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

arp.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 "arp.h"
#include "config.h"
#include "debug.h"
#include "ethernet.h"
#include "ip.h"
#include "macros.h"
#include "nethelp.h"

// timing parameters
#define ArpTicksMax 150 // maximum age of ARP table entries (in 200ms steps)
#define ArpNoMacTicksMax 50     // maximum age of ARP table entries without
                                // MAC (in 200ms steps)
#define ArpRetryTicks 8 // time after which to retry ARP query (must be power 
                        // of 2, in 200ms steps)

// ARP table
#define ArpTabFlagInUse 0x01
#define ArpTabFlagMacOk 0x02
struct ArpTable {
  unsigned char Flags;  // flags - see constants
  unsigned char Ticks;  // age of entry in 200ms steps
  unsigned char Mac[6];
  unsigned char Ip[4];
} ArpTab[4];

// initialize
void ArpInit(void)      // (extern)
{
  unsigned char i;

// empty ARP tabale
  for (i = 0; i < count(ArpTab); i++)
    ArpTab[i].Flags = 0;
}

// send an ARP request
static void ArpSendRequest(unsigned char *pIp)
{
  struct ArpPacket ArpRequest;

debug_arp_printf("send req ip=%u.%u.%u.%u", pIp[0], pIp[1], pIp[2], pIp[3]);

// build ARP request
  ArpRequest.ArpHdr.HwType = htons(0x0001);     // ethernet
  ArpRequest.ArpHdr.ProtoType = htons(0x0800);  // IP
  ArpRequest.ArpHdr.HwLen = 0x06;       // length of a MAC address
  ArpRequest.ArpHdr.ProtoLen = 0x04;    // length of an IP address
  ArpRequest.ArpHdr.Op = htons(0x0001); // ARP request
  mac_cpy(ArpRequest.ArpHdr.SrcMac, ConfigMac); // own MAC
  ip_cpy(ArpRequest.ArpHdr.SrcIp, ConfigIp);    // own IP
  mac_cpy(ArpRequest.ArpHdr.DestMac, "\xFF\xFF\xFF\xFF\xFF\xFF");       // broadcast 
                                                                        // MAC
  ip_cpy(ArpRequest.ArpHdr.DestIp, pIp);        // requested IP

// sent ARP request
  mac_cpy(ArpRequest.EthHdr.Dest, ArpRequest.ArpHdr.DestMac);   // ethernet
                                                                // destination 
                                                                // address
  ArpRequest.EthHdr.Type = htons(0x0806);       // ethernet packet type: ARP
  EthernetSend((unsigned char *)&ArpRequest, sizeof(ArpRequest));
}

// tick procedure - call every 200ms
void ArpTick200(void)   // (extern)
{
  unsigned char i;

// increase age of ARP table entires and remove timed out ones
  for (i = 0; i < count(ArpTab); i++) {
    if (ArpTab[i].Flags & ArpTabFlagInUse)      // entry in use
    {
      ArpTab[i].Ticks++;        // increase age
      if (ArpTab[i].Flags & ArpTabFlagMacOk)    // entry has got a MAC
      {
        if (ArpTab[i].Ticks > ArpTicksMax)      // too old
          ArpTab[i].Flags = 0;  // remove entry
      } else    // entry has not got a MAC
      {
        if (ArpTab[i].Ticks > ArpNoMacTicksMax) // too old
          ArpTab[i].Flags = 0;  // remove entry
        else if ((ArpTab[i].Ticks & (ArpRetryTicks - 1)) == 0)  // retry ARP
                                                                // request
          ArpSendRequest(ArpTab[i].Ip);
      }
    }
  }
}

// process a received ARP packet
void ArpRecv(unsigned char *pData, unsigned short Length)       // (extern)
{
  struct ArpPacket *pArpPack;

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

// convert pointer to ARP packet
  // (this saves us from always casting pData)
  pArpPack = (struct ArpPacket *)pData;

// not IP over ethernet
  if (pArpPack->ArpHdr.HwType != htons(0x0001) ||       // ethernet
      pArpPack->ArpHdr.ProtoType != htons(0x0800) ||    // IP
      pArpPack->ArpHdr.HwLen != 0x06 || // length of a MAC address
      pArpPack->ArpHdr.ProtoLen != 0x04)        // length of an IP address
    // we do not support other protocols than IP over ethernet
    return;

// source MAC is broadcast MAC
  if (mac_eq(pArpPack->ArpHdr.SrcMac, "\xFF\xFF\xFF\xFF\xFF\xFF"))
    // broadcast MAC cannot be source, this is some kind of attack, get lost!
    return;

// ARP request for own IP address
  if (pArpPack->ArpHdr.Op == htons(0x0001) &&   // ARP request
      ip_eq(pArpPack->ArpHdr.DestIp, ConfigIp)) // own IP address
  {
    struct ArpPacket ArpReply;
    // build ARP reply
    ArpReply.ArpHdr.HwType = htons(0x0001);     // ethernet
    ArpReply.ArpHdr.ProtoType = htons(0x0800);  // IP
    ArpReply.ArpHdr.HwLen = 0x06;       // length of a MAC address
    ArpReply.ArpHdr.ProtoLen = 0x04;    // length of an IP address
    ArpReply.ArpHdr.Op = htons(0x0002); // ARP reply
    mac_cpy(ArpReply.ArpHdr.SrcMac, ConfigMac); // own MAC
    ip_cpy(ArpReply.ArpHdr.SrcIp, ConfigIp);    // own IP
    mac_cpy(ArpReply.ArpHdr.DestMac, pArpPack->ArpHdr.SrcMac);  // requestor's 
                                                                // MAC
    ip_cpy(ArpReply.ArpHdr.DestIp, pArpPack->ArpHdr.SrcIp);     // requestor's 
                                                                // IP

debug_arp_printf
        ("recv req src=%02X:%02X:%02X:%02X:%02X:%02X ip=%u.%u.%u.%u",
         pArpPack->ArpHdr.SrcMac[0], pArpPack->ArpHdr.SrcMac[1],
         pArpPack->ArpHdr.SrcMac[2], pArpPack->ArpHdr.SrcMac[3],
         pArpPack->ArpHdr.SrcMac[4], pArpPack->ArpHdr.SrcMac[5],
         pArpPack->ArpHdr.SrcIp[0], pArpPack->ArpHdr.SrcIp[1],
         pArpPack->ArpHdr.SrcIp[2], pArpPack->ArpHdr.SrcIp[3]);

// sent ARP reply
    mac_cpy(ArpReply.EthHdr.Dest, ArpReply.ArpHdr.DestMac);     // ethernet
                                                                // destination 
                                                                // address
    ArpReply.EthHdr.Type = htons(0x0806);       // ethernet packet type: ARP
    EthernetSend((unsigned char *)&ArpReply, sizeof(ArpReply));
    return;
  }
  // ARP reply to own MAC address and own IP address
  if (pArpPack->ArpHdr.Op == htons(0x0002) &&   // ARP reply
      mac_eq(pArpPack->ArpHdr.DestMac, ConfigMac) &&    // own MAC address
      ip_eq(pArpPack->ArpHdr.DestIp, ConfigIp)) // own IP address
  {
    unsigned char i;

debug_arp_printf
        ("recv reply src=%02X:%02X:%02X:%02X:%02X:%02X ip=%u.%u.%u.%u",
         pArpPack->ArpHdr.SrcMac[0], pArpPack->ArpHdr.SrcMac[1],
         pArpPack->ArpHdr.SrcMac[2], pArpPack->ArpHdr.SrcMac[3],
         pArpPack->ArpHdr.SrcMac[4], pArpPack->ArpHdr.SrcMac[5],
         pArpPack->ArpHdr.SrcIp[0], pArpPack->ArpHdr.SrcIp[1],
         pArpPack->ArpHdr.SrcIp[2], pArpPack->ArpHdr.SrcIp[3]);

// search IP in ARP tabale
    for (i = 0; i < count(ArpTab); i++)
      if ((ArpTab[i].Flags & ArpTabFlagInUse) &&
          ip_eq(pArpPack->ArpHdr.SrcIp, ArpTab[i].Ip))
        break;
    // if found in ARP table
    // (we do not want to put an entry in the ARP table
    // if we have not asked for the MAC of this IP)
    if (i < count(ArpTab)) {
      // update ARP table entry
      ArpTab[i].Flags = ArpTabFlagInUse | ArpTabFlagMacOk;
      ArpTab[i].Ticks = 0;
      mac_cpy(ArpTab[i].Mac, pArpPack->ArpHdr.SrcMac);
      // notify IP
      // - IP might be waiting for the MAC to transmit a packet
      IpGotMac(ArpTab[i].Ip, ArpTab[i].Mac);
    }
    return;
  }

}

// lookup the MAC for an IP address
// returns 0x00 in case of success, 0x01 if the MAC address is unknown
unsigned char ArpLookup(unsigned char *pIp, unsigned char *pMac)        // (extern)
{
  unsigned char i, j;

// own IP
  if (ip_eq(pIp, ConfigIp))
    // own IP may not be looked up via ARP
    return 0x01;

// search IP in ARP tabale
  for (i = 0; i < count(ArpTab); i++)
    if ((ArpTab[i].Flags & ArpTabFlagInUse) && ip_eq(pIp, ArpTab[i].Ip))
      break;

// not found
  if (i >= count(ArpTab)) {
    // find a free entry
    for (i = 0; i < count(ArpTab); i++)
      if (!(ArpTab[i].Flags & ArpTabFlagInUse))
        break;

// no free entry
    if (i >= count(ArpTab)) {
      // find oldest entry
      i = 0;
      for (j = 1; j < count(ArpTab); j++)
        if (ArpTab[j].Ticks > ArpTab[i].Ticks)
          i = j;
    }
    // set up this entry
    ArpTab[i].Flags = ArpTabFlagInUse;
    ArpTab[i].Ticks = 0;
    ip_cpy(ArpTab[i].Ip, pIp);
  }
  // MAC available
  if (ArpTab[i].Flags & ArpTabFlagMacOk) {
    // return MAC and success
    mac_cpy(pMac, ArpTab[i].Mac);
    return 0x00;
  }
  // send ARP request
  ArpSendRequest(pIp);

// return no success for now
  return 0x01;
}

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