From 694be09b7be057aa342e6cfe61815032942e5f95 Mon Sep 17 00:00:00 2001 From: Aaron Hill Date: Tue, 15 Sep 2020 23:35:08 -0400 Subject: Add Linux-specific pidfd process extensions MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Background: Over the last year, pidfd support was added to the Linux kernel. This allows interacting with other processes. In particular, this allows waiting on a child process with a timeout in a race-free way, bypassing all of the awful signal-handler tricks that are usually required. Pidfds can be obtained for a child process (as well as any other process) via the `pidfd_open` syscall. Unfortunately, this requires several conditions to hold in order to be race-free (i.e. the pid is not reused). Per `man pidfd_open`: ``` · the disposition of SIGCHLD has not been explicitly set to SIG_IGN (see sigaction(2)); · the SA_NOCLDWAIT flag was not specified while establishing a han‐ dler for SIGCHLD or while setting the disposition of that signal to SIG_DFL (see sigaction(2)); and · the zombie process was not reaped elsewhere in the program (e.g., either by an asynchronously executed signal handler or by wait(2) or similar in another thread). If any of these conditions does not hold, then the child process (along with a PID file descriptor that refers to it) should instead be created using clone(2) with the CLONE_PIDFD flag. ``` Sadly, these conditions are impossible to guarantee once any libraries are used. For example, C code runnng in a different thread could call `wait()`, which is impossible to detect from Rust code trying to open a pidfd. While pid reuse issues should (hopefully) be rare in practice, we can do better. By passing the `CLONE_PIDFD` flag to `clone()` or `clone3()`, we can obtain a pidfd for the child process in a guaranteed race-free manner. This PR: This PR adds Linux-specific process extension methods to allow obtaining pidfds for processes spawned via the standard `Command` API. Other than being made available to user code, the standard library does not make use of these pidfds in any way. In particular, the implementation of `Child::wait` is completely unchanged. Two Linux-specific helper methods are added: `CommandExt::create_pidfd` and `ChildExt::pidfd`. These methods are intended to serve as a building block for libraries to build higher-level abstractions - in particular, waiting on a process with a timeout. I've included a basic test, which verifies that pidfds are created iff the `create_pidfd` method is used. This test is somewhat special - it should always succeed on systems with the `clone3` system call available, and always fail on systems without `clone3` available. I'm not sure how to best ensure this programatically. This PR relies on the newer `clone3` system call to pass the `CLONE_FD`, rather than the older `clone` system call. `clone3` was added to Linux in the same release as pidfds, so this shouldn't unnecessarily limit the kernel versions that this code supports. Unresolved questions: * What should the name of the feature gate be for these newly added methods? * Should the `pidfd` method distinguish between an error occurring and `create_pidfd` not being called? --- src/test/ui/command/command-create-pidfd.rs | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) create mode 100644 src/test/ui/command/command-create-pidfd.rs (limited to 'src/test/ui/command/command-create-pidfd.rs') diff --git a/src/test/ui/command/command-create-pidfd.rs b/src/test/ui/command/command-create-pidfd.rs new file mode 100644 index 00000000000..248ae3457d7 --- /dev/null +++ b/src/test/ui/command/command-create-pidfd.rs @@ -0,0 +1,27 @@ +// run-pass +// linux-only - pidfds are a linux-specific concept + +#![feature(linux_pidfd)] +use std::os::linux::process::{CommandExt, ChildExt}; +use std::process::Command; + +fn main() { + // We don't assert the precise value, since the standard libarary + // may be opened other file descriptors before our code ran. + let _ = Command::new("echo") + .create_pidfd(true) + .spawn() + .unwrap() + .pidfd().expect("failed to obtain pidfd"); + + let _ = Command::new("echo") + .create_pidfd(false) + .spawn() + .unwrap() + .pidfd().expect_err("pidfd should not have been created when create_pid(false) is set"); + + let _ = Command::new("echo") + .spawn() + .unwrap() + .pidfd().expect_err("pidfd should not have been created"); +} -- cgit 1.4.1-3-g733a5 From 619fd96868b2cc83b7f205ff11ff897aebb5ef93 Mon Sep 17 00:00:00 2001 From: Dominik Stolz Date: Sat, 6 Feb 2021 14:15:49 +0100 Subject: Add PidFd type and seal traits Improve docs Split do_fork into two Make do_fork unsafe Add target attribute to create_pidfd field in Command Add method to get create_pidfd value --- library/std/src/os/linux/process.rs | 146 ++++++++++++--- library/std/src/sys/unix/process/process_common.rs | 43 ++++- library/std/src/sys/unix/process/process_unix.rs | 200 ++++++++++++--------- src/test/ui/command/command-create-pidfd.rs | 6 +- 4 files changed, 282 insertions(+), 113 deletions(-) (limited to 'src/test/ui/command/command-create-pidfd.rs') diff --git a/library/std/src/os/linux/process.rs b/library/std/src/os/linux/process.rs index 661d3cef7a0..435c0227c7e 100644 --- a/library/std/src/os/linux/process.rs +++ b/library/std/src/os/linux/process.rs @@ -2,40 +2,142 @@ #![unstable(feature = "linux_pidfd", issue = "none")] -use crate::process; -use crate::sys_common::AsInnerMut; use crate::io::Result; +use crate::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd}; +use crate::process; +use crate::sys::fd::FileDesc; +use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner}; -/// Os-specific extensions to [`process::Child`] +/// This type represents a file descriptor that refers to a process. +/// +/// A `PidFd` can be obtained by setting the corresponding option on [`Command`] +/// with [`create_pidfd`]. Subsequently, the created pidfd can be retrieved +/// from the [`Child`] by calling [`pidfd`] or [`take_pidfd`]. +/// +/// Example: +/// ```no_run +/// #![feature(linux_pidfd)] +/// use std::os::linux::process::{CommandExt, ChildExt}; +/// use std::process::Command; +/// +/// let mut child = Command::new("echo") +/// .create_pidfd(true) +/// .spawn() +/// .expect("Failed to spawn child"); /// -/// [`process::Child`]: crate::process::Child -pub trait ChildExt { - /// Obtains the pidfd created for this child process, if available. +/// let pidfd = child +/// .take_pidfd() +/// .expect("Failed to retrieve pidfd"); +/// +/// // The file descriptor will be closed when `pidfd` is dropped. +/// ``` +/// Refer to the man page of `pidfd_open(2)` for further details. +/// +/// [`Command`]: process::Command +/// [`create_pidfd`]: CommandExt::create_pidfd +/// [`Child`]: process::Child +/// [`pidfd`]: fn@ChildExt::pidfd +/// [`take_pidfd`]: ChildExt::take_pidfd +#[derive(Debug)] +pub struct PidFd { + inner: FileDesc, +} + +impl AsInner for PidFd { + fn as_inner(&self) -> &FileDesc { + &self.inner + } +} + +impl FromInner for PidFd { + fn from_inner(inner: FileDesc) -> PidFd { + PidFd { inner } + } +} + +impl IntoInner for PidFd { + fn into_inner(self) -> FileDesc { + self.inner + } +} + +impl AsRawFd for PidFd { + fn as_raw_fd(&self) -> RawFd { + self.as_inner().raw() + } +} + +impl FromRawFd for PidFd { + unsafe fn from_raw_fd(fd: RawFd) -> Self { + Self::from_inner(FileDesc::new(fd)) + } +} + +impl IntoRawFd for PidFd { + fn into_raw_fd(self) -> RawFd { + self.into_inner().into_raw() + } +} + +mod private_child_ext { + pub trait Sealed {} + impl Sealed for crate::process::Child {} +} + +/// Os-specific extensions for [`Child`] +/// +/// [`Child`]: process::Child +pub trait ChildExt: private_child_ext::Sealed { + /// Obtains a reference to the [`PidFd`] created for this [`Child`], if available. + /// + /// A pidfd will only be available if its creation was requested with + /// [`create_pidfd`] when the corresponding [`Command`] was created. /// - /// A pidfd will only ever be available if `create_pidfd(true)` was called - /// when the corresponding `Command` was created. + /// Even if requested, a pidfd may not be available due to an older + /// version of Linux being in use, or if some other error occurred. + /// + /// [`Command`]: process::Command + /// [`create_pidfd`]: CommandExt::create_pidfd + /// [`Child`]: process::Child + fn pidfd(&self) -> Result<&PidFd>; + + /// Takes ownership of the [`PidFd`] created for this [`Child`], if available. /// - /// Even if `create_pidfd(true)` is called, a pidfd may not be available - /// due to an older version of Linux being in use, or if - /// some other error occured. + /// A pidfd will only be available if its creation was requested with + /// [`create_pidfd`] when the corresponding [`Command`] was created. /// - /// See `man pidfd_open` for more details about pidfds. - fn pidfd(&self) -> Result; + /// Even if requested, a pidfd may not be available due to an older + /// version of Linux being in use, or if some other error occurred. + /// + /// [`Command`]: process::Command + /// [`create_pidfd`]: CommandExt::create_pidfd + /// [`Child`]: process::Child + fn take_pidfd(&mut self) -> Result; +} + +mod private_command_ext { + pub trait Sealed {} + impl Sealed for crate::process::Command {} } -/// Os-specific extensions to [`process::Command`] +/// Os-specific extensions for [`Command`] /// -/// [`process::Command`]: crate::process::Command -pub trait CommandExt { - /// Sets whether or this `Command` will attempt to create a pidfd - /// for the child. If this method is never called, a pidfd will - /// not be crated. +/// [`Command`]: process::Command +pub trait CommandExt: private_command_ext::Sealed { + /// Sets whether a [`PidFd`](struct@PidFd) should be created for the [`Child`] + /// spawned by this [`Command`]. + /// By default, no pidfd will be created. /// - /// The pidfd can be retrieved from the child via [`ChildExt::pidfd`] + /// The pidfd can be retrieved from the child with [`pidfd`] or [`take_pidfd`]. /// /// A pidfd will only be created if it is possible to do so - /// in a guaranteed race-free manner (e.g. if the `clone3` system call is - /// supported). Otherwise, [`ChildExit::pidfd`] will return an error. + /// in a guaranteed race-free manner (e.g. if the `clone3` system call + /// is supported). Otherwise, [`pidfd`] will return an error. + /// + /// [`Command`]: process::Command + /// [`Child`]: process::Child + /// [`pidfd`]: fn@ChildExt::pidfd + /// [`take_pidfd`]: ChildExt::take_pidfd fn create_pidfd(&mut self, val: bool) -> &mut process::Command; } diff --git a/library/std/src/sys/unix/process/process_common.rs b/library/std/src/sys/unix/process/process_common.rs index f7a7a9968b8..80cae5a3d79 100644 --- a/library/std/src/sys/unix/process/process_common.rs +++ b/library/std/src/sys/unix/process/process_common.rs @@ -79,7 +79,8 @@ pub struct Command { stdin: Option, stdout: Option, stderr: Option, - pub(crate) make_pidfd: bool, + #[cfg(target_os = "linux")] + create_pidfd: bool, } // Create a new type for argv, so that we can make it `Send` and `Sync` @@ -125,6 +126,7 @@ pub enum Stdio { } impl Command { + #[cfg(not(target_os = "linux"))] pub fn new(program: &OsStr) -> Command { let mut saw_nul = false; let program = os2c(program, &mut saw_nul); @@ -142,7 +144,28 @@ impl Command { stdin: None, stdout: None, stderr: None, - make_pidfd: false, + } + } + + #[cfg(target_os = "linux")] + pub fn new(program: &OsStr) -> Command { + let mut saw_nul = false; + let program = os2c(program, &mut saw_nul); + Command { + argv: Argv(vec![program.as_ptr(), ptr::null()]), + args: vec![program.clone()], + program, + env: Default::default(), + cwd: None, + uid: None, + gid: None, + saw_nul, + closures: Vec::new(), + groups: None, + stdin: None, + stdout: None, + stderr: None, + create_pidfd: false, } } @@ -178,9 +201,21 @@ impl Command { pub fn groups(&mut self, groups: &[gid_t]) { self.groups = Some(Box::from(groups)); } - + + #[cfg(target_os = "linux")] pub fn create_pidfd(&mut self, val: bool) { - self.make_pidfd = val; + self.create_pidfd = val; + } + + #[cfg(not(target_os = "linux"))] + #[allow(dead_code)] + pub fn get_create_pidfd(&self) -> bool { + false + } + + #[cfg(target_os = "linux")] + pub fn get_create_pidfd(&self) -> bool { + self.create_pidfd } pub fn saw_nul(&self) -> bool { diff --git a/library/std/src/sys/unix/process/process_unix.rs b/library/std/src/sys/unix/process/process_unix.rs index 674c694e4fc..f7112a73efa 100644 --- a/library/std/src/sys/unix/process/process_unix.rs +++ b/library/std/src/sys/unix/process/process_unix.rs @@ -8,7 +8,9 @@ use crate::ptr; use crate::sys; use crate::sys::cvt; use crate::sys::process::process_common::*; -use crate::sync::atomic::{AtomicBool, Ordering}; + +#[cfg(target_os = "linux")] +use crate::os::linux::process::PidFd; #[cfg(target_os = "linux")] use crate::sys::weak::syscall; @@ -66,7 +68,7 @@ impl Command { // in its own process. Thus the parent drops the lock guard while the child // forgets it to avoid unlocking it on a new thread, which would be invalid. let env_lock = sys::os::env_read_lock(); - let (pid, pidfd) = self.do_fork()?; + let (pid, pidfd) = unsafe { self.do_fork()? }; if pid == 0 { crate::panic::always_abort(); @@ -95,7 +97,7 @@ impl Command { drop(env_lock); drop(output); - let mut p = Process { pid, status: None, pidfd }; + let mut p = Process::new(pid, pidfd); let mut bytes = [0; 8]; // loop to handle EINTR @@ -127,84 +129,91 @@ impl Command { } } - // Attempts to fork the process. If successful, returns - // Ok((0, -1)) in the child, and Ok((child_pid, child_pidfd)) in the parent. - fn do_fork(&mut self) -> Result<(libc::c_long, libc::pid_t), io::Error> { - // If we fail to create a pidfd for any reason, this will - // stay as -1, which indicates an error - let mut pidfd: libc::pid_t = -1; - - // On Linux, attempt to use the `clone3` syscall, which - // supports more argument (in particular, the ability to create a pidfd). - // If this fails, we will fall through this block to a call to `fork()` - cfg_if::cfg_if! { - if #[cfg(target_os = "linux")] { - static HAS_CLONE3: AtomicBool = AtomicBool::new(true); - - const CLONE_PIDFD: u64 = 0x00001000; - - #[repr(C)] - struct clone_args { - flags: u64, - pidfd: u64, - child_tid: u64, - parent_tid: u64, - exit_signal: u64, - stack: u64, - stack_size: u64, - tls: u64, - set_tid: u64, - set_tid_size: u64, - cgroup: u64, - } + // Attempts to fork the process. If successful, returns Ok((0, -1)) + // in the child, and Ok((child_pid, -1)) in the parent. + #[cfg(not(target_os = "linux"))] + unsafe fn do_fork(&mut self) -> Result<(pid_t, pid_t), io::Error> { + cvt(libc::fork()).map(|res| (res, -1)) + } - syscall! { - fn clone3(cl_args: *mut clone_args, len: libc::size_t) -> libc::c_long - } + // Attempts to fork the process. If successful, returns Ok((0, -1)) + // in the child, and Ok((child_pid, child_pidfd)) in the parent. + #[cfg(target_os = "linux")] + unsafe fn do_fork(&mut self) -> Result<(pid_t, pid_t), io::Error> { + use crate::sync::atomic::{AtomicBool, Ordering}; + + static HAS_CLONE3: AtomicBool = AtomicBool::new(true); + const CLONE_PIDFD: u64 = 0x00001000; + + #[repr(C)] + struct clone_args { + flags: u64, + pidfd: u64, + child_tid: u64, + parent_tid: u64, + exit_signal: u64, + stack: u64, + stack_size: u64, + tls: u64, + set_tid: u64, + set_tid_size: u64, + cgroup: u64, + } - if HAS_CLONE3.load(Ordering::Relaxed) { - let mut flags = 0; - if self.make_pidfd { - flags |= CLONE_PIDFD; - } + syscall! { + fn clone3(cl_args: *mut clone_args, len: libc::size_t) -> libc::c_long + } - let mut args = clone_args { - flags, - pidfd: &mut pidfd as *mut libc::pid_t as u64, - child_tid: 0, - parent_tid: 0, - exit_signal: libc::SIGCHLD as u64, - stack: 0, - stack_size: 0, - tls: 0, - set_tid: 0, - set_tid_size: 0, - cgroup: 0 - }; - - let args_ptr = &mut args as *mut clone_args; - let args_size = crate::mem::size_of::(); - - let res = cvt(unsafe { clone3(args_ptr, args_size) }); - match res { - Ok(n) => return Ok((n, pidfd)), - Err(e) => match e.raw_os_error() { - // Multiple threads can race to execute this store, - // but that's fine - that just means that multiple threads - // will have tried and failed to execute the same syscall, - // with no other side effects. - Some(libc::ENOSYS) => HAS_CLONE3.store(false, Ordering::Relaxed), - _ => return Err(e) - } - } - } + // If we fail to create a pidfd for any reason, this will + // stay as -1, which indicates an error. + let mut pidfd: pid_t = -1; + + // Attempt to use the `clone3` syscall, which supports more arguments + // (in particular, the ability to create a pidfd). If this fails, + // we will fall through this block to a call to `fork()` + if HAS_CLONE3.load(Ordering::Relaxed) { + let mut flags = 0; + if self.get_create_pidfd() { + flags |= CLONE_PIDFD; + } + + let mut args = clone_args { + flags, + pidfd: &mut pidfd as *mut pid_t as u64, + child_tid: 0, + parent_tid: 0, + exit_signal: libc::SIGCHLD as u64, + stack: 0, + stack_size: 0, + tls: 0, + set_tid: 0, + set_tid_size: 0, + cgroup: 0, + }; + + let args_ptr = &mut args as *mut clone_args; + let args_size = crate::mem::size_of::(); + + let res = cvt(clone3(args_ptr, args_size)); + match res { + Ok(n) => return Ok((n as pid_t, pidfd)), + Err(e) => match e.raw_os_error() { + // Multiple threads can race to execute this store, + // but that's fine - that just means that multiple threads + // will have tried and failed to execute the same syscall, + // with no other side effects. + Some(libc::ENOSYS) => HAS_CLONE3.store(false, Ordering::Relaxed), + // Fallback to fork if `EPERM` is returned. (e.g. blocked by seccomp) + Some(libc::EPERM) => {} + _ => return Err(e), + }, } } - // If we get here, we are either not on Linux, - // or we are on Linux and the 'clone3' syscall does not exist - cvt(unsafe { libc::fork() }.into()).map(|res| (res, pidfd)) - } + // If we get here, the 'clone3' syscall does not exist + // or we do not have permission to call it + cvt(libc::fork()).map(|res| (res, pidfd)) + } pub fn exec(&mut self, default: Stdio) -> io::Error { let envp = self.capture_env(); @@ -360,6 +369,8 @@ impl Command { #[cfg(not(any( target_os = "macos", target_os = "freebsd", + all(target_os = "linux", target_env = "gnu"), + all(target_os = "linux", target_env = "musl"), )))] fn posix_spawn( &mut self, @@ -374,6 +385,8 @@ impl Command { #[cfg(any( target_os = "macos", target_os = "freebsd", + all(target_os = "linux", target_env = "gnu"), + all(target_os = "linux", target_env = "musl"), ))] fn posix_spawn( &mut self, @@ -388,6 +401,7 @@ impl Command { || (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); } @@ -432,7 +446,7 @@ impl Command { None => None, }; - let mut p = Process { pid: 0, status: None }; + let mut p = Process::new(0, -1); struct PosixSpawnFileActions<'a>(&'a mut MaybeUninit); @@ -522,14 +536,26 @@ pub struct Process { pid: pid_t, status: Option, // On Linux, stores the pidfd created for this child. - // This is -1 if the user did not request pidfd creation, + // This is None if the user did not request pidfd creation, // or if the pidfd could not be created for some reason // (e.g. the `clone3` syscall was not available). #[cfg(target_os = "linux")] - pidfd: libc::c_int, + pidfd: Option, } impl Process { + #[cfg(target_os = "linux")] + fn new(pid: pid_t, pidfd: pid_t) -> Self { + use crate::sys_common::FromInner; + let pidfd = (pidfd >= 0).then(|| PidFd::from_inner(sys::fd::FileDesc::new(pidfd))); + Process { pid, status: None, pidfd } + } + + #[cfg(not(target_os = "linux"))] + fn new(pid: pid_t, _pidfd: pid_t) -> Self { + Process { pid, status: None } + } + pub fn id(&self) -> u32 { self.pid as u32 } @@ -669,12 +695,18 @@ impl ExitStatusError { #[cfg(target_os = "linux")] #[unstable(feature = "linux_pidfd", issue = "none")] impl crate::os::linux::process::ChildExt for crate::process::Child { - fn pidfd(&self) -> crate::io::Result { - if self.handle.pidfd > 0 { - Ok(self.handle.pidfd) - } else { - Err(crate::io::Error::from(crate::io::ErrorKind::Other)) - } + fn pidfd(&self) -> io::Result<&PidFd> { + self.handle + .pidfd + .as_ref() + .ok_or_else(|| Error::new(ErrorKind::Other, "No pidfd was created.")) + } + + fn take_pidfd(&mut self) -> io::Result { + self.handle + .pidfd + .take() + .ok_or_else(|| Error::new(ErrorKind::Other, "No pidfd was created.")) } } diff --git a/src/test/ui/command/command-create-pidfd.rs b/src/test/ui/command/command-create-pidfd.rs index 248ae3457d7..db728be09df 100644 --- a/src/test/ui/command/command-create-pidfd.rs +++ b/src/test/ui/command/command-create-pidfd.rs @@ -1,13 +1,13 @@ // run-pass -// linux-only - pidfds are a linux-specific concept +// only-linux - pidfds are a linux-specific concept #![feature(linux_pidfd)] use std::os::linux::process::{CommandExt, ChildExt}; use std::process::Command; fn main() { - // We don't assert the precise value, since the standard libarary - // may be opened other file descriptors before our code ran. + // We don't assert the precise value, since the standard library + // might have opened other file descriptors before our code runs. let _ = Command::new("echo") .create_pidfd(true) .spawn() -- cgit 1.4.1-3-g733a5 From 4a832d32f232a68acdabfd29e526d2a4b6366a1c Mon Sep 17 00:00:00 2001 From: Dominik Stolz Date: Sat, 10 Jul 2021 12:58:30 +0200 Subject: Check whether clone3 syscall exists in pidfd test --- src/test/ui/command/command-create-pidfd.rs | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) (limited to 'src/test/ui/command/command-create-pidfd.rs') diff --git a/src/test/ui/command/command-create-pidfd.rs b/src/test/ui/command/command-create-pidfd.rs index db728be09df..93321ac536a 100644 --- a/src/test/ui/command/command-create-pidfd.rs +++ b/src/test/ui/command/command-create-pidfd.rs @@ -2,10 +2,28 @@ // only-linux - pidfds are a linux-specific concept #![feature(linux_pidfd)] -use std::os::linux::process::{CommandExt, ChildExt}; +#![feature(rustc_private)] + +extern crate libc; + +use std::io::Error; +use std::os::linux::process::{ChildExt, CommandExt}; use std::process::Command; +fn has_clone3() -> bool { + let res = unsafe { libc::syscall(libc::SYS_clone3, 0, 0) }; + let err = (res == -1) + .then(|| Error::last_os_error()) + .expect("probe syscall should not succeed"); + err.raw_os_error() != Some(libc::ENOSYS) +} + fn main() { + // pidfds require the clone3 syscall + if !has_clone3() { + return; + } + // We don't assert the precise value, since the standard library // might have opened other file descriptors before our code runs. let _ = Command::new("echo") -- cgit 1.4.1-3-g733a5