Allow use of loopback addresses in IP stack (127.0.0.0/8) (#754)

Authored-by: Adam St. Amand <[email protected]>

Author: adam-stamand

source/FreeRTOS_ARP.c

@@ -413,7 +413,8 @@ BaseType_t xCheckRequiresARPResolution( const NetworkBufferDescriptor_t * pxNetw
     const IPPacket_t * pxIPPacket = ( ( IPPacket_t * ) pxNetworkBuffer->pucEthernetBuffer );
     const IPHeader_t * pxIPHeader = &( pxIPPacket->xIPHeader );
 
-    if( ( pxIPHeader->ulSourceIPAddress & xNetworkAddressing.ulNetMask ) == ( *ipLOCAL_IP_ADDRESS_POINTER & xNetworkAddressing.ulNetMask ) )
+    if( ( ( pxIPHeader->ulSourceIPAddress & xNetworkAddressing.ulNetMask ) == ( *ipLOCAL_IP_ADDRESS_POINTER & xNetworkAddressing.ulNetMask ) ) &&
+        ( ( pxIPHeader->ulDestinationIPAddress & ipLOOPBACK_NETMASK ) != ( ipLOOPBACK_ADDRESS & ipLOOPBACK_NETMASK ) ) )
     {
         /* If the IP is on the same subnet and we do not have an ARP entry already,
          * then we should send out ARP for finding the MAC address. */
@@ -726,7 +727,8 @@ eARPLookupResult_t eARPGetCacheEntry( uint32_t * pulIPAddress,
          * can be done. */
         eReturn = eCantSendPacket;
     }
-    else if( *ipLOCAL_IP_ADDRESS_POINTER == *pulIPAddress )
+    else if( ( *ipLOCAL_IP_ADDRESS_POINTER == *pulIPAddress ) ||
+             ( ( *pulIPAddress & ipLOOPBACK_NETMASK ) == ( ipLOOPBACK_ADDRESS & ipLOOPBACK_NETMASK ) ) )
     {
         /* The address of this device. May be useful for the loopback device. */
         eReturn = eARPCacheHit;

source/FreeRTOS_IP.c

@@ -1446,6 +1446,8 @@ static eFrameProcessingResult_t prvAllowIPPacket( const IPPacket_t * const pxIPP
             else if( ( ulDestinationIPAddress != *ipLOCAL_IP_ADDRESS_POINTER ) &&
                      /* Is it the global broadcast address 255.255.255.255 ? */
                      ( ulDestinationIPAddress != ipBROADCAST_IP_ADDRESS ) &&
+                     /* Is it a loopback address ? */
+                     ( ( ulDestinationIPAddress & ipLOOPBACK_NETMASK ) != ( ipLOOPBACK_ADDRESS & ipLOOPBACK_NETMASK ) ) &&
                      /* Is it a specific broadcast address 192.168.1.255 ? */
                      ( ulDestinationIPAddress != xNetworkAddressing.ulBroadcastAddress ) &&
                      #if ( ipconfigUSE_LLMNR == 1 )

source/include/FreeRTOS_IP_Private.h

@@ -387,6 +387,10 @@ extern const BaseType_t xBufferAllocFixedSize;
  * rather than duplicated in its own variable. */
 #define ipLOCAL_MAC_ADDRESS            ( xDefaultPartUDPPacketHeader.ucBytes )
 
+/* The loopback address block is defined as part of rfc5735 */
+#define ipLOOPBACK_ADDRESS             ( FreeRTOS_inet_addr_quick( 127, 0, 0, 0 ) )
+#define ipLOOPBACK_NETMASK             ( FreeRTOS_inet_addr_quick( 255, 0, 0, 0 ) )
+
 /* ICMP packets are sent using the same function as UDP packets.  The port
  * number is used to distinguish between the two, as 0 is an invalid UDP port. */
 #define ipPACKET_CONTAINS_ICMP_DATA    ( 0 )

test/unit-test/FreeRTOS_ARP/FreeRTOS_ARP_utest.c

@@ -945,6 +945,29 @@ void test_xCheckRequiresARPResolution_OnLocalNetwork_InCache( void )
     TEST_ASSERT_EQUAL( pdFALSE, xResult );
 }
 
+void test_xCheckRequiresARPResolution_OnLocalNetwork_Loopback( void )
+{
+    NetworkBufferDescriptor_t xNetworkBuffer, * pxNetworkBuffer;
+    uint8_t ucEthernetBuffer[ ipconfigNETWORK_MTU ];
+    BaseType_t xResult;
+
+    pxNetworkBuffer = &xNetworkBuffer;
+    pxNetworkBuffer->pucEthernetBuffer = ucEthernetBuffer;
+
+    IPPacket_t * pxIPPacket = ( ( IPPacket_t * ) pxNetworkBuffer->pucEthernetBuffer );
+    IPHeader_t * pxIPHeader = &( pxIPPacket->xIPHeader );
+
+    *ipLOCAL_IP_ADDRESS_POINTER = ipLOOPBACK_ADDRESS;
+
+    /* Make sure there is a match on source IP and loopback address */
+    pxIPHeader->ulDestinationIPAddress = *ipLOCAL_IP_ADDRESS_POINTER;
+    pxIPHeader->ulSourceIPAddress = *ipLOCAL_IP_ADDRESS_POINTER & xNetworkAddressing.ulNetMask;
+
+    xResult = xCheckRequiresARPResolution( pxNetworkBuffer );
+
+    TEST_ASSERT_EQUAL( pdFALSE, xResult );
+}
+
 
 void test_ulARPRemoveCacheEntryByMac_NoMatch( void )
 {
@@ -1322,6 +1345,23 @@ void test_eARPGetCacheEntry_IPMatchesOtherBroadcastAddr( void )
     /* =================================================== */
 }
 
+void test_eARPGetCacheEntry_IPMatchesLoopbackAddr( void )
+{
+    uint32_t ulIPAddress;
+    MACAddress_t xMACAddress;
+    eARPLookupResult_t eResult;
+    uint32_t ulSavedGatewayAddress;
+
+    /* =================================================== */
+    ulIPAddress = ipLOOPBACK_ADDRESS;
+    /* Not worried about what these functions do. */
+    xIsIPv4Multicast_ExpectAndReturn( ulIPAddress, 0UL );
+    eResult = eARPGetCacheEntry( &ulIPAddress, &xMACAddress );
+    TEST_ASSERT_EQUAL_MESSAGE( eARPCacheHit, eResult, "Test 3" );
+    TEST_ASSERT_EQUAL_MEMORY_MESSAGE( &ipLOCAL_MAC_ADDRESS, &xMACAddress, sizeof( xMACAddress ), "Test 3" );
+    /* =================================================== */
+}
+
 void test_eARPGetCacheEntry_LocalIPIsZero( void )
 {
     uint32_t ulIPAddress;

test/unit-test/FreeRTOS_IP/FreeRTOS_IP_utest.c

@@ -2249,6 +2249,41 @@ void test_prvAllowIPPacket_IncorrectProtocolChecksum( void )
     TEST_ASSERT_EQUAL( eReleaseBuffer, eResult );
 }
 
+void test_prvAllowIPPacket_LoopbackDest( void )
+{
+    eFrameProcessingResult_t eResult;
+    IPPacket_t * pxIPPacket;
+    NetworkBufferDescriptor_t * pxNetworkBuffer, xNetworkBuffer;
+    UBaseType_t uxHeaderLength = 0;
+    uint8_t ucEthBuffer[ ipconfigTCP_MSS ];
+    IPHeader_t * pxIPHeader;
+
+    memset( ucEthBuffer, 0, ipconfigTCP_MSS );
+
+    pxNetworkBuffer = &xNetworkBuffer;
+    pxNetworkBuffer->pucEthernetBuffer = ucEthBuffer;
+    pxIPPacket = ( IPPacket_t * ) pxNetworkBuffer->pucEthernetBuffer;
+    pxIPHeader = &( pxIPPacket->xIPHeader );
+
+    *ipLOCAL_IP_ADDRESS_POINTER = 0xFFFFFFFF;
+
+    pxIPHeader->ucVersionHeaderLength = 0x45;
+
+    pxIPHeader->ulDestinationIPAddress = ipLOOPBACK_ADDRESS;
+
+    memcpy( pxIPPacket->xEthernetHeader.xDestinationAddress.ucBytes, &ipLOCAL_MAC_ADDRESS, sizeof( MACAddress_t ) );
+
+    pxIPHeader->ulSourceIPAddress = 0xC0C00101;
+
+    usGenerateChecksum_ExpectAndReturn( 0U, ( uint8_t * ) &( pxIPHeader->ucVersionHeaderLength ), ( size_t ) uxHeaderLength, ipCORRECT_CRC );
+
+    usGenerateProtocolChecksum_ExpectAndReturn( ( uint8_t * ) ( pxNetworkBuffer->pucEthernetBuffer ), pxNetworkBuffer->xDataLength, pdFALSE, ipCORRECT_CRC );
+
+    eResult = prvAllowIPPacket( pxIPPacket, pxNetworkBuffer, uxHeaderLength );
+
+    TEST_ASSERT_EQUAL( eProcessBuffer, eResult );
+}
+
 void test_prvAllowIPPacket_HappyPath( void )
 {
     eFrameProcessingResult_t eResult;