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process_unix.rs
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process_unix.rs
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// 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 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, 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";
let envp = self.capture_env();
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, envp.as_ref());
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 {
let envp = self.capture_env();
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, envp.as_ref()) },
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,
maybe_envp: Option<&CStringArray>
) -> 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 cfg!(not(any(target_os = "l4re"))) {
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(envp) = maybe_envp {
*sys::os::environ() = envp.as_ptr();
}
// emscripten has no signal support.
#[cfg(not(any(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::<libc::sigset_t>());
} 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<ExitStatus>,
}
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<ExitStatus> {
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<Option<ExitStatus>> {
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)))
}
}
}