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Bad ‘ctor’ initialization — CodeQL query help documentation

ID: rust/ctor-initialization
Kind: path-problem
Security severity: 
Severity: error
Precision: high
Tags:
   - reliability
   - correctness
   - external/cwe/cwe-696
   - external/cwe/cwe-665
Query suites:
   - rust-security-and-quality.qls

Click to see the query in the CodeQL repository

Calling functions and methods in the Rust std library from a #[ctor] or #[dtor] function is not safe. This is because the std library only guarantees stability and portability between the beginning and the end of main, whereas #[ctor] functions are called before main, and #[dtor] functions are called after it.

Recommendation

Do not call any part of the std library from a #[ctor] or #[dtor] function. Instead either:

  • Move the code to a different location, such as inside your program’s main function.

  • Rewrite the code using an alternative library.

Example

In the following example, a #[ctor] function uses the println! macro which calls std library functions. This may cause unexpected behavior at runtime.

#[ctor::ctor]
fn bad_example() {
    println!("Hello, world!"); // BAD: the println! macro calls std library functions
}

The issue can be fixed by replacing println! with something that does not rely on the std library. In the fixed code below, we used the libc_println! macro from the libc-print library:

#[ctor::ctor]
fn good_example() {
    libc_print::libc_println!("Hello, world!"); // GOOD: libc-print does not use the std library
}

References