1 files changed, 407 insertions, 0 deletions
diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
new file mode 100644
index 000000000..9a5b13066
--- /dev/null
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -0,0 +1,407 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tcp
+
+import (
+	"crypto/rand"
+	"crypto/sha1"
+	"encoding/binary"
+	"hash"
+	"io"
+	"sync"
+	"time"
+
+	"gvisor.googlesource.com/gvisor/pkg/sleep"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/seqnum"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
+	"gvisor.googlesource.com/gvisor/pkg/waiter"
+)
+
+const (
+	// tsLen is the length, in bits, of the timestamp in the SYN cookie.
+	tsLen = 8
+
+	// tsMask is a mask for timestamp values (i.e., tsLen bits).
+	tsMask = (1 << tsLen) - 1
+
+	// tsOffset is the offset, in bits, of the timestamp in the SYN cookie.
+	tsOffset = 24
+
+	// hashMask is the mask for hash values (i.e., tsOffset bits).
+	hashMask = (1 << tsOffset) - 1
+
+	// maxTSDiff is the maximum allowed difference between a received cookie
+	// timestamp and the current timestamp. If the difference is greater
+	// than maxTSDiff, the cookie is expired.
+	maxTSDiff = 2
+)
+
+var (
+	// SynRcvdCountThreshold is the global maximum number of connections
+	// that are allowed to be in SYN-RCVD state before TCP starts using SYN
+	// cookies to accept connections.
+	//
+	// It is an exported variable only for testing, and should not otherwise
+	// be used by importers of this package.
+	SynRcvdCountThreshold uint64 = 1000
+
+	// mssTable is a slice containing the possible MSS values that we
+	// encode in the SYN cookie with two bits.
+	mssTable = []uint16{536, 1300, 1440, 1460}
+)
+
+func encodeMSS(mss uint16) uint32 {
+	for i := len(mssTable) - 1; i > 0; i-- {
+		if mss >= mssTable[i] {
+			return uint32(i)
+		}
+	}
+	return 0
+}
+
+// syncRcvdCount is the number of endpoints in the SYN-RCVD state. The value is
+// protected by a mutex so that we can increment only when it's guaranteed not
+// to go above a threshold.
+var synRcvdCount struct {
+	sync.Mutex
+	value uint64
+}
+
+// listenContext is used by a listening endpoint to store state used while
+// listening for connections. This struct is allocated by the listen goroutine
+// and must not be accessed or have its methods called concurrently as they
+// may mutate the stored objects.
+type listenContext struct {
+	stack  *stack.Stack
+	rcvWnd seqnum.Size
+	nonce  [2][sha1.BlockSize]byte
+
+	hasherMu sync.Mutex
+	hasher   hash.Hash
+	v6only   bool
+	netProto tcpip.NetworkProtocolNumber
+}
+
+// timeStamp returns an 8-bit timestamp with a granularity of 64 seconds.
+func timeStamp() uint32 {
+	return uint32(time.Now().Unix()>>6) & tsMask
+}
+
+// incSynRcvdCount tries to increment the global number of endpoints in SYN-RCVD
+// state. It succeeds if the increment doesn't make the count go beyond the
+// threshold, and fails otherwise.
+func incSynRcvdCount() bool {
+	synRcvdCount.Lock()
+	defer synRcvdCount.Unlock()
+
+	if synRcvdCount.value >= SynRcvdCountThreshold {
+		return false
+	}
+
+	synRcvdCount.value++
+
+	return true
+}
+
+// decSynRcvdCount atomically decrements the global number of endpoints in
+// SYN-RCVD state. It must only be called if a previous call to incSynRcvdCount
+// succeeded.
+func decSynRcvdCount() {
+	synRcvdCount.Lock()
+	defer synRcvdCount.Unlock()
+
+	synRcvdCount.value--
+}
+
+// newListenContext creates a new listen context.
+func newListenContext(stack *stack.Stack, rcvWnd seqnum.Size, v6only bool, netProto tcpip.NetworkProtocolNumber) *listenContext {
+	l := &listenContext{
+		stack:    stack,
+		rcvWnd:   rcvWnd,
+		hasher:   sha1.New(),
+		v6only:   v6only,
+		netProto: netProto,
+	}
+
+	rand.Read(l.nonce[0][:])
+	rand.Read(l.nonce[1][:])
+
+	return l
+}
+
+// cookieHash calculates the cookieHash for the given id, timestamp and nonce
+// index. The hash is used to create and validate cookies.
+func (l *listenContext) cookieHash(id stack.TransportEndpointID, ts uint32, nonceIndex int) uint32 {
+
+	// Initialize block with fixed-size data: local ports and v.
+	var payload [8]byte
+	binary.BigEndian.PutUint16(payload[0:], id.LocalPort)
+	binary.BigEndian.PutUint16(payload[2:], id.RemotePort)
+	binary.BigEndian.PutUint32(payload[4:], ts)
+
+	// Feed everything to the hasher.
+	l.hasherMu.Lock()
+	l.hasher.Reset()
+	l.hasher.Write(payload[:])
+	l.hasher.Write(l.nonce[nonceIndex][:])
+	io.WriteString(l.hasher, string(id.LocalAddress))
+	io.WriteString(l.hasher, string(id.RemoteAddress))
+
+	// Finalize the calculation of the hash and return the first 4 bytes.
+	h := make([]byte, 0, sha1.Size)
+	h = l.hasher.Sum(h)
+	l.hasherMu.Unlock()
+
+	return binary.BigEndian.Uint32(h[:])
+}
+
+// createCookie creates a SYN cookie for the given id and incoming sequence
+// number.
+func (l *listenContext) createCookie(id stack.TransportEndpointID, seq seqnum.Value, data uint32) seqnum.Value {
+	ts := timeStamp()
+	v := l.cookieHash(id, 0, 0) + uint32(seq) + (ts << tsOffset)
+	v += (l.cookieHash(id, ts, 1) + data) & hashMask
+	return seqnum.Value(v)
+}
+
+// isCookieValid checks if the supplied cookie is valid for the given id and
+// sequence number. If it is, it also returns the data originally encoded in the
+// cookie when createCookie was called.
+func (l *listenContext) isCookieValid(id stack.TransportEndpointID, cookie seqnum.Value, seq seqnum.Value) (uint32, bool) {
+	ts := timeStamp()
+	v := uint32(cookie) - l.cookieHash(id, 0, 0) - uint32(seq)
+	cookieTS := v >> tsOffset
+	if ((ts - cookieTS) & tsMask) > maxTSDiff {
+		return 0, false
+	}
+
+	return (v - l.cookieHash(id, cookieTS, 1)) & hashMask, true
+}
+
+// createConnectedEndpoint creates a new connected endpoint, with the connection
+// parameters given by the arguments.
+func (l *listenContext) createConnectedEndpoint(s *segment, iss seqnum.Value, irs seqnum.Value, rcvdSynOpts *header.TCPSynOptions) (*endpoint, *tcpip.Error) {
+	// Create a new endpoint.
+	netProto := l.netProto
+	if netProto == 0 {
+		netProto = s.route.NetProto
+	}
+	n := newEndpoint(l.stack, netProto, nil)
+	n.v6only = l.v6only
+	n.id = s.id
+	n.boundNICID = s.route.NICID()
+	n.route = s.route.Clone()
+	n.effectiveNetProtos = []tcpip.NetworkProtocolNumber{s.route.NetProto}
+	n.rcvBufSize = int(l.rcvWnd)
+
+	n.maybeEnableTimestamp(rcvdSynOpts)
+	n.maybeEnableSACKPermitted(rcvdSynOpts)
+
+	// Register new endpoint so that packets are routed to it.
+	if err := n.stack.RegisterTransportEndpoint(n.boundNICID, n.effectiveNetProtos, ProtocolNumber, n.id, n); err != nil {
+		n.Close()
+		return nil, err
+	}
+
+	n.isRegistered = true
+	n.state = stateConnected
+
+	// Create sender and receiver.
+	//
+	// The receiver at least temporarily has a zero receive window scale,
+	// but the caller may change it (before starting the protocol loop).
+	n.snd = newSender(n, iss, irs, s.window, rcvdSynOpts.MSS, rcvdSynOpts.WS)
+	n.rcv = newReceiver(n, irs, l.rcvWnd, 0)
+
+	return n, nil
+}
+
+// createEndpoint creates a new endpoint in connected state and then performs
+// the TCP 3-way handshake.
+func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *header.TCPSynOptions) (*endpoint, *tcpip.Error) {
+	// Create new endpoint.
+	irs := s.sequenceNumber
+	cookie := l.createCookie(s.id, irs, encodeMSS(opts.MSS))
+	ep, err := l.createConnectedEndpoint(s, cookie, irs, opts)
+	if err != nil {
+		return nil, err
+	}
+
+	// Perform the 3-way handshake.
+	h, err := newHandshake(ep, l.rcvWnd)
+	if err != nil {
+		ep.Close()
+		return nil, err
+	}
+
+	h.resetToSynRcvd(cookie, irs, opts)
+	if err := h.execute(); err != nil {
+		ep.Close()
+		return nil, err
+	}
+
+	// Update the receive window scaling. We can't do it before the
+	// handshake because it's possible that the peer doesn't support window
+	// scaling.
+	ep.rcv.rcvWndScale = h.effectiveRcvWndScale()
+
+	return ep, nil
+}
+
+// deliverAccepted delivers the newly-accepted endpoint to the listener. If the
+// endpoint has transitioned out of the listen state, the new endpoint is closed
+// instead.
+func (e *endpoint) deliverAccepted(n *endpoint) {
+	e.mu.RLock()
+	if e.state == stateListen {
+		e.acceptedChan <- n
+		e.waiterQueue.Notify(waiter.EventIn)
+	} else {
+		n.Close()
+	}
+	e.mu.RUnlock()
+}
+
+// handleSynSegment is called in its own goroutine once the listening endpoint
+// receives a SYN segment. It is responsible for completing the handshake and
+// queueing the new endpoint for acceptance.
+//
+// A limited number of these goroutines are allowed before TCP starts using SYN
+// cookies to accept connections.
+func (e *endpoint) handleSynSegment(ctx *listenContext, s *segment, opts *header.TCPSynOptions) {
+	defer decSynRcvdCount()
+	defer s.decRef()
+
+	n, err := ctx.createEndpointAndPerformHandshake(s, opts)
+	if err != nil {
+		return
+	}
+
+	e.deliverAccepted(n)
+}
+
+// handleListenSegment is called when a listening endpoint receives a segment
+// and needs to handle it.
+func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
+	switch s.flags {
+	case flagSyn:
+		opts := parseSynSegmentOptions(s)
+		if incSynRcvdCount() {
+			s.incRef()
+			go e.handleSynSegment(ctx, s, &opts) // S/R-FIXME
+		} else {
+			cookie := ctx.createCookie(s.id, s.sequenceNumber, encodeMSS(opts.MSS))
+			// Send SYN with window scaling because we currently
+			// dont't encode this information in the cookie.
+			//
+			// Enable Timestamp option if the original syn did have
+			// the timestamp option specified.
+			synOpts := header.TCPSynOptions{
+				WS:    -1,
+				TS:    opts.TS,
+				TSVal: tcpTimeStamp(timeStampOffset()),
+				TSEcr: opts.TSVal,
+			}
+			sendSynTCP(&s.route, s.id, flagSyn|flagAck, cookie, s.sequenceNumber+1, ctx.rcvWnd, synOpts)
+		}
+
+	case flagAck:
+		if data, ok := ctx.isCookieValid(s.id, s.ackNumber-1, s.sequenceNumber-1); ok && int(data) < len(mssTable) {
+			// Create newly accepted endpoint and deliver it.
+			rcvdSynOptions := &header.TCPSynOptions{
+				MSS: mssTable[data],
+				// Disable Window scaling as original SYN is
+				// lost.
+				WS: -1,
+			}
+			// When syn cookies are in use we enable timestamp only
+			// if the ack specifies the timestamp option assuming
+			// that the other end did in fact negotiate the
+			// timestamp option in the original SYN.
+			if s.parsedOptions.TS {
+				rcvdSynOptions.TS = true
+				rcvdSynOptions.TSVal = s.parsedOptions.TSVal
+				rcvdSynOptions.TSEcr = s.parsedOptions.TSEcr
+			}
+			n, err := ctx.createConnectedEndpoint(s, s.ackNumber-1, s.sequenceNumber-1, rcvdSynOptions)
+			if err == nil {
+				// clear the tsOffset for the newly created
+				// endpoint as the Timestamp was already
+				// randomly offset when the original SYN-ACK was
+				// sent above.
+				n.tsOffset = 0
+				e.deliverAccepted(n)
+			}
+		}
+	}
+}
+
+// protocolListenLoop is the main loop of a listening TCP endpoint. It runs in
+// its own goroutine and is responsible for handling connection requests.
+func (e *endpoint) protocolListenLoop(rcvWnd seqnum.Size) *tcpip.Error {
+	defer func() {
+		// Mark endpoint as closed. This will prevent goroutines running
+		// handleSynSegment() from attempting to queue new connections
+		// to the endpoint.
+		e.mu.Lock()
+		e.state = stateClosed
+		e.mu.Unlock()
+
+		// Notify waiters that the endpoint is shutdown.
+		e.waiterQueue.Notify(waiter.EventIn | waiter.EventOut)
+
+		// Do cleanup if needed.
+		e.completeWorker()
+	}()
+
+	e.mu.Lock()
+	v6only := e.v6only
+	e.mu.Unlock()
+
+	ctx := newListenContext(e.stack, rcvWnd, v6only, e.netProto)
+
+	s := sleep.Sleeper{}
+	s.AddWaker(&e.notificationWaker, wakerForNotification)
+	s.AddWaker(&e.newSegmentWaker, wakerForNewSegment)
+	for {
+		switch index, _ := s.Fetch(true); index {
+		case wakerForNotification:
+			n := e.fetchNotifications()
+			if n&notifyClose != 0 {
+				return nil
+			}
+			if n&notifyDrain != 0 {
+				for s := e.segmentQueue.dequeue(); s != nil; s = e.segmentQueue.dequeue() {
+					e.handleListenSegment(ctx, s)
+					s.decRef()
+				}
+				e.drainDone <- struct{}{}
+				return nil
+			}
+
+		case wakerForNewSegment:
+			// Process at most maxSegmentsPerWake segments.
+			mayRequeue := true
+			for i := 0; i < maxSegmentsPerWake; i++ {
+				s := e.segmentQueue.dequeue()
+				if s == nil {
+					mayRequeue = false
+					break
+				}
+
+				e.handleListenSegment(ctx, s)
+				s.decRef()
+			}
+
+			// If the queue is not empty, make sure we'll wake up
+			// in the next iteration.
+			if mayRequeue && !e.segmentQueue.empty() {
+				e.newSegmentWaker.Assert()
+			}
+		}
+	}
+}