diff --git a/library/std/src/sys/pal/unix/linux/pidfd/tests.rs b/library/std/src/sys/pal/unix/linux/pidfd/tests.rs index 6d9532f2ef1ff..fb928c76fbd04 100644 --- a/library/std/src/sys/pal/unix/linux/pidfd/tests.rs +++ b/library/std/src/sys/pal/unix/linux/pidfd/tests.rs @@ -1,7 +1,7 @@ use crate::assert_matches::assert_matches; use crate::os::fd::{AsRawFd, RawFd}; -use crate::os::linux::process::{ChildExt, CommandExt}; -use crate::os::unix::process::ExitStatusExt; +use crate::os::linux::process::{ChildExt, CommandExt as _}; +use crate::os::unix::process::{CommandExt as _, ExitStatusExt}; use crate::process::Command; #[test] @@ -21,6 +21,7 @@ fn test_command_pidfd() { let flags = super::cvt(unsafe { libc::fcntl(pidfd.as_raw_fd(), libc::F_GETFD) }).unwrap(); assert!(flags & libc::FD_CLOEXEC != 0); } + assert!(child.id() > 0 && child.id() < -1i32 as u32); let status = child.wait().expect("error waiting on pidfd"); assert_eq!(status.code(), Some(1)); @@ -42,6 +43,17 @@ fn test_command_pidfd() { .unwrap() .pidfd() .expect_err("pidfd should not have been created"); + + // exercise the fork/exec path since the earlier attempts may have used pidfd_spawnp() + let mut child = + unsafe { Command::new("false").pre_exec(|| Ok(())) }.create_pidfd(true).spawn().unwrap(); + + assert!(child.id() > 0 && child.id() < -1i32 as u32); + + if pidfd_open_available { + assert!(child.pidfd().is_ok()) + } + child.wait().expect("error waiting on child"); } #[test] diff --git a/library/std/src/sys/pal/unix/mod.rs b/library/std/src/sys/pal/unix/mod.rs index 16fc2011d7085..262f9c704a882 100644 --- a/library/std/src/sys/pal/unix/mod.rs +++ b/library/std/src/sys/pal/unix/mod.rs @@ -305,10 +305,13 @@ macro_rules! impl_is_minus_one { impl_is_minus_one! { i8 i16 i32 i64 isize } +/// Convert native return values to Result using the *-1 means error is in `errno`* convention. +/// Non-error values are `Ok`-wrapped. pub fn cvt(t: T) -> crate::io::Result { if t.is_minus_one() { Err(crate::io::Error::last_os_error()) } else { Ok(t) } } +/// `-1` → look at `errno` → retry on `EINTR`. Otherwise `Ok()`-wrap the closure return value. pub fn cvt_r(mut f: F) -> crate::io::Result where T: IsMinusOne, @@ -323,6 +326,7 @@ where } #[allow(dead_code)] // Not used on all platforms. +/// Zero means `Ok()`, all other values are treated as raw OS errors. Does not look at `errno`. pub fn cvt_nz(error: libc::c_int) -> crate::io::Result<()> { if error == 0 { Ok(()) } else { Err(crate::io::Error::from_raw_os_error(error)) } } diff --git a/library/std/src/sys/pal/unix/process/process_unix.rs b/library/std/src/sys/pal/unix/process/process_unix.rs index 32382d9a50cf4..abd4a334783e4 100644 --- a/library/std/src/sys/pal/unix/process/process_unix.rs +++ b/library/std/src/sys/pal/unix/process/process_unix.rs @@ -449,17 +449,82 @@ impl Command { use crate::mem::MaybeUninit; use crate::sys::weak::weak; use crate::sys::{self, cvt_nz, on_broken_pipe_flag_used}; + #[cfg(target_os = "linux")] + use core::sync::atomic::{AtomicU8, Ordering}; if self.get_gid().is_some() || self.get_uid().is_some() || (self.env_saw_path() && !self.program_is_path()) || !self.get_closures().is_empty() || self.get_groups().is_some() - || self.get_create_pidfd() { return Ok(None); } + cfg_if::cfg_if! { + if #[cfg(target_os = "linux")] { + weak! { + fn pidfd_spawnp( + *mut libc::c_int, + *const libc::c_char, + *const libc::posix_spawn_file_actions_t, + *const libc::posix_spawnattr_t, + *const *mut libc::c_char, + *const *mut libc::c_char + ) -> libc::c_int + } + + weak! { fn pidfd_getpid(libc::c_int) -> libc::c_int } + + static PIDFD_SUPPORTED: AtomicU8 = AtomicU8::new(0); + const UNKNOWN: u8 = 0; + const SPAWN: u8 = 1; + // Obtaining a pidfd via the fork+exec path might work + const FORK_EXEC: u8 = 2; + // Neither pidfd_spawn nor fork/exec will get us a pidfd. + // Instead we'll just posix_spawn if the other preconditions are met. + const NO: u8 = 3; + + if self.get_create_pidfd() { + let mut support = PIDFD_SUPPORTED.load(Ordering::Relaxed); + if support == FORK_EXEC { + return Ok(None); + } + if support == UNKNOWN { + support = NO; + let our_pid = crate::process::id(); + let pidfd = cvt(unsafe { libc::syscall(libc::SYS_pidfd_open, our_pid, 0) } as c_int); + match pidfd { + Ok(pidfd) => { + support = FORK_EXEC; + if let Some(Ok(pid)) = pidfd_getpid.get().map(|f| cvt(unsafe { f(pidfd) } as i32)) { + if pidfd_spawnp.get().is_some() && pid as u32 == our_pid { + support = SPAWN + } + } + unsafe { libc::close(pidfd) }; + } + Err(e) if e.raw_os_error() == Some(libc::EMFILE) => { + // We're temporarily(?) out of file descriptors. In this case obtaining a pidfd would also fail + // Don't update the support flag so we can probe again later. + return Err(e) + } + _ => {} + } + PIDFD_SUPPORTED.store(support, Ordering::Relaxed); + if support == FORK_EXEC { + return Ok(None); + } + } + core::assert_matches::debug_assert_matches!(support, SPAWN | NO); + } + } else { + if self.get_create_pidfd() { + unreachable!("only implemented on linux") + } + } + } + // Only glibc 2.24+ posix_spawn() supports returning ENOENT directly. #[cfg(all(target_os = "linux", target_env = "gnu"))] { @@ -543,9 +608,6 @@ impl Command { let pgroup = self.get_pgroup(); - // Safety: -1 indicates we don't have a pidfd. - let mut p = unsafe { Process::new(0, -1) }; - struct PosixSpawnFileActions<'a>(&'a mut MaybeUninit); impl Drop for PosixSpawnFileActions<'_> { @@ -640,6 +702,47 @@ impl Command { #[cfg(target_os = "nto")] let spawn_fn = retrying_libc_posix_spawnp; + #[cfg(target_os = "linux")] + if self.get_create_pidfd() && PIDFD_SUPPORTED.load(Ordering::Relaxed) == SPAWN { + let mut pidfd: libc::c_int = -1; + let spawn_res = pidfd_spawnp.get().unwrap()( + &mut pidfd, + self.get_program_cstr().as_ptr(), + file_actions.0.as_ptr(), + attrs.0.as_ptr(), + self.get_argv().as_ptr() as *const _, + envp as *const _, + ); + + let spawn_res = cvt_nz(spawn_res); + if let Err(ref e) = spawn_res + && e.raw_os_error() == Some(libc::ENOSYS) + { + PIDFD_SUPPORTED.store(FORK_EXEC, Ordering::Relaxed); + return Ok(None); + } + spawn_res?; + + let pid = match cvt(pidfd_getpid.get().unwrap()(pidfd)) { + Ok(pid) => pid, + Err(e) => { + // The child has been spawned and we are holding its pidfd. + // But we cannot obtain its pid even though pidfd_getpid support was verified earlier. + // This might happen if libc can't open procfs because the file descriptor limit has been reached. + libc::close(pidfd); + return Err(Error::new( + e.kind(), + "pidfd_spawnp succeeded but the child's PID could not be obtained", + )); + } + }; + + return Ok(Some(Process::new(pid, pidfd))); + } + + // Safety: -1 indicates we don't have a pidfd. + let mut p = Process::new(0, -1); + let spawn_res = spawn_fn( &mut p.pid, self.get_program_cstr().as_ptr(), @@ -786,6 +889,12 @@ pub struct Process { impl Process { #[cfg(target_os = "linux")] + /// # Safety + /// + /// `pidfd` must either be -1 (representing no file descriptor) or a valid, exclusively owned file + /// descriptor (See [I/O Safety]). + /// + /// [I/O Safety]: crate::io#io-safety unsafe fn new(pid: pid_t, pidfd: pid_t) -> Self { use crate::os::unix::io::FromRawFd; use crate::sys_common::FromInner;