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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).)
This commit is contained in:
Suhas Daftuar
2019-03-09 12:55:06 -05:00
parent b83f51a4bb
commit 3a5e885306
5 changed files with 75 additions and 40 deletions
Download Patch File Download Diff File Expand all files Collapse all files

33
src/net.h
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@@ -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 */
@@ -126,7 +128,8 @@ public:
{
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;
@@ -150,10 +153,12 @@ public:
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;
@@ -192,7 +197,7 @@ public:
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);
@@ -248,7 +253,7 @@ public:
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();
@@ -350,7 +355,7 @@ private:
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);
@@ -409,9 +414,17 @@ private:
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;
@@ -437,7 +450,7 @@ private:
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;
@@ -756,7 +769,7 @@ public:
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;