tcp: annotate data-races around icsk->icsk_syn_retries

do_tcp_getsockopt() and reqsk_timer_handler() read
icsk->icsk_syn_retries while another cpu might change its value.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230719212857.3943972-7-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/inet_connection_sock.c

@@ -1019,7 +1019,7 @@ static void reqsk_timer_handler(struct timer_list *t)
 
 	icsk = inet_csk(sk_listener);
 	net = sock_net(sk_listener);
-	max_syn_ack_retries = icsk->icsk_syn_retries ? :
+	max_syn_ack_retries = READ_ONCE(icsk->icsk_syn_retries) ? :
 		READ_ONCE(net->ipv4.sysctl_tcp_synack_retries);
 	/* Normally all the openreqs are young and become mature
 	 * (i.e. converted to established socket) for first timeout.

net/ipv4/tcp.c

@@ -3291,7 +3291,7 @@ int tcp_sock_set_syncnt(struct sock *sk, int val)
 		return -EINVAL;
 
 	lock_sock(sk);
-	inet_csk(sk)->icsk_syn_retries = val;
+	WRITE_ONCE(inet_csk(sk)->icsk_syn_retries, val);
 	release_sock(sk);
 	return 0;
 }
@@ -3572,7 +3572,7 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 		if (val < 1 || val > MAX_TCP_SYNCNT)
 			err = -EINVAL;
 		else
-			icsk->icsk_syn_retries = val;
+			WRITE_ONCE(icsk->icsk_syn_retries, val);
 		break;
 
 	case TCP_SAVE_SYN:
@@ -3993,7 +3993,7 @@ int do_tcp_getsockopt(struct sock *sk, int level,
 		val = keepalive_probes(tp);
 		break;
 	case TCP_SYNCNT:
-		val = icsk->icsk_syn_retries ? :
+		val = READ_ONCE(icsk->icsk_syn_retries) ? :
 			READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);
 		break;
 	case TCP_LINGER2: