Integer Overflow Vulnerabilities and Their Protection

Integer overflow is a common programming issue, especially in blockchain smart contract development, which requires extra attention. Integer overflow occurs when the calculation result exceeds the range that the integer type can represent.

Integer overflow can be divided into two cases: overflow and underflow. Overflow refers to the result exceeding the maximum value, for example, adding 1 to the maximum value of uint32 type, 4,294,967,295, will result in 0. Underflow refers to the result being less than the minimum value, for example, subtracting 1 from 0 of uint32 type will result in 4,294,967,295.

Taking BeautyChain's BEC token as an example, attackers have exploited an integer overflow vulnerability to obtain a large number of tokens. In its batchTransfer function, amount = cnt * _value may overflow, causing the require statement that checks the balance to fail.

To prevent integer overflow, Rust developers can take the following measures when developing smart contracts:

1. Configure integer overflow checks in release mode in Cargo.toml.

2. Use the uint crate to support larger integer types, such as U256, U512, etc.

3. Use uint type conversion functions to check for overflow, such as as_u128().

4. Use Safe Math functions such as checked_add(), checked_sub(), etc. for safe operations.

5. Unwrap or expect the Option result returned by the Safe Math function.

By using these methods, the security risks posed by integer overflow can be effectively avoided. In smart contract development, one should always be vigilant about integer overflow issues and take necessary protective measures.