accounts/abi: return an error if attempting to pack a negative big.Int into a uint val

accounts/abi/pack.go

@@ -33,11 +33,24 @@ func packBytesSlice(bytes []byte, l int) []byte {
 	return append(len, common.RightPadBytes(bytes, (l+31)/32*32)...)
 }
 
+func validateNum(t Type, reflectValue reflect.Value) error {
+	if t.T == UintTy && reflectValue.Kind() == reflect.Ptr {
+		val := new(big.Int).Set(reflectValue.Interface().(*big.Int))
+		if val.Sign() == -1 {
+			return fmt.Errorf("cannot pack negative big.Int value to a uint type")
+		}
+	}
+	return nil
+}
+
 // packElement packs the given reflect value according to the abi specification in
 // t.
 func packElement(t Type, reflectValue reflect.Value) ([]byte, error) {
 	switch t.T {
 	case IntTy, UintTy:
+		if err := validateNum(t, reflectValue); err != nil {
+			return nil, err
+		}
 		return packNum(reflectValue), nil
 	case StringTy:
 		return packBytesSlice([]byte(reflectValue.String()), reflectValue.Len()), nil

accounts/abi/pack_test.go

@@ -177,6 +177,13 @@ func TestMethodPack(t *testing.T) {
 	if !bytes.Equal(packed, sig) {
 		t.Errorf("expected %x got %x", sig, packed)
 	}
+
+	_, err = abi.Pack("send", big.NewInt(-1))
+	if err == nil {
+		t.Fatal("expected error when trying to pack negative big.Int into uint256 value")
+	}
+
+	// TODO: examine what happens if we supply a negative non-big int to a method expect smaller uint val
 }
 
 func TestPackNumber(t *testing.T) {