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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 "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,
};
/**
***
**/
#define dbgmsg( handshake, ... ) \
do { \
if( tr_deepLoggingIsActive( ) ) \
tr_deepLog( __FILE__, __LINE__, tr_peerIoGetAddrStr( handshake->io ), __VA_ARGS__ ); \
} while( 0 )
static const char*
getStateName( const handshake_state_t state )
{
const char * str = "f00!";
switch( state )
{
case AWAITING_HANDSHAKE:
str = "awaiting handshake"; break;
case AWAITING_PEER_ID:
str = "awaiting peer id"; break;
case AWAITING_YA:
str = "awaiting ya"; break;
case AWAITING_PAD_A:
str = "awaiting pad a"; break;
case AWAITING_CRYPTO_PROVIDE:
str = "awaiting crypto_provide"; break;
case AWAITING_PAD_C:
str = "awaiting pad c"; break;
case AWAITING_IA:
str = "awaiting ia"; break;
case AWAITING_YB:
str = "awaiting yb"; break;
case AWAITING_VC:
str = "awaiting vc"; break;
case AWAITING_CRYPTO_SELECT:
str = "awaiting crypto select"; break;
case AWAITING_PAD_D:
str = "awaiting pad d"; break;
}
return str;
}
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_peerIoEnableLTEP( handshake->io, HANDSHAKE_HAS_LTEP( reserved ) );
tr_peerIoEnableFEXT( handshake->io, HANDSHAKE_HAS_FASTEXT( reserved ) );
tr_peerIoEnableDHT( handshake->io, HANDSHAKE_HAS_DHT( 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 ], *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, 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 a %s handshake",
( isEncrypted ? "encrypted" : "plaintext" ) );
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 )
{
const uint8_t key[VC_LENGTH] = { 0, 0, 0, 0, 0, 0, 0, 0 };
const int key_len = VC_LENGTH;
uint8_t tmp[VC_LENGTH];
/* 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 )
{
uint32_t crypto_select;
uint16_t pad_d_len;
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 provide" );
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_peerIoEnableLTEP( handshake->io, HANDSHAKE_HAS_LTEP( reserved ) );
tr_peerIoEnableFEXT( handshake->io, HANDSHAKE_HAS_FASTEXT( reserved ) );
tr_peerIoEnableDHT( handshake->io, HANDSHAKE_HAS_DHT( 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, *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 );
dbgmsg( handshake, "sending B->A: Diffie Hellman Yb, PadB" );
/* send our public key to the peer */
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;
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 );
tr_torrent * tor = NULL;
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( );
dbgmsg( handshake, "sending vc" );
/* send VC */
{
uint8_t vc[VC_LENGTH];
memset( vc, 0, VC_LENGTH );
evbuffer_add( outbuf, vc, VC_LENGTH );
}
/* 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 )
{
tr_handshake * handshake = arg;
struct evbuffer * inbuf = tr_peerIoGetReadBuffer( io );
ReadState ret;
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 =
tr_peerIoHasTorrentHash( io ) ?
tr_torrentFindFromHash( handshake->session,
tr_peerIoGetTorrentHash( io ) ) :
NULL;
/* Don't mark a peer as non-uTP unless it's really a connect failure. */
if( tor && ( errcode == ETIMEDOUT || errcode == ECONNREFUSED ) ) {
tr_torrentLock( tor );
tr_peerMgrSetUtpFailed( tor,
tr_peerIoGetAddress( io, NULL ),
true );
tr_torrentUnlock( tor );
}
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 );
assert( handshake->io );
return handshake->io;
}
struct tr_peerIo*
tr_handshakeStealIO( tr_handshake * handshake )
{
struct tr_peerIo * io;
assert( handshake );
assert( handshake->io );
io = handshake->io;
handshake->io = NULL;
return io;
}
const tr_address *
tr_handshakeGetAddr( const struct tr_handshake * handshake,
tr_port * port )
{
assert( handshake );
assert( handshake->io );
return tr_peerIoGetAddress( handshake->io, port );
}
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