Deny using relay chain for reserve transfers

polkadot-parachains/canvas-kusama/src/xcm_config.rs

@@ -24,6 +24,7 @@ use frame_support::{
 };
 use frame_system::EnsureRoot;
 use pallet_xcm::{EnsureXcm, IsMajorityOfBody, XcmPassthrough};
+use parachains_common::{DenyThenTry, IsReserveTransferToRelayChain};
 use polkadot_parachain::primitives::Sibling;
 use xcm::latest::prelude::*;
 use xcm_builder::{
@@ -117,16 +118,19 @@ match_types! {
 	};
 }
 
-pub type Barrier = (
-	TakeWeightCredit,
-	AllowTopLevelPaidExecutionFrom<Everything>,
-	// Parent and its exec plurality get free execution
-	AllowUnpaidExecutionFrom<ParentOrParentsExecutivePlurality>,
-	// Expected responses are OK.
-	AllowKnownQueryResponses<PolkadotXcm>,
-	// Subscriptions for version tracking are OK.
-	AllowSubscriptionsFrom<ParentOrSiblings>,
-);
+pub type Barrier = DenyThenTry<
+	IsReserveTransferToRelayChain,
+	(
+		TakeWeightCredit,
+		AllowTopLevelPaidExecutionFrom<Everything>,
+		// Parent and its exec plurality get free execution
+		AllowUnpaidExecutionFrom<ParentOrParentsExecutivePlurality>,
+		// Expected responses are OK.
+		AllowKnownQueryResponses<PolkadotXcm>,
+		// Subscriptions for version tracking are OK.
+		AllowSubscriptionsFrom<ParentOrSiblings>,
+	),
+>;
 
 pub struct XcmConfig;
 impl xcm_executor::Config for XcmConfig {

polkadot-parachains/parachains-common/src/lib.rs

@@ -17,8 +17,15 @@
 
 pub mod impls;
 pub use constants::*;
+use core::marker::PhantomData;
+use frame_support::weights::Weight;
 pub use opaque::*;
 pub use types::*;
+use xcm::{
+	opaque::v2::prelude::{DepositReserveAsset, TransferReserveAsset},
+	v2::{Junctions, MultiLocation, Xcm},
+};
+use xcm_executor::traits::ShouldExecute;
 /// Common types of parachains.
 mod types {
 	use sp_runtime::traits::{IdentifyAccount, Verify};
@@ -109,3 +116,61 @@ pub mod opaque {
 	/// Opaque block identifier type.
 	pub type BlockId = generic::BlockId<Block>;
 }
+
+//TODO: move DenyThenTry to polkadot's xcm module.
+/// Deny executing the xcm message if it matches any of the Deny filter regardless of anything else.
+/// If it passes the Deny, and matches one of the Allow cases then it is let through.
+pub struct DenyThenTry<Deny, Allow>
+where
+	Deny: ShouldExecute,
+	Allow: ShouldExecute,
+{
+	_deny: PhantomData<Deny>,
+	_allow: PhantomData<Allow>,
+}
+
+impl<Deny, Allow> ShouldExecute for DenyThenTry<Deny, Allow>
+where
+	Deny: ShouldExecute,
+	Allow: ShouldExecute,
+{
+	fn should_execute<Call>(
+		origin: &MultiLocation,
+		message: &mut Xcm<Call>,
+		max_weight: Weight,
+		weight_credit: &mut Weight,
+	) -> Result<(), ()> {
+		if Deny::should_execute(origin, message, max_weight, weight_credit).is_ok() {
+			return Err(())
+		}
+		Allow::should_execute(origin, message, max_weight, weight_credit)
+	}
+}
+
+// See issue #5233
+pub struct IsReserveTransferToRelayChain;
+impl ShouldExecute for IsReserveTransferToRelayChain {
+	fn should_execute<Call>(
+		_origin: &MultiLocation,
+		message: &mut Xcm<Call>,
+		_max_weight: Weight,
+		_weight_credit: &mut Weight,
+	) -> Result<(), ()> {
+		if message.0.iter().any(|inst| {
+			matches!(
+				inst,
+				DepositReserveAsset {
+					dest: MultiLocation { parents: 1, interior: Junctions::Here },
+					..
+				} | TransferReserveAsset {
+					dest: MultiLocation { parents: 1, interior: Junctions::Here },
+					..
+				}
+			)
+		}) {
+			Ok(())
+		} else {
+			Err(())
+		}
+	}
+}

polkadot-parachains/statemine/src/xcm_config.rs

@@ -23,7 +23,7 @@ use frame_support::{
 	weights::Weight,
 };
 use pallet_xcm::XcmPassthrough;
-use parachains_common::impls::ToStakingPot;
+use parachains_common::{impls::ToStakingPot, DenyThenTry, IsReserveTransferToRelayChain};
 use polkadot_parachain::primitives::Sibling;
 use xcm::latest::prelude::*;
 use xcm_builder::{
@@ -139,16 +139,19 @@ match_types! {
 	};
 }
 
-pub type Barrier = (
-	TakeWeightCredit,
-	AllowTopLevelPaidExecutionFrom<Everything>,
-	// Parent and its exec plurality get free execution
-	AllowUnpaidExecutionFrom<ParentOrParentsExecutivePlurality>,
-	// Expected responses are OK.
-	AllowKnownQueryResponses<PolkadotXcm>,
-	// Subscriptions for version tracking are OK.
-	AllowSubscriptionsFrom<ParentOrSiblings>,
-);
+pub type Barrier = DenyThenTry<
+	IsReserveTransferToRelayChain,
+	(
+		TakeWeightCredit,
+		AllowTopLevelPaidExecutionFrom<Everything>,
+		// Parent and its exec plurality get free execution
+		AllowUnpaidExecutionFrom<ParentOrParentsExecutivePlurality>,
+		// Expected responses are OK.
+		AllowKnownQueryResponses<PolkadotXcm>,
+		// Subscriptions for version tracking are OK.
+		AllowSubscriptionsFrom<ParentOrSiblings>,
+	),
+>;
 
 pub struct XcmConfig;
 impl xcm_executor::Config for XcmConfig {

polkadot-parachains/statemint/src/xcm_config.rs

@@ -23,7 +23,7 @@ use frame_support::{
 	weights::Weight,
 };
 use pallet_xcm::XcmPassthrough;
-use parachains_common::impls::ToStakingPot;
+use parachains_common::{impls::ToStakingPot, DenyThenTry, IsReserveTransferToRelayChain};
 use polkadot_parachain::primitives::Sibling;
 use xcm::latest::prelude::*;
 use xcm_builder::{
@@ -139,16 +139,19 @@ match_types! {
 	};
 }
 
-pub type Barrier = (
-	TakeWeightCredit,
-	AllowTopLevelPaidExecutionFrom<Everything>,
-	// Parent and its exec plurality get free execution
-	AllowUnpaidExecutionFrom<ParentOrParentsExecutivePlurality>,
-	// Expected responses are OK.
-	AllowKnownQueryResponses<PolkadotXcm>,
-	// Subscriptions for version tracking are OK.
-	AllowSubscriptionsFrom<ParentOrSiblings>,
-);
+pub type Barrier = DenyThenTry<
+	IsReserveTransferToRelayChain,
+	(
+		TakeWeightCredit,
+		AllowTopLevelPaidExecutionFrom<Everything>,
+		// Parent and its exec plurality get free execution
+		AllowUnpaidExecutionFrom<ParentOrParentsExecutivePlurality>,
+		// Expected responses are OK.
+		AllowKnownQueryResponses<PolkadotXcm>,
+		// Subscriptions for version tracking are OK.
+		AllowSubscriptionsFrom<ParentOrSiblings>,
+	),
+>;
 
 pub struct XcmConfig;
 impl xcm_executor::Config for XcmConfig {

polkadot-parachains/westmint/src/xcm_config.rs

@@ -23,7 +23,7 @@ use frame_support::{
 	weights::Weight,
 };
 use pallet_xcm::XcmPassthrough;
-use parachains_common::impls::ToStakingPot;
+use parachains_common::{impls::ToStakingPot, DenyThenTry, IsReserveTransferToRelayChain};
 use polkadot_parachain::primitives::Sibling;
 use xcm::latest::prelude::*;
 use xcm_builder::{
@@ -135,16 +135,19 @@ match_types! {
 	};
 }
 
-pub type Barrier = (
-	TakeWeightCredit,
-	AllowTopLevelPaidExecutionFrom<Everything>,
-	// Parent and its plurality get free execution
-	AllowUnpaidExecutionFrom<ParentOrParentsPlurality>,
-	// Expected responses are OK.
-	AllowKnownQueryResponses<PolkadotXcm>,
-	// Subscriptions for version tracking are OK.
-	AllowSubscriptionsFrom<Everything>,
-);
+pub type Barrier = DenyThenTry<
+	IsReserveTransferToRelayChain,
+	(
+		TakeWeightCredit,
+		AllowTopLevelPaidExecutionFrom<Everything>,
+		// Parent and its plurality get free execution
+		AllowUnpaidExecutionFrom<ParentOrParentsPlurality>,
+		// Expected responses are OK.
+		AllowKnownQueryResponses<PolkadotXcm>,
+		// Subscriptions for version tracking are OK.
+		AllowSubscriptionsFrom<Everything>,
+	),
+>;
 
 pub struct XcmConfig;
 impl xcm_executor::Config for XcmConfig {