Add support for TCP receive buffer auto tuning.

The implementation is similar to linux where we track the number of bytes
consumed by the application to grow the receive buffer of a given TCP endpoint.

This ensures that the advertised window grows at a reasonable rate to accomodate
for the sender's rate and prevents large amounts of data being held in stack
buffers if the application is not actively reading or not reading fast enough.

The original paper that was used to implement the linux receive buffer auto-
tuning is available @ https://public.lanl.gov/radiant/pubs/drs/lacsi2001.pdf

NOTE: Linux does not implement DRS as defined in that paper, it's just a good
reference to understand the solution space.

Updates #230

PiperOrigin-RevId: 253168283

1 files changed, 11 insertions, 3 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()