rhook

Hook libc functions with an easy API

Usage

1- Import the trait [RunHook]

2- Create an Command with Command::new and add hooks to it via add_hook and add_hooks methods

3- Confirm the hooks with set_hooks method this step is necessary

3.1- Hooks are closures that takes no input and return an option of the libc function as output.

If the closure return None that is equivalent to returning Some(original_function(args)) in other words it will run and use the original function output

Inside the closure you have access to the libc function input + some imports from std (see src/scaffold.rs)

4- Now you can carry on with the usual Command methods (output, spawn,status,..)

Tricks:

The closure used for hooks have acess to many things: (imported by https://github.com/sigmaSd/Rhook/blob/master/src/scaffold.rs)

• closure input (which is the libc function input)
• closure output (which is the libc function output)
• The original function with the following name original_$libcfn this is useful in particular to avoid recursion
• Some varaibles to make coding easier: transmute ManuallyDrop CString and a static mut COUNTER
• You can find the input/output of a function by looking it up here libc
• Add .map_err(|e|println("{}",e)) after set_hooks in order to prettify the dynamic library compiling error while debugging
• If you take ownership of an input value inside of the closure, be sure to use ManuallyDrop so you don't free it

Example

Say you want to limit the bandwidth of a program

Usually downloading calls libc::recv function

So our goal is to throttle it with a simple sleep

To do that with this crate: (taking speedtest program as an example)

1- Look up its doc's here recv to see what the function's input/output is

2- use this crate

use rhook::{RunHook, Hook};

std::process::Command::new("speedtest").add_hook(Hook::recv(stringify!(||{
 std::thread::sleep(std::time::Duration::from_millis(10));
 // since we're not doing any modification to the output you can just return None here
 Some(original_recv(socket, buf, len, flags))
}))).set_hooks().unwrap().spawn();

Thats it! Note that you have acess inside the closure to the original function denoted by the prefix original_ + the function name

Check out the examples for more info

License: MIT