vm: add default limit to SI serialization context

Follow the notion of https://github.com/neo-project/neo/pull/2948.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

pkg/vm/stackitem/json.go

@@ -65,9 +65,12 @@ func ToJSON(item Item) ([]byte, error) {
 }
 
 // sliceNoPointer represents a sub-slice of a known slice.
-// It doesn't contain any pointer and uses less memory than `[]byte`.
+// It doesn't contain any pointer and uses the same amount of memory as `[]byte`,
+// but at the same type has additional information about the number of items in
+// the stackitem (including the stackitem itself).
 type sliceNoPointer struct {
 	start, end int
+	itemsCount int
 }
 
 func toJSON(data []byte, seen map[Item]sliceNoPointer, item Item) ([]byte, error) {
@@ -105,7 +108,7 @@ func toJSON(data []byte, seen map[Item]sliceNoPointer, item Item) ([]byte, error
 			}
 		}
 		data = append(data, ']')
-		seen[item] = sliceNoPointer{start, len(data)}
+		seen[item] = sliceNoPointer{start: start, end: len(data)}
 	case *Map:
 		data = append(data, '{')
 		for i := range it.value {
@@ -126,7 +129,7 @@ func toJSON(data []byte, seen map[Item]sliceNoPointer, item Item) ([]byte, error
 			}
 		}
 		data = append(data, '}')
-		seen[item] = sliceNoPointer{start, len(data)}
+		seen[item] = sliceNoPointer{start: start, end: len(data)}
 	case *BigInteger:
 		if it.Big().CmpAbs(big.NewInt(MaxAllowedInteger)) == 1 {
 			return nil, fmt.Errorf("%w (MaxAllowedInteger)", ErrInvalidValue)
@@ -420,7 +423,7 @@ func toJSONWithTypes(data []byte, item Item, seen map[Item]sliceNoPointer) ([]by
 		data = append(data, '}')
 
 		if isBuffer {
-			seen[item] = sliceNoPointer{start, len(data)}
+			seen[item] = sliceNoPointer{start: start, end: len(data)}
 		}
 	} else {
 		if len(data)+2 > MaxSize { // also take care of '}'
@@ -428,7 +431,7 @@ func toJSONWithTypes(data []byte, item Item, seen map[Item]sliceNoPointer) ([]by
 		}
 		data = append(data, ']', '}')
 
-		seen[item] = sliceNoPointer{start, len(data)}
+		seen[item] = sliceNoPointer{start: start, end: len(data)}
 	}
 	return data, nil
 }

pkg/vm/stackitem/serialization.go

@@ -14,6 +14,10 @@ import (
 // (including itself).
 const MaxDeserialized = 2048
 
+// MaxSerialized is the maximum number one serialized item can contain
+// (including itself).
+const MaxSerialized = MaxDeserialized
+
 // typicalNumOfItems is the number of items covering most serialization needs.
 // It's a hint used for map creation, so it does not limit anything, it's just
 // a microoptimization to avoid excessive reallocations. Most of the serialized
@@ -33,6 +37,7 @@ type SerializationContext struct {
 	uv           [9]byte
 	data         []byte
 	allowInvalid bool
+	limit        int
 	seen         map[Item]sliceNoPointer
 }
 
@@ -45,10 +50,20 @@ type deserContext struct {
 
 // Serialize encodes the given Item into a byte slice.
 func Serialize(item Item) ([]byte, error) {
+	return SerializeLimited(item, MaxSerialized)
+}
+
+// SerializeLimited encodes the given Item into a byte slice using custom
+// limit to restrict the maximum serialized number of elements.
+func SerializeLimited(item Item, limit int) ([]byte, error) {
 	sc := SerializationContext{
 		allowInvalid: false,
+		limit:        MaxSerialized,
 		seen:         make(map[Item]sliceNoPointer, typicalNumOfItems),
 	}
+	if limit > 0 {
+		sc.limit = limit
+	}
 	err := sc.serialize(item)
 	if err != nil {
 		return nil, err
@@ -76,6 +91,7 @@ func EncodeBinary(item Item, w *io.BinWriter) {
 func EncodeBinaryProtected(item Item, w *io.BinWriter) {
 	sc := SerializationContext{
 		allowInvalid: true,
+		limit:        MaxSerialized,
 		seen:         make(map[Item]sliceNoPointer, typicalNumOfItems),
 	}
 	err := sc.serialize(item)
@@ -88,19 +104,21 @@ func EncodeBinaryProtected(item Item, w *io.BinWriter) {
 
 func (w *SerializationContext) writeArray(item Item, arr []Item, start int) error {
 	w.seen[item] = sliceNoPointer{}
+	limit := w.limit
 	w.appendVarUint(uint64(len(arr)))
 	for i := range arr {
 		if err := w.serialize(arr[i]); err != nil {
 			return err
 		}
 	}
-	w.seen[item] = sliceNoPointer{start, len(w.data)}
+	w.seen[item] = sliceNoPointer{start, len(w.data), limit - w.limit + 1} // number of items including the array itself.
 	return nil
 }
 
 // NewSerializationContext returns reusable stack item serialization context.
 func NewSerializationContext() *SerializationContext {
 	return &SerializationContext{
+		limit: MaxSerialized,
 		seen:  make(map[Item]sliceNoPointer, typicalNumOfItems),
 	}
 }
@@ -108,8 +126,10 @@ func NewSerializationContext() *SerializationContext {
 // Serialize returns flat slice of bytes with the given item. The process can be protected
 // from bad elements if appropriate flag is given (otherwise an error is returned on
 // encountering any of them). The buffer returned is only valid until the call to Serialize.
+// The number of serialized items is restricted with MaxSerialized.
 func (w *SerializationContext) Serialize(item Item, protected bool) ([]byte, error) {
 	w.allowInvalid = protected
+	w.limit = MaxSerialized
 	if w.data != nil {
 		w.data = w.data[:0]
 	}
@@ -135,10 +155,17 @@ func (w *SerializationContext) serialize(item Item) error {
 		if len(w.data)+v.end-v.start > MaxSize {
 			return ErrTooBig
 		}
+		w.limit -= v.itemsCount
+		if w.limit < 0 {
+			return errTooBigElements
+		}
 		w.data = append(w.data, w.data[v.start:v.end]...)
 		return nil
 	}
-
+	w.limit--
+	if w.limit < 0 {
+		return errTooBigElements
+	}
 	start := len(w.data)
 	switch t := item.(type) {
 	case *ByteArray:
@@ -188,6 +215,7 @@ func (w *SerializationContext) serialize(item Item) error {
 		}
 	case *Map:
 		w.seen[item] = sliceNoPointer{}
+		limit := w.limit
 
 		elems := t.value
 		w.data = append(w.data, byte(MapT))
@@ -200,7 +228,7 @@ func (w *SerializationContext) serialize(item Item) error {
 				return err
 			}
 		}
-		w.seen[item] = sliceNoPointer{start, len(w.data)}
+		w.seen[item] = sliceNoPointer{start, len(w.data), limit - w.limit + 1} // number of items including Map itself.
 	case Null:
 		w.data = append(w.data, byte(AnyT))
 	case nil:

pkg/vm/stackitem/serialization_test.go

@@ -1,6 +1,7 @@
 package stackitem
 
 import (
+	"strconv"
 	"testing"
 
 	"github.com/nspcc-dev/neo-go/pkg/io"
@@ -23,7 +24,19 @@ func TestSerializationMaxErr(t *testing.T) {
 }
 
 func testSerialize(t *testing.T, expectedErr error, item Item) {
-	data, err := Serialize(item)
+	testSerializeLimited(t, expectedErr, item, -1)
+}
+
+func testSerializeLimited(t *testing.T, expectedErr error, item Item, limit int) {
+	var (
+		data []byte
+		err  error
+	)
+	if limit > 0 {
+		data, err = SerializeLimited(item, limit)
+	} else {
+		data, err = Serialize(item)
+	}
 	if expectedErr != nil {
 		require.ErrorIs(t, err, expectedErr)
 		return
@@ -58,7 +71,9 @@ func TestSerialize(t *testing.T) {
 		testSerialize(t, nil, newItem(items))
 
 		items = append(items, zeroByteArray)
-		data, err := Serialize(newItem(items))
+		_, err := Serialize(newItem(items))
+		require.ErrorIs(t, err, errTooBigElements)
+		data, err := SerializeLimited(newItem(items), MaxSerialized+1) // a tiny hack to check deserialization error.
 		require.NoError(t, err)
 		_, err = Deserialize(data)
 		require.ErrorIs(t, err, ErrTooBig)
@@ -165,13 +180,70 @@ func TestSerialize(t *testing.T) {
 		for i := 0; i <= MaxDeserialized; i++ {
 			m.Add(Make(i), zeroByteArray)
 		}
-		data, err := Serialize(m)
+		_, err := Serialize(m)
+		require.ErrorIs(t, err, errTooBigElements)
+		data, err := SerializeLimited(m, (MaxSerialized+1)*2+1) // a tiny hack to check deserialization error.
 		require.NoError(t, err)
 		_, err = Deserialize(data)
 		require.ErrorIs(t, err, ErrTooBig)
 	})
 }
 
+func TestSerializeLimited(t *testing.T) {
+	const customLimit = 10
+
+	smallArray := make([]Item, customLimit-1)
+	for i := range smallArray {
+		smallArray[i] = NewBool(true)
+	}
+	bigArray := make([]Item, customLimit)
+	for i := range bigArray {
+		bigArray[i] = NewBool(true)
+	}
+	t.Run("array", func(t *testing.T) {
+		testSerializeLimited(t, nil, NewArray(smallArray), customLimit)
+		testSerializeLimited(t, errTooBigElements, NewArray(bigArray), customLimit)
+	})
+	t.Run("struct", func(t *testing.T) {
+		testSerializeLimited(t, nil, NewStruct(smallArray), customLimit)
+		testSerializeLimited(t, errTooBigElements, NewStruct(bigArray), customLimit)
+	})
+	t.Run("map", func(t *testing.T) {
+		smallMap := make([]MapElement, (customLimit-1)/2)
+		for i := range smallMap {
+			smallMap[i] = MapElement{
+				Key:   NewByteArray([]byte(strconv.Itoa(i))),
+				Value: NewBool(true),
+			}
+		}
+		bigMap := make([]MapElement, customLimit/2)
+		for i := range bigMap {
+			bigMap[i] = MapElement{
+				Key:   NewByteArray([]byte("key")),
+				Value: NewBool(true),
+			}
+		}
+		testSerializeLimited(t, nil, NewMapWithValue(smallMap), customLimit)
+		testSerializeLimited(t, errTooBigElements, NewMapWithValue(bigMap), customLimit)
+	})
+	t.Run("seen", func(t *testing.T) {
+		t.Run("OK", func(t *testing.T) {
+			tinyArray := NewArray(make([]Item, (customLimit-3)/2)) // 1 for outer array, 1+1 for two inner arrays and the rest are for arrays' elements.
+			for i := range tinyArray.value {
+				tinyArray.value[i] = NewBool(true)
+			}
+			testSerializeLimited(t, nil, NewArray([]Item{tinyArray, tinyArray}), customLimit)
+		})
+		t.Run("big", func(t *testing.T) {
+			tinyArray := NewArray(make([]Item, (customLimit-2)/2)) // should break on the second array serialisation.
+			for i := range tinyArray.value {
+				tinyArray.value[i] = NewBool(true)
+			}
+			testSerializeLimited(t, errTooBigElements, NewArray([]Item{tinyArray, tinyArray}), customLimit)
+		})
+	})
+}
+
 func TestEmptyDeserialization(t *testing.T) {
 	empty := []byte{}
 	_, err := Deserialize(empty)
@@ -202,7 +274,7 @@ func TestDeserializeTooManyElements(t *testing.T) {
 	require.NoError(t, err)
 
 	item = Make([]Item{item})
-	data, err = Serialize(item)
+	data, err = SerializeLimited(item, MaxSerialized+1) // tiny hack to avoid serialization error.
 	require.NoError(t, err)
 	_, err = Deserialize(data)
 	require.ErrorIs(t, err, ErrTooBig)
@@ -214,14 +286,14 @@ func TestDeserializeLimited(t *testing.T) {
 	for i := 0; i < customLimit-1; i++ { // 1 for zero inner element.
 		item = Make([]Item{item})
 	}
-	data, err := Serialize(item)
+	data, err := SerializeLimited(item, customLimit) // tiny hack to avoid serialization error.
 	require.NoError(t, err)
 	actual, err := DeserializeLimited(data, customLimit)
 	require.NoError(t, err)
 	require.Equal(t, item, actual)
 
 	item = Make([]Item{item})
-	data, err = Serialize(item)
+	data, err = SerializeLimited(item, customLimit+1) // tiny hack to avoid serialization error.
 	require.NoError(t, err)
 	_, err = DeserializeLimited(data, customLimit)
 	require.Error(t, err)