UDP packet not sent via raw sockets on linux - c

Question

I have been learning raw sockets for the past few days and I am unable to send UDP packets over RAW sockets. I tried writing code for this but UDP packets were not sent. (I was capturing packets via wireshark, only IPv4 packets were sent, containing headers upto IP layer). I searched a lot on the internet and tried various codes as well which I found on the internet but still couldn't send UDP packets (not seen on wireshark). Can someone suggest changes in code or point to some resource regarding this.
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <linux/ip.h>
#include <linux/udp.h>
#define PCKT_LEN 8192
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);
}
int main(int argc, char const *argv[])
{
if (argc != 5) {
printf("Error: Invalid parameters!\n");
printf("Usage: %s <source hostname/IP> <source port> <target hostname/IP> <target port>\n", argv[0]);
exit(1);
}
u_int16_t src_port, dst_port;
u_int32_t src_addr, dst_addr;
src_addr = inet_addr(argv[1]);
dst_addr = inet_addr(argv[3]);
src_port = atoi(argv[2]);
dst_port = atoi(argv[4]);
int sd;
char buffer[PCKT_LEN];
struct iphdr *ip = (struct iphdr *) buffer;
struct udphdr *udp = (struct udphdr *) (buffer + sizeof(struct iphdr));
struct sockaddr_in sin;
int one = 1;
const int *val = &one;
memset(buffer, 0, PCKT_LEN);
// create a raw socket with UDP protocol
sd = socket(PF_INET, SOCK_RAW, IPPROTO_UDP);
if (sd < 0) {
perror("socket() error");
exit(2);
}
printf("OK: a raw socket is created.\n");
// 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(2);
}
printf("OK: socket option IP_HDRINCL is set.\n");
sin.sin_family = AF_INET;
sin.sin_port = htons(dst_port);
sin.sin_addr.s_addr = dst_addr;
// fabricate the IP header
ip->ihl = 5;
ip->version = 4;
ip->tos = 16; // low delay
ip->tot_len = sizeof(struct iphdr) + sizeof(struct udphdr);
ip->id = htons(54321);
ip->ttl = 64; // hops
ip->protocol = 17; // UDP
// source IP address, can use spoofed address here
ip->saddr = src_addr;
ip->daddr = dst_addr;
// fabricate the UDP header
udp->source = htons(src_port);
// destination port number
udp->dest = htons(dst_port);
udp->len = htons(sizeof(struct udphdr));
// calculate the checksum for integrity
ip->check = csum((unsigned short *)buffer,
sizeof(struct iphdr) + sizeof(struct udphdr));
if (sendto(sd, buffer, ip->tot_len, 0,
(struct sockaddr *)&sin, sizeof(sin)) < 0)
{
perror("sendto()");
exit(3);
}
printf("OK: one packet is sent.\n");
close(sd);
return 0;
}