creating ip header using IP_HDRINCL option not doing anything - c

Question

i wanted to send an icmp packet by writing my own IP header so i used the IP_HDRINCL option the code compiled and runs without any errors but there is no packet being sent when i run the program and capture packets using wireshark no error message from the program as well
here is the code:
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#define BUFFSIZE 2048
char sendbuf[BUFFSIZE];
int seqno=0;
unsigned short chksum(void *data,int bytes){
unsigned int sum=0;
unsigned short *octate=data,result;
while(bytes>1){
sum+=*octate++;
bytes-=2;
}
if(bytes==1){
sum+=*(unsigned char *)octate;
}
while(sum>>16){
sum=(sum>>16)+(sum&0xffff);
}
result=~sum;
return result;
}
struct addrinfo * getaddr(char *name){ //convert user input host to address structure
int e;
struct addrinfo hints,*res;
memset(&hints,0,sizeof(hints));
hints.ai_flags=AI_CANONNAME;
hints.ai_family=AF_INET;
if(e=getaddrinfo(name,0,&hints,&res)!=0){
printf("getaddrinfo error: %s\n",gai_strerror(e));
}
return res;
}
void create_packet(struct sockaddr *d){
/* Creating IP Packet */
struct ip *ip;
ip=(struct ip*)sendbuf;
ip->ip_v=4;
ip->ip_hl=5;
ip->ip_tos=0;
ip->ip_len=20+8;
ip->ip_id=8848;
ip->ip_off=IP_DF;
ip->ip_ttl=7;
ip->ip_p=IPPROTO_ICMP;
char srcip[]="192.168.1.69";
struct addrinfo *source = getaddr(srcip);
struct sockaddr_in *dest=(struct sockaddr_in *)d;
struct sockaddr_in *src=(struct sockaddr_in *)source->ai_addr;
ip->ip_src=src->sin_addr;
ip->ip_dst=dest->sin_addr;
ip->ip_sum=0;
ip->ip_sum=chksum(ip,sizeof(*ip));
/* Creating ICMP Packet */
struct icmp *icmp;
icmp=(struct icmp *)(sendbuf+20);
icmp->icmp_type=ICMP_ECHO;
icmp->icmp_code=0;
icmp->icmp_id=getpid();
icmp->icmp_seq=++seqno;
icmp->icmp_cksum=0;
icmp->icmp_cksum=chksum(icmp,8);
}
void main(int argc,char **argv){
int sock;
int on=1;
struct addrinfo *addr=getaddr(argv[1]);
if((sock=socket(AF_INET,SOCK_RAW,IPPROTO_ICMP))==-1){
perror("socket error: ");
return;
}
if(setsockopt(sock,IPPROTO_IP,IP_HDRINCL,&on,sizeof(on))==-1){
perror("setsockopt error");
return;
}
create_packet(addr->ai_addr);
if(sendto(sock,sendbuf,28,0,addr->ai_addr,addr->ai_addrlen)==-1){
perror("sendto error");
return;
}
}

Answer 1

While I can't be certain based on your code alone, I suspect that you're running this program on a little-endian processor (x86-based), and IP expects its numbers in big-endian order. This means that any multi-byte fields (ip_len, ip_off) are written in the wrong order. I suspect that if you change the following 2 lines:
ip->ip_len=20+8;
ip->ip_off=IP_DF;
to this:
ip->ip_len=htons(20+8);
ip->ip_off=htons(IP_DF);
that the packets will be properly sent.
Incidentally the ip->ip_id field is also in big-endian order, but unless you're sending multiple fragments it doesn't much matter.