use crate::io::{self, Error, ErrorKind}; use crate::ptr; use crate::sys::cvt; use crate::sys::process::process_common::*; use crate::sys; use libc::{c_int, gid_t, pid_t, uid_t}; //////////////////////////////////////////////////////////////////////////////// // Command //////////////////////////////////////////////////////////////////////////////// impl Command { pub fn spawn(&mut self, default: Stdio, needs_stdin: bool) -> io::Result<(Process, StdioPipes)> { const CLOEXEC_MSG_FOOTER: &[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)?; if let Some(ret) = self.posix_spawn(&theirs, envp.as_ref())? { return Ok((ret, ours)) } let (input, output) = sys::pipe::anon_pipe()?; // Whatever happens after the fork is almost for sure going to touch or // look at the environment in one way or another (PATH in `execvp` or // accessing the `environ` pointer ourselves). Make sure no other thread // is accessing the environment when we do the fork itself. // // Note that as soon as we're done with the fork there's no need to hold // a lock any more because the parent won't do anything and the child is // in its own process. let result = unsafe { let _env_lock = sys::os::env_lock(); cvt(libc::fork())? }; let pid = unsafe { match result { 0 => { drop(input); let Err(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 { // Similar to when forking, we want to ensure that access to // the environment is synchronized, so make sure to grab the // environment lock before we try to exec. let _lock = sys::os::env_lock(); let Err(e) = self.do_exec(theirs, envp.as_ref()); e } } 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> ) -> Result { use crate::sys::{self, cvt_r}; if let Some(fd) = stdio.stdin.fd() { cvt_r(|| libc::dup2(fd, libc::STDIN_FILENO))?; } if let Some(fd) = stdio.stdout.fd() { cvt_r(|| libc::dup2(fd, libc::STDOUT_FILENO))?; } if let Some(fd) = stdio.stderr.fd() { cvt_r(|| libc::dup2(fd, libc::STDERR_FILENO))?; } if cfg!(not(any(target_os = "l4re"))) { if let Some(u) = self.get_gid() { cvt(libc::setgid(u as gid_t))?; } if let Some(u) = self.get_uid() { //FIXME: Redox kernel does not support setgroups yet if cfg!(not(target_os = "redox")) { // 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()); } cvt(libc::setuid(u as uid_t))?; } } if let Some(ref cwd) = *self.get_cwd() { cvt(libc::chdir(cwd.as_ptr()))?; } // emscripten has no signal support. #[cfg(not(any(target_os = "emscripten")))] { use crate::mem::MaybeUninit; // 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 = MaybeUninit::::uninit(); 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 set.as_mut_ptr().write_bytes(0u8, 1); } else { cvt(libc::sigemptyset(set.as_mut_ptr()))?; } cvt(libc::pthread_sigmask(libc::SIG_SETMASK, set.as_ptr(), ptr::null_mut()))?; let ret = sys::signal(libc::SIGPIPE, libc::SIG_DFL); if ret == libc::SIG_ERR { return Err(io::Error::last_os_error()) } } for callback in self.get_closures().iter_mut() { callback()?; } // Although we're performing an exec here we may also return with an // error from this function (without actually exec'ing) in which case we // want to be sure to restore the global environment back to what it // once was, ensuring that our temporary override, when free'd, doesn't // corrupt our process's environment. let mut _reset = None; if let Some(envp) = maybe_envp { struct Reset(*const *const libc::c_char); impl Drop for Reset { fn drop(&mut self) { unsafe { *sys::os::environ() = self.0; } } } _reset = Some(Reset(*sys::os::environ())); *sys::os::environ() = envp.as_ptr(); } libc::execvp(self.get_argv()[0], self.get_argv().as_ptr()); Err(io::Error::last_os_error()) } #[cfg(not(any(target_os = "macos", target_os = "freebsd", all(target_os = "linux", target_env = "gnu"))))] fn posix_spawn(&mut self, _: &ChildPipes, _: Option<&CStringArray>) -> io::Result> { Ok(None) } // Only support platforms for which posix_spawn() can return ENOENT // directly. #[cfg(any(target_os = "macos", target_os = "freebsd", all(target_os = "linux", target_env = "gnu")))] fn posix_spawn(&mut self, stdio: &ChildPipes, envp: Option<&CStringArray>) -> io::Result> { use crate::mem::MaybeUninit; use crate::sys; if self.get_gid().is_some() || self.get_uid().is_some() || self.env_saw_path() || !self.get_closures().is_empty() { return Ok(None) } // Only glibc 2.24+ posix_spawn() supports returning ENOENT directly. #[cfg(all(target_os = "linux", target_env = "gnu"))] { if let Some(version) = sys::os::glibc_version() { if version < (2, 24) { return Ok(None) } } else { return Ok(None) } } // Solaris and glibc 2.29+ can set a new working directory, and maybe // others will gain this non-POSIX function too. We'll check for this // weak symbol as soon as it's needed, so we can return early otherwise // to do a manual chdir before exec. weak! { fn posix_spawn_file_actions_addchdir_np( *mut libc::posix_spawn_file_actions_t, *const libc::c_char ) -> libc::c_int } let addchdir = match self.get_cwd() { Some(cwd) => match posix_spawn_file_actions_addchdir_np.get() { Some(f) => Some((f, cwd)), None => return Ok(None), }, None => None, }; let mut p = Process { pid: 0, status: None }; struct PosixSpawnFileActions(MaybeUninit); impl Drop for PosixSpawnFileActions { fn drop(&mut self) { unsafe { libc::posix_spawn_file_actions_destroy(self.0.as_mut_ptr()); } } } struct PosixSpawnattr(MaybeUninit); impl Drop for PosixSpawnattr { fn drop(&mut self) { unsafe { libc::posix_spawnattr_destroy(self.0.as_mut_ptr()); } } } unsafe { let mut file_actions = PosixSpawnFileActions(MaybeUninit::uninit()); let mut attrs = PosixSpawnattr(MaybeUninit::uninit()); libc::posix_spawnattr_init(attrs.0.as_mut_ptr()); libc::posix_spawn_file_actions_init(file_actions.0.as_mut_ptr()); if let Some(fd) = stdio.stdin.fd() { cvt(libc::posix_spawn_file_actions_adddup2(file_actions.0.as_mut_ptr(), fd, libc::STDIN_FILENO))?; } if let Some(fd) = stdio.stdout.fd() { cvt(libc::posix_spawn_file_actions_adddup2(file_actions.0.as_mut_ptr(), fd, libc::STDOUT_FILENO))?; } if let Some(fd) = stdio.stderr.fd() { cvt(libc::posix_spawn_file_actions_adddup2(file_actions.0.as_mut_ptr(), fd, libc::STDERR_FILENO))?; } if let Some((f, cwd)) = addchdir { cvt(f(file_actions.0.as_mut_ptr(), cwd.as_ptr()))?; } let mut set = MaybeUninit::::uninit(); cvt(libc::sigemptyset(set.as_mut_ptr()))?; cvt(libc::posix_spawnattr_setsigmask(attrs.0.as_mut_ptr(), set.as_ptr()))?; cvt(libc::sigaddset(set.as_mut_ptr(), libc::SIGPIPE))?; cvt(libc::posix_spawnattr_setsigdefault(attrs.0.as_mut_ptr(), set.as_ptr()))?; let flags = libc::POSIX_SPAWN_SETSIGDEF | libc::POSIX_SPAWN_SETSIGMASK; cvt(libc::posix_spawnattr_setflags(attrs.0.as_mut_ptr(), flags as _))?; // Make sure we synchronize access to the global `environ` resource let _env_lock = sys::os::env_lock(); let envp = envp.map(|c| c.as_ptr()) .unwrap_or_else(|| *sys::os::environ() as *const _); let ret = libc::posix_spawnp( &mut p.pid, self.get_argv()[0], file_actions.0.as_ptr(), attrs.0.as_ptr(), self.get_argv().as_ptr() as *const _, envp as *const _, ); if ret == 0 { Ok(Some(p)) } else { Err(io::Error::from_raw_os_error(ret)) } } } } //////////////////////////////////////////////////////////////////////////////// // 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 crate::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))) } } }