T04: own Unix pty so a failed chdir fails the start; closing logs and reaps
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use std::{
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collections::HashMap,
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ffi::{CStr, CString},
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fs::File,
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io::{self, ErrorKind, Read},
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mem::MaybeUninit,
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os::{
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fd::AsRawFd,
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unix::{ffi::OsStrExt, net::UnixStream, process::CommandExt},
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},
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path::Path,
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process::{Child, Command},
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sync::Arc,
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};
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use alacritty_terminal::{
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event::{OnResize, WindowSize},
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tty::{ChildEvent, EventedPty, EventedReadWrite, ToWinsize},
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};
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use polling::{Event, PollMode, Poller};
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use rustix_openpty::{
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openpty,
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rustix::termios::{self, InputModes, OptionalActions},
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};
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use signal_hook::{
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SigId,
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consts::SIGCHLD,
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low_level::{pipe, unregister},
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};
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/// The keys alacritty's event loop reads pty readiness by.
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const READ_WRITE: usize = 0;
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const CHILD: usize = 1;
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/// A program on a pseudo-terminal, started here so a failed `chdir` fails the start.
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pub(crate) struct Pty {
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child: Child,
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file: File,
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signals: UnixStream,
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sig: SigId,
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}
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impl Pty {
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pub fn id(&self) -> u32 {
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self.child.id()
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}
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}
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/// Starts `program`, or the login shell, in `cwd` on a new pty of `size`.
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pub(crate) fn spawn(
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program: Option<&(String, Vec<String>)>,
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cwd: &Path,
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env: &HashMap<String, String>,
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size: WindowSize,
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) -> io::Result<Pty> {
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let pair = openpty(None, Some(&size.to_winsize()))?;
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let (master, slave) = (pair.controller, pair.user);
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let mut modes = termios::tcgetattr(&master)?;
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modes.input_modes.set(InputModes::IUTF8, true);
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termios::tcsetattr(&master, OptionalActions::Now, &modes)?;
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let user = User::find()?;
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let mut command = match program {
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Some((program, args)) => {
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let mut command = Command::new(program);
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command.args(args);
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command
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}
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None => login_shell(&user),
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};
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command.stdin(slave.try_clone()?);
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command.stderr(slave.try_clone()?);
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command.stdout(slave.try_clone()?);
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command.env("USER", &user.name).env("HOME", &user.home);
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command.envs(env);
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command.env_remove("XDG_ACTIVATION_TOKEN");
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command.env_remove("DESKTOP_STARTUP_ID");
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let folder = CString::new(cwd.as_os_str().as_bytes())?;
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let (master_fd, slave_fd) = (master.as_raw_fd(), slave.as_raw_fd());
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// SAFETY: the hook calls only async-signal-safe libc functions.
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unsafe {
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command.pre_exec(move || {
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if libc::setsid() == -1 || libc::chdir(folder.as_ptr()) == -1 {
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return Err(io::Error::last_os_error());
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}
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if libc::ioctl(slave_fd, libc::TIOCSCTTY as _, 0) == -1 {
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return Err(io::Error::last_os_error());
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}
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libc::close(slave_fd);
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libc::close(master_fd);
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for signal in [
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libc::SIGCHLD,
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libc::SIGHUP,
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libc::SIGINT,
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libc::SIGQUIT,
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libc::SIGTERM,
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libc::SIGALRM,
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] {
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libc::signal(signal, libc::SIG_DFL);
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}
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Ok(())
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});
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}
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let (sender, signals) = UnixStream::pair()?;
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let sig = pipe::register(SIGCHLD, sender)?;
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signals.set_nonblocking(true)?;
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let child = match command.spawn() {
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Ok(child) => child,
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Err(error) => {
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unregister(sig);
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return Err(error);
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}
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};
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drop(slave);
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let flags = unsafe { libc::fcntl(master_fd, libc::F_GETFL, 0) };
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if flags == -1
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|| unsafe { libc::fcntl(master_fd, libc::F_SETFL, flags | libc::O_NONBLOCK) } == -1
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{
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return Err(io::Error::last_os_error());
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}
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Ok(Pty {
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child,
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file: File::from(master),
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signals,
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sig,
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})
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}
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/// macOS runs the shell through `login` so it is a login shell on a tty, as Terminal does.
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#[cfg(target_os = "macos")]
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fn login_shell(user: &User) -> Command {
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let name = user.shell.rsplit('/').next().unwrap_or(&user.shell);
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let hush = Path::new(&user.home).join(".hushlogin").exists();
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let mut command = Command::new("/usr/bin/login");
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command.args([
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if hush { "-qflp" } else { "-flp" },
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&user.name,
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"/bin/zsh",
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"-fc",
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&format!("exec -a -{name} {}", user.shell),
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]);
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command
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}
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#[cfg(not(target_os = "macos"))]
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fn login_shell(user: &User) -> Command {
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Command::new(&user.shell)
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}
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struct User {
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name: String,
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home: String,
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shell: String,
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}
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impl User {
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/// USER, HOME and SHELL, each from the password entry when the variable is unset.
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fn find() -> io::Result<Self> {
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let entry = || -> io::Result<(String, String, String)> {
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let mut buffer = vec![0 as libc::c_char; 4096];
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let mut entry = MaybeUninit::<libc::passwd>::uninit();
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let mut found = std::ptr::null_mut();
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let status = unsafe {
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libc::getpwuid_r(
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libc::getuid(),
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entry.as_mut_ptr(),
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buffer.as_mut_ptr(),
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buffer.len(),
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&mut found,
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)
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};
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if status != 0 || found.is_null() {
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return Err(io::Error::other("pty: no password entry for this user"));
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}
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let entry = unsafe { entry.assume_init() };
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let text = |field: *const libc::c_char| {
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unsafe { CStr::from_ptr(field) }
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.to_string_lossy()
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.into_owned()
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};
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Ok((
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text(entry.pw_name),
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text(entry.pw_dir),
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text(entry.pw_shell),
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))
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};
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let (name, home, shell) = match (
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std::env::var("USER"),
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std::env::var("HOME"),
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std::env::var("SHELL"),
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) {
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(Ok(name), Ok(home), Ok(shell)) => (name, home, shell),
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(name, home, shell) => {
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let (pw_name, pw_home, pw_shell) = entry()?;
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(
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name.unwrap_or(pw_name),
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home.unwrap_or(pw_home),
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shell.unwrap_or(pw_shell),
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)
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}
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};
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Ok(Self { name, home, shell })
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}
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}
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impl EventedReadWrite for Pty {
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type Reader = File;
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type Writer = File;
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unsafe fn register(
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&mut self,
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poll: &Arc<Poller>,
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mut interest: Event,
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mode: PollMode,
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) -> io::Result<()> {
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interest.key = READ_WRITE;
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unsafe {
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poll.add_with_mode(&self.file, interest, mode)?;
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poll.add_with_mode(&self.signals, Event::readable(CHILD), PollMode::Level)
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}
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}
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fn reregister(
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&mut self,
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poll: &Arc<Poller>,
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mut interest: Event,
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mode: PollMode,
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) -> io::Result<()> {
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interest.key = READ_WRITE;
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poll.modify_with_mode(&self.file, interest, mode)?;
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poll.modify_with_mode(&self.signals, Event::readable(CHILD), PollMode::Level)
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}
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fn deregister(&mut self, poll: &Arc<Poller>) -> io::Result<()> {
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poll.delete(&self.file)?;
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poll.delete(&self.signals)
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}
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fn reader(&mut self) -> &mut File {
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&mut self.file
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}
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fn writer(&mut self) -> &mut File {
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&mut self.file
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}
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}
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impl EventedPty for Pty {
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fn next_child_event(&mut self) -> Option<ChildEvent> {
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let mut byte = [0u8; 1];
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if let Err(error) = self.signals.read(&mut byte) {
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if error.kind() != ErrorKind::WouldBlock {
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log::error!("pty {}: the SIGCHLD pipe failed: {error}", self.id());
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}
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return None;
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}
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match self.child.try_wait() {
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Ok(None) => None,
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Ok(status) => Some(ChildEvent::Exited(status)),
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Err(error) => {
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log::error!(
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"pty {}: cannot read the program's state: {error}",
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self.id()
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);
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None
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}
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}
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}
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}
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impl OnResize for Pty {
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fn on_resize(&mut self, size: WindowSize) {
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let winsize = size.to_winsize();
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if unsafe { libc::ioctl(self.file.as_raw_fd(), libc::TIOCSWINSZ, &winsize) } == -1 {
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log::error!(
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"pty {}: resize failed: {}",
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self.id(),
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io::Error::last_os_error()
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);
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}
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}
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}
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impl Drop for Pty {
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fn drop(&mut self) {
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unsafe { libc::kill(self.child.id() as libc::pid_t, libc::SIGHUP) };
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unregister(self.sig);
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match self.child.wait() {
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Ok(status) => log::info!("pty {}: hung up, {status}", self.id()),
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Err(error) => log::error!("pty {}: cannot reap the program: {error}", self.id()),
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}
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}
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}
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