Discard UDPv6 with zero checksum. (#790)

* Reject UDPv6 if checksum is 0.

* Fix MISRA violations.

Author: ActoryOu

source/FreeRTOS_Sockets.c

@@ -5487,7 +5487,7 @@ BaseType_t xSocketSetSocketID( const Socket_t xSocket,
     FreeRTOS_Socket_t * pxSocket = ( FreeRTOS_Socket_t * ) xSocket;
     BaseType_t xReturn = -pdFREERTOS_ERRNO_EINVAL;
 
-    if( xSocketValid( pxSocket ) )
+    if( xSocketValid( pxSocket ) == pdTRUE )
     {
         xReturn = 0;
         pxSocket->pvSocketID = pvSocketID;
@@ -5509,7 +5509,7 @@ void * pvSocketGetSocketID( const ConstSocket_t xSocket )
     const FreeRTOS_Socket_t * pxSocket = ( const FreeRTOS_Socket_t * ) xSocket;
     void * pvReturn = NULL;
 
-    if( xSocketValid( pxSocket ) )
+    if( xSocketValid( pxSocket ) == pdTRUE )
     {
         pvReturn = pxSocket->pvSocketID;
     }

source/FreeRTOS_UDP_IPv6.c

@@ -446,6 +446,17 @@ BaseType_t xProcessReceivedUDPPacket_IPv6( NetworkBufferDescriptor_t * pxNetwork
 
     do
     {
+        /* UDPv6 doesn't allow zero-checksum, refer to RFC2460 - section 8.1.
+         * Some platforms (such as Zynq) pass the packet to upper layer for flexibility to allow zero-checksum. */
+        if( pxUDPPacket_IPv6->xUDPHeader.usChecksum == 0U )
+        {
+            FreeRTOS_debug_printf( ( "xProcessReceivedUDPPacket_IPv6: Drop packets with checksum %d\n",
+                                     pxUDPPacket_IPv6->xUDPHeader.usChecksum ) );
+
+            xReturn = pdFAIL;
+            break;
+        }
+
         if( pxSocket != NULL )
         {
             if( xCheckRequiresARPResolution( pxNetworkBuffer ) == pdTRUE )