i have a C program that's able to receive ICMP requests and display them, but however will not send out any ICMP requests itself from what I've seen using Wireshark.
I have included the required libraries and i'm using a IP header file and ICMP header file that's omitted.
Any help would be appreciated. Please ignore the random Printf statements, there just to help me out.
Thanks
**
***IP.h*****
#ifndef __IP_H__
#define __IP_H__
struct iphdr {
uint8_t hdrlen:4;
uint8_t version:4;
uint8_t ecn:2;
uint8_t dscp:6;
uint16_t length;
uint16_t ident;
uint16_t fragoff:13;
uint16_t flags:3;
uint8_t ttl;
uint8_t protocol;
uint16_t checksum;
uint32_t srcip;
uint32_t dstip;
uint32_t options[ ];
} __attribute__((__packed__));
#endif // __IP_H__
****ICMP.H****
#ifndef __ICMP_H__
#define __ICMP_H__
struct icmphdr {
uint8_t type;
uint8_t code;
uint16_t checksum;
uint16_t id;
uint16_t seqNum;
uint32_t data[ ];
} __attribute__((__packed__));
char * messages[ ] = {
"Echo reply",
"Type 1",
"Type 2",
"Destination unreachable",
"Source quench",
"Redirect",
"Type 6",
"Type 7",
"Echo request",
"Router advertisement",
"Router discovery",
"Time exceeded",
"Parameter problem",
"Timestamp request",
"Timestamp reply",
"Information request (obsol.)",
"Information reply (obsol.)",
"Address mask request",
"Address mask reply"
};
#endif // __ICMP_H__
****Main C File ****
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include "ip.h"
#include "icmp.h"
struct timeval timeout;
struct timeval end;
#define BUF_SIZE 1024
#define ICMP 1
#define ECHO_REQ 8
#define ECHO_REPL 0
#define HOSTADDR "8.8.8.8"
char *
iptos (uint32_t ipaddr) {
static char ips[16];
sprintf(ips, "%d.%d.%d.%d",
(ipaddr >> 24),
(ipaddr >> 16) & 0xff,
(ipaddr >> 8) & 0xff,
(ipaddr ) & 0xff );
return ips;
}
uint16_t
sum (uint16_t initial, void * buffer, int bytes) {
uint32_t total;
uint16_t * ptr;
int words;
total = initial;
ptr = (uint16_t *) buffer;
words = (bytes + 1) / 2; // +1 & truncation on / handles any odd byte at end
while (words--) total += *ptr++;
while (total & 0xffff0000) total = (total >> 16) + (total & 0xffff);
return (uint16_t) total;
}
void
some_function ( ) {
struct sockaddr_storage peer_addr;
socklen_t peer_addrlen;
struct sockaddr_in addr;
struct sockaddr_in dstaddr;
struct iphdr * ip;
struct icmphdr * icmp;
struct timeval * sent;
int skt;
int sequence;
long int length;
fd_set rdfds;
int ready;
int rtt;
char buff [BUF_SIZE];
skt = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
if (skt < 0) {
perror ("socket()");
exit (1);
}
addr.sin_family = AF_INET;
addr.sin_port = 0;
addr.sin_addr.s_addr = INADDR_ANY;
if (bind (skt, (struct sockaddr *)&addr, sizeof(struct sockaddr_in))) {
perror ("Can't bind socket");
exit (1);
}
printf("aaa");
ip = (struct iphdr *)buff;
peer_addrlen = (socklen_t) sizeof (struct sockaddr_storage);
memset (&dstaddr, 0, sizeof(struct sockaddr_in));
dstaddr.sin_addr.s_addr = inet_addr(HOSTADDR);
dstaddr.sin_family = AF_INET;
memset (buff, 0, sizeof(buff));
icmp = (struct icmphdr *) buff;
icmp->type = ECHO_REQ;
icmp->id = htons(getpid( ) & 0xffff);
icmp->seqNum = htons(sequence++);
printf("aabba");
if (gettimeofday ((struct timeval *)icmp->data, NULL)) {
perror ("Can't establish send time");
exit (1);
}
length = sizeof(struct icmphdr) + sizeof(struct timeval);
icmp->checksum = ~htons(sum (0, buff, length));
printf("aaa");
if (sendto (skt, buff, length, 0,
(struct sockaddr *) &dstaddr, sizeof(struct sockaddr_in)) <= 0) {
perror ("sendto()");
exit (1);
}
printf("aaa");
timeout.tv_sec = 1;
timeout.tv_usec = 0;
FD_ZERO(&rdfds);
FD_SET (skt, &rdfds);
ready = select (skt + 1, &rdfds, NULL, NULL, &timeout);
if (ready < 0) {
perror ("Select()");
exit (1);
}
memset (buff, 0, sizeof(buff));
if (recvfrom (skt, buff, sizeof(buff), 0,
(struct sockaddr *) &peer_addr, &peer_addrlen) <= 0) exit (1);
if (gettimeofday (&end, NULL)) { // Timestamp reception
perror ("Can't establish time of receipt");
exit (1);
}
if (ip->version != 4 ||
sum (0, buff, sizeof(struct iphdr)) != 0xffff ||
ip->protocol != ICMP)
exit(1);
length = ntohs(ip->length) - ip->hdrlen * 4; // Length of IP payload
icmp = (struct icmphdr *)((uint32_t *)ip + ip->hdrlen); // Find ICMP hdr
if (icmp->type != ECHO_REPL || sum (0, icmp, length) != 0xffff) {
fprintf (stderr, "Received %s\n", messages[icmp->type]);
exit (1);
}
sent = (struct timeval *)icmp->data;
if ((rtt = (end.tv_usec - sent->tv_usec) / 100) < 0)
rtt += 10000; // We've cycled to a new second
rtt += (end.tv_sec - sent->tv_sec) * 10000; // Add any seconds
printf ("%ld bytes from %s: icmp_req=%d ttl=%d time=%0.1f ms\n",
length,
iptos(ntohl(ip->srcip)),
ntohs(icmp->seqNum),
ip->ttl,
((float)rtt) / 10);
}
int main(){
printf("aaa");
some_function();
return(0);
}
The problem is the wrong checksum.
Change this line
icmp->checksum = htons(sum (0, buff, length));
with
icmp->checksum = ~(sum (0, buff, length));
the sum function already care about byte order, no need to translate it again with htons
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