#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <unistd.h>

struct ipheader {
  unsigned char      iph_ihl:4, iph_ver:4;
  unsigned char      iph_tos;
  unsigned short int iph_len;
  unsigned short int iph_ident;
  unsigned short int iph_flag:3, iph_offset:13;
  unsigned char      iph_ttl;
  unsigned char      iph_protocol;
  unsigned short int iph_chksum;
  struct  in_addr    iph_sourceip;
  struct  in_addr    iph_destip;
};

struct icmpheader {
  unsigned char icmp_type;
  unsigned char icmp_code;
  unsigned short int icmp_chksum;
  unsigned short int icmp_id;
  unsigned short int icmp_seq;
};

unsigned short in_cksum (unsigned short *buf, int length)
{
   unsigned short *w = buf;
   int nleft = length;
   int sum = 0;
   unsigned short temp=0;

   while (nleft > 1)  {
       sum += *w++;
       nleft -= 2;
   }

   if (nleft == 1) {
        *(u_char *)(&temp) = *(u_char *)w ;
        sum += temp;
   }

   sum = (sum >> 16) + (sum & 0xffff);
   sum += (sum >> 16);
   return (unsigned short)(~sum);
}

void send_raw_ip_packet(struct ipheader* ip)
{
    struct sockaddr_in dest_info;
    int enable = 1;

    int sock = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
    setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &enable, sizeof(enable));

    dest_info.sin_family = AF_INET;
    dest_info.sin_addr = ip->iph_destip;

    sendto(sock, ip, ntohs(ip->iph_len), 0, (struct sockaddr *)&dest_info, sizeof(dest_info));
    close(sock);
}

int main() {
   char buffer[1500];
   memset(buffer, 0, 1500);

   struct icmpheader *icmp = (struct icmpheader *)(buffer + sizeof(struct ipheader));
   icmp->icmp_type = 8; // ICMP Echo Request
   icmp->icmp_chksum = 0;
   icmp->icmp_chksum = in_cksum((unsigned short *)icmp, sizeof(struct icmpheader));

   struct ipheader *ip = (struct ipheader *) buffer;
   ip->iph_ver = 4;
   ip->iph_ihl = 5;
   ip->iph_ttl = 20;
   ip->iph_sourceip.s_addr = inet_addr("1.2.3.4");
   ip->iph_destip.s_addr = inet_addr("10.9.0.5");
   ip->iph_protocol = IPPROTO_ICMP;
   ip->iph_len = htons(sizeof(struct ipheader) + sizeof(struct icmpheader));

   send_raw_ip_packet(ip);
   printf("Spoofed ICMP packet sent from 1.2.3.4 to 10.9.0.5\n");

   return 0;
}
