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feat: add FMA for operator fee (#186)
* add FMA for operator fee * feedbacks * feat: add more failure modes * fix: TOC * feat: remove generic items * feat: add a generic item * fix: handle feedbacks * fix: handle more feedbacks * handle blmalone feedbacks * feat: add database growth rate action * feat: add Database Growth simulation * feat: move to "Implementing Actions" --------- Co-authored-by: Ratan Kaliani <[email protected]>
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‎security/fma-operator-fee.md‎

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# [Operator Fee]: Failure Modes and Recovery Path Analysis
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<!-- START doctoc generated TOC please keep comment here to allow auto update -->
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<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
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- [Introduction](#introduction)
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- [Failure Modes and Recovery Paths](#failure-modes-and-recovery-paths)
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- [FM1: Operator Fee scalars are set to incorrect values](#fm1-operator-fee-scalars-are-set-to-incorrect-values)
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- [FM2: Broken Fee Estimation (Wallets)](#fm2-broken-fee-estimation-wallets)
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- [FM3: Bug in Receipt Hydrating Logic](#fm3-bug-in-receipt-hydrating-logic)
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- [FM4: Database Growth Impact on Nodes](#fm4-database-growth-impact-on-nodes)
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- [Action Items](#action-items)
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<!-- END doctoc generated TOC please keep comment here to allow auto update -->
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| | |
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| ------------------ | -------------------------------------------------- |
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| Author | leruaa |
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| Created at | 2025-01-08 |
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| Initial Reviewers | Mark Tyneway |
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| Need Approval From | Blaine Malone |
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| Status | Implementing Actions |
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## Introduction
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This document covers initial deployment of Operator Fee.
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The OperatorFee is a new transaction fee that allows new OP chain variants to account for their unique cost structure. For example, the existing fee structure isn't friendly to chains using alt-DA's, since the l1fee only accounts for Ethereum's blobGasFee instead of an alt-DA's fee.
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Also, For OP Stack variants that want to utilize ZK proofs, the cost of ZK proving a transaction is a significant resource that is not taken into consideration in the current fee structure.
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Below are references for this project:
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- [Design Doc](../protocol/operator-fee.md)
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- [Spec](https://github.com/ethereum-optimism/specs/pull/382)
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## Failure Modes and Recovery Paths
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### FM1: Operator Fee scalars are set to incorrect values
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- **Description:**
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If the operator fee scalars are incorrectly initialized or updated, there is a risk that the transactions fees will be too high. This could lead to a situation where the chain becomes unusable.
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- **Risk Assessment:**
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High impact, low likelihood.
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**Mitigations:**
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Before setting or updating the operator fee params, the operator should carefully read the [corresponding specs](https://specs.optimism.io/protocol/isthmus/exec-engine.html#operator-fee) and simulate the impact of operator fee on the whole transaction cost.
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- **Detection:**
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By default, the operator fee parameters are set to 0 and the feature is disabled. There are [E2E tests](https://github.com/ethereum-optimism/optimism/blob/develop/op-e2e/system/fees/fees_test.go) that ensure there is no impact on the transaction cost when the operator fee is disabled.
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On chains that enable operator fee, the operator should monitor the transaction cost and ensure that the operator fee is not too high.
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- **Recovery Path(s)**:
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If the operator fee parameters are set to unreasonable values, the rollup operator should update the `operatorFeeScalar` and `operatorFeeConstant` to reasonable values as soon as possible.
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With cast it can be done like this: `cast send <l1_system_config_address> "setOperatorFeeScalars(uint32, uint64)" <operator_fee_scalar> <operator_fee_constant>`
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### FM2: Broken Fee Estimation (Wallets)
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- **Description:**
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If wallets fail to update their fee estimation logic, users will no longer be shown the accurate costs of a transaction.
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- **Risk Assessment:**
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This failure mode can only happen on chains that enable the operator fee feature.
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Medium impact, medium likelihood.
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**Mitigations:**
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Coordinate with wallet providers to update their fee estimation logic. This includes MetaMask, Coinbase Wallet, and others.
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- **Detection:**
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Using a given wallet, compare the estimated transaction cost with the actual transaction cost, and check if the difference relates to the operator fee, using the formula.
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- **Recovery Path(s)**:
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Notify wallets of the new fee structure and ask them to update their fee estimation logic if the operator fee is enabled.
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### FM3: Bug in Receipt Hydrating Logic
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- **Description:**
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If there is a bug in the receipt hydrating logic, the operator fee may not be correctly reflected in transaction receipts, leading to incorrect fee reporting and potential accounting issues.
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- **Risk Assessment:**
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Medium impact, low likelihood.
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- **Mitigations:**
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Action and E2E tests covering the receipt hydration logic has been added.
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* [Fee E2E test](https://github.com/ethereum-optimism/optimism/blob/develop/op-e2e/system/fees/fees_test.go)
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* [Operator Fee Consistency action test](https://github.com/ethereum-optimism/optimism/blob/develop/op-e2e/actions/proofs/operator_fee_test.go)
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- **Detection:**
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The action or E2E tests or local testing may pick up an issue.
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- **Recovery Path(s):**
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Deploy fix for receipt hydration logic. Historical receipts will remain incorrect but can be recalculated using on-chain data if needed. The fix would be on the execution layer and will not require a hardfork.
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### FM4: Database Growth Impact on Nodes
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- **Description:**
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The addition of operator fee fields increases the size of transaction receipts, leading to faster database growth. This could accelerate the need for solutions like EIP-4444 or other history expiry mechanisms.
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- **Risk Assessment:**
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Medium impact, high likelihood.
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- **Mitigations:**
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Implement history expiry solutions like EIP-4444 when available.
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- **Detection:**
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- Monitor database growth rate compared to pre operator fee baseline.
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- Track disk usage metrics across internal nodes.
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The following simulation can give a view of the impact of operator fee on the node storage: Operator fee adds 12 bytes per L2 block (4 for operator fee scalar, 8 for operator fee constant). It also add 12 bytes
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per transaction (in the transaction receipt) So, with the arbitrary number of 20 txs per block we have:
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```
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(12 bytes + 240 bytes / 2 seconds) x 365 days × 24 hours × 60 minutes × 60 seconds = 3,973,536,000 bytes in 1 year.
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```
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So, about 3,7 GB for 1 year.
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- **Recovery Path(s):**
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- Use archive nodes to maintain historical data.
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- Consider implementing receipt compression retroactively if needed.
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### Generic items we need to take into account: `L1Block` badly hydrated
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- **Description:** At each hardfork, new data can be add to the `L1Block` contract, and the method called to hydrate it change (for instance
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`setL1BlockValuesEcotone` to `setL1BlockValuesIsthmus`). If there is a bug in a future method ending up to operator fee params no
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longer being updated in the `L1Block` contract, the operator fee will no longer be taken into account in transactions fee.
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- **Risk Assessment:** medium severity / low likelihood
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- **Mitigations:**
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The [Operator Fee Constistency](https://github.com/ethereum-optimism/optimism/blob/develop/op-e2e/actions/proofs/operator_fee_test.go ) action test runs with all known hardforks activated at genesis, and checks that operator fee parameters are correctly reported to the `L1Block` contract.
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- **Detection:**
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The action or E2E tests or local testing may pick up an issue.
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- **Recovery Path(s):**
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- If the bug is located in op-node, a new version must be deployed.
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- If the bug is located in the `L1Block` contract, the contract must be upgraded to fix the bug.
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## Action Items
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Below is what needs to be done before launch to reduce the chances of the above failure modes occurring, and to ensure they can be detected and recovered from:
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- [ ] Coordinate with wallet providers to update their fee estimation logic
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- [ ] Implement automated monitoring on dabase growth rate

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