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/*
* itunnel - an ICMP tunnel by edi / teso
* usage: it [-i id] [-s packetsize] host
* establishes a bidirectional ICMP
* 'connection' with 'host' by listening
* to ICMP packets with a specific id
* (default: 7530). uses stdin and stdout
* and needs to run as root.
*
*/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <netdb.h>
struct icmp
{
u_int8_t type;
u_int8_t code;
u_int16_t cksum;
u_int16_t id;
u_int16_t seq;
};
u_short in_cksum(u_short *, int);
/* icmp_tunnel - does the ICMP tunneling :-)
int sock - ICMP socket used to communicate
struct sockaddr_in *target - other side
int infd - input
int outfd - output
int packetsize - ...
u_int16_t id - ...
*/
int icmp_tunnel(int sock, struct sockaddr_in *target, int infd, int outfd, int packetsize, u_int16_t id) {
char* packet;
struct icmp *icmp, *icmpr;
int len;
int result;
fd_set fs;
struct sockaddr_in from;
int fromlen;
int num;
len = sizeof (struct icmp);
packet = malloc (len+packetsize);
memset (packet, 0, len+packetsize);
icmp = (struct icmp*)(packet);
icmpr = (struct icmp*)(packet+sizeof(struct ip));
while (1) {
FD_ZERO (&fs);
FD_SET (infd, &fs);
FD_SET (sock, &fs);
select (infd>sock?infd+1:sock+1, &fs, NULL, NULL, NULL);
if (FD_ISSET (infd, &fs)) {
result = read (infd, packet+len, packetsize);
if (!result) {
return 0;
} else if (result==-1) {
perror ("read");
return -1;
}
icmp->type = 0;
icmp->code = 0;
icmp->id = id;
icmp->seq = 0;
icmp->cksum = 0;
icmp->cksum = in_cksum((u_short*)packet, len+result);
result = sendto (sock, (char*)packet, len+result, 0, (struct sockaddr*)target, sizeof (struct sockaddr_in));
if (result==-1) {
perror ("sendto");
return -1;
}
}
if (FD_ISSET (sock, &fs)) {
fromlen = sizeof (struct sockaddr_in);
num = recvfrom (sock, packet, len+packetsize, 0, (struct sockaddr*)&from, &fromlen);
if (icmpr->id == id) {
write (outfd, packet+sizeof(struct ip)+sizeof(struct icmp), num-sizeof(struct ip)-sizeof(struct icmp));
}
}
}
return 0;
}
int main (int argc, char** argv) {
struct sockaddr_in target;
int s;
int packetsize = 100;
char* desthost = NULL;
u_int16_t id = 7530;
argv++;
argc--;
while (argc--) {
if (!strcmp(*argv, "-i")) {
if (!argc--) {
fprintf (stderr, "need argument\n");
return -1;
}
argv++;
id = atoi(*argv++);
} else if (!strcmp(*argv, "-s")) {
if (!argc--) {
fprintf (stderr, "need argument\n");
return -1;
}
argv++;
packetsize = atoi(*argv++);
} else desthost = *argv++;
}
if (!desthost) {
fprintf (stderr, "no destination\n");
return -1;
}
if ((target.sin_addr.s_addr = inet_addr (desthost)) == -1) {
struct hostent* he;
if (!(he = gethostbyname (desthost))) {
herror ("gethostbyname");
return -1;
}
memcpy (&target.sin_addr.s_addr, he->h_addr, he->h_length);
}
target.sin_family = AF_INET;
if ( (s = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1) {
perror ("socket");
return -1;
}
icmp_tunnel(s, &target, STDIN_FILENO, STDOUT_FILENO, packetsize, id);
close(s);
return 0;
}
unsigned short
in_cksum (addr, len)
u_short *addr;
int len;
{
register int nleft = len;
register u_short *w = addr;
register int sum = 0;
u_short answer = 0;
while (nleft > 1) { sum += *w++; nleft -= 2; }
if (nleft == 1) { *(u_char *) (&answer) = *(u_char *) w; sum += answer; }
sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
sum += (sum >> 16); /* add carry */
answer = ~sum; /* truncate to 16 bits */
return (answer);
}
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