From 9faa0563b38f5f1445392581a9cb27015dcc8dd7 Mon Sep 17 00:00:00 2001
From: Michael Bohn <michael.bohn@freiheit.com>
Date: Mon, 23 Dec 2024 14:50:01 +0100
Subject: [PATCH 1/3] clone returned byte slice in MarshalValue

---
 bson/marshal.go      |  3 ++-
 bson/marshal_test.go | 58 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/bson/marshal.go b/bson/marshal.go
index fdec2fe896..5f2a182d78 100644
--- a/bson/marshal.go
+++ b/bson/marshal.go
@@ -9,6 +9,7 @@ package bson
 import (
 	"bytes"
 	"encoding/json"
+	"slices"
 	"sync"
 )
 
@@ -133,7 +134,7 @@ func MarshalValue(val interface{}) (Type, []byte, error) {
 		return 0, nil, err
 	}
 	typ := sw.Next(2)
-	return Type(typ[0]), sw.Bytes(), nil
+	return Type(typ[0]), slices.Clone(sw.Bytes()), nil
 }
 
 // MarshalExtJSON returns the extended JSON encoding of val.
diff --git a/bson/marshal_test.go b/bson/marshal_test.go
index 8ede9627ba..43bc337521 100644
--- a/bson/marshal_test.go
+++ b/bson/marshal_test.go
@@ -326,3 +326,61 @@ func TestMarshalConcurrently(t *testing.T) {
 	}
 	wg.Wait()
 }
+
+type testStruct struct {
+	TestData RawValue `bson:"testData"`
+}
+
+func TestSharedUseOfMarshalledBytes(t *testing.T) {
+	type testValue struct {
+		value string
+	}
+
+	type sharedTestCase struct {
+		name      string
+		testData  *testStruct
+		wantValue string
+	}
+
+	// fill the pool with some buffers
+	for i := 0; i < 100; i++ {
+		mustMarshalValue(testValue{value: fmt.Sprintf("marshalled foo bar %d", i)})
+	}
+
+	testCases := []sharedTestCase{
+		{
+			name:      "case 1",
+			testData:  mustMarshalValue(testValue{value: "Case 1 Value"}),
+			wantValue: "Case 1 Value",
+		},
+		{
+			name:      "case 2",
+			testData:  mustMarshalValue(testValue{value: "Case 2 Value"}),
+			wantValue: "Case 2 Value",
+		},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			want := mustMarshalValue(testValue{value: tc.wantValue})
+			if d := cmp.Diff(tc.testData, want); d != "" {
+				t.Errorf("diff: %s", d)
+			}
+		})
+	}
+}
+
+func mustMarshalValue(data any) *testStruct {
+	dataType, dataBytes, err := MarshalValue(data)
+	if err != nil {
+		panic(fmt.Sprintf("unable to marshal data: %s", err))
+	}
+
+	return &testStruct{
+		TestData: RawValue{
+			Type:  dataType,
+			Value: dataBytes,
+		},
+	}
+}

From fc53dd63a7e55fa9c65ab88978b8d7e074aed8b8 Mon Sep 17 00:00:00 2001
From: Michael Bohn <michael.bohn@freiheit.com>
Date: Sat, 4 Jan 2025 14:39:59 +0100
Subject: [PATCH 2/3] clone pre go 1.21 compatible way

---
 bson/marshal.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/bson/marshal.go b/bson/marshal.go
index 5f2a182d78..1ab60b1707 100644
--- a/bson/marshal.go
+++ b/bson/marshal.go
@@ -9,7 +9,6 @@ package bson
 import (
 	"bytes"
 	"encoding/json"
-	"slices"
 	"sync"
 )
 
@@ -134,7 +133,8 @@ func MarshalValue(val interface{}) (Type, []byte, error) {
 		return 0, nil, err
 	}
 	typ := sw.Next(2)
-	return Type(typ[0]), slices.Clone(sw.Bytes()), nil
+	clone := append([]byte(nil), sw.Bytes()...)
+	return Type(typ[0]), clone, nil
 }
 
 // MarshalExtJSON returns the extended JSON encoding of val.

From ddf29bfdd3111d35580bd6a9ddbe2bb06017dd6d Mon Sep 17 00:00:00 2001
From: Michael Bohn <michael.bohn@freiheit.com>
Date: Sat, 4 Jan 2025 14:57:15 +0100
Subject: [PATCH 3/3] add a comment explaining the clone

---
 bson/marshal.go | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/bson/marshal.go b/bson/marshal.go
index 1ab60b1707..5cdeece8c1 100644
--- a/bson/marshal.go
+++ b/bson/marshal.go
@@ -133,7 +133,9 @@ func MarshalValue(val interface{}) (Type, []byte, error) {
 		return 0, nil, err
 	}
 	typ := sw.Next(2)
-	clone := append([]byte(nil), sw.Bytes()...)
+	clone := append([]byte(nil), sw.Bytes()...) // Don't hand out a shared reference to byte buffer bytes
+	// and fully copy the data. The byte buffer is (potentially) reused
+	// and handing out only a reference to the bytes may lead to race-conditions with the buffer.
 	return Type(typ[0]), clone, nil
 }