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Upgradeability Checks

Feist Josselin edited this page May 21, 2019 · 9 revisions

Upgradeability Checks

slither-check-upgradability is meant to help to review contracts using the delegatecall proxy pattern.

The tool checks that:

Usage

slither-check-upgradability proxy.sol ProxyName implem.sol ContractName

If a second version of the contract is to be checked, use:

slither-check-upgradeability proxy.sol ProxyName implem.sol ContractName implem_v2.sol ContractNameV2

proxy.sol/implem.sol can be a Truffle directory, for example:

slither-check-upgradability . ProxyName . ContractName

Proxy contract

If you use zos, you will have the proxy and the contract in different directories.

Likely, you will use one of the proxy from https://github.com/zeppelinos/zos. Clone the zos, and install the dependencies:

git clone https://github.com/zeppelinos/zos
cd zos/packages/lib
npm install
rm contracts/mocks/WithConstructorImplementation.sol

Note: contracts/mocks/WithConstructorImplementation.sol must be removed as it contains a name clash collision with contracts/mocks/Invalid.sol

Then from your project directory:

slither-check-upgradeability /path/to/zos/packages/lib/ UpgradeabilityProxy . ContractName

According to your setup, you might choose another proxy name than UpgradeabilityProxy.

Checks

Functions ids checks

slither-check-upgradeability checks that:

  • There is no function id collision between the proxy and the implementation
  • The proxy does not shadow any functions from the implementation

Variables order checks

slither-check-upgradeability checks that:

  • The variables are declared in the same order between the proxy and the implementation
  • The variables are declared in the implementation first and second version

slither-check-upgradeability will warn if the proxy has state variables. Consider using the Unstructured storage pattern for those variables.

Initialization checks

Contracts based on delegatecallproxy cannot be initialized through constructors. As a result, init functions must be used. These functions do not benefitfrom:

  • The Solidity C3 linearization. As a result, an init function can be called multiple times, or never.
  • The init functions must be calleable only once.
  • Race conditions can occur during deployement.

If the contract uses the zos library (and the Initializable contract), the util checks that:

  • All the initalize functions call the initializer modifier
  • All the inherits initalize functions are called
  • initialize functions are never called twice

Additionally, slither-check-upgradeability prints the functions that must be called during initialization.

If the contract uses another schema, no check is performed. In that case, the tool warns:

Initializable contract not found, the contract does not follow a standard initalization schema.
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