Check that incoming peer request chunk lengths don't exceed the upload rate limiter burst size

Should fix #759.

client.go

@@ -973,7 +973,7 @@ func (cl *Client) runHandshookConn(c *PeerConn, t *Torrent) error {
 		return fmt.Errorf("adding connection: %w", err)
 	}
 	defer t.dropConnection(c)
-	c.startWriter()
+	c.startMessageWriter()
 	cl.sendInitialMessages(c, t)
 	c.initUpdateRequestsTimer()
 	err := c.mainReadLoop()

peer-conn-msg-writer.go

@@ -12,7 +12,7 @@ import (
 	pp "github.com/anacrolix/torrent/peer_protocol"
 )
 
-func (pc *PeerConn) startWriter() {
+func (pc *PeerConn) initMessageWriter() {
 	w := &pc.messageWriter
 	*w = peerConnMsgWriter{
 		fillWriteBuffer: func() {
@@ -33,12 +33,18 @@ func (pc *PeerConn) startWriter() {
 		},
 		writeBuffer: new(bytes.Buffer),
 	}
-	go func() {
+}
+
+func (pc *PeerConn) startMessageWriter() {
+	pc.initMessageWriter()
+	go pc.messageWriterRunner()
+}
+
+func (pc *PeerConn) messageWriterRunner() {
 	defer pc.locker().Unlock()
 	defer pc.close()
 	defer pc.locker().Lock()
 	pc.messageWriter.run(pc.t.cl.config.KeepAliveTimeout)
-	}()
 }
 
 type peerConnMsgWriter struct {

peerconn.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"golang.org/x/time/rate"
 	"io"
 	"math/rand"
 	"net"
@@ -986,10 +987,22 @@ func (c *PeerConn) reject(r Request) {
 	delete(c.peerRequests, r)
 }
 
-func (c *PeerConn) onReadRequest(r Request) error {
+func (c *PeerConn) maximumPeerRequestChunkLength() (_ Option[int]) {
+	uploadRateLimiter := c.t.cl.config.UploadRateLimiter
+	if uploadRateLimiter.Limit() == rate.Inf {
+		return
+	}
+	return Some(uploadRateLimiter.Burst())
+}
+
+// startFetch is for testing purposes currently.
+func (c *PeerConn) onReadRequest(r Request, startFetch bool) error {
 	requestedChunkLengths.Add(strconv.FormatUint(r.Length.Uint64(), 10), 1)
 	if _, ok := c.peerRequests[r]; ok {
 		torrent.Add("duplicate requests received", 1)
+		if c.fastEnabled() {
+			return errors.New("received duplicate request with fast enabled")
+		}
 		return nil
 	}
 	if c.choking {
@@ -1009,10 +1022,18 @@ func (c *PeerConn) onReadRequest(r Request) error {
 		// BEP 6 says we may close here if we choose.
 		return nil
 	}
+	if opt := c.maximumPeerRequestChunkLength(); opt.Ok && int(r.Length) > opt.Value {
+		err := fmt.Errorf("peer requested chunk too long (%v)", r.Length)
+		c.logger.Levelf(log.Warning, err.Error())
+		if c.fastEnabled() {
+			c.reject(r)
+			return nil
+		} else {
+			return err
+		}
+	}
 	if !c.t.havePiece(pieceIndex(r.Index)) {
-		// This isn't necessarily them screwing up. We can drop pieces
-		// from our storage, and can't communicate this to peers
-		// except by reconnecting.
+		// TODO: Tell the peer we don't have the piece, and reject this request.
 		requestsReceivedForMissingPieces.Add(1)
 		return fmt.Errorf("peer requested piece we don't have: %v", r.Index.Int())
 	}
@@ -1026,7 +1047,10 @@ func (c *PeerConn) onReadRequest(r Request) error {
 	}
 	value := &peerRequestState{}
 	c.peerRequests[r] = value
+	if startFetch {
+		// TODO: Limit peer request data read concurrency.
 		go c.peerRequestDataReader(r, value)
+	}
 	return nil
 }
 
@@ -1222,7 +1246,7 @@ func (c *PeerConn) mainReadLoop() (err error) {
 			err = c.peerSentBitfield(msg.Bitfield)
 		case pp.Request:
 			r := newRequestFromMessage(&msg)
-			err = c.onReadRequest(r)
+			err = c.onReadRequest(r, true)
 		case pp.Piece:
 			c.doChunkReadStats(int64(len(msg.Piece)))
 			err = c.receiveChunk(&msg)

peerconn_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"golang.org/x/time/rate"
 	"io"
 	"net"
 	"sync"
@@ -32,7 +33,7 @@ func TestSendBitfieldThenHave(t *testing.T) {
 	r, w := io.Pipe()
 	// c.r = r
 	c.w = w
-	c.startWriter()
+	c.startMessageWriter()
 	c.locker().Lock()
 	c.t._completedPieces.Add(1)
 	c.postBitfield( /*[]bool{false, true, false}*/ )
@@ -282,3 +283,32 @@ func TestPreferredNetworkDirection(t *testing.T) {
 	// No difference
 	c.Assert(pc(1, 2, false, false, false).hasPreferredNetworkOver(pc(1, 2, false, false, false)), qt.IsFalse)
 }
+
+func TestReceiveLargeRequest(t *testing.T) {
+	c := qt.New(t)
+	cl := newTestingClient(t)
+	pc := cl.newConnection(nil, false, nil, "test", "")
+	tor := cl.newTorrentForTesting()
+	tor.info = &metainfo.Info{PieceLength: 3 << 20}
+	pc.setTorrent(tor)
+	tor._completedPieces.Add(0)
+	pc.PeerExtensionBytes.SetBit(pp.ExtensionBitFast, true)
+	pc.choking = false
+	pc.initMessageWriter()
+	req := Request{}
+	req.Length = defaultChunkSize
+	c.Assert(pc.fastEnabled(), qt.IsTrue)
+	c.Check(pc.onReadRequest(req, false), qt.IsNil)
+	c.Check(pc.peerRequests, qt.HasLen, 1)
+	req.Length = 2 << 20
+	c.Check(pc.onReadRequest(req, false), qt.IsNil)
+	c.Check(pc.peerRequests, qt.HasLen, 2)
+	pc.peerRequests = nil
+	pc.t.cl.config.UploadRateLimiter = rate.NewLimiter(1, defaultChunkSize)
+	req.Length = defaultChunkSize
+	c.Check(pc.onReadRequest(req, false), qt.IsNil)
+	c.Check(pc.peerRequests, qt.HasLen, 1)
+	req.Length = 2 << 20
+	c.Check(pc.onReadRequest(req, false), qt.IsNil)
+	c.Check(pc.messageWriter.writeBuffer.Len(), qt.Equals, 17)
+}