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transmission/libtransmission/handshake.cc

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// This file Copyright © 2017-2022 Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
#include <algorithm>
#include <array>
#include <cerrno>
#include <chrono>
#include <cstring>
#include <string_view>
#include <utility>
#include <event2/buffer.h>
#include <fmt/format.h>
#include "transmission.h"
#include "clients.h"
#include "crypto-utils.h"
#include "handshake.h"
#include "log.h"
#include "peer-io.h"
#include "tr-assert.h"
#include "utils.h"
using namespace std::literals;
/* enable LibTransmission extension protocol */
#define ENABLE_LTEP
/* fast extensions */
#define ENABLE_FAST
/* DHT */
#define ENABLE_DHT
/***
****
***/
#define HANDSHAKE_NAME "\023BitTorrent protocol"
// bittorrent handshake constants
static auto constexpr HANDSHAKE_NAME_LEN = int{ 20 };
static auto constexpr HANDSHAKE_FLAGS_LEN = int{ 8 };
static auto constexpr HANDSHAKE_SIZE = int{ 68 };
static auto constexpr INCOMING_HANDSHAKE_LEN = int{ 48 };
// encryption constants
static auto constexpr PadA_MAXLEN = int{ 512 };
static auto constexpr PadB_MAXLEN = int{ 512 };
static auto constexpr PadC_MAXLEN = int{ 512 };
static auto constexpr CRYPTO_PROVIDE_PLAINTEXT = int{ 1 };
static auto constexpr CRYPTO_PROVIDE_CRYPTO = int{ 2 };
// "VC is a verification constant that is used to verify whether the
// other side knows S and SKEY and thus defeats replay attacks of the
// SKEY hash. As of this version VC is a String of 8 bytes set to 0x00.
using vc_t = std::array<std::byte, 8>;
static auto constexpr VC = vc_t{};
// how long to wait before giving up on a handshake
static auto constexpr HandshakeTimeoutSec = 30s;
#ifdef ENABLE_LTEP
#define HANDSHAKE_HAS_LTEP(bits) (((bits)[5] & 0x10) != 0)
#define HANDSHAKE_SET_LTEP(bits) ((bits)[5] |= 0x10)
#else
#define HANDSHAKE_HAS_LTEP(bits) (false)
#define HANDSHAKE_SET_LTEP(bits) ((void)0)
#endif
#ifdef ENABLE_FAST
#define HANDSHAKE_HAS_FASTEXT(bits) (((bits)[7] & 0x04) != 0)
#define HANDSHAKE_SET_FASTEXT(bits) ((bits)[7] |= 0x04)
#else
#define HANDSHAKE_HAS_FASTEXT(bits) (false)
#define HANDSHAKE_SET_FASTEXT(bits) ((void)0)
#endif
#ifdef ENABLE_DHT
#define HANDSHAKE_HAS_DHT(bits) (((bits)[7] & 0x01) != 0)
#define HANDSHAKE_SET_DHT(bits) ((bits)[7] |= 0x01)
#else
#define HANDSHAKE_HAS_DHT(bits) (false)
#define HANDSHAKE_SET_DHT(bits) ((void)0)
#endif
/**
***
**/
using DH = tr_message_stream_encryption::DH;
enum handshake_state_t
{
/* incoming */
AWAITING_HANDSHAKE,
AWAITING_PEER_ID,
AWAITING_YA,
AWAITING_PAD_A,
AWAITING_CRYPTO_PROVIDE,
AWAITING_PAD_C,
AWAITING_IA,
AWAITING_PAYLOAD_STREAM,
/* outgoing */
AWAITING_YB,
AWAITING_VC,
AWAITING_CRYPTO_SELECT,
AWAITING_PAD_D,
/* */
N_STATES
};
struct tr_handshake
{
tr_handshake(std::shared_ptr<tr_handshake_mediator> mediator_in, tr_encryption_mode encryption_mode_in)
: mediator{ std::move(mediator_in) }
, dh{ mediator->privateKey() }
, encryption_mode{ encryption_mode_in }
{
}
tr_handshake(tr_handshake&&) = delete;
tr_handshake(tr_handshake const&) = delete;
tr_handshake& operator=(tr_handshake&&) = delete;
tr_handshake& operator=(tr_handshake const&) = delete;
~tr_handshake()
{
if (io != nullptr)
{
tr_peerIoUnref(io); /* balanced by the ref in tr_handshakeNew */
}
}
[[nodiscard]] auto constexpr isIncoming() const noexcept
{
return io->isIncoming();
}
std::shared_ptr<tr_handshake_mediator> const mediator;
bool haveReadAnythingFromPeer = false;
bool haveSentBitTorrentHandshake = false;
tr_peerIo* io = nullptr;
DH dh = {};
handshake_state_t state = AWAITING_HANDSHAKE;
tr_encryption_mode encryption_mode;
uint16_t pad_c_len = {};
uint16_t pad_d_len = {};
uint16_t ia_len = {};
uint32_t crypto_select = {};
uint32_t crypto_provide = {};
std::unique_ptr<libtransmission::Timer> timeout_timer;
std::optional<tr_peer_id_t> peer_id;
tr_handshake_done_func done_func = nullptr;
void* done_func_user_data = nullptr;
};
/**
***
**/
#define tr_logAddTraceHand(handshake, msg) tr_logAddTrace(msg, (handshake)->io->addrStr())
static char const* getStateName(handshake_state_t const state)
{
static char const* const state_strings[N_STATES] = {
"awaiting handshake", /* AWAITING_HANDSHAKE */
"awaiting peer id", /* AWAITING_PEER_ID */
"awaiting ya", /* AWAITING_YA */
"awaiting pad a", /* AWAITING_PAD_A */
"awaiting crypto_provide", /* AWAITING_CRYPTO_PROVIDE */
"awaiting pad c", /* AWAITING_PAD_C */
"awaiting ia", /* AWAITING_IA */
"awaiting payload stream", /* AWAITING_PAYLOAD_STREAM */
"awaiting yb", /* AWAITING_YB */
"awaiting vc", /* AWAITING_VC */
"awaiting crypto select", /* AWAITING_CRYPTO_SELECT */
"awaiting pad d" /* AWAITING_PAD_D */
};
return state < N_STATES ? state_strings[state] : "unknown state";
}
static void setState(tr_handshake* handshake, handshake_state_t state)
{
tr_logAddTraceHand(handshake, fmt::format("setting to state [{}]", getStateName(state)));
handshake->state = state;
}
static void setReadState(tr_handshake* handshake, handshake_state_t state)
{
setState(handshake, state);
}
static bool buildHandshakeMessage(tr_handshake* handshake, uint8_t* buf)
{
auto const info_hash = handshake->io->torrentHash();
auto const info = info_hash ? handshake->mediator->torrentInfo(*info_hash) : std::nullopt;
if (!info)
{
return false;
}
uint8_t* walk = buf;
walk = std::copy_n(HANDSHAKE_NAME, HANDSHAKE_NAME_LEN, walk);
memset(walk, 0, HANDSHAKE_FLAGS_LEN);
HANDSHAKE_SET_LTEP(walk);
HANDSHAKE_SET_FASTEXT(walk);
/* Note that this doesn't depend on whether the torrent is private.
* We don't accept DHT peers for a private torrent,
* but we participate in the DHT regardless. */
if (handshake->mediator->isDHTEnabled())
{
HANDSHAKE_SET_DHT(walk);
}
walk += HANDSHAKE_FLAGS_LEN;
walk = std::copy_n(reinterpret_cast<char const*>(std::data(*info_hash)), std::size(*info_hash), walk);
walk = std::copy(std::begin(info->client_peer_id), std::end(info->client_peer_id), walk);
TR_ASSERT(walk - buf == HANDSHAKE_SIZE);
return true;
}
static ReadState tr_handshakeDone(tr_handshake* handshake, bool is_connected);
enum handshake_parse_err_t
{
HANDSHAKE_OK,
HANDSHAKE_ENCRYPTION_WRONG,
HANDSHAKE_BAD_TORRENT,
HANDSHAKE_PEER_IS_SELF,
};
static handshake_parse_err_t parseHandshake(tr_handshake* handshake, struct evbuffer* inbuf)
{
uint8_t name[HANDSHAKE_NAME_LEN];
uint8_t reserved[HANDSHAKE_FLAGS_LEN];
tr_logAddTraceHand(handshake, fmt::format("payload: need {}, got {}", HANDSHAKE_SIZE, evbuffer_get_length(inbuf)));
if (evbuffer_get_length(inbuf) < HANDSHAKE_SIZE)
{
return HANDSHAKE_ENCRYPTION_WRONG;
}
/* confirm the protocol */
tr_peerIoReadBytes(handshake->io, inbuf, name, HANDSHAKE_NAME_LEN);
if (memcmp(name, HANDSHAKE_NAME, HANDSHAKE_NAME_LEN) != 0)
{
return HANDSHAKE_ENCRYPTION_WRONG;
}
/* read the reserved bytes */
tr_peerIoReadBytes(handshake->io, inbuf, reserved, HANDSHAKE_FLAGS_LEN);
/* torrent hash */
auto hash = tr_sha1_digest_t{};
tr_peerIoReadBytes(handshake->io, inbuf, std::data(hash), std::size(hash));
if (auto const torrent_hash = handshake->io->torrentHash(); !torrent_hash || *torrent_hash != hash)
{
tr_logAddTraceHand(handshake, "peer returned the wrong hash. wtf?");
return HANDSHAKE_BAD_TORRENT;
}
// peer_id
auto peer_id = tr_peer_id_t{};
tr_peerIoReadBytes(handshake->io, inbuf, std::data(peer_id), std::size(peer_id));
handshake->peer_id = peer_id;
/* peer id */
auto const peer_id_sv = std::string_view{ std::data(peer_id), std::size(peer_id) };
tr_logAddTraceHand(handshake, fmt::format("peer-id is '{}'", peer_id_sv));
if (auto const info = handshake->mediator->torrentInfo(hash); info && info->client_peer_id == peer_id)
{
tr_logAddTraceHand(handshake, "streuth! we've connected to ourselves.");
return HANDSHAKE_PEER_IS_SELF;
}
/**
*** Extensions
**/
handshake->io->enableDHT(HANDSHAKE_HAS_DHT(reserved));
handshake->io->enableLTEP(HANDSHAKE_HAS_LTEP(reserved));
handshake->io->enableFEXT(HANDSHAKE_HAS_FASTEXT(reserved));
return HANDSHAKE_OK;
}
/***
****
**** OUTGOING CONNECTIONS
****
***/
template<size_t PadMax>
static void sendPublicKeyAndPad(tr_handshake* handshake)
{
auto const public_key = handshake->dh.publicKey();
auto outbuf = std::array<std::byte, std::size(public_key) + PadMax>{};
auto const data = std::data(outbuf);
auto walk = data;
walk = std::copy(std::begin(public_key), std::end(public_key), walk);
walk += handshake->mediator->pad(walk, PadMax);
tr_peerIoWriteBytes(handshake->io, data, walk - data, false);
}
// 1 A->B: our public key (Ya) and some padding (PadA)
static void sendYa(tr_handshake* handshake)
{
sendPublicKeyAndPad<PadA_MAXLEN>(handshake);
setReadState(handshake, AWAITING_YB);
}
static uint32_t getCryptoProvide(tr_handshake const* handshake)
{
uint32_t provide = 0;
switch (handshake->encryption_mode)
{
case TR_ENCRYPTION_REQUIRED:
case TR_ENCRYPTION_PREFERRED:
provide |= CRYPTO_PROVIDE_CRYPTO;
break;
case TR_CLEAR_PREFERRED:
provide |= CRYPTO_PROVIDE_CRYPTO | CRYPTO_PROVIDE_PLAINTEXT;
break;
}
return provide;
}
static uint32_t getCryptoSelect(tr_handshake const* handshake, uint32_t crypto_provide)
{
uint32_t choices[2];
int nChoices = 0;
switch (handshake->encryption_mode)
{
case TR_ENCRYPTION_REQUIRED:
choices[nChoices++] = CRYPTO_PROVIDE_CRYPTO;
break;
case TR_ENCRYPTION_PREFERRED:
choices[nChoices++] = CRYPTO_PROVIDE_CRYPTO;
choices[nChoices++] = CRYPTO_PROVIDE_PLAINTEXT;
break;
case TR_CLEAR_PREFERRED:
choices[nChoices++] = CRYPTO_PROVIDE_PLAINTEXT;
choices[nChoices++] = CRYPTO_PROVIDE_CRYPTO;
break;
}
for (int i = 0; i < nChoices; ++i)
{
if ((crypto_provide & choices[i]) != 0)
{
return choices[i];
}
}
return 0;
}
static ReadState readYb(tr_handshake* handshake, struct evbuffer* inbuf)
{
size_t needlen = HANDSHAKE_NAME_LEN;
if (evbuffer_get_length(inbuf) < needlen)
{
return READ_LATER;
}
bool const isEncrypted = memcmp(evbuffer_pullup(inbuf, HANDSHAKE_NAME_LEN), HANDSHAKE_NAME, HANDSHAKE_NAME_LEN) != 0;
auto peer_public_key = DH::key_bigend_t{};
if (isEncrypted)
{
needlen = std::size(peer_public_key);
if (evbuffer_get_length(inbuf) < needlen)
{
return READ_LATER;
}
}
tr_logAddTraceHand(handshake, isEncrypted ? "got an encrypted handshake" : "got a plain handshake");
if (!isEncrypted)
{
setState(handshake, AWAITING_HANDSHAKE);
return READ_NOW;
}
handshake->haveReadAnythingFromPeer = true;
// get the peer's public key
evbuffer_remove(inbuf, std::data(peer_public_key), std::size(peer_public_key));
handshake->dh.setPeerPublicKey(peer_public_key);
/* now send these: HASH('req1', S), HASH('req2', SKEY) xor HASH('req3', S),
* ENCRYPT(VC, crypto_provide, len(PadC), PadC, len(IA)), ENCRYPT(IA) */
evbuffer* const outbuf = evbuffer_new();
/* HASH('req1', S) */
auto const req1 = tr_sha1::digest("req1"sv, handshake->dh.secret());
evbuffer_add(outbuf, std::data(req1), std::size(req1));
auto const info_hash = handshake->io->torrentHash();
if (!info_hash)
{
tr_logAddTraceHand(handshake, "error while computing req2/req3 hash after Yb");
return tr_handshakeDone(handshake, false);
}
/* HASH('req2', SKEY) xor HASH('req3', S) */
{
auto const req2 = tr_sha1::digest("req2"sv, *info_hash);
auto const req3 = tr_sha1::digest("req3"sv, handshake->dh.secret());
auto buf = tr_sha1_digest_t{};
for (size_t i = 0, n = std::size(buf); i < n; ++i)
{
buf[i] = req2[i] ^ req3[i];
}
evbuffer_add(outbuf, std::data(buf), std::size(buf));
}
/* ENCRYPT(VC, crypto_provide, len(PadC), PadC
* PadC is reserved for future extensions to the handshake...
* standard practice at this time is for it to be zero-length */
tr_peerIoWriteBuf(handshake->io, outbuf, false);
handshake->io->encryptInit(handshake->io->isIncoming(), handshake->dh, *info_hash);
evbuffer_add(outbuf, std::data(VC), std::size(VC));
evbuffer_add_uint32(outbuf, getCryptoProvide(handshake));
evbuffer_add_uint16(outbuf, 0);
/* ENCRYPT len(IA)), ENCRYPT(IA) */
if (uint8_t msg[HANDSHAKE_SIZE]; buildHandshakeMessage(handshake, msg))
{
evbuffer_add_uint16(outbuf, sizeof(msg));
evbuffer_add(outbuf, msg, sizeof(msg));
handshake->haveSentBitTorrentHandshake = true;
}
else
{
return tr_handshakeDone(handshake, false);
}
/* send it */
handshake->io->decryptInit(handshake->io->isIncoming(), handshake->dh, *info_hash);
setReadState(handshake, AWAITING_VC);
tr_peerIoWriteBuf(handshake->io, outbuf, false);
/* cleanup */
evbuffer_free(outbuf);
return READ_NOW;
}
// MSE spec: "Since the length of [PadB is] unknown,
// A will be able to resynchronize on ENCRYPT(VC)"
static ReadState readVC(tr_handshake* handshake, struct evbuffer* inbuf)
{
// find the end of PadB by looking for `ENCRYPT(VC)`
auto needle = VC;
auto filter = tr_message_stream_encryption::Filter{};
filter.encryptInit(true, handshake->dh, *handshake->io->torrentHash());
filter.encrypt(std::size(needle), std::data(needle));
for (size_t i = 0; i < PadB_MAXLEN; ++i)
{
if (evbuffer_get_length(inbuf) < std::size(needle))
{
tr_logAddTraceHand(handshake, "not enough bytes... returning read_more");
return READ_LATER;
}
auto const* peek = reinterpret_cast<std::byte const*>(evbuffer_pullup(inbuf, std::size(needle)));
if (std::equal(std::begin(needle), std::end(needle), peek))
{
tr_logAddTraceHand(handshake, "got it!");
// We already know it's a match; now we just need to
// consume it from the read buffer.
tr_peerIoReadBytes(handshake->io, inbuf, std::data(needle), std::size(needle));
setState(handshake, AWAITING_CRYPTO_SELECT);
return READ_NOW;
}
evbuffer_drain(inbuf, 1);
}
tr_logAddTraceHand(handshake, "couldn't find ENCRYPT(VC)");
return tr_handshakeDone(handshake, false);
}
static ReadState readCryptoSelect(tr_handshake* handshake, struct evbuffer* inbuf)
{
static size_t const needlen = sizeof(uint32_t) + sizeof(uint16_t);
if (evbuffer_get_length(inbuf) < needlen)
{
return READ_LATER;
}
uint32_t crypto_select = 0;
tr_peerIoReadUint32(handshake->io, inbuf, &crypto_select);
handshake->crypto_select = crypto_select;
tr_logAddTraceHand(handshake, fmt::format("crypto select is {}", crypto_select));
if ((crypto_select & getCryptoProvide(handshake)) == 0)
{
tr_logAddTraceHand(handshake, "peer selected an encryption option we didn't offer");
return tr_handshakeDone(handshake, false);
}
uint16_t pad_d_len = 0;
tr_peerIoReadUint16(handshake->io, inbuf, &pad_d_len);
tr_logAddTraceHand(handshake, fmt::format("pad_d_len is {}", pad_d_len));
if (pad_d_len > 512)
{
tr_logAddTraceHand(handshake, "encryption handshake: pad_d_len is too long");
return tr_handshakeDone(handshake, false);
}
handshake->pad_d_len = pad_d_len;
setState(handshake, AWAITING_PAD_D);
return READ_NOW;
}
static ReadState readPadD(tr_handshake* handshake, struct evbuffer* inbuf)
{
size_t const needlen = handshake->pad_d_len;
tr_logAddTraceHand(handshake, fmt::format("pad d: need {}, got {}", needlen, evbuffer_get_length(inbuf)));
if (evbuffer_get_length(inbuf) < needlen)
{
return READ_LATER;
}
tr_peerIoDrain(handshake->io, inbuf, needlen);
setState(handshake, AWAITING_HANDSHAKE);
return READ_NOW;
}
/***
****
**** INCOMING CONNECTIONS
****
***/
static ReadState readHandshake(tr_handshake* handshake, struct evbuffer* inbuf)
{
tr_logAddTraceHand(handshake, fmt::format("payload: need {}, got {}", INCOMING_HANDSHAKE_LEN, evbuffer_get_length(inbuf)));
if (evbuffer_get_length(inbuf) < INCOMING_HANDSHAKE_LEN)
{
return READ_LATER;
}
handshake->haveReadAnythingFromPeer = true;
uint8_t pstrlen = evbuffer_pullup(inbuf, 1)[0]; /* peek, don't read. We may be handing inbuf to AWAITING_YA */
if (pstrlen == 19) /* unencrypted */
{
if (handshake->encryption_mode == TR_ENCRYPTION_REQUIRED)
{
tr_logAddTraceHand(handshake, "peer is unencrypted, and we're disallowing that");
return tr_handshakeDone(handshake, false);
}
}
else /* encrypted or corrupt */
{
if (handshake->isIncoming())
{
tr_logAddTraceHand(handshake, "I think peer is sending us an encrypted handshake...");
setState(handshake, AWAITING_YA);
return READ_NOW;
}
handshake->io->decrypt(1, &pstrlen);
if (pstrlen != 19)
{
tr_logAddTraceHand(handshake, "I think peer has sent us a corrupt handshake...");
return tr_handshakeDone(handshake, false);
}
}
evbuffer_drain(inbuf, 1);
/* pstr (BitTorrent) */
TR_ASSERT(pstrlen == 19);
uint8_t pstr[20];
tr_peerIoReadBytes(handshake->io, inbuf, pstr, pstrlen);
pstr[pstrlen] = '\0';
if (strncmp((char const*)pstr, "BitTorrent protocol", 19) != 0)
{
return tr_handshakeDone(handshake, false);
}
/* reserved bytes */
uint8_t reserved[HANDSHAKE_FLAGS_LEN];
tr_peerIoReadBytes(handshake->io, inbuf, reserved, sizeof(reserved));
/**
*** Extensions
**/
handshake->io->enableDHT(HANDSHAKE_HAS_DHT(reserved));
handshake->io->enableLTEP(HANDSHAKE_HAS_LTEP(reserved));
handshake->io->enableFEXT(HANDSHAKE_HAS_FASTEXT(reserved));
/* torrent hash */
auto hash = tr_sha1_digest_t{};
tr_peerIoReadBytes(handshake->io, inbuf, std::data(hash), std::size(hash));
if (handshake->isIncoming())
{
if (!handshake->mediator->torrentInfo(hash))
{
tr_logAddTraceHand(handshake, "peer is trying to connect to us for a torrent we don't have.");
return tr_handshakeDone(handshake, false);
}
handshake->io->setTorrentHash(hash);
}
else /* outgoing */
{
auto const torrent_hash = handshake->io->torrentHash();
if (!torrent_hash || *torrent_hash != hash)
{
tr_logAddTraceHand(handshake, "peer returned the wrong hash. wtf?");
return tr_handshakeDone(handshake, false);
}
}
/**
*** If it's an incoming message, we need to send a response handshake
**/
if (!handshake->haveSentBitTorrentHandshake)
{
uint8_t msg[HANDSHAKE_SIZE];
if (!buildHandshakeMessage(handshake, msg))
{
return tr_handshakeDone(handshake, false);
}
tr_peerIoWriteBytes(handshake->io, msg, sizeof(msg), false);
handshake->haveSentBitTorrentHandshake = true;
}
setReadState(handshake, AWAITING_PEER_ID);
return READ_NOW;
}
static ReadState readPeerId(tr_handshake* handshake, struct evbuffer* inbuf)
{
// read the peer_id
auto peer_id = tr_peer_id_t{};
if (evbuffer_get_length(inbuf) < std::size(peer_id))
{
return READ_LATER;
}
tr_peerIoReadBytes(handshake->io, inbuf, std::data(peer_id), std::size(peer_id));
handshake->peer_id = peer_id;
char client[128] = {};
tr_clientForId(client, sizeof(client), peer_id);
tr_logAddTraceHand(handshake, fmt::format("peer-id is '{}' ... isIncoming is {}", client, handshake->isIncoming()));
// if we've somehow connected to ourselves, don't keep the connection
auto const hash = handshake->io->torrentHash();
auto const info = hash ? handshake->mediator->torrentInfo(*hash) : std::nullopt;
auto const connected_to_self = info && info->client_peer_id == peer_id;
return tr_handshakeDone(handshake, !connected_to_self);
}
static ReadState readYa(tr_handshake* handshake, struct evbuffer* inbuf)
{
auto peer_public_key = DH::key_bigend_t{};
tr_logAddTraceHand(
handshake,
fmt::format("in readYa... need {}, have {}", std::size(peer_public_key), evbuffer_get_length(inbuf)));
if (evbuffer_get_length(inbuf) < std::size(peer_public_key))
{
return READ_LATER;
}
/* read the incoming peer's public key */
evbuffer_remove(inbuf, std::data(peer_public_key), std::size(peer_public_key));
handshake->dh.setPeerPublicKey(peer_public_key);
// send our public key to the peer
tr_logAddTraceHand(handshake, "sending B->A: Diffie Hellman Yb, PadB");
sendPublicKeyAndPad<PadB_MAXLEN>(handshake);
setReadState(handshake, AWAITING_PAD_A);
return READ_NOW;
}
static ReadState readPadA(tr_handshake* handshake, struct evbuffer* inbuf)
{
// find the end of PadA by looking for HASH('req1', S)
auto const needle = tr_sha1::digest("req1"sv, handshake->dh.secret());
for (size_t i = 0; i < PadA_MAXLEN; ++i)
{
if (evbuffer_get_length(inbuf) < std::size(needle))
{
tr_logAddTraceHand(handshake, "not enough bytes... returning read_more");
return READ_LATER;
}
auto const* peek = reinterpret_cast<std::byte const*>(evbuffer_pullup(inbuf, std::size(needle)));
if (std::equal(std::begin(needle), std::end(needle), peek))
{
tr_logAddTraceHand(handshake, "found it... looking setting to awaiting_crypto_provide");
evbuffer_drain(inbuf, std::size(needle));
setState(handshake, AWAITING_CRYPTO_PROVIDE);
return READ_NOW;
}
evbuffer_drain(inbuf, 1);
}
tr_logAddTraceHand(handshake, "couldn't find HASH('req', S)");
return tr_handshakeDone(handshake, false);
}
static ReadState readCryptoProvide(tr_handshake* handshake, struct evbuffer* inbuf)
{
/* HASH('req2', SKEY) xor HASH('req3', S), ENCRYPT(VC, crypto_provide, len(PadC)) */
uint16_t padc_len = 0;
uint32_t crypto_provide = 0;
size_t const needlen = SHA_DIGEST_LENGTH + /* HASH('req2', SKEY) xor HASH('req3', S) */
std::size(VC) + sizeof(crypto_provide) + sizeof(padc_len);
if (evbuffer_get_length(inbuf) < needlen)
{
return READ_LATER;
}
/* This next piece is HASH('req2', SKEY) xor HASH('req3', S) ...
* we can get the first half of that (the obfuscatedTorrentHash)
* by building the latter and xor'ing it with what the peer sent us */
tr_logAddTraceHand(handshake, "reading obfuscated torrent hash...");
auto req2 = tr_sha1_digest_t{};
evbuffer_remove(inbuf, std::data(req2), std::size(req2));
auto const req3 = tr_sha1::digest("req3"sv, handshake->dh.secret());
auto obfuscated_hash = tr_sha1_digest_t{};
for (size_t i = 0; i < std::size(obfuscated_hash); ++i)
{
obfuscated_hash[i] = req2[i] ^ req3[i];
}
if (auto const info = handshake->mediator->torrentInfoFromObfuscated(obfuscated_hash); info)
{
bool const client_is_seed = info->is_done;
bool const peer_is_seed = handshake->mediator->isPeerKnownSeed(info->id, handshake->io->address());
tr_logAddTraceHand(handshake, fmt::format("got INCOMING connection's encrypted handshake for torrent [{}]", info->id));
handshake->io->setTorrentHash(info->info_hash);
if (client_is_seed && peer_is_seed)
{
tr_logAddTraceHand(handshake, "another seed tried to reconnect to us!");
return tr_handshakeDone(handshake, false);
}
}
else
{
tr_logAddTraceHand(handshake, "can't find that torrent...");
return tr_handshakeDone(handshake, false);
}
/* next part: ENCRYPT(VC, crypto_provide, len(PadC), */
handshake->io->decryptInit(handshake->io->isIncoming(), handshake->dh, *handshake->io->torrentHash());
auto vc_in = vc_t{};
tr_peerIoReadBytes(handshake->io, inbuf, std::data(vc_in), std::size(vc_in));
tr_peerIoReadUint32(handshake->io, inbuf, &crypto_provide);
handshake->crypto_provide = crypto_provide;
tr_logAddTraceHand(handshake, fmt::format("crypto_provide is {}", crypto_provide));
tr_peerIoReadUint16(handshake->io, inbuf, &padc_len);
tr_logAddTraceHand(handshake, fmt::format("padc is {}", padc_len));
if (padc_len > PadC_MAXLEN)
{
tr_logAddTraceHand(handshake, "peer's PadC is too big");
return tr_handshakeDone(handshake, false);
}
handshake->pad_c_len = padc_len;
setState(handshake, AWAITING_PAD_C);
return READ_NOW;
}
static ReadState readPadC(tr_handshake* handshake, struct evbuffer* inbuf)
{
uint16_t ia_len = 0;
if (auto const needlen = handshake->pad_c_len + sizeof(uint16_t); evbuffer_get_length(inbuf) < needlen)
{
return READ_LATER;
}
// read the throwaway padc
auto pad_c = std::array<char, PadC_MAXLEN>{};
tr_peerIoReadBytes(handshake->io, inbuf, std::data(pad_c), handshake->pad_c_len);
/* read ia_len */
tr_peerIoReadUint16(handshake->io, inbuf, &ia_len);
tr_logAddTraceHand(handshake, fmt::format("ia_len is {}", ia_len));
handshake->ia_len = ia_len;
setState(handshake, AWAITING_IA);
return READ_NOW;
}
static ReadState readIA(tr_handshake* handshake, struct evbuffer const* inbuf)
{
size_t const needlen = handshake->ia_len;
tr_logAddTraceHand(handshake, fmt::format("reading IA... have {}, need {}", evbuffer_get_length(inbuf), needlen));
if (evbuffer_get_length(inbuf) < needlen)
{
return READ_LATER;
}
/**
*** B->A: ENCRYPT(VC, crypto_select, len(padD), padD), ENCRYPT2(Payload Stream)
**/
handshake->io->encryptInit(handshake->io->isIncoming(), handshake->dh, *handshake->io->torrentHash());
evbuffer* const outbuf = evbuffer_new();
// send VC
tr_logAddTraceHand(handshake, "sending vc");
evbuffer_add(outbuf, std::data(VC), std::size(VC));
/* send crypto_select */
uint32_t const crypto_select = getCryptoSelect(handshake, handshake->crypto_provide);
if (crypto_select != 0)
{
tr_logAddTraceHand(handshake, fmt::format("selecting crypto mode '{}'", crypto_select));
evbuffer_add_uint32(outbuf, crypto_select);
}
else
{
tr_logAddTraceHand(handshake, "peer didn't offer an encryption mode we like.");
evbuffer_free(outbuf);
return tr_handshakeDone(handshake, false);
}
tr_logAddTraceHand(handshake, "sending pad d");
/* ENCRYPT(VC, crypto_provide, len(PadD), PadD
* PadD is reserved for future extensions to the handshake...
* standard practice at this time is for it to be zero-length */
{
uint16_t const len = 0;
evbuffer_add_uint16(outbuf, len);
}
/* maybe de-encrypt our connection */
if (crypto_select == CRYPTO_PROVIDE_PLAINTEXT)
{
tr_peerIoWriteBuf(handshake->io, outbuf, false);
}
tr_logAddTraceHand(handshake, "sending handshake");
/* send our handshake */
if (uint8_t msg[HANDSHAKE_SIZE]; buildHandshakeMessage(handshake, msg))
{
evbuffer_add(outbuf, msg, sizeof(msg));
handshake->haveSentBitTorrentHandshake = true;
}
else
{
return tr_handshakeDone(handshake, false);
}
/* send it out */
tr_peerIoWriteBuf(handshake->io, outbuf, false);
evbuffer_free(outbuf);
/* now await the handshake */
setState(handshake, AWAITING_PAYLOAD_STREAM);
return READ_NOW;
}
static ReadState readPayloadStream(tr_handshake* handshake, struct evbuffer* inbuf)
{
size_t const needlen = HANDSHAKE_SIZE;
tr_logAddTraceHand(
handshake,
fmt::format("reading payload stream... have {}, need {}", evbuffer_get_length(inbuf), needlen));
if (evbuffer_get_length(inbuf) < needlen)
{
return READ_LATER;
}
/* parse the handshake ... */
handshake_parse_err_t const i = parseHandshake(handshake, inbuf);
tr_logAddTraceHand(handshake, fmt::format("parseHandshake returned {}", i));
if (i != HANDSHAKE_OK)
{
return tr_handshakeDone(handshake, false);
}
/* we've completed the BT handshake... pass the work on to peer-msgs */
return tr_handshakeDone(handshake, true);
}
/***
****
****
****
***/
static ReadState canRead(tr_peerIo* io, void* vhandshake, size_t* piece)
{
TR_ASSERT(tr_isPeerIo(io));
auto* handshake = static_cast<tr_handshake*>(vhandshake);
evbuffer* const inbuf = io->getReadBuffer();
bool readyForMore = true;
/* no piece data in handshake */
*piece = 0;
tr_logAddTraceHand(handshake, fmt::format("handling canRead; state is [{}]", getStateName(handshake->state)));
ReadState ret = READ_NOW;
while (readyForMore)
{
switch (handshake->state)
{
case AWAITING_HANDSHAKE:
ret = readHandshake(handshake, inbuf);
break;
case AWAITING_PEER_ID:
ret = readPeerId(handshake, inbuf);
break;
case AWAITING_YA:
ret = readYa(handshake, inbuf);
break;
case AWAITING_PAD_A:
ret = readPadA(handshake, inbuf);
break;
case AWAITING_CRYPTO_PROVIDE:
ret = readCryptoProvide(handshake, inbuf);
break;
case AWAITING_PAD_C:
ret = readPadC(handshake, inbuf);
break;
case AWAITING_IA:
ret = readIA(handshake, inbuf);
break;
case AWAITING_PAYLOAD_STREAM:
ret = readPayloadStream(handshake, inbuf);
break;
case AWAITING_YB:
ret = readYb(handshake, inbuf);
break;
case AWAITING_VC:
ret = readVC(handshake, inbuf);
break;
case AWAITING_CRYPTO_SELECT:
ret = readCryptoSelect(handshake, inbuf);
break;
case AWAITING_PAD_D:
ret = readPadD(handshake, inbuf);
break;
default:
#ifdef TR_ENABLE_ASSERTS
TR_ASSERT_MSG(false, fmt::format(FMT_STRING("unhandled handshake state {:d}"), handshake->state));
#else
ret = READ_ERR;
break;
#endif
}
if (ret != READ_NOW)
{
readyForMore = false;
}
else if (handshake->state == AWAITING_PAD_C)
{
readyForMore = evbuffer_get_length(inbuf) >= handshake->pad_c_len;
}
else if (handshake->state == AWAITING_PAD_D)
{
readyForMore = evbuffer_get_length(inbuf) >= handshake->pad_d_len;
}
else if (handshake->state == AWAITING_IA)
{
readyForMore = evbuffer_get_length(inbuf) >= handshake->ia_len;
}
}
return ret;
}
static bool fireDoneFunc(tr_handshake* handshake, bool isConnected)
{
auto result = tr_handshake_result{};
result.handshake = handshake;
result.io = handshake->io;
result.readAnythingFromPeer = handshake->haveReadAnythingFromPeer;
result.isConnected = isConnected;
result.userData = handshake->done_func_user_data;
result.peer_id = handshake->peer_id;
bool const success = (*handshake->done_func)(result);
return success;
}
static ReadState tr_handshakeDone(tr_handshake* handshake, bool is_connected)
{
tr_logAddTraceHand(handshake, is_connected ? "handshakeDone: connected" : "handshakeDone: aborting");
tr_peerIoSetIOFuncs(handshake->io, nullptr, nullptr, nullptr, nullptr);
bool const success = fireDoneFunc(handshake, is_connected);
delete handshake;
return success ? READ_LATER : READ_ERR;
}
void tr_handshakeAbort(tr_handshake* handshake)
{
if (handshake != nullptr)
{
tr_handshakeDone(handshake, false);
}
}
static void gotError(tr_peerIo* io, short what, void* vhandshake)
{
int const errcode = errno;
auto* handshake = static_cast<tr_handshake*>(vhandshake);
if (io->socket.type == TR_PEER_SOCKET_TYPE_UTP && !io->isIncoming() && handshake->state == AWAITING_YB)
{
// the peer probably doesn't speak uTP.
auto const hash = io->torrentHash();
auto const info = hash ? handshake->mediator->torrentInfo(*hash) : std::nullopt;
/* Don't mark a peer as non-uTP unless it's really a connect failure. */
if ((errcode == ETIMEDOUT || errcode == ECONNREFUSED) && info)
{
handshake->mediator->setUTPFailed(*hash, io->address());
}
if (tr_peerIoReconnect(handshake->io) == 0)
{
uint8_t msg[HANDSHAKE_SIZE];
buildHandshakeMessage(handshake, msg);
handshake->haveSentBitTorrentHandshake = true;
setReadState(handshake, AWAITING_HANDSHAKE);
tr_peerIoWriteBytes(handshake->io, msg, sizeof(msg), false);
}
}
/* if the error happened while we were sending a public key, we might
* have encountered a peer that doesn't do encryption... reconnect and
* try a plaintext handshake */
if ((handshake->state == AWAITING_YB || handshake->state == AWAITING_VC) &&
handshake->encryption_mode != TR_ENCRYPTION_REQUIRED && tr_peerIoReconnect(handshake->io) == 0)
{
uint8_t msg[HANDSHAKE_SIZE];
tr_logAddTraceHand(handshake, "handshake failed, trying plaintext...");
buildHandshakeMessage(handshake, msg);
handshake->haveSentBitTorrentHandshake = true;
setReadState(handshake, AWAITING_HANDSHAKE);
tr_peerIoWriteBytes(handshake->io, msg, sizeof(msg), false);
}
else
{
tr_logAddTraceHand(
handshake,
fmt::format("libevent got an error what=={}, errno={} ({})", what, errcode, tr_strerror(errcode)));
tr_handshakeDone(handshake, false);
}
}
/**
***
**/
tr_handshake* tr_handshakeNew(
std::shared_ptr<tr_handshake_mediator> mediator,
tr_peerIo* io,
tr_encryption_mode encryption_mode,
tr_handshake_done_func done_func,
void* done_func_user_data)
{
auto* const handshake = new tr_handshake{ std::move(mediator), encryption_mode };
handshake->io = io;
handshake->done_func = done_func;
handshake->done_func_user_data = done_func_user_data;
handshake->timeout_timer = handshake->mediator->createTimer();
handshake->timeout_timer->setCallback([handshake]() { tr_handshakeAbort(handshake); });
handshake->timeout_timer->startSingleShot(HandshakeTimeoutSec);
tr_peerIoRef(io); /* balanced by the unref in ~tr_handshake() */
tr_peerIoSetIOFuncs(handshake->io, canRead, nullptr, gotError, handshake);
if (handshake->isIncoming())
{
setReadState(handshake, AWAITING_HANDSHAKE);
}
else if (encryption_mode != TR_CLEAR_PREFERRED)
{
sendYa(handshake);
}
else
{
uint8_t msg[HANDSHAKE_SIZE];
buildHandshakeMessage(handshake, msg);
handshake->haveSentBitTorrentHandshake = true;
setReadState(handshake, AWAITING_HANDSHAKE);
tr_peerIoWriteBytes(handshake->io, msg, sizeof(msg), false);
}
return handshake;
}
tr_peerIo* tr_handshakeStealIO(tr_handshake* handshake)
{
TR_ASSERT(handshake != nullptr);
TR_ASSERT(handshake->io != nullptr);
tr_peerIo* io = handshake->io;
handshake->io = nullptr;
return io;
}
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