Unsound usages of unsafe implementation about c_void

[llooFlashooll]

Hi, I am scanning this crate in the latest version using my own static analyzer tool.

Unsafe pointer conversion is found at:

pub fn create_with_value(name: &str, value: &T) -> Result<Self, CreateError> {
        let name_c = CString::new(name)?;

        let existing = unsafe { XPLMFindDataRef(name_c.as_ptr()) };
        if !existing.is_null() {
            return Err(CreateError::Exists);
        }

        let value = value.to_storage();
        let mut value_box = Box::new(value);
        let value_ptr: *mut T::Storage = value_box.as_mut();

        let id = unsafe {
            XPLMRegisterDataAccessor(
                name_c.as_ptr(),
                T::sim_type(),
                Self::writeable(),
                Self::int_read(),
                Self::int_write(),
                Self::float_read(),
                Self::float_write(),
                Self::double_read(),
                Self::double_write(),
                Self::int_array_read(),
                Self::int_array_write(),
                Self::float_array_read(),
                Self::float_array_write(),
                Self::byte_array_read(),
                Self::byte_array_write(),
                value_ptr as *mut c_void,
                value_ptr as *mut c_void,
            )
        };

        assert!(!id.is_null());
        Ok(OwnedData {
            id,
            value: value_box,
            access_phantom: PhantomData,
        })
    }

This unsound implementation would create memory issues such as overflow, underflow, or misalignment. The attacker can manipulate the argument value associated with the c_void pointer with an unexpected type or layout, which can lead to an out-of-bounds memory access bug. The c_void pointer is passed through the FFI (XPLMRegisterDataAccessor) as both read and write references, which can further corrupt the C/C++ code.

This would cause undefined behaviors in Rust. Adversaries can manipulate the associated argument to cause memory safety bugs. I am reporting this issue for your attention.