From 8ee90afae6b279600e35f1b45745ec1b8e482cfb Mon Sep 17 00:00:00 2001
From: Svyatoslav Nikolsky <svyatonik@gmail.com>
Date: Mon, 1 Feb 2021 23:53:33 +0300
Subject: [PATCH] Pre-dispatch call filter (#687)

* pre-dispatch call filter

* swap filter <-> weight

* clippy

* fmt
---
 bridges/bin/millau/runtime/src/lib.rs    |  1 +
 bridges/bin/rialto/runtime/src/lib.rs    |  1 +
 bridges/modules/call-dispatch/src/lib.rs | 55 +++++++++++++++++++++++-
 3 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/bridges/bin/millau/runtime/src/lib.rs b/bridges/bin/millau/runtime/src/lib.rs
index d85be22b24..3164c8a9d8 100644
--- a/bridges/bin/millau/runtime/src/lib.rs
+++ b/bridges/bin/millau/runtime/src/lib.rs
@@ -215,6 +215,7 @@ impl pallet_bridge_call_dispatch::Config for Runtime {
 	type Event = Event;
 	type MessageId = (bp_message_lane::LaneId, bp_message_lane::MessageNonce);
 	type Call = Call;
+	type CallFilter = ();
 	type EncodedCall = crate::rialto_messages::FromRialtoEncodedCall;
 	type SourceChainAccountId = bp_rialto::AccountId;
 	type TargetChainAccountPublic = MultiSigner;
diff --git a/bridges/bin/rialto/runtime/src/lib.rs b/bridges/bin/rialto/runtime/src/lib.rs
index d45164f6ad..677ca283c4 100644
--- a/bridges/bin/rialto/runtime/src/lib.rs
+++ b/bridges/bin/rialto/runtime/src/lib.rs
@@ -266,6 +266,7 @@ impl pallet_bridge_call_dispatch::Config for Runtime {
 	type Event = Event;
 	type MessageId = (bp_message_lane::LaneId, bp_message_lane::MessageNonce);
 	type Call = Call;
+	type CallFilter = ();
 	type EncodedCall = crate::millau_messages::FromMillauEncodedCall;
 	type SourceChainAccountId = bp_millau::AccountId;
 	type TargetChainAccountPublic = MultiSigner;
diff --git a/bridges/modules/call-dispatch/src/lib.rs b/bridges/modules/call-dispatch/src/lib.rs
index b68ff3aa5e..1f932dcfe3 100644
--- a/bridges/modules/call-dispatch/src/lib.rs
+++ b/bridges/modules/call-dispatch/src/lib.rs
@@ -31,7 +31,7 @@ use frame_support::{
 	decl_event, decl_module, decl_storage,
 	dispatch::{Dispatchable, Parameter},
 	ensure,
-	traits::Get,
+	traits::{Filter, Get},
 	weights::{extract_actual_weight, GetDispatchInfo},
 	RuntimeDebug,
 };
@@ -134,6 +134,11 @@ pub trait Config<I = DefaultInstance>: frame_system::Config {
 			Origin = <Self as frame_system::Config>::Origin,
 			PostInfo = frame_support::dispatch::PostDispatchInfo,
 		>;
+	/// Pre-dispatch filter for incoming calls.
+	///
+	/// The pallet will filter all incoming calls right before they're dispatched. If this filter
+	/// rejects the call, special event (`Event::MessageCallRejected`) is emitted.
+	type CallFilter: Filter<<Self as Config<I>>::Call>;
 	/// The type that is used to wrap the `Self::Call` when it is moved over bridge.
 	///
 	/// The idea behind this is to avoid `Call` conversion/decoding until we'll be sure
@@ -172,6 +177,8 @@ decl_event!(
 		MessageDispatched(InstanceId, MessageId, DispatchResult),
 		/// We have failed to decode Call from the message.
 		MessageCallDecodeFailed(InstanceId, MessageId),
+		/// The call from the message has been rejected by the call filter.
+		MessageCallRejected(InstanceId, MessageId),
 		/// Phantom member, never used. Needed to handle multiple pallet instances.
 		_Dummy(PhantomData<I>),
 	}
@@ -269,6 +276,18 @@ impl<T: Config<I>, I: Instance> MessageDispatch<T::MessageId> for Module<T, I> {
 			}
 		};
 
+		// filter the call
+		if !T::CallFilter::filter(&call) {
+			frame_support::debug::trace!(
+				"Message {:?}/{:?}: the call ({:?}) is rejected by filter",
+				bridge,
+				id,
+				call,
+			);
+			Self::deposit_event(RawEvent::MessageCallRejected(bridge, id));
+			return;
+		}
+
 		// verify weight
 		// (we want passed weight to be at least equal to pre-dispatch weight of the call
 		// because otherwise Calls may be dispatched at lower price)
@@ -488,6 +507,7 @@ mod tests {
 		type TargetChainAccountPublic = TestAccountPublic;
 		type TargetChainSignature = TestSignature;
 		type Call = Call;
+		type CallFilter = TestCallFilter;
 		type EncodedCall = EncodedCall;
 		type AccountIdConverter = AccountIdConverter;
 	}
@@ -501,6 +521,14 @@ mod tests {
 		}
 	}
 
+	pub struct TestCallFilter;
+
+	impl Filter<Call> for TestCallFilter {
+		fn filter(call: &Call) -> bool {
+			!matches!(*call, Call::System(frame_system::Call::fill_block(_)))
+		}
+	}
+
 	const TEST_SPEC_VERSION: SpecVersion = 0;
 	const TEST_WEIGHT: Weight = 1_000_000_000;
 
@@ -668,6 +696,31 @@ mod tests {
 		});
 	}
 
+	#[test]
+	fn should_emit_event_for_rejected_calls() {
+		new_test_ext().execute_with(|| {
+			let bridge = b"ethb".to_owned();
+			let id = [0; 4];
+
+			let call = Call::System(<frame_system::Call<TestRuntime>>::fill_block(Perbill::from_percent(75)));
+			let weight = call.get_dispatch_info().weight;
+			let mut message = prepare_root_message(call);
+			message.weight = weight;
+
+			System::set_block_number(1);
+			CallDispatch::dispatch(bridge, id, Ok(message));
+
+			assert_eq!(
+				System::events(),
+				vec![EventRecord {
+					phase: Phase::Initialization,
+					event: TestEvent::call_dispatch(Event::<TestRuntime>::MessageCallRejected(bridge, id)),
+					topics: vec![],
+				}],
+			);
+		});
+	}
+
 	#[test]
 	fn should_dispatch_bridge_message_from_root_origin() {
 		new_test_ext().execute_with(|| {