library/std/src/sys/unix/process/process_unix.rs

   1 use crate::convert::TryInto;
   2 use crate::fmt;
   3 use crate::io::{self, Error, ErrorKind};
   4 use crate::ptr;
   5 use crate::sys;
   6 use crate::sys::cvt;
   7 use crate::sys::process::process_common::*;
   8
   9 #[cfg(target_os = "vxworks")]
  10 use libc::RTP_ID as pid_t;
  11
  12 #[cfg(not(target_os = "vxworks"))]
  13 use libc::{c_int, gid_t, pid_t, uid_t};
  14
  15 ////////////////////////////////////////////////////////////////////////////////
  16 // Command
  17 ////////////////////////////////////////////////////////////////////////////////
  18
  19 impl Command {
  20     pub fn spawn(
  21         &mut self,
  22         default: Stdio,
  23         needs_stdin: bool,
  24     ) -> io::Result<(Process, StdioPipes)> {
  25         const CLOEXEC_MSG_FOOTER: [u8; 4] = *b"NOEX";
  26
  27         let envp = self.capture_env();
  28
  29         if self.saw_nul() {
  30             return Err(io::Error::new(ErrorKind::InvalidInput, "nul byte found in provided data"));
  31         }
  32
  33         let (ours, theirs) = self.setup_io(default, needs_stdin)?;
  34
  35         if let Some(ret) = self.posix_spawn(&theirs, envp.as_ref())? {
  36             return Ok((ret, ours));
  37         }
  38
  39         let (input, output) = sys::pipe::anon_pipe()?;
  40
  41         // Whatever happens after the fork is almost for sure going to touch or
  42         // look at the environment in one way or another (PATH in `execvp` or
  43         // accessing the `environ` pointer ourselves). Make sure no other thread
  44         // is accessing the environment when we do the fork itself.
  45         //
  46         // Note that as soon as we're done with the fork there's no need to hold
  47         // a lock any more because the parent won't do anything and the child is
  48         // in its own process.
  49         let result = unsafe {
  50             let _env_lock = sys::os::env_lock();
  51             cvt(libc::fork())?
  52         };
  53
  54         let pid = unsafe {
  55             match result {
  56                 0 => {
  57                     drop(input);
  58                     let Err(err) = self.do_exec(theirs, envp.as_ref());
  59                     let errno = err.raw_os_error().unwrap_or(libc::EINVAL) as u32;
  60                     let errno = errno.to_be_bytes();
  61                     let bytes = [
  62                         errno[0],
  63                         errno[1],
  64                         errno[2],
  65                         errno[3],
  66                         CLOEXEC_MSG_FOOTER[0],
  67                         CLOEXEC_MSG_FOOTER[1],
  68                         CLOEXEC_MSG_FOOTER[2],
  69                         CLOEXEC_MSG_FOOTER[3],
  70                     ];
  71                     // pipe I/O up to PIPE_BUF bytes should be atomic, and then
  72                     // we want to be sure we *don't* run at_exit destructors as
  73                     // we're being torn down regardless
  74                     rtassert!(output.write(&bytes).is_ok());
  75                     libc::_exit(1)
  76                 }
  77                 n => n,
  78             }
  79         };
  80
  81         let mut p = Process { pid, status: None };
  82         drop(output);
  83         let mut bytes = [0; 8];
  84
  85         // loop to handle EINTR
  86         loop {
  87             match input.read(&mut bytes) {
  88                 Ok(0) => return Ok((p, ours)),
  89                 Ok(8) => {
  90                     let (errno, footer) = bytes.split_at(4);
  91                     assert_eq!(
  92                         CLOEXEC_MSG_FOOTER, footer,
  93                         "Validation on the CLOEXEC pipe failed: {:?}",
  94                         bytes
  95                     );
  96                     let errno = i32::from_be_bytes(errno.try_into().unwrap());
  97                     assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
  98                     return Err(Error::from_raw_os_error(errno));
  99                 }
 100                 Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
 101                 Err(e) => {
 102                     assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
 103                     panic!("the CLOEXEC pipe failed: {:?}", e)
 104                 }
 105                 Ok(..) => {
 106                     // pipe I/O up to PIPE_BUF bytes should be atomic
 107                     assert!(p.wait().is_ok(), "wait() should either return Ok or panic");
 108                     panic!("short read on the CLOEXEC pipe")
 109                 }
 110             }
 111         }
 112     }
 113
 114     pub fn exec(&mut self, default: Stdio) -> io::Error {
 115         let envp = self.capture_env();
 116
 117         if self.saw_nul() {
 118             return io::Error::new(ErrorKind::InvalidInput, "nul byte found in provided data");
 119         }
 120
 121         match self.setup_io(default, true) {
 122             Ok((_, theirs)) => {
 123                 unsafe {
 124                     // Similar to when forking, we want to ensure that access to
 125                     // the environment is synchronized, so make sure to grab the
 126                     // environment lock before we try to exec.
 127                     let _lock = sys::os::env_lock();
 128
 129                     let Err(e) = self.do_exec(theirs, envp.as_ref());
 130                     e
 131                 }
 132             }
 133             Err(e) => e,
 134         }
 135     }
 136
 137     // And at this point we've reached a special time in the life of the
 138     // child. The child must now be considered hamstrung and unable to
 139     // do anything other than syscalls really. Consider the following
 140     // scenario:
 141     //
 142     //      1. Thread A of process 1 grabs the malloc() mutex
 143     //      2. Thread B of process 1 forks(), creating thread C
 144     //      3. Thread C of process 2 then attempts to malloc()
 145     //      4. The memory of process 2 is the same as the memory of
 146     //         process 1, so the mutex is locked.
 147     //
 148     // This situation looks a lot like deadlock, right? It turns out
 149     // that this is what pthread_atfork() takes care of, which is
 150     // presumably implemented across platforms. The first thing that
 151     // threads to *before* forking is to do things like grab the malloc
 152     // mutex, and then after the fork they unlock it.
 153     //
 154     // Despite this information, libnative's spawn has been witnessed to
 155     // deadlock on both macOS and FreeBSD. I'm not entirely sure why, but
 156     // all collected backtraces point at malloc/free traffic in the
 157     // child spawned process.
 158     //
 159     // For this reason, the block of code below should contain 0
 160     // invocations of either malloc of free (or their related friends).
 161     //
 162     // As an example of not having malloc/free traffic, we don't close
 163     // this file descriptor by dropping the FileDesc (which contains an
 164     // allocation). Instead we just close it manually. This will never
 165     // have the drop glue anyway because this code never returns (the
 166     // child will either exec() or invoke libc::exit)
 167     unsafe fn do_exec(
 168         &mut self,
 169         stdio: ChildPipes,
 170         maybe_envp: Option<&CStringArray>,
 171     ) -> Result<!, io::Error> {
 172         use crate::sys::{self, cvt_r};
 173
 174         if let Some(fd) = stdio.stdin.fd() {
 175             cvt_r(|| libc::dup2(fd, libc::STDIN_FILENO))?;
 176         }
 177         if let Some(fd) = stdio.stdout.fd() {
 178             cvt_r(|| libc::dup2(fd, libc::STDOUT_FILENO))?;
 179         }
 180         if let Some(fd) = stdio.stderr.fd() {
 181             cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO))?;
 182         }
 183
 184         #[cfg(not(target_os = "l4re"))]
 185         {
 186             if let Some(_g) = self.get_groups() {
 187                 //FIXME: Redox kernel does not support setgroups yet
 188                 #[cfg(not(target_os = "redox"))]
 189                 cvt(libc::setgroups(_g.len().try_into().unwrap(), _g.as_ptr()))?;
 190             }
 191             if let Some(u) = self.get_gid() {
 192                 cvt(libc::setgid(u as gid_t))?;
 193             }
 194             if let Some(u) = self.get_uid() {
 195                 // When dropping privileges from root, the `setgroups` call
 196                 // will remove any extraneous groups. We only drop groups
 197                 // if the current uid is 0 and we weren't given an explicit
 198                 // set of groups. If we don't call this, then even though our
 199                 // uid has dropped, we may still have groups that enable us to
 200                 // do super-user things.
 201                 //FIXME: Redox kernel does not support setgroups yet
 202                 #[cfg(not(target_os = "redox"))]
 203                 if libc::getuid() == 0 && self.get_groups().is_none() {
 204                     cvt(libc::setgroups(0, ptr::null()))?;
 205                 }
 206                 cvt(libc::setuid(u as uid_t))?;
 207             }
 208         }
 209         if let Some(ref cwd) = *self.get_cwd() {
 210             cvt(libc::chdir(cwd.as_ptr()))?;
 211         }
 212
 213         // emscripten has no signal support.
 214         #[cfg(not(target_os = "emscripten"))]
 215         {
 216             use crate::mem::MaybeUninit;
 217             // Reset signal handling so the child process starts in a
 218             // standardized state. libstd ignores SIGPIPE, and signal-handling
 219             // libraries often set a mask. Child processes inherit ignored
 220             // signals and the signal mask from their parent, but most
 221             // UNIX programs do not reset these things on their own, so we
 222             // need to clean things up now to avoid confusing the program
 223             // we're about to run.
 224             let mut set = MaybeUninit::<libc::sigset_t>::uninit();
 225             cvt(sigemptyset(set.as_mut_ptr()))?;
 226             cvt(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(), ptr::null_mut()))?;
 227             let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL);
 228             if ret == libc::SIG_ERR {
 229                 return Err(io::Error::last_os_error());
 230             }
 231         }
 232
 233         for callback in self.get_closures().iter_mut() {
 234             callback()?;
 235         }
 236
 237         // Although we're performing an exec here we may also return with an
 238         // error from this function (without actually exec'ing) in which case we
 239         // want to be sure to restore the global environment back to what it
 240         // once was, ensuring that our temporary override, when free'd, doesn't
 241         // corrupt our process's environment.
 242         let mut _reset = None;
 243         if let Some(envp) = maybe_envp {
 244             struct Reset(*const *const libc::c_char);
 245
 246             impl Drop for Reset {
 247                 fn drop(&mut self) {
 248                     unsafe {
 249                         *sys::os::environ() = self.0;
 250                     }
 251                 }
 252             }
 253
 254             _reset = Some(Reset(*sys::os::environ()));
 255             *sys::os::environ() = envp.as_ptr();
 256         }
 257
 258         libc::execvp(self.get_program_cstr().as_ptr(), self.get_argv().as_ptr());
 259         Err(io::Error::last_os_error())
 260     }
 261
 262     #[cfg(not(any(
 263         target_os = "macos",
 264         target_os = "freebsd",
 265         all(target_os = "linux", target_env = "gnu"),
 266         all(target_os = "linux", target_env = "musl"),
 267     )))]
 268     fn posix_spawn(
 269         &mut self,
 270         _: &ChildPipes,
 271         _: Option<&CStringArray>,
 272     ) -> io::Result<Option<Process>> {
 273         Ok(None)
 274     }
 275
 276     // Only support platforms for which posix_spawn() can return ENOENT
 277     // directly.
 278     #[cfg(any(
 279         target_os = "macos",
 280         target_os = "freebsd",
 281         all(target_os = "linux", target_env = "gnu"),
 282         all(target_os = "linux", target_env = "musl"),
 283     ))]
 284     fn posix_spawn(
 285         &mut self,
 286         stdio: &ChildPipes,
 287         envp: Option<&CStringArray>,
 288     ) -> io::Result<Option<Process>> {
 289         use crate::mem::MaybeUninit;
 290         use crate::sys::{self, cvt_nz};
 291
 292         if self.get_gid().is_some()
 293             || self.get_uid().is_some()
 294             || (self.env_saw_path() && !self.program_is_path())
 295             || !self.get_closures().is_empty()
 296             || self.get_groups().is_some()
 297         {
 298             return Ok(None);
 299         }
 300
 301         // Only glibc 2.24+ posix_spawn() supports returning ENOENT directly.
 302         #[cfg(all(target_os = "linux", target_env = "gnu"))]
 303         {
 304             if let Some(version) = sys::os::glibc_version() {
 305                 if version < (2, 24) {
 306                     return Ok(None);
 307                 }
 308             } else {
 309                 return Ok(None);
 310             }
 311         }
 312
 313         // Solaris, glibc 2.29+, and musl 1.24+ can set a new working directory,
 314         // and maybe others will gain this non-POSIX function too. We'll check
 315         // for this weak symbol as soon as it's needed, so we can return early
 316         // otherwise to do a manual chdir before exec.
 317         weak! {
 318             fn posix_spawn_file_actions_addchdir_np(
 319                 *mut libc::posix_spawn_file_actions_t,
 320                 *const libc::c_char
 321             ) -> libc::c_int
 322         }
 323         let addchdir = match self.get_cwd() {
 324             Some(cwd) => {
 325                 if cfg!(target_os = "macos") {
 326                     // There is a bug in macOS where a relative executable
 327                     // path like "../myprogram" will cause `posix_spawn` to
 328                     // successfully launch the program, but erroneously return
 329                     // ENOENT when used with posix_spawn_file_actions_addchdir_np
 330                     // which was introduced in macOS 10.15.
 331                     return Ok(None);
 332                 }
 333                 match posix_spawn_file_actions_addchdir_np.get() {
 334                     Some(f) => Some((f, cwd)),
 335                     None => return Ok(None),
 336                 }
 337             }
 338             None => None,
 339         };
 340
 341         let mut p = Process { pid: 0, status: None };
 342
 343         struct PosixSpawnFileActions<'a>(&'a mut MaybeUninit<libc::posix_spawn_file_actions_t>);
 344
 345         impl Drop for PosixSpawnFileActions<'_> {
 346             fn drop(&mut self) {
 347                 unsafe {
 348                     libc::posix_spawn_file_actions_destroy(self.0.as_mut_ptr());
 349                 }
 350             }
 351         }
 352
 353         struct PosixSpawnattr<'a>(&'a mut MaybeUninit<libc::posix_spawnattr_t>);
 354
 355         impl Drop for PosixSpawnattr<'_> {
 356             fn drop(&mut self) {
 357                 unsafe {
 358                     libc::posix_spawnattr_destroy(self.0.as_mut_ptr());
 359                 }
 360             }
 361         }
 362
 363         unsafe {
 364             let mut attrs = MaybeUninit::uninit();
 365             cvt_nz(libc::posix_spawnattr_init(attrs.as_mut_ptr()))?;
 366             let attrs = PosixSpawnattr(&mut attrs);
 367
 368             let mut file_actions = MaybeUninit::uninit();
 369             cvt_nz(libc::posix_spawn_file_actions_init(file_actions.as_mut_ptr()))?;
 370             let file_actions = PosixSpawnFileActions(&mut file_actions);
 371
 372             if let Some(fd) = stdio.stdin.fd() {
 373                 cvt_nz(libc::posix_spawn_file_actions_adddup2(
 374                     file_actions.0.as_mut_ptr(),
 375                     fd,
 376                     libc::STDIN_FILENO,
 377                 ))?;
 378             }
 379             if let Some(fd) = stdio.stdout.fd() {
 380                 cvt_nz(libc::posix_spawn_file_actions_adddup2(
 381                     file_actions.0.as_mut_ptr(),
 382                     fd,
 383                     libc::STDOUT_FILENO,
 384                 ))?;
 385             }
 386             if let Some(fd) = stdio.stderr.fd() {
 387                 cvt_nz(libc::posix_spawn_file_actions_adddup2(
 388                     file_actions.0.as_mut_ptr(),
 389                     fd,
 390                     libc::STDERR_FILENO,
 391                 ))?;
 392             }
 393             if let Some((f, cwd)) = addchdir {
 394                 cvt_nz(f(file_actions.0.as_mut_ptr(), cwd.as_ptr()))?;
 395             }
 396
 397             let mut set = MaybeUninit::<libc::sigset_t>::uninit();
 398             cvt(sigemptyset(set.as_mut_ptr()))?;
 399             cvt_nz(libc::posix_spawnattr_setsigmask(attrs.0.as_mut_ptr(), set.as_ptr()))?;
 400             cvt(sigaddset(set.as_mut_ptr(), libc::SIGPIPE))?;
 401             cvt_nz(libc::posix_spawnattr_setsigdefault(attrs.0.as_mut_ptr(), set.as_ptr()))?;
 402
 403             let flags = libc::POSIX_SPAWN_SETSIGDEF | libc::POSIX_SPAWN_SETSIGMASK;
 404             cvt_nz(libc::posix_spawnattr_setflags(attrs.0.as_mut_ptr(), flags as _))?;
 405
 406             // Make sure we synchronize access to the global `environ` resource
 407             let _env_lock = sys::os::env_lock();
 408             let envp = envp.map(|c| c.as_ptr()).unwrap_or_else(|| *sys::os::environ() as *const _);
 409             cvt_nz(libc::posix_spawnp(
 410                 &mut p.pid,
 411                 self.get_program_cstr().as_ptr(),
 412                 file_actions.0.as_ptr(),
 413                 attrs.0.as_ptr(),
 414                 self.get_argv().as_ptr() as *const _,
 415                 envp as *const _,
 416             ))?;
 417             Ok(Some(p))
 418         }
 419     }
 420 }
 421
 422 ////////////////////////////////////////////////////////////////////////////////
 423 // Processes
 424 ////////////////////////////////////////////////////////////////////////////////
 425
 426 /// The unique ID of the process (this should never be negative).
 427 pub struct Process {
 428     pid: pid_t,
 429     status: Option<ExitStatus>,
 430 }
 431
 432 impl Process {
 433     pub fn id(&self) -> u32 {
 434         self.pid as u32
 435     }
 436
 437     pub fn kill(&mut self) -> io::Result<()> {
 438         // If we've already waited on this process then the pid can be recycled
 439         // and used for another process, and we probably shouldn't be killing
 440         // random processes, so just return an error.
 441         if self.status.is_some() {
 442             Err(Error::new(
 443                 ErrorKind::InvalidInput,
 444                 "invalid argument: can't kill an exited process",
 445             ))
 446         } else {
 447             cvt(unsafe { libc::kill(self.pid, libc::SIGKILL) }).map(drop)
 448         }
 449     }
 450
 451     pub fn wait(&mut self) -> io::Result<ExitStatus> {
 452         use crate::sys::cvt_r;
 453         if let Some(status) = self.status {
 454             return Ok(status);
 455         }
 456         let mut status = 0 as c_int;
 457         cvt_r(|| unsafe { libc::waitpid(self.pid, &mut status, 0) })?;
 458         self.status = Some(ExitStatus::new(status));
 459         Ok(ExitStatus::new(status))
 460     }
 461
 462     pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
 463         if let Some(status) = self.status {
 464             return Ok(Some(status));
 465         }
 466         let mut status = 0 as c_int;
 467         let pid = cvt(unsafe { libc::waitpid(self.pid, &mut status, libc::WNOHANG) })?;
 468         if pid == 0 {
 469             Ok(None)
 470         } else {
 471             self.status = Some(ExitStatus::new(status));
 472             Ok(Some(ExitStatus::new(status)))
 473         }
 474     }
 475 }
 476
 477 /// Unix exit statuses
 478 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
 479 pub struct ExitStatus(c_int);
 480
 481 impl ExitStatus {
 482     pub fn new(status: c_int) -> ExitStatus {
 483         ExitStatus(status)
 484     }
 485
 486     fn exited(&self) -> bool {
 487         libc::WIFEXITED(self.0)
 488     }
 489
 490     pub fn success(&self) -> bool {
 491         self.code() == Some(0)
 492     }
 493
 494     pub fn code(&self) -> Option<i32> {
 495         if self.exited() { Some(libc::WEXITSTATUS(self.0)) } else { None }
 496     }
 497
 498     pub fn signal(&self) -> Option<i32> {
 499         if libc::WIFSIGNALED(self.0) { Some(libc::WTERMSIG(self.0)) } else { None }
 500     }
 501
 502     pub fn core_dumped(&self) -> bool {
 503         libc::WIFSIGNALED(self.0) && libc::WCOREDUMP(self.0)
 504     }
 505
 506     pub fn stopped_signal(&self) -> Option<i32> {
 507         if libc::WIFSTOPPED(self.0) { Some(libc::WSTOPSIG(self.0)) } else { None }
 508     }
 509
 510     pub fn continued(&self) -> bool {
 511         libc::WIFCONTINUED(self.0)
 512     }
 513
 514     pub fn into_raw(&self) -> c_int {
 515         self.0
 516     }
 517 }
 518
 519 /// Converts a raw `c_int` to a type-safe `ExitStatus` by wrapping it without copying.
 520 impl From<c_int> for ExitStatus {
 521     fn from(a: c_int) -> ExitStatus {
 522         ExitStatus(a)
 523     }
 524 }
 525
 526 impl fmt::Display for ExitStatus {
 527     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 528         if let Some(code) = self.code() {
 529             write!(f, "exit code: {}", code)
 530         } else {
 531             let signal = self.signal().unwrap();
 532             write!(f, "signal: {}", signal)
 533         }
 534     }
 535 }