// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. use io::{self, Error, ErrorKind}; use libc::{self, c_int, gid_t, pid_t, uid_t}; use ptr; use sys::cvt; use sys::process::process_common::*; //////////////////////////////////////////////////////////////////////////////// // Command //////////////////////////////////////////////////////////////////////////////// impl Command { pub fn spawn(&mut self, default: Stdio, needs_stdin: bool) -> io::Result<(Process, StdioPipes)> { use sys; const CLOEXEC_MSG_FOOTER: &'static [u8] = b"NOEX"; if self.saw_nul() { return Err(io::Error::new(ErrorKind::InvalidInput, "nul byte found in provided data")); } let (ours, theirs) = self.setup_io(default, needs_stdin)?; let (input, output) = sys::pipe::anon_pipe()?; let pid = unsafe { match cvt(libc::fork())? { 0 => { drop(input); let err = self.do_exec(theirs); let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32; let bytes = [ (errno >> 24) as u8, (errno >> 16) as u8, (errno >> 8) as u8, (errno >> 0) as u8, CLOEXEC_MSG_FOOTER[0], CLOEXEC_MSG_FOOTER[1], CLOEXEC_MSG_FOOTER[2], CLOEXEC_MSG_FOOTER[3] ]; // pipe I/O up to PIPE_BUF bytes should be atomic, and then // we want to be sure we *don't* run at_exit destructors as // we're being torn down regardless assert!(output.write(&bytes).is_ok()); libc::_exit(1) } n => n, } }; let mut p = Process { pid: pid, status: None }; drop(output); let mut bytes = [0; 8]; // loop to handle EINTR loop { match input.read(&mut bytes) { Ok(0) => return Ok((p, ours)), Ok(8) => { assert!(combine(CLOEXEC_MSG_FOOTER) == combine(&bytes[4.. 8]), "Validation on the CLOEXEC pipe failed: {:?}", bytes); let errno = combine(&bytes[0.. 4]); assert!(p.wait().is_ok(), "wait() should either return Ok or panic"); return Err(Error::from_raw_os_error(errno)) } Err(ref e) if e.kind() == ErrorKind::Interrupted => {} Err(e) => { assert!(p.wait().is_ok(), "wait() should either return Ok or panic"); panic!("the CLOEXEC pipe failed: {:?}", e) }, Ok(..) => { // pipe I/O up to PIPE_BUF bytes should be atomic assert!(p.wait().is_ok(), "wait() should either return Ok or panic"); panic!("short read on the CLOEXEC pipe") } } } fn combine(arr: &[u8]) -> i32 { let a = arr[0] as u32; let b = arr[1] as u32; let c = arr[2] as u32; let d = arr[3] as u32; ((a << 24) | (b << 16) | (c << 8) | (d << 0)) as i32 } } pub fn exec(&mut self, default: Stdio) -> io::Error { if self.saw_nul() { return io::Error::new(ErrorKind::InvalidInput, "nul byte found in provided data") } match self.setup_io(default, true) { Ok((_, theirs)) => unsafe { self.do_exec(theirs) }, Err(e) => e, } } // And at this point we've reached a special time in the life of the // child. The child must now be considered hamstrung and unable to // do anything other than syscalls really. Consider the following // scenario: // // 1. Thread A of process 1 grabs the malloc() mutex // 2. Thread B of process 1 forks(), creating thread C // 3. Thread C of process 2 then attempts to malloc() // 4. The memory of process 2 is the same as the memory of // process 1, so the mutex is locked. // // This situation looks a lot like deadlock, right? It turns out // that this is what pthread_atfork() takes care of, which is // presumably implemented across platforms. The first thing that // threads to *before* forking is to do things like grab the malloc // mutex, and then after the fork they unlock it. // // Despite this information, libnative's spawn has been witnessed to // deadlock on both macOS and FreeBSD. I'm not entirely sure why, but // all collected backtraces point at malloc/free traffic in the // child spawned process. // // For this reason, the block of code below should contain 0 // invocations of either malloc of free (or their related friends). // // As an example of not having malloc/free traffic, we don't close // this file descriptor by dropping the FileDesc (which contains an // allocation). Instead we just close it manually. This will never // have the drop glue anyway because this code never returns (the // child will either exec() or invoke libc::exit) unsafe fn do_exec(&mut self, stdio: ChildPipes) -> io::Error { use sys::{self, cvt_r}; macro_rules! t { ($e:expr) => (match $e { Ok(e) => e, Err(e) => return e, }) } if let Some(fd) = stdio.stdin.fd() { t!(cvt_r(|| libc::dup2(fd, libc::STDIN_FILENO))); } if let Some(fd) = stdio.stdout.fd() { t!(cvt_r(|| libc::dup2(fd, libc::STDOUT_FILENO))); } if let Some(fd) = stdio.stderr.fd() { t!(cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO))); } if let Some(u) = self.get_gid() { t!(cvt(libc::setgid(u as gid_t))); } if let Some(u) = self.get_uid() { // When dropping privileges from root, the `setgroups` call // will remove any extraneous groups. If we don't call this, // then even though our uid has dropped, we may still have // groups that enable us to do super-user things. This will // fail if we aren't root, so don't bother checking the // return value, this is just done as an optimistic // privilege dropping function. let _ = libc::setgroups(0, ptr::null()); t!(cvt(libc::setuid(u as uid_t))); } if let Some(ref cwd) = *self.get_cwd() { t!(cvt(libc::chdir(cwd.as_ptr()))); } if let Some(ref envp) = *self.get_envp() { *sys::os::environ() = envp.as_ptr(); } // NaCl has no signal support. #[cfg(not(any(target_os = "nacl", target_os = "emscripten")))] { use mem; // Reset signal handling so the child process starts in a // standardized state. libstd ignores SIGPIPE, and signal-handling // libraries often set a mask. Child processes inherit ignored // signals and the signal mask from their parent, but most // UNIX programs do not reset these things on their own, so we // need to clean things up now to avoid confusing the program // we're about to run. let mut set: libc::sigset_t = mem::uninitialized(); if cfg!(target_os = "android") { // Implementing sigemptyset allow us to support older Android // versions. See the comment about Android and sig* functions in // process_common.rs libc::memset(&mut set as *mut _ as *mut _, 0, mem::size_of::()); } else { t!(cvt(libc::sigemptyset(&mut set))); } t!(cvt(libc::pthread_sigmask(libc::SIG_SETMASK, &set, ptr::null_mut()))); let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL); if ret == libc::SIG_ERR { return io::Error::last_os_error() } } for callback in self.get_closures().iter_mut() { t!(callback()); } libc::execvp(self.get_argv()[0], self.get_argv().as_ptr()); io::Error::last_os_error() } } //////////////////////////////////////////////////////////////////////////////// // Processes //////////////////////////////////////////////////////////////////////////////// /// The unique id of the process (this should never be negative). pub struct Process { pid: pid_t, status: Option, } impl Process { pub fn id(&self) -> u32 { self.pid as u32 } pub fn kill(&mut self) -> io::Result<()> { // If we've already waited on this process then the pid can be recycled // and used for another process, and we probably shouldn't be killing // random processes, so just return an error. if self.status.is_some() { Err(Error::new(ErrorKind::InvalidInput, "invalid argument: can't kill an exited process")) } else { cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(|_| ()) } } pub fn wait(&mut self) -> io::Result { use sys::cvt_r; if let Some(status) = self.status { return Ok(status) } let mut status = 0 as c_int; cvt_r(|| unsafe { libc::waitpid(self.pid, &mut status, 0) })?; self.status = Some(ExitStatus::new(status)); Ok(ExitStatus::new(status)) } pub fn try_wait(&mut self) -> io::Result> { if let Some(status) = self.status { return Ok(Some(status)) } let mut status = 0 as c_int; let pid = cvt(unsafe { libc::waitpid(self.pid, &mut status, libc::WNOHANG) })?; if pid == 0 { Ok(None) } else { self.status = Some(ExitStatus::new(status)); Ok(Some(ExitStatus::new(status))) } } }