XCM paid execution barrier supports more origin altering instructions

polkadot/xcm/xcm-builder/src/barriers.rs

@@ -57,8 +57,9 @@ const MAX_ASSETS_FOR_BUY_EXECUTION: usize = 2;
 /// Allows execution from `origin` if it is contained in `T` (i.e. `T::Contains(origin)`) taking
 /// payments into account.
 ///
-/// Only allows for `TeleportAsset`, `WithdrawAsset`, `ClaimAsset` and `ReserveAssetDeposit` XCMs
-/// because they are the only ones that place assets in the Holding Register to pay for execution.
+/// Only allows for `WithdrawAsset`, `ReceiveTeleportedAsset`, `ReserveAssetDeposited` and
+/// `ClaimAsset` XCMs because they are the only ones that place assets in the Holding Register to
+/// pay for execution.
 pub struct AllowTopLevelPaidExecutionFrom<T>(PhantomData<T>);
 impl<T: Contains<Location>> ShouldExecute for AllowTopLevelPaidExecutionFrom<T> {
 	fn should_execute<RuntimeCall>(
@@ -81,9 +82,9 @@ impl<T: Contains<Location>> ShouldExecute for AllowTopLevelPaidExecutionFrom<T>
 		instructions[..end]
 			.matcher()
 			.match_next_inst(|inst| match inst {
+				WithdrawAsset(ref assets) |
 				ReceiveTeleportedAsset(ref assets) |
 				ReserveAssetDeposited(ref assets) |
-				WithdrawAsset(ref assets) |
 				ClaimAsset { ref assets, .. } =>
 					if assets.len() <= MAX_ASSETS_FOR_BUY_EXECUTION {
 						Ok(())
@@ -92,7 +93,10 @@ impl<T: Contains<Location>> ShouldExecute for AllowTopLevelPaidExecutionFrom<T>
 					},
 				_ => Err(ProcessMessageError::BadFormat),
 			})?
-			.skip_inst_while(|inst| matches!(inst, ClearOrigin))?
+			.skip_inst_while(|inst| {
+				matches!(inst, ClearOrigin | AliasOrigin(..)) ||
+					matches!(inst, DescendOrigin(child) if child != &Here)
+			})?
 			.match_next_inst(|inst| match inst {
 				BuyExecution { weight_limit: Limited(ref mut weight), .. }
 					if weight.all_gte(max_weight) =>

polkadot/xcm/xcm-builder/src/tests/barriers.rs

@@ -283,6 +283,56 @@ fn allow_paid_should_work() {
 	assert_eq!(r, Ok(()))
 }
 
+#[test]
+fn allow_paid_should_deprivilege_origin() {
+	AllowPaidFrom::set(vec![Parent.into()]);
+	let fees = (Parent, 1).into();
+
+	let mut paying_message_clears_origin = Xcm::<()>(vec![
+		ReserveAssetDeposited((Parent, 100).into()),
+		ClearOrigin,
+		BuyExecution { fees, weight_limit: Limited(Weight::from_parts(30, 30)) },
+		DepositAsset { assets: AllCounted(1).into(), beneficiary: Here.into() },
+	]);
+	let r = AllowTopLevelPaidExecutionFrom::<IsInVec<AllowPaidFrom>>::should_execute(
+		&Parent.into(),
+		paying_message_clears_origin.inner_mut(),
+		Weight::from_parts(30, 30),
+		&mut props(Weight::zero()),
+	);
+	assert_eq!(r, Ok(()));
+
+	let mut paying_message_aliases_origin = paying_message_clears_origin.clone();
+	paying_message_aliases_origin.0[1] = AliasOrigin(Parachain(1).into());
+	let r = AllowTopLevelPaidExecutionFrom::<IsInVec<AllowPaidFrom>>::should_execute(
+		&Parent.into(),
+		paying_message_aliases_origin.inner_mut(),
+		Weight::from_parts(30, 30),
+		&mut props(Weight::zero()),
+	);
+	assert_eq!(r, Ok(()));
+
+	let mut paying_message_descends_origin = paying_message_clears_origin.clone();
+	paying_message_descends_origin.0[1] = DescendOrigin(Parachain(1).into());
+	let r = AllowTopLevelPaidExecutionFrom::<IsInVec<AllowPaidFrom>>::should_execute(
+		&Parent.into(),
+		paying_message_descends_origin.inner_mut(),
+		Weight::from_parts(30, 30),
+		&mut props(Weight::zero()),
+	);
+	assert_eq!(r, Ok(()));
+
+	let mut paying_message_fake_descends_origin = paying_message_clears_origin.clone();
+	paying_message_fake_descends_origin.0[1] = DescendOrigin(Here.into());
+	let r = AllowTopLevelPaidExecutionFrom::<IsInVec<AllowPaidFrom>>::should_execute(
+		&Parent.into(),
+		paying_message_fake_descends_origin.inner_mut(),
+		Weight::from_parts(30, 30),
+		&mut props(Weight::zero()),
+	);
+	assert_eq!(r, Err(ProcessMessageError::Overweight(Weight::from_parts(30, 30))));
+}
+
 #[test]
 fn suspension_should_work() {
 	TestSuspender::set_suspended(true);

prdoc/pr_5917.prdoc

@@ -0,0 +1,14 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: "XCM paid execution barrier supports more origin altering instructions"
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      Updates the `AllowTopLevelPaidExecutionFrom` barrier to also support messages that
+      use `DescendOrigin` or `AliasOrigin` for altering the computed origin during execution.
+
+crates:
+  - name: staging-xcm-builder
+    bump: patch