#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <unistd.h>

#include <netdb.h>

#include <sys/types.h>

#include <sys/time.h>

#include <sys/resource.h>

#include <sys/wait.h>

#include <time.h>

#include <pcap.h>

#include "thc-ipv6.h"

extern int thc_socket;

extern char *do_hdr;

extern int do_hdr_off;

int type = 0, passive = 0, active = 0;

char *interface;

void help(char *prg) {

printf("%s %s (c) 2016 by %s %s\n\n", prg, VERSION, AUTHOR, RESOURCE);

printf("Syntax: %s [-ap] interface\n\n", prg);

printf("This tool answers to keep-alive requests on PPPoE and 6in4 tunnels; for PPPoE\nit also sends keep-alive requests.\n");

printf("Note that the appropriate environment variable THC_IPV6_{PPPOE|6IN4} must be set\n");

printf("Option -a will actively send alive requests every 15 seconds.\n");

printf("Option -p will not send replies to alive requests.\n");

exit(-1);

}

void intercept(u_char *foo, const struct pcap_pkthdr *header, const unsigned char *data) {

unsigned char *ipv6hdr, *pkt, buf[1500];

int len = header->caplen, pkt_len = 0;

unsigned int *seq, offset = 0;

unsigned short int *orig, *seen;

thc_ipv6_hdr hdr;

if (debug) {

printf("DEBUG: packet received\n");

thc_dump_data((unsigned char *)data, len, "Received packet on tunnel");

}

if (type == 2) { // 6in4

len -= do_hdr_size;

ipv6hdr = (unsigned char*) (data + do_hdr_size);

if ((ipv6hdr[0] & 240) != 0x60)

return;

if (len < 48 || ipv6hdr[6] != NXT_ICMP6 || ipv6hdr[41] != 0)

return;

seq = (unsigned int *) (ipv6hdr + 44);

if (ipv6hdr[40] == ICMP6_PINGREQUEST) {

printf("Keep-alive ping request ID 0x%x seen\n", htonl(*seq));

if (passive == 0) {

if ((pkt = thc_create_ipv6_extended(interface, PREFER_GLOBAL, &pkt_len, ipv6hdr + 24, ipv6hdr + 8, 255, 0, 0, 0, 0)) == NULL)

return;

if (thc_add_icmp6(pkt, &pkt_len, ICMP6_PINGREPLY, 0, htonl(*seq), (unsigned char *) ipv6hdr + 40 + 8, len - 40 - 8, 0) < 0)

return;

if (thc_generate_and_send_pkt(interface, NULL, NULL, pkt, &pkt_len) < 0)

return;

pkt = thc_destroy_packet(pkt);

printf("Keep-alive ping reply ID 0x%x sent\n", htonl(*seq));

}

}

if (passive && ipv6hdr[40] == ICMP6_PINGREPLY)

printf("Keep-alive ping reply ID 0x%x seen\n", htonl(*seq));

} else { // PPPoE

seen = (unsigned short int *) (data + 20 + offset + do_hdr_off);

if (len < 40 || len > 1500 || htons(*seen) != 0xc021)

return;

seen = (unsigned short int *) (data + 16 + offset + do_hdr_off);

if (memcmp(data + 16 + offset + do_hdr_off, do_hdr + 16 + offset + do_hdr_off, 2) != 0) {

orig = (unsigned short int*) (do_hdr + 16 + offset + do_hdr_off);

fprintf(stderr, "Warning: PPPoE SessionID is different to that defined in the environment variable! ((specified) %04x != %04x (seen))\n", htons(*orig), htons(*seen));

}

if (data[22 + offset + do_hdr_off] == 9) {

printf("Keep-alive request ID 0x%04x seen\n", htons(*seen));

if (passive == 0) {

memcpy(buf + 12, data + 12, len - 12);

memcpy(buf + 6, data, 6);

memcpy(buf, data + 6, 6);

buf[22 + offset + do_hdr_off] = 10;

hdr.pkt = buf;

hdr.pkt_len = len;

if (thc_send_pkt(interface, (unsigned char*) &hdr, &len) < 0) {

fprintf(stderr, "Error: could not send packet to interface %s (%d)\n", interface, thc_socket);

exit(-1);

}

printf("Keep-alive reply ID 0x%04x sent\n", htons(*seen));

}

} else {

if (passive && data[22 + offset + do_hdr_off] == 10)

printf("Keep-alive reply ID 0x%04x seen\n", htons(*seen));

}

}

return;

}

int main(int argc, char *argv[]) {

char sndbuf[128], data[] = { 0x09, 0x0a, 0x00, 0x0c, 0xfa, 0xce, 0xba, 0xbe, 0x1f, 0x1e, 0x1d, 0x1c };

time_t passed = 0;

pcap_t *p;

thc_ipv6_hdr hdr;

int sndbuflen = 0, i;

if (argc < 2 || strncmp(argv[1], "-h", 2) == 0)

help(argv[0]);

while ((i = getopt(argc, argv, "adp")) >= 0) {

switch(i) {

case 'a':

active = 1;

break;

case 'd':

debug = 1;

break;

case 'p':

passive = 1;

break;

default:

fprintf(stderr, "Error: invalid option -%c\n", i);

exit(-1);

}

}

if (getenv("THC_IPV6_PPPOE") != NULL)

type = 1;

else if (getenv("THC_IPV6_6IN4") != NULL)

type = 2;

if (type == 0) {

fprintf(stderr, "Error: neither the THC_IPV6_PPPOE nor THC_IPV6_6IN4 environment variable is set\n");

exit(-1);

}

if (type == 2 && active)

fprintf(stderr, "Error: active ping6 sending in for THC_IPV6_6IN4 is not possible. Please use thcping6 or alive6 to perform the active alive packet sending.\n");

interface = argv[optind];

if (thc_get_own_mac(interface) == NULL) {

fprintf(stderr, "Error: invalid interface %s\n", interface);

exit(-1);

}

printf("Started %s keep-alive watcher on %s (Press Control-C to end) ...\n", type == 1 ? "PPPoE" : "6in4", argv[optind]);

if (active == 1 && type == 1) {

if ((p = thc_pcap_init_promisc(interface, "it does not matter what we put here")) == NULL) {

fprintf(stderr, "Error: Could not set interface into promiscious mode\n");

exit(-1);

}

memcpy(sndbuf, do_hdr, do_hdr_size);

sndbuf[18 + do_hdr_off] = 0x00;

sndbuf[19 + do_hdr_off] = sizeof(data) + 2;

sndbuf[20 + do_hdr_off] = 0xc0;

sndbuf[21 + do_hdr_off] = 0x21;

memcpy(sndbuf + do_hdr_size, data, sizeof(data));

sndbuflen = do_hdr_size + sizeof(data);

hdr.pkt = sndbuf;

hdr.pkt_len = sndbuflen;

while (1) {

thc_pcap_check(p, (char *) intercept, NULL);

usleep(100);

if (passed <= time(NULL)) {

if (thc_send_pkt(interface, (unsigned char*) &hdr, &sndbuflen) < 0) {

fprintf(stderr, "Error: could not send packet to interface %s\n", interface);

return -1;

}

passed = time(NULL) + 15;

}

}

} else {

thc_pcap_function(interface, "it does not matter what we put here", (char *) intercept, 1, NULL);

fprintf(stderr, "Error: Could not set interface into promiscious mode\n");

exit(-1);

}

return -1; // never reached unless error

}