netlink: annotate data races around sk_state

netlink_getsockbyportid() reads sk_state while a concurrent
netlink_connect() can change its value.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/netlink/af_netlink.c

@@ -1098,7 +1098,8 @@ static int netlink_connect(struct socket *sock, struct sockaddr *addr,
 		return -EINVAL;
 
 	if (addr->sa_family == AF_UNSPEC) {
-		sk->sk_state	= NETLINK_UNCONNECTED;
+		/* paired with READ_ONCE() in netlink_getsockbyportid() */
+		WRITE_ONCE(sk->sk_state, NETLINK_UNCONNECTED);
 		/* dst_portid and dst_group can be read locklessly */
 		WRITE_ONCE(nlk->dst_portid, 0);
 		WRITE_ONCE(nlk->dst_group, 0);
@@ -1122,7 +1123,8 @@ static int netlink_connect(struct socket *sock, struct sockaddr *addr,
 		err = netlink_autobind(sock);
 
 	if (err == 0) {
-		sk->sk_state	= NETLINK_CONNECTED;
+		/* paired with READ_ONCE() in netlink_getsockbyportid() */
+		WRITE_ONCE(sk->sk_state, NETLINK_CONNECTED);
 		/* dst_portid and dst_group can be read locklessly */
 		WRITE_ONCE(nlk->dst_portid, nladdr->nl_pid);
 		WRITE_ONCE(nlk->dst_group, ffs(nladdr->nl_groups));
@@ -1174,8 +1176,8 @@ static struct sock *netlink_getsockbyportid(struct sock *ssk, u32 portid)
 
 	/* Don't bother queuing skb if kernel socket has no input function */
 	nlk = nlk_sk(sock);
-	/* dst_portid can be changed in netlink_connect() */
-	if (sock->sk_state == NETLINK_CONNECTED &&
+	/* dst_portid and sk_state can be changed in netlink_connect() */
+	if (READ_ONCE(sock->sk_state) == NETLINK_CONNECTED &&
 	    READ_ONCE(nlk->dst_portid) != nlk_sk(ssk)->portid) {
 		sock_put(sock);
 		return ERR_PTR(-ECONNREFUSED);