Add ACE check on first data ACK

minuscat · Feb 3, 2024 · 5d809aa · 5d809aa
1 parent bde09fe
commit 5d809aa
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Showing 4 changed files with 19 additions and 2 deletions.
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
@@ -234,7 +234,8 @@ struct tcp_sock {
 		syn_ect_rcv:2,	/* ... needed durign 3WHS + first seqno */
 		ecn_fail:1;	/* ECN reflector detected path mangling */
 	u8	accecn_no_respond:1, /* AccECN no response on feedback */
-		accecn_no_options:1; /* AccECN no options send out */
+		accecn_no_options:1, /* AccECN no options send out */
+		first_data_ack:1;    /* Check for first data ack */
 	u8	saw_accecn_opt:2,    /* An AccECN option was seen */
 		fast_ack_mode:2, /* which fast ack mode ? */
 		unused:4;

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
@@ -3035,6 +3035,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->ecn_fail = 0;
 	tp->accecn_no_respond = 0;
 	tp->accecn_no_options = 0;
+	tp->first_data_ack = 0;
 	tcp_accecn_init_counters(tp);
 	tp->prev_ecnfield = 0;
 	tp->accecn_opt_tstamp = 0;

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
@@ -703,6 +703,21 @@ static u32 __tcp_accecn_process(struct sock *sk, const struct sk_buff *skb,
 	if (flag & FLAG_SYN_ACKED)
 		return 0;
 
+	/* [CY] 3.2.2.4. Testing for Zeroing of the ACE Field - If AccECN has been successfully negotiated, the Data Sender
+	 * MAY check the value of the ACE counter in the first feedback packet (with or without data) that arrives after the
+	 * 3-way handshake.  If the value of this ACE field is found to be zero (0b000), for the remainder of the half-
+	 * connection the Data Sender ought to send non-ECN-capable packets and it is advised not to respond to any feedback
+	 * of CE markings.
+	 */
+	if (!tp->first_data_ack) {
+		tp->first_data_ack = 1;
+		if (!tcp_accecn_ace(tcp_hdr(skb))) {
+			tp->ecn_fail = 1;
+			tp->accecn_no_respond = 1;
+			return 0;
+		}
+	}
+
 	if (tp->received_ce_pending >= TCP_ACCECN_ACE_MAX_DELTA)
 		inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
 

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
@@ -438,7 +438,7 @@ static void tcp_ecn_openreq_child(struct sock *sk,
 	const struct tcp_request_sock *treq = tcp_rsk(req);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	/* [CY] 3.1.5. Implications of AccECN Mode - A TCP Server in AccECN mode: MUST NOT set ECT oni
+	/* [CY] 3.1.5. Implications of AccECN Mode - 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.
 	 */