UDP: Add ipconfigUDP_PASS_ZERO_CHECKSUM_PACKETS compile time constant

libraries/freertos_plus/standard/freertos_plus_tcp/include/FreeRTOSIPConfigDefaults.h

@@ -314,7 +314,11 @@ from the FreeRTOSIPConfig.h configuration header file. */
 #endif
 
 #ifndef ipconfigALLOW_SOCKET_SEND_WITHOUT_BIND
-	#define ipconfigALLOW_SOCKET_SEND_WITHOUT_BIND 1
+	#define ipconfigALLOW_SOCKET_SEND_WITHOUT_BIND	1
+#endif
+
+#ifndef ipconfigUDP_PASS_ZERO_CHECKSUM_PACKETS
+	#define ipconfigUDP_PASS_ZERO_CHECKSUM_PACKETS	0
 #endif
 
 #ifndef ipconfigUDP_TIME_TO_LIVE

libraries/freertos_plus/standard/freertos_plus_tcp/source/FreeRTOS_IP.c

@@ -125,10 +125,12 @@ events are posted to the network event queue. */
 handled.  The value is chosen simply to be easy to spot when debugging. */
 #define ipUNHANDLED_PROTOCOL		0x4321U
 
-/* Returned to indicate a valid checksum when the checksum does not need to be
-calculated. */
+/* Returned to indicate a valid checksum. */
 #define ipCORRECT_CRC				0xffffU
 
+/* Returned to indicate incorrect checksum. */
+#define ipWRONG_CRC					0x0000U
+
 /* Returned as the (invalid) checksum when the length of the data being checked
 had an invalid length. */
 #define ipINVALID_LENGTH			0x1234U
@@ -2029,8 +2031,18 @@ BaseType_t location = 0;
 	}
 	else if( ( *pusChecksum == 0U ) && ( ucProtocol == ( uint8_t ) ipPROTOCOL_UDP ) )
 	{
-		/* Sender hasn't set the checksum, no use to calculate it. */
-		usChecksum = ipCORRECT_CRC;
+		#if( ipconfigUDP_PASS_ZERO_CHECKSUM_PACKETS == 0 )
+		{
+			/* Sender hasn't set the checksum, drop the packet because
+			ipconfigUDP_PASS_ZERO_CHECKSUM_PACKETS is not set. */
+			usChecksum = ipWRONG_CRC;
+		}
+		#else
+		{
+			/* Sender hasn't set the checksum, no use to calculate it. */
+			usChecksum = ipCORRECT_CRC;
+		}
+		#endif
 		location = 8;
 		goto error_exit;
 	}