Add a filter for filtering unsupported MultiLocation

xtokens/src/lib.rs

@@ -22,7 +22,13 @@
 #![allow(clippy::unused_unit)]
 #![allow(clippy::large_enum_variant)]
 
-use frame_support::{log, pallet_prelude::*, require_transactional, traits::Get, transactional, Parameter};
+use frame_support::{
+	log,
+	pallet_prelude::*,
+	require_transactional,
+	traits::{Contains, Get},
+	transactional, Parameter,
+};
 use frame_system::{ensure_signed, pallet_prelude::*};
 use sp_runtime::{
 	traits::{AtLeast32BitUnsigned, Convert, MaybeSerializeDeserialize, Member, Zero},
@@ -88,6 +94,9 @@ pub mod module {
 		/// XCM executor.
 		type XcmExecutor: ExecuteXcm<Self::Call>;
 
+		/// MultiLocation filter
+		type MultiLocationsFilter: Contains<MultiLocation>;
+
 		/// Means of measuring the weight consumed by an XCM message locally.
 		type Weigher: WeightBounds<Self::Call>;
 
@@ -158,6 +167,8 @@ pub mod module {
 		AssetIndexNonExistent,
 		/// Fee is not enough.
 		FeeNotEnough,
+		/// Not supported MultiLocation
+		NotSupportedMultiLocation,
 	}
 
 	#[pallet::hooks]
@@ -372,6 +383,10 @@ pub mod module {
 				T::CurrencyIdConvert::convert(currency_id).ok_or(Error::<T>::NotCrossChainTransferableCurrency)?;
 
 			ensure!(!amount.is_zero(), Error::<T>::ZeroAmount);
+			ensure!(
+				T::MultiLocationsFilter::contains(&dest),
+				Error::<T>::NotSupportedMultiLocation
+			);
 
 			let asset: MultiAsset = (location, amount.into()).into();
 			Self::do_transfer_multiassets(who, vec![asset.clone()].into(), asset, dest, dest_weight)
@@ -390,6 +405,10 @@ pub mod module {
 
 			ensure!(!amount.is_zero(), Error::<T>::ZeroAmount);
 			ensure!(!fee.is_zero(), Error::<T>::ZeroFee);
+			ensure!(
+				T::MultiLocationsFilter::contains(&dest),
+				Error::<T>::NotSupportedMultiLocation
+			);
 
 			let asset = (location.clone(), amount.into()).into();
 			let fee_asset: MultiAsset = (location, fee.into()).into();
@@ -451,6 +470,11 @@ pub mod module {
 				let location: MultiLocation = T::CurrencyIdConvert::convert(currency_id.clone())
 					.ok_or(Error::<T>::NotCrossChainTransferableCurrency)?;
 				ensure!(!amount.is_zero(), Error::<T>::ZeroAmount);
+				ensure!(
+					T::MultiLocationsFilter::contains(&dest),
+					Error::<T>::NotSupportedMultiLocation
+				);
+
 				// Push contains saturated addition, so we should be able to use it safely
 				assets.push((location, (*amount).into()).into())
 			}

xtokens/src/mock/para.rs

@@ -3,7 +3,7 @@ use crate as orml_xtokens;
 
 use frame_support::{
 	construct_runtime, parameter_types,
-	traits::{Everything, Get, Nothing},
+	traits::{Contains, Everything, Get, Nothing},
 	weights::{constants::WEIGHT_PER_SECOND, Weight},
 };
 use frame_system::EnsureRoot;
@@ -270,6 +270,52 @@ parameter_types! {
 	pub SelfLocation: MultiLocation = MultiLocation::new(1, X1(Parachain(ParachainInfo::get().into())));
 	pub const BaseXcmWeight: Weight = 100_000_000;
 	pub const MaxAssetsForTransfer: usize = 3;
+	pub SupportedMultiLocations: Vec<MultiLocation> = vec![
+		MultiLocation::new(
+			1,
+			X1(Parachain(1))
+		),
+		MultiLocation::new(
+			1,
+			X1(Parachain(2))
+		),
+		MultiLocation::new(
+			1,
+			X1(Parachain(3))
+		),
+		// There's a test that uses para id = 100
+		MultiLocation::new(
+			1,
+			X1(Parachain(100))
+		)
+	];
+}
+
+pub struct WhiteListingMultiLocations;
+impl Contains<MultiLocation> for WhiteListingMultiLocations {
+	fn contains(dest: &MultiLocation) -> bool {
+		if dest.parent_count() != 1 {
+			return false;
+		}
+
+		if let Junctions::X1(Junction::AccountId32 { .. }) = dest.interior() {
+			// parent = 1, and the junctions is the variant X1
+			// means the asset will be sent to relaychain.
+			true
+		} else {
+			// if the asset is sent to parachain,
+			// the junctions must have the variant Parachain
+			dest.interior().iter().any(|i| match i {
+				Junction::Parachain(parachain_id) => SupportedMultiLocations::get().iter().any(|location| {
+					location
+						.interior
+						.iter()
+						.any(|junc| *junc == Junction::Parachain(*parachain_id))
+				}),
+				_ => false, // No parachain id found.
+			})
+		}
+	}
 }
 
 parameter_type_with_key! {
@@ -289,6 +335,7 @@ impl orml_xtokens::Config for Runtime {
 	type CurrencyIdConvert = CurrencyIdConvert;
 	type AccountIdToMultiLocation = AccountIdToMultiLocation;
 	type SelfLocation = SelfLocation;
+	type MultiLocationsFilter = WhiteListingMultiLocations;
 	type MinXcmFee = ParachainMinFee;
 	type XcmExecutor = XcmExecutor<XcmConfig>;
 	type Weigher = FixedWeightBounds<UnitWeightCost, Call, MaxInstructions>;

xtokens/src/tests.rs

@@ -1335,3 +1335,32 @@ fn send_with_zero_amount() {
 
 	// TODO: should have more tests after https://github.com/paritytech/polkadot/issues/4996
 }
+
+#[test]
+fn unsupported_multilocation_should_be_filtered() {
+	TestNet::reset();
+
+	ParaB::execute_with(|| {
+		assert_ok!(ParaTokens::deposit(CurrencyId::B, &ALICE, 1_000));
+		assert_noop!(
+			ParaXTokens::transfer(
+				Some(ALICE).into(),
+				CurrencyId::B,
+				500,
+				Box::new(
+					(
+						Parent,
+						Parachain(4), // parachain 4 is not supported list.
+						Junction::AccountId32 {
+							network: NetworkId::Any,
+							id: BOB.into(),
+						},
+					)
+						.into()
+				),
+				40,
+			),
+			Error::<para::Runtime>::NotSupportedMultiLocation
+		);
+	});
+}