pallet-xcm: use XcmTeleportFilter for teleported fees in reserve transfers (#2322)

Disallow reserve transfers that use teleportable fees if `(origin,
fees)` matches `XcmTeleportFilter`.

Add regression tests for filtering based on `XcmTeleportFilter` for both
`(limited_)reserve_transfer_assets()` and `(limited_)teleport_assets`
extrinsics.

polkadot/xcm/pallet-xcm/src/lib.rs

@@ -1379,7 +1379,7 @@ impl<T: Config> Pallet<T> {
 				TransferType::DestinationReserve =>
 					Self::destination_reserve_fees_instructions(dest, fees, weight_limit)?,
 				TransferType::Teleport =>
-					Self::teleport_fees_instructions(dest, fees, weight_limit)?,
+					Self::teleport_fees_instructions(origin_location, dest, fees, weight_limit)?,
 				TransferType::RemoteReserve(_) =>
 					return Err(Error::<T>::InvalidAssetUnsupportedReserve.into()),
 			});
@@ -1715,10 +1715,14 @@ impl<T: Config> Pallet<T> {
 	}
 
 	fn teleport_fees_instructions(
+		origin: MultiLocation,
 		dest: MultiLocation,
 		fees: MultiAsset,
 		weight_limit: WeightLimit,
 	) -> Result<(Xcm<<T as Config>::RuntimeCall>, Xcm<()>), Error<T>> {
+		let value = (origin, vec![fees.clone()]);
+		ensure!(T::XcmTeleportFilter::contains(&value), Error::<T>::Filtered);
+
 		let context = T::UniversalLocation::get();
 		let reanchored_fees = fees
 			.clone()

polkadot/xcm/pallet-xcm/src/mock.rs

@@ -18,7 +18,8 @@ use codec::Encode;
 use frame_support::{
 	construct_runtime, match_types, parameter_types,
 	traits::{
-		AsEnsureOriginWithArg, ConstU128, ConstU32, Equals, Everything, EverythingBut, Nothing,
+		AsEnsureOriginWithArg, ConstU128, ConstU32, Contains, Equals, Everything, EverythingBut,
+		Nothing,
 	},
 	weights::Weight,
 };
@@ -341,6 +342,9 @@ pub const USDT_PARA_ID: u32 = 2003;
 // This child parachain is not configured as trusted reserve or teleport location for any assets.
 pub const OTHER_PARA_ID: u32 = 2009;
 
+// This child parachain is used for filtered/disallowed assets.
+pub const FILTERED_PARA_ID: u32 = 2010;
+
 parameter_types! {
 	pub const RelayLocation: MultiLocation = Here.into_location();
 	pub const NativeAsset: MultiAsset = MultiAsset {
@@ -384,6 +388,17 @@ parameter_types! {
 			interior: X1(Parachain(USDT_PARA_ID)),
 		}),
 	};
+	pub const FilteredTeleportLocation: MultiLocation = MultiLocation {
+		parents: 0,
+		interior: X1(Parachain(FILTERED_PARA_ID))
+	};
+	pub const FilteredTeleportAsset: MultiAsset = MultiAsset {
+		fun: Fungible(10),
+		id: Concrete(MultiLocation {
+			parents: 0,
+			interior: X1(Parachain(FILTERED_PARA_ID)),
+		}),
+	};
 	pub const AnyNetwork: Option<NetworkId> = None;
 	pub UniversalLocation: InteriorMultiLocation = Here;
 	pub UnitWeightCost: u64 = 1_000;
@@ -430,6 +445,7 @@ parameter_types! {
 	pub TrustedLocal: (MultiAssetFilter, MultiLocation) = (All.into(), Here.into());
 	pub TrustedSystemPara: (MultiAssetFilter, MultiLocation) = (NativeAsset::get().into(), SystemParachainLocation::get());
 	pub TrustedUsdt: (MultiAssetFilter, MultiLocation) = (Usdt::get().into(), UsdtTeleportLocation::get());
+	pub TrustedFilteredTeleport: (MultiAssetFilter, MultiLocation) = (FilteredTeleportAsset::get().into(), FilteredTeleportLocation::get());
 	pub TeleportUsdtToForeign: (MultiAssetFilter, MultiLocation) = (Usdt::get().into(), ForeignReserveLocation::get());
 	pub TrustedForeign: (MultiAssetFilter, MultiLocation) = (ForeignAsset::get().into(), ForeignReserveLocation::get());
 	pub TrustedUsdc: (MultiAssetFilter, MultiLocation) = (Usdc::get().into(), UsdcReserveLocation::get());
@@ -466,6 +482,7 @@ impl xcm_executor::Config for XcmConfig {
 		Case<TrustedSystemPara>,
 		Case<TrustedUsdt>,
 		Case<TeleportUsdtToForeign>,
+		Case<TrustedFilteredTeleport>,
 	);
 	type UniversalLocation = UniversalLocation;
 	type Barrier = Barrier;
@@ -496,6 +513,14 @@ parameter_types! {
 	pub static AdvertisedXcmVersion: pallet_xcm::XcmVersion = 3;
 }
 
+pub struct XcmTeleportFiltered;
+impl Contains<(MultiLocation, Vec<MultiAsset>)> for XcmTeleportFiltered {
+	fn contains(t: &(MultiLocation, Vec<MultiAsset>)) -> bool {
+		let filtered = FilteredTeleportAsset::get();
+		t.1.iter().any(|asset| asset == &filtered)
+	}
+}
+
 impl pallet_xcm::Config for Test {
 	type RuntimeEvent = RuntimeEvent;
 	type SendXcmOrigin = xcm_builder::EnsureXcmOrigin<RuntimeOrigin, LocalOriginToLocation>;
@@ -503,7 +528,7 @@ impl pallet_xcm::Config for Test {
 	type ExecuteXcmOrigin = xcm_builder::EnsureXcmOrigin<RuntimeOrigin, LocalOriginToLocation>;
 	type XcmExecuteFilter = Everything;
 	type XcmExecutor = XcmExecutor<XcmConfig>;
-	type XcmTeleportFilter = Everything;
+	type XcmTeleportFilter = EverythingBut<XcmTeleportFiltered>;
 	type XcmReserveTransferFilter = Everything;
 	type Weigher = FixedWeightBounds<BaseXcmWeight, RuntimeCall, MaxInstructions>;
 	type UniversalLocation = UniversalLocation;

polkadot/xcm/pallet-xcm/src/tests/assets_transfer.rs

@@ -117,6 +117,30 @@ fn limited_teleport_assets_works() {
 	);
 }
 
+/// `limited_teleport_assets` should fail for filtered assets
+#[test]
+fn limited_teleport_filtered_assets_disallowed() {
+	let beneficiary: MultiLocation = AccountId32 { network: None, id: BOB.into() }.into();
+	new_test_ext_with_balances(vec![(ALICE, INITIAL_BALANCE)]).execute_with(|| {
+		let result = XcmPallet::limited_teleport_assets(
+			RuntimeOrigin::signed(ALICE),
+			Box::new(FilteredTeleportLocation::get().into()),
+			Box::new(beneficiary.into()),
+			Box::new(FilteredTeleportAsset::get().into()),
+			0,
+			Unlimited,
+		);
+		assert_eq!(
+			result,
+			Err(DispatchError::Module(ModuleError {
+				index: 4,
+				error: [2, 0, 0, 0],
+				message: Some("Filtered")
+			}))
+		);
+	});
+}
+
 /// Test `reserve_transfer_assets_with_paid_router_works`
 ///
 /// Asserts that the sender's balance is decreased and the beneficiary's balance
@@ -1403,3 +1427,33 @@ fn reserve_transfer_assets_with_teleportable_asset_fails() {
 		assert_eq!(Assets::active_issuance(usdt_id_multilocation), usdt_initial_local_amount);
 	});
 }
+
+/// Test `reserve_transfer_assets` with teleportable fee that is filtered - should fail.
+#[test]
+fn reserve_transfer_assets_with_filtered_teleported_fee_disallowed() {
+	let beneficiary: MultiLocation = AccountId32 { network: None, id: BOB.into() }.into();
+	new_test_ext_with_balances(vec![(ALICE, INITIAL_BALANCE)]).execute_with(|| {
+		let (assets, fee_index, _, _) = into_multiassets_checked(
+			// FilteredTeleportAsset for fees - teleportable but filtered
+			FilteredTeleportAsset::get().into(),
+			// native asset to transfer (not used for fees) - local reserve
+			(MultiLocation::here(), SEND_AMOUNT).into(),
+		);
+		let result = XcmPallet::limited_reserve_transfer_assets(
+			RuntimeOrigin::signed(ALICE),
+			Box::new(FilteredTeleportLocation::get().into()),
+			Box::new(beneficiary.into()),
+			Box::new(assets.into()),
+			fee_index as u32,
+			Unlimited,
+		);
+		assert_eq!(
+			result,
+			Err(DispatchError::Module(ModuleError {
+				index: 4,
+				error: [2, 0, 0, 0],
+				message: Some("Filtered")
+			}))
+		);
+	});
+}