Raw Sockets Help

This is a discussion on Raw Sockets Help within the C Programming forums, part of the General Programming Boards category; Hi, I've been messing around with raw sockets today, basically trying to recieve all incoming packets to dump the Ip ...

  1. #1
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    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;
    }

  2. #2
    Registered User ssharish2005's Avatar
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    You get seg fal because u havn&#180;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&#180;t allocated space you can;t dereference its member elements, which u are doing it.

    ssharish2005

  3. #3
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    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.

  4. #4
    and the hat of wrongness Salem's Avatar
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    > while (read (fd, buffer, BUF_SIZE) > 0)
    > bzero(buffer, BUF_SIZE);
    You read a buffer, then immediately erase it.

    > struct iphdr *ip;
    Try
    struct iphdr ip;

    Then inside the loop
    memcpy( &ip, buffer, sizeof ip );

    Then
    printf("&#37;d", ip.version);
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  5. #5
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    Thank you very much

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