Trying Su

It’s been a while since I’ve written a log about my work, mostly because I’ve gone back to the drawing board for a bit. The reason I will be detailing below. However, I think I have come up with a solution that seems to be working well so far. Almost to an MVP level.

The way it works is by delegating the task of setting the correct permissions to su and then calling the child process with the correct permissions.

Note: su is a POSIX utility that allows you to run a command with a substitute user and group ID. It is included in the GNU coreutils package and is available on all Linux systems.

The way I am using it is by calling su with the username of the user, that can be passed using the flag -c. This will run the command as the user specified. The username can be parsed using the uid that we have already parsed. This Uid can be simply obtained from the passwd file.

So now, when we have to launch the child process, we can either directly add this to the send_command function in the SWHKD codebase or we can also spawn a green thread that will work off of a channel to get the command to run and then run it with su.

Direct call:

let mut child = Command::new("su");
child.arg(uname);
child.arg("-c");
child.arg(commands_to_send);

if let Err(e) = child.spawn() {
    log::error!("Child error: {}", e);
}

Green thread:

let (tx, rx) = mpsc::channel();
let uname = get_username(uid);
let commands_to_send = Vec::from(commands);

for command in commands_to_send {
    tx.send(command).unwrap();
}

tokio::spawn(move || {
    let commands_to_send = rx.recv().unwrap();
    let mut child = Command::new("su");
    child.arg(uname);
    child.arg("-c");
    child.arg(commands_to_send);

    if let Err(e) = child.spawn() {
        log::error!("Child error: {}", e);
    }
});

This is the basic idea of how I am planning to implement this. I will be working on this in the coming days and will update the log with the progress.

However, a very basic implementation looks as follows:

As you can see, there are still some issues that need to be resolved. The initial login with sudo would not be required when called from a window manager, but it is required when called from the terminal.

Moreover, the env variables are not being passed correctly, which in some cases is causing the GTK applications to not be able to read their cache. This too can be resolved by passing the env variables correctly.

I will be working on these issues in the coming days and will update the log with the progress.