sysenc: special case unmarshaling into []byte

internal/sysenc/marshal.go

@@ -11,6 +11,8 @@ import (
 	"unsafe"
 
 	"github.com/cilium/ebpf/internal"
+
+	"golang.org/x/exp/slices"
 )
 
 // Marshal turns data into a byte slice using the system's native endianness.
@@ -88,6 +90,11 @@ func Unmarshal(data interface{}, buf []byte) error {
 		*value = string(buf)
 		return nil
 
+	case *[]byte:
+		// Backwards compat: unmarshaling into a slice replaces the whole slice.
+		*value = slices.Clone(buf)
+		return nil
+
 	default:
 		if dataBuf := unsafeBackingMemory(data); len(dataBuf) == len(buf) {
 			copy(dataBuf, buf)

map.go

@@ -1411,11 +1411,7 @@ func (mi *MapIterator) Next(keyOut, valueOut interface{}) bool {
 			return false
 		}
 
-		// The user can get access to nextKey since unmarshalBytes
-		// does not copy when unmarshaling into a []byte.
-		// Make a copy to prevent accidental corruption of
-		// iterator state.
-		copy(mi.curKey, nextKey)
+		mi.curKey = nextKey
 
 		mi.count++
 		mi.err = mi.target.Lookup(nextKey, valueOut)

map_test.go

@@ -48,7 +48,6 @@ func newHash(t *testing.T) *Map {
 
 func TestMap(t *testing.T) {
 	m := createArray(t)
-	defer m.Close()
 
 	t.Log(m)
 
@@ -76,6 +75,10 @@ func TestMap(t *testing.T) {
 		t.Error("Want value 42, got", v)
 	}
 
+	var slice []byte
+	qt.Assert(t, m.Lookup(uint32(0), &slice), qt.IsNil)
+	qt.Assert(t, slice, qt.DeepEquals, internal.NativeEndian.AppendUint32(nil, 42))
+
 	var k uint32
 	if err := m.NextKey(uint32(0), &k); err != nil {
 		t.Fatal("Can't get:", err)
@@ -430,7 +433,6 @@ func TestMapCloneNil(t *testing.T) {
 func TestMapPin(t *testing.T) {
 	m := createArray(t)
 	c := qt.New(t)
-	defer m.Close()
 
 	if err := m.Put(uint32(0), uint32(42)); err != nil {
 		t.Fatal("Can't put:", err)
@@ -557,7 +559,6 @@ func TestMapPinMultiple(t *testing.T) {
 func TestMapPinWithEmptyPath(t *testing.T) {
 	m := createArray(t)
 	c := qt.New(t)
-	defer m.Close()
 
 	err := m.Pin("")
 
@@ -694,7 +695,6 @@ func TestMapLoadPinnedWithOptions(t *testing.T) {
 	testutils.SkipOnOldKernel(t, "4.15", "file_flags in BPF_OBJ_GET")
 
 	array := createArray(t)
-	defer array.Close()
 
 	tmp := testutils.TempBPFFS(t)
 
@@ -780,6 +780,7 @@ func createArray(t *testing.T) *Map {
 	if err != nil {
 		t.Fatal(err)
 	}
+	t.Cleanup(func() { m.Close() })
 	return m
 }
 
@@ -1276,7 +1277,6 @@ func TestIterateMapInMap(t *testing.T) {
 	defer parent.Close()
 
 	a := createArray(t)
-	defer a.Close()
 
 	if err := parent.Put(idx, a); err != nil {
 		t.Fatal(err)
@@ -1529,7 +1529,6 @@ func TestMapName(t *testing.T) {
 
 func TestMapFromFD(t *testing.T) {
 	m := createArray(t)
-	defer m.Close()
 
 	if err := m.Put(uint32(0), uint32(123)); err != nil {
 		t.Fatal(err)
@@ -1597,7 +1596,6 @@ func TestMapContents(t *testing.T) {
 
 func TestMapFreeze(t *testing.T) {
 	arr := createArray(t)
-	defer arr.Close()
 
 	err := arr.Freeze()
 	testutils.SkipIfNotSupported(t, err)

prog_test.go

@@ -713,7 +713,6 @@ func TestProgramRejectIncorrectByteOrder(t *testing.T) {
 
 func TestProgramSpecTag(t *testing.T) {
 	arr := createArray(t)
-	defer arr.Close()
 
 	spec := &ProgramSpec{
 		Type: SocketFilter,