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Add 2 outbound block-relay-only connections
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Transaction relay is primarily optimized for balancing redundancy/robustness
with bandwidth minimization -- as a result transaction relay leaks information
that adversaries can use to infer the network topology.

Network topology is better kept private for (at least) two reasons:

(a) Knowledge of the network graph can make it easier to find the source IP of
a given transaction.

(b) Knowledge of the network graph could be used to split a target node or
nodes from the honest network (eg by knowing which peers to attack in order to
achieve a network split).

We can eliminate the risks of (b) by separating block relay from transaction
relay; inferring network connectivity from the relay of blocks/block headers is
much more expensive for an adversary.

After this commit, bitcoind will make 2 additional outbound connections that
are only used for block relay. (In the future, we might consider rotating our
transaction-relay peers to help limit the effects of (a).)
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@sdaftuar
sdaftuar committed Sep 4, 2019
1 parent b83f51a commit 3a5e885
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Showing 5 changed files with 75 additions and 40 deletions.
3 changes: 2 additions & 1 deletion src/init.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1753,7 +1753,8 @@ bool AppInitMain(InitInterfaces& interfaces)
CConnman::Options connOptions;
connOptions.nLocalServices = nLocalServices;
connOptions.nMaxConnections = nMaxConnections;
connOptions.nMaxOutbound = std::min(MAX_OUTBOUND_CONNECTIONS, connOptions.nMaxConnections);
connOptions.m_max_outbound_full_relay = std::min(MAX_OUTBOUND_FULL_RELAY_CONNECTIONS, connOptions.nMaxConnections);
connOptions.m_max_outbound_block_relay = std::min(MAX_BLOCKS_ONLY_CONNECTIONS, connOptions.nMaxConnections-connOptions.m_max_outbound_full_relay);
connOptions.nMaxAddnode = MAX_ADDNODE_CONNECTIONS;
connOptions.nMaxFeeler = 1;
connOptions.nBestHeight = chain_active_height;
Expand Down
42 changes: 28 additions & 14 deletions src/net.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -352,7 +352,7 @@ static CAddress GetBindAddress(SOCKET sock)
return addr_bind;
}

CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCountFailure, bool manual_connection)
CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCountFailure, bool manual_connection, bool block_relay_only)
{
if (pszDest == nullptr) {
if (IsLocal(addrConnect))
Expand Down Expand Up @@ -442,7 +442,7 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
NodeId id = GetNewNodeId();
uint64_t nonce = GetDeterministicRandomizer(RANDOMIZER_ID_LOCALHOSTNONCE).Write(id).Finalize();
CAddress addr_bind = GetBindAddress(hSocket);
CNode* pnode = new CNode(id, nLocalServices, GetBestHeight(), hSocket, addrConnect, CalculateKeyedNetGroup(addrConnect), nonce, addr_bind, pszDest ? pszDest : "", false);
CNode* pnode = new CNode(id, nLocalServices, GetBestHeight(), hSocket, addrConnect, CalculateKeyedNetGroup(addrConnect), nonce, addr_bind, pszDest ? pszDest : "", false, block_relay_only);
pnode->AddRef();

return pnode;
Expand Down Expand Up @@ -905,7 +905,7 @@ void CConnman::AcceptConnection(const ListenSocket& hListenSocket) {
SOCKET hSocket = accept(hListenSocket.socket, (struct sockaddr*)&sockaddr, &len);
CAddress addr;
int nInbound = 0;
int nMaxInbound = nMaxConnections - (nMaxOutbound + nMaxFeeler);
int nMaxInbound = nMaxConnections - m_max_outbound;

if (hSocket != INVALID_SOCKET) {
if (!addr.SetSockAddr((const struct sockaddr*)&sockaddr)) {
Expand Down Expand Up @@ -1666,7 +1666,7 @@ int CConnman::GetExtraOutboundCount()
}
}
}
return std::max(nOutbound - nMaxOutbound, 0);
return std::max(nOutbound - m_max_outbound_full_relay - m_max_outbound_block_relay, 0);
}

void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
Expand Down Expand Up @@ -1726,7 +1726,8 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
CAddress addrConnect;

// Only connect out to one peer per network group (/16 for IPv4).
int nOutbound = 0;
int nOutboundFullRelay = 0;
int nOutboundBlockRelay = 0;
std::set<std::vector<unsigned char> > setConnected;
{
LOCK(cs_vNodes);
Expand All @@ -1738,7 +1739,11 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
// also have the added issue that they're attacker controlled and could be used
// to prevent us from connecting to particular hosts if we used them here.
setConnected.insert(pnode->addr.GetGroup());
nOutbound++;
if (pnode->m_tx_relay == nullptr) {
nOutboundBlockRelay++;
} else if (!pnode->fFeeler) {
nOutboundFullRelay++;
}
}
}
}
Expand All @@ -1757,7 +1762,7 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
//
bool fFeeler = false;

if (nOutbound >= nMaxOutbound && !GetTryNewOutboundPeer()) {
if (nOutboundFullRelay >= m_max_outbound_full_relay && nOutboundBlockRelay >= m_max_outbound_block_relay && !GetTryNewOutboundPeer()) {
int64_t nTime = GetTimeMicros(); // The current time right now (in microseconds).
if (nTime > nNextFeeler) {
nNextFeeler = PoissonNextSend(nTime, FEELER_INTERVAL);
Expand Down Expand Up @@ -1831,7 +1836,14 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
LogPrint(BCLog::NET, "Making feeler connection to %s\n", addrConnect.ToString());
}

OpenNetworkConnection(addrConnect, (int)setConnected.size() >= std::min(nMaxConnections - 1, 2), &grant, nullptr, false, fFeeler);
// Open this connection as block-relay-only if we're already at our
// full-relay capacity, but not yet at our block-relay peer limit.
// (It should not be possible for fFeeler to be set if we're not
// also at our block-relay peer limit, but check against that as
// well for sanity.)
bool block_relay_only = nOutboundBlockRelay < m_max_outbound_block_relay && !fFeeler && nOutboundFullRelay >= m_max_outbound_full_relay;

OpenNetworkConnection(addrConnect, (int)setConnected.size() >= std::min(nMaxConnections - 1, 2), &grant, nullptr, false, fFeeler, false, block_relay_only);
}
}
}
Expand Down Expand Up @@ -1918,7 +1930,7 @@ void CConnman::ThreadOpenAddedConnections()
}

// if successful, this moves the passed grant to the constructed node
void CConnman::OpenNetworkConnection(const CAddress& addrConnect, bool fCountFailure, CSemaphoreGrant *grantOutbound, const char *pszDest, bool fOneShot, bool fFeeler, bool manual_connection)
void CConnman::OpenNetworkConnection(const CAddress& addrConnect, bool fCountFailure, CSemaphoreGrant *grantOutbound, const char *pszDest, bool fOneShot, bool fFeeler, bool manual_connection, bool block_relay_only)
{
//
// Initiate outbound network connection
Expand All @@ -1937,7 +1949,7 @@ void CConnman::OpenNetworkConnection(const CAddress& addrConnect, bool fCountFai
} else if (FindNode(std::string(pszDest)))
return;

CNode* pnode = ConnectNode(addrConnect, pszDest, fCountFailure, manual_connection);
CNode* pnode = ConnectNode(addrConnect, pszDest, fCountFailure, manual_connection, block_relay_only);

if (!pnode)
return;
Expand Down Expand Up @@ -2240,7 +2252,7 @@ bool CConnman::Start(CScheduler& scheduler, const Options& connOptions)

if (semOutbound == nullptr) {
// initialize semaphore
semOutbound = MakeUnique<CSemaphore>(std::min((nMaxOutbound + nMaxFeeler), nMaxConnections));
semOutbound = MakeUnique<CSemaphore>(std::min(m_max_outbound, nMaxConnections));
}
if (semAddnode == nullptr) {
// initialize semaphore
Expand Down Expand Up @@ -2318,7 +2330,7 @@ void CConnman::Interrupt()
InterruptSocks5(true);

if (semOutbound) {
for (int i=0; i<(nMaxOutbound + nMaxFeeler); i++) {
for (int i=0; i<m_max_outbound; i++) {
semOutbound->post();
}
}
Expand Down Expand Up @@ -2628,7 +2640,7 @@ int CConnman::GetBestHeight() const

unsigned int CConnman::GetReceiveFloodSize() const { return nReceiveFloodSize; }

CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn, SOCKET hSocketIn, const CAddress& addrIn, uint64_t nKeyedNetGroupIn, uint64_t nLocalHostNonceIn, const CAddress& addrBindIn, const std::string& addrNameIn, bool fInboundIn)
CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn, SOCKET hSocketIn, const CAddress& addrIn, uint64_t nKeyedNetGroupIn, uint64_t nLocalHostNonceIn, const CAddress& addrBindIn, const std::string& addrNameIn, bool fInboundIn, bool block_relay_only)
: nTimeConnected(GetSystemTimeInSeconds()),
addr(addrIn),
addrBind(addrBindIn),
Expand All @@ -2643,7 +2655,9 @@ CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn
hSocket = hSocketIn;
addrName = addrNameIn == "" ? addr.ToStringIPPort() : addrNameIn;
hashContinue = uint256();
m_tx_relay = MakeUnique<TxRelay>();
if (!block_relay_only) {
m_tx_relay = MakeUnique<TxRelay>();
}

for (const std::string &msg : getAllNetMessageTypes())
mapRecvBytesPerMsgCmd[msg] = 0;
Expand Down
33 changes: 23 additions & 10 deletions src/net.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -56,10 +56,12 @@ static const unsigned int MAX_ADDR_TO_SEND = 1000;
static const unsigned int MAX_PROTOCOL_MESSAGE_LENGTH = 4 * 1000 * 1000;
/** Maximum length of the user agent string in `version` message */
static const unsigned int MAX_SUBVERSION_LENGTH = 256;
/** Maximum number of automatic outgoing nodes */
static const int MAX_OUTBOUND_CONNECTIONS = 8;
/** Maximum number of automatic outgoing nodes over which we'll relay everything (blocks, tx, addrs, etc) */
static const int MAX_OUTBOUND_FULL_RELAY_CONNECTIONS = 8;
/** Maximum number of addnode outgoing nodes */
static const int MAX_ADDNODE_CONNECTIONS = 8;
/** Maximum number of block-relay-only outgoing connections */
static const int MAX_BLOCKS_ONLY_CONNECTIONS = 2;
/** -listen default */
static const bool DEFAULT_LISTEN = true;
/** -upnp default */
Expand Down Expand Up @@ -126,7 +128,8 @@ class CConnman
{
ServiceFlags nLocalServices = NODE_NONE;
int nMaxConnections = 0;
int nMaxOutbound = 0;
int m_max_outbound_full_relay = 0;
int m_max_outbound_block_relay = 0;
int nMaxAddnode = 0;
int nMaxFeeler = 0;
int nBestHeight = 0;
Expand All @@ -150,10 +153,12 @@ class CConnman
void Init(const Options& connOptions) {
nLocalServices = connOptions.nLocalServices;
nMaxConnections = connOptions.nMaxConnections;
nMaxOutbound = std::min(connOptions.nMaxOutbound, connOptions.nMaxConnections);
m_max_outbound_full_relay = std::min(connOptions.m_max_outbound_full_relay, connOptions.nMaxConnections);
m_max_outbound_block_relay = connOptions.m_max_outbound_block_relay;
m_use_addrman_outgoing = connOptions.m_use_addrman_outgoing;
nMaxAddnode = connOptions.nMaxAddnode;
nMaxFeeler = connOptions.nMaxFeeler;
m_max_outbound = m_max_outbound_full_relay + m_max_outbound_block_relay + nMaxFeeler;
nBestHeight = connOptions.nBestHeight;
clientInterface = connOptions.uiInterface;
m_banman = connOptions.m_banman;
Expand Down Expand Up @@ -192,7 +197,7 @@ class CConnman
bool GetNetworkActive() const { return fNetworkActive; };
bool GetUseAddrmanOutgoing() const { return m_use_addrman_outgoing; };
void SetNetworkActive(bool active);
void OpenNetworkConnection(const CAddress& addrConnect, bool fCountFailure, CSemaphoreGrant *grantOutbound = nullptr, const char *strDest = nullptr, bool fOneShot = false, bool fFeeler = false, bool manual_connection = false);
void OpenNetworkConnection(const CAddress& addrConnect, bool fCountFailure, CSemaphoreGrant *grantOutbound = nullptr, const char *strDest = nullptr, bool fOneShot = false, bool fFeeler = false, bool manual_connection = false, bool block_relay_only = false);
bool CheckIncomingNonce(uint64_t nonce);

bool ForNode(NodeId id, std::function<bool(CNode* pnode)> func);
Expand Down Expand Up @@ -248,7 +253,7 @@ class CConnman
void AddNewAddresses(const std::vector<CAddress>& vAddr, const CAddress& addrFrom, int64_t nTimePenalty = 0);
std::vector<CAddress> GetAddresses();

// This allows temporarily exceeding nMaxOutbound, with the goal of finding
// This allows temporarily exceeding m_max_outbound_full_relay, with the goal of finding
// a peer that is better than all our current peers.
void SetTryNewOutboundPeer(bool flag);
bool GetTryNewOutboundPeer();
Expand Down Expand Up @@ -350,7 +355,7 @@ class CConnman
CNode* FindNode(const CService& addr);

bool AttemptToEvictConnection();
CNode* ConnectNode(CAddress addrConnect, const char *pszDest, bool fCountFailure, bool manual_connection);
CNode* ConnectNode(CAddress addrConnect, const char *pszDest, bool fCountFailure, bool manual_connection, bool block_relay_only);
void AddWhitelistPermissionFlags(NetPermissionFlags& flags, const CNetAddr &addr) const;

void DeleteNode(CNode* pnode);
Expand Down Expand Up @@ -409,9 +414,17 @@ class CConnman
std::unique_ptr<CSemaphore> semOutbound;
std::unique_ptr<CSemaphore> semAddnode;
int nMaxConnections;
int nMaxOutbound;

// How many full-relay (tx, block, addr) outbound peers we want
int m_max_outbound_full_relay;

// How many block-relay only outbound peers we want
// We do not relay tx or addr messages with these peers
int m_max_outbound_block_relay;

int nMaxAddnode;
int nMaxFeeler;
int m_max_outbound;
bool m_use_addrman_outgoing;
std::atomic<int> nBestHeight;
CClientUIInterface* clientInterface;
Expand All @@ -437,7 +450,7 @@ class CConnman
std::thread threadMessageHandler;

/** flag for deciding to connect to an extra outbound peer,
* in excess of nMaxOutbound
* in excess of m_max_outbound_full_relay
* This takes the place of a feeler connection */
std::atomic_bool m_try_another_outbound_peer;

Expand Down Expand Up @@ -756,7 +769,7 @@ class CNode

std::set<uint256> orphan_work_set;

CNode(NodeId id, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn, SOCKET hSocketIn, const CAddress &addrIn, uint64_t nKeyedNetGroupIn, uint64_t nLocalHostNonceIn, const CAddress &addrBindIn, const std::string &addrNameIn = "", bool fInboundIn = false);
CNode(NodeId id, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn, SOCKET hSocketIn, const CAddress &addrIn, uint64_t nKeyedNetGroupIn, uint64_t nLocalHostNonceIn, const CAddress &addrBindIn, const std::string &addrNameIn = "", bool fInboundIn = false, bool block_relay_only = false);
~CNode();
CNode(const CNode&) = delete;
CNode& operator=(const CNode&) = delete;
Expand Down
25 changes: 16 additions & 9 deletions src/net_processing.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -262,7 +262,7 @@ struct CNodeState {
bool fSupportsDesiredCmpctVersion;

/** State used to enforce CHAIN_SYNC_TIMEOUT
* Only in effect for outbound, non-manual connections, with
* Only in effect for outbound, non-manual, full-relay connections, with
* m_protect == false
* Algorithm: if a peer's best known block has less work than our tip,
* set a timeout CHAIN_SYNC_TIMEOUT seconds in the future:
Expand Down Expand Up @@ -425,7 +425,7 @@ static void PushNodeVersion(CNode *pnode, CConnman* connman, int64_t nTime)
CAddress addrMe = CAddress(CService(), nLocalNodeServices);

connman->PushMessage(pnode, CNetMsgMaker(INIT_PROTO_VERSION).Make(NetMsgType::VERSION, PROTOCOL_VERSION, (uint64_t)nLocalNodeServices, nTime, addrYou, addrMe,
nonce, strSubVersion, nNodeStartingHeight, ::g_relay_txes));
nonce, strSubVersion, nNodeStartingHeight, ::g_relay_txes && pnode->m_tx_relay != nullptr));

if (fLogIPs) {
LogPrint(BCLog::NET, "send version message: version %d, blocks=%d, us=%s, them=%s, peer=%d\n", PROTOCOL_VERSION, nNodeStartingHeight, addrMe.ToString(), addrYou.ToString(), nodeid);
Expand Down Expand Up @@ -757,7 +757,7 @@ void UpdateLastBlockAnnounceTime(NodeId node, int64_t time_in_seconds)
}

// Returns true for outbound peers, excluding manual connections, feelers, and
// one-shots
// one-shots.
static bool IsOutboundDisconnectionCandidate(const CNode *node)
{
return !(node->fInbound || node->m_manual_connection || node->fFeeler || node->fOneShot);
Expand Down Expand Up @@ -1772,9 +1772,11 @@ bool static ProcessHeadersMessage(CNode *pfrom, CConnman *connman, const std::ve
}
}

if (!pfrom->fDisconnect && IsOutboundDisconnectionCandidate(pfrom) && nodestate->pindexBestKnownBlock != nullptr) {
// If this is an outbound peer, check to see if we should protect
if (!pfrom->fDisconnect && IsOutboundDisconnectionCandidate(pfrom) && nodestate->pindexBestKnownBlock != nullptr && pfrom->m_tx_relay != nullptr) {
// If this is an outbound full-relay peer, check to see if we should protect
// it from the bad/lagging chain logic.
// Note that block-relay-only peers are already implicitly protected, so we
// only consider setting m_protect for the full-relay peers.
if (g_outbound_peers_with_protect_from_disconnect < MAX_OUTBOUND_PEERS_TO_PROTECT_FROM_DISCONNECT && nodestate->pindexBestKnownBlock->nChainWork >= ::ChainActive().Tip()->nChainWork && !nodestate->m_chain_sync.m_protect) {
LogPrint(BCLog::NET, "Protecting outbound peer=%d from eviction\n", pfrom->GetId());
nodestate->m_chain_sync.m_protect = true;
Expand Down Expand Up @@ -2088,9 +2090,10 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
// Mark this node as currently connected, so we update its timestamp later.
LOCK(cs_main);
State(pfrom->GetId())->fCurrentlyConnected = true;
LogPrintf("New outbound peer connected: version: %d, blocks=%d, peer=%d%s\n",
pfrom->nVersion.load(), pfrom->nStartingHeight, pfrom->GetId(),
(fLogIPs ? strprintf(", peeraddr=%s", pfrom->addr.ToString()) : ""));
LogPrintf("New outbound peer connected: version: %d, blocks=%d, peer=%d%s (%s)\n",
pfrom->nVersion.load(), pfrom->nStartingHeight,
pfrom->GetId(), (fLogIPs ? strprintf(", peeraddr=%s", pfrom->addr.ToString()) : ""),
pfrom->m_tx_relay == nullptr ? "block-relay" : "full-relay");
}

if (pfrom->nVersion >= SENDHEADERS_VERSION) {
Expand Down Expand Up @@ -2214,7 +2217,9 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
return false;
}

bool fBlocksOnly = !g_relay_txes;
// We won't accept tx inv's if we're in blocks-only mode, or this is a
// block-relay-only peer
bool fBlocksOnly = !g_relay_txes || (pfrom->m_tx_relay == nullptr);

// Allow whitelisted peers to send data other than blocks in blocks only mode if whitelistrelay is true
if (pfrom->HasPermission(PF_RELAY))
Expand Down Expand Up @@ -3453,6 +3458,8 @@ void PeerLogicValidation::EvictExtraOutboundPeers(int64_t time_in_seconds)
if (state == nullptr) return; // shouldn't be possible, but just in case
// Don't evict our protected peers
if (state->m_chain_sync.m_protect) return;
// Don't evict our block-relay-only peers.
if (pnode->m_tx_relay == nullptr) return;
if (state->m_last_block_announcement < oldest_block_announcement || (state->m_last_block_announcement == oldest_block_announcement && pnode->GetId() > worst_peer)) {
worst_peer = pnode->GetId();
oldest_block_announcement = state->m_last_block_announcement;
Expand Down
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