package pex import ( "errors" "fmt" "sync" "time" "github.com/gogo/protobuf/proto" "github.com/tendermint/tendermint/libs/cmap" tmmath "github.com/tendermint/tendermint/libs/math" tmrand "github.com/tendermint/tendermint/libs/rand" "github.com/tendermint/tendermint/libs/service" "github.com/tendermint/tendermint/p2p" "github.com/tendermint/tendermint/p2p/conn" tmp2p "github.com/tendermint/tendermint/proto/p2p" ) type Peer = p2p.Peer const ( // PexChannel is a channel for PEX messages PexChannel = byte(0x00) // over-estimate of max NetAddress size // hexID (40) + IP (16) + Port (2) + Name (100) ... // NOTE: dont use massive DNS name .. maxAddressSize = 256 // NOTE: amplificaiton factor! // small request results in up to maxMsgSize response maxMsgSize = maxAddressSize * maxGetSelection // ensure we have enough peers defaultEnsurePeersPeriod = 30 * time.Second // Seed/Crawler constants // minTimeBetweenCrawls is a minimum time between attempts to crawl a peer. minTimeBetweenCrawls = 2 * time.Minute // check some peers every this crawlPeerPeriod = 30 * time.Second maxAttemptsToDial = 16 // ~ 35h in total (last attempt - 18h) // if node connects to seed, it does not have any trusted peers. // Especially in the beginning, node should have more trusted peers than // untrusted. biasToSelectNewPeers = 30 // 70 to select good peers // if a peer is marked bad, it will be banned for at least this time period defaultBanTime = 24 * time.Hour ) type errMaxAttemptsToDial struct { } func (e errMaxAttemptsToDial) Error() string { return fmt.Sprintf("reached max attempts %d to dial", maxAttemptsToDial) } type errTooEarlyToDial struct { backoffDuration time.Duration lastDialed time.Time } func (e errTooEarlyToDial) Error() string { return fmt.Sprintf( "too early to dial (backoff duration: %d, last dialed: %v, time since: %v)", e.backoffDuration, e.lastDialed, time.Since(e.lastDialed)) } // Reactor handles PEX (peer exchange) and ensures that an // adequate number of peers are connected to the switch. // // It uses `AddrBook` (address book) to store `NetAddress`es of the peers. // // ## Preventing abuse // // Only accept pexAddrsMsg from peers we sent a corresponding pexRequestMsg too. // Only accept one pexRequestMsg every ~defaultEnsurePeersPeriod. type Reactor struct { p2p.BaseReactor book AddrBook config *ReactorConfig ensurePeersPeriod time.Duration // TODO: should go in the config // maps to prevent abuse requestsSent *cmap.CMap // ID->struct{}: unanswered send requests lastReceivedRequests *cmap.CMap // ID->time.Time: last time peer requested from us seedAddrs []*p2p.NetAddress attemptsToDial sync.Map // address (string) -> {number of attempts (int), last time dialed (time.Time)} // seed/crawled mode fields crawlPeerInfos map[p2p.ID]crawlPeerInfo } func (r *Reactor) minReceiveRequestInterval() time.Duration { // NOTE: must be less than ensurePeersPeriod, otherwise we'll request // peers too quickly from others and they'll think we're bad! return r.ensurePeersPeriod / 3 } // ReactorConfig holds reactor specific configuration data. type ReactorConfig struct { // Seed/Crawler mode SeedMode bool // We want seeds to only advertise good peers. Therefore they should wait at // least as long as we expect it to take for a peer to become good before // disconnecting. SeedDisconnectWaitPeriod time.Duration // Maximum pause when redialing a persistent peer (if zero, exponential backoff is used) PersistentPeersMaxDialPeriod time.Duration // Seeds is a list of addresses reactor may use // if it can't connect to peers in the addrbook. Seeds []string } type _attemptsToDial struct { number int lastDialed time.Time } // NewReactor creates new PEX reactor. func NewReactor(b AddrBook, config *ReactorConfig) *Reactor { r := &Reactor{ book: b, config: config, ensurePeersPeriod: defaultEnsurePeersPeriod, requestsSent: cmap.NewCMap(), lastReceivedRequests: cmap.NewCMap(), crawlPeerInfos: make(map[p2p.ID]crawlPeerInfo), } r.BaseReactor = *p2p.NewBaseReactor("PEX", r) return r } // OnStart implements BaseService func (r *Reactor) OnStart() error { err := r.book.Start() if err != nil && err != service.ErrAlreadyStarted { return err } numOnline, seedAddrs, err := r.checkSeeds() if err != nil { return err } else if numOnline == 0 && r.book.Empty() { return errors.New("address book is empty and couldn't resolve any seed nodes") } r.seedAddrs = seedAddrs // Check if this node should run // in seed/crawler mode if r.config.SeedMode { go r.crawlPeersRoutine() } else { go r.ensurePeersRoutine() } return nil } // OnStop implements BaseService func (r *Reactor) OnStop() { r.book.Stop() } // GetChannels implements Reactor func (r *Reactor) GetChannels() []*conn.ChannelDescriptor { return []*conn.ChannelDescriptor{ { ID: PexChannel, Priority: 1, SendQueueCapacity: 10, RecvMessageCapacity: maxMsgSize, }, } } // AddPeer implements Reactor by adding peer to the address book (if inbound) // or by requesting more addresses (if outbound). func (r *Reactor) AddPeer(p Peer) { if p.IsOutbound() { // For outbound peers, the address is already in the books - // either via DialPeersAsync or r.Receive. // Ask it for more peers if we need. if r.book.NeedMoreAddrs() { r.RequestAddrs(p) } } else { // inbound peer is its own source addr, err := p.NodeInfo().NetAddress() if err != nil { r.Logger.Error("Failed to get peer NetAddress", "err", err, "peer", p) return } // Make it explicit that addr and src are the same for an inbound peer. src := addr // add to book. dont RequestAddrs right away because // we don't trust inbound as much - let ensurePeersRoutine handle it. err = r.book.AddAddress(addr, src) r.logErrAddrBook(err) } } // RemovePeer implements Reactor by resetting peer's requests info. func (r *Reactor) RemovePeer(p Peer, reason interface{}) { id := string(p.ID()) r.requestsSent.Delete(id) r.lastReceivedRequests.Delete(id) } func (r *Reactor) logErrAddrBook(err error) { if err != nil { switch err.(type) { case ErrAddrBookNilAddr: r.Logger.Error("Failed to add new address", "err", err) default: // non-routable, self, full book, private, etc. r.Logger.Debug("Failed to add new address", "err", err) } } } // Receive implements Reactor by handling incoming PEX messages. func (r *Reactor) Receive(chID byte, src Peer, msgBytes []byte) { msg, err := decodeMsg(msgBytes) if err != nil { r.Logger.Error("Error decoding message", "src", src, "chId", chID, "msg", msg, "err", err, "bytes", msgBytes) r.Switch.StopPeerForError(src, err) return } r.Logger.Debug("Received message", "src", src, "chId", chID, "msg", msg) switch msg := msg.(type) { case *tmp2p.PexRequest: // NOTE: this is a prime candidate for amplification attacks, // so it's important we // 1) restrict how frequently peers can request // 2) limit the output size // If we're a seed and this is an inbound peer, // respond once and disconnect. if r.config.SeedMode && !src.IsOutbound() { id := string(src.ID()) v := r.lastReceivedRequests.Get(id) if v != nil { // FlushStop/StopPeer are already // running in a go-routine. return } r.lastReceivedRequests.Set(id, time.Now()) // Send addrs and disconnect r.SendAddrs(src, r.book.GetSelectionWithBias(biasToSelectNewPeers)) go func() { // In a go-routine so it doesn't block .Receive. src.FlushStop() r.Switch.StopPeerGracefully(src) }() } else { // Check we're not receiving requests too frequently. if err := r.receiveRequest(src); err != nil { r.Switch.StopPeerForError(src, err) r.book.MarkBad(src.SocketAddr(), defaultBanTime) return } r.SendAddrs(src, r.book.GetSelection()) } case *tmp2p.PexAddrs: // If we asked for addresses, add them to the book addrs, err := p2p.NetAddressesFromProto(msg.Addrs) if err != nil { r.Switch.StopPeerForError(src, err) r.book.MarkBad(src.SocketAddr(), defaultBanTime) return } err = r.ReceiveAddrs(addrs, src) if err != nil { r.Switch.StopPeerForError(src, err) if err == ErrUnsolicitedList { r.book.MarkBad(src.SocketAddr(), defaultBanTime) } return } default: r.Logger.Error(fmt.Sprintf("Unknown message type %T", msg)) } } // enforces a minimum amount of time between requests func (r *Reactor) receiveRequest(src Peer) error { id := string(src.ID()) v := r.lastReceivedRequests.Get(id) if v == nil { // initialize with empty time lastReceived := time.Time{} r.lastReceivedRequests.Set(id, lastReceived) return nil } lastReceived := v.(time.Time) if lastReceived.Equal(time.Time{}) { // first time gets a free pass. then we start tracking the time lastReceived = time.Now() r.lastReceivedRequests.Set(id, lastReceived) return nil } now := time.Now() minInterval := r.minReceiveRequestInterval() if now.Sub(lastReceived) < minInterval { return fmt.Errorf( "peer (%v) sent next PEX request too soon. lastReceived: %v, now: %v, minInterval: %v. Disconnecting", src.ID(), lastReceived, now, minInterval, ) } r.lastReceivedRequests.Set(id, now) return nil } // RequestAddrs asks peer for more addresses if we do not already have a // request out for this peer. func (r *Reactor) RequestAddrs(p Peer) { id := string(p.ID()) if r.requestsSent.Has(id) { return } r.Logger.Debug("Request addrs", "from", p) r.requestsSent.Set(id, struct{}{}) p.Send(PexChannel, mustEncode(&tmp2p.PexRequest{})) } // ReceiveAddrs adds the given addrs to the addrbook if theres an open // request for this peer and deletes the open request. // If there's no open request for the src peer, it returns an error. func (r *Reactor) ReceiveAddrs(addrs []*p2p.NetAddress, src Peer) error { id := string(src.ID()) if !r.requestsSent.Has(id) { return ErrUnsolicitedList } r.requestsSent.Delete(id) srcAddr, err := src.NodeInfo().NetAddress() if err != nil { return err } srcIsSeed := false for _, seedAddr := range r.seedAddrs { if seedAddr.Equals(srcAddr) { srcIsSeed = true break } } for _, netAddr := range addrs { // NOTE: we check netAddr validity and routability in book#AddAddress. err = r.book.AddAddress(netAddr, srcAddr) if err != nil { r.logErrAddrBook(err) // XXX: should we be strict about incoming data and disconnect from a // peer here too? continue } // If this address came from a seed node, try to connect to it without // waiting (#2093) if srcIsSeed { r.Logger.Info("Will dial address, which came from seed", "addr", netAddr, "seed", srcAddr) go func(addr *p2p.NetAddress) { err := r.dialPeer(addr) if err != nil { switch err.(type) { case errMaxAttemptsToDial, errTooEarlyToDial, p2p.ErrCurrentlyDialingOrExistingAddress: r.Logger.Debug(err.Error(), "addr", addr) default: r.Logger.Error(err.Error(), "addr", addr) } } }(netAddr) } } return nil } // SendAddrs sends addrs to the peer. func (r *Reactor) SendAddrs(p Peer, netAddrs []*p2p.NetAddress) { p.Send(PexChannel, mustEncode(&tmp2p.PexAddrs{Addrs: p2p.NetAddressesToProto(netAddrs)})) } // SetEnsurePeersPeriod sets period to ensure peers connected. func (r *Reactor) SetEnsurePeersPeriod(d time.Duration) { r.ensurePeersPeriod = d } // Ensures that sufficient peers are connected. (continuous) func (r *Reactor) ensurePeersRoutine() { var ( seed = tmrand.NewRand() jitter = seed.Int63n(r.ensurePeersPeriod.Nanoseconds()) ) // Randomize first round of communication to avoid thundering herd. // If no peers are present directly start connecting so we guarantee swift // setup with the help of configured seeds. if r.nodeHasSomePeersOrDialingAny() { time.Sleep(time.Duration(jitter)) } // fire once immediately. // ensures we dial the seeds right away if the book is empty r.ensurePeers() // fire periodically ticker := time.NewTicker(r.ensurePeersPeriod) for { select { case <-ticker.C: r.ensurePeers() case <-r.Quit(): ticker.Stop() return } } } // ensurePeers ensures that sufficient peers are connected. (once) // // heuristic that we haven't perfected yet, or, perhaps is manually edited by // the node operator. It should not be used to compute what addresses are // already connected or not. func (r *Reactor) ensurePeers() { var ( out, in, dial = r.Switch.NumPeers() numToDial = r.Switch.MaxNumOutboundPeers() - (out + dial) ) r.Logger.Info( "Ensure peers", "numOutPeers", out, "numInPeers", in, "numDialing", dial, "numToDial", numToDial, ) if numToDial <= 0 { return } // bias to prefer more vetted peers when we have fewer connections. // not perfect, but somewhate ensures that we prioritize connecting to more-vetted // NOTE: range here is [10, 90]. Too high ? newBias := tmmath.MinInt(out, 8)*10 + 10 toDial := make(map[p2p.ID]*p2p.NetAddress) // Try maxAttempts times to pick numToDial addresses to dial maxAttempts := numToDial * 3 for i := 0; i < maxAttempts && len(toDial) < numToDial; i++ { try := r.book.PickAddress(newBias) if try == nil { continue } if _, selected := toDial[try.ID]; selected { continue } if r.Switch.IsDialingOrExistingAddress(try) { continue } // TODO: consider moving some checks from toDial into here // so we don't even consider dialing peers that we want to wait // before dialling again, or have dialed too many times already r.Logger.Info("Will dial address", "addr", try) toDial[try.ID] = try } // Dial picked addresses for _, addr := range toDial { go func(addr *p2p.NetAddress) { err := r.dialPeer(addr) if err != nil { switch err.(type) { case errMaxAttemptsToDial, errTooEarlyToDial: r.Logger.Debug(err.Error(), "addr", addr) default: r.Logger.Error(err.Error(), "addr", addr) } } }(addr) } if r.book.NeedMoreAddrs() { // Check if banned nodes can be reinstated r.book.ReinstateBadPeers() } if r.book.NeedMoreAddrs() { // 1) Pick a random peer and ask for more. peers := r.Switch.Peers().List() peersCount := len(peers) if peersCount > 0 { peer := peers[tmrand.Int()%peersCount] r.Logger.Info("We need more addresses. Sending pexRequest to random peer", "peer", peer) r.RequestAddrs(peer) } // 2) Dial seeds if we are not dialing anyone. // This is done in addition to asking a peer for addresses to work-around // peers not participating in PEX. if len(toDial) == 0 { r.Logger.Info("No addresses to dial. Falling back to seeds") r.dialSeeds() } } } func (r *Reactor) dialAttemptsInfo(addr *p2p.NetAddress) (attempts int, lastDialed time.Time) { _attempts, ok := r.attemptsToDial.Load(addr.DialString()) if !ok { return } atd := _attempts.(_attemptsToDial) return atd.number, atd.lastDialed } func (r *Reactor) dialPeer(addr *p2p.NetAddress) error { attempts, lastDialed := r.dialAttemptsInfo(addr) if !r.Switch.IsPeerPersistent(addr) && attempts > maxAttemptsToDial { r.book.MarkBad(addr, defaultBanTime) return errMaxAttemptsToDial{} } // exponential backoff if it's not our first attempt to dial given address if attempts > 0 { jitter := time.Duration(tmrand.Float64() * float64(time.Second)) // 1s == (1e9 ns) backoffDuration := jitter + ((1 << uint(attempts)) * time.Second) backoffDuration = r.maxBackoffDurationForPeer(addr, backoffDuration) sinceLastDialed := time.Since(lastDialed) if sinceLastDialed < backoffDuration { return errTooEarlyToDial{backoffDuration, lastDialed} } } err := r.Switch.DialPeerWithAddress(addr) if err != nil { if _, ok := err.(p2p.ErrCurrentlyDialingOrExistingAddress); ok { return err } markAddrInBookBasedOnErr(addr, r.book, err) switch err.(type) { case p2p.ErrSwitchAuthenticationFailure: // NOTE: addr is removed from addrbook in markAddrInBookBasedOnErr r.attemptsToDial.Delete(addr.DialString()) default: r.attemptsToDial.Store(addr.DialString(), _attemptsToDial{attempts + 1, time.Now()}) } return fmt.Errorf("dialing failed (attempts: %d): %w", attempts+1, err) } // cleanup any history r.attemptsToDial.Delete(addr.DialString()) return nil } // maxBackoffDurationForPeer caps the backoff duration for persistent peers. func (r *Reactor) maxBackoffDurationForPeer(addr *p2p.NetAddress, planned time.Duration) time.Duration { if r.config.PersistentPeersMaxDialPeriod > 0 && planned > r.config.PersistentPeersMaxDialPeriod && r.Switch.IsPeerPersistent(addr) { return r.config.PersistentPeersMaxDialPeriod } return planned } // checkSeeds checks that addresses are well formed. // Returns number of seeds we can connect to, along with all seeds addrs. // return err if user provided any badly formatted seed addresses. // Doesn't error if the seed node can't be reached. // numOnline returns -1 if no seed nodes were in the initial configuration. func (r *Reactor) checkSeeds() (numOnline int, netAddrs []*p2p.NetAddress, err error) { lSeeds := len(r.config.Seeds) if lSeeds == 0 { return -1, nil, nil } netAddrs, errs := p2p.NewNetAddressStrings(r.config.Seeds) numOnline = lSeeds - len(errs) for _, err := range errs { switch e := err.(type) { case p2p.ErrNetAddressLookup: r.Logger.Error("Connecting to seed failed", "err", e) default: return 0, nil, fmt.Errorf("seed node configuration has error: %w", e) } } return numOnline, netAddrs, nil } // randomly dial seeds until we connect to one or exhaust them func (r *Reactor) dialSeeds() { perm := tmrand.Perm(len(r.seedAddrs)) // perm := r.Switch.rng.Perm(lSeeds) for _, i := range perm { // dial a random seed seedAddr := r.seedAddrs[i] err := r.Switch.DialPeerWithAddress(seedAddr) switch err.(type) { case nil, p2p.ErrCurrentlyDialingOrExistingAddress: return } r.Switch.Logger.Error("Error dialing seed", "err", err, "seed", seedAddr) } // do not write error message if there were no seeds specified in config if len(r.seedAddrs) > 0 { r.Switch.Logger.Error("Couldn't connect to any seeds") } } // AttemptsToDial returns the number of attempts to dial specific address. It // returns 0 if never attempted or successfully connected. func (r *Reactor) AttemptsToDial(addr *p2p.NetAddress) int { lAttempts, attempted := r.attemptsToDial.Load(addr.DialString()) if attempted { return lAttempts.(_attemptsToDial).number } return 0 } //---------------------------------------------------------- // Explores the network searching for more peers. (continuous) // Seed/Crawler Mode causes this node to quickly disconnect // from peers, except other seed nodes. func (r *Reactor) crawlPeersRoutine() { // If we have any seed nodes, consult them first if len(r.seedAddrs) > 0 { r.dialSeeds() } else { // Do an initial crawl r.crawlPeers(r.book.GetSelection()) } // Fire periodically ticker := time.NewTicker(crawlPeerPeriod) for { select { case <-ticker.C: r.attemptDisconnects() r.crawlPeers(r.book.GetSelection()) r.cleanupCrawlPeerInfos() case <-r.Quit(): return } } } // nodeHasSomePeersOrDialingAny returns true if the node is connected to some // peers or dialing them currently. func (r *Reactor) nodeHasSomePeersOrDialingAny() bool { out, in, dial := r.Switch.NumPeers() return out+in+dial > 0 } // crawlPeerInfo handles temporary data needed for the network crawling // performed during seed/crawler mode. type crawlPeerInfo struct { Addr *p2p.NetAddress `json:"addr"` // The last time we crawled the peer or attempted to do so. LastCrawled time.Time `json:"last_crawled"` } // crawlPeers will crawl the network looking for new peer addresses. func (r *Reactor) crawlPeers(addrs []*p2p.NetAddress) { now := time.Now() for _, addr := range addrs { peerInfo, ok := r.crawlPeerInfos[addr.ID] // Do not attempt to connect with peers we recently crawled. if ok && now.Sub(peerInfo.LastCrawled) < minTimeBetweenCrawls { continue } // Record crawling attempt. r.crawlPeerInfos[addr.ID] = crawlPeerInfo{ Addr: addr, LastCrawled: now, } err := r.dialPeer(addr) if err != nil { switch err.(type) { case errMaxAttemptsToDial, errTooEarlyToDial, p2p.ErrCurrentlyDialingOrExistingAddress: r.Logger.Debug(err.Error(), "addr", addr) default: r.Logger.Error(err.Error(), "addr", addr) } continue } peer := r.Switch.Peers().Get(addr.ID) if peer != nil { r.RequestAddrs(peer) } } } func (r *Reactor) cleanupCrawlPeerInfos() { for id, info := range r.crawlPeerInfos { // If we did not crawl a peer for 24 hours, it means the peer was removed // from the addrbook => remove // // 10000 addresses / maxGetSelection = 40 cycles to get all addresses in // the ideal case, // 40 * crawlPeerPeriod ~ 20 minutes if time.Since(info.LastCrawled) > 24*time.Hour { delete(r.crawlPeerInfos, id) } } } // attemptDisconnects checks if we've been with each peer long enough to disconnect func (r *Reactor) attemptDisconnects() { for _, peer := range r.Switch.Peers().List() { if peer.Status().Duration < r.config.SeedDisconnectWaitPeriod { continue } if peer.IsPersistent() { continue } r.Switch.StopPeerGracefully(peer) } } func markAddrInBookBasedOnErr(addr *p2p.NetAddress, book AddrBook, err error) { // TODO: detect more "bad peer" scenarios switch err.(type) { case p2p.ErrSwitchAuthenticationFailure: book.MarkBad(addr, defaultBanTime) default: book.MarkAttempt(addr) } } //----------------------------------------------------------------------------- // Messages // mustEncode proto encodes a tmp2p.Message func mustEncode(pb proto.Message) []byte { msg := tmp2p.Message{} switch pb := pb.(type) { case *tmp2p.PexRequest: msg.Sum = &tmp2p.Message_PexRequest{PexRequest: pb} case *tmp2p.PexAddrs: msg.Sum = &tmp2p.Message_PexAddrs{PexAddrs: pb} default: panic(fmt.Sprintf("Unknown message type %T", pb)) } bz, err := proto.Marshal(&msg) if err != nil { panic(fmt.Errorf("unable to marshal %T: %w", pb, err)) } return bz } func decodeMsg(bz []byte) (proto.Message, error) { pb := &tmp2p.Message{} err := proto.Unmarshal(bz, pb) if err != nil { return nil, err } switch msg := pb.Sum.(type) { case *tmp2p.Message_PexRequest: return msg.PexRequest, nil case *tmp2p.Message_PexAddrs: return msg.PexAddrs, nil default: return nil, fmt.Errorf("unknown message: %T", msg) } }