Thread: Raw Sockets Help

Hi, I've been messing around with raw sockets today, basically trying to recieve all incoming packets to dump the Ip header (this is just for curiosity not malicious intent, and i do mean that.). My problem is , how do i convert my read buffer to a struct iphdr.. infact im not fully sure im doing any this right.. as i am still quite new to c.

any help would be great, heres the code.

Code:

#include <stdio.h>
#include <strings.h>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h> 

#define BUF_SIZE 8192

int main(){
	unsigned char buffer[BUF_SIZE];
	unsigned char ipbuf[20];
	struct iphdr *ip;

	int fd = socket(PF_INET, SOCK_RAW, 6);
	
	while (read (fd, buffer, BUF_SIZE) > 0){
		bzero(buffer, BUF_SIZE);
		
 		int i;	
  		for(i=0;i<20;i++){
  			ipbuf[i] = buffer[i]; //get first 20 bytes (ip header)
  		}
  		
  		ip = ipbuf; 
  		printf("%d", ip->version); //i get segmentation fault here
 	}
 	return 0;
}

You get seg fal because u havn´t allocated space for your IP. And you are trying to assign a char * to struct iphdr *, did u enable your warning while compiling your code. The compiler might have complained about it.

Hence your havn´t allocated space you can;t dereference its member elements, which u are doing it.

ssharish2005

right, so should i do something like this...

Code:

ip = malloc(sizeof(struct iphdr));

?

im still confused as to how convert the buffer to the iphdr struct...

sorry if im a pain in bum.

Thank you very much