Make System Parachains trusted Teleporters (#1368)

Make System Parachain trusted Teleporters of each other.

Migration of https://github.com/paritytech/cumulus/pull/2842

---------

Co-authored-by: command-bot <>
Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

cumulus/parachains/common/src/xcm_config.rs

@@ -15,6 +15,7 @@
 
 use crate::impls::AccountIdOf;
 use core::marker::PhantomData;
+use cumulus_primitives_core::{IsSystem, ParaId};
 use frame_support::{
 	traits::{fungibles::Inspect, tokens::ConversionToAssetBalance, ContainsPair},
 	weights::Weight,
@@ -78,3 +79,85 @@ impl<Location: Get<MultiLocation>> ContainsPair<MultiAsset, MultiLocation>
 		matches!(asset.id, Concrete(ref id) if id == origin && origin == &Location::get())
 	}
 }
+
+/// Accepts an asset if it is a concrete asset from the system (Relay Chain or system parachain).
+pub struct ConcreteAssetFromSystem<AssetLocation>(PhantomData<AssetLocation>);
+impl<AssetLocation: Get<MultiLocation>> ContainsPair<MultiAsset, MultiLocation>
+	for ConcreteAssetFromSystem<AssetLocation>
+{
+	fn contains(asset: &MultiAsset, origin: &MultiLocation) -> bool {
+		log::trace!(target: "xcm::contains", "ConcreteAssetFromSystem asset: {:?}, origin: {:?}", asset, origin);
+		let is_system = match origin {
+			// The Relay Chain
+			MultiLocation { parents: 1, interior: Here } => true,
+			// System parachain
+			MultiLocation { parents: 1, interior: X1(Parachain(id)) } =>
+				ParaId::from(*id).is_system(),
+			// Others
+			_ => false,
+		};
+		matches!(asset.id, Concrete(id) if id == AssetLocation::get()) && is_system
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use frame_support::parameter_types;
+
+	use super::{
+		ConcreteAssetFromSystem, ContainsPair, GeneralIndex, Here, MultiAsset, MultiLocation,
+		PalletInstance, Parachain, Parent,
+	};
+
+	parameter_types! {
+		pub const RelayLocation: MultiLocation = MultiLocation::parent();
+	}
+
+	#[test]
+	fn concrete_asset_from_relay_works() {
+		let expected_asset: MultiAsset = (Parent, 1000000).into();
+		let expected_origin: MultiLocation = (Parent, Here).into();
+
+		assert!(<ConcreteAssetFromSystem<RelayLocation>>::contains(
+			&expected_asset,
+			&expected_origin
+		));
+	}
+
+	#[test]
+	fn concrete_asset_from_sibling_system_para_fails_for_wrong_asset() {
+		let unexpected_assets: Vec<MultiAsset> = vec![
+			(Here, 1000000).into(),
+			((PalletInstance(50), GeneralIndex(1)), 1000000).into(),
+			((Parent, Parachain(1000), PalletInstance(50), GeneralIndex(1)), 1000000).into(),
+		];
+		let expected_origin: MultiLocation = (Parent, Parachain(1000)).into();
+
+		unexpected_assets.iter().for_each(|asset| {
+			assert!(!<ConcreteAssetFromSystem<RelayLocation>>::contains(asset, &expected_origin));
+		});
+	}
+
+	#[test]
+	fn concrete_asset_from_sibling_system_para_works_for_correct_asset() {
+		// (para_id, expected_result)
+		let test_data = vec![
+			(0, true),
+			(1, true),
+			(1000, true),
+			(1999, true),
+			(2000, false), // Not a System Parachain
+			(2001, false), // Not a System Parachain
+		];
+
+		let expected_asset: MultiAsset = (Parent, 1000000).into();
+
+		for (para_id, expected_result) in test_data {
+			let origin: MultiLocation = (Parent, Parachain(para_id)).into();
+			assert_eq!(
+				expected_result,
+				<ConcreteAssetFromSystem<RelayLocation>>::contains(&expected_asset, &origin)
+			);
+		}
+	}
+}