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/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
It is considered beerware. Prost. Skol. Cheers or whatever.
$id$ */
/* System */
#include <arpa/inet.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Libowfat */
#include "io.h"
#include "ip6.h"
#include "socket.h"
/* Opentracker */
#include "ot_rijndael.h"
#include "ot_stats.h"
#include "ot_udp.h"
#include "trackerlogic.h"
#if 0
static const uint8_t g_static_connid[8] = { 0x23, 0x42, 0x05, 0x17, 0xde, 0x41, 0x50, 0xff };
#endif
static uint32_t g_rijndael_round_key[44] = {0};
static uint32_t g_key_of_the_hour[2] = {0};
static ot_time g_hour_of_the_key;
static void udp_generate_rijndael_round_key() {
uint32_t key[16];
#ifdef WANT_ARC4RANDOM
arc4random_buf(&key[0], sizeof(key));
#else
key[0] = random();
key[1] = random();
key[2] = random();
key[3] = random();
#endif
rijndaelKeySetupEnc128(g_rijndael_round_key, (uint8_t *)key);
#ifdef WANT_ARC4RANDOM
g_key_of_the_hour[0] = arc4random();
#else
g_key_of_the_hour[0] = random();
#endif
g_hour_of_the_key = g_now_minutes;
}
/* Generate current and previous connection id for ip */
static void udp_make_connectionid(uint32_t connid[2], const ot_ip6 remoteip, int age) {
uint32_t plain[4], crypt[4];
int i;
if (g_now_minutes + 60 > g_hour_of_the_key) {
g_hour_of_the_key = g_now_minutes;
g_key_of_the_hour[1] = g_key_of_the_hour[0];
#ifdef WANT_ARC4RANDOM
g_key_of_the_hour[0] = arc4random();
#else
g_key_of_the_hour[0] = random();
#endif
}
memcpy(plain, remoteip, sizeof(plain));
for (i = 0; i < 4; ++i)
plain[i] ^= g_key_of_the_hour[age];
rijndaelEncrypt128(g_rijndael_round_key, (uint8_t *)remoteip, (uint8_t *)crypt);
connid[0] = crypt[0] ^ crypt[1];
connid[1] = crypt[2] ^ crypt[3];
}
/* UDP implementation according to http://xbtt.sourceforge.net/udp_tracker_protocol.html */
int handle_udp6(int64 serversocket, struct ot_workstruct *ws) {
ot_ip6 remoteip;
uint32_t *inpacket = (uint32_t *)ws->inbuf;
uint32_t *outpacket = (uint32_t *)ws->outbuf;
uint32_t left, event, scopeid;
uint32_t connid[2];
uint32_t action;
uint16_t port, remoteport;
size_t byte_count, scrape_count;
byte_count = socket_recv6(serversocket, ws->inbuf, G_INBUF_SIZE, remoteip, &remoteport, &scopeid);
if (!byte_count)
return 0;
stats_issue_event(EVENT_ACCEPT, FLAG_UDP, (uintptr_t)remoteip);
stats_issue_event(EVENT_READ, FLAG_UDP, byte_count);
/* Minimum udp tracker packet size, also catches error */
if (byte_count < 16)
return 1;
/* Get action to take. Ignore error messages and broken packets */
action = ntohl(inpacket[2]);
if (action > 2)
return 1;
/* Generate the connection id we give out and expect to and from
the requesting ip address, this prevents udp spoofing */
udp_make_connectionid(connid, remoteip, 0);
/* Initialise hash pointer */
ws->hash = NULL;
ws->peer_id = NULL;
/* If action is not 0 (connect), then we expect the derived
connection id in first 64 bit */
if ((action > 0) && (inpacket[0] != connid[0] || inpacket[1] != connid[1])) {
/* If connection id does not match, try the one that was
valid in the previous hour. Only if this also does not
match, return an error packet */
udp_make_connectionid(connid, remoteip, 1);
if (inpacket[0] != connid[0] || inpacket[1] != connid[1]) {
const size_t s = sizeof("Connection ID missmatch.");
outpacket[0] = htonl(3);
outpacket[1] = inpacket[3];
memcpy(&outpacket[2], "Connection ID missmatch.", s);
socket_send6(serversocket, ws->outbuf, 8 + s, remoteip, remoteport, 0);
stats_issue_event(EVENT_CONNID_MISSMATCH, FLAG_UDP, 8 + s);
return 1;
}
}
switch (action) {
case 0: /* This is a connect action */
/* look for udp bittorrent magic id */
if ((ntohl(inpacket[0]) != 0x00000417) || (ntohl(inpacket[1]) != 0x27101980))
return 1;
outpacket[0] = 0;
outpacket[1] = inpacket[3];
outpacket[2] = connid[0];
outpacket[3] = connid[1];
socket_send6(serversocket, ws->outbuf, 16, remoteip, remoteport, 0);
stats_issue_event(EVENT_CONNECT, FLAG_UDP, 16);
break;
case 1: /* This is an announce action */
/* Minimum udp announce packet size */
if (byte_count < 98)
return 1;
/* We do only want to know, if it is zero */
left = inpacket[64 / 4] | inpacket[68 / 4];
event = ntohl(inpacket[80 / 4]);
port = *(uint16_t *)(((char *)inpacket) + 96);
ws->hash = (ot_hash *)(((char *)inpacket) + 16);
OT_SETIP(ws->peer, remoteip);
OT_SETPORT(ws->peer, &port);
OT_PEERFLAG(ws->peer) = 0;
switch (event) {
case 1:
OT_PEERFLAG(ws->peer) |= PEER_FLAG_COMPLETED;
break;
case 3:
OT_PEERFLAG(ws->peer) |= PEER_FLAG_STOPPED;
break;
default:
break;
}
if (!left)
OT_PEERFLAG(ws->peer) |= PEER_FLAG_SEEDING;
outpacket[0] = htonl(1); /* announce action */
outpacket[1] = inpacket[12 / 4];
if (OT_PEERFLAG(ws->peer) & PEER_FLAG_STOPPED) { /* Peer is gone. */
ws->reply = ws->outbuf;
ws->reply_size = remove_peer_from_torrent(FLAG_UDP, ws);
} else {
/* Limit amount of peers to OT_MAX_PEERS_UDP */
uint32_t numwant = ntohl(inpacket[92 / 4]);
size_t max_peers = ip6_isv4mapped(remoteip) ? OT_MAX_PEERS_UDP4 : OT_MAX_PEERS_UDP6;
if (numwant > max_peers)
numwant = max_peers;
ws->reply = ws->outbuf + 8;
ws->reply_size = 8 + add_peer_to_torrent_and_return_peers(FLAG_UDP, ws, numwant);
}
socket_send6(serversocket, ws->outbuf, ws->reply_size, remoteip, remoteport, 0);
stats_issue_event(EVENT_ANNOUNCE, FLAG_UDP, ws->reply_size);
break;
case 2: /* This is a scrape action */
outpacket[0] = htonl(2); /* scrape action */
outpacket[1] = inpacket[12 / 4];
for (scrape_count = 0; (scrape_count * 20 < byte_count - 16) && (scrape_count <= 74); scrape_count++)
return_udp_scrape_for_torrent(*(ot_hash *)(((char *)inpacket) + 16 + 20 * scrape_count), ((char *)outpacket) + 8 + 12 * scrape_count);
socket_send6(serversocket, ws->outbuf, 8 + 12 * scrape_count, remoteip, remoteport, 0);
stats_issue_event(EVENT_SCRAPE, FLAG_UDP, scrape_count);
break;
}
return 1;
}
static void *udp_worker(void *args) {
int64 sock = (int64)args;
struct ot_workstruct ws;
memset(&ws, 0, sizeof(ws));
ws.inbuf = malloc(G_INBUF_SIZE);
ws.outbuf = malloc(G_OUTBUF_SIZE);
#ifdef _DEBUG_HTTPERROR
ws.debugbuf = malloc(G_DEBUGBUF_SIZE);
#endif
while (g_opentracker_running)
handle_udp6(sock, &ws);
free(ws.inbuf);
free(ws.outbuf);
#ifdef _DEBUG_HTTPERROR
free(ws.debugbuf);
#endif
return NULL;
}
void udp_init(int64 sock, unsigned int worker_count) {
pthread_t thread_id;
if (!g_rijndael_round_key[0])
udp_generate_rijndael_round_key();
#ifdef _DEBUG
fprintf(stderr, " installing %d workers on udp socket %ld\n", worker_count, (unsigned long)sock);
#endif
while (worker_count--)
pthread_create(&thread_id, NULL, udp_worker, (void *)sock);
}
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