tcp: Get a proper dst before checking it.

tcp_peer_is_proven needs a proper route to make the
determination, but dst always is NULL. This bug may
be there at the beginning of git tree. This does not
look serious enough to deserve backports to stable
versions.
Signed-off-by: NTonghao Zhang <xiangxia.m.yue@gmail.com>
Acked-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -6111,6 +6111,10 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	if (tmp_opt.tstamp_ok)
 		tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
 
+	dst = af_ops->route_req(sk, &fl, req);
+	if (!dst)
+		goto drop_and_free;
+
 	if (!want_cookie && !isn) {
 		/* Kill the following clause, if you dislike this way. */
 		if (!net->ipv4.sysctl_tcp_syncookies &&
@@ -6131,11 +6135,6 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 
 		isn = af_ops->init_seq(skb);
 	}
-	if (!dst) {
-		dst = af_ops->route_req(sk, &fl, req);
-		if (!dst)
-			goto drop_and_free;
-	}
 
 	tcp_ecn_create_request(req, skb, sk, dst);