lower limit for message weight (paritytech#536)

* lower limit for message weight

* fmt

* do not include tx overhead in weights returned by weight_limits_of_message_on_bridged_chain

* Use correct chain in comment

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

bridges/bin/millau/runtime/src/rialto_messages.rs

@@ -30,6 +30,7 @@ use frame_support::{
 	RuntimeDebug,
 };
 use sp_core::storage::StorageKey;
+use sp_std::{convert::TryFrom, ops::RangeInclusive};
 
 /// Storage key of the Millau -> Rialto message in the runtime storage.
 pub fn message_key(lane: &LaneId, nonce: MessageNonce) -> StorageKey {
@@ -87,9 +88,15 @@ impl MessageBridge for WithRialtoMessageBridge {
 	type ThisChain = Millau;
 	type BridgedChain = Rialto;
 
-	fn maximal_dispatch_weight_of_message_on_bridged_chain() -> Weight {
+	fn weight_limits_of_message_on_bridged_chain(message_payload: &[u8]) -> RangeInclusive<Weight> {
 		// we don't want to relay too large messages + keep reserve for future upgrades
-		bp_rialto::MAXIMUM_EXTRINSIC_WEIGHT / 2
+		let upper_limit = bp_rialto::MAXIMUM_EXTRINSIC_WEIGHT / 2;
+
+		// given Rialto chain parameters (`TransactionByteFee`, `WeightToFee`, `FeeMultiplierUpdate`),
+		// the minimal weight of the message may be computed as message.length()
+		let lower_limit = Weight::try_from(message_payload.len()).unwrap_or(Weight::MAX);
+
+		lower_limit..=upper_limit
 	}
 
 	fn weight_of_delivery_transaction() -> Weight {
@@ -160,8 +167,9 @@ impl TargetHeaderChain<ToRialtoMessagePayload, bp_rialto::AccountId> for Rialto
 	type MessagesDeliveryProof = ToRialtoMessagesDeliveryProof;
 
 	fn verify_message(payload: &ToRialtoMessagePayload) -> Result<(), Self::Error> {
-		if payload.weight > WithRialtoMessageBridge::maximal_dispatch_weight_of_message_on_bridged_chain() {
-			return Err("Too large weight declared");
+		let weight_limits = WithRialtoMessageBridge::weight_limits_of_message_on_bridged_chain(&payload.call);
+		if !weight_limits.contains(&payload.weight) {
+			return Err("Incorrect message weight declared");
 		}
 
 		Ok(())

bridges/bin/rialto/runtime/src/millau_messages.rs

@@ -30,6 +30,7 @@ use frame_support::{
 	RuntimeDebug,
 };
 use sp_core::storage::StorageKey;
+use sp_std::{convert::TryFrom, ops::RangeInclusive};
 
 /// Storage key of the Rialto -> Millau message in the runtime storage.
 pub fn message_key(lane: &LaneId, nonce: MessageNonce) -> StorageKey {
@@ -87,9 +88,15 @@ impl MessageBridge for WithMillauMessageBridge {
 	type ThisChain = Rialto;
 	type BridgedChain = Millau;
 
-	fn maximal_dispatch_weight_of_message_on_bridged_chain() -> Weight {
+	fn weight_limits_of_message_on_bridged_chain(message_payload: &[u8]) -> RangeInclusive<Weight> {
 		// we don't want to relay too large messages + keep reserve for future upgrades
-		bp_millau::MAXIMUM_EXTRINSIC_WEIGHT / 2
+		let upper_limit = bp_millau::MAXIMUM_EXTRINSIC_WEIGHT / 2;
+
+		// given Millau chain parameters (`TransactionByteFee`, `WeightToFee`, `FeeMultiplierUpdate`),
+		// the minimal weight of the message may be computed as message.length()
+		let lower_limit = Weight::try_from(message_payload.len()).unwrap_or(Weight::MAX);
+
+		lower_limit..=upper_limit
 	}
 
 	fn weight_of_delivery_transaction() -> Weight {
@@ -160,8 +167,9 @@ impl TargetHeaderChain<ToMillauMessagePayload, bp_millau::AccountId> for Millau
 	type MessagesDeliveryProof = ToMillauMessagesDeliveryProof;
 
 	fn verify_message(payload: &ToMillauMessagePayload) -> Result<(), Self::Error> {
-		if payload.weight > WithMillauMessageBridge::maximal_dispatch_weight_of_message_on_bridged_chain() {
-			return Err("Payload has weight larger than maximum allowed weight");
+		let weight_limits = WithMillauMessageBridge::weight_limits_of_message_on_bridged_chain(&payload.call);
+		if !weight_limits.contains(&payload.weight) {
+			return Err("Incorrect message weight declared");
 		}
 
 		Ok(())

bridges/bin/runtime-common/src/messages.rs

@@ -30,7 +30,7 @@ use bp_runtime::InstanceId;
 use codec::{Compact, Decode, Input};
 use frame_support::{traits::Instance, RuntimeDebug};
 use sp_runtime::traits::{CheckedAdd, CheckedDiv, CheckedMul};
-use sp_std::{cmp::PartialOrd, marker::PhantomData, vec::Vec};
+use sp_std::{cmp::PartialOrd, marker::PhantomData, ops::RangeInclusive, vec::Vec};
 use sp_trie::StorageProof;
 
 /// Bidirectional message bridge.
@@ -46,8 +46,18 @@ pub trait MessageBridge {
 	/// Bridged chain in context of message bridge.
 	type BridgedChain: ChainWithMessageLanes;
 
-	/// Maximal (dispatch) weight of the message that we are able to send to Bridged chain.
-	fn maximal_dispatch_weight_of_message_on_bridged_chain() -> WeightOf<BridgedChain<Self>>;
+	/// Returns feasible weights range for given message payload on the target chain.
+	///
+	/// If message is being sent with the weight that is out of this range, then it
+	/// should be rejected.
+	///
+	/// Weights returned from this function shall not include transaction overhead
+	/// (like weight of signature and signed extensions verification), because they're
+	/// already accounted by the `weight_of_delivery_transaction`. So this function should
+	/// return pure call dispatch weights range.
+	fn weight_limits_of_message_on_bridged_chain(
+		message_payload: &[u8],
+	) -> RangeInclusive<WeightOf<BridgedChain<Self>>>;
 
 	/// Maximal weight of single message delivery transaction on Bridged chain.
 	fn weight_of_delivery_transaction() -> WeightOf<BridgedChain<Self>>;
@@ -425,7 +435,7 @@ mod tests {
 		type ThisChain = ThisChain;
 		type BridgedChain = BridgedChain;
 
-		fn maximal_dispatch_weight_of_message_on_bridged_chain() -> Weight {
+		fn weight_limits_of_message_on_bridged_chain(_message_payload: &[u8]) -> RangeInclusive<Weight> {
 			unreachable!()
 		}
 
@@ -464,7 +474,7 @@ mod tests {
 		type ThisChain = BridgedChain;
 		type BridgedChain = ThisChain;
 
-		fn maximal_dispatch_weight_of_message_on_bridged_chain() -> Weight {
+		fn weight_limits_of_message_on_bridged_chain(_message_payload: &[u8]) -> RangeInclusive<Weight> {
 			unreachable!()
 		}