tcp: annotate data-races around tp->keepalive_probes

do_tcp_getsockopt() reads tp->keepalive_probes while another cpu
might change its value.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: edumazet

include/net/tcp.h

@@ -1533,9 +1533,14 @@ static inline int keepalive_time_when(const struct tcp_sock *tp)
 static inline int keepalive_probes(const struct tcp_sock *tp)
 {
 	struct net *net = sock_net((struct sock *)tp);
+	int val;
+
+	/* Paired with WRITE_ONCE() in tcp_sock_set_keepcnt()
+	 * and do_tcp_setsockopt().
+	 */
+	val = READ_ONCE(tp->keepalive_probes);
 
-	return tp->keepalive_probes ? :
-		READ_ONCE(net->ipv4.sysctl_tcp_keepalive_probes);
+	return val ? : READ_ONCE(net->ipv4.sysctl_tcp_keepalive_probes);
 }
 
 static inline u32 keepalive_time_elapsed(const struct tcp_sock *tp)

net/ipv4/tcp.c

@@ -3357,7 +3357,8 @@ int tcp_sock_set_keepcnt(struct sock *sk, int val)
 		return -EINVAL;
 
 	lock_sock(sk);
-	tcp_sk(sk)->keepalive_probes = val;
+	/* Paired with READ_ONCE() in keepalive_probes() */
+	WRITE_ONCE(tcp_sk(sk)->keepalive_probes, val);
 	release_sock(sk);
 	return 0;
 }
@@ -3565,7 +3566,7 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 		if (val < 1 || val > MAX_TCP_KEEPCNT)
 			err = -EINVAL;
 		else
-			tp->keepalive_probes = val;
+			WRITE_ONCE(tp->keepalive_probes, val);
 		break;
 	case TCP_SYNCNT:
 		if (val < 1 || val > MAX_TCP_SYNCNT)