icmp.c

   1 // L2TPNS: icmp
   2
   3 char const *cvs_id_icmp = "$Id: icmp.c,v 1.3 2004/06/28 02:43:13 fred_nerk Exp $";
   4
   5 #include <arpa/inet.h>
   6 #include <netdb.h>
   7 #include <netinet/in.h>
   8 #include <asm/types.h>
   9 #include <linux/ip.h>
  10 #include <linux/icmp.h>
  11 #include <stdio.h>
  12 #include <sys/socket.h>
  13 #include <unistd.h>
  14 #include <sys/types.h>
  15 #include <sys/wait.h>
  16 #include <memory.h>
  17
  18 #include "l2tpns.h"
  19
  20 __u16 _checksum(unsigned char *addr, int count);
  21
  22 void host_unreachable(ipt destination, u16 id, ipt source, char *packet, int packet_len)
  23 {
  24         char buf[128] = {0};
  25         struct iphdr *iph;
  26         struct icmphdr *icmp;
  27         char *data;
  28         int len = 0, on = 1, icmp_socket;
  29         struct sockaddr_in whereto = {0};
  30
  31         if (!(icmp_socket = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)))
  32                 return;
  33         setsockopt(icmp_socket, IPPROTO_IP, IP_HDRINCL, (char *)&on, sizeof(on));
  34
  35         whereto.sin_addr.s_addr = destination;
  36         whereto.sin_family = AF_INET;
  37
  38         iph = (struct iphdr *)(buf);
  39         len = sizeof(struct iphdr);
  40         icmp = (struct icmphdr *)(buf + len);
  41         len += sizeof(struct icmphdr);
  42         data = (char *)(buf + len);
  43         len += (packet_len < 64) ? packet_len : 64;
  44         memcpy(data, packet, (packet_len < 64) ? packet_len : 64);
  45
  46         iph->tos = 0;
  47         iph->id = id;
  48         iph->frag_off = 0;
  49         iph->ttl = 30;
  50         iph->check = 0;
  51         iph->version = 4;
  52         iph->ihl = 5;
  53         iph->protocol = 1;
  54         iph->check = 0;
  55         iph->daddr = destination;
  56         iph->saddr = source;
  57
  58         iph->tot_len = ntohs(len);
  59
  60         icmp->type = ICMP_DEST_UNREACH;
  61         icmp->code = ICMP_HOST_UNREACH;
  62         icmp->checksum = _checksum((char *)icmp, sizeof(struct icmphdr) + ((packet_len < 64) ? packet_len : 64));
  63
  64         iph->check = _checksum((char *)iph, sizeof(struct iphdr));
  65
  66         sendto(icmp_socket, (char *)buf, len, 0, (struct sockaddr *)&whereto, sizeof(struct sockaddr));
  67         close(icmp_socket);
  68 }
  69
  70 __u16 _checksum(unsigned char *addr, int count)
  71 {
  72         register long sum = 0;
  73
  74         for (; count > 1; count -= 2)
  75         {
  76                 sum += ntohs(*(u32 *)addr);
  77                 addr += 2;
  78         }
  79
  80         if (count > 1) sum += *(unsigned char *)addr;
  81
  82         // take only 16 bits out of the 32 bit sum and add up the carries
  83         while (sum >> 16)
  84                 sum = (sum & 0xFFFF) + (sum >> 16);
  85
  86         // one's complement the result
  87         sum = ~sum;
  88
  89         return htons((u16) sum);
  90 }