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transmission/libtransmission/handshake.c

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/*
* This file Copyright (C) Mnemosyne LLC
*
* This file is licensed by the GPL version 2. Works owned by the
* Transmission project are granted a special exemption to clause 2 (b)
* so that the bulk of its code can remain under the MIT license.
* This exemption does not extend to derived works not owned by
* the Transmission project.
*
* $Id$
*/
#include <assert.h>
#include <errno.h>
#include <string.h> /* strcmp (), strlen () */
#include <event2/buffer.h>
#include <event2/event.h>
#include "transmission.h"
#include "clients.h"
#include "crypto.h"
#include "handshake.h"
#include "log.h"
#include "peer-io.h"
#include "peer-mgr.h"
#include "session.h"
#include "torrent.h"
#include "tr-dht.h"
#include "utils.h"
/* enable LibTransmission extension protocol */
#define ENABLE_LTEP * /
/* fast extensions */
#define ENABLE_FAST * /
/* DHT */
#define ENABLE_DHT * /
/***
****
***/
#define HANDSHAKE_NAME "\023BitTorrent protocol"
enum
{
/* BitTorrent Handshake Constants */
HANDSHAKE_NAME_LEN = 20,
HANDSHAKE_FLAGS_LEN = 8,
HANDSHAKE_SIZE = 68,
INCOMING_HANDSHAKE_LEN = 48,
/* Encryption Constants */
PadA_MAXLEN = 512,
PadB_MAXLEN = 512,
PadC_MAXLEN = 512,
PadD_MAXLEN = 512,
VC_LENGTH = 8,
CRYPTO_PROVIDE_PLAINTEXT = 1,
CRYPTO_PROVIDE_CRYPTO = 2,
/* how long to wait before giving up on a handshake */
HANDSHAKE_TIMEOUT_SEC = 30
};
#ifdef ENABLE_LTEP
#define HANDSHAKE_HAS_LTEP(bits)(((bits)[5] & 0x10) ? 1 : 0)
#define HANDSHAKE_SET_LTEP(bits)((bits)[5] |= 0x10)
#else
#define HANDSHAKE_HAS_LTEP(bits)(0)
#define HANDSHAKE_SET_LTEP(bits)((void)0)
#endif
#ifdef ENABLE_FAST
#define HANDSHAKE_HAS_FASTEXT(bits)(((bits)[7] & 0x04) ? 1 : 0)
#define HANDSHAKE_SET_FASTEXT(bits)((bits)[7] |= 0x04)
#else
#define HANDSHAKE_HAS_FASTEXT(bits)(0)
#define HANDSHAKE_SET_FASTEXT(bits)((void)0)
#endif
#ifdef ENABLE_DHT
#define HANDSHAKE_HAS_DHT(bits)(((bits)[7] & 0x01) ? 1 : 0)
#define HANDSHAKE_SET_DHT(bits)((bits)[7] |= 0x01)
#else
#define HANDSHAKE_HAS_DHT(bits)(0)
#define HANDSHAKE_SET_DHT(bits)((void)0)
#endif
/* http://www.azureuswiki.com/index.php/Extension_negotiation_protocol
these macros are to be used if both extended messaging and the
azureus protocol is supported, they indicate which protocol is preferred */
#define HANDSHAKE_GET_EXTPREF(reserved) ((reserved)[5] & 0x03)
#define HANDSHAKE_SET_EXTPREF(reserved, val)((reserved)[5] |= 0x03 & (val))
typedef uint8_t handshake_state_t;
struct tr_handshake
{
bool haveReadAnythingFromPeer;
bool havePeerID;
bool haveSentBitTorrentHandshake;
tr_peerIo * io;
tr_crypto * crypto;
tr_session * session;
uint8_t mySecret[KEY_LEN];
handshake_state_t state;
tr_encryption_mode encryptionMode;
uint16_t pad_c_len;
uint16_t pad_d_len;
uint16_t ia_len;
uint32_t crypto_select;
uint32_t crypto_provide;
uint8_t myReq1[SHA_DIGEST_LENGTH];
handshakeDoneCB doneCB;
void * doneUserData;
struct event * timeout_timer;
};
/**
***
**/
enum
{
/* 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
};
/**
***
**/
#define dbgmsg(handshake, ...) \
do { \
if (tr_logGetDeepEnabled ()) \
tr_logAddDeep (__FILE__, __LINE__, tr_peerIoGetAddrStr (handshake->io), __VA_ARGS__); \
} while (0)
static const char*
getStateName (const handshake_state_t state)
{
static const char * 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)
{
dbgmsg (handshake, "setting to state [%s]", getStateName (state));
handshake->state = state;
}
static void
setReadState (tr_handshake * handshake, handshake_state_t state)
{
setState (handshake, state);
}
static void
buildHandshakeMessage (tr_handshake * handshake, uint8_t * buf)
{
uint8_t * walk = buf;
const uint8_t * torrentHash = tr_cryptoGetTorrentHash (handshake->crypto);
const tr_torrent * tor = tr_torrentFindFromHash (handshake->session, torrentHash);
const uint8_t * peer_id = tor && *tor->peer_id ? tor->peer_id : tr_getPeerId (handshake->session);
memcpy (walk, HANDSHAKE_NAME, HANDSHAKE_NAME_LEN);
walk += HANDSHAKE_NAME_LEN;
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 (tr_dhtEnabled (handshake->session))
HANDSHAKE_SET_DHT (walk);
walk += HANDSHAKE_FLAGS_LEN;
memcpy (walk, torrentHash, SHA_DIGEST_LENGTH);
walk += SHA_DIGEST_LENGTH;
memcpy (walk, peer_id, PEER_ID_LEN);
walk += PEER_ID_LEN;
assert (walk - buf == HANDSHAKE_SIZE);
}
static int tr_handshakeDone (tr_handshake * handshake,
bool isConnected);
enum
{
HANDSHAKE_OK,
HANDSHAKE_ENCRYPTION_WRONG,
HANDSHAKE_BAD_TORRENT,
HANDSHAKE_PEER_IS_SELF,
};
static int
parseHandshake (tr_handshake * handshake,
struct evbuffer * inbuf)
{
uint8_t name[HANDSHAKE_NAME_LEN];
uint8_t reserved[HANDSHAKE_FLAGS_LEN];
uint8_t hash[SHA_DIGEST_LENGTH];
const tr_torrent * tor;
const uint8_t * tor_peer_id;
uint8_t peer_id[PEER_ID_LEN];
dbgmsg (handshake, "payload: need %d, got %zu",
HANDSHAKE_SIZE, evbuffer_get_length (inbuf));
if (evbuffer_get_length (inbuf) < HANDSHAKE_SIZE)
return READ_LATER;
/* confirm the protocol */
tr_peerIoReadBytes (handshake->io, inbuf, name, HANDSHAKE_NAME_LEN);
if (memcmp (name, HANDSHAKE_NAME, HANDSHAKE_NAME_LEN))
return HANDSHAKE_ENCRYPTION_WRONG;
/* read the reserved bytes */
tr_peerIoReadBytes (handshake->io, inbuf, reserved, HANDSHAKE_FLAGS_LEN);
/* torrent hash */
tr_peerIoReadBytes (handshake->io, inbuf, hash, sizeof (hash));
assert (tr_peerIoHasTorrentHash (handshake->io));
if (!tr_torrentExists (handshake->session, hash)
|| memcmp (hash, tr_peerIoGetTorrentHash (handshake->io), SHA_DIGEST_LENGTH))
{
dbgmsg (handshake, "peer returned the wrong hash. wtf?");
return HANDSHAKE_BAD_TORRENT;
}
/* peer_id */
tr_peerIoReadBytes (handshake->io, inbuf, peer_id, sizeof (peer_id));
tr_peerIoSetPeersId (handshake->io, peer_id);
/* peer id */
handshake->havePeerID = true;
dbgmsg (handshake, "peer-id is [%*.*s]", PEER_ID_LEN, PEER_ID_LEN, peer_id);
tor = tr_torrentFindFromHash (handshake->session, hash);
tor_peer_id = tor ? tor->peer_id : tr_getPeerId (handshake->session);
if (!memcmp (peer_id, tor_peer_id, PEER_ID_LEN))
{
dbgmsg (handshake, "streuth! we've connected to ourselves.");
return HANDSHAKE_PEER_IS_SELF;
}
/**
*** Extensions
**/
tr_peerIoEnableDHT (handshake->io, HANDSHAKE_HAS_DHT (reserved));
tr_peerIoEnableLTEP (handshake->io, HANDSHAKE_HAS_LTEP (reserved));
tr_peerIoEnableFEXT (handshake->io, HANDSHAKE_HAS_FASTEXT (reserved));
return HANDSHAKE_OK;
}
/***
****
**** OUTGOING CONNECTIONS
****
***/
/* 1 A->B: Diffie Hellman Ya, PadA */
static void
sendYa (tr_handshake * handshake)
{
int len;
const uint8_t * public_key;
char outbuf[ KEY_LEN + PadA_MAXLEN ];
char *walk = outbuf;
/* add our public key (Ya) */
public_key = tr_cryptoGetMyPublicKey (handshake->crypto, &len);
assert (len == KEY_LEN);
assert (public_key);
memcpy (walk, public_key, len);
walk += len;
/* add some bullshit padding */
len = tr_cryptoRandInt (PadA_MAXLEN);
tr_cryptoRandBuf (walk, len);
walk += len;
/* send it */
setReadState (handshake, AWAITING_YB);
tr_peerIoWriteBytes (handshake->io, outbuf, walk - outbuf, false);
}
static uint32_t
getCryptoProvide (const tr_handshake * handshake)
{
uint32_t provide = 0;
switch (handshake->encryptionMode)
{
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 (const tr_handshake * handshake,
uint32_t crypto_provide)
{
uint32_t choices[2];
int i;
int nChoices = 0;
switch (handshake->encryptionMode)
{
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 (i=0; i<nChoices; ++i)
if (crypto_provide & choices[i])
return choices[i];
return 0;
}
static int
readYb (tr_handshake * handshake, struct evbuffer * inbuf)
{
int isEncrypted;
const uint8_t * secret;
uint8_t yb[KEY_LEN];
struct evbuffer * outbuf;
size_t needlen = HANDSHAKE_NAME_LEN;
if (evbuffer_get_length (inbuf) < needlen)
return READ_LATER;
isEncrypted = memcmp (evbuffer_pullup (inbuf, HANDSHAKE_NAME_LEN), HANDSHAKE_NAME, HANDSHAKE_NAME_LEN);
if (isEncrypted)
{
needlen = KEY_LEN;
if (evbuffer_get_length (inbuf) < needlen)
return READ_LATER;
}
dbgmsg (handshake, "got an %s handshake", (isEncrypted ? "encrypted" : "plain"));
tr_peerIoSetEncryption (handshake->io, isEncrypted ? PEER_ENCRYPTION_RC4
: PEER_ENCRYPTION_NONE);
if (!isEncrypted)
{
setState (handshake, AWAITING_HANDSHAKE);
return READ_NOW;
}
handshake->haveReadAnythingFromPeer = true;
/* compute the secret */
evbuffer_remove (inbuf, yb, KEY_LEN);
secret = tr_cryptoComputeSecret (handshake->crypto, yb);
memcpy (handshake->mySecret, secret, KEY_LEN);
/* now send these: HASH ('req1', S), HASH ('req2', SKEY) xor HASH ('req3', S),
* ENCRYPT (VC, crypto_provide, len (PadC), PadC, len (IA)), ENCRYPT (IA) */
outbuf = evbuffer_new ();
/* HASH ('req1', S) */
{
uint8_t req1[SHA_DIGEST_LENGTH];
tr_sha1 (req1, "req1", 4, secret, KEY_LEN, NULL);
evbuffer_add (outbuf, req1, SHA_DIGEST_LENGTH);
}
/* HASH ('req2', SKEY) xor HASH ('req3', S) */
{
int i;
uint8_t req2[SHA_DIGEST_LENGTH];
uint8_t req3[SHA_DIGEST_LENGTH];
uint8_t buf[SHA_DIGEST_LENGTH];
tr_sha1 (req2, "req2", 4, tr_cryptoGetTorrentHash (handshake->crypto), SHA_DIGEST_LENGTH, NULL);
tr_sha1 (req3, "req3", 4, secret, KEY_LEN, NULL);
for (i=0; i<SHA_DIGEST_LENGTH; ++i)
buf[i] = req2[i] ^ req3[i];
evbuffer_add (outbuf, buf, SHA_DIGEST_LENGTH);
}
/* 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 */
{
uint8_t vc[VC_LENGTH] = { 0, 0, 0, 0, 0, 0, 0, 0 };
tr_peerIoWriteBuf (handshake->io, outbuf, false);
tr_cryptoEncryptInit (handshake->crypto);
tr_peerIoSetEncryption (handshake->io, PEER_ENCRYPTION_RC4);
evbuffer_add (outbuf, vc, VC_LENGTH);
evbuffer_add_uint32 (outbuf, getCryptoProvide (handshake));
evbuffer_add_uint16 (outbuf, 0);
}
/* ENCRYPT len (IA)), ENCRYPT (IA) */
{
uint8_t msg[HANDSHAKE_SIZE];
buildHandshakeMessage (handshake, msg);
evbuffer_add_uint16 (outbuf, sizeof (msg));
evbuffer_add (outbuf, msg, sizeof (msg));
handshake->haveSentBitTorrentHandshake = 1;
}
/* send it */
tr_cryptoDecryptInit (handshake->crypto);
setReadState (handshake, AWAITING_VC);
tr_peerIoWriteBuf (handshake->io, outbuf, false);
/* cleanup */
evbuffer_free (outbuf);
return READ_LATER;
}
static int
readVC (tr_handshake * handshake,
struct evbuffer * inbuf)
{
uint8_t tmp[VC_LENGTH];
const int key_len = VC_LENGTH;
const uint8_t key[VC_LENGTH] = { 0, 0, 0, 0, 0, 0, 0, 0 };
/* note: this works w/o having to `unwind' the buffer if
* we read too much, but it is pretty brute-force.
* it would be nice to make this cleaner. */
for (;;)
{
if (evbuffer_get_length (inbuf) < VC_LENGTH)
{
dbgmsg (handshake, "not enough bytes... returning read_more");
return READ_LATER;
}
memcpy (tmp, evbuffer_pullup (inbuf, key_len), key_len);
tr_cryptoDecryptInit (handshake->crypto);
tr_cryptoDecrypt (handshake->crypto, key_len, tmp, tmp);
if (!memcmp (tmp, key, key_len))
break;
evbuffer_drain (inbuf, 1);
}
dbgmsg (handshake, "got it!");
evbuffer_drain (inbuf, key_len);
setState (handshake, AWAITING_CRYPTO_SELECT);
return READ_NOW;
}
static int
readCryptoSelect (tr_handshake * handshake,
struct evbuffer * inbuf)
{
uint16_t pad_d_len;
uint32_t crypto_select;
static const size_t needlen = sizeof (uint32_t) + sizeof (uint16_t);
if (evbuffer_get_length (inbuf) < needlen)
return READ_LATER;
tr_peerIoReadUint32 (handshake->io, inbuf, &crypto_select);
handshake->crypto_select = crypto_select;
dbgmsg (handshake, "crypto select is %d", (int)crypto_select);
if (!(crypto_select & getCryptoProvide (handshake)))
{
dbgmsg (handshake, "peer selected an encryption option we didn't offer");
return tr_handshakeDone (handshake, false);
}
tr_peerIoReadUint16 (handshake->io, inbuf, &pad_d_len);
dbgmsg (handshake, "pad_d_len is %d", (int)pad_d_len);
if (pad_d_len > 512)
{
dbgmsg (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 int
readPadD (tr_handshake * handshake,
struct evbuffer * inbuf)
{
const size_t needlen = handshake->pad_d_len;
dbgmsg (handshake, "pad d: need %zu, got %zu",
needlen, evbuffer_get_length (inbuf));
if (evbuffer_get_length (inbuf) < needlen)
return READ_LATER;
tr_peerIoDrain (handshake->io, inbuf, needlen);
tr_peerIoSetEncryption (handshake->io, handshake->crypto_select);
setState (handshake, AWAITING_HANDSHAKE);
return READ_NOW;
}
/***
****
**** INCOMING CONNECTIONS
****
***/
static int
readHandshake (tr_handshake * handshake,
struct evbuffer * inbuf)
{
uint8_t pstrlen;
uint8_t pstr[20];
uint8_t reserved[HANDSHAKE_FLAGS_LEN];
uint8_t hash[SHA_DIGEST_LENGTH];
dbgmsg (handshake, "payload: need %d, got %zu",
INCOMING_HANDSHAKE_LEN, evbuffer_get_length (inbuf));
if (evbuffer_get_length (inbuf) < INCOMING_HANDSHAKE_LEN)
return READ_LATER;
handshake->haveReadAnythingFromPeer = true;
pstrlen = evbuffer_pullup (inbuf, 1)[0]; /* peek, don't read. We may be
handing inbuf to AWAITING_YA */
if (pstrlen == 19) /* unencrypted */
{
tr_peerIoSetEncryption (handshake->io, PEER_ENCRYPTION_NONE);
if (handshake->encryptionMode == TR_ENCRYPTION_REQUIRED)
{
dbgmsg (handshake, "peer is unencrypted, and we're disallowing that");
return tr_handshakeDone (handshake, false);
}
}
else /* encrypted or corrupt */
{
tr_peerIoSetEncryption (handshake->io, PEER_ENCRYPTION_RC4);
if (tr_peerIoIsIncoming (handshake->io))
{
dbgmsg (handshake, "I think peer is sending us an encrypted handshake...");
setState (handshake, AWAITING_YA);
return READ_NOW;
}
tr_cryptoDecrypt (handshake->crypto, 1, &pstrlen, &pstrlen);
if (pstrlen != 19)
{
dbgmsg (handshake, "I think peer has sent us a corrupt handshake...");
return tr_handshakeDone (handshake, false);
}
}
evbuffer_drain (inbuf, 1);
/* pstr (BitTorrent) */
assert (pstrlen == 19);
tr_peerIoReadBytes (handshake->io, inbuf, pstr, pstrlen);
pstr[pstrlen] = '\0';
if (memcmp (pstr, "BitTorrent protocol", 19))
return tr_handshakeDone (handshake, false);
/* reserved bytes */
tr_peerIoReadBytes (handshake->io, inbuf, reserved, sizeof (reserved));
/**
*** Extensions
**/
tr_peerIoEnableDHT (handshake->io, HANDSHAKE_HAS_DHT (reserved));
tr_peerIoEnableLTEP (handshake->io, HANDSHAKE_HAS_LTEP (reserved));
tr_peerIoEnableFEXT (handshake->io, HANDSHAKE_HAS_FASTEXT (reserved));
/* torrent hash */
tr_peerIoReadBytes (handshake->io, inbuf, hash, sizeof (hash));
if (tr_peerIoIsIncoming (handshake->io))
{
if (!tr_torrentExists (handshake->session, hash))
{
dbgmsg (handshake, "peer is trying to connect to us for a torrent we don't have.");
return tr_handshakeDone (handshake, false);
}
else
{
assert (!tr_peerIoHasTorrentHash (handshake->io));
tr_peerIoSetTorrentHash (handshake->io, hash);
}
}
else /* outgoing */
{
assert (tr_peerIoHasTorrentHash (handshake->io));
if (memcmp (hash, tr_peerIoGetTorrentHash (handshake->io), SHA_DIGEST_LENGTH))
{
dbgmsg (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];
buildHandshakeMessage (handshake, msg);
tr_peerIoWriteBytes (handshake->io, msg, sizeof (msg), false);
handshake->haveSentBitTorrentHandshake = 1;
}
setReadState (handshake, AWAITING_PEER_ID);
return READ_NOW;
}
static int
readPeerId (tr_handshake * handshake,
struct evbuffer * inbuf)
{
bool peerIsGood;
char client[128];
tr_torrent * tor;
const uint8_t * tor_peer_id;
uint8_t peer_id[PEER_ID_LEN];
if (evbuffer_get_length (inbuf) < PEER_ID_LEN)
return READ_LATER;
/* peer id */
tr_peerIoReadBytes (handshake->io, inbuf, peer_id, PEER_ID_LEN);
tr_peerIoSetPeersId (handshake->io, peer_id);
handshake->havePeerID = true;
tr_clientForId (client, sizeof (client), peer_id);
dbgmsg (handshake, "peer-id is [%s] ... isIncoming is %d", client,
tr_peerIoIsIncoming (handshake->io));
/* if we've somehow connected to ourselves, don't keep the connection */
tor = tr_torrentFindFromHash (handshake->session, tr_peerIoGetTorrentHash (handshake->io));
tor_peer_id = tor ? tor->peer_id : tr_getPeerId (handshake->session);
peerIsGood = memcmp (peer_id, tor_peer_id, PEER_ID_LEN) != 0;
dbgmsg (handshake, "isPeerGood == %d", (int)peerIsGood);
return tr_handshakeDone (handshake, peerIsGood);
}
static int
readYa (tr_handshake * handshake,
struct evbuffer * inbuf)
{
uint8_t ya[KEY_LEN];
uint8_t * walk, outbuf[KEY_LEN + PadB_MAXLEN];
const uint8_t * myKey;
const uint8_t * secret;
int len;
dbgmsg (handshake, "in readYa... need %d, have %zu",
KEY_LEN, evbuffer_get_length (inbuf));
if (evbuffer_get_length (inbuf) < KEY_LEN)
return READ_LATER;
/* read the incoming peer's public key */
evbuffer_remove (inbuf, ya, KEY_LEN);
secret = tr_cryptoComputeSecret (handshake->crypto, ya);
memcpy (handshake->mySecret, secret, KEY_LEN);
tr_sha1 (handshake->myReq1, "req1", 4, secret, KEY_LEN, NULL);
/* send our public key to the peer */
dbgmsg (handshake, "sending B->A: Diffie Hellman Yb, PadB");
walk = outbuf;
myKey = tr_cryptoGetMyPublicKey (handshake->crypto, &len);
memcpy (walk, myKey, len);
walk += len;
len = tr_cryptoRandInt (PadB_MAXLEN);
tr_cryptoRandBuf (walk, len);
walk += len;
setReadState (handshake, AWAITING_PAD_A);
tr_peerIoWriteBytes (handshake->io, outbuf, walk - outbuf, false);
return READ_NOW;
}
static int
readPadA (tr_handshake * handshake, struct evbuffer * inbuf)
{
/* resynchronizing on HASH ('req1',S) */
struct evbuffer_ptr ptr = evbuffer_search (inbuf, (const char*)handshake->myReq1, SHA_DIGEST_LENGTH, NULL);
if (ptr.pos != -1) /* match */
{
evbuffer_drain (inbuf, ptr.pos);
dbgmsg (handshake, "found it... looking setting to awaiting_crypto_provide");
setState (handshake, AWAITING_CRYPTO_PROVIDE);
return READ_NOW;
}
else
{
const size_t len = evbuffer_get_length (inbuf);
if (len > SHA_DIGEST_LENGTH)
evbuffer_drain (inbuf, len - SHA_DIGEST_LENGTH);
return READ_LATER;
}
}
static int
readCryptoProvide (tr_handshake * handshake,
struct evbuffer * inbuf)
{
/* HASH ('req2', SKEY) xor HASH ('req3', S), ENCRYPT (VC, crypto_provide, len (PadC)) */
int i;
uint8_t vc_in[VC_LENGTH];
uint8_t req2[SHA_DIGEST_LENGTH];
uint8_t req3[SHA_DIGEST_LENGTH];
uint8_t obfuscatedTorrentHash[SHA_DIGEST_LENGTH];
uint16_t padc_len = 0;
uint32_t crypto_provide = 0;
tr_torrent * tor;
const size_t needlen = SHA_DIGEST_LENGTH /* HASH ('req1',s) */
+ SHA_DIGEST_LENGTH /* HASH ('req2', SKEY) xor HASH ('req3', S) */
+ VC_LENGTH
+ sizeof (crypto_provide)
+ sizeof (padc_len);
if (evbuffer_get_length (inbuf) < needlen)
return READ_LATER;
/* TODO: confirm they sent HASH ('req1',S) here? */
evbuffer_drain (inbuf, SHA_DIGEST_LENGTH);
/* This next piece is HASH ('req2', SKEY) xor HASH ('req3', S) ...
* we can get the first half of that (the obufscatedTorrentHash)
* by building the latter and xor'ing it with what the peer sent us */
dbgmsg (handshake, "reading obfuscated torrent hash...");
evbuffer_remove (inbuf, req2, SHA_DIGEST_LENGTH);
tr_sha1 (req3, "req3", 4, handshake->mySecret, KEY_LEN, NULL);
for (i=0; i<SHA_DIGEST_LENGTH; ++i)
obfuscatedTorrentHash[i] = req2[i] ^ req3[i];
if ((tor = tr_torrentFindFromObfuscatedHash (handshake->session, obfuscatedTorrentHash)))
{
const bool clientIsSeed = tr_torrentIsSeed (tor);
const bool peerIsSeed = tr_peerMgrPeerIsSeed (tor, tr_peerIoGetAddress (handshake->io, NULL));
dbgmsg (handshake, "got INCOMING connection's encrypted handshake for torrent [%s]", tr_torrentName (tor));
tr_peerIoSetTorrentHash (handshake->io, tor->info.hash);
if (clientIsSeed && peerIsSeed)
{
dbgmsg (handshake, "another seed tried to reconnect to us!");
return tr_handshakeDone (handshake, false);
}
}
else
{
dbgmsg (handshake, "can't find that torrent...");
return tr_handshakeDone (handshake, false);
}
/* next part: ENCRYPT (VC, crypto_provide, len (PadC), */
tr_cryptoDecryptInit (handshake->crypto);
tr_peerIoReadBytes (handshake->io, inbuf, vc_in, VC_LENGTH);
tr_peerIoReadUint32 (handshake->io, inbuf, &crypto_provide);
handshake->crypto_provide = crypto_provide;
dbgmsg (handshake, "crypto_provide is %d", (int)crypto_provide);
tr_peerIoReadUint16 (handshake->io, inbuf, &padc_len);
dbgmsg (handshake, "padc is %d", (int)padc_len);
handshake->pad_c_len = padc_len;
setState (handshake, AWAITING_PAD_C);
return READ_NOW;
}
static int
readPadC (tr_handshake * handshake,
struct evbuffer * inbuf)
{
char * padc;
uint16_t ia_len;
const size_t needlen = handshake->pad_c_len + sizeof (uint16_t);
if (evbuffer_get_length (inbuf) < needlen)
return READ_LATER;
/* read the throwaway padc */
padc = tr_new (char, handshake->pad_c_len);
tr_peerIoReadBytes (handshake->io, inbuf, padc, handshake->pad_c_len);
tr_free (padc);
/* read ia_len */
tr_peerIoReadUint16 (handshake->io, inbuf, &ia_len);
dbgmsg (handshake, "ia_len is %d", (int)ia_len);
handshake->ia_len = ia_len;
setState (handshake, AWAITING_IA);
return READ_NOW;
}
static int
readIA (tr_handshake * handshake,
struct evbuffer * inbuf)
{
const size_t needlen = handshake->ia_len;
struct evbuffer * outbuf;
uint32_t crypto_select;
dbgmsg (handshake, "reading IA... have %zu, need %zu",
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)
**/
tr_cryptoEncryptInit (handshake->crypto);
outbuf = evbuffer_new ();
{
/* send VC */
uint8_t vc[VC_LENGTH];
memset (vc, 0, VC_LENGTH);
evbuffer_add (outbuf, vc, VC_LENGTH);
dbgmsg (handshake, "sending vc");
}
/* send crypto_select */
crypto_select = getCryptoSelect (handshake, handshake->crypto_provide);
if (crypto_select)
{
dbgmsg (handshake, "selecting crypto mode '%d'", (int)crypto_select);
evbuffer_add_uint32 (outbuf, crypto_select);
}
else
{
dbgmsg (handshake, "peer didn't offer an encryption mode we like.");
evbuffer_free (outbuf);
return tr_handshakeDone (handshake, false);
}
dbgmsg (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 */
{
const uint16_t 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_peerIoSetEncryption (handshake->io, PEER_ENCRYPTION_NONE);
}
dbgmsg (handshake, "sending handshake");
/* send our handshake */
{
uint8_t msg[HANDSHAKE_SIZE];
buildHandshakeMessage (handshake, msg);
evbuffer_add (outbuf, msg, sizeof (msg));
handshake->haveSentBitTorrentHandshake = 1;
}
/* 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 int
readPayloadStream (tr_handshake * handshake,
struct evbuffer * inbuf)
{
int i;
const size_t needlen = HANDSHAKE_SIZE;
dbgmsg (handshake, "reading payload stream... have %zu, need %zu",
evbuffer_get_length (inbuf), needlen);
if (evbuffer_get_length (inbuf) < needlen)
return READ_LATER;
/* parse the handshake ... */
i = parseHandshake (handshake, inbuf);
dbgmsg (handshake, "parseHandshake returned %d", 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 (struct tr_peerIo * io, void * arg, size_t * piece)
{
ReadState ret;
tr_handshake * handshake = arg;
struct evbuffer * inbuf = tr_peerIoGetReadBuffer (io);
bool readyForMore = true;
assert (tr_isPeerIo (io));
/* no piece data in handshake */
*piece = 0;
dbgmsg (handshake, "handling canRead; state is [%s]",
getStateName (handshake->state));
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:
assert (0);
}
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)
{
const uint8_t * peer_id = isConnected && handshake->havePeerID
? tr_peerIoGetPeersId (handshake->io)
: NULL;
const bool success = (*handshake->doneCB)(handshake,
handshake->io,
handshake->haveReadAnythingFromPeer,
isConnected,
peer_id,
handshake->doneUserData);
return success;
}
static void
tr_handshakeFree (tr_handshake * handshake)
{
if (handshake->io)
tr_peerIoUnref (handshake->io); /* balanced by the ref in tr_handshakeNew */
event_free (handshake->timeout_timer);
tr_free (handshake);
}
static int
tr_handshakeDone (tr_handshake * handshake, bool isOK)
{
bool success;
dbgmsg (handshake, "handshakeDone: %s", isOK ? "connected" : "aborting");
tr_peerIoSetIOFuncs (handshake->io, NULL, NULL, NULL, NULL);
success = fireDoneFunc (handshake, isOK);
tr_handshakeFree (handshake);
return success ? READ_LATER : READ_ERR;
}
void
tr_handshakeAbort (tr_handshake * handshake)
{
if (handshake != NULL)
tr_handshakeDone (handshake, false);
}
static void
gotError (tr_peerIo * io,
short what,
void * vhandshake)
{
int errcode = errno;
tr_handshake * handshake = vhandshake;
if (io->utp_socket && !io->isIncoming && handshake->state == AWAITING_YB)
{
/* This peer probably doesn't speak uTP. */
tr_torrent *tor;
if (tr_peerIoHasTorrentHash (io))
tor = tr_torrentFindFromHash (handshake->session, tr_peerIoGetTorrentHash (io));
else
tor = NULL;
/* Don't mark a peer as non-uTP unless it's really a connect failure. */
if ((errcode == ETIMEDOUT || errcode == ECONNREFUSED) && tr_isTorrent(tor))
tr_peerMgrSetUtpFailed (tor, tr_peerIoGetAddress (io, NULL), true);
if (!tr_peerIoReconnect (handshake->io))
{
uint8_t msg[HANDSHAKE_SIZE];
buildHandshakeMessage (handshake, msg);
handshake->haveSentBitTorrentHandshake = 1;
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->encryptionMode != TR_ENCRYPTION_REQUIRED)
&& (!tr_peerIoReconnect (handshake->io)))
{
uint8_t msg[HANDSHAKE_SIZE];
dbgmsg (handshake, "handshake failed, trying plaintext...");
buildHandshakeMessage (handshake, msg);
handshake->haveSentBitTorrentHandshake = 1;
setReadState (handshake, AWAITING_HANDSHAKE);
tr_peerIoWriteBytes (handshake->io, msg, sizeof (msg), false);
}
else
{
dbgmsg (handshake, "libevent got an error what==%d, errno=%d (%s)",
(int)what, errno, tr_strerror (errno));
tr_handshakeDone (handshake, false);
}
}
/**
***
**/
static void
handshakeTimeout (int foo UNUSED, short bar UNUSED, void * handshake)
{
tr_handshakeAbort (handshake);
}
tr_handshake*
tr_handshakeNew (tr_peerIo * io,
tr_encryption_mode encryptionMode,
handshakeDoneCB doneCB,
void * doneUserData)
{
tr_handshake * handshake;
tr_session * session = tr_peerIoGetSession (io);
handshake = tr_new0 (tr_handshake, 1);
handshake->io = io;
handshake->crypto = tr_peerIoGetCrypto (io);
handshake->encryptionMode = encryptionMode;
handshake->doneCB = doneCB;
handshake->doneUserData = doneUserData;
handshake->session = session;
handshake->timeout_timer = evtimer_new (session->event_base, handshakeTimeout, handshake);
tr_timerAdd (handshake->timeout_timer, HANDSHAKE_TIMEOUT_SEC, 0);
tr_peerIoRef (io); /* balanced by the unref in tr_handshakeFree */
tr_peerIoSetIOFuncs (handshake->io, canRead, NULL, gotError, handshake);
tr_peerIoSetEncryption (io, PEER_ENCRYPTION_NONE);
if (tr_peerIoIsIncoming (handshake->io))
{
setReadState (handshake, AWAITING_HANDSHAKE);
}
else if (encryptionMode != TR_CLEAR_PREFERRED)
{
sendYa (handshake);
}
else
{
uint8_t msg[HANDSHAKE_SIZE];
buildHandshakeMessage (handshake, msg);
handshake->haveSentBitTorrentHandshake = 1;
setReadState (handshake, AWAITING_HANDSHAKE);
tr_peerIoWriteBytes (handshake->io, msg, sizeof (msg), false);
}
return handshake;
}
struct tr_peerIo*
tr_handshakeGetIO (tr_handshake * handshake)
{
assert (handshake != NULL);
assert (handshake->io != NULL);
return handshake->io;
}
struct tr_peerIo*
tr_handshakeStealIO (tr_handshake * handshake)
{
struct tr_peerIo * io;
assert (handshake != NULL);
assert (handshake->io != NULL);
io = handshake->io;
handshake->io = NULL;
return io;
}
const tr_address *
tr_handshakeGetAddr (const struct tr_handshake * handshake,
tr_port * port)
{
assert (handshake != NULL);
assert (handshake->io != NULL);
return tr_peerIoGetAddress (handshake->io, port);
}
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