Rust Smart Contracts Development Diary (7) Contract Security and Permission Control

This article will introduce permission control in Rust smart contracts from two perspectives:

1. Visibility of contract methods
2. Access control of privileged functions

1. Contract Function Visibility

Visibility control of contract functions is crucial for protecting key functionalities. For example, in the security incident of Bancor Network exchange in June 2020, the risk to user assets arose because a critical transfer function was mistakenly set to public.

In Rust smart contracts, there are the following types of function visibility:

• pub fn: public function, callable from external sources
• fn: Internal function, can only be called within the contract
• pub(crate) fn: restrict calling within crate

Additionally, defining a function in an impl block that is not modified by #[near_bindgen] can also make it an internal function.

For the callback function, it must be set to public but also ensure that it can only be called by the contract itself. This functionality can be achieved using the #[private] macro.

It should be noted that the default visibility in Rust is private, which is different from the default public in some versions of Solidity. The exceptions are that items in pub trait and pub enum are public by default.

2. Access Control of Privileged Functions

In addition to function visibility, a whitelist mechanism needs to be established to control access to privileged functions. Similar to the onlyOwner modifier in Solidity, an Ownable trait can be implemented:

rust pub trait Ownable { fn assert_owner(&self) { assert_eq!(env::predecessor_account_id(), self.get_owner()); } AccountId; fn set_owner(&mut self, owner: AccountId); }

This trait can restrict only the owner from calling certain privileged functions. Based on this principle, more complex whitelists can be set up to achieve fine-grained access control.

3. Other Access Control Methods

Other access control methods such as contract invocation timing control, multi-signature invocation mechanism, and DAO governance can also be considered. These will be detailed in subsequent articles.