From 67d845be32e159c2897a5203b584b00c326c1fc8 Mon Sep 17 00:00:00 2001
From: "Jost, Chris" <79271064+chrJost@users.noreply.github.com>
Date: Wed, 5 Jul 2023 11:22:22 +0200
Subject: [PATCH] add nullpointer check in LWIP::socket_close

---
 connectivity/lwipstack/source/LWIPStack.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/connectivity/lwipstack/source/LWIPStack.cpp b/connectivity/lwipstack/source/LWIPStack.cpp
index c67887e62d..210b6e1b75 100644
--- a/connectivity/lwipstack/source/LWIPStack.cpp
+++ b/connectivity/lwipstack/source/LWIPStack.cpp
@@ -287,8 +287,9 @@ nsapi_error_t LWIP::socket_close(nsapi_socket_t handle)
     /* Check if TCP FSM is in ESTABLISHED state.
      * Then give extra time for connection close handshaking  until TIME_WAIT state.
      * The purpose is to prevent eth/wifi driver stop and  FIN ACK corrupt.
-     * This may happend if network interface disconnect follows immediately after socket_close.*/
-    if (NETCONNTYPE_GROUP(s->conn->type) == NETCONN_TCP && s->conn->pcb.tcp->state == ESTABLISHED) {
+     * This may happend if network interface disconnect follows immediately after socket_close.
+     * In case of a TCP RESET flag, the pcb structure is already deleted, therefore check for nullpointer.*/
+    if (NETCONNTYPE_GROUP(s->conn->type) == NETCONN_TCP && (nullptr == s->conn->pcb.tcp || s->conn->pcb.tcp->state == ESTABLISHED)) {
         _event_flag.clear(TCP_CLOSED_FLAG);
         netconn_shutdown(s->conn, false, true);
         _event_flag.wait_any(TCP_CLOSED_FLAG, TCP_CLOSE_TIMEOUT);