Merge 3d71c627 (automated)

10 files changed, 387 insertions, 51 deletions

diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
index 9b1ad6a28..52fd1bfa3 100644
--- a/pkg/tcpip/transport/tcp/accept.go
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -213,6 +213,7 @@ func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, i
 	n.route = s.route.Clone()
 	n.effectiveNetProtos = []tcpip.NetworkProtocolNumber{s.route.NetProto}
 	n.rcvBufSize = int(l.rcvWnd)
+	n.amss = mssForRoute(&n.route)
 
 	n.maybeEnableTimestamp(rcvdSynOpts)
 	n.maybeEnableSACKPermitted(rcvdSynOpts)
@@ -232,7 +233,11 @@ func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, i
 	// 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)
+	n.rcv = newReceiver(n, irs, seqnum.Size(n.initialReceiveWindow()), 0, seqnum.Size(n.receiveBufferSize()))
+	// Bootstrap the auto tuning algorithm. Starting at zero will result in
+	// a large step function on the first window adjustment causing the
+	// window to grow to a really large value.
+	n.rcvAutoParams.prevCopied = n.initialReceiveWindow()
 
 	return n, nil
 }
@@ -249,7 +254,7 @@ func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *head
 	}
 
 	// Perform the 3-way handshake.
-	h := newHandshake(ep, l.rcvWnd)
+	h := newHandshake(ep, seqnum.Size(ep.initialReceiveWindow()))
 
 	h.resetToSynRcvd(cookie, irs, opts)
 	if err := h.execute(); err != nil {
@@ -359,16 +364,19 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
 				return
 			}
 			cookie := ctx.createCookie(s.id, s.sequenceNumber, encodeMSS(opts.MSS))
-			// Send SYN with window scaling because we currently
+
+			// Send SYN without 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.
+			mss := mssForRoute(&s.route)
 			synOpts := header.TCPSynOptions{
 				WS:    -1,
 				TS:    opts.TS,
 				TSVal: tcpTimeStamp(timeStampOffset()),
 				TSEcr: opts.TSVal,
+				MSS:   uint16(mss),
 			}
 			sendSynTCP(&s.route, s.id, header.TCPFlagSyn|header.TCPFlagAck, cookie, s.sequenceNumber+1, ctx.rcvWnd, synOpts)
 			e.stack.Stats().TCP.ListenOverflowSynCookieSent.Increment()
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index 84e3dd26c..00d2ae524 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -78,6 +78,9 @@ type handshake struct {
 	// mss is the maximum segment size received from the peer.
 	mss uint16
 
+	// amss is the maximum segment size advertised by us to the peer.
+	amss uint16
+
 	// sndWndScale is the send window scale, as defined in RFC 1323. A
 	// negative value means no scaling is supported by the peer.
 	sndWndScale int
@@ -87,11 +90,24 @@ type handshake struct {
 }
 
 func newHandshake(ep *endpoint, rcvWnd seqnum.Size) handshake {
+	rcvWndScale := ep.rcvWndScaleForHandshake()
+
+	// Round-down the rcvWnd to a multiple of wndScale. This ensures that the
+	// window offered in SYN won't be reduced due to the loss of precision if
+	// window scaling is enabled after the handshake.
+	rcvWnd = (rcvWnd >> uint8(rcvWndScale)) << uint8(rcvWndScale)
+
+	// Ensure we can always accept at least 1 byte if the scale specified
+	// was too high for the provided rcvWnd.
+	if rcvWnd == 0 {
+		rcvWnd = 1
+	}
+
 	h := handshake{
 		ep:          ep,
 		active:      true,
 		rcvWnd:      rcvWnd,
-		rcvWndScale: FindWndScale(rcvWnd),
+		rcvWndScale: int(rcvWndScale),
 	}
 	h.resetState()
 	return h
@@ -224,7 +240,7 @@ func (h *handshake) synSentState(s *segment) *tcpip.Error {
 	h.ep.state = StateSynRecv
 	h.ep.mu.Unlock()
 	synOpts := header.TCPSynOptions{
-		WS:    h.rcvWndScale,
+		WS:    int(h.effectiveRcvWndScale()),
 		TS:    rcvSynOpts.TS,
 		TSVal: h.ep.timestamp(),
 		TSEcr: h.ep.recentTS,
@@ -233,6 +249,7 @@ func (h *handshake) synSentState(s *segment) *tcpip.Error {
 		// permits SACK. This is not explicitly defined in the RFC but
 		// this is the behaviour implemented by Linux.
 		SACKPermitted: rcvSynOpts.SACKPermitted,
+		MSS:           h.ep.amss,
 	}
 	sendSynTCP(&s.route, h.ep.id, h.flags, h.iss, h.ackNum, h.rcvWnd, synOpts)
 
@@ -277,6 +294,7 @@ func (h *handshake) synRcvdState(s *segment) *tcpip.Error {
 			TSVal:         h.ep.timestamp(),
 			TSEcr:         h.ep.recentTS,
 			SACKPermitted: h.ep.sackPermitted,
+			MSS:           h.ep.amss,
 		}
 		sendSynTCP(&s.route, h.ep.id, h.flags, h.iss, h.ackNum, h.rcvWnd, synOpts)
 		return nil
@@ -419,12 +437,15 @@ func (h *handshake) execute() *tcpip.Error {
 
 	// Send the initial SYN segment and loop until the handshake is
 	// completed.
+	h.ep.amss = mssForRoute(&h.ep.route)
+
 	synOpts := header.TCPSynOptions{
 		WS:            h.rcvWndScale,
 		TS:            true,
 		TSVal:         h.ep.timestamp(),
 		TSEcr:         h.ep.recentTS,
 		SACKPermitted: bool(sackEnabled),
+		MSS:           h.ep.amss,
 	}
 
 	// Execute is also called in a listen context so we want to make sure we
@@ -433,6 +454,11 @@ func (h *handshake) execute() *tcpip.Error {
 	if h.state == handshakeSynRcvd {
 		synOpts.TS = h.ep.sendTSOk
 		synOpts.SACKPermitted = h.ep.sackPermitted && bool(sackEnabled)
+		if h.sndWndScale < 0 {
+			// Disable window scaling if the peer did not send us
+			// the window scaling option.
+			synOpts.WS = -1
+		}
 	}
 	sendSynTCP(&h.ep.route, h.ep.id, h.flags, h.iss, h.ackNum, h.rcvWnd, synOpts)
 	for h.state != handshakeCompleted {
@@ -554,13 +580,6 @@ func makeSynOptions(opts header.TCPSynOptions) []byte {
 }
 
 func sendSynTCP(r *stack.Route, id stack.TransportEndpointID, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size, opts header.TCPSynOptions) *tcpip.Error {
-	// The MSS in opts is automatically calculated as this function is
-	// called from many places and we don't want every call point being
-	// embedded with the MSS calculation.
-	if opts.MSS == 0 {
-		opts.MSS = uint16(r.MTU() - header.TCPMinimumSize)
-	}
-
 	options := makeSynOptions(opts)
 	err := sendTCP(r, id, buffer.VectorisedView{}, r.DefaultTTL(), flags, seq, ack, rcvWnd, options, nil)
 	putOptions(options)
@@ -861,7 +880,8 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 		// This is an active connection, so we must initiate the 3-way
 		// handshake, and then inform potential waiters about its
 		// completion.
-		h := newHandshake(e, seqnum.Size(e.receiveBufferAvailable()))
+		initialRcvWnd := e.initialReceiveWindow()
+		h := newHandshake(e, seqnum.Size(initialRcvWnd))
 		e.mu.Lock()
 		h.ep.state = StateSynSent
 		e.mu.Unlock()
@@ -886,8 +906,14 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 		// (indicated by a negative send window scale).
 		e.snd = newSender(e, h.iss, h.ackNum-1, h.sndWnd, h.mss, h.sndWndScale)
 
+		rcvBufSize := seqnum.Size(e.receiveBufferSize())
 		e.rcvListMu.Lock()
-		e.rcv = newReceiver(e, h.ackNum-1, h.rcvWnd, h.effectiveRcvWndScale())
+		e.rcv = newReceiver(e, h.ackNum-1, h.rcvWnd, h.effectiveRcvWndScale(), rcvBufSize)
+		// boot strap the auto tuning algorithm. Starting at zero will
+		// result in a large step function on the first proper causing
+		// the window to just go to a really large value after the first
+		// RTT itself.
+		e.rcvAutoParams.prevCopied = initialRcvWnd
 		e.rcvListMu.Unlock()
 	}
 
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 9614b2958..1aa1f12b4 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -132,6 +132,42 @@ type SACKInfo struct {
 	NumBlocks int
 }
 
+// rcvBufAutoTuneParams are used to hold state variables to compute
+// the auto tuned recv buffer size.
+//
+// +stateify savable
+type rcvBufAutoTuneParams struct {
+	// measureTime is the time at which the current measurement
+	// was started.
+	measureTime time.Time `state:".(unixTime)"`
+
+	// copied is the number of bytes copied out of the receive
+	// buffers since this measure began.
+	copied int
+
+	// prevCopied is the number of bytes copied out of the receive
+	// buffers in the previous RTT period.
+	prevCopied int
+
+	// rtt is the non-smoothed minimum RTT as measured by observing the time
+	// between when a byte is first acknowledged and the receipt of data
+	// that is at least one window beyond the sequence number that was
+	// acknowledged.
+	rtt time.Duration
+
+	// rttMeasureSeqNumber is the highest acceptable sequence number at the
+	// time this RTT measurement period began.
+	rttMeasureSeqNumber seqnum.Value
+
+	// rttMeasureTime is the absolute time at which the current rtt
+	// measurement period began.
+	rttMeasureTime time.Time `state:".(unixTime)"`
+
+	// disabled is true if an explicit receive buffer is set for the
+	// endpoint.
+	disabled bool
+}
+
 // endpoint represents a TCP endpoint. This struct serves as the interface
 // between users of the endpoint and the protocol implementation; it is legal to
 // have concurrent goroutines make calls into the endpoint, they are properly
@@ -165,11 +201,12 @@ type endpoint struct {
 	// to indicate to users that no more data is coming.
 	//
 	// rcvListMu can be taken after the endpoint mu below.
-	rcvListMu  sync.Mutex  `state:"nosave"`
-	rcvList    segmentList `state:"wait"`
-	rcvClosed  bool
-	rcvBufSize int
-	rcvBufUsed int
+	rcvListMu     sync.Mutex  `state:"nosave"`
+	rcvList       segmentList `state:"wait"`
+	rcvClosed     bool
+	rcvBufSize    int
+	rcvBufUsed    int
+	rcvAutoParams rcvBufAutoTuneParams
 
 	// The following fields are protected by the mutex.
 	mu sync.RWMutex `state:"nosave"`
@@ -339,6 +376,9 @@ type endpoint struct {
 	bindAddress       tcpip.Address
 	connectingAddress tcpip.Address
 
+	// amss is the advertised MSS to the peer by this endpoint.
+	amss uint16
+
 	gso *stack.GSO
 }
 
@@ -373,8 +413,8 @@ func newEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, waite
 		netProto:    netProto,
 		waiterQueue: waiterQueue,
 		state:       StateInitial,
-		rcvBufSize:  DefaultBufferSize,
-		sndBufSize:  DefaultBufferSize,
+		rcvBufSize:  DefaultReceiveBufferSize,
+		sndBufSize:  DefaultSendBufferSize,
 		sndMTU:      int(math.MaxInt32),
 		reuseAddr:   true,
 		keepalive: keepalive{
@@ -400,6 +440,11 @@ func newEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, waite
 		e.cc = cs
 	}
 
+	var mrb tcpip.ModerateReceiveBufferOption
+	if err := stack.TransportProtocolOption(ProtocolNumber, &mrb); err == nil {
+		e.rcvAutoParams.disabled = !bool(mrb)
+	}
+
 	if p := stack.GetTCPProbe(); p != nil {
 		e.probe = p
 	}
@@ -408,6 +453,7 @@ func newEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, waite
 	e.workMu.Init()
 	e.workMu.Lock()
 	e.tsOffset = timeStampOffset()
+
 	return e
 }
 
@@ -551,6 +597,83 @@ func (e *endpoint) cleanupLocked() {
 	tcpip.DeleteDanglingEndpoint(e)
 }
 
+// initialReceiveWindow returns the initial receive window to advertise in the
+// SYN/SYN-ACK.
+func (e *endpoint) initialReceiveWindow() int {
+	rcvWnd := e.receiveBufferAvailable()
+	if rcvWnd > math.MaxUint16 {
+		rcvWnd = math.MaxUint16
+	}
+	routeWnd := InitialCwnd * int(mssForRoute(&e.route)) * 2
+	if rcvWnd > routeWnd {
+		rcvWnd = routeWnd
+	}
+	return rcvWnd
+}
+
+// ModerateRecvBuf adjusts the receive buffer and the advertised window
+// based on the number of bytes copied to user space.
+func (e *endpoint) ModerateRecvBuf(copied int) {
+	e.rcvListMu.Lock()
+	if e.rcvAutoParams.disabled {
+		e.rcvListMu.Unlock()
+		return
+	}
+	now := time.Now()
+	if rtt := e.rcvAutoParams.rtt; rtt == 0 || now.Sub(e.rcvAutoParams.measureTime) < rtt {
+		e.rcvAutoParams.copied += copied
+		e.rcvListMu.Unlock()
+		return
+	}
+	prevRTTCopied := e.rcvAutoParams.copied + copied
+	prevCopied := e.rcvAutoParams.prevCopied
+	rcvWnd := 0
+	if prevRTTCopied > prevCopied {
+		// The minimal receive window based on what was copied by the app
+		// in the immediate preceding RTT and some extra buffer for 16
+		// segments to account for variations.
+		// We multiply by 2 to account for packet losses.
+		rcvWnd = prevRTTCopied*2 + 16*int(e.amss)
+
+		// Scale for slow start based on bytes copied in this RTT vs previous.
+		grow := (rcvWnd * (prevRTTCopied - prevCopied)) / prevCopied
+
+		// Multiply growth factor by 2 again to account for sender being
+		// in slow-start where the sender grows it's congestion window
+		// by 100% per RTT.
+		rcvWnd += grow * 2
+
+		// Make sure auto tuned buffer size can always receive upto 2x
+		// the initial window of 10 segments.
+		if minRcvWnd := int(e.amss) * InitialCwnd * 2; rcvWnd < minRcvWnd {
+			rcvWnd = minRcvWnd
+		}
+
+		// Cap the auto tuned buffer size by the maximum permissible
+		// receive buffer size.
+		if max := e.maxReceiveBufferSize(); rcvWnd > max {
+			rcvWnd = max
+		}
+
+		// We do not adjust downwards as that can cause the receiver to
+		// reject valid data that might already be in flight as the
+		// acceptable window will shrink.
+		if rcvWnd > e.rcvBufSize {
+			e.rcvBufSize = rcvWnd
+			e.notifyProtocolGoroutine(notifyReceiveWindowChanged)
+		}
+
+		// We only update prevCopied when we grow the buffer because in cases
+		// where prevCopied > prevRTTCopied the existing buffer is already big
+		// enough to handle the current rate and we don't need to do any
+		// adjustments.
+		e.rcvAutoParams.prevCopied = prevRTTCopied
+	}
+	e.rcvAutoParams.measureTime = now
+	e.rcvAutoParams.copied = 0
+	e.rcvListMu.Unlock()
+}
+
 // Read reads data from the endpoint.
 func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
 	e.mu.RLock()
@@ -821,6 +944,7 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 
 		wasZero := e.zeroReceiveWindow(scale)
 		e.rcvBufSize = size
+		e.rcvAutoParams.disabled = true
 		if wasZero && !e.zeroReceiveWindow(scale) {
 			mask |= notifyNonZeroReceiveWindow
 		}
@@ -1657,6 +1781,33 @@ func (e *endpoint) receiveBufferSize() int {
 	return size
 }
 
+func (e *endpoint) maxReceiveBufferSize() int {
+	var rs ReceiveBufferSizeOption
+	if err := e.stack.TransportProtocolOption(ProtocolNumber, &rs); err != nil {
+		// As a fallback return the hardcoded max buffer size.
+		return MaxBufferSize
+	}
+	return rs.Max
+}
+
+// rcvWndScaleForHandshake computes the receive window scale to offer to the
+// peer when window scaling is enabled (true by default). If auto-tuning is
+// disabled then the window scaling factor is based on the size of the
+// receiveBuffer otherwise we use the max permissible receive buffer size to
+// compute the scale.
+func (e *endpoint) rcvWndScaleForHandshake() int {
+	bufSizeForScale := e.receiveBufferSize()
+
+	e.rcvListMu.Lock()
+	autoTuningDisabled := e.rcvAutoParams.disabled
+	e.rcvListMu.Unlock()
+	if autoTuningDisabled {
+		return FindWndScale(seqnum.Size(bufSizeForScale))
+	}
+
+	return FindWndScale(seqnum.Size(e.maxReceiveBufferSize()))
+}
+
 // updateRecentTimestamp updates the recent timestamp using the algorithm
 // described in https://tools.ietf.org/html/rfc7323#section-4.3
 func (e *endpoint) updateRecentTimestamp(tsVal uint32, maxSentAck seqnum.Value, segSeq seqnum.Value) {
@@ -1749,6 +1900,13 @@ func (e *endpoint) completeState() stack.TCPEndpointState {
 	s.RcvBufSize = e.rcvBufSize
 	s.RcvBufUsed = e.rcvBufUsed
 	s.RcvClosed = e.rcvClosed
+	s.RcvAutoParams.MeasureTime = e.rcvAutoParams.measureTime
+	s.RcvAutoParams.CopiedBytes = e.rcvAutoParams.copied
+	s.RcvAutoParams.PrevCopiedBytes = e.rcvAutoParams.prevCopied
+	s.RcvAutoParams.RTT = e.rcvAutoParams.rtt
+	s.RcvAutoParams.RTTMeasureSeqNumber = e.rcvAutoParams.rttMeasureSeqNumber
+	s.RcvAutoParams.RTTMeasureTime = e.rcvAutoParams.rttMeasureTime
+	s.RcvAutoParams.Disabled = e.rcvAutoParams.disabled
 	e.rcvListMu.Unlock()
 
 	// Endpoint TCP Option state.
@@ -1802,13 +1960,13 @@ func (e *endpoint) completeState() stack.TCPEndpointState {
 		RTTMeasureTime:   e.snd.rttMeasureTime,
 		Closed:           e.snd.closed,
 		RTO:              e.snd.rto,
-		SRTTInited:       e.snd.srttInited,
 		MaxPayloadSize:   e.snd.maxPayloadSize,
 		SndWndScale:      e.snd.sndWndScale,
 		MaxSentAck:       e.snd.maxSentAck,
 	}
 	e.snd.rtt.Lock()
 	s.Sender.SRTT = e.snd.rtt.srtt
+	s.Sender.SRTTInited = e.snd.rtt.srttInited
 	e.snd.rtt.Unlock()
 
 	if cubic, ok := e.snd.cc.(*cubicState); ok {
@@ -1856,3 +2014,7 @@ func (e *endpoint) State() uint32 {
 	defer e.mu.Unlock()
 	return uint32(e.state)
 }
+
+func mssForRoute(r *stack.Route) uint16 {
+	return uint16(r.MTU() - header.TCPMinimumSize)
+}
diff --git a/pkg/tcpip/transport/tcp/endpoint_state.go b/pkg/tcpip/transport/tcp/endpoint_state.go
index 58be61927..ec61a3886 100644
--- a/pkg/tcpip/transport/tcp/endpoint_state.go
+++ b/pkg/tcpip/transport/tcp/endpoint_state.go
@@ -360,3 +360,23 @@ func loadError(s string) *tcpip.Error {
 
 	return e
 }
+
+// saveMeasureTime is invoked by stateify.
+func (r *rcvBufAutoTuneParams) saveMeasureTime() unixTime {
+	return unixTime{r.measureTime.Unix(), r.measureTime.UnixNano()}
+}
+
+// loadMeasureTime is invoked by stateify.
+func (r *rcvBufAutoTuneParams) loadMeasureTime(unix unixTime) {
+	r.measureTime = time.Unix(unix.second, unix.nano)
+}
+
+// saveRttMeasureTime is invoked by stateify.
+func (r *rcvBufAutoTuneParams) saveRttMeasureTime() unixTime {
+	return unixTime{r.rttMeasureTime.Unix(), r.rttMeasureTime.UnixNano()}
+}
+
+// loadRttMeasureTime is invoked by stateify.
+func (r *rcvBufAutoTuneParams) loadRttMeasureTime(unix unixTime) {
+	r.rttMeasureTime = time.Unix(unix.second, unix.nano)
+}
diff --git a/pkg/tcpip/transport/tcp/forwarder.go b/pkg/tcpip/transport/tcp/forwarder.go
index 2ce94aeb9..63666f0b3 100644
--- a/pkg/tcpip/transport/tcp/forwarder.go
+++ b/pkg/tcpip/transport/tcp/forwarder.go
@@ -47,7 +47,7 @@ type Forwarder struct {
 // If rcvWnd is set to zero, the default buffer size is used instead.
 func NewForwarder(s *stack.Stack, rcvWnd, maxInFlight int, handler func(*ForwarderRequest)) *Forwarder {
 	if rcvWnd == 0 {
-		rcvWnd = DefaultBufferSize
+		rcvWnd = DefaultReceiveBufferSize
 	}
 	return &Forwarder{
 		maxInFlight: maxInFlight,
diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index 919e4ce24..ee04dcfcc 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -41,13 +41,18 @@ const (
 	ProtocolNumber = header.TCPProtocolNumber
 
 	// MinBufferSize is the smallest size of a receive or send buffer.
-	minBufferSize = 4 << 10 // 4096 bytes.
+	MinBufferSize = 4 << 10 // 4096 bytes.
 
-	// DefaultBufferSize is the default size of the receive and send buffers.
-	DefaultBufferSize = 1 << 20 // 1MB
+	// DefaultSendBufferSize is the default size of the send buffer for
+	// an endpoint.
+	DefaultSendBufferSize = 1 << 20 // 1MB
 
-	// MaxBufferSize is the largest size a receive and send buffer can grow to.
-	maxBufferSize = 4 << 20 // 4MB
+	// DefaultReceiveBufferSize is the default size of the receive buffer
+	// for an endpoint.
+	DefaultReceiveBufferSize = 1 << 20 // 1MB
+
+	// MaxBufferSize is the largest size a receive/send buffer can grow to.
+	MaxBufferSize = 4 << 20 // 4MB
 
 	// MaxUnprocessedSegments is the maximum number of unprocessed segments
 	// that can be queued for a given endpoint.
@@ -86,6 +91,7 @@ type protocol struct {
 	recvBufferSize             ReceiveBufferSizeOption
 	congestionControl          string
 	availableCongestionControl []string
+	moderateReceiveBuffer      bool
 }
 
 // Number returns the tcp protocol number.
@@ -192,6 +198,13 @@ func (p *protocol) SetOption(option interface{}) *tcpip.Error {
 		// linux returns ENOENT when an invalid congestion control
 		// is specified.
 		return tcpip.ErrNoSuchFile
+
+	case tcpip.ModerateReceiveBufferOption:
+		p.mu.Lock()
+		p.moderateReceiveBuffer = bool(v)
+		p.mu.Unlock()
+		return nil
+
 	default:
 		return tcpip.ErrUnknownProtocolOption
 	}
@@ -217,16 +230,25 @@ func (p *protocol) Option(option interface{}) *tcpip.Error {
 		*v = p.recvBufferSize
 		p.mu.Unlock()
 		return nil
+
 	case *tcpip.CongestionControlOption:
 		p.mu.Lock()
 		*v = tcpip.CongestionControlOption(p.congestionControl)
 		p.mu.Unlock()
 		return nil
+
 	case *tcpip.AvailableCongestionControlOption:
 		p.mu.Lock()
 		*v = tcpip.AvailableCongestionControlOption(strings.Join(p.availableCongestionControl, " "))
 		p.mu.Unlock()
 		return nil
+
+	case *tcpip.ModerateReceiveBufferOption:
+		p.mu.Lock()
+		*v = tcpip.ModerateReceiveBufferOption(p.moderateReceiveBuffer)
+		p.mu.Unlock()
+		return nil
+
 	default:
 		return tcpip.ErrUnknownProtocolOption
 	}
@@ -235,8 +257,8 @@ func (p *protocol) Option(option interface{}) *tcpip.Error {
 func init() {
 	stack.RegisterTransportProtocolFactory(ProtocolName, func() stack.TransportProtocol {
 		return &protocol{
-			sendBufferSize:             SendBufferSizeOption{minBufferSize, DefaultBufferSize, maxBufferSize},
-			recvBufferSize:             ReceiveBufferSizeOption{minBufferSize, DefaultBufferSize, maxBufferSize},
+			sendBufferSize:             SendBufferSizeOption{MinBufferSize, DefaultSendBufferSize, MaxBufferSize},
+			recvBufferSize:             ReceiveBufferSizeOption{MinBufferSize, DefaultReceiveBufferSize, MaxBufferSize},
 			congestionControl:          ccReno,
 			availableCongestionControl: []string{ccReno, ccCubic},
 		}
diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go
index 8d9de9bf9..e90f9a7d9 100644
--- a/pkg/tcpip/transport/tcp/rcv.go
+++ b/pkg/tcpip/transport/tcp/rcv.go
@@ -16,6 +16,7 @@ package tcp
 
 import (
 	"container/heap"
+	"time"
 
 	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/seqnum"
@@ -38,6 +39,9 @@ type receiver struct {
 	// shrinking it.
 	rcvAcc seqnum.Value
 
+	// rcvWnd is the non-scaled receive window last advertised to the peer.
+	rcvWnd seqnum.Size
+
 	rcvWndScale uint8
 
 	closed bool
@@ -47,13 +51,14 @@ type receiver struct {
 	pendingBufSize      seqnum.Size
 }
 
-func newReceiver(ep *endpoint, irs seqnum.Value, rcvWnd seqnum.Size, rcvWndScale uint8) *receiver {
+func newReceiver(ep *endpoint, irs seqnum.Value, rcvWnd seqnum.Size, rcvWndScale uint8, pendingBufSize seqnum.Size) *receiver {
 	return &receiver{
 		ep:             ep,
 		rcvNxt:         irs + 1,
 		rcvAcc:         irs.Add(rcvWnd + 1),
+		rcvWnd:         rcvWnd,
 		rcvWndScale:    rcvWndScale,
-		pendingBufSize: rcvWnd,
+		pendingBufSize: pendingBufSize,
 	}
 }
 
@@ -72,14 +77,16 @@ func (r *receiver) acceptable(segSeq seqnum.Value, segLen seqnum.Size) bool {
 // getSendParams returns the parameters needed by the sender when building
 // segments to send.
 func (r *receiver) getSendParams() (rcvNxt seqnum.Value, rcvWnd seqnum.Size) {
-	// Calculate the window size based on the current buffer size.
-	n := r.ep.receiveBufferAvailable()
-	acc := r.rcvNxt.Add(seqnum.Size(n))
+	// Calculate the window size based on the available buffer space.
+	receiveBufferAvailable := r.ep.receiveBufferAvailable()
+	acc := r.rcvNxt.Add(seqnum.Size(receiveBufferAvailable))
 	if r.rcvAcc.LessThan(acc) {
 		r.rcvAcc = acc
 	}
-
-	return r.rcvNxt, r.rcvNxt.Size(r.rcvAcc) >> r.rcvWndScale
+	// Stash away the non-scaled receive window as we use it for measuring
+	// receiver's estimated RTT.
+	r.rcvWnd = r.rcvNxt.Size(r.rcvAcc)
+	return r.rcvNxt, r.rcvWnd >> r.rcvWndScale
 }
 
 // nonZeroWindow is called when the receive window grows from zero to nonzero;
@@ -130,6 +137,21 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 	// Update the segment that we're expecting to consume.
 	r.rcvNxt = segSeq.Add(segLen)
 
+	// In cases of a misbehaving sender which could send more than the
+	// advertised window, we could end up in a situation where we get a
+	// segment that exceeds the window advertised. Instead of partially
+	// accepting the segment and discarding bytes beyond the advertised
+	// window, we accept the whole segment and make sure r.rcvAcc is moved
+	// forward to match r.rcvNxt to indicate that the window is now closed.
+	//
+	// In absence of this check the r.acceptable() check fails and accepts
+	// segments that should be dropped because rcvWnd is calculated as
+	// the size of the interval (rcvNxt, rcvAcc] which becomes extremely
+	// large if rcvAcc is ever less than rcvNxt.
+	if r.rcvAcc.LessThan(r.rcvNxt) {
+		r.rcvAcc = r.rcvNxt
+	}
+
 	// Trim SACK Blocks to remove any SACK information that covers
 	// sequence numbers that have been consumed.
 	TrimSACKBlockList(&r.ep.sack, r.rcvNxt)
@@ -198,6 +220,39 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 	return true
 }
 
+// updateRTT updates the receiver RTT measurement based on the sequence number
+// of the received segment.
+func (r *receiver) updateRTT() {
+	// From: https://public.lanl.gov/radiant/pubs/drs/sc2001-poster.pdf
+	//
+	// A system that is only transmitting acknowledgements can still
+	// estimate the round-trip time by observing the time between when a byte
+	// is first acknowledged and the receipt of data that is at least one
+	// window beyond the sequence number that was acknowledged.
+	r.ep.rcvListMu.Lock()
+	if r.ep.rcvAutoParams.rttMeasureTime.IsZero() {
+		// New measurement.
+		r.ep.rcvAutoParams.rttMeasureTime = time.Now()
+		r.ep.rcvAutoParams.rttMeasureSeqNumber = r.rcvNxt.Add(r.rcvWnd)
+		r.ep.rcvListMu.Unlock()
+		return
+	}
+	if r.rcvNxt.LessThan(r.ep.rcvAutoParams.rttMeasureSeqNumber) {
+		r.ep.rcvListMu.Unlock()
+		return
+	}
+	rtt := time.Since(r.ep.rcvAutoParams.rttMeasureTime)
+	// We only store the minimum observed RTT here as this is only used in
+	// absence of a SRTT available from either timestamps or a sender
+	// measurement of RTT.
+	if r.ep.rcvAutoParams.rtt == 0 || rtt < r.ep.rcvAutoParams.rtt {
+		r.ep.rcvAutoParams.rtt = rtt
+	}
+	r.ep.rcvAutoParams.rttMeasureTime = time.Now()
+	r.ep.rcvAutoParams.rttMeasureSeqNumber = r.rcvNxt.Add(r.rcvWnd)
+	r.ep.rcvListMu.Unlock()
+}
+
 // handleRcvdSegment handles TCP segments directed at the connection managed by
 // r as they arrive. It is called by the protocol main loop.
 func (r *receiver) handleRcvdSegment(s *segment) {
@@ -226,10 +281,9 @@ func (r *receiver) handleRcvdSegment(s *segment) {
 				r.pendingBufUsed += s.logicalLen()
 				s.incRef()
 				heap.Push(&r.pendingRcvdSegments, s)
+				UpdateSACKBlocks(&r.ep.sack, segSeq, segSeq.Add(segLen), r.rcvNxt)
 			}
 
-			UpdateSACKBlocks(&r.ep.sack, segSeq, segSeq.Add(segLen), r.rcvNxt)
-
 			// Immediately send an ack so that the peer knows it may
 			// have to retransmit.
 			r.ep.snd.sendAck()
@@ -237,6 +291,12 @@ func (r *receiver) handleRcvdSegment(s *segment) {
 		return
 	}
 
+	// Since we consumed a segment update the receiver's RTT estimate
+	// if required.
+	if segLen > 0 {
+		r.updateRTT()
+	}
+
 	// By consuming the current segment, we may have filled a gap in the
 	// sequence number domain that allows pending segments to be consumed
 	// now. So try to do it.
diff --git a/pkg/tcpip/transport/tcp/sack.go b/pkg/tcpip/transport/tcp/sack.go
index 52c5d9867..7be86d68e 100644
--- a/pkg/tcpip/transport/tcp/sack.go
+++ b/pkg/tcpip/transport/tcp/sack.go
@@ -31,6 +31,13 @@ const (
 // segment identified by segStart->segEnd.
 func UpdateSACKBlocks(sack *SACKInfo, segStart seqnum.Value, segEnd seqnum.Value, rcvNxt seqnum.Value) {
 	newSB := header.SACKBlock{Start: segStart, End: segEnd}
+
+	// Ignore any invalid SACK blocks or blocks that are before rcvNxt as
+	// those bytes have already been acked.
+	if newSB.End.LessThanEq(newSB.Start) || newSB.End.LessThan(rcvNxt) {
+		return
+	}
+
 	if sack.NumBlocks == 0 {
 		sack.Blocks[0] = newSB
 		sack.NumBlocks = 1
@@ -39,9 +46,8 @@ func UpdateSACKBlocks(sack *SACKInfo, segStart seqnum.Value, segEnd seqnum.Value
 	var n = 0
 	for i := 0; i < sack.NumBlocks; i++ {
 		start, end := sack.Blocks[i].Start, sack.Blocks[i].End
-		if end.LessThanEq(start) || start.LessThanEq(rcvNxt) {
-			// Discard any invalid blocks where end is before start
-			// and discard any sack blocks that are before rcvNxt as
+		if end.LessThanEq(rcvNxt) {
+			// Discard any sack blocks that are before rcvNxt as
 			// those have already been acked.
 			continue
 		}
diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index 297861462..0fee7ab72 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -121,9 +121,8 @@ type sender struct {
 	// rtt.srtt, rtt.rttvar, and rto are the "smoothed round-trip time",
 	// "round-trip time variation" and "retransmit timeout", as defined in
 	// section 2 of RFC 6298.
-	rtt        rtt
-	rto        time.Duration
-	srttInited bool
+	rtt rtt
+	rto time.Duration
 
 	// maxPayloadSize is the maximum size of the payload of a given segment.
 	// It is initialized on demand.
@@ -150,8 +149,9 @@ type sender struct {
 type rtt struct {
 	sync.Mutex `state:"nosave"`
 
-	srtt   time.Duration
-	rttvar time.Duration
+	srtt       time.Duration
+	rttvar     time.Duration
+	srttInited bool
 }
 
 // fastRecovery holds information related to fast recovery from a packet loss.
@@ -323,10 +323,10 @@ func (s *sender) sendAck() {
 // available. This is done in accordance with section 2 of RFC 6298.
 func (s *sender) updateRTO(rtt time.Duration) {
 	s.rtt.Lock()
-	if !s.srttInited {
+	if !s.rtt.srttInited {
 		s.rtt.rttvar = rtt / 2
 		s.rtt.srtt = rtt
-		s.srttInited = true
+		s.rtt.srttInited = true
 	} else {
 		diff := s.rtt.srtt - rtt
 		if diff < 0 {
diff --git a/pkg/tcpip/transport/tcp/tcp_state_autogen.go b/pkg/tcpip/transport/tcp/tcp_state_autogen.go
index 1674c6a08..601ff758d 100755
--- a/pkg/tcpip/transport/tcp/tcp_state_autogen.go
+++ b/pkg/tcpip/transport/tcp/tcp_state_autogen.go
@@ -50,6 +50,31 @@ func (x *SACKInfo) load(m state.Map) {
 	m.Load("NumBlocks", &x.NumBlocks)
 }
 
+func (x *rcvBufAutoTuneParams) beforeSave() {}
+func (x *rcvBufAutoTuneParams) save(m state.Map) {
+	x.beforeSave()
+	var measureTime unixTime = x.saveMeasureTime()
+	m.SaveValue("measureTime", measureTime)
+	var rttMeasureTime unixTime = x.saveRttMeasureTime()
+	m.SaveValue("rttMeasureTime", rttMeasureTime)
+	m.Save("copied", &x.copied)
+	m.Save("prevCopied", &x.prevCopied)
+	m.Save("rtt", &x.rtt)
+	m.Save("rttMeasureSeqNumber", &x.rttMeasureSeqNumber)
+	m.Save("disabled", &x.disabled)
+}
+
+func (x *rcvBufAutoTuneParams) afterLoad() {}
+func (x *rcvBufAutoTuneParams) load(m state.Map) {
+	m.Load("copied", &x.copied)
+	m.Load("prevCopied", &x.prevCopied)
+	m.Load("rtt", &x.rtt)
+	m.Load("rttMeasureSeqNumber", &x.rttMeasureSeqNumber)
+	m.Load("disabled", &x.disabled)
+	m.LoadValue("measureTime", new(unixTime), func(y interface{}) { x.loadMeasureTime(y.(unixTime)) })
+	m.LoadValue("rttMeasureTime", new(unixTime), func(y interface{}) { x.loadRttMeasureTime(y.(unixTime)) })
+}
+
 func (x *endpoint) save(m state.Map) {
 	x.beforeSave()
 	var lastError string = x.saveLastError()
@@ -66,6 +91,7 @@ func (x *endpoint) save(m state.Map) {
 	m.Save("rcvClosed", &x.rcvClosed)
 	m.Save("rcvBufSize", &x.rcvBufSize)
 	m.Save("rcvBufUsed", &x.rcvBufUsed)
+	m.Save("rcvAutoParams", &x.rcvAutoParams)
 	m.Save("id", &x.id)
 	m.Save("isRegistered", &x.isRegistered)
 	m.Save("v6only", &x.v6only)
@@ -100,6 +126,7 @@ func (x *endpoint) save(m state.Map) {
 	m.Save("snd", &x.snd)
 	m.Save("bindAddress", &x.bindAddress)
 	m.Save("connectingAddress", &x.connectingAddress)
+	m.Save("amss", &x.amss)
 	m.Save("gso", &x.gso)
 }
 
@@ -110,6 +137,7 @@ func (x *endpoint) load(m state.Map) {
 	m.Load("rcvClosed", &x.rcvClosed)
 	m.Load("rcvBufSize", &x.rcvBufSize)
 	m.Load("rcvBufUsed", &x.rcvBufUsed)
+	m.Load("rcvAutoParams", &x.rcvAutoParams)
 	m.Load("id", &x.id)
 	m.Load("isRegistered", &x.isRegistered)
 	m.Load("v6only", &x.v6only)
@@ -144,6 +172,7 @@ func (x *endpoint) load(m state.Map) {
 	m.LoadWait("snd", &x.snd)
 	m.Load("bindAddress", &x.bindAddress)
 	m.Load("connectingAddress", &x.connectingAddress)
+	m.Load("amss", &x.amss)
 	m.Load("gso", &x.gso)
 	m.LoadValue("lastError", new(string), func(y interface{}) { x.loadLastError(y.(string)) })
 	m.LoadValue("state", new(EndpointState), func(y interface{}) { x.loadState(y.(EndpointState)) })
@@ -177,6 +206,7 @@ func (x *receiver) save(m state.Map) {
 	m.Save("ep", &x.ep)
 	m.Save("rcvNxt", &x.rcvNxt)
 	m.Save("rcvAcc", &x.rcvAcc)
+	m.Save("rcvWnd", &x.rcvWnd)
 	m.Save("rcvWndScale", &x.rcvWndScale)
 	m.Save("closed", &x.closed)
 	m.Save("pendingRcvdSegments", &x.pendingRcvdSegments)
@@ -189,6 +219,7 @@ func (x *receiver) load(m state.Map) {
 	m.Load("ep", &x.ep)
 	m.Load("rcvNxt", &x.rcvNxt)
 	m.Load("rcvAcc", &x.rcvAcc)
+	m.Load("rcvWnd", &x.rcvWnd)
 	m.Load("rcvWndScale", &x.rcvWndScale)
 	m.Load("closed", &x.closed)
 	m.Load("pendingRcvdSegments", &x.pendingRcvdSegments)
@@ -302,7 +333,6 @@ func (x *sender) save(m state.Map) {
 	m.Save("writeList", &x.writeList)
 	m.Save("rtt", &x.rtt)
 	m.Save("rto", &x.rto)
-	m.Save("srttInited", &x.srttInited)
 	m.Save("maxPayloadSize", &x.maxPayloadSize)
 	m.Save("gso", &x.gso)
 	m.Save("sndWndScale", &x.sndWndScale)
@@ -328,7 +358,6 @@ func (x *sender) load(m state.Map) {
 	m.Load("writeList", &x.writeList)
 	m.Load("rtt", &x.rtt)
 	m.Load("rto", &x.rto)
-	m.Load("srttInited", &x.srttInited)
 	m.Load("maxPayloadSize", &x.maxPayloadSize)
 	m.Load("gso", &x.gso)
 	m.Load("sndWndScale", &x.sndWndScale)
@@ -344,12 +373,14 @@ func (x *rtt) save(m state.Map) {
 	x.beforeSave()
 	m.Save("srtt", &x.srtt)
 	m.Save("rttvar", &x.rttvar)
+	m.Save("srttInited", &x.srttInited)
 }
 
 func (x *rtt) afterLoad() {}
 func (x *rtt) load(m state.Map) {
 	m.Load("srtt", &x.srtt)
 	m.Load("rttvar", &x.rttvar)
+	m.Load("srttInited", &x.srttInited)
 }
 
 func (x *fastRecovery) beforeSave() {}
@@ -415,6 +446,7 @@ func (x *segmentEntry) load(m state.Map) {
 func init() {
 	state.Register("tcp.cubicState", (*cubicState)(nil), state.Fns{Save: (*cubicState).save, Load: (*cubicState).load})
 	state.Register("tcp.SACKInfo", (*SACKInfo)(nil), state.Fns{Save: (*SACKInfo).save, Load: (*SACKInfo).load})
+	state.Register("tcp.rcvBufAutoTuneParams", (*rcvBufAutoTuneParams)(nil), state.Fns{Save: (*rcvBufAutoTuneParams).save, Load: (*rcvBufAutoTuneParams).load})
 	state.Register("tcp.endpoint", (*endpoint)(nil), state.Fns{Save: (*endpoint).save, Load: (*endpoint).load})
 	state.Register("tcp.keepalive", (*keepalive)(nil), state.Fns{Save: (*keepalive).save, Load: (*keepalive).load})
 	state.Register("tcp.receiver", (*receiver)(nil), state.Fns{Save: (*receiver).save, Load: (*receiver).load})