firmware.dartboard/udp.c (e8658d5) - flaneth · BlinkenArea

udp.c

/* flaneth - flash and ethernet - dartboard mod
 * version 0.1 date 2008-11-09
 * Copyright (C) 2007-2008 Stefan Schuermans <stefan@schuermans.info>
 * Copyleft: GNU public license V2 - http://www.gnu.org/copyleft/gpl.html
 * a BlinkenArea project - http://www.blinkenarea.org/
 */

#include "config.h"
#include "checksum.h"
#include "dart.h"
#include "debug.h"
#include "dhcp.h"
#include "ethernet.h"
#include "ip.h"
#include "macros.h"
#include "nethelp.h"
#include "udp.h"

// some kind of "token bucket" for UDP echo
#define UdpEchoTicks 10 // allowed rate of UDP echo replies (in 200ms steps)
unsigned char UdpEchoTickCnt = 0; // tick counter
#define UdpEchoReliesMax 3 // maximum value for UdpEchoReplies
unsigned char UdpEchoReplies = 0; // number of UDP echo replies that may be sent at the moment

// tick procedure - call every 200ms
void UdpTick200( void ) // (extern)
{
  // count ticks
  UdpEchoTickCnt++;
  // time to allow one reply more
  if( UdpEchoTickCnt >= UdpEchoTicks )
  {
    UdpEchoTickCnt = 0;

// increase reply count if not at maximum
    if( UdpEchoReplies < UdpEchoReliesMax )
      UdpEchoReplies++;
  }
}

// process a received UDP echo packet
static void UdpEchoRecv( unsigned char * pData, unsigned short Length )
{
  struct UdpPacket * pUdpPack;

// convert pointer to UDP packet
  // (this saves us from always casting pData)
  pUdpPack = (struct UdpPacket *)pData;

// source port is UDP echo port
  if( pUdpPack->UdpHdr.SrcPort == htons( 7 ) )
    // ignore this packet
    // - UDP echo answer to another UDP echo port will result in endless echoing
    return;

// only reply with allowed packet rate
  if( UdpEchoReplies == 0 )
  {
    debug_udp_printf( "echo len=%u (dropped)", Length );
    return;
  }
  UdpEchoReplies--;

debug_udp_printf( "echo len=%u", Length );

// send an UDP echo
  // - use same buffer to send reply
  // - this saves us from allocating a new buffer
  // - this saves us from copying the data
  pUdpPack->UdpHdr.DestPort = pUdpPack->UdpHdr.SrcPort; // back to originationg port
  pUdpPack->UdpHdr.SrcPort = htons( 7 ); // UDP echo port
  ip_cpy( pUdpPack->IpHdr.Dest, pUdpPack->IpHdr.Src ); // back to originating IP
  UdpSend( pData, Length );
}

// process a received UDP packet
void UdpRecv( unsigned char * pData, unsigned short Length ) // (extern)
{
  struct UdpPacket * pUdpPack;
  unsigned int len;

// packet too short
  if( Length < sizeof( struct UdpPacket ) )
    return;

// convert pointer to UDP packet
  // (this saves us from always casting pData)
  pUdpPack = (struct UdpPacket *)pData;

// ignore packets sent from or to port 0
  // - this might be some attack
  if( pUdpPack->UdpHdr.SrcPort == htons( 0 ) ||
      pUdpPack->UdpHdr.DestPort == htons( 0 ) )
    return;

// check total length
  len = sizeof( struct EthernetHeader ) + sizeof( struct IpHeader ) + ntohs( pUdpPack->UdpHdr.Length ); // length according to UDP header
  if( Length < len ) // packet is truncated
    return;
  Length = len; // remove IP padding from packet (maybe Length > len)

// test checksum
  if( Checksum( (unsigned char*)&pUdpPack->IpHdr.Src,
                Length - sizeof( struct EthernetHeader ) - sizeof( struct IpHeader ) + 8,
                0x0011,
                ntohs( pUdpPack->UdpHdr.Length ) ) != 0 )
    return;

debug_udp_printf( "recv src=%u dest=%u len=%u",
                    ntohs( pUdpPack->UdpHdr.SrcPort ),
                    ntohs( pUdpPack->UdpHdr.DestPort ),
                    Length );

// branch according to destination port
  switch( ntohs( pUdpPack->UdpHdr.DestPort ) )
  {
    // UDP echo
    case 7:
      UdpEchoRecv( pData, Length );
      break;
    // DHCP
    case 68:
      DhcpRecv( pData, Length );
      break;
    // dart board
    case 501:
      DartRequest( pUdpPack->IpHdr.Src,
                   ntohs( pUdpPack->UdpHdr.SrcPort ) );
      break;
  }
}

// send an UDP packet
// pData must point to a struct UdpPacket with UdpHdr.SrcPort, UdpHdr.DestPort and IpHdr.Dest already initialized
void UdpSend( unsigned char * pData, unsigned short Length ) // (extern)
{
  struct UdpPacket * pUdpPack;
  unsigned int chk;

// packet too short
  if( Length < sizeof( struct UdpPacket ) )
    return;

// convert pointer to UDP packet
  // (this saves us from always casting pData)
  pUdpPack = (struct UdpPacket *)pData;

debug_udp_printf( "send src=%u dest=%u len=%u",
                    ntohs( pUdpPack->UdpHdr.SrcPort ),
                    ntohs( pUdpPack->UdpHdr.DestPort ),
                    Length );

// fill in header values
  pUdpPack->UdpHdr.Length = htons( Length - sizeof( struct EthernetHeader ) - sizeof( struct IpHeader ) );
  pUdpPack->UdpHdr.Chk = 0x0000;
  ip_cpy( pUdpPack->IpHdr.Src, ConfigIp ); // put IP already here into IP header
                                           // because it is needed for calculation of UDP checksum

// generate checksum
  chk = Checksum( (unsigned char *)&pUdpPack->IpHdr.Src,
                  Length - sizeof( struct EthernetHeader ) - sizeof( struct IpHeader ) + 8,
                  0x0011,
                  ntohs( pUdpPack->UdpHdr.Length ) );
  pUdpPack->UdpHdr.Chk = htons( chk );

// send UDP packet
  pUdpPack->IpHdr.Proto = 0x11; // UDP
  IpSend( pData, Length );
}

flaneth

initial commit after making CF identify work