IP Packet Injection. Original Source: http://code.securitytube.net/IP-Packet-Injection.c

IP-Packet-Injection.c

#include<stdio.h>
#include<stdlib.h>
#include<sys/socket.h>
#include<features.h>
#include<linux/if_packet.h>
#include<linux/if_ether.h>
#include<errno.h>
#include<sys/ioctl.h>
#include<net/if.h>
#include<net/ethernet.h>
#include<linux/ip.h>
#include<arpa/inet.h>
#include<string.h>


#define SRC_ETHER_ADDR  "aa:aa:aa:aa:aa:aa"
#define DST_ETHER_ADDR	"bb:bb:bb:bb:bb:bb"
#define SRC_IP	"192.168.0.10"
#define DST_IP	"192.168.0.11"


int CreateRawSocket(int protocol_to_sniff)
{
	int rawsock;

	if((rawsock = socket(PF_PACKET, SOCK_RAW, htons(protocol_to_sniff)))== -1)
	{
		perror("Error creating raw socket: ");
		exit(-1);
	}

	return rawsock;
}

int BindRawSocketToInterface(char *device, int rawsock, int protocol)
{
	
	struct sockaddr_ll sll;
	struct ifreq ifr;

	bzero(&sll, sizeof(sll));
	bzero(&ifr, sizeof(ifr));
	
	/* First Get the Interface Index  */


	strncpy((char *)ifr.ifr_name, device, IFNAMSIZ);
	if((ioctl(rawsock, SIOCGIFINDEX, &ifr)) == -1)
	{
		printf("Error getting Interface index !\n");
		exit(-1);
	}

	/* Bind our raw socket to this interface */

	sll.sll_family = AF_PACKET;
	sll.sll_ifindex = ifr.ifr_ifindex;
	sll.sll_protocol = htons(protocol); 


	if((bind(rawsock, (struct sockaddr *)&sll, sizeof(sll)))== -1)
	{
		perror("Error binding raw socket to interface\n");
		exit(-1);
	}

	return 1;
	
}


int SendRawPacket(int rawsock, unsigned char *pkt, int pkt_len)
{
	int sent= 0;

	/* A simple write on the socket ..thats all it takes ! */

	if((sent = write(rawsock, pkt, pkt_len)) != pkt_len)
	{
		/* Error */
		printf("Could only send %d bytes of packet of length %d\n", sent, pkt_len);
		return 0;
	}

	return 1;
	

}

unsigned char* CreateEthernetHeader(char *src_mac, char *dst_mac, int protocol)
{
	struct ethhdr *ethernet_header;

	
	ethernet_header = (struct ethhdr *)malloc(sizeof(struct ethhdr));

	/* copy the Src mac addr */

	memcpy(ethernet_header->h_source, (void *)ether_aton(src_mac), 6);

	/* copy the Dst mac addr */

	memcpy(ethernet_header->h_dest, (void *)ether_aton(dst_mac), 6);

	/* copy the protocol */

	ethernet_header->h_proto = htons(protocol);

	/* done ...send the header back */

	return ((unsigned char *)ethernet_header);


}

/* Ripped from Richard Stevans Book */

unsigned short ComputeIpChecksum(unsigned char *header, int len)
{
         long sum = 0;  /* assume 32 bit long, 16 bit short */
	 unsigned short *ip_header = (unsigned short *)header;

         while(len > 1){
             sum += *((unsigned short*) ip_header)++;
             if(sum & 0x80000000)   /* if high order bit set, fold */
               sum = (sum & 0xFFFF) + (sum >> 16);
             len -= 2;
         }

         if(len)       /* take care of left over byte */
             sum += (unsigned short) *(unsigned char *)ip_header;
          
         while(sum>>16)
             sum = (sum & 0xFFFF) + (sum >> 16);

        return ~sum;
}


unsigned char *CreateIPHeader(/* Customize this as an exercise */)
{
	struct iphdr *ip_header;

	ip_header = (struct iphdr *)malloc(sizeof(struct iphdr));

	ip_header->version = 4;
	ip_header->ihl = (sizeof(struct iphdr))/4 ;
	ip_header->tos = 0;
	ip_header->tot_len = htons(sizeof(struct iphdr));
	ip_header->id = htons(111);
	ip_header->frag_off = 0;
	ip_header->ttl = 111;
	ip_header->protocol = IPPROTO_TCP;
	ip_header->check = 0; /* We will calculate the checksum later */
	(in_addr_t)ip_header->saddr = inet_addr(SRC_IP);
	(in_addr_t)ip_header->daddr = inet_addr(DST_IP);


	/* Calculate the IP checksum now : 
	   The IP Checksum is only over the IP header */

	ip_header->check = ComputeIpChecksum((unsigned char *)ip_header, ip_header->ihl*4);

	return ((unsigned char *)ip_header);

}


/* argv[1] is the device e.g. eth0    */
 
main(int argc, char **argv)
{

	int raw;
	unsigned char *packet;
	unsigned char *ethernet_header;
	unsigned char *ip_header;
	int pkt_len;

	
	/* Create the raw socket */

	raw = CreateRawSocket(ETH_P_ALL);

	/* Bind raw socket to interface */

	BindRawSocketToInterface(argv[1], raw, ETH_P_ALL);

	/* create Ethernet header */

	ethernet_header = CreateEthernetHeader(SRC_ETHER_ADDR, DST_ETHER_ADDR, ETHERTYPE_IP);

	/* Create IP Header */

	ip_header = CreateIPHeader();
	
	/* Packet length = ETH + IP header */

	pkt_len = sizeof(struct ethhdr) + sizeof(struct iphdr);

	/* Allocate memory */

	packet = (unsigned char *)malloc(pkt_len);

	/* Copy the Ethernet header first */

	memcpy(packet, ethernet_header, sizeof(struct ethhdr));

	/* Copy the IP header -- but after the ethernet header */

	memcpy((packet + sizeof(struct ethhdr)), ip_header, sizeof(struct iphdr));

	/* send the packet on the wire */
	
	if(!SendRawPacket(raw, packet, pkt_len))
	{
		perror("Error sending packet");
	}
	else
		printf("Packet sent successfully\n");

	/* Free the headers back to the heavenly heap */

	free(ethernet_header);
	free(ip_header);
	free(packet);

	close(raw);

	return 0;
}

i tried to use different source IP address and destination address and using different mac addresses too for both source and destination on the code .
but i got the "segmentation fault" error when trying to execute it using : ./iptest eth0
can you please tell me why this is happening ?
thanks in advance :)