Enforce max length for MultiAssets for some instructions

xcm/src/v3/mod.rs

@@ -42,7 +42,7 @@ pub use junction::{BodyId, BodyPart, Junction, NetworkId};
 pub use junctions::Junctions;
 pub use multiasset::{
 	AssetId, AssetInstance, Fungibility, MultiAsset, MultiAssetFilter, MultiAssets,
-	WildFungibility, WildMultiAsset,
+	WildFungibility, WildMultiAsset, MAX_ITEMS_IN_MULTIASSETS,
 };
 pub use multilocation::{
 	Ancestor, AncestorThen, InteriorMultiLocation, MultiLocation, Parent, ParentThen,
@@ -188,7 +188,7 @@ pub mod prelude {
 			WeightLimit::{self, *},
 			WildFungibility::{self, Fungible as WildFungible, NonFungible as WildNonFungible},
 			WildMultiAsset::{self, *},
-			XcmContext, XcmHash, XcmWeightInfo, VERSION as XCM_VERSION,
+			XcmContext, XcmHash, XcmWeightInfo, MAX_ITEMS_IN_MULTIASSETS, VERSION as XCM_VERSION,
 		};
 	}
 	pub use super::{Instruction, Xcm};

xcm/src/v3/multiasset.rs

@@ -508,7 +508,7 @@ pub struct MultiAssets(Vec<MultiAsset>);
 
 /// Maximum number of items we expect in a single `MultiAssets` value. Note this is not (yet)
 /// enforced, and just serves to provide a sensible `max_encoded_len` for `MultiAssets`.
-const MAX_ITEMS_IN_MULTIASSETS: usize = 20;
+pub const MAX_ITEMS_IN_MULTIASSETS: usize = 20;
 
 impl MaxEncodedLen for MultiAssets {
 	fn max_encoded_len() -> usize {

xcm/src/v3/traits.rs

@@ -157,6 +157,9 @@ pub enum Error {
 	WeightNotComputable,
 	/// Recursion stack limit reached
 	ExceedsStackLimit,
+	/// Assets exceeded maximum
+	// TODO (XCMv4): Add to spec
+	TooManyAssets,
 }
 
 impl MaxEncodedLen for Error {

xcm/xcm-executor/src/lib.rs

@@ -479,6 +479,9 @@ impl<Config: config::Config> XcmExecutor<Config> {
 			WithdrawAsset(assets) => {
 				// Take `assets` from the origin account (on-chain) and place in holding.
 				let origin = *self.origin_ref().ok_or(XcmError::BadOrigin)?;
+				if assets.len() > MAX_ITEMS_IN_MULTIASSETS {
+					return Err(XcmError::TooManyAssets)
+				}
 				for asset in assets.into_inner().into_iter() {
 					Config::AssetTransactor::withdraw_asset(&asset, &origin, Some(&self.context))?;
 					self.subsume_asset(asset)?;
@@ -488,6 +491,9 @@ impl<Config: config::Config> XcmExecutor<Config> {
 			ReserveAssetDeposited(assets) => {
 				// check whether we trust origin to be our reserve location for this asset.
 				let origin = *self.origin_ref().ok_or(XcmError::BadOrigin)?;
+				if assets.len() > MAX_ITEMS_IN_MULTIASSETS {
+					return Err(XcmError::TooManyAssets)
+				}
 				for asset in assets.into_inner().into_iter() {
 					// Must ensure that we recognise the asset as being managed by the origin.
 					ensure!(
@@ -526,6 +532,9 @@ impl<Config: config::Config> XcmExecutor<Config> {
 			},
 			ReceiveTeleportedAsset(assets) => {
 				let origin = *self.origin_ref().ok_or(XcmError::BadOrigin)?;
+				if assets.len() > MAX_ITEMS_IN_MULTIASSETS {
+					return Err(XcmError::TooManyAssets)
+				}
 				// check whether we trust origin to teleport this asset to us via config trait.
 				for asset in assets.inner() {
 					// We only trust the origin to send us assets that they identify as their
@@ -719,6 +728,9 @@ impl<Config: config::Config> XcmExecutor<Config> {
 			},
 			ClaimAsset { assets, ticket } => {
 				let origin = self.origin_ref().ok_or(XcmError::BadOrigin)?;
+				if assets.len() > MAX_ITEMS_IN_MULTIASSETS {
+					return Err(XcmError::TooManyAssets)
+				}
 				let ok = Config::AssetClaims::claim_assets(origin, &ticket, &assets, &self.context);
 				ensure!(ok, XcmError::UnknownClaim);
 				for asset in assets.into_inner().into_iter() {

xcm/xcm-simulator/example/src/lib.rs

@@ -145,7 +145,7 @@ mod tests {
 	use codec::Encode;
 	use frame_support::{assert_ok, weights::Weight};
 	use xcm::latest::QueryResponseInfo;
-	use xcm_simulator::TestExt;
+	use xcm_simulator::{fake_message_hash, TestExt, XcmExecutor};
 
 	// Helper function for forming buy execution message
 	fn buy_execution<C>(fees: impl Into<MultiAsset>) -> Instruction<C> {
@@ -649,4 +649,57 @@ mod tests {
 			);
 		});
 	}
+
+	#[test]
+	fn too_many_assets_throws_error() {
+		use crate::Outcome::Incomplete;
+		use xcm_simulator::XcmError::TooManyAssets;
+
+		let assets = MultiAssets::from(vec![
+			(Here, 1).into(),
+			(Parent, 1).into(),
+			(MultiLocation::new(2, Here), 1).into(),
+			(MultiLocation::new(3, Here), 1).into(),
+			(MultiLocation::new(4, Here), 1).into(),
+			(MultiLocation::new(5, Here), 1).into(),
+			(MultiLocation::new(6, Here), 1).into(),
+			(MultiLocation::new(7, Here), 1).into(),
+			(MultiLocation::new(8, Here), 1).into(),
+			(MultiLocation::new(9, Here), 1).into(),
+			(MultiLocation::new(10, Here), 1).into(),
+			(MultiLocation::new(11, Here), 1).into(),
+			(MultiLocation::new(12, Here), 1).into(),
+			(MultiLocation::new(13, Here), 1).into(),
+			(MultiLocation::new(14, Here), 1).into(),
+			(MultiLocation::new(15, Here), 1).into(),
+			(MultiLocation::new(16, Here), 1).into(),
+			(MultiLocation::new(17, Here), 1).into(),
+			(MultiLocation::new(18, Here), 1).into(),
+			(MultiLocation::new(19, Here), 1).into(),
+			(MultiLocation::new(20, Here), 1).into(),
+		]);
+		let message = Xcm(vec![WithdrawAsset(assets.clone())]);
+		let hash = fake_message_hash(&message);
+		let result =
+			XcmExecutor::<parachain::XcmConfig>::execute_xcm(Here, message, hash, Weight::MAX);
+		assert!(matches!(result, Incomplete(_, TooManyAssets)));
+
+		let message = Xcm(vec![ReserveAssetDeposited(assets.clone())]);
+		let hash = fake_message_hash(&message);
+		let result =
+			XcmExecutor::<parachain::XcmConfig>::execute_xcm(Here, message, hash, Weight::MAX);
+		assert!(matches!(result, Incomplete(_, TooManyAssets)));
+
+		let message = Xcm(vec![ReceiveTeleportedAsset(assets.clone())]);
+		let hash = fake_message_hash(&message);
+		let result =
+			XcmExecutor::<parachain::XcmConfig>::execute_xcm(Here, message, hash, Weight::MAX);
+		assert!(matches!(result, Incomplete(_, TooManyAssets)));
+
+		let message = Xcm(vec![ClaimAsset { assets: assets.clone(), ticket: Here.into() }]);
+		let hash = fake_message_hash(&message);
+		let result =
+			XcmExecutor::<parachain::XcmConfig>::execute_xcm(Here, message, hash, Weight::MAX);
+		assert!(matches!(result, Incomplete(_, TooManyAssets)));
+	}
 }