Problem Sending/Receiving Packets Into/From Network

[GEFORCEXTREME]

Hi guys,

I've been looking into packet sniffing with libpcap and sending packets with raw packets.

I edited the code I got from a raw packet guide/tutorial. However I've failed to verify that I'm actually sending out the packets with another program written with libpcap and also Wireshark (www.wireshark.org), a packet sniffer.

The code is as follow.



// Must be run by root lol! Just datagram, no payload/data

#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/udp.h>

#define PCKT_LEN 8192 // The packet length

// Can create separate header file (.h) for all headers' structure

// The IP header's structure
struct ipheader
{
unsigned char iph_ihl:5, iph_ver:4;
unsigned char iph_tos;
unsigned short int iph_len;
unsigned short int iph_ident;
unsigned char iph_flag;
unsigned short int iph_offset;
unsigned char iph_ttl;
unsigned char iph_protocol;
unsigned short int iph_chksum;
unsigned int iph_sourceip;
unsigned int iph_destip;
};

// UDP header's structure
struct udpheader
{
unsigned short int udph_srcport;
unsigned short int udph_destport;
unsigned short int udph_len;
unsigned short int udph_chksum;
};
// total udp header length: 8 bytes (=64 bits)

// Function for checksum calculation. From the RFC,
// the checksum algorithm is:
// "The checksum field is the 16 bit one's complement of the one's
// complement sum of all 16 bit words in the header. For purposes of
// computing the checksum, the value of the checksum field is zero."
unsigned short csum(unsigned short *buf, int nwords)
{ //
unsigned long sum;

for(sum=0; nwords>0; nwords--)
sum += *buf++;

sum = (sum >> 16) + (sum &0xffff);

sum += (sum >> 16);

return (unsigned short)(~sum);
}

#define SOURCE_PORT 1884
#define SPOOF_IP_ADDRESS "192.168.1.199"

// Source IP, source port, target IP, target port from the command line arguments
int main(int argc, char *argv[])
{
int sd;

// No data/payload just datagram
char buffer[PCKT_LEN];

// Our own headers' structures
struct ipheader *ip = (struct ipheader *)buffer;
//struct tcpheader *tcp = (struct tcpheader *) (buffer + sizeof(struct ipheader));
struct udpheader *udp = (struct udpheader *)(buffer + sizeof(struct ipheader));

// Source and destination addresses: IP and port
struct sockaddr_in sin, din;

int one = 1;
const int *val = &one;

memset(buffer, 0, PCKT_LEN);

if(argc != 3)
{
printf("- Invalid parameters!!!\n");
//printf("- Usage %s <source hostname/IP> <source port> <target hostname/IP> <target port>\n", argv[0]);
printf("- Usage %s <target hostname/IP> <target port>\n", argv[0]);
exit(-1);
}

// Create a raw socket with UDP protocol
sd = socket(PF_INET, SOCK_RAW, IPPROTO_UDP);
if(sd < 0)
{
perror("socket() error");
// If something wrong just exit
exit(-1);
}
else
printf("socket() - Using SOCK_RAW socket and UDP protocol is OK.\n");

// The source is redundant, may be used later if needed

// The address family
sin.sin_family = AF_INET;
din.sin_family = AF_INET;

// Port numbers
sin.sin_port = htons(SOURCE_PORT);
din.sin_port = htons(atoi(argv[2]));

// IP addresses
sin.sin_addr.s_addr = INADDR_ANY; // get my IP
din.sin_addr.s_addr = inet_addr(argv[1]);

#if 1
// Fabricate the IP header or we can use the
// standard header structures but assign our own values.
ip->iph_ihl = 5; // header length in bytes
ip->iph_ver = 4; // IPv4
ip->iph_tos = 16; // type of service, low delay
ip->iph_len = sizeof(struct ipheader) + sizeof(struct udpheader);
ip->iph_ident = htons(54321);
ip->iph_ttl = 64; // hops
ip->iph_protocol = 17; // UDP
#endif

// Source IP address, can use spoofed address here!!! cool!!!!!
ip->iph_sourceip = inet_addr(argv[1]);
// The destination IP address
ip->iph_destip = inet_addr(argv[1]);
#if 1
// Fabricate the UDP header. Source port number, redundant
udp->udph_srcport = htons(SOURCE_PORT);
// Destination port number
udp->udph_destport = htons(atoi(argv[2]));

udp->udph_len = htons(sizeof(struct udpheader));
#endif
// Calculate the checksum for integrity
ip->iph_chksum = csum((unsigned short *)buffer, sizeof(struct ipheader) + sizeof(struct udpheader));

// Inform the kernel do not fill up the packet structure. we will build our own...
if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) < 0)
{
perror("setsockopt() error");
exit(-1);
}
else
printf("setsockopt() is OK.\n");

// Send loop, send for every 2 second for 100 count
printf("Trying...\n");
printf("Using raw socket and UDP protocol\n");
printf("Using Target IP: %s port: %u.\n", argv[1], atoi(argv[2]));

int count;
for(count = 1; count <=20; count++)
{
if(sendto(sd, buffer, ip->iph_len, 0, (struct sockaddr *)&din, sizeof(din)) < 0) // Verify
{
perror("sendto() error");
exit(-1);
}
else
{
printf("Count #%u - sendto() is OK.\n", count);
sleep(2);
}
}

close(sd);

return 0;
}

If anyone understands why, please tell me. Thanks.