Mimo August 2022 contest - JC's results

Table of Contents:

L-01 Unused receive() function will lock Ether in contract

N-01 Lock pragmas to specific compiler version N-02 Use a more recent version of solidity

L-01 Unused receive() function will lock Ether in contract

If the intention is for the Ether to be used, the function should call another function, otherwise it should revert.

There is 1 instance: https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L38

N-01 Lock pragmas to specific compiler version

Contracts should be deployed with the same compiler version and flags that they have been tested with thoroughly. Locking the pragma helps to ensure that contracts do not accidentally get deployed using, for example, an outdated compiler version that might introduce bugs that affect the contract system negatively. see https://swcregistry.io/docs/SWC-103

Instances include: MIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L2

MIMOProxyFactory.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxyFactory.sol#L2

MIMOProxyRegistry.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxyRegistry.sol#L2

IMIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/interfaces/IMIMOProxy.sol#L2

IMIMOProxyFactory.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/interfaces/IMIMOProxyFactory.sol#L2

IMIMOProxyRegistry.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/interfaces/IMIMOProxyRegistry.sol#L2

N-02 Use a more recent version of solidity

Use a solidity version of at least 0.8.12 to get string.concat() instead of abi.encodePacked(<str>,<str>) Use a solidity version of at least 0.8.13 to get the ability to use using for with a list of free functions

Instances: all contracts (27)

Table of Contents:

G-01 State variables only set in the constructor should be declared immutable G-02 ++i costs less gas than i++, especially when it's used in for loops G-03 ++i/i++ should be unchecked{++i}/unchecked{i++} G-04 <array>.length should not be looked up in every loop of a for-loop G-05 Using storage instead of memory for structs/arrays saves gas G-06 Comparison operators G-07 Use a more recent version of solidity G-08 Using private rather than public for constants saves gas G-09 calldata instead of memory for read-only function parameter G-11 Using > 0 costs more gas than != 0 when used on a uint in a require() statement G-12 Empty blocks should be removed or emit something G-13 Using bools for storage incurs overhead G-14 Using storage instead of memory for structs/arrays saves gas

G-01 State variables only set in the constructor should be declared immutable

Avoids a Gsset (20000 gas) in the constructor, and replaces each Gwarmacces (100 gas) with a PUSH32 (3 gas).

There is 1 instance: MIMOProxyRegistry.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxyRegistry.sol#L16

G-02 ++i costs less gas than i++, especially when it's used in for loops

There is 1 instance: MIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L132

G-03 ++i/i++ should be unchecked{++i}/unchecked{i++}

There is 1 instance: MIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L132

G-04 <array>.length should not be looked up in every loop of a for-loop

There is 1 instance: MIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L132

G-05 Using storage instead of memory for structs/arrays saves gas

There is 1 instance: MIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L131

G-06 Comparison operators

In the EVM, there is no opcode for >= or <=. When using greater than or equal, two operations are performed: > and =. Using strict comparison operators hence saves gas.

There are 5 instances: MIMOEmptyVault.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOEmptyVault.sol#L96

MIMOLeverage.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOLeverage.sol#L130

MIMORebalance.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMORebalance.sol#L130

MIMOAutoAction.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoAction.sol#L45

MIMOManagedAction.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/MIMOManagedAction.sol#L120

G-07 Use a more recent version of solidity

Use a solidity version of at least 0.8.12 to get string.concat() instead of abi.encodePacked(<str>,<str>) Use a solidity version of at least 0.8.13 to get the ability to use using for with a list of free functions

Instances: all contracts (27)

G-08 Using private rather than public for constants saves gas

If needed, the value can be read from the verified contract source code. Savings are due to the compiler not having to create non-payable getter functions for deployment calldata, and not adding another entry to the method ID table.

There is 1 instance: Project.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxyFactory.sol#L19

G-09 calldata instead of memory for read-only function parameter

If a reference type function parameter is read-only, it is cheaper in gas to use calldata instead of memory. Calldata is a non-modifiable, non-persistent area where function arguments are stored, and behaves mostly like memory. Try to use calldata as a data location because it will avoid copies and also makes sure that the data cannot be modified.

There are 9 instances: MIMOAutoRebalance.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoRebalance.sol#L166 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoRebalance.sol#L167 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoRebalance.sol#L205 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoRebalance.sol#L206 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoRebalance.sol#L237 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoRebalance.sol#L263

MIMOManagedAction.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/MIMOManagedAction.sol#L116

MIMOManagedRebalance.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/MIMOManagedRebalance.sol#L143 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/MIMOManagedRebalance.sol#L180

G-10 internal functions only called once can be inlined to save gas

Not inlining costs 20 to 40 gas because of two extra JUMP instructions and additional stack operations needed for function calls.

There are 7 instances: MIMOSwap.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOSwap.sol#L40-L44

MIMOAutoAction.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoAction.sol#L92-L96

MIMOAutoRebalance.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoRebalance.sol#L165-L172 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoRebalance.sol#L204-L212 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/MIMOAutoRebalance.sol#L236-L240

MIMOManagedAction.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/MIMOManagedAction.sol#L115-L119

MIMOManagedRebalance.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/MIMOManagedRebalance.sol#L179-L187

G-11 Using > 0 costs more gas than != 0 when used on a uint in a require() statement

This change saves 6 gas per instance.

There is 1 instance: MIMORebalance.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMORebalance.sol#L135

G-12 Empty blocks should be removed or emit something

The code should be refactored such that they no longer exist, or the block should do something useful, such as emitting an event or reverting. If the contract is meant to be extended, the contract should be abstract and the function signatures be added without any default implementation. If the block is an empty if-statement block to avoid doing subsequent checks in the else-if/else conditions, the else-if/else conditions should be nested under the negation of the if-statement, because they involve different classes of checks, which may lead to the introduction of errors when the code is later modified (if(x){}else if(y){...}else{...} => if(!x){if(y){...}else{...}})

There are 2 instances: MIMOFlashloan.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOFlashloan.sol#L44

MIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L38

G-13 Using bools for storage incurs overhead

Booleans are more expensive than uint256 or any type that takes up a full word because each write operation emits an extra SLOAD to first read the slot's contents, replace the bits taken up by the boolean, and then write back. This is the compiler's defense against contract upgrades and pointer aliasing, and it cannot be disabled. https://github.com/OpenZeppelin/openzeppelin-contracts/blob/58f635312aa21f947cae5f8578638a85aa2519f5/contracts/security/ReentrancyGuard.sol#L23-L27

There are 9 instances: MIMOSwap.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOSwap.sol#L52

IMIMOAutoAction.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/automated/interfaces/IMIMOAutoAction.sol#L9

MIMOManagedAction.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/MIMOManagedAction.sol#L17 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/MIMOManagedAction.sol#L55

IMIMOManagedAction.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/interfaces/IMIMOManagedAction.sol#L13 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/managed/interfaces/IMIMOManagedAction.sol#L13

MIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L78 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L108

IMIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/interfaces/IMIMOProxy.sol#L67

G-14 Using storage instead of memory for structs/arrays saves gas

When fetching data from a storage location, assigning the data to a memory variable causes all fields of the struct/array to be read from storage, which incurs a Gcoldsload (2100 gas) for each field of the struct/array. If the fields are read from the new memory variable, they incur an additional MLOAD rather than a cheap stack read. Instead of declearing the variable with the memory keyword, declaring the variable with the storage keyword and caching any fields that need to be re-read in stack variables, will be much cheaper, only incuring the Gcoldsload for the fields actually read. The only time it makes sense to read the whole struct/array into a memory variable, is if the full struct/array is being returned by the function, is being passed to a function that requires memory, or if the array/struct is being read from another memory array/struct

There are 6 instances: MIMOEmptyVault.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOEmptyVault.sol#L49

MIMOFlashloan.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOFlashloan.sol#L52 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOFlashloan.sol#L53 https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOFlashloan.sol#L54

MIMOSwap.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/actions/MIMOSwap.sol#L52

MIMOProxy.sol https://github.com/code-423n4/2022-08-mimo/blob/eb1a5016b69f72bc1e4fd3600a65e908bd228f13/contracts/proxy/MIMOProxy.sol#L131