// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package discover
import (
"bytes"
"container/list"
"crypto/ecdsa"
"errors"
"fmt"
"net"
"time"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/log"
"github.com/ethereum/go-ethereum/p2p/nat"
"github.com/ethereum/go-ethereum/p2p/netutil"
"github.com/ethereum/go-ethereum/rlp"
)
const Version = 4
// Errors
var (
errPacketTooSmall = errors.New("too small")
errBadHash = errors.New("bad hash")
errExpired = errors.New("expired")
errUnsolicitedReply = errors.New("unsolicited reply")
errUnknownNode = errors.New("unknown node")
errTimeout = errors.New("RPC timeout")
errClockWarp = errors.New("reply deadline too far in the future")
errClosed = errors.New("socket closed")
)
// Timeouts
const (
respTimeout = 500 * time.Millisecond
sendTimeout = 500 * time.Millisecond
expiration = 20 * time.Second
ntpFailureThreshold = 32 // Continuous timeouts after which to check NTP
ntpWarningCooldown = 10 * time.Minute // Minimum amount of time to pass before repeating NTP warning
driftThreshold = 10 * time.Second // Allowed clock drift before warning user
)
// RPC packet types
const (
pingPacket = iota + 1 // zero is 'reserved'
pongPacket
findnodePacket
neighborsPacket
)
// RPC request structures
type (
ping struct {
Version uint
From, To rpcEndpoint
Expiration uint64
// Ignore additional fields (for forward compatibility).
Rest []rlp.RawValue `rlp:"tail"`
}
// pong is the reply to ping.
pong struct {
// This field should mirror the UDP envelope address
// of the ping packet, which provides a way to discover the
// the external address (after NAT).
To rpcEndpoint
ReplyTok []byte // This contains the hash of the ping packet.
Expiration uint64 // Absolute timestamp at which the packet becomes invalid.
// Ignore additional fields (for forward compatibility).
Rest []rlp.RawValue `rlp:"tail"`
}
// findnode is a query for nodes close to the given target.
findnode struct {
Target NodeID // doesn't need to be an actual public key
Expiration uint64
// Ignore additional fields (for forward compatibility).
Rest []rlp.RawValue `rlp:"tail"`
}
// reply to findnode
neighbors struct {
Nodes []rpcNode
Expiration uint64
// Ignore additional fields (for forward compatibility).
Rest []rlp.RawValue `rlp:"tail"`
}
rpcNode struct {
IP net.IP // len 4 for IPv4 or 16 for IPv6
UDP uint16 // for discovery protocol
TCP uint16 // for RLPx protocol
ID NodeID
}
rpcEndpoint struct {
IP net.IP // len 4 for IPv4 or 16 for IPv6
UDP uint16 // for discovery protocol
TCP uint16 // for RLPx protocol
}
)
func makeEndpoint(addr *net.UDPAddr, tcpPort uint16) rpcEndpoint {
ip := addr.IP.To4()
if ip == nil {
ip = addr.IP.To16()
}
return rpcEndpoint{IP: ip, UDP: uint16(addr.Port), TCP: tcpPort}
}
func (t *udp) nodeFromRPC(sender *net.UDPAddr, rn rpcNode) (*Node, error) {
if rn.UDP <= 1024 {
return nil, errors.New("low port")
}
if err := netutil.CheckRelayIP(sender.IP, rn.IP); err != nil {
return nil, err
}
if t.netrestrict != nil && !t.netrestrict.Contains(rn.IP) {
return nil, errors.New("not contained in netrestrict whitelist")
}
n := NewNode(rn.ID, rn.IP, rn.UDP, rn.TCP)
err := n.validateComplete()
return n, err
}
func nodeToRPC(n *Node) rpcNode {
return rpcNode{ID: n.ID, IP: n.IP, UDP: n.UDP, TCP: n.TCP}
}
type packet interface {
handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error
name() string
}
type conn interface {
ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err error)
WriteToUDP(b []byte, addr *net.UDPAddr) (n int, err error)
Close() error
LocalAddr() net.Addr
}
// udp implements the RPC protocol.
type udp struct {
conn conn
netrestrict *netutil.Netlist
priv *ecdsa.PrivateKey
ourEndpoint rpcEndpoint
addpending chan *pending
gotreply chan reply
closing chan struct{}
nat nat.Interface
*Table
}
// pending represents a pending reply.
//
// some implementations of the protocol wish to send more than one
// reply packet to findnode. in general, any neighbors packet cannot
// be matched up with a specific findnode packet.
//
// our implementation handles this by storing a callback function for
// each pending reply. incoming packets from a node are dispatched
// to all the callback functions for that node.
type pending struct {
// these fields must match in the reply.
from NodeID
ptype byte
// time when the request must complete
deadline time.Time
// callback is called when a matching reply arrives. if it returns
// true, the callback is removed from the pending reply queue.
// if it returns false, the reply is considered incomplete and
// the callback will be invoked again for the next matching reply.
callback func(resp interface{}) (done bool)
// errc receives nil when the callback indicates completion or an
// error if no further reply is received within the timeout.
errc chan<- error
}
type reply struct {
from NodeID
ptype byte
data interface{}
// loop indicates whether there was
// a matching request by sending on this channel.
matched chan<- bool
}
// ReadPacket is sent to the unhandled channel when it could not be processed
type ReadPacket struct {
Data []byte
Addr *net.UDPAddr
}
// Config holds Table-related settings.
type Config struct {
// These settings are required and configure the UDP listener:
PrivateKey *ecdsa.PrivateKey
// These settings are optional:
AnnounceAddr *net.UDPAddr // local address announced in the DHT
NodeDBPath string // if set, the node database is stored at this filesystem location
NetRestrict *netutil.Netlist // network whitelist
Bootnodes []*Node // list of bootstrap nodes
Unhandled chan<- ReadPacket // unhandled packets are sent on this channel
}
// ListenUDP returns a new table that listens for UDP packets on laddr.
func ListenUDP(c conn, cfg Config) (*Table, error) {
tab, _, err := newUDP(c, cfg)
if err != nil {
return nil, err
}
log.Info("UDP listener up", "self", tab.self)
return tab, nil
}
func newUDP(c conn, cfg Config) (*Table, *udp, error) {
udp := &udp{
conn: c,
priv: cfg.PrivateKey,
netrestrict: cfg.NetRestrict,
closing: make(chan struct{}),
gotreply: make(chan reply),
addpending: make(chan *pending),
}
realaddr := c.LocalAddr().(*net.UDPAddr)
if cfg.AnnounceAddr != nil {
realaddr = cfg.AnnounceAddr
}
// TODO: separate TCP port
udp.ourEndpoint = makeEndpoint(realaddr, uint16(realaddr.Port))
tab, err := newTable(udp, PubkeyID(&cfg.PrivateKey.PublicKey), realaddr, cfg.NodeDBPath, cfg.Bootnodes)
if err != nil {
return nil, nil, err
}
udp.Table = tab
go udp.loop()
go udp.readLoop(cfg.Unhandled)
return udp.Table, udp, nil
}
func (t *udp) close() {
close(t.closing)
t.conn.Close()
// TODO: wait for the loops to end.
}
// ping sends a ping message to the given node and waits for a reply.
func (t *udp) ping(toid NodeID, toaddr *net.UDPAddr) error {
req := &ping{
Version: Version,
From: t.ourEndpoint,
To: makeEndpoint(toaddr, 0), // TODO: maybe use known TCP port from DB
Expiration: uint64(time.Now().Add(expiration).Unix()),
}
packet, hash, err := encodePacket(t.priv, pingPacket, req)
if err != nil {
return err
}
errc := t.pending(toid, pongPacket, func(p interface{}) bool {
return bytes.Equal(p.(*pong).ReplyTok, hash)
})
t.write(toaddr, req.name(), packet)
return <-errc
}
func (t *udp) waitping(from NodeID) error {
return <-t.pending(from, pingPacket, func(interface{}) bool { return true })
}
// findnode sends a findnode request to the given node and waits until
// the node has sent up to k neighbors.
func (t *udp) findnode(toid NodeID, toaddr *net.UDPAddr, target NodeID) ([]*Node, error) {
nodes := make([]*Node, 0, bucketSize)
nreceived := 0
errc := t.pending(toid, neighborsPacket, func(r interface{}) bool {
reply := r.(*neighbors)
for _, rn := range reply.Nodes {
nreceived++
n, err := t.nodeFromRPC(toaddr, rn)
if err != nil {
log.Trace("Invalid neighbor node received", "ip", rn.IP, "addr", toaddr, "err", err)
continue
}
nodes = append(nodes, n)
}
return nreceived >= bucketSize
})
t.send(toaddr, findnodePacket, &findnode{
Target: target,
Expiration: uint64(time.Now().Add(expiration).Unix()),
})
err := <-errc
return nodes, err
}
// pending adds a reply callback to the pending reply queue.
// see the documentation of type pending for a detailed explanation.
func (t *udp) pending(id NodeID, ptype byte, callback func(interface{}) bool) <-chan error {
ch := make(chan error, 1)
p := &pending{from: id, ptype: ptype, callback: callback, errc: ch}
select {
case t.addpending <- p:
// loop will handle it
case <-t.closing:
ch <- errClosed
}
return ch
}
func (t *udp) handleReply(from NodeID, ptype byte, req packet) bool {
matched := make(chan bool, 1)
select {
case t.gotreply <- reply{from, ptype, req, matched}:
// loop will handle it
return <-matched
case <-t.closing:
return false
}
}
// loop runs in its own goroutine. it keeps track of
// the refresh timer and the pending reply queue.
func (t *udp) loop() {
var (
plist = list.New()
timeout = time.NewTimer(0)
nextTimeout *pending // head of plist when timeout was last reset
contTimeouts = 0 // number of continuous timeouts to do NTP checks
ntpWarnTime = time.Unix(0, 0)
)
<-timeout.C // ignore first timeout
defer timeout.Stop()
resetTimeout := func() {
if plist.Front() == nil || nextTimeout == plist.Front().Value {
return
}
// Start the timer so it fires when the next pending reply has expired.
now := time.Now()
for el := plist.Front(); el != nil; el = el.Next() {
nextTimeout = el.Value.(*pending)
if dist := nextTimeout.deadline.Sub(now); dist < 2*respTimeout {
timeout.Reset(dist)
return
}
// Remove pending replies whose deadline is too far in the
// future. These can occur if the system clock jumped
// backwards after the deadline was assigned.
nextTimeout.errc <- errClockWarp
plist.Remove(el)
}
nextTimeout = nil
timeout.Stop()
}
for {
resetTimeout()
select {
case <-t.closing:
for el := plist.Front(); el != nil; el = el.Next() {
el.Value.(*pending).errc <- errClosed
}
return
case p := <-t.addpending:
p.deadline = time.Now().Add(respTimeout)
plist.PushBack(p)
case r := <-t.gotreply:
var matched bool
for el := plist.Front(); el != nil; el = el.Next() {
p := el.Value.(*pending)
if p.from == r.from && p.ptype == r.ptype {
matched = true
// Remove the matcher if its callback indicates
// that all replies have been received. This is
// required for packet types that expect multiple
// reply packets.
if p.callback(r.data) {
p.errc <- nil
plist.Remove(el)
}
// Reset the continuous timeout counter (time drift detection)
contTimeouts = 0
}
}
r.matched <- matched
case now := <-timeout.C:
nextTimeout = nil
// Notify and remove callbacks whose deadline is in the past.
for el := plist.Front(); el != nil; el = el.Next() {
p := el.Value.(*pending)
if now.After(p.deadline) || now.Equal(p.deadline) {
p.errc <- errTimeout
plist.Remove(el)
contTimeouts++
}
}
// If we've accumulated too many timeouts, do an NTP time sync check
if contTimeouts > ntpFailureThreshold {
if time.Since(ntpWarnTime) >= ntpWarningCooldown {
ntpWarnTime = time.Now()
go checkClockDrift()
}
contTimeouts = 0
}
}
}
}
const (
macSize = 256 / 8
sigSize = 520 / 8
headSize = macSize + sigSize // space of packet frame data
)
var (
headSpace = make([]byte, headSize)
// Neighbors replies are sent across multiple packets to
// stay below the 1280 byte limit. We compute the maximum number
// of entries by stuffing a packet until it grows too large.
maxNeighbors int
)
func init() {
p := neighbors{Expiration: ^uint64(0)}
maxSizeNode := rpcNode{IP: make(net.IP, 16), UDP: ^uint16(0), TCP: ^uint16(0)}
for n := 0; ; n++ {
p.Nodes = append(p.Nodes, maxSizeNode)
size, _, err := rlp.EncodeToReader(p)
if err != nil {
// If this ever happens, it will be caught by the unit tests.
panic("cannot encode: " + err.Error())
}
if headSize+size+1 >= 1280 {
maxNeighbors = n
break
}
}
}
func (t *udp) send(toaddr *net.UDPAddr, ptype byte, req packet) ([]byte, error) {
packet, hash, err := encodePacket(t.priv, ptype, req)
if err != nil {
return hash, err
}
return hash, t.write(toaddr, req.name(), packet)
}
func (t *udp) write(toaddr *net.UDPAddr, what string, packet []byte) error {
_, err := t.conn.WriteToUDP(packet, toaddr)
log.Trace(">> "+what, "addr", toaddr, "err", err)
return err
}
func encodePacket(priv *ecdsa.PrivateKey, ptype byte, req interface{}) (packet, hash []byte, err error) {
b := new(bytes.Buffer)
b.Write(headSpace)
b.WriteByte(ptype)
if err := rlp.Encode(b, req); err != nil {
log.Error("Can't encode discv4 packet", "err", err)
return nil, nil, err
}
packet = b.Bytes()
sig, err := crypto.Sign(crypto.Keccak256(packet[headSize:]), priv)
if err != nil {
log.Error("Can't sign discv4 packet", "err", err)
return nil, nil, err
}
copy(packet[macSize:], sig)
// add the hash to the front. Note: this doesn't protect the
// packet in any way. Our public key will be part of this hash in
// The future.
hash = crypto.Keccak256(packet[macSize:])
copy(packet, hash)
return packet, hash, nil
}
// readLoop runs in its own goroutine. it handles incoming UDP packets.
func (t *udp) readLoop(unhandled chan<- ReadPacket) {
defer t.conn.Close()
if unhandled != nil {
defer close(unhandled)
}
// Discovery packets are defined to be no larger than 1280 bytes.
// Packets larger than this size will be cut at the end and treated
// as invalid because their hash won't match.
buf := make([]byte, 1280)
for {
nbytes, from, err := t.conn.ReadFromUDP(buf)
if netutil.IsTemporaryError(err) {
// Ignore temporary read errors.
log.Debug("Temporary UDP read error", "err", err)
continue
} else if err != nil {
// Shut down the loop for permament errors.
log.Debug("UDP read error", "err", err)
return
}
if t.handlePacket(from, buf[:nbytes]) != nil && unhandled != nil {
select {
case unhandled <- ReadPacket{buf[:nbytes], from}:
default:
}
}
}
}
func (t *udp) handlePacket(from *net.UDPAddr, buf []byte) error {
packet, fromID, hash, err := decodePacket(buf)
if err != nil {
log.Debug("Bad discv4 packet", "addr", from, "err", err)
return err
}
err = packet.handle(t, from, fromID, hash)
log.Trace("<< "+packet.name(), "addr", from, "err", err)
return err
}
func decodePacket(buf []byte) (packet, NodeID, []byte, error) {
if len(buf) < headSize+1 {
return nil, NodeID{}, nil, errPacketTooSmall
}
hash, sig, sigdata := buf[:macSize], buf[macSize:headSize], buf[headSize:]
shouldhash := crypto.Keccak256(buf[macSize:])
if !bytes.Equal(hash, shouldhash) {
return nil, NodeID{}, nil, errBadHash
}
fromID, err := recoverNodeID(crypto.Keccak256(buf[headSize:]), sig)
if err != nil {
return nil, NodeID{}, hash, err
}
var req packet
switch ptype := sigdata[0]; ptype {
case pingPacket:
req = new(ping)
case pongPacket:
req = new(pong)
case findnodePacket:
req = new(findnode)
case neighborsPacket:
req = new(neighbors)
default:
return nil, fromID, hash, fmt.Errorf("unknown type: %d", ptype)
}
s := rlp.NewStream(bytes.NewReader(sigdata[1:]), 0)
err = s.Decode(req)
return req, fromID, hash, err
}
func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
if expired(req.Expiration) {
return errExpired
}
t.send(from, pongPacket, &pong{
To: makeEndpoint(from, req.From.TCP),
ReplyTok: mac,
Expiration: uint64(time.Now().Add(expiration).Unix()),
})
if !t.handleReply(fromID, pingPacket, req) {
// Note: we're ignoring the provided IP address right now
go t.bond(true, fromID, from, req.From.TCP)
}
return nil
}
func (req *ping) name() string { return "PING/v4" }
func (req *pong) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
if expired(req.Expiration) {
return errExpired
}
if !t.handleReply(fromID, pongPacket, req) {
return errUnsolicitedReply
}
return nil
}
func (req *pong) name() string { return "PONG/v4" }
func (req *findnode) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
if expired(req.Expiration) {
return errExpired
}
if !t.db.hasBond(fromID) {
// No bond exists, we don't process the packet. This prevents
// 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 a much bigger packet than findnode) to the victim.
return errUnknownNode
}
target := crypto.Keccak256Hash(req.Target[:])
t.mutex.Lock()
closest := t.closest(target, bucketSize).entries
t.mutex.Unlock()
p := neighbors{Expiration: uint64(time.Now().Add(expiration).Unix())}
var sent bool
// Send neighbors in chunks with at most maxNeighbors per packet
// to stay below the 1280 byte limit.
for _, n := range closest {
if netutil.CheckRelayIP(from.IP, n.IP) == nil {
p.Nodes = append(p.Nodes, nodeToRPC(n))
}
if len(p.Nodes) == maxNeighbors {
t.send(from, neighborsPacket, &p)
p.Nodes = p.Nodes[:0]
sent = true
}
}
if len(p.Nodes) > 0 || !sent {
t.send(from, neighborsPacket, &p)
}
return nil
}
func (req *findnode) name() string { return "FINDNODE/v4" }
func (req *neighbors) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
if expired(req.Expiration) {
return errExpired
}
if !t.handleReply(fromID, neighborsPacket, req) {
return errUnsolicitedReply
}
return nil
}
func (req *neighbors) name() string { return "NEIGHBORS/v4" }
func expired(ts uint64) bool {
return time.Unix(int64(ts), 0).Before(time.Now())
}
