Overwrite string length in a fat pointer via /proc on Unix

str_length_hack.rs

fn main() {
    use std::fs::OpenOptions;
    use std::io::{Seek, SeekFrom, Write};

    let foo = "hello";
    let fat_ptr_ptr = &foo as *const _ as u64;

    println!("{fat_ptr_ptr}");
    println!("before = {foo}");

    let mut mem = OpenOptions::new().read(true).write(true).open("/proc/self/mem").unwrap();

    //let ptr = foo.as_ptr();
    mem.seek(SeekFrom::Start(fat_ptr_ptr as u64 + 8)).unwrap();
    let buf = &[2u8];
    mem.write(buf).unwrap();

    println!("after = {}", foo);
}