firmware/udp.c (2342395) - flaneth · BlinkenArea

udp.c

/* flaneth - flash and ethernet
   Copyright (C) 2007-2012 Stefan Schuermans <stefan@blinkenarea.org>
   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 "debug.h"
#include "dhcp.h"
#include "ethernet.h"
#include "ip.h"
#include "macros.h"
#include "nethelp.h"
#include "ser62500.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;
    // serial output with 62500 baud in 9N2 protocol
  case 62500:
    Ser62500Send9N2(pData + sizeof(struct UdpPacket),
                    Length - sizeof(struct UdpPacket));
    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);
}

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