fix: hardening

src/EthernetClient.cpp

@@ -186,16 +186,18 @@ void EthernetClient::flush()
 
 void EthernetClient::stop()
 {
-  if (_tcp_client == NULL) {
-    return;
-  }
-
-  // close tcp connection if not closed yet
-  if (status() != TCP_CLOSING) {
-    tcp_connection_close(_tcp_client->pcb, _tcp_client);
+  if (_tcp_client != NULL) {
+    // close tcp connection if not closed yet
+    if (status() != TCP_CLOSING) {
+      if (_tcp_client->pcb == NULL) {
+        _tcp_client->state = TCP_CLOSING;
+      } else {
+        tcp_connection_close(_tcp_client->pcb, _tcp_client);
+      }
+    }
+    mem_free(_tcp_client);
+    _tcp_client = NULL;
   }
-  mem_free(_tcp_client);
-  _tcp_client = NULL;
 }
 
 uint8_t EthernetClient::connected()

src/lwipopts_default.h

@@ -126,7 +126,7 @@ a lot of data that needs to be copied, this should be set high. */
 #define TCP_SND_QUEUELEN        (2* TCP_SND_BUF/TCP_MSS)
 
 /* TCP receive window. */
-#define TCP_WND                 (3*TCP_MSS)
+#define TCP_WND                 (4*TCP_MSS)
 
 #define LWIP_TCP_KEEPALIVE                  1   /* Keep the TCP link active. Important for MQTT/TLS */
 #define LWIP_RANDOMIZE_INITIAL_LOCAL_PORTS  1   /* Prevent the same port to be used after reset.

src/utility/stm32_eth.cpp

@@ -1079,7 +1079,9 @@ void tcp_connection_close(struct tcp_pcb *tpcb, struct tcp_struct *tcp)
   tcp_accept(tpcb, NULL);
 
   /* close tcp connection */
-  tcp_close(tpcb);
+  if (tcp_close(tpcb) != ERR_OK) {
+    tcp_abort(tpcb);
+  }
 
   tcp->pcb = NULL;
   tcp->state = TCP_CLOSING;