path: root/src/export_fun.rs

//! allow sub-programs to invoke arbitrary user-defined functions via a unix socket

use libc::gid_t;
use libc::uid_t;
use nix::poll::PollFd;
use nix::poll::PollFlags;
use nix::poll::poll;

use crate::Session;
use crate::defer;
use crate::rw::*;
use crate::run::get_command_kind;
use std::env::current_exe;
use std::ffi::OsStr;
use std::fs;
use std::fs::File;
use std::io;
use std::io::IoSliceMut;
use std::io::Read;
use std::io::Write;
use std::os::fd::AsFd;
use std::os::fd::FromRawFd;
use std::os::fd::OwnedFd;
use std::os::unix::ffi::OsStrExt;
use std::os::unix::fs::symlink;
use std::os::unix::net::AncillaryData;
use std::os::unix::net::SocketAncillary;
use std::os::unix::net::SocketCred;
use std::os::unix::net::UnixListener;
use std::os::unix::net::UnixStream;
use std::path::PathBuf;
use std::process::Command;
use std::process::exit;
use std::sync::Arc;
use std::sync::Mutex;
use std::sync::mpsc;
use std::sync::mpsc::Receiver;
use std::thread;
use std::time::Duration;

const PATH: &str = "PATH";
const DATA: &str = "PISH_DATA";

fn get_uid() -> gid_t {
    unsafe { libc::getuid() }
}

fn get_gid() -> gid_t {
    unsafe { libc::getgid() }
}

fn handle_server(session: Arc<Mutex<Session>>, mut stream: UnixStream) -> io::Result<()> {
    // TODO: figure out how to get a reasonable limit on CLI arg len
    let mut buf = [0u8; 8192];
    let mut iov = [IoSliceMut::new(&mut buf)];

    let mut ancillary_buf = [0u8; 128];
    let mut ancillary = SocketAncillary::new(&mut ancillary_buf);

    let mut fds: Vec<i32> = Vec::new();

    let bytelen = stream.recv_vectored_with_ancillary(&mut iov, &mut ancillary)?;

    let mut explicit_auth = false;

    for msg in ancillary.messages() {
        let Ok(msg) = msg else { continue };
        match msg {
            AncillaryData::ScmRights(rights) => {
                for fd in rights {
                    fds.push(fd);
                }
            }
            AncillaryData::ScmCredentials(creds) => {
                for cred in creds {
                    eprintln!("cred: {}/{}", cred.get_uid(), cred.get_gid());
                    if cred.get_gid() == get_gid() && cred.get_uid() == get_uid() {
                        explicit_auth = true;
                    }
                }
            }
        }
    }

    let mut implicit_auth = false;
    if let Ok(peer) = stream.peer_cred()
        && peer.uid == get_uid()
        && peer.gid == get_gid()
    {
        implicit_auth = true;
    }

    if !explicit_auth && !implicit_auth {
        return Ok(());
    }

    if fds.len() != 3 {
        // malformed
        return Ok(());
    }

    let Ok(cli_args) = crate::serialization::deserialize_cli_args(&buf[..bytelen]) else {
        // cli args malformed
        return Ok(());
    };

    if cli_args.is_empty() {
        // malformed
        return Ok(());
    };

    let se = session.lock().unwrap();
    match get_command_kind(&se, cli_args[0].as_slice()) {
        crate::run::CommandKind::Fun(_) => (),
        crate::run::CommandKind::Path(_) | crate::run::CommandKind::Builtin(_) => {
            return Ok(());
        }
    }
    drop(se);

    let stdin = File::from(unsafe { OwnedFd::from_raw_fd(fds[0]) });
    let stdout = File::from(unsafe { OwnedFd::from_raw_fd(fds[1]) });

    let res = crate::run::Executor::execute_fun(
        session,
        cli_args,
        Input::File(stdin),
        Output::File(stdout),
    );

    let exit_code = match res {
        Ok(_) => 0,
        Err(e) => match e {
            crate::run::ExecError::ExecError(x) => x,
            _ => -3,
        },
    };

    let _ = stream.set_write_timeout(Some(Duration::from_secs(1)));
    stream.write_all(&exit_code.to_le_bytes())?;

    Ok(())
}

fn handle_client(mut stream: UnixStream, uid: uid_t, gid: gid_t) -> io::Result<()> {
    // give up all my file descriptors
    let mut ancillary_buffer = [0; 128];
    let mut ancillary = SocketAncillary::new(&mut ancillary_buffer[..]);
    assert!(ancillary.add_fds(&[0, 1, 2]));

    // add credentials
    let mut creds = SocketCred::new();
    creds.set_pid(std::process::id() as _);
    creds.set_uid(uid);
    creds.set_gid(gid);
    assert!(ancillary.add_creds(&[creds]));

    // cli params
    let buf = crate::serialization::serialize_cli_args();
    let bufs = &mut [io::IoSlice::new(&buf[..])][..];

    // send
    stream.send_vectored_with_ancillary(bufs, &mut ancillary)?;

    // recv exit code
    let mut exit_buf = [0; 4];
    let res = stream.read_exact(&mut exit_buf);

    let exit_code = match res {
        Ok(_) => i32::from_le_bytes(exit_buf),
        Err(_) => -2,
    };

    exit(exit_code)
}

/// sets up the commands `PATH` to allow it to invoke this shell sessions user-defined functions
pub fn prepare_command(session: Arc<Mutex<Session>>, cmd: &mut Command) {
    let Ok(session) = session.lock() else {
        return;
    };

    let Some(sr) = session.socket_running.as_ref() else {
        return;
    };

    let my_path = std::env::var_os(PATH).expect("no PATH - seriously?");
    let mut new_path = sr.bin_path.as_os_str().as_bytes().to_vec();
    new_path.push(b':');
    new_path.extend_from_slice(my_path.as_bytes());

    // we attach uid/gid such that launched subprocess know as which user to authenticate
    // it might be sudo-ed, which can again authenticate as the expected uid/gid
    // a subprocess with CAP_ADMIN can also impersonate uid/gids to the best of my
    // knowledge
    let mut data = Vec::new();
    data.extend_from_slice(sr.socket_path.as_os_str().as_bytes());
    data.push(b':');
    data.extend_from_slice(get_uid().to_string().as_bytes());
    data.push(b':');
    data.extend_from_slice(get_gid().to_string().as_bytes());

    cmd.env(PATH, OsStr::from_bytes(&new_path));
    cmd.env(DATA, OsStr::from_bytes(&data));
}

pub fn maybe_run_defined_function() {
    let Some(program_name) = std::env::args_os().next() else {
        return;
    };

    let program_name = program_name.as_bytes();

    if program_name.contains(&b'/') {
        return;
    }

    if program_name == b"pish" {
        return;
    }

    let Some(data) = std::env::var_os(DATA) else {
        return;
    };

    let data = data.as_bytes().to_vec();
    let mut it = data.split(|x| *x == b':');
    let socket = it.next().unwrap();
    let uid: uid_t = String::from_utf8_lossy(it.next().unwrap()).parse().unwrap();
    let gid: gid_t = String::from_utf8_lossy(it.next().unwrap()).parse().unwrap();

    if let Ok(stream) = UnixStream::connect(OsStr::from_bytes(&socket)) {
        let _ = handle_client(stream, uid, gid);
    }

    exit(-1);
}

fn unique_string() -> String {
    use std::collections::hash_map::DefaultHasher;
    use std::hash::{Hash, Hasher};
    use std::process;
    use std::time::{SystemTime, UNIX_EPOCH};

    let pid = process::id();
    let now = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap()
        .as_nanos();

    let mut hasher = DefaultHasher::new();
    pid.hash(&mut hasher);
    now.hash(&mut hasher);

    let hash = hasher.finish();
    let hex = format!("{:016x}", hash);

    hex[..12.min(hex.len())].to_string()
}

pub struct SocketRunning {
    bin_path: PathBuf,
    socket_path: PathBuf,
    recv: Receiver<()>,
}

#[must_use]
struct SocketDropper {
    session: Arc<Mutex<Session>>,
}

impl Drop for SocketDropper {
    fn drop(&mut self) {
        // mark socket for closing by `take`ing the socket_running value
        let session = &self.session;
        let Ok(mut se) = session.lock() else { return };
        let Some(sr) = se.socket_running.take() else {
            return;
        };

        // need to unlock since background thread also accesses session
        drop(se);

        // wait 1s for background to exit
        if let Err(e) = sr.recv.recv_timeout(Duration::from_secs(1)) {
            eprintln!(
                "background thread is still running({e:?}, session might not be cleaned up\r"
            );
        }
    }
}

#[must_use]
pub fn listen(session: Arc<Mutex<Session>>) -> impl Drop {
    let session_id = unique_string();
    let session_dir = crate::basedir::data_dir().join("session").join(session_id);
    let bin_dir = session_dir.join("bin");
    std::fs::create_dir_all(&bin_dir).unwrap();
    let socket_path = session_dir.join("cmd.sock");

    let (send, recv) = mpsc::channel();

    {
        let mut se = session.lock().unwrap();
        assert!(se.socket_running.is_none());
        se.socket_running = Some(SocketRunning {
            bin_path: bin_dir,
            socket_path: socket_path.clone(),
            recv,
        });
    }

    let se = session.clone();
    thread::spawn(move || {
        defer! {
            let _ = fs::remove_dir_all(session_dir);
            let _ = send.send(());
        };

        let listener = UnixListener::bind(socket_path).unwrap();
        listener.set_nonblocking(true).unwrap();
        let timeout_ms: u16 = 200;

        loop {
            // poll socket with timeout
            let mut poll_fds = [PollFd::new(listener.as_fd(), PollFlags::POLLIN)];
            let is_ready = match poll(&mut poll_fds, timeout_ms) {
                Ok(0) => false,
                Ok(_) => true,
                Err(_) => false,
            };

            // check if we should terminate
            match se.lock() {
                Err(_) => break,
                Ok(se) if se.socket_running.is_none() => break,
                _ => (),
            }

            if is_ready && let Ok((stream, _addr)) = listener.accept() {
                let se = se.clone();
                thread::spawn(move || handle_server(se, stream));
            }
        }
    });

    SocketDropper { session }
}

fn create_function_hook_res(
    session: Arc<Mutex<Session>>,
    fun_name: &[u8],
) -> Result<(), Box<dyn std::error::Error>> {
    let session = session.lock().map_err(|e| format!("{e:?}"))?;
    let sock_run = session.socket_running.as_ref().ok_or("no socket running")?;
    let exe_path = current_exe()?;
    let symlink_path = sock_run.bin_path.join(OsStr::from_bytes(fun_name));
    symlink(exe_path, symlink_path)?;
    Ok(())
}

pub fn create_function_hook(session: Arc<Mutex<Session>>, fun_name: &[u8]) {
    if let Err(e) = create_function_hook_res(session, fun_name) {
        println!("failed to create function hook: {e:?}");
    }
}