p2p/discover: implement node bonding
This a fix for an attack vector where the discovery protocol could be used to amplify traffic in a DDOS attack. A malicious actor would send a findnode request with the IP address and UDP port of the target as the source address. The recipient of the findnode packet would then send a neighbors packet (which is 16x the size of findnode) to the victim. Our solution is to require a 'bond' with the sender of findnode. If no bond exists, the findnode packet is not processed. A bond between nodes α and β is created when α replies to a ping from β. This (initial) version of the bonding implementation might still be vulnerable against replay attacks during the expiration time window. We will add stricter source address validation later.
This commit is contained in:
Felix Lange
@ -14,9 +14,10 @@ import (
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)
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const (
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alpha = 3 // Kademlia concurrency factor
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bucketSize = 16 // Kademlia bucket size
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nBuckets = nodeIDBits + 1 // Number of buckets
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alpha = 3 // Kademlia concurrency factor
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bucketSize = 16 // Kademlia bucket size
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nBuckets = nodeIDBits + 1 // Number of buckets
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maxBondingPingPongs = 10
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)
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type Table struct {
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@ -24,27 +25,50 @@ type Table struct {
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buckets [nBuckets]*bucket // index of known nodes by distance
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nursery []*Node // bootstrap nodes
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bondmu sync.Mutex
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bonding map[NodeID]*bondproc
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bondslots chan struct{} // limits total number of active bonding processes
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net transport
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self *Node // metadata of the local node
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db *nodeDB
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}
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type bondproc struct {
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err error
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n *Node
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done chan struct{}
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}
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// transport is implemented by the UDP transport.
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// it is an interface so we can test without opening lots of UDP
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// sockets and without generating a private key.
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type transport interface {
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ping(*Node) error
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findnode(e *Node, target NodeID) ([]*Node, error)
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ping(NodeID, *net.UDPAddr) error
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waitping(NodeID) error
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findnode(toid NodeID, addr *net.UDPAddr, target NodeID) ([]*Node, error)
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close()
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}
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// bucket contains nodes, ordered by their last activity.
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// the entry that was most recently active is the last element
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// in entries.
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type bucket struct {
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lastLookup time.Time
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entries []*Node
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}
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func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr) *Table {
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tab := &Table{net: t, self: newNode(ourID, ourAddr)}
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tab := &Table{
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net: t,
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db: new(nodeDB),
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self: newNode(ourID, ourAddr),
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bonding: make(map[NodeID]*bondproc),
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bondslots: make(chan struct{}, maxBondingPingPongs),
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}
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for i := 0; i < cap(tab.bondslots); i++ {
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tab.bondslots <- struct{}{}
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}
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for i := range tab.buckets {
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tab.buckets[i] = new(bucket)
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}
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@ -107,8 +131,8 @@ func (tab *Table) Lookup(target NodeID) []*Node {
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asked[n.ID] = true
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pendingQueries++
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go func() {
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result, _ := tab.net.findnode(n, target)
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reply <- result
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r, _ := tab.net.findnode(n.ID, n.addr(), target)
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reply <- tab.bondall(r)
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}()
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}
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}
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@ -116,13 +140,11 @@ func (tab *Table) Lookup(target NodeID) []*Node {
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// we have asked all closest nodes, stop the search
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break
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}
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// wait for the next reply
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for _, n := range <-reply {
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cn := n
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if !seen[n.ID] {
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if n != nil && !seen[n.ID] {
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seen[n.ID] = true
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result.push(cn, bucketSize)
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result.push(n, bucketSize)
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}
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}
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pendingQueries--
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@ -145,8 +167,9 @@ func (tab *Table) refresh() {
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result := tab.Lookup(randomID(tab.self.ID, ld))
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if len(result) == 0 {
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// bootstrap the table with a self lookup
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all := tab.bondall(tab.nursery)
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tab.mutex.Lock()
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tab.add(tab.nursery)
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tab.add(all)
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tab.mutex.Unlock()
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tab.Lookup(tab.self.ID)
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// TODO: the Kademlia paper says that we're supposed to perform
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@ -176,45 +199,105 @@ func (tab *Table) len() (n int) {
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return n
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}
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// bumpOrAdd updates the activity timestamp for the given node and
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// attempts to insert the node into a bucket. The returned Node might
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// not be part of the table. The caller must hold tab.mutex.
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func (tab *Table) bumpOrAdd(node NodeID, from *net.UDPAddr) (n *Node) {
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b := tab.buckets[logdist(tab.self.ID, node)]
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if n = b.bump(node); n == nil {
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n = newNode(node, from)
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if len(b.entries) == bucketSize {
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tab.pingReplace(n, b)
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} else {
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b.entries = append(b.entries, n)
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// bondall bonds with all given nodes concurrently and returns
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// those nodes for which bonding has probably succeeded.
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func (tab *Table) bondall(nodes []*Node) (result []*Node) {
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rc := make(chan *Node, len(nodes))
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for i := range nodes {
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go func(n *Node) {
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nn, _ := tab.bond(false, n.ID, n.addr(), uint16(n.TCPPort))
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rc <- nn
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}(nodes[i])
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}
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for _ = range nodes {
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if n := <-rc; n != nil {
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result = append(result, n)
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}
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}
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return n
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return result
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}
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func (tab *Table) pingReplace(n *Node, b *bucket) {
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old := b.entries[bucketSize-1]
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go func() {
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if err := tab.net.ping(old); err == nil {
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// it responded, we don't need to replace it.
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// bond ensures the local node has a bond with the given remote node.
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// It also attempts to insert the node into the table if bonding succeeds.
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// The caller must not hold tab.mutex.
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//
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// A bond is must be established before sending findnode requests.
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// Both sides must have completed a ping/pong exchange for a bond to
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// exist. The total number of active bonding processes is limited in
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// order to restrain network use.
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//
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// bond is meant to operate idempotently in that bonding with a remote
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// node which still remembers a previously established bond will work.
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// The remote node will simply not send a ping back, causing waitping
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// to time out.
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//
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// If pinged is true, the remote node has just pinged us and one half
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// of the process can be skipped.
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func (tab *Table) bond(pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) (*Node, error) {
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var n *Node
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if n = tab.db.get(id); n == nil {
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tab.bondmu.Lock()
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w := tab.bonding[id]
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if w != nil {
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// Wait for an existing bonding process to complete.
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tab.bondmu.Unlock()
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<-w.done
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} else {
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// Register a new bonding process.
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w = &bondproc{done: make(chan struct{})}
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tab.bonding[id] = w
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tab.bondmu.Unlock()
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// Do the ping/pong. The result goes into w.
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tab.pingpong(w, pinged, id, addr, tcpPort)
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// Unregister the process after it's done.
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tab.bondmu.Lock()
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delete(tab.bonding, id)
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tab.bondmu.Unlock()
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}
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n = w.n
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if w.err != nil {
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return nil, w.err
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}
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}
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tab.mutex.Lock()
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defer tab.mutex.Unlock()
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if b := tab.buckets[logdist(tab.self.ID, n.ID)]; !b.bump(n) {
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tab.pingreplace(n, b)
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}
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return n, nil
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}
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func (tab *Table) pingpong(w *bondproc, pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) {
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<-tab.bondslots
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defer func() { tab.bondslots <- struct{}{} }()
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if w.err = tab.net.ping(id, addr); w.err != nil {
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close(w.done)
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return
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}
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if !pinged {
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// Give the remote node a chance to ping us before we start
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// sending findnode requests. If they still remember us,
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// waitping will simply time out.
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tab.net.waitping(id)
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}
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w.n = tab.db.add(id, addr, tcpPort)
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close(w.done)
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}
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func (tab *Table) pingreplace(new *Node, b *bucket) {
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if len(b.entries) == bucketSize {
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oldest := b.entries[bucketSize-1]
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if err := tab.net.ping(oldest.ID, oldest.addr()); err == nil {
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// The node responded, we don't need to replace it.
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return
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}
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// it didn't respond, replace the node if it is still the oldest node.
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tab.mutex.Lock()
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if len(b.entries) > 0 && b.entries[len(b.entries)-1] == old {
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// slide down other entries and put the new one in front.
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// TODO: insert in correct position to keep the order
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copy(b.entries[1:], b.entries)
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b.entries[0] = n
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}
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tab.mutex.Unlock()
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}()
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}
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// bump updates the activity timestamp for the given node.
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// The caller must hold tab.mutex.
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func (tab *Table) bump(node NodeID) {
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tab.buckets[logdist(tab.self.ID, node)].bump(node)
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} else {
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// Add a slot at the end so the last entry doesn't
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// fall off when adding the new node.
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b.entries = append(b.entries, nil)
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}
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copy(b.entries[1:], b.entries)
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b.entries[0] = new
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}
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// add puts the entries into the table if their corresponding
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@ -240,17 +323,17 @@ outer:
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}
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}
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func (b *bucket) bump(id NodeID) *Node {
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for i, n := range b.entries {
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if n.ID == id {
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n.active = time.Now()
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func (b *bucket) bump(n *Node) bool {
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for i := range b.entries {
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if b.entries[i].ID == n.ID {
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n.bumpActive()
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// move it to the front
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copy(b.entries[1:], b.entries[:i+1])
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b.entries[0] = n
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return n
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return true
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}
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}
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return nil
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return false
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}
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// nodesByDistance is a list of nodes, ordered by
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