2 files changed, 20 insertions, 4 deletions
diff --git a/pkg/tcpip/transport/tcp/sack_scoreboard.go b/pkg/tcpip/transport/tcp/sack_scoreboard.go
index 67f25f050..21878ad82 100644
--- a/pkg/tcpip/transport/tcp/sack_scoreboard.go
+++ b/pkg/tcpip/transport/tcp/sack_scoreboard.go
@@ -77,7 +77,7 @@ func (s *SACKScoreboard) Insert(r header.SACKBlock) {
 		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) {
+		if r.End.LessThan(sacked.Start) {
 			return false
 		}
 		// There is some overlap at this point, merge the blocks and
@@ -167,7 +167,11 @@ func (s *SACKScoreboard) String() string {
 
 // Delete removes all SACK information prior to seq.
 func (s *SACKScoreboard) Delete(seq seqnum.Value) {
+	if s.Empty() {
+		return
+	}
 	toDelete := []btree.Item{}
+	toInsert := []btree.Item{}
 	r := header.SACKBlock{seq, seq.Add(1)}
 	s.ranges.DescendLessOrEqual(r, func(i btree.Item) bool {
 		if i == r {
@@ -179,13 +183,16 @@ func (s *SACKScoreboard) Delete(seq seqnum.Value) {
 			s.sacked -= sb.Start.Size(sb.End)
 		} else {
 			newSB := header.SACKBlock{seq, sb.End}
-			s.ranges.ReplaceOrInsert(newSB)
+			toInsert = append(toInsert, newSB)
 			s.sacked -= sb.Start.Size(seq)
 		}
 		return true
 	})
-	for _, i := range toDelete {
-		s.ranges.Delete(i)
+	for _, sb := range toDelete {
+		s.ranges.Delete(sb)
+	}
+	for _, sb := range toInsert {
+		s.ranges.ReplaceOrInsert(sb)
 	}
 }
 
diff --git a/pkg/tcpip/transport/tcp/sack_scoreboard_test.go b/pkg/tcpip/transport/tcp/sack_scoreboard_test.go
index 1a1178999..3cf2ff451 100644
--- a/pkg/tcpip/transport/tcp/sack_scoreboard_test.go
+++ b/pkg/tcpip/transport/tcp/sack_scoreboard_test.go
@@ -77,6 +77,15 @@ func TestSACKScoreboardIsSACKED(t *testing.T) {
 			},
 			4294254144,
 		},
+		{
+			"Test disjoint SACKBlocks out of order",
+			[]header.SACKBlock{{827450276, 827454536}, {827426028, 827428868}},
+			[]blockTest{
+				{header.SACKBlock{827426028, 827428867}, true},
+				{header.SACKBlock{827450168, 827450275}, false},
+			},
+			827426000,
+		},
 	}
 	for _, tc := range testCases {
 		sb := initScoreboard(tc.scoreboardBlocks, tc.iss)