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-rw-r--r--pkg/tcpip/transport/tcp/endpoint.go74
-rw-r--r--pkg/tcpip/transport/tcp/rcv.go6
-rw-r--r--pkg/tcpip/transport/tcp/tcp_test.go151
3 files changed, 199 insertions, 32 deletions
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 920b24975..830bc1e3e 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -885,8 +885,14 @@ func (e *endpoint) ModerateRecvBuf(copied int) {
// reject valid data that might already be in flight as the
// acceptable window will shrink.
if rcvWnd > e.rcvBufSize {
+ availBefore := e.receiveBufferAvailableLocked()
e.rcvBufSize = rcvWnd
- e.notifyProtocolGoroutine(notifyReceiveWindowChanged)
+ availAfter := e.receiveBufferAvailableLocked()
+ mask := uint32(notifyReceiveWindowChanged)
+ if crossed, above := e.windowCrossedACKThreshold(availAfter - availBefore); crossed && above {
+ mask |= notifyNonZeroReceiveWindow
+ }
+ e.notifyProtocolGoroutine(mask)
}
// We only update prevCopied when we grow the buffer because in cases
@@ -955,11 +961,12 @@ func (e *endpoint) readLocked() (buffer.View, *tcpip.Error) {
}
e.rcvBufUsed -= len(v)
- // If the window was zero before this read and if the read freed up
- // enough buffer space for the scaled window to be non-zero then notify
- // the protocol goroutine to send a window update.
- if e.zeroWindow && !e.zeroReceiveWindow(e.rcv.rcvWndScale) {
- e.zeroWindow = false
+
+ // If the window was small before this read and if the read freed up
+ // enough buffer space, to either fit an aMSS or half a receive buffer
+ // (whichever smaller), then notify the protocol goroutine to send a
+ // window update.
+ if crossed, above := e.windowCrossedACKThreshold(len(v)); crossed && above {
e.notifyProtocolGoroutine(notifyNonZeroReceiveWindow)
}
@@ -1133,16 +1140,38 @@ func (e *endpoint) Peek(vec [][]byte) (int64, tcpip.ControlMessages, *tcpip.Erro
return num, tcpip.ControlMessages{}, nil
}
-// zeroReceiveWindow checks if the receive window to be announced now would be
-// zero, based on the amount of available buffer and the receive window scaling.
+// windowCrossedACKThreshold checks if the receive window to be announced now
+// would be under aMSS or under half receive buffer, whichever smaller. This is
+// useful as a receive side silly window syndrome prevention mechanism. If
+// window grows to reasonable value, we should send ACK to the sender to inform
+// the rx space is now large. We also want ensure a series of small read()'s
+// won't trigger a flood of spurious tiny ACK's.
//
-// It must be called with rcvListMu held.
-func (e *endpoint) zeroReceiveWindow(scale uint8) bool {
- if e.rcvBufUsed >= e.rcvBufSize {
- return true
+// For large receive buffers, the threshold is aMSS - once reader reads more
+// than aMSS we'll send ACK. For tiny receive buffers, the threshold is half of
+// receive buffer size. This is chosen arbitrairly.
+// crossed will be true if the window size crossed the ACK threshold.
+// above will be true if the new window is >= ACK threshold and false
+// otherwise.
+func (e *endpoint) windowCrossedACKThreshold(deltaBefore int) (crossed bool, above bool) {
+ newAvail := e.receiveBufferAvailableLocked()
+ oldAvail := newAvail - deltaBefore
+ if oldAvail < 0 {
+ oldAvail = 0
+ }
+
+ threshold := int(e.amss)
+ if threshold > e.rcvBufSize/2 {
+ threshold = e.rcvBufSize / 2
}
- return ((e.rcvBufSize - e.rcvBufUsed) >> scale) == 0
+ switch {
+ case oldAvail < threshold && newAvail >= threshold:
+ return true, true
+ case oldAvail >= threshold && newAvail < threshold:
+ return true, false
+ }
+ return false, false
}
// SetSockOptBool sets a socket option.
@@ -1204,10 +1233,16 @@ func (e *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) *tcpip.Error {
size = math.MaxInt32 / 2
}
+ availBefore := e.receiveBufferAvailableLocked()
e.rcvBufSize = size
+ availAfter := e.receiveBufferAvailableLocked()
+
e.rcvAutoParams.disabled = true
- if e.zeroWindow && !e.zeroReceiveWindow(scale) {
- e.zeroWindow = false
+
+ // Immediately send an ACK to uncork the sender silly window
+ // syndrome prevetion, when our available space grows above aMSS
+ // or half receive buffer, whichever smaller.
+ if crossed, above := e.windowCrossedACKThreshold(availAfter - availBefore); crossed && above {
mask |= notifyNonZeroReceiveWindow
}
e.rcvListMu.Unlock()
@@ -2225,13 +2260,10 @@ func (e *endpoint) readyToRead(s *segment) {
if s != nil {
s.incRef()
e.rcvBufUsed += s.data.Size()
- // Check if the receive window is now closed. If so make sure
- // we set the zero window before we deliver the segment to ensure
- // that a subsequent read of the segment will correctly trigger
- // a non-zero notification.
- if avail := e.receiveBufferAvailableLocked(); avail>>e.rcv.rcvWndScale == 0 {
+ // Increase counter if the receive window falls down below MSS
+ // or half receive buffer size, whichever smaller.
+ if crossed, above := e.windowCrossedACKThreshold(-s.data.Size()); crossed && !above {
e.stats.ReceiveErrors.ZeroRcvWindowState.Increment()
- e.zeroWindow = true
}
e.rcvList.PushBack(s)
} else {
diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go
index 0a5534959..05c8488f8 100644
--- a/pkg/tcpip/transport/tcp/rcv.go
+++ b/pkg/tcpip/transport/tcp/rcv.go
@@ -98,12 +98,6 @@ func (r *receiver) getSendParams() (rcvNxt seqnum.Value, rcvWnd seqnum.Size) {
// in such cases we may need to send an ack to indicate to our peer that it can
// resume sending data.
func (r *receiver) nonZeroWindow() {
- if (r.rcvAcc-r.rcvNxt)>>r.rcvWndScale != 0 {
- // We never got around to announcing a zero window size, so we
- // don't need to immediately announce a nonzero one.
- return
- }
-
// Immediately send an ack.
r.ep.snd.sendAck()
}
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index 1aa0733d0..6edfa8dce 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -2091,10 +2091,14 @@ func TestZeroScaledWindowReceive(t *testing.T) {
)
}
- // Read some data. An ack should be sent in response to that.
- v, _, err := c.EP.Read(nil)
- if err != nil {
- t.Fatalf("Read failed: %v", err)
+ // Read at least 1MSS of data. An ack should be sent in response to that.
+ sz := 0
+ for sz < defaultMTU {
+ v, _, err := c.EP.Read(nil)
+ if err != nil {
+ t.Fatalf("Read failed: %v", err)
+ }
+ sz += len(v)
}
checker.IPv4(t, c.GetPacket(),
@@ -2103,7 +2107,7 @@ func TestZeroScaledWindowReceive(t *testing.T) {
checker.DstPort(context.TestPort),
checker.SeqNum(uint32(c.IRS)+1),
checker.AckNum(uint32(790+sent)),
- checker.Window(uint16(len(v)>>ws)),
+ checker.Window(uint16(sz>>ws)),
checker.TCPFlags(header.TCPFlagAck),
),
)
@@ -6556,3 +6560,140 @@ func TestKeepaliveWithUserTimeout(t *testing.T) {
t.Errorf("got c.Stack().Stats().TCP.EstablishedTimedout = %v, want = %v", got, want)
}
}
+
+func TestIncreaseWindowOnReceive(t *testing.T) {
+ // This test ensures that the endpoint sends an ack,
+ // after recv() when the window grows to more than 1 MSS.
+ c := context.New(t, defaultMTU)
+ defer c.Cleanup()
+
+ const rcvBuf = 65535 * 10
+ c.CreateConnected(789, 30000, rcvBuf)
+
+ // Write chunks of ~30000 bytes. It's important that two
+ // payloads make it equal or longer than MSS.
+ remain := rcvBuf
+ sent := 0
+ data := make([]byte, defaultMTU/2)
+ lastWnd := uint16(0)
+
+ for remain > len(data) {
+ c.SendPacket(data, &context.Headers{
+ SrcPort: context.TestPort,
+ DstPort: c.Port,
+ Flags: header.TCPFlagAck,
+ SeqNum: seqnum.Value(790 + sent),
+ AckNum: c.IRS.Add(1),
+ RcvWnd: 30000,
+ })
+ sent += len(data)
+ remain -= len(data)
+
+ lastWnd = uint16(remain)
+ if remain > 0xffff {
+ lastWnd = 0xffff
+ }
+ checker.IPv4(t, c.GetPacket(),
+ checker.PayloadLen(header.TCPMinimumSize),
+ checker.TCP(
+ checker.DstPort(context.TestPort),
+ checker.SeqNum(uint32(c.IRS)+1),
+ checker.AckNum(uint32(790+sent)),
+ checker.Window(lastWnd),
+ checker.TCPFlags(header.TCPFlagAck),
+ ),
+ )
+ }
+
+ if lastWnd == 0xffff || lastWnd == 0 {
+ t.Fatalf("expected small, non-zero window: %d", lastWnd)
+ }
+
+ // We now have < 1 MSS in the buffer space. Read the data! An
+ // ack should be sent in response to that. The window was not
+ // zero, but it grew to larger than MSS.
+ if _, _, err := c.EP.Read(nil); err != nil {
+ t.Fatalf("Read failed: %v", err)
+ }
+
+ if _, _, err := c.EP.Read(nil); err != nil {
+ t.Fatalf("Read failed: %v", err)
+ }
+
+ // After reading two packets, we surely crossed MSS. See the ack:
+ checker.IPv4(t, c.GetPacket(),
+ checker.PayloadLen(header.TCPMinimumSize),
+ checker.TCP(
+ checker.DstPort(context.TestPort),
+ checker.SeqNum(uint32(c.IRS)+1),
+ checker.AckNum(uint32(790+sent)),
+ checker.Window(uint16(0xffff)),
+ checker.TCPFlags(header.TCPFlagAck),
+ ),
+ )
+}
+
+func TestIncreaseWindowOnBufferResize(t *testing.T) {
+ // This test ensures that the endpoint sends an ack,
+ // after available recv buffer grows to more than 1 MSS.
+ c := context.New(t, defaultMTU)
+ defer c.Cleanup()
+
+ const rcvBuf = 65535 * 10
+ c.CreateConnected(789, 30000, rcvBuf)
+
+ // Write chunks of ~30000 bytes. It's important that two
+ // payloads make it equal or longer than MSS.
+ remain := rcvBuf
+ sent := 0
+ data := make([]byte, defaultMTU/2)
+ lastWnd := uint16(0)
+
+ for remain > len(data) {
+ c.SendPacket(data, &context.Headers{
+ SrcPort: context.TestPort,
+ DstPort: c.Port,
+ Flags: header.TCPFlagAck,
+ SeqNum: seqnum.Value(790 + sent),
+ AckNum: c.IRS.Add(1),
+ RcvWnd: 30000,
+ })
+ sent += len(data)
+ remain -= len(data)
+
+ lastWnd = uint16(remain)
+ if remain > 0xffff {
+ lastWnd = 0xffff
+ }
+ checker.IPv4(t, c.GetPacket(),
+ checker.PayloadLen(header.TCPMinimumSize),
+ checker.TCP(
+ checker.DstPort(context.TestPort),
+ checker.SeqNum(uint32(c.IRS)+1),
+ checker.AckNum(uint32(790+sent)),
+ checker.Window(lastWnd),
+ checker.TCPFlags(header.TCPFlagAck),
+ ),
+ )
+ }
+
+ if lastWnd == 0xffff || lastWnd == 0 {
+ t.Fatalf("expected small, non-zero window: %d", lastWnd)
+ }
+
+ // Increasing the buffer from should generate an ACK,
+ // since window grew from small value to larger equal MSS
+ c.EP.SetSockOptInt(tcpip.ReceiveBufferSizeOption, rcvBuf*2)
+
+ // After reading two packets, we surely crossed MSS. See the ack:
+ checker.IPv4(t, c.GetPacket(),
+ checker.PayloadLen(header.TCPMinimumSize),
+ checker.TCP(
+ checker.DstPort(context.TestPort),
+ checker.SeqNum(uint32(c.IRS)+1),
+ checker.AckNum(uint32(790+sent)),
+ checker.Window(uint16(0xffff)),
+ checker.TCPFlags(header.TCPFlagAck),
+ ),
+ )
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-01 01:29:43 +0000