upgrayedd

"Two Ds for a double dose of debugging."

[!WARNING] You do not need this library. Do not use this library, especially in production systems. It is not safe, even if you only use safe Rust with it. It cannot be made safe.

upgrayedd is a convenience proc macro for building function interposition tools in Rust. When used in a shared library build (which is the only way you should be using it), it makes LD_PRELOAD-style interposition look like (relatively) idiomatic Rust.

Usage

Interposing on an OpenSSL API:

use upgrayedd::upgrayedd;

#[upgrayedd]
fn X509_VERIFY_PARAM_set_auth_level(param: *mut std::ffi::c_void, level: std::ffi::c_int) {
    eprintln!("before!");
    unsafe { upgrayedd(param, level) };
    eprintln!("after!");
}

Rewriting parameters:

use upgrayedd::upgrayedd;

#[upgrayedd]
fn frobulate(size: libc::size_t) {
    unsafe { upgrayedd(size + 42) };
}

Stubbing functions out:

use upgrayedd::upgrayedd;

#[upgrayedd]
fn verify_cert(cert: *mut std::ffi::c_void) -> libc::c_int {
    // nothing to see here
    1
}

See the docs for more usage examples.

Limitations

• Fundamentally unsafe. Again: please do not use this for anything serious.
• Hooking "basic" routines (like malloc and free) may or may not work, depending on what you put in your hook. In particular, if you accidentally recurse while holding a lock (which is easy to do when hooking malloc and calling println!), you'll probably end up deadlocking.
• Bad things will definitely happen if you try to pass Rust types into wrapped C functions, which upgrayedd will happily let you do.
• Bad things will definitely happen if you supply the wrong function signature, which upgrayedd will happily let you do.
• Only C functions can currently be wrapped; C++ would probably work with small tweaks.
• Currently Linux only. Other OSes would probably work with small tweaks.