Commit b40671b5 authored by Chia-Yu Chang's avatar Chia-Yu Chang Committed by Paolo Abeni
Browse files

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: default avatarIlpo Järvinen <ij@kernel.org>
Signed-off-by: default avatarChia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250916082434.100722-9-chia-yu.chang@nokia-bell-labs.com


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent aa55a7dd

include/linux/tcp.h

+3 −1
Original line number Diff line number Diff line
@@ -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 */

include/net/tcp_ecn.h

+48 −3
Original line number Diff line number Diff line
@@ -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)) {

include/uapi/linux/tcp.h

+2 −0
Original line number Diff line number Diff line
@@ -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 */

net/ipv4/tcp.c

+3 −0
Original line number Diff line number Diff line
@@ -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];

net/ipv4/tcp_input.c

+33 −2
Original line number Diff line number Diff line
@@ -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;