* An AccECN option was seen */
u32 tcp_tx_delay; /* delay (in usec) added to TX packets */
/* RTT measurement */

49
include/net/tcp_ecn.h
View File

@ -91,6 +91,11 @@ static inline void tcp_accecn_fail_mode_set(struct tcp_sock *tp, u8 mode)
tp->accecn_fail_mode |= mode;
}
#define TCP_ACCECN_OPT_NOT_SEEN 0x0
#define TCP_ACCECN_OPT_EMPTY_SEEN 0x1
#define TCP_ACCECN_OPT_COUNTER_SEEN 0x2
#define TCP_ACCECN_OPT_FAIL_SEEN 0x3
static inline u8 tcp_accecn_ace(const struct tcphdr *th)
{
return (th->ae << 2) | (th->cwr << 1) | th->ece;
@ -146,6 +151,14 @@ static inline bool tcp_accecn_validate_syn_feedback(struct sock *sk, u8 ace,
return true;
}
static inline void tcp_accecn_saw_opt_fail_recv(struct tcp_sock *tp,
u8 saw_opt)
{
tp->saw_accecn_opt = saw_opt;
if (tp->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN)
tcp_accecn_fail_mode_set(tp, TCP_ACCECN_OPT_FAIL_RECV);
}
/* Validate the 3rd ACK based on the ACE field, see Table 4 of AccECN spec */
static inline void tcp_accecn_third_ack(struct sock *sk,
const struct sk_buff *skb, u8 sent_ect)
@ -428,9 +441,35 @@ static inline void tcp_accecn_set_ace(struct tcp_sock *tp, struct sk_buff *skb,
}
}
static inline u8 tcp_accecn_option_init(const struct sk_buff *skb,
u8 opt_offset)
{
u8 *ptr = skb_transport_header(skb) + opt_offset;
unsigned int optlen = ptr[1] - 2;
if (WARN_ON_ONCE(ptr[0] != TCPOPT_ACCECN0 && ptr[0] != TCPOPT_ACCECN1))
return TCP_ACCECN_OPT_FAIL_SEEN;
ptr += 2;
/* Detect option zeroing: an AccECN connection "MAY check that the
* initial value of the EE0B field or the EE1B field is non-zero"
*/
if (optlen < TCPOLEN_ACCECN_PERFIELD)
return TCP_ACCECN_OPT_EMPTY_SEEN;
if (get_unaligned_be24(ptr) == 0)
return TCP_ACCECN_OPT_FAIL_SEEN;
if (optlen < TCPOLEN_ACCECN_PERFIELD * 3)
return TCP_ACCECN_OPT_COUNTER_SEEN;
ptr += TCPOLEN_ACCECN_PERFIELD * 2;
if (get_unaligned_be24(ptr) == 0)
return TCP_ACCECN_OPT_FAIL_SEEN;
return TCP_ACCECN_OPT_COUNTER_SEEN;
}
/* See Table 2 of the AccECN draft */
static inline void tcp_ecn_rcv_synack(struct sock *sk, const struct tcphdr *th,
u8 ip_dsfield)
static inline void tcp_ecn_rcv_synack(struct sock *sk, const struct sk_buff *skb,
const struct tcphdr *th, u8 ip_dsfield)
{
struct tcp_sock *tp = tcp_sk(sk);
u8 ace = tcp_accecn_ace(th);
@ -469,7 +508,13 @@ static inline void tcp_ecn_rcv_synack(struct sock *sk, const struct tcphdr *th,
default:
tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
tp->syn_ect_rcv = 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);
tcp_accecn_saw_opt_fail_recv(tp, saw_opt);
tp->accecn_opt_demand = 2;
}
if (INET_ECN_is_ce(ip_dsfield) &&
tcp_accecn_validate_syn_feedback(sk, ace,
tp->syn_ect_snt)) {

2
include/uapi/linux/tcp.h
View File

@ -323,6 +323,8 @@ struct tcp_info {
__u32 tcpi_received_e1_bytes;
__u32 tcpi_received_e0_bytes;
__u32 tcpi_received_ce_bytes;
__u16 tcpi_accecn_fail_mode;
__u16 tcpi_accecn_opt_seen;
};
/* netlink attributes types for SCM_TIMESTAMPING_OPT_STATS */

3
net/ipv4/tcp.c
View File

@ -3409,6 +3409,7 @@ int tcp_disconnect(struct sock *sk, int flags)
tp->delivered = 0;
tp->delivered_ce = 0;
tp->accecn_fail_mode = 0;
tp->saw_accecn_opt = TCP_ACCECN_OPT_NOT_SEEN;
tcp_accecn_init_counters(tp);
tp->prev_ecnfield = 0;
tp->accecn_opt_tstamp = 0;
@ -4287,6 +4288,8 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
if (tp->rto_stamp)
info->tcpi_total_rto_time += tcp_clock_ms() - tp->rto_stamp;
info->tcpi_accecn_fail_mode = tp->accecn_fail_mode;
info->tcpi_accecn_opt_seen = tp->saw_accecn_opt;
info->tcpi_received_ce = tp->received_ce;
info->tcpi_delivered_e1_bytes = tp->delivered_ecn_bytes[ect1_idx];
info->tcpi_delivered_e0_bytes = tp->delivered_ecn_bytes[ect0_idx];

33
net/ipv4/tcp_input.c
View File

@ -398,7 +398,22 @@ static bool tcp_accecn_process_option(struct tcp_sock *tp,
unsigned int i;
u8 *ptr;
if (tcp_accecn_opt_fail_recv(tp))
return false;
if (!(flag & FLAG_SLOWPATH) || !tp->rx_opt.accecn) {
if (!tp->saw_accecn_opt) {
/* Too late to enable after this point due to
* potential counter wraps
*/
if (tp->bytes_sent >= (1 << 23) - 1) {
u8 saw_opt = TCP_ACCECN_OPT_FAIL_SEEN;
tcp_accecn_saw_opt_fail_recv(tp, saw_opt);
}
return false;
}
if (estimate_ecnfield) {
u8 ecnfield = estimate_ecnfield - 1;
@ -415,6 +430,13 @@ static bool tcp_accecn_process_option(struct tcp_sock *tp,
order1 = (ptr[0] == TCPOPT_ACCECN1);
ptr += 2;
if (tp->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
tp->saw_accecn_opt = tcp_accecn_option_init(skb,
tp->rx_opt.accecn);
if (tp->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN)
tcp_accecn_fail_mode_set(tp, TCP_ACCECN_OPT_FAIL_RECV);
}
res = !!estimate_ecnfield;
for (i = 0; i < 3; i++) {
u32 init_offset;
@ -6123,8 +6145,14 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
if (th->syn) {
if (tcp_ecn_mode_accecn(tp)) {
accecn_reflector = true;
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);
tcp_accecn_saw_opt_fail_recv(tp, saw_opt);
tcp_accecn_opt_demand_min(sk, 1);
}
}
if (sk->sk_state == TCP_SYN_RECV && sk->sk_socket && th->ack &&
TCP_SKB_CB(skb)->seq + 1 == TCP_SKB_CB(skb)->end_seq &&
TCP_SKB_CB(skb)->seq + 1 == tp->rcv_nxt &&
@ -6606,7 +6634,8 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
*/
if (tcp_ecn_mode_any(tp))
tcp_ecn_rcv_synack(sk, th, TCP_SKB_CB(skb)->ip_dsfield);
tcp_ecn_rcv_synack(sk, skb, th,
TCP_SKB_CB(skb)->ip_dsfield);
tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
tcp_try_undo_spurious_syn(sk);
@ -7177,6 +7206,8 @@ static void tcp_openreq_init(struct request_sock *req,
tcp_rsk(req)->snt_tsval_first = 0;
tcp_rsk(req)->last_oow_ack_time = 0;
tcp_rsk(req)->accecn_ok = 0;
tcp_rsk(req)->saw_accecn_opt = TCP_ACCECN_OPT_NOT_SEEN;
tcp_rsk(req)->accecn_fail_mode = 0;
tcp_rsk(req)->syn_ect_rcv = 0;
tcp_rsk(req)->syn_ect_snt = 0;
req->mss = rx_opt->mss_clamp;

14
net/ipv4/tcp_minisocks.c
View File

@ -463,6 +463,7 @@ static void tcp_ecn_openreq_child(struct sock *sk,
tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
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;
tp->prev_ecnfield = treq->syn_ect_rcv;
tp->accecn_opt_demand = 1;
tcp_ecn_received_counters_payload(sk, skb);
@ -678,6 +679,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
bool own_req;
tmp_opt.saw_tstamp = 0;
tmp_opt.accecn = 0;
if (th->doff > (sizeof(struct tcphdr)>>2)) {
tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL);
@ -855,6 +857,18 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
if (!(flg & TCP_FLAG_ACK))
return NULL;
if (tcp_rsk(req)->accecn_ok && tmp_opt.accecn &&
tcp_rsk(req)->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
u8 saw_opt = tcp_accecn_option_init(skb, tmp_opt.accecn);
tcp_rsk(req)->saw_accecn_opt = saw_opt;
if (tcp_rsk(req)->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN) {
u8 fail_mode = TCP_ACCECN_OPT_FAIL_RECV;
tcp_rsk(req)->accecn_fail_mode |= fail_mode;
}
}
/* For Fast Open no more processing is needed (sk is the
* child socket).
*/

11
net/ipv4/tcp_output.c
View File

@ -985,9 +985,14 @@ static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
}
}
/* Simultaneous open SYN/ACK needs AccECN option but not SYN */
/* Simultaneous open SYN/ACK needs AccECN option but not SYN.
* It is attempted to negotiate the use of AccECN also on the first
* retransmitted SYN, as mentioned in "3.1.4.1. Retransmitted SYNs"
* of AccECN draft.
*/
if (unlikely((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK) &&
tcp_ecn_mode_accecn(tp) &&
inet_csk(sk)->icsk_retransmits < 2 &&
READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) &&
remaining >= TCPOLEN_ACCECN_BASE)) {
opts->use_synack_ecn_bytes = 1;
@ -1076,7 +1081,7 @@ static unsigned int tcp_synack_options(const struct sock *sk,
if (treq->accecn_ok &&
READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option) &&
remaining >= TCPOLEN_ACCECN_BASE) {
req->num_timeout < 1 && remaining >= TCPOLEN_ACCECN_BASE) {
opts->use_synack_ecn_bytes = 1;
remaining -= tcp_options_fit_accecn(opts, 0, remaining);
}
@ -1156,7 +1161,7 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb
if (tcp_ecn_mode_accecn(tp)) {
int ecn_opt = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option);
if (ecn_opt &&
if (ecn_opt && tp->saw_accecn_opt && !tcp_accecn_opt_fail_send(tp) &&
(ecn_opt >= TCP_ACCECN_OPTION_FULL || tp->accecn_opt_demand ||
tcp_accecn_option_beacon_check(sk))) {
opts->use_synack_ecn_bytes = 0;