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merge bitcoin#25500: Move inbound eviction logic to its own translation unit

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Kittywhiskers Van Gogh 2022-05-26 15:40:21 +02:00
parent b50febc0f0
commit 54bb3a438f
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GPG Key ID: 30CD0C065E5C4AAD
10 changed files with 431 additions and 352 deletions
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4
src/Makefile.am
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@ -271,7 +271,9 @@ BITCOIN_CORE_H = \
node/blockstorage.h \ node/blockstorage.h \
node/coin.h \ node/coin.h \
node/coinstats.h \ node/coinstats.h \
node/connection_types.h \
node/context.h \ node/context.h \
node/eviction.h \
node/psbt.h \ node/psbt.h \
node/transaction.h \ node/transaction.h \
node/ui_interface.h \ node/ui_interface.h \
@ -499,7 +501,9 @@ libbitcoin_server_a_SOURCES = \
node/blockstorage.cpp \ node/blockstorage.cpp \
node/coin.cpp \ node/coin.cpp \
node/coinstats.cpp \ node/coinstats.cpp \
node/connection_types.cpp \
node/context.cpp \ node/context.cpp \
node/eviction.cpp \
node/interfaces.cpp \ node/interfaces.cpp \
node/psbt.cpp \ node/psbt.cpp \
node/transaction.cpp \ node/transaction.cpp \

231
src/net.cpp
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@ -17,6 +17,7 @@
#include <compat.h> #include <compat.h>
#include <consensus/consensus.h> #include <consensus/consensus.h>
#include <crypto/sha256.h> #include <crypto/sha256.h>
#include <node/eviction.h>
#include <fs.h> #include <fs.h>
#include <i2p.h> #include <i2p.h>
#include <memusage.h> #include <memusage.h>
@ -680,26 +681,6 @@ bool CNode::IsBlockRelayOnly() const {
return (ignores_incoming_txs && !HasPermission(NetPermissionFlags::Relay)) || IsBlockOnlyConn(); return (ignores_incoming_txs && !HasPermission(NetPermissionFlags::Relay)) || IsBlockOnlyConn();
} }
std::string ConnectionTypeAsString(ConnectionType conn_type)
{
switch (conn_type) {
case ConnectionType::INBOUND:
return "inbound";
case ConnectionType::MANUAL:
return "manual";
case ConnectionType::FEELER:
return "feeler";
case ConnectionType::OUTBOUND_FULL_RELAY:
return "outbound-full-relay";
case ConnectionType::BLOCK_RELAY:
return "block-relay-only";
case ConnectionType::ADDR_FETCH:
return "addr-fetch";
} // no default case, so the compiler can warn about missing cases
assert(false);
}
CService CNode::GetAddrLocal() const CService CNode::GetAddrLocal() const
{ {
AssertLockNotHeld(m_addr_local_mutex); AssertLockNotHeld(m_addr_local_mutex);
@ -1085,210 +1066,6 @@ std::pair<size_t, bool> CConnman::SocketSendData(CNode& node) const
return {nSentSize, data_left}; return {nSentSize, data_left};
} }
static bool ReverseCompareNodeMinPingTime(const NodeEvictionCandidate& a, const NodeEvictionCandidate& b)
{
return a.m_min_ping_time > b.m_min_ping_time;
}
static bool ReverseCompareNodeTimeConnected(const NodeEvictionCandidate& a, const NodeEvictionCandidate& b)
{
return a.m_connected > b.m_connected;
}
static bool CompareNetGroupKeyed(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b) {
return a.nKeyedNetGroup < b.nKeyedNetGroup;
}
static bool CompareNodeBlockTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
{
// There is a fall-through here because it is common for a node to have many peers which have not yet relayed a block.
if (a.m_last_block_time != b.m_last_block_time) return a.m_last_block_time < b.m_last_block_time;
if (a.fRelevantServices != b.fRelevantServices) return b.fRelevantServices;
return a.m_connected > b.m_connected;
}
static bool CompareNodeTXTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
{
// There is a fall-through here because it is common for a node to have more than a few peers that have not yet relayed txn.
if (a.m_last_tx_time != b.m_last_tx_time) return a.m_last_tx_time < b.m_last_tx_time;
if (a.m_relay_txs != b.m_relay_txs) return b.m_relay_txs;
if (a.fBloomFilter != b.fBloomFilter) return a.fBloomFilter;
return a.m_connected > b.m_connected;
}
// Pick out the potential block-relay only peers, and sort them by last block time.
static bool CompareNodeBlockRelayOnlyTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
{
if (a.m_relay_txs != b.m_relay_txs) return a.m_relay_txs;
if (a.m_last_block_time != b.m_last_block_time) return a.m_last_block_time < b.m_last_block_time;
if (a.fRelevantServices != b.fRelevantServices) return b.fRelevantServices;
return a.m_connected > b.m_connected;
}
/**
* Sort eviction candidates by network/localhost and connection uptime.
* Candidates near the beginning are more likely to be evicted, and those
* near the end are more likely to be protected, e.g. less likely to be evicted.
* - First, nodes that are not `is_local` and that do not belong to `network`,
* sorted by increasing uptime (from most recently connected to connected longer).
* - Then, nodes that are `is_local` or belong to `network`, sorted by increasing uptime.
*/
struct CompareNodeNetworkTime {
const bool m_is_local;
const Network m_network;
CompareNodeNetworkTime(bool is_local, Network network) : m_is_local(is_local), m_network(network) {}
bool operator()(const NodeEvictionCandidate& a, const NodeEvictionCandidate& b) const
{
if (m_is_local && a.m_is_local != b.m_is_local) return b.m_is_local;
if ((a.m_network == m_network) != (b.m_network == m_network)) return b.m_network == m_network;
return a.m_connected > b.m_connected;
};
};
//! Sort an array by the specified comparator, then erase the last K elements where predicate is true.
template <typename T, typename Comparator>
static void EraseLastKElements(
std::vector<T>& elements, Comparator comparator, size_t k,
std::function<bool(const NodeEvictionCandidate&)> predicate = [](const NodeEvictionCandidate& n) { return true; })
{
std::sort(elements.begin(), elements.end(), comparator);
size_t eraseSize = std::min(k, elements.size());
elements.erase(std::remove_if(elements.end() - eraseSize, elements.end(), predicate), elements.end());
}
void ProtectEvictionCandidatesByRatio(std::vector<NodeEvictionCandidate>& eviction_candidates)
{
// Protect the half of the remaining nodes which have been connected the longest.
// This replicates the non-eviction implicit behavior, and precludes attacks that start later.
// To favorise the diversity of our peer connections, reserve up to half of these protected
// spots for Tor/onion, localhost, I2P, and CJDNS peers, even if they're not longest uptime
// overall. This helps protect these higher-latency peers that tend to be otherwise
// disadvantaged under our eviction criteria.
const size_t initial_size = eviction_candidates.size();
const size_t total_protect_size{initial_size / 2};
// Disadvantaged networks to protect. In the case of equal counts, earlier array members
// have the first opportunity to recover unused slots from the previous iteration.
struct Net { bool is_local; Network id; size_t count; };
std::array<Net, 4> networks{
{{false, NET_CJDNS, 0}, {false, NET_I2P, 0}, {/*localhost=*/true, NET_MAX, 0}, {false, NET_ONION, 0}}};
// Count and store the number of eviction candidates per network.
for (Net& n : networks) {
n.count = std::count_if(eviction_candidates.cbegin(), eviction_candidates.cend(),
[&n](const NodeEvictionCandidate& c) {
return n.is_local ? c.m_is_local : c.m_network == n.id;
});
}
// Sort `networks` by ascending candidate count, to give networks having fewer candidates
// the first opportunity to recover unused protected slots from the previous iteration.
std::stable_sort(networks.begin(), networks.end(), [](Net a, Net b) { return a.count < b.count; });
// Protect up to 25% of the eviction candidates by disadvantaged network.
const size_t max_protect_by_network{total_protect_size / 2};
size_t num_protected{0};
while (num_protected < max_protect_by_network) {
// Count the number of disadvantaged networks from which we have peers to protect.
auto num_networks = std::count_if(networks.begin(), networks.end(), [](const Net& n) { return n.count; });
if (num_networks == 0) {
break;
}
const size_t disadvantaged_to_protect{max_protect_by_network - num_protected};
const size_t protect_per_network{std::max(disadvantaged_to_protect / num_networks, static_cast<size_t>(1))};
// Early exit flag if there are no remaining candidates by disadvantaged network.
bool protected_at_least_one{false};
for (Net& n : networks) {
if (n.count == 0) continue;
const size_t before = eviction_candidates.size();
EraseLastKElements(eviction_candidates, CompareNodeNetworkTime(n.is_local, n.id),
protect_per_network, [&n](const NodeEvictionCandidate& c) {
return n.is_local ? c.m_is_local : c.m_network == n.id;
});
const size_t after = eviction_candidates.size();
if (before > after) {
protected_at_least_one = true;
const size_t delta{before - after};
num_protected += delta;
if (num_protected >= max_protect_by_network) {
break;
}
n.count -= delta;
}
}
if (!protected_at_least_one) {
break;
}
}
// Calculate how many we removed, and update our total number of peers that
// we want to protect based on uptime accordingly.
assert(num_protected == initial_size - eviction_candidates.size());
const size_t remaining_to_protect{total_protect_size - num_protected};
EraseLastKElements(eviction_candidates, ReverseCompareNodeTimeConnected, remaining_to_protect);
}
[[nodiscard]] std::optional<NodeId> SelectNodeToEvict(std::vector<NodeEvictionCandidate>&& vEvictionCandidates)
{
// Protect connections with certain characteristics
// Deterministically select 4 peers to protect by netgroup.
// An attacker cannot predict which netgroups will be protected
EraseLastKElements(vEvictionCandidates, CompareNetGroupKeyed, 4);
// Protect the 8 nodes with the lowest minimum ping time.
// An attacker cannot manipulate this metric without physically moving nodes closer to the target.
EraseLastKElements(vEvictionCandidates, ReverseCompareNodeMinPingTime, 8);
// Protect 4 nodes that most recently sent us novel transactions accepted into our mempool.
// An attacker cannot manipulate this metric without performing useful work.
EraseLastKElements(vEvictionCandidates, CompareNodeTXTime, 4);
// Protect up to 8 non-tx-relay peers that have sent us novel blocks.
EraseLastKElements(vEvictionCandidates, CompareNodeBlockRelayOnlyTime, 8,
[](const NodeEvictionCandidate& n) { return !n.m_relay_txs && n.fRelevantServices; });
// Protect 4 nodes that most recently sent us novel blocks.
// An attacker cannot manipulate this metric without performing useful work.
EraseLastKElements(vEvictionCandidates, CompareNodeBlockTime, 4);
// Protect some of the remaining eviction candidates by ratios of desirable
// or disadvantaged characteristics.
ProtectEvictionCandidatesByRatio(vEvictionCandidates);
if (vEvictionCandidates.empty()) return std::nullopt;
// If any remaining peers are preferred for eviction consider only them.
// This happens after the other preferences since if a peer is really the best by other criteria (esp relaying blocks)
// then we probably don't want to evict it no matter what.
if (std::any_of(vEvictionCandidates.begin(),vEvictionCandidates.end(),[](NodeEvictionCandidate const &n){return n.prefer_evict;})) {
vEvictionCandidates.erase(std::remove_if(vEvictionCandidates.begin(),vEvictionCandidates.end(),
[](NodeEvictionCandidate const &n){return !n.prefer_evict;}),vEvictionCandidates.end());
}
// Identify the network group with the most connections and youngest member.
// (vEvictionCandidates is already sorted by reverse connect time)
uint64_t naMostConnections;
unsigned int nMostConnections = 0;
std::chrono::seconds nMostConnectionsTime{0};
std::map<uint64_t, std::vector<NodeEvictionCandidate> > mapNetGroupNodes;
for (const NodeEvictionCandidate &node : vEvictionCandidates) {
std::vector<NodeEvictionCandidate> &group = mapNetGroupNodes[node.nKeyedNetGroup];
group.push_back(node);
const auto grouptime{group[0].m_connected};
if (group.size() > nMostConnections || (group.size() == nMostConnections && grouptime > nMostConnectionsTime)) {
nMostConnections = group.size();
nMostConnectionsTime = grouptime;
naMostConnections = node.nKeyedNetGroup;
}
}
// Reduce to the network group with the most connections
vEvictionCandidates = std::move(mapNetGroupNodes[naMostConnections]);
// Disconnect from the network group with the most connections
return vEvictionCandidates.front().id;
}
/** Try to find a connection to evict when the node is full. /** Try to find a connection to evict when the node is full.
* Extreme care must be taken to avoid opening the node to attacker * Extreme care must be taken to avoid opening the node to attacker
* triggered network partitioning. * triggered network partitioning.
@ -1304,10 +1081,6 @@ bool CConnman::AttemptToEvictConnection()
LOCK(m_nodes_mutex); LOCK(m_nodes_mutex);
for (const CNode* node : m_nodes) { for (const CNode* node : m_nodes) {
if (node->HasPermission(NetPermissionFlags::NoBan))
continue;
if (!node->IsInboundConn())
continue;
if (node->fDisconnect) if (node->fDisconnect)
continue; continue;
@ -1343,6 +1116,8 @@ bool CConnman::AttemptToEvictConnection()
Desig(prefer_evict) node->m_prefer_evict, Desig(prefer_evict) node->m_prefer_evict,
Desig(m_is_local) node->addr.IsLocal(), Desig(m_is_local) node->addr.IsLocal(),
Desig(m_network) node->ConnectedThroughNetwork(), Desig(m_network) node->ConnectedThroughNetwork(),
Desig(m_noban) node->HasPermission(NetPermissionFlags::NoBan),
Desig(m_conn_type) node->m_conn_type,
}; };
vEvictionCandidates.push_back(candidate); vEvictionCandidates.push_back(candidate);
} }

125
src/net.h
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@ -19,6 +19,7 @@
#include <netaddress.h> #include <netaddress.h>
#include <netbase.h> #include <netbase.h>
#include <netgroup.h> #include <netgroup.h>
#include <node/connection_types.h>
#include <policy/feerate.h> #include <policy/feerate.h>
#include <protocol.h> #include <protocol.h>
#include <random.h> #include <random.h>
@ -158,78 +159,6 @@ struct CSerializedNetMsg {
size_t GetMemoryUsage() const noexcept; size_t GetMemoryUsage() const noexcept;
}; };
/** Different types of connections to a peer. This enum encapsulates the
* information we have available at the time of opening or accepting the
* connection. Aside from INBOUND, all types are initiated by us.
*
* If adding or removing types, please update CONNECTION_TYPE_DOC in
* src/rpc/net.cpp and src/qt/rpcconsole.cpp, as well as the descriptions in
* src/qt/guiutil.cpp and src/bitcoin-cli.cpp::NetinfoRequestHandler. */
enum class ConnectionType {
/**
* Inbound connections are those initiated by a peer. This is the only
* property we know at the time of connection, until P2P messages are
* exchanged.
*/
INBOUND,
/**
* These are the default connections that we use to connect with the
* network. There is no restriction on what is relayed; by default we relay
* blocks, addresses & transactions. We automatically attempt to open
* MAX_OUTBOUND_FULL_RELAY_CONNECTIONS using addresses from our AddrMan.
*/
OUTBOUND_FULL_RELAY,
/**
* We open manual connections to addresses that users explicitly requested
* via the addnode RPC or the -addnode/-connect configuration options. Even if a
* manual connection is misbehaving, we do not automatically disconnect or
* add it to our discouragement filter.
*/
MANUAL,
/**
* Feeler connections are short-lived connections made to check that a node
* is alive. They can be useful for:
* - test-before-evict: if one of the peers is considered for eviction from
* our AddrMan because another peer is mapped to the same slot in the tried table,
* evict only if this longer-known peer is offline.
* - move node addresses from New to Tried table, so that we have more
* connectable addresses in our AddrMan.
* Note that in the literature ("Eclipse Attacks on Bitcoin’s Peer-to-Peer Network")
* only the latter feature is referred to as "feeler connections",
* although in our codebase feeler connections encompass test-before-evict as well.
* We make these connections approximately every FEELER_INTERVAL:
* first we resolve previously found collisions if they exist (test-before-evict),
* otherwise we connect to a node from the new table.
*/
FEELER,
/**
* We use block-relay-only connections to help prevent against partition
* attacks. By not relaying transactions or addresses, these connections
* are harder to detect by a third party, thus helping obfuscate the
* network topology. We automatically attempt to open
* MAX_BLOCK_RELAY_ONLY_ANCHORS using addresses from our anchors.dat. Then
* addresses from our AddrMan if MAX_BLOCK_RELAY_ONLY_CONNECTIONS
* isn't reached yet.
*/
BLOCK_RELAY,
/**
* AddrFetch connections are short lived connections used to solicit
* addresses from peers. These are initiated to addresses submitted via the
* -seednode command line argument, or under certain conditions when the
* AddrMan is empty.
*/
ADDR_FETCH,
};
/** Convert ConnectionType enum to a string value */
std::string ConnectionTypeAsString(ConnectionType conn_type);
/** /**
* Look up IP addresses from all interfaces on the machine and add them to the * Look up IP addresses from all interfaces on the machine and add them to the
* list of local addresses to self-advertise. * list of local addresses to self-advertise.
@ -1711,62 +1640,10 @@ extern std::function<void(const CAddress& addr,
bool is_incoming)> bool is_incoming)>
CaptureMessage; CaptureMessage;
struct NodeEvictionCandidate
{
NodeId id;
std::chrono::seconds m_connected;
std::chrono::microseconds m_min_ping_time;
std::chrono::seconds m_last_block_time;
std::chrono::seconds m_last_tx_time;
bool fRelevantServices;
bool m_relay_txs;
bool fBloomFilter;
uint64_t nKeyedNetGroup;
bool prefer_evict;
bool m_is_local;
Network m_network;
};
/**
* Select an inbound peer to evict after filtering out (protecting) peers having
* distinct, difficult-to-forge characteristics. The protection logic picks out
* fixed numbers of desirable peers per various criteria, followed by (mostly)
* ratios of desirable or disadvantaged peers. If any eviction candidates
* remain, the selection logic chooses a peer to evict.
*/
[[nodiscard]] std::optional<NodeId> SelectNodeToEvict(std::vector<NodeEvictionCandidate>&& vEvictionCandidates);
class CExplicitNetCleanup class CExplicitNetCleanup
{ {
public: public:
static void callCleanup(); static void callCleanup();
}; };
extern RecursiveMutex cs_main;
/** Protect desirable or disadvantaged inbound peers from eviction by ratio.
*
* This function protects half of the peers which have been connected the
* longest, to replicate the non-eviction implicit behavior and preclude attacks
* that start later.
*
* Half of these protected spots (1/4 of the total) are reserved for the
* following categories of peers, sorted by longest uptime, even if they're not
* longest uptime overall:
*
* - onion peers connected via our tor control service
*
* - localhost peers, as manually configured hidden services not using
* `-bind=addr[:port]=onion` will not be detected as inbound onion connections
*
* - I2P peers
*
* - CJDNS peers
*
* This helps protect these privacy network peers, which tend to be otherwise
* disadvantaged under our eviction criteria for their higher min ping times
* relative to IPv4/IPv6 peers, and favorise the diversity of peer connections.
*/
void ProtectEvictionCandidatesByRatio(std::vector<NodeEvictionCandidate>& vEvictionCandidates);
#endif // BITCOIN_NET_H #endif // BITCOIN_NET_H

26
src/node/connection_types.cpp Normal file
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@ -0,0 +1,26 @@
// Copyright (c) 2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <node/connection_types.h>
#include <cassert>
std::string ConnectionTypeAsString(ConnectionType conn_type)
{
switch (conn_type) {
case ConnectionType::INBOUND:
return "inbound";
case ConnectionType::MANUAL:
return "manual";
case ConnectionType::FEELER:
return "feeler";
case ConnectionType::OUTBOUND_FULL_RELAY:
return "outbound-full-relay";
case ConnectionType::BLOCK_RELAY:
return "block-relay-only";
case ConnectionType::ADDR_FETCH:
return "addr-fetch";
} // no default case, so the compiler can warn about missing cases
assert(false);
}

82
src/node/connection_types.h Normal file
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@ -0,0 +1,82 @@
// Copyright (c) 2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_NODE_CONNECTION_TYPES_H
#define BITCOIN_NODE_CONNECTION_TYPES_H
#include <string>
/** Different types of connections to a peer. This enum encapsulates the
* information we have available at the time of opening or accepting the
* connection. Aside from INBOUND, all types are initiated by us.
*
* If adding or removing types, please update CONNECTION_TYPE_DOC in
* src/rpc/net.cpp and src/qt/rpcconsole.cpp, as well as the descriptions in
* src/qt/guiutil.cpp and src/bitcoin-cli.cpp::NetinfoRequestHandler. */
enum class ConnectionType {
/**
* Inbound connections are those initiated by a peer. This is the only
* property we know at the time of connection, until P2P messages are
* exchanged.
*/
INBOUND,
/**
* These are the default connections that we use to connect with the
* network. There is no restriction on what is relayed; by default we relay
* blocks, addresses & transactions. We automatically attempt to open
* MAX_OUTBOUND_FULL_RELAY_CONNECTIONS using addresses from our AddrMan.
*/
OUTBOUND_FULL_RELAY,
/**
* We open manual connections to addresses that users explicitly requested
* via the addnode RPC or the -addnode/-connect configuration options. Even if a
* manual connection is misbehaving, we do not automatically disconnect or
* add it to our discouragement filter.
*/
MANUAL,
/**
* Feeler connections are short-lived connections made to check that a node
* is alive. They can be useful for:
* - test-before-evict: if one of the peers is considered for eviction from
* our AddrMan because another peer is mapped to the same slot in the tried table,
* evict only if this longer-known peer is offline.
* - move node addresses from New to Tried table, so that we have more
* connectable addresses in our AddrMan.
* Note that in the literature ("Eclipse Attacks on Bitcoin’s Peer-to-Peer Network")
* only the latter feature is referred to as "feeler connections",
* although in our codebase feeler connections encompass test-before-evict as well.
* We make these connections approximately every FEELER_INTERVAL:
* first we resolve previously found collisions if they exist (test-before-evict),
* otherwise we connect to a node from the new table.
*/
FEELER,
/**
* We use block-relay-only connections to help prevent against partition
* attacks. By not relaying transactions or addresses, these connections
* are harder to detect by a third party, thus helping obfuscate the
* network topology. We automatically attempt to open
* MAX_BLOCK_RELAY_ONLY_ANCHORS using addresses from our anchors.dat. Then
* addresses from our AddrMan if MAX_BLOCK_RELAY_ONLY_CONNECTIONS
* isn't reached yet.
*/
BLOCK_RELAY,
/**
* AddrFetch connections are short lived connections used to solicit
* addresses from peers. These are initiated to addresses submitted via the
* -seednode command line argument, or under certain conditions when the
* AddrMan is empty.
*/
ADDR_FETCH,
};
/** Convert ConnectionType enum to a string value */
std::string ConnectionTypeAsString(ConnectionType conn_type);
#endif // BITCOIN_NODE_CONNECTION_TYPES_H

240
src/node/eviction.cpp Normal file
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@ -0,0 +1,240 @@
// Copyright (c) 2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <node/eviction.h>
#include <algorithm>
#include <array>
#include <chrono>
#include <cstdint>
#include <functional>
#include <map>
#include <vector>
static bool ReverseCompareNodeMinPingTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
{
return a.m_min_ping_time > b.m_min_ping_time;
}
static bool ReverseCompareNodeTimeConnected(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
{
return a.m_connected > b.m_connected;
}
static bool CompareNetGroupKeyed(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b) {
return a.nKeyedNetGroup < b.nKeyedNetGroup;
}
static bool CompareNodeBlockTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
{
// There is a fall-through here because it is common for a node to have many peers which have not yet relayed a block.
if (a.m_last_block_time != b.m_last_block_time) return a.m_last_block_time < b.m_last_block_time;
if (a.fRelevantServices != b.fRelevantServices) return b.fRelevantServices;
return a.m_connected > b.m_connected;
}
static bool CompareNodeTXTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
{
// There is a fall-through here because it is common for a node to have more than a few peers that have not yet relayed txn.
if (a.m_last_tx_time != b.m_last_tx_time) return a.m_last_tx_time < b.m_last_tx_time;
if (a.m_relay_txs != b.m_relay_txs) return b.m_relay_txs;
if (a.fBloomFilter != b.fBloomFilter) return a.fBloomFilter;
return a.m_connected > b.m_connected;
}
// Pick out the potential block-relay only peers, and sort them by last block time.
static bool CompareNodeBlockRelayOnlyTime(const NodeEvictionCandidate &a, const NodeEvictionCandidate &b)
{
if (a.m_relay_txs != b.m_relay_txs) return a.m_relay_txs;
if (a.m_last_block_time != b.m_last_block_time) return a.m_last_block_time < b.m_last_block_time;
if (a.fRelevantServices != b.fRelevantServices) return b.fRelevantServices;
return a.m_connected > b.m_connected;
}
/**
* Sort eviction candidates by network/localhost and connection uptime.
* Candidates near the beginning are more likely to be evicted, and those
* near the end are more likely to be protected, e.g. less likely to be evicted.
* - First, nodes that are not `is_local` and that do not belong to `network`,
* sorted by increasing uptime (from most recently connected to connected longer).
* - Then, nodes that are `is_local` or belong to `network`, sorted by increasing uptime.
*/
struct CompareNodeNetworkTime {
const bool m_is_local;
const Network m_network;
CompareNodeNetworkTime(bool is_local, Network network) : m_is_local(is_local), m_network(network) {}
bool operator()(const NodeEvictionCandidate& a, const NodeEvictionCandidate& b) const
{
if (m_is_local && a.m_is_local != b.m_is_local) return b.m_is_local;
if ((a.m_network == m_network) != (b.m_network == m_network)) return b.m_network == m_network;
return a.m_connected > b.m_connected;
};
};
//! Sort an array by the specified comparator, then erase the last K elements where predicate is true.
template <typename T, typename Comparator>
static void EraseLastKElements(
std::vector<T>& elements, Comparator comparator, size_t k,
std::function<bool(const NodeEvictionCandidate&)> predicate = [](const NodeEvictionCandidate& n) { return true; })
{
std::sort(elements.begin(), elements.end(), comparator);
size_t eraseSize = std::min(k, elements.size());
elements.erase(std::remove_if(elements.end() - eraseSize, elements.end(), predicate), elements.end());
}
void ProtectNoBanConnections(std::vector<NodeEvictionCandidate>& eviction_candidates)
{
eviction_candidates.erase(std::remove_if(eviction_candidates.begin(), eviction_candidates.end(),
[](NodeEvictionCandidate const& n) {
return n.m_noban;
}),
eviction_candidates.end());
}
void ProtectOutboundConnections(std::vector<NodeEvictionCandidate>& eviction_candidates)
{
eviction_candidates.erase(std::remove_if(eviction_candidates.begin(), eviction_candidates.end(),
[](NodeEvictionCandidate const& n) {
return n.m_conn_type != ConnectionType::INBOUND;
}),
eviction_candidates.end());
}
void ProtectEvictionCandidatesByRatio(std::vector<NodeEvictionCandidate>& eviction_candidates)
{
// Protect the half of the remaining nodes which have been connected the longest.
// This replicates the non-eviction implicit behavior, and precludes attacks that start later.
// To favorise the diversity of our peer connections, reserve up to half of these protected
// spots for Tor/onion, localhost, I2P, and CJDNS peers, even if they're not longest uptime
// overall. This helps protect these higher-latency peers that tend to be otherwise
// disadvantaged under our eviction criteria.
const size_t initial_size = eviction_candidates.size();
const size_t total_protect_size{initial_size / 2};
// Disadvantaged networks to protect. In the case of equal counts, earlier array members
// have the first opportunity to recover unused slots from the previous iteration.
struct Net { bool is_local; Network id; size_t count; };
std::array<Net, 4> networks{
{{false, NET_CJDNS, 0}, {false, NET_I2P, 0}, {/*localhost=*/true, NET_MAX, 0}, {false, NET_ONION, 0}}};
// Count and store the number of eviction candidates per network.
for (Net& n : networks) {
n.count = std::count_if(eviction_candidates.cbegin(), eviction_candidates.cend(),
[&n](const NodeEvictionCandidate& c) {
return n.is_local ? c.m_is_local : c.m_network == n.id;
});
}
// Sort `networks` by ascending candidate count, to give networks having fewer candidates
// the first opportunity to recover unused protected slots from the previous iteration.
std::stable_sort(networks.begin(), networks.end(), [](Net a, Net b) { return a.count < b.count; });
// Protect up to 25% of the eviction candidates by disadvantaged network.
const size_t max_protect_by_network{total_protect_size / 2};
size_t num_protected{0};
while (num_protected < max_protect_by_network) {
// Count the number of disadvantaged networks from which we have peers to protect.
auto num_networks = std::count_if(networks.begin(), networks.end(), [](const Net& n) { return n.count; });
if (num_networks == 0) {
break;
}
const size_t disadvantaged_to_protect{max_protect_by_network - num_protected};
const size_t protect_per_network{std::max(disadvantaged_to_protect / num_networks, static_cast<size_t>(1))};
// Early exit flag if there are no remaining candidates by disadvantaged network.
bool protected_at_least_one{false};
for (Net& n : networks) {
if (n.count == 0) continue;
const size_t before = eviction_candidates.size();
EraseLastKElements(eviction_candidates, CompareNodeNetworkTime(n.is_local, n.id),
protect_per_network, [&n](const NodeEvictionCandidate& c) {
return n.is_local ? c.m_is_local : c.m_network == n.id;
});
const size_t after = eviction_candidates.size();
if (before > after) {
protected_at_least_one = true;
const size_t delta{before - after};
num_protected += delta;
if (num_protected >= max_protect_by_network) {
break;
}
n.count -= delta;
}
}
if (!protected_at_least_one) {
break;
}
}
// Calculate how many we removed, and update our total number of peers that
// we want to protect based on uptime accordingly.
assert(num_protected == initial_size - eviction_candidates.size());
const size_t remaining_to_protect{total_protect_size - num_protected};
EraseLastKElements(eviction_candidates, ReverseCompareNodeTimeConnected, remaining_to_protect);
}
[[nodiscard]] std::optional<NodeId> SelectNodeToEvict(std::vector<NodeEvictionCandidate>&& vEvictionCandidates)
{
// Protect connections with certain characteristics
ProtectNoBanConnections(vEvictionCandidates);
ProtectOutboundConnections(vEvictionCandidates);
// Deterministically select 4 peers to protect by netgroup.
// An attacker cannot predict which netgroups will be protected
EraseLastKElements(vEvictionCandidates, CompareNetGroupKeyed, 4);
// Protect the 8 nodes with the lowest minimum ping time.
// An attacker cannot manipulate this metric without physically moving nodes closer to the target.
EraseLastKElements(vEvictionCandidates, ReverseCompareNodeMinPingTime, 8);
// Protect 4 nodes that most recently sent us novel transactions accepted into our mempool.
// An attacker cannot manipulate this metric without performing useful work.
EraseLastKElements(vEvictionCandidates, CompareNodeTXTime, 4);
// Protect up to 8 non-tx-relay peers that have sent us novel blocks.
EraseLastKElements(vEvictionCandidates, CompareNodeBlockRelayOnlyTime, 8,
[](const NodeEvictionCandidate& n) { return !n.m_relay_txs && n.fRelevantServices; });
// Protect 4 nodes that most recently sent us novel blocks.
// An attacker cannot manipulate this metric without performing useful work.
EraseLastKElements(vEvictionCandidates, CompareNodeBlockTime, 4);
// Protect some of the remaining eviction candidates by ratios of desirable
// or disadvantaged characteristics.
ProtectEvictionCandidatesByRatio(vEvictionCandidates);
if (vEvictionCandidates.empty()) return std::nullopt;
// If any remaining peers are preferred for eviction consider only them.
// This happens after the other preferences since if a peer is really the best by other criteria (esp relaying blocks)
// then we probably don't want to evict it no matter what.
if (std::any_of(vEvictionCandidates.begin(),vEvictionCandidates.end(),[](NodeEvictionCandidate const &n){return n.prefer_evict;})) {
vEvictionCandidates.erase(std::remove_if(vEvictionCandidates.begin(),vEvictionCandidates.end(),
[](NodeEvictionCandidate const &n){return !n.prefer_evict;}),vEvictionCandidates.end());
}
// Identify the network group with the most connections and youngest member.
// (vEvictionCandidates is already sorted by reverse connect time)
uint64_t naMostConnections;
unsigned int nMostConnections = 0;
std::chrono::seconds nMostConnectionsTime{0};
std::map<uint64_t, std::vector<NodeEvictionCandidate> > mapNetGroupNodes;
for (const NodeEvictionCandidate &node : vEvictionCandidates) {
std::vector<NodeEvictionCandidate> &group = mapNetGroupNodes[node.nKeyedNetGroup];
group.push_back(node);
const auto grouptime{group[0].m_connected};
if (group.size() > nMostConnections || (group.size() == nMostConnections && grouptime > nMostConnectionsTime)) {
nMostConnections = group.size();
nMostConnectionsTime = grouptime;
naMostConnections = node.nKeyedNetGroup;
}
}
// Reduce to the network group with the most connections
vEvictionCandidates = std::move(mapNetGroupNodes[naMostConnections]);
// Disconnect from the network group with the most connections
return vEvictionCandidates.front().id;
}

69
src/node/eviction.h Normal file
View File

@ -0,0 +1,69 @@
// Copyright (c) 2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_NODE_EVICTION_H
#define BITCOIN_NODE_EVICTION_H
#include <node/connection_types.h>
#include <net_permissions.h>
#include <chrono>
#include <cstdint>
#include <optional>
#include <vector>
typedef int64_t NodeId;
struct NodeEvictionCandidate {
NodeId id;
std::chrono::seconds m_connected;
std::chrono::microseconds m_min_ping_time;
std::chrono::seconds m_last_block_time;
std::chrono::seconds m_last_tx_time;
bool fRelevantServices;
bool m_relay_txs;
bool fBloomFilter;
uint64_t nKeyedNetGroup;
bool prefer_evict;
bool m_is_local;
Network m_network;
bool m_noban;
ConnectionType m_conn_type;
};
/**
* Select an inbound peer to evict after filtering out (protecting) peers having
* distinct, difficult-to-forge characteristics. The protection logic picks out
* fixed numbers of desirable peers per various criteria, followed by (mostly)
* ratios of desirable or disadvantaged peers. If any eviction candidates
* remain, the selection logic chooses a peer to evict.
*/
[[nodiscard]] std::optional<NodeId> SelectNodeToEvict(std::vector<NodeEvictionCandidate>&& vEvictionCandidates);
/** Protect desirable or disadvantaged inbound peers from eviction by ratio.
*
* This function protects half of the peers which have been connected the
* longest, to replicate the non-eviction implicit behavior and preclude attacks
* that start later.
*
* Half of these protected spots (1/4 of the total) are reserved for the
* following categories of peers, sorted by longest uptime, even if they're not
* longest uptime overall:
*
* - onion peers connected via our tor control service
*
* - localhost peers, as manually configured hidden services not using
* `-bind=addr[:port]=onion` will not be detected as inbound onion connections
*
* - I2P peers
*
* - CJDNS peers
*
* This helps protect these privacy network peers, which tend to be otherwise
* disadvantaged under our eviction criteria for their higher min ping times
* relative to IPv4/IPv6 peers, and favorise the diversity of peer connections.
*/
void ProtectEvictionCandidatesByRatio(std::vector<NodeEvictionCandidate>& vEvictionCandidates);
#endif // BITCOIN_NODE_EVICTION_H

2
src/test/fuzz/node_eviction.cpp
View File

@ -32,6 +32,8 @@ FUZZ_TARGET(node_eviction)
/* prefer_evict */ fuzzed_data_provider.ConsumeBool(), /* prefer_evict */ fuzzed_data_provider.ConsumeBool(),
/* m_is_local */ fuzzed_data_provider.ConsumeBool(), /* m_is_local */ fuzzed_data_provider.ConsumeBool(),
/* m_network */ fuzzed_data_provider.PickValueInArray(ALL_NETWORKS), /* m_network */ fuzzed_data_provider.PickValueInArray(ALL_NETWORKS),
/* m_noban */ fuzzed_data_provider.ConsumeBool(),
/* m_conn_type */ fuzzed_data_provider.PickValueInArray(ALL_CONNECTION_TYPES),
}); });
} }
// Make a copy since eviction_candidates may be in some valid but otherwise // Make a copy since eviction_candidates may be in some valid but otherwise

3
src/test/util/net.cpp
View File

@ -5,6 +5,7 @@
#include <test/util/net.h> #include <test/util/net.h>
#include <chainparams.h> #include <chainparams.h>
#include <node/eviction.h>
#include <net.h> #include <net.h>
#include <net_processing.h> #include <net_processing.h>
#include <netmessagemaker.h> #include <netmessagemaker.h>
@ -128,6 +129,8 @@ std::vector<NodeEvictionCandidate> GetRandomNodeEvictionCandidates(int n_candida
/* prefer_evict */ random_context.randbool(), /* prefer_evict */ random_context.randbool(),
/* m_is_local */ random_context.randbool(), /* m_is_local */ random_context.randbool(),
/* m_network */ ALL_NETWORKS[random_context.randrange(ALL_NETWORKS.size())], /* m_network */ ALL_NETWORKS[random_context.randrange(ALL_NETWORKS.size())],
/* m_noban */ false,
/* m_conn_type */ConnectionType::INBOUND,
}); });
} }
return candidates; return candidates;

1
src/test/util/net.h
View File

@ -6,6 +6,7 @@
#define BITCOIN_TEST_UTIL_NET_H #define BITCOIN_TEST_UTIL_NET_H
#include <compat.h> #include <compat.h>
#include <node/eviction.h>
#include <netaddress.h> #include <netaddress.h>
#include <net.h> #include <net.h>
#include <util/sock.h> #include <util/sock.h>