Merge pull request #13837 from benpicco/dhcpv6-stale_replies

sys/net/dhcpv6: discard stale replies

sys/net/application_layer/dhcpv6/client.c

@@ -369,6 +369,15 @@ static bool _check_sid_opt(dhcpv6_opt_duid_t *sid)
             (memcmp(sid->duid, server.duid.u8, server.duid_len) == 0));
 }
 
+/* discard stale messages in the receive buffer */
+static void _flush_stale_replies(sock_udp_t *sock)
+{
+    int res;
+    while ((res = sock_udp_recv(sock, recv_buf, sizeof(recv_buf), 0, NULL)) >= 0) {
+        DEBUG("DHCPv6 client: discarding %d stale bytes\n", res);
+    }
+}
+
 static int _preparse_advertise(uint8_t *adv, size_t len, uint8_t **buf)
 {
     dhcpv6_opt_duid_t *cid = NULL, *sid = NULL;
@@ -696,6 +705,7 @@ static void _solicit_servers(event_t *event)
                                 ARRAY_SIZE(oro_opts));
     msg_len += _add_ia_pd_from_config(&send_buf[msg_len]);
     DEBUG("DHCPv6 client: send SOLICIT\n");
+    _flush_stale_replies(&sock);
     res = sock_udp_send(&sock, send_buf, msg_len, &remote);
     assert(res > 0);    /* something went terribly wrong */
     while (((res = sock_udp_recv(&sock, recv_buf, sizeof(recv_buf),
@@ -802,6 +812,7 @@ static void _request_renew_rebind(uint8_t type)
     msg_len += _compose_oro_opt((dhcpv6_opt_oro_t *)&send_buf[msg_len], oro_opts,
                                 ARRAY_SIZE(oro_opts));
     msg_len += _add_ia_pd_from_config(&send_buf[msg_len]);
+    _flush_stale_replies(&sock);
     while (sock_udp_send(&sock, send_buf, msg_len, &remote) <= 0) {}
     while (((res = sock_udp_recv(&sock, recv_buf, sizeof(recv_buf),
                                  retrans_timeout, NULL)) <= 0) ||