Bound number of assets which can be withdrawn to pay for execution. (#7641)

* Bound number of assets which can be withdrawn to pay for execution.

* ".git/.scripts/commands/fmt/fmt.sh"

* Include ClaimAsset in limiting the assets

* Change max assets to constant

---------

Co-authored-by: command-bot <>
Co-authored-by: Francisco Aguirre <[email protected]>

Author: gavofyork

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

@@ -52,6 +52,8 @@ impl ShouldExecute for TakeWeightCredit {
 	}
 }
 
+const MAX_ASSETS_FOR_BUY_EXECUTION: usize = 1;
+
 /// Allows execution from `origin` if it is contained in `T` (i.e. `T::Contains(origin)`) taking
 /// payments into account.
 ///
@@ -79,10 +81,10 @@ impl<T: Contains<MultiLocation>> ShouldExecute for AllowTopLevelPaidExecutionFro
 		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))?