Add an implementation of a SACK scoreboard as per RFC6675.

PiperOrigin-RevId: 220866996
Change-Id: I89d48215df57c00d6a6ec512fc18712a2ea9080b

3 files changed, 388 insertions, 8 deletions

diff --git a/pkg/tcpip/transport/tcp/BUILD b/pkg/tcpip/transport/tcp/BUILD
index 5a77ee232..18e6a5dc6 100644
--- a/pkg/tcpip/transport/tcp/BUILD
+++ b/pkg/tcpip/transport/tcp/BUILD
@@ -28,6 +28,7 @@ go_library(
         "rcv.go",
         "reno.go",
         "sack.go",
+        "sack_scoreboard.go",
         "segment.go",
         "segment_heap.go",
         "segment_queue.go",
@@ -50,14 +51,24 @@ go_library(
         "//pkg/tcpip/stack",
         "//pkg/tmutex",
         "//pkg/waiter",
+        "@com_github_google_btree//:go_default_library",
     ],
 )
 
+filegroup(
+    name = "autogen",
+    srcs = [
+        "tcp_segment_list.go",
+    ],
+    visibility = ["//:sandbox"],
+)
+
 go_test(
     name = "tcp_test",
     size = "small",
     srcs = [
         "dual_stack_test.go",
+        "sack_scoreboard_test.go",
         "tcp_sack_test.go",
         "tcp_test.go",
         "tcp_timestamp_test.go",
@@ -79,11 +90,3 @@ go_test(
         "//pkg/waiter",
     ],
 )
-
-filegroup(
-    name = "autogen",
-    srcs = [
-        "tcp_segment_list.go",
-    ],
-    visibility = ["//:sandbox"],
-)
diff --git a/pkg/tcpip/transport/tcp/sack_scoreboard.go b/pkg/tcpip/transport/tcp/sack_scoreboard.go
new file mode 100644
index 000000000..d251d32db
--- /dev/null
+++ b/pkg/tcpip/transport/tcp/sack_scoreboard.go
@@ -0,0 +1,227 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tcp
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/google/btree"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/seqnum"
+)
+
+// maxSACKBlocks is the maximum number of distinct SACKBlocks the scoreboard
+// will track. Once there are 100 distinct blocks, new insertions will fail.
+const maxSACKBlocks = 100
+
+// SACKScoreboard stores a set of disjoint SACK ranges.
+type SACKScoreboard struct {
+	smss      uint16
+	maxSACKED seqnum.Value
+	sacked    seqnum.Size
+	ranges    *btree.BTree
+}
+
+// NewSACKScoreboard returns a new SACK Scoreboard.
+func NewSACKScoreboard(smss uint16, iss seqnum.Value) *SACKScoreboard {
+	return &SACKScoreboard{
+		smss:      smss,
+		ranges:    btree.New(2),
+		maxSACKED: iss,
+	}
+}
+
+// Insert inserts/merges the provided SACKBlock into the scoreboard.
+func (s *SACKScoreboard) Insert(r header.SACKBlock) {
+	if s.ranges.Len() >= maxSACKBlocks {
+		return
+	}
+
+	// Check if we can merge the new range with a range before or after it.
+	var toDelete []btree.Item
+	if s.maxSACKED.LessThan(r.End - 1) {
+		s.maxSACKED = r.End - 1
+	}
+	s.ranges.AscendGreaterOrEqual(r, func(i btree.Item) bool {
+		if i == r {
+			return true
+		}
+		sacked := i.(header.SACKBlock)
+		// There is a hole between these two SACK blocks, so we can't
+		// merge anymore.
+		if r.End.LessThan(r.Start) {
+			return false
+		}
+		// There is some overlap at this point, merge the blocks and
+		// delete the other one.
+		//
+		// ----sS--------sE
+		// r.S---------------rE
+		//               -------sE
+		if sacked.End.LessThan(r.End) {
+			// sacked is contained in the newly inserted range.
+			// Delete this block.
+			toDelete = append(toDelete, i)
+			return true
+		}
+		// sacked covers a range past end of the newly inserted
+		// block.
+		r.End = sacked.End
+		toDelete = append(toDelete, i)
+		return true
+	})
+
+	s.ranges.DescendLessOrEqual(r, func(i btree.Item) bool {
+		if i == r {
+			return true
+		}
+		sacked := i.(header.SACKBlock)
+		// sA------sE
+		//            rA----rE
+		if sacked.End.LessThan(r.Start) {
+			return false
+		}
+		// The previous range extends into the current block. Merge it
+		// into the newly inserted range and delete the other one.
+		//
+		//   <-rA---rE----<---rE--->
+		// sA--------------sE
+		r.Start = sacked.Start
+		// Extend r to cover sacked if sacked extends past r.
+		if r.End.LessThan(sacked.End) {
+			r.End = sacked.End
+		}
+		toDelete = append(toDelete, i)
+		return true
+	})
+	for _, i := range toDelete {
+		if sb := s.ranges.Delete(i); sb != nil {
+			sb := i.(header.SACKBlock)
+			s.sacked -= sb.Start.Size(sb.End)
+		}
+	}
+
+	replaced := s.ranges.ReplaceOrInsert(r)
+	if replaced == nil {
+		s.sacked += r.Start.Size(r.End)
+	}
+}
+
+// IsSACKED returns true if the a given range of sequence numbers denoted by r
+// are already covered by SACK information in the scoreboard.
+func (s *SACKScoreboard) IsSACKED(r header.SACKBlock) bool {
+	found := false
+	s.ranges.DescendLessOrEqual(r, func(i btree.Item) bool {
+		sacked := i.(header.SACKBlock)
+		if sacked.End.LessThan(r.Start) {
+			return false
+		}
+		if sacked.Contains(r) {
+			found = true
+			return false
+		}
+		return true
+	})
+	return found
+}
+
+// Dump prints the state of the scoreboard structure.
+func (s *SACKScoreboard) String() string {
+	var str strings.Builder
+	str.WriteString("SACKScoreboard: {")
+	s.ranges.Ascend(func(i btree.Item) bool {
+		str.WriteString(fmt.Sprintf("%v,", i))
+		return true
+	})
+	str.WriteString("}\n")
+	return str.String()
+}
+
+// Delete removes all SACK information prior to seq.
+func (s *SACKScoreboard) Delete(seq seqnum.Value) {
+	toDelete := []btree.Item{}
+	r := header.SACKBlock{seq, seq.Add(1)}
+	s.ranges.DescendLessOrEqual(r, func(i btree.Item) bool {
+		if i == r {
+			return true
+		}
+		sb := i.(header.SACKBlock)
+		toDelete = append(toDelete, i)
+		if sb.End.LessThanEq(seq) {
+			s.sacked -= sb.Start.Size(sb.End)
+		} else {
+			newSB := header.SACKBlock{seq, sb.End}
+			s.ranges.ReplaceOrInsert(newSB)
+			s.sacked -= sb.Start.Size(seq)
+		}
+		return true
+	})
+	for _, i := range toDelete {
+		s.ranges.Delete(i)
+	}
+}
+
+// Copy provides a copy of the SACK scoreboard.
+func (s *SACKScoreboard) Copy() (sackBlocks []header.SACKBlock, maxSACKED seqnum.Value) {
+	s.ranges.Ascend(func(i btree.Item) bool {
+		sackBlocks = append(sackBlocks, i.(header.SACKBlock))
+		return true
+	})
+	return sackBlocks, s.maxSACKED
+}
+
+// IsLost implements the IsLost(SeqNum) operation defined in RFC 3517 section 4.
+//
+// This routine returns whether the given sequence number is considered to be
+// lost. The routine returns true when either nDupAckThreshold discontiguous
+// SACKed sequences have arrived above 'SeqNum' or (nDupAckThreshold * SMSS)
+// bytes with sequence numbers greater than 'SeqNum' have been SACKed.
+// Otherwise, the routine returns false.
+func (s *SACKScoreboard) IsLost(r header.SACKBlock) bool {
+	nDupSACK := 0
+	nDupSACKBytes := seqnum.Size(0)
+	isLost := false
+	s.ranges.AscendGreaterOrEqual(r, func(i btree.Item) bool {
+		sacked := i.(header.SACKBlock)
+		if sacked.Contains(r) {
+			return false
+		}
+		nDupSACKBytes += sacked.Start.Size(sacked.End)
+		nDupSACK++
+		if nDupSACK >= nDupAckThreshold || nDupSACKBytes >= seqnum.Size(nDupAckThreshold*s.smss) {
+			isLost = true
+			return false
+		}
+		return true
+	})
+	return isLost
+}
+
+// Empty returns true if the SACK scoreboard has no entries, false otherwise.
+func (s *SACKScoreboard) Empty() bool {
+	return s.ranges.Len() == 0
+}
+
+// Sacked returns the current number of bytes held in the SACK scoreboard.
+func (s *SACKScoreboard) Sacked() seqnum.Size {
+	return s.sacked
+}
+
+// MaxSACKED returns the highest sequence number ever inserted in the SACK
+// scoreboard.
+func (s *SACKScoreboard) MaxSACKED() seqnum.Value {
+	return s.maxSACKED
+}
diff --git a/pkg/tcpip/transport/tcp/sack_scoreboard_test.go b/pkg/tcpip/transport/tcp/sack_scoreboard_test.go
new file mode 100644
index 000000000..db4b52aca
--- /dev/null
+++ b/pkg/tcpip/transport/tcp/sack_scoreboard_test.go
@@ -0,0 +1,150 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tcp_test
+
+import (
+	"testing"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/seqnum"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/transport/tcp"
+)
+
+const smss = 1500
+
+func initScoreboard(blocks []header.SACKBlock, iss seqnum.Value) *tcp.SACKScoreboard {
+	s := tcp.NewSACKScoreboard(smss, iss)
+	for _, blk := range blocks {
+		s.Insert(blk)
+	}
+	return s
+}
+
+func TestSACKScoreboardIsSACKED(t *testing.T) {
+	type blockTest struct {
+		block  header.SACKBlock
+		sacked bool
+	}
+	testCases := []struct {
+		comment          string
+		scoreboardBlocks []header.SACKBlock
+		blockTests       []blockTest
+		iss              seqnum.Value
+	}{
+		{
+			"Test holes and unsacked SACK blocks in SACKed ranges and insertion of overlapping SACK blocks",
+			[]header.SACKBlock{{10, 20}, {10, 30}, {30, 40}, {41, 50}, {5, 10}, {1, 50}, {111, 120}, {101, 110}, {52, 120}},
+			[]blockTest{
+				{header.SACKBlock{15, 21}, true},
+				{header.SACKBlock{200, 201}, false},
+				{header.SACKBlock{50, 51}, false},
+				{header.SACKBlock{53, 120}, true},
+			},
+			0,
+		},
+		{
+			"Test disjoint SACKBlocks",
+			[]header.SACKBlock{{2288624809, 2288810057}, {2288811477, 2288838565}},
+			[]blockTest{
+				{header.SACKBlock{2288624809, 2288810057}, true},
+				{header.SACKBlock{2288811477, 2288838565}, true},
+				{header.SACKBlock{2288810057, 2288811477}, false},
+			},
+			2288624809,
+		},
+		{
+			"Test sequence number wrap around",
+			[]header.SACKBlock{{4294254144, 225652}, {5340409, 5350509}},
+			[]blockTest{
+				{header.SACKBlock{4294254144, 4294254145}, true},
+				{header.SACKBlock{4294254143, 4294254144}, false},
+				{header.SACKBlock{4294254144, 1}, true},
+				{header.SACKBlock{225652, 5350509}, false},
+				{header.SACKBlock{5340409, 5350509}, true},
+				{header.SACKBlock{5350509, 5350609}, false},
+			},
+			4294254144,
+		},
+	}
+	for _, tc := range testCases {
+		sb := initScoreboard(tc.scoreboardBlocks, tc.iss)
+		for _, blkTest := range tc.blockTests {
+			if want, got := blkTest.sacked, sb.IsSACKED(blkTest.block); got != want {
+				t.Errorf("%s: s.IsSACKED(%v) = %v, want %v", tc.comment, blkTest.block, got, want)
+			}
+		}
+	}
+}
+
+func TestSACKScoreboardIsLost(t *testing.T) {
+	s := tcp.NewSACKScoreboard(10, 0)
+	s.Insert(header.SACKBlock{1, 50})
+	s.Insert(header.SACKBlock{51, 100})
+	s.Insert(header.SACKBlock{111, 120})
+	s.Insert(header.SACKBlock{101, 110})
+	s.Insert(header.SACKBlock{121, 151})
+	testCases := []struct {
+		block header.SACKBlock
+		lost  bool
+	}{
+		{header.SACKBlock{0, 1}, true},
+		{header.SACKBlock{1, 2}, false},
+		{header.SACKBlock{1, 45}, false},
+		{header.SACKBlock{50, 51}, true},
+		// This one should return true because there are > 3* 10 (smss)
+		// bytes that have been sacked above this sequence number.
+		{header.SACKBlock{119, 120}, true},
+		{header.SACKBlock{120, 121}, true},
+		{header.SACKBlock{125, 126}, false},
+	}
+	for _, tc := range testCases {
+		if want, got := tc.lost, s.IsLost(tc.block); got != want {
+			t.Errorf("s.IsLost(%v) = %v, want %v", tc.block, got, want)
+		}
+	}
+}
+
+func TestSACKScoreboardDelete(t *testing.T) {
+	blocks := []header.SACKBlock{{4294254144, 225652}, {5340409, 5350509}}
+	s := initScoreboard(blocks, 4294254143)
+	s.Delete(5340408)
+	if s.Empty() {
+		t.Fatalf("s.Empty() = true, want false")
+	}
+	if got, want := s.Sacked(), blocks[1].Start.Size(blocks[1].End); got != want {
+		t.Fatalf("incorrect sacked bytes in scoreboard got: %v, want: %v", got, want)
+	}
+	s.Delete(5340410)
+	if s.Empty() {
+		t.Fatal("s.Empty() = true, want false")
+	}
+	newSB := header.SACKBlock{5340410, 5350509}
+	if !s.IsSACKED(newSB) {
+		t.Fatalf("s.IsSACKED(%v) = false, want true, scoreboard: %v", newSB, s)
+	}
+	s.Delete(5350509)
+	lastOctet := header.SACKBlock{5350508, 5350509}
+	if s.IsSACKED(lastOctet) {
+		t.Fatalf("s.IsSACKED(%v) = false, want true", lastOctet)
+	}
+
+	s.Delete(5350510)
+	if !s.Empty() {
+		t.Fatal("s.Empty() = false, want true")
+	}
+	if got, want := s.Sacked(), seqnum.Size(0); got != want {
+		t.Fatalf("incorrect sacked bytes in scoreboard got: %v, want: %v", got, want)
+	}
+}