Bad 'ctor' initialization

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 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 behaviour 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 use 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

• GitHub: rust-ctor - Warnings.
• Rust Programming Language: Crate std - Use before and after main().
• Common Weakness Enumeration: CWE-696.
• Common Weakness Enumeration: CWE-665.