Ability to charge extra fee for operational transaction to prevent spam

[xlc]

Previous issue: paritytech/substrate#10424

I believe it is currently possible to spam & congest a network by submitting a lot of operational transactions. They will fail but they will be included prior than normal transactions unless a sufficiently high tip is added.

This could also potentially block some critical operational transactions.

A simple solution is modify the transaction fee for any operational transaction to add a high enough base fee, and refund it if the transaction succeeds. This will raise the cost of attack via failing operational transactions.

[ggwpez]

Did you have an attack of this kind or is it just an observation?

[xlc]

There have been many attacks on Eth to spam & full the blocks to take advantages over some smart contracts. Similar attack can happen on DeFi chains for example when handling big liquidations. Acala is for example using orml oracle pallet to feed price and it is operational tx. It would be possible for someone to spam the blocks to delay the proper oracle feed and take advantages of that.

[rainbowpromise]

Hello @xlc
Hello @ggwpez

Could you provide a reference in the code?

[xlc]

The fee code is located at https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/transaction-payment/src/lib.rs