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author | dergoegge <n.goeggi@gmail.com> | 2022-05-26 16:07:04 +0200 |
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committer | dergoegge <n.goeggi@gmail.com> | 2022-07-06 18:13:54 +0200 |
commit | 0101d2bc3c3bcf698d6cc2a237a680fc52395987 (patch) | |
tree | 7b5429e73afc057679b828d907034c3bf9be9273 /src/node/eviction.cpp | |
parent | c741d748d4d9836940b99091cc7be09c65efcb79 (diff) | |
download | bitcoin-0101d2bc3c3bcf698d6cc2a237a680fc52395987.tar.xz |
[net] Move eviction logic to its own file
Diffstat (limited to 'src/node/eviction.cpp')
-rw-r--r-- | src/node/eviction.cpp | 240 |
1 files changed, 240 insertions, 0 deletions
diff --git a/src/node/eviction.cpp b/src/node/eviction.cpp new file mode 100644 index 0000000000..33406931d4 --- /dev/null +++ b/src/node/eviction.cpp @@ -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; +} |