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Sourcecode: l2tpns version File versions

icmp.c

// L2TPNS: icmp

char const *cvs_id_icmp = "$Id: icmp.c,v 1.6 2004/12/16 08:49:53 bodea Exp $";

#include <arpa/inet.h>
#include <netdb.h>
#include <netinet/in.h>
#include <asm/types.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <stdio.h>
#include <sys/socket.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <memory.h>

#include "l2tpns.h"

static uint16_t _checksum(unsigned char *addr, int count);

void host_unreachable(in_addr_t destination, uint16_t id, in_addr_t source, char *packet, int packet_len)
{
      char buf[128] = {0};
      struct iphdr *iph;
      struct icmphdr *icmp;
      char *data;
      int len = 0, on = 1, icmp_socket;
      struct sockaddr_in whereto = {0};

      if ((icmp_socket = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0)
            return;

      setsockopt(icmp_socket, IPPROTO_IP, IP_HDRINCL, (char *)&on, sizeof(on));

      whereto.sin_addr.s_addr = destination;
      whereto.sin_family = AF_INET;

      iph = (struct iphdr *)(buf);
      len = sizeof(struct iphdr);
      icmp = (struct icmphdr *)(buf + len);
      len += sizeof(struct icmphdr);
      data = (char *)(buf + len);
      len += (packet_len < 64) ? packet_len : 64;
      memcpy(data, packet, (packet_len < 64) ? packet_len : 64);

      iph->tos = 0;
      iph->id = id;
      iph->frag_off = 0;
      iph->ttl = 30;
      iph->check = 0;
      iph->version = 4;
      iph->ihl = 5;
      iph->protocol = 1;
      iph->check = 0;
      iph->daddr = destination;
      iph->saddr = source;

      iph->tot_len = ntohs(len);

      icmp->type = ICMP_DEST_UNREACH;
      icmp->code = ICMP_HOST_UNREACH;
      icmp->checksum = _checksum((char *) icmp, sizeof(struct icmphdr) + ((packet_len < 64) ? packet_len : 64));

      iph->check = _checksum((char *) iph, sizeof(struct iphdr));

      sendto(icmp_socket, (char *)buf, len, 0, (struct sockaddr *)&whereto, sizeof(struct sockaddr));
      close(icmp_socket);
}

static uint16_t _checksum(unsigned char *addr, int count)
{
      register long sum = 0;

      for (; count > 1; count -= 2)
      {
            sum += ntohs(*(uint32_t *) addr);
            addr += 2;
      }

      if (count > 1) sum += *(unsigned char *)addr;

      // take only 16 bits out of the 32 bit sum and add up the carries
      while (sum >> 16)
            sum = (sum & 0xFFFF) + (sum >> 16);

      // one's complement the result
      sum = ~sum;

      return htons((uint16_t) sum);
}

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