handle overflow (open-web3-stack#667)

(cherry picked from commit 1c80da4)

Author: xlc

xtokens/src/lib.rs

@@ -26,7 +26,7 @@ use frame_support::{pallet_prelude::*, require_transactional, traits::Get, trans
 use frame_system::{ensure_signed, pallet_prelude::*};
 use sp_runtime::{
 	traits::{AtLeast32BitUnsigned, Convert, MaybeSerializeDeserialize, Member, Zero},
-	DispatchError,
+	ArithmeticError, DispatchError,
 };
 use sp_std::{convert::TryInto, prelude::*, result::Result};
 
@@ -384,6 +384,12 @@ pub mod module {
 			// For now fee and asset id should be identical
 			// We can relax this assumption in the future
 			ensure!(fee.id == asset.id, Error::<T>::DistincAssetAndFeeId);
+			// Workaround issue of https://github.com/paritytech/polkadot/pull/4492
+			// TODO: remove this on next Substrate version
+			ensure!(
+				fungible_amount(&asset).checked_add(fungible_amount(&fee)).is_some(),
+				ArithmeticError::Overflow
+			);
 
 			let (transfer_kind, dest, reserve, recipient) = Self::transfer_kind(&asset, &dest)?;
 			let mut msg = match transfer_kind {

xtokens/src/tests.rs

@@ -733,3 +733,36 @@ fn send_with_insufficient_fee_traps_assets() {
 		}));
 	})
 }
+
+#[test]
+fn send_with_fee_should_handle_overflow() {
+	TestNet::reset();
+
+	ParaA::execute_with(|| {
+		assert_ok!(ParaTokens::deposit(CurrencyId::A, &ALICE, 1_000));
+
+		assert_noop!(
+			ParaXTokens::transfer_with_fee(
+				Some(ALICE).into(),
+				CurrencyId::A,
+				u128::MAX,
+				1,
+				Box::new(
+					MultiLocation::new(
+						1,
+						X2(
+							Parachain(2),
+							Junction::AccountId32 {
+								network: NetworkId::Any,
+								id: BOB.into(),
+							}
+						)
+					)
+					.into()
+				),
+				40,
+			),
+			ArithmeticError::Overflow
+		);
+	});
+}