Fix segmentation fault error in response echo message (#3984)

src/protocols/echo/EchoClient.cpp

@@ -101,7 +101,7 @@ void EchoClient::OnMessageReceived(ExchangeContext * ec, const PacketHeader & pa
     {
         ec->Close();
         mExchangeCtx = nullptr;
-        ExitNow();
+        return;
     }
 
     // Remove the EC from the app state now. OnEchoResponseReceived can call
@@ -116,8 +116,6 @@ void EchoClient::OnMessageReceived(ExchangeContext * ec, const PacketHeader & pa
     {
         OnEchoResponseReceived(packetHeader.GetSourceNodeId().ValueOr(0), std::move(payload));
     }
-
-exit:;
 }
 
 void EchoClient::OnResponseTimeout(ExchangeContext * ec)

src/protocols/echo/EchoServer.cpp

@@ -55,21 +55,30 @@ void EchoServer::Shutdown()
 void EchoServer::OnMessageReceived(ExchangeContext * ec, const PacketHeader & packetHeader, uint32_t protocolId, uint8_t msgType,
                                    System::PacketBufferHandle payload)
 {
+    System::PacketBufferHandle response;
+
     // NOTE: we already know this is an Echo Request message because we explicitly registered with the
     // Exchange Manager for unsolicited Echo Requests.
 
     // Call the registered OnEchoRequestReceived handler, if any.
     if (OnEchoRequestReceived != nullptr)
+    {
+        response = payload.Retain();
         OnEchoRequestReceived(ec->GetPeerNodeId(), std::move(payload));
+    }
+    else
+    {
+        response = std::move(payload);
+    }
 
     // Since we are re-using the inbound EchoRequest buffer to send the EchoResponse, if necessary,
     // adjust the position of the payload within the buffer to ensure there is enough room for the
     // outgoing network headers.  This is necessary because in some network stack configurations,
     // the incoming header size may be smaller than the outgoing size.
-    payload->EnsureReservedSize(CHIP_SYSTEM_CONFIG_HEADER_RESERVE_SIZE);
+    response->EnsureReservedSize(CHIP_SYSTEM_CONFIG_HEADER_RESERVE_SIZE);
 
     // Send an Echo Response back to the sender.
-    ec->SendMessage(kProtocol_Echo, kEchoMessageType_EchoResponse, payload.Release_ForNow());
+    ec->SendMessage(kProtocol_Echo, kEchoMessageType_EchoResponse, response.Release_ForNow());
 
     // Discard the exchange context.
     ec->Close();