les/utils: UDP rate limiter (#21930)
* les/utils: Limiter * les/utils: dropped prior weight vs variable cost logic, using fixed weights * les/utils: always create node selector in addressGroup * les/utils: renamed request weight to request cost * les/utils: simplified and improved the DoS penalty mechanism * les/utils: minor fixes * les/utils: made selection weight calculation nicer * les/utils: fixed linter warning * les/utils: more precise and reliable probabilistic test * les/utils: fixed linter warning
This commit is contained in:
Felföldi Zsolt
GitHub
405
les/utils/limiter.go
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405
les/utils/limiter.go
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// Copyright 2020 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package utils
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import (
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"sort"
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"sync"
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"github.com/ethereum/go-ethereum/p2p/enode"
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)
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const maxSelectionWeight = 1000000000 // maximum selection weight of each individual node/address group
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// Limiter protects a network request serving mechanism from denial-of-service attacks.
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// It limits the total amount of resources used for serving requests while ensuring that
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// the most valuable connections always have a reasonable chance of being served.
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type Limiter struct {
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lock sync.Mutex
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cond *sync.Cond
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quit bool
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nodes map[enode.ID]*nodeQueue
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addresses map[string]*addressGroup
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addressSelect, valueSelect *WeightedRandomSelect
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maxValue float64
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maxCost, sumCost, sumCostLimit uint
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selectAddressNext bool
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}
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// nodeQueue represents queued requests coming from a single node ID
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type nodeQueue struct {
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queue []request // always nil if penaltyCost != 0
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id enode.ID
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address string
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value float64
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flatWeight, valueWeight uint64 // current selection weights in the address/value selectors
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sumCost uint // summed cost of requests queued by the node
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penaltyCost uint // cumulative cost of dropped requests since last processed request
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groupIndex int
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}
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// addressGroup is a group of node IDs that have sent their last requests from the same
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// network address
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type addressGroup struct {
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nodes []*nodeQueue
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nodeSelect *WeightedRandomSelect
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sumFlatWeight, groupWeight uint64
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}
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// request represents an incoming request scheduled for processing
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type request struct {
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process chan chan struct{}
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cost uint
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}
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// flatWeight distributes weights equally between each active network address
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func flatWeight(item interface{}) uint64 { return item.(*nodeQueue).flatWeight }
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// add adds the node queue to the address group. It is the caller's responsibility to
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// add the address group to the address map and the address selector if it wasn't
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// there before.
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func (ag *addressGroup) add(nq *nodeQueue) {
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if nq.groupIndex != -1 {
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panic("added node queue is already in an address group")
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}
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l := len(ag.nodes)
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nq.groupIndex = l
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ag.nodes = append(ag.nodes, nq)
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ag.sumFlatWeight += nq.flatWeight
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ag.groupWeight = ag.sumFlatWeight / uint64(l+1)
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ag.nodeSelect.Update(ag.nodes[l])
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}
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// update updates the selection weight of the node queue inside the address group.
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// It is the caller's responsibility to update the group's selection weight in the
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// address selector.
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func (ag *addressGroup) update(nq *nodeQueue, weight uint64) {
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if nq.groupIndex == -1 || nq.groupIndex >= len(ag.nodes) || ag.nodes[nq.groupIndex] != nq {
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panic("updated node queue is not in this address group")
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}
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ag.sumFlatWeight += weight - nq.flatWeight
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nq.flatWeight = weight
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ag.groupWeight = ag.sumFlatWeight / uint64(len(ag.nodes))
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ag.nodeSelect.Update(nq)
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}
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// remove removes the node queue from the address group. It is the caller's responsibility
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// to remove the address group from the address map if it is empty.
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func (ag *addressGroup) remove(nq *nodeQueue) {
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if nq.groupIndex == -1 || nq.groupIndex >= len(ag.nodes) || ag.nodes[nq.groupIndex] != nq {
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panic("removed node queue is not in this address group")
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}
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l := len(ag.nodes) - 1
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if nq.groupIndex != l {
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ag.nodes[nq.groupIndex] = ag.nodes[l]
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ag.nodes[nq.groupIndex].groupIndex = nq.groupIndex
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}
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nq.groupIndex = -1
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ag.nodes = ag.nodes[:l]
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ag.sumFlatWeight -= nq.flatWeight
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if l >= 1 {
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ag.groupWeight = ag.sumFlatWeight / uint64(l)
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} else {
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ag.groupWeight = 0
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}
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ag.nodeSelect.Remove(nq)
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}
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// choose selects one of the node queues belonging to the address group
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func (ag *addressGroup) choose() *nodeQueue {
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return ag.nodeSelect.Choose().(*nodeQueue)
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}
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// NewLimiter creates a new Limiter
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func NewLimiter(sumCostLimit uint) *Limiter {
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l := &Limiter{
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addressSelect: NewWeightedRandomSelect(func(item interface{}) uint64 { return item.(*addressGroup).groupWeight }),
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valueSelect: NewWeightedRandomSelect(func(item interface{}) uint64 { return item.(*nodeQueue).valueWeight }),
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nodes: make(map[enode.ID]*nodeQueue),
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addresses: make(map[string]*addressGroup),
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sumCostLimit: sumCostLimit,
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}
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l.cond = sync.NewCond(&l.lock)
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go l.processLoop()
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return l
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}
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// selectionWeights calculates the selection weights of a node for both the address and
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// the value selector. The selection weight depends on the next request cost or the
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// summed cost of recently dropped requests.
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func (l *Limiter) selectionWeights(reqCost uint, value float64) (flatWeight, valueWeight uint64) {
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if value > l.maxValue {
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l.maxValue = value
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}
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if value > 0 {
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// normalize value to <= 1
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value /= l.maxValue
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}
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if reqCost > l.maxCost {
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l.maxCost = reqCost
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}
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relCost := float64(reqCost) / float64(l.maxCost)
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var f float64
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if relCost <= 0.001 {
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f = 1
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} else {
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f = 0.001 / relCost
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}
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f *= maxSelectionWeight
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flatWeight, valueWeight = uint64(f), uint64(f*value)
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if flatWeight == 0 {
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flatWeight = 1
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}
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return
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}
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// Add adds a new request to the node queue belonging to the given id. Value belongs
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// to the requesting node. A higher value gives the request a higher chance of being
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// served quickly in case of heavy load or a DDoS attack. Cost is a rough estimate
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// of the serving cost of the request. A lower cost also gives the request a
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// better chance.
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func (l *Limiter) Add(id enode.ID, address string, value float64, reqCost uint) chan chan struct{} {
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l.lock.Lock()
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defer l.lock.Unlock()
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process := make(chan chan struct{}, 1)
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if l.quit {
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close(process)
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return process
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}
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if reqCost == 0 {
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reqCost = 1
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}
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if nq, ok := l.nodes[id]; ok {
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if nq.queue != nil {
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nq.queue = append(nq.queue, request{process, reqCost})
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nq.sumCost += reqCost
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nq.value = value
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if address != nq.address {
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// known id sending request from a new address, move to different address group
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l.removeFromGroup(nq)
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l.addToGroup(nq, address)
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}
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} else {
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// already waiting on a penalty, just add to the penalty cost and drop the request
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nq.penaltyCost += reqCost
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l.update(nq)
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close(process)
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return process
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}
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} else {
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nq := &nodeQueue{
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queue: []request{{process, reqCost}},
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id: id,
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value: value,
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sumCost: reqCost,
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groupIndex: -1,
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}
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nq.flatWeight, nq.valueWeight = l.selectionWeights(reqCost, value)
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if len(l.nodes) == 0 {
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l.cond.Signal()
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}
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l.nodes[id] = nq
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if nq.valueWeight != 0 {
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l.valueSelect.Update(nq)
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}
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l.addToGroup(nq, address)
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}
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l.sumCost += reqCost
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if l.sumCost > l.sumCostLimit {
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l.dropRequests()
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}
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return process
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}
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// update updates the selection weights of the node queue
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func (l *Limiter) update(nq *nodeQueue) {
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var cost uint
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if nq.queue != nil {
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cost = nq.queue[0].cost
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} else {
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cost = nq.penaltyCost
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}
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flatWeight, valueWeight := l.selectionWeights(cost, nq.value)
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ag := l.addresses[nq.address]
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ag.update(nq, flatWeight)
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l.addressSelect.Update(ag)
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nq.valueWeight = valueWeight
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l.valueSelect.Update(nq)
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}
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// addToGroup adds the node queue to the given address group. The group is created if
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// it does not exist yet.
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func (l *Limiter) addToGroup(nq *nodeQueue, address string) {
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nq.address = address
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ag := l.addresses[address]
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if ag == nil {
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ag = &addressGroup{nodeSelect: NewWeightedRandomSelect(flatWeight)}
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l.addresses[address] = ag
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}
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ag.add(nq)
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l.addressSelect.Update(ag)
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}
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// removeFromGroup removes the node queue from its address group
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func (l *Limiter) removeFromGroup(nq *nodeQueue) {
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ag := l.addresses[nq.address]
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ag.remove(nq)
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if len(ag.nodes) == 0 {
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delete(l.addresses, nq.address)
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}
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l.addressSelect.Update(ag)
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}
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// remove removes the node queue from its address group, the nodes map and the value
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// selector
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func (l *Limiter) remove(nq *nodeQueue) {
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l.removeFromGroup(nq)
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if nq.valueWeight != 0 {
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l.valueSelect.Remove(nq)
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}
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delete(l.nodes, nq.id)
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}
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// choose selects the next node queue to process.
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func (l *Limiter) choose() *nodeQueue {
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if l.valueSelect.IsEmpty() || l.selectAddressNext {
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if ag, ok := l.addressSelect.Choose().(*addressGroup); ok {
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l.selectAddressNext = false
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return ag.choose()
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}
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}
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nq, _ := l.valueSelect.Choose().(*nodeQueue)
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l.selectAddressNext = true
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return nq
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}
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// processLoop processes requests sequentially
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func (l *Limiter) processLoop() {
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l.lock.Lock()
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defer l.lock.Unlock()
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for {
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if l.quit {
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for _, nq := range l.nodes {
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for _, request := range nq.queue {
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close(request.process)
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}
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}
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return
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}
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nq := l.choose()
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if nq == nil {
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l.cond.Wait()
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continue
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}
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if nq.queue != nil {
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request := nq.queue[0]
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nq.queue = nq.queue[1:]
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nq.sumCost -= request.cost
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l.sumCost -= request.cost
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l.lock.Unlock()
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ch := make(chan struct{})
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request.process <- ch
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<-ch
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l.lock.Lock()
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if len(nq.queue) > 0 {
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l.update(nq)
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} else {
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l.remove(nq)
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}
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} else {
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// penalized queue removed, next request will be added to a clean queue
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l.remove(nq)
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}
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}
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}
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// Stop stops the processing loop. All queued and future requests are rejected.
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func (l *Limiter) Stop() {
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l.lock.Lock()
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defer l.lock.Unlock()
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l.quit = true
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l.cond.Signal()
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}
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type (
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dropList []dropListItem
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dropListItem struct {
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nq *nodeQueue
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priority float64
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}
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)
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func (l dropList) Len() int {
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return len(l)
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}
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func (l dropList) Less(i, j int) bool {
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return l[i].priority < l[j].priority
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}
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func (l dropList) Swap(i, j int) {
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l[i], l[j] = l[j], l[i]
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}
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// dropRequests selects the nodes with the highest queued request cost to selection
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// weight ratio and drops their queued request. The empty node queues stay in the
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// selectors with a low selection weight in order to penalize these nodes.
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func (l *Limiter) dropRequests() {
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var (
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sumValue float64
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list dropList
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)
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for _, nq := range l.nodes {
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sumValue += nq.value
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}
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for _, nq := range l.nodes {
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if nq.sumCost == 0 {
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continue
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}
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w := 1 / float64(len(l.addresses)*len(l.addresses[nq.address].nodes))
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if sumValue > 0 {
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w += nq.value / sumValue
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}
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list = append(list, dropListItem{
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nq: nq,
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priority: w / float64(nq.sumCost),
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})
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}
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sort.Sort(list)
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for _, item := range list {
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for _, request := range item.nq.queue {
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close(request.process)
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}
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// make the queue penalized; no more requests are accepted until the node is
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// selected based on the penalty cost which is the cumulative cost of all dropped
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// requests. This ensures that sending excess requests is always penalized
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// and incentivizes the sender to stop for a while if no replies are received.
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item.nq.queue = nil
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item.nq.penaltyCost = item.nq.sumCost
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l.sumCost -= item.nq.sumCost // penalty costs are not counted in sumCost
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item.nq.sumCost = 0
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l.update(item.nq)
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if l.sumCost <= l.sumCostLimit/2 {
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return
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}
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}
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}
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