prog, map: add nil checks for value marshaller

In case of programs or maps as map value types, the value marshalling
results in a panic in case of a nil pointer. For other types this is not a
problem since sysenc.Marshal does a nil check.

This commit adds a nil check to the internal helper for marshalling
programs and maps.

Signed-off-by: Tobias Böhm <[email protected]>

map.go

@@ -1589,6 +1589,10 @@ func unmarshalMap(buf sysenc.Buffer) (*Map, error) {
 
 // marshalMap marshals the fd of a map into a buffer in host endianness.
 func marshalMap(m *Map, length int) ([]byte, error) {
+	if m == nil {
+		return nil, errors.New("map cannot be nil")
+	}
+
 	if length != 4 {
 		return nil, fmt.Errorf("can't marshal map to %d bytes", length)
 	}

map_test.go

@@ -1385,7 +1385,13 @@ func TestIterateMapInMap(t *testing.T) {
 	parent := createMapInMap(t, ArrayOfMaps)
 	defer parent.Close()
 
-	a := createArray(t)
+	var a *Map
+
+	if err := parent.Put(idx, a); err == nil {
+		t.Fatal("Put accepts nil map")
+	}
+
+	a = createArray(t)
 
 	if err := parent.Put(idx, a); err != nil {
 		t.Fatal(err)

prog.go

@@ -893,6 +893,10 @@ func unmarshalProgram(buf sysenc.Buffer) (*Program, error) {
 }
 
 func marshalProgram(p *Program, length int) ([]byte, error) {
+	if p == nil {
+		return nil, errors.New("program cannot be nil")
+	}
+
 	if length != 4 {
 		return nil, fmt.Errorf("can't marshal program to %d bytes", length)
 	}

prog_test.go

@@ -596,7 +596,13 @@ func TestProgramMarshaling(t *testing.T) {
 	arr := createProgramArray(t)
 	defer arr.Close()
 
-	prog := mustSocketFilter(t)
+	var prog *Program
+
+	if err := arr.Put(idx, prog); err == nil {
+		t.Fatal("Put accepts nil program")
+	}
+
+	prog = mustSocketFilter(t)
 
 	if err := arr.Put(idx, prog); err != nil {
 		t.Fatal("Can't put program:", err)