Bound number of assets which can be withdrawn to pay for execution.

xcm/xcm-builder/src/barriers.rs

@@ -72,17 +72,18 @@ impl<T: Contains<MultiLocation>> ShouldExecute for AllowTopLevelPaidExecutionFro
 		);
 
 		ensure!(T::contains(origin), ProcessMessageError::Unsupported);
+		let max_assets_for_buy_execution = 1;
 		// We will read up to 5 instructions. This allows up to 3 `ClearOrigin` instructions. We
 		// allow for more than one since anything beyond the first is a no-op and it's conceivable
 		// that composition of operations might result in more than one being appended.
 		let end = instructions.len().min(5);
 		instructions[..end]
 			.matcher()
 			.match_next_inst(|inst| match inst {
-				ReceiveTeleportedAsset(..) |
-				WithdrawAsset(..) |
-				ReserveAssetDeposited(..) |
-				ClaimAsset { .. } => Ok(()),
+				ReceiveTeleportedAsset(..) | ReserveAssetDeposited(..) => Ok(()),
+				WithdrawAsset(ref assets) if assets.len() <= max_assets_for_buy_execution => Ok(()),
+				ClaimAsset { ref assets, .. } if assets.len() <= max_assets_for_buy_execution =>
+					Ok(()),
 				_ => Err(ProcessMessageError::BadFormat),
 			})?
 			.skip_inst_while(|inst| matches!(inst, ClearOrigin))?