[SOLVED] creating IP header using IP_HDRINCL option is not working

m.r_m0j0 · 11-23-2021, 09:46 PM

i wanted to send icmp packet with custom ip header so i wrote the following code but when i run the program nothing happens there is no packet in wireshark and there is no error from the program and i don't know what is happening

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;
	}

}

astrogeek · 11-24-2021, 07:29 PM

Welcome to LQ and the Programming forum!

I have not had a chance to look at your code and have not recently done much socket programming, so no specific advice to offer.

It is always helpful to those offering help if you can tell us what you have done to troubleshoot it so far, and where you are getting stuck understanding what is happening. That helps others to more quickly understand the problem and will often lead you to a better understanding yourself, and sometimes lead to a solution!

I would suggest that you check each of those lib function calls and verify the args are valid and that you are correctly handling their return values. And add few temporary messages to show you the state of important values at various points, which should lead you to the point that something is failing or not as expected.

Good luck!

m.r_m0j0 · 11-25-2021, 05:24 AM

Yes I have solved the problem. I forgot to change the endianness while creating the header using htons() for fields having multiple bytes(ip_off,ip_len) worked