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authorValentin Popov <valentin@popov.link>2024-07-19 15:37:58 +0300
committerValentin Popov <valentin@popov.link>2024-07-19 15:37:58 +0300
commita990de90fe41456a23e58bd087d2f107d321f3a1 (patch)
tree15afc392522a9e85dc3332235e311b7d39352ea9 /vendor/rustix/src/procfs.rs
parent3d48cd3f81164bbfc1a755dc1d4a9a02f98c8ddd (diff)
downloadfparkan-a990de90fe41456a23e58bd087d2f107d321f3a1.tar.xz
fparkan-a990de90fe41456a23e58bd087d2f107d321f3a1.zip
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-//! Utilities for working with `/proc`, where Linux's `procfs` is typically
-//! mounted.
-//!
-//! `/proc` serves as an adjunct to Linux's main syscall surface area,
-//! providing additional features with an awkward interface.
-//!
-//! This module does a considerable amount of work to determine whether `/proc`
-//! is mounted, with actual `procfs`, and without any additional mount points
-//! on top of the paths we open.
-//!
-//! Why all the effort to detect bind mount points? People are doing all kinds
-//! of things with Linux containers these days, with many different privilege
-//! schemes, and we want to avoid making any unnecessary assumptions. Rustix
-//! and its users will sometimes use procfs *implicitly* (when Linux gives them
-//! no better options), in ways that aren't obvious from their public APIs.
-//! These filesystem accesses might not be visible to someone auditing the main
-//! code of an application for places which may be influenced by the filesystem
-//! namespace. So with the checking here, they may fail, but they won't be able
-//! to succeed with bogus results.
-
-use crate::fd::{AsFd, BorrowedFd, OwnedFd};
-use crate::ffi::CStr;
-use crate::fs::{
- fstat, fstatfs, major, openat, renameat, FileType, FsWord, Mode, OFlags, RawDir, Stat, CWD,
- PROC_SUPER_MAGIC,
-};
-use crate::io;
-use crate::path::DecInt;
-#[cfg(feature = "rustc-dep-of-std")]
-use core::lazy::OnceCell;
-use core::mem::MaybeUninit;
-#[cfg(not(feature = "rustc-dep-of-std"))]
-use once_cell::sync::OnceCell;
-
-/// Linux's procfs always uses inode 1 for its root directory.
-const PROC_ROOT_INO: u64 = 1;
-
-// Identify an entry within "/proc", to determine which anomalies to check for.
-#[derive(Copy, Clone, Debug)]
-enum Kind {
- Proc,
- Pid,
- Fd,
- File,
- Symlink,
-}
-
-/// Check a subdirectory of "/proc" for anomalies.
-fn check_proc_entry(
- kind: Kind,
- entry: BorrowedFd<'_>,
- proc_stat: Option<&Stat>,
-) -> io::Result<Stat> {
- let entry_stat = fstat(entry)?;
- check_proc_entry_with_stat(kind, entry, entry_stat, proc_stat)
-}
-
-/// Check a subdirectory of "/proc" for anomalies, using the provided `Stat`.
-fn check_proc_entry_with_stat(
- kind: Kind,
- entry: BorrowedFd<'_>,
- entry_stat: Stat,
- proc_stat: Option<&Stat>,
-) -> io::Result<Stat> {
- // Check the filesystem magic.
- check_procfs(entry)?;
-
- match kind {
- Kind::Proc => check_proc_root(entry, &entry_stat)?,
- Kind::Pid | Kind::Fd => check_proc_subdir(entry, &entry_stat, proc_stat)?,
- Kind::File => check_proc_file(&entry_stat, proc_stat)?,
- Kind::Symlink => check_proc_symlink(&entry_stat, proc_stat)?,
- }
-
- // "/proc" directories are typically mounted r-xr-xr-x.
- // "/proc/self/fd" is r-x------. Allow them to have fewer permissions, but
- // not more.
- match kind {
- Kind::Symlink => {
- // On Linux, symlinks don't have their own permissions.
- }
- _ => {
- let expected_mode = if let Kind::Fd = kind { 0o500 } else { 0o555 };
- if entry_stat.st_mode & 0o777 & !expected_mode != 0 {
- return Err(io::Errno::NOTSUP);
- }
- }
- }
-
- match kind {
- Kind::Fd => {
- // Check that the "/proc/self/fd" directory doesn't have any
- // extraneous links into it (which might include unexpected
- // subdirectories).
- if entry_stat.st_nlink != 2 {
- return Err(io::Errno::NOTSUP);
- }
- }
- Kind::Pid | Kind::Proc => {
- // Check that the "/proc" and "/proc/self" directories aren't
- // empty.
- if entry_stat.st_nlink <= 2 {
- return Err(io::Errno::NOTSUP);
- }
- }
- Kind::File => {
- // Check that files in procfs don't have extraneous hard links to
- // them (which might indicate hard links to other things).
- if entry_stat.st_nlink != 1 {
- return Err(io::Errno::NOTSUP);
- }
- }
- Kind::Symlink => {
- // Check that symlinks in procfs don't have extraneous hard links
- // to them (which might indicate hard links to other things).
- if entry_stat.st_nlink != 1 {
- return Err(io::Errno::NOTSUP);
- }
- }
- }
-
- Ok(entry_stat)
-}
-
-fn check_proc_root(entry: BorrowedFd<'_>, stat: &Stat) -> io::Result<()> {
- // We use `O_DIRECTORY` for proc directories, so open should fail if we
- // don't get a directory when we expect one.
- assert_eq!(FileType::from_raw_mode(stat.st_mode), FileType::Directory);
-
- // Check the root inode number.
- if stat.st_ino != PROC_ROOT_INO {
- return Err(io::Errno::NOTSUP);
- }
-
- // Proc is a non-device filesystem, so check for major number 0.
- // <https://www.kernel.org/doc/Documentation/admin-guide/devices.txt>
- if major(stat.st_dev) != 0 {
- return Err(io::Errno::NOTSUP);
- }
-
- // Check that "/proc" is a mountpoint.
- if !is_mountpoint(entry) {
- return Err(io::Errno::NOTSUP);
- }
-
- Ok(())
-}
-
-fn check_proc_subdir(
- entry: BorrowedFd<'_>,
- stat: &Stat,
- proc_stat: Option<&Stat>,
-) -> io::Result<()> {
- // We use `O_DIRECTORY` for proc directories, so open should fail if we
- // don't get a directory when we expect one.
- assert_eq!(FileType::from_raw_mode(stat.st_mode), FileType::Directory);
-
- check_proc_nonroot(stat, proc_stat)?;
-
- // Check that subdirectories of "/proc" are not mount points.
- if is_mountpoint(entry) {
- return Err(io::Errno::NOTSUP);
- }
-
- Ok(())
-}
-
-fn check_proc_file(stat: &Stat, proc_stat: Option<&Stat>) -> io::Result<()> {
- // Check that we have a regular file.
- if FileType::from_raw_mode(stat.st_mode) != FileType::RegularFile {
- return Err(io::Errno::NOTSUP);
- }
-
- check_proc_nonroot(stat, proc_stat)?;
-
- Ok(())
-}
-
-fn check_proc_symlink(stat: &Stat, proc_stat: Option<&Stat>) -> io::Result<()> {
- // Check that we have a symbolic link.
- if FileType::from_raw_mode(stat.st_mode) != FileType::Symlink {
- return Err(io::Errno::NOTSUP);
- }
-
- check_proc_nonroot(stat, proc_stat)?;
-
- Ok(())
-}
-
-fn check_proc_nonroot(stat: &Stat, proc_stat: Option<&Stat>) -> io::Result<()> {
- // Check that we haven't been linked back to the root of "/proc".
- if stat.st_ino == PROC_ROOT_INO {
- return Err(io::Errno::NOTSUP);
- }
-
- // Check that we're still in procfs.
- if stat.st_dev != proc_stat.unwrap().st_dev {
- return Err(io::Errno::NOTSUP);
- }
-
- Ok(())
-}
-
-/// Check that `file` is opened on a `procfs` filesystem.
-fn check_procfs(file: BorrowedFd<'_>) -> io::Result<()> {
- let statfs = fstatfs(file)?;
- let f_type = statfs.f_type;
- if f_type != FsWord::from(PROC_SUPER_MAGIC) {
- return Err(io::Errno::NOTSUP);
- }
-
- Ok(())
-}
-
-/// Check whether the given directory handle is a mount point.
-fn is_mountpoint(file: BorrowedFd<'_>) -> bool {
- // We use a `renameat` call that would otherwise fail, but which fails with
- // `XDEV` first if it would cross a mount point.
- let err = renameat(file, cstr!("../."), file, cstr!(".")).unwrap_err();
- match err {
- io::Errno::XDEV => true, // the rename failed due to crossing a mount point
- io::Errno::BUSY => false, // the rename failed normally
- _ => panic!("Unexpected error from `renameat`: {:?}", err),
- }
-}
-
-/// Open a directory in `/proc`, mapping all errors to `io::Errno::NOTSUP`.
-fn proc_opendirat<P: crate::path::Arg, Fd: AsFd>(dirfd: Fd, path: P) -> io::Result<OwnedFd> {
- // We don't add `PATH` here because that disables `DIRECTORY`. And we don't
- // add `NOATIME` for the same reason as the comment in `open_and_check_file`.
- let oflags = OFlags::NOFOLLOW | OFlags::DIRECTORY | OFlags::CLOEXEC | OFlags::NOCTTY;
- openat(dirfd, path, oflags, Mode::empty()).map_err(|_err| io::Errno::NOTSUP)
-}
-
-/// Returns a handle to Linux's `/proc` directory.
-///
-/// This ensures that `/proc` is procfs, that nothing is mounted on top of it,
-/// and that it looks normal. It also returns the `Stat` of `/proc`.
-///
-/// # References
-/// - [Linux]
-///
-/// [Linux]: https://man7.org/linux/man-pages/man5/proc.5.html
-fn proc() -> io::Result<(BorrowedFd<'static>, &'static Stat)> {
- static PROC: StaticFd = StaticFd::new();
-
- // `OnceBox` is "racey" in that the initialization function may run
- // multiple times. We're ok with that, since the initialization function
- // has no side effects.
- PROC.get_or_try_init(|| {
- // Open "/proc".
- let proc = proc_opendirat(CWD, cstr!("/proc"))?;
- let proc_stat =
- check_proc_entry(Kind::Proc, proc.as_fd(), None).map_err(|_err| io::Errno::NOTSUP)?;
-
- Ok(new_static_fd(proc, proc_stat))
- })
- .map(|(fd, stat)| (fd.as_fd(), stat))
-}
-
-/// Returns a handle to Linux's `/proc/self` directory.
-///
-/// This ensures that `/proc/self` is procfs, that nothing is mounted on top of
-/// it, and that it looks normal. It also returns the `Stat` of `/proc/self`.
-///
-/// # References
-/// - [Linux]
-///
-/// [Linux]: https://man7.org/linux/man-pages/man5/proc.5.html
-#[allow(unsafe_code)]
-fn proc_self() -> io::Result<(BorrowedFd<'static>, &'static Stat)> {
- static PROC_SELF: StaticFd = StaticFd::new();
-
- // The init function here may run multiple times; see above.
- PROC_SELF
- .get_or_try_init(|| {
- let (proc, proc_stat) = proc()?;
-
- // `getpid` would return our pid in our own pid namespace, so
- // instead use `readlink` on the `self` symlink to learn our pid in
- // the procfs namespace.
- let self_symlink = open_and_check_file(proc, proc_stat, cstr!("self"), Kind::Symlink)?;
- let mut buf = [MaybeUninit::<u8>::uninit(); 20];
- let len = crate::backend::fs::syscalls::readlinkat(
- self_symlink.as_fd(),
- cstr!(""),
- &mut buf,
- )?;
- let pid: &[u8] = unsafe { core::mem::transmute(&buf[..len]) };
-
- // Open "/proc/self". Use our pid to compute the name rather than
- // literally using "self", as "self" is a symlink.
- let proc_self = proc_opendirat(proc, pid)?;
- let proc_self_stat = check_proc_entry(Kind::Pid, proc_self.as_fd(), Some(proc_stat))
- .map_err(|_err| io::Errno::NOTSUP)?;
-
- Ok(new_static_fd(proc_self, proc_self_stat))
- })
- .map(|(owned, stat)| (owned.as_fd(), stat))
-}
-
-/// Returns a handle to Linux's `/proc/self/fd` directory.
-///
-/// This ensures that `/proc/self/fd` is `procfs`, that nothing is mounted on
-/// top of it, and that it looks normal.
-///
-/// # References
-/// - [Linux]
-///
-/// [Linux]: https://man7.org/linux/man-pages/man5/proc.5.html
-#[cfg_attr(doc_cfg, doc(cfg(feature = "procfs")))]
-pub fn proc_self_fd() -> io::Result<BorrowedFd<'static>> {
- static PROC_SELF_FD: StaticFd = StaticFd::new();
-
- // The init function here may run multiple times; see above.
- PROC_SELF_FD
- .get_or_try_init(|| {
- let (_, proc_stat) = proc()?;
-
- let (proc_self, _proc_self_stat) = proc_self()?;
-
- // Open "/proc/self/fd".
- let proc_self_fd = proc_opendirat(proc_self, cstr!("fd"))?;
- let proc_self_fd_stat =
- check_proc_entry(Kind::Fd, proc_self_fd.as_fd(), Some(proc_stat))
- .map_err(|_err| io::Errno::NOTSUP)?;
-
- Ok(new_static_fd(proc_self_fd, proc_self_fd_stat))
- })
- .map(|(owned, _stat)| owned.as_fd())
-}
-
-type StaticFd = OnceCell<(OwnedFd, Stat)>;
-
-#[inline]
-fn new_static_fd(fd: OwnedFd, stat: Stat) -> (OwnedFd, Stat) {
- (fd, stat)
-}
-
-/// Returns a handle to Linux's `/proc/self/fdinfo` directory.
-///
-/// This ensures that `/proc/self/fdinfo` is `procfs`, that nothing is mounted
-/// on top of it, and that it looks normal. It also returns the `Stat` of
-/// `/proc/self/fd`.
-///
-/// # References
-/// - [Linux]
-///
-/// [Linux]: https://man7.org/linux/man-pages/man5/proc.5.html
-fn proc_self_fdinfo() -> io::Result<(BorrowedFd<'static>, &'static Stat)> {
- static PROC_SELF_FDINFO: StaticFd = StaticFd::new();
-
- PROC_SELF_FDINFO
- .get_or_try_init(|| {
- let (_, proc_stat) = proc()?;
-
- let (proc_self, _proc_self_stat) = proc_self()?;
-
- // Open "/proc/self/fdinfo".
- let proc_self_fdinfo = proc_opendirat(proc_self, cstr!("fdinfo"))?;
- let proc_self_fdinfo_stat =
- check_proc_entry(Kind::Fd, proc_self_fdinfo.as_fd(), Some(proc_stat))
- .map_err(|_err| io::Errno::NOTSUP)?;
-
- Ok((proc_self_fdinfo, proc_self_fdinfo_stat))
- })
- .map(|(owned, stat)| (owned.as_fd(), stat))
-}
-
-/// Returns a handle to a Linux `/proc/self/fdinfo/<fd>` file.
-///
-/// This ensures that `/proc/self/fdinfo/<fd>` is `procfs`, that nothing is
-/// mounted on top of it, and that it looks normal.
-///
-/// # References
-/// - [Linux]
-///
-/// [Linux]: https://man7.org/linux/man-pages/man5/proc.5.html
-#[inline]
-#[cfg_attr(doc_cfg, doc(cfg(feature = "procfs")))]
-pub fn proc_self_fdinfo_fd<Fd: AsFd>(fd: Fd) -> io::Result<OwnedFd> {
- _proc_self_fdinfo(fd.as_fd())
-}
-
-fn _proc_self_fdinfo(fd: BorrowedFd<'_>) -> io::Result<OwnedFd> {
- let (proc_self_fdinfo, proc_self_fdinfo_stat) = proc_self_fdinfo()?;
- let fd_str = DecInt::from_fd(fd);
- open_and_check_file(
- proc_self_fdinfo,
- proc_self_fdinfo_stat,
- fd_str.as_c_str(),
- Kind::File,
- )
-}
-
-/// Returns a handle to a Linux `/proc/self/pagemap` file.
-///
-/// This ensures that `/proc/self/pagemap` is `procfs`, that nothing is
-/// mounted on top of it, and that it looks normal.
-///
-/// # References
-/// - [Linux]
-/// - [Linux pagemap]
-///
-/// [Linux]: https://man7.org/linux/man-pages/man5/proc.5.html
-/// [Linux pagemap]: https://www.kernel.org/doc/Documentation/vm/pagemap.txt
-#[inline]
-#[cfg_attr(doc_cfg, doc(cfg(feature = "procfs")))]
-pub fn proc_self_pagemap() -> io::Result<OwnedFd> {
- proc_self_file(cstr!("pagemap"))
-}
-
-/// Returns a handle to a Linux `/proc/self/maps` file.
-///
-/// This ensures that `/proc/self/maps` is `procfs`, that nothing is
-/// mounted on top of it, and that it looks normal.
-///
-/// # References
-/// - [Linux]
-///
-/// [Linux]: https://man7.org/linux/man-pages/man5/proc.5.html
-#[inline]
-#[cfg_attr(doc_cfg, doc(cfg(feature = "procfs")))]
-pub fn proc_self_maps() -> io::Result<OwnedFd> {
- proc_self_file(cstr!("maps"))
-}
-
-/// Returns a handle to a Linux `/proc/self/status` file.
-///
-/// This ensures that `/proc/self/status` is `procfs`, that nothing is
-/// mounted on top of it, and that it looks normal.
-///
-/// # References
-/// - [Linux]
-///
-/// [Linux]: https://man7.org/linux/man-pages/man5/proc.5.html
-#[inline]
-#[cfg_attr(doc_cfg, doc(cfg(feature = "procfs")))]
-pub fn proc_self_status() -> io::Result<OwnedFd> {
- proc_self_file(cstr!("status"))
-}
-
-/// Open a file under `/proc/self`.
-fn proc_self_file(name: &CStr) -> io::Result<OwnedFd> {
- let (proc_self, proc_self_stat) = proc_self()?;
- open_and_check_file(proc_self, proc_self_stat, name, Kind::File)
-}
-
-/// Open a procfs file within in `dir` and check it for bind mounts.
-fn open_and_check_file(
- dir: BorrowedFd<'_>,
- dir_stat: &Stat,
- name: &CStr,
- kind: Kind,
-) -> io::Result<OwnedFd> {
- let (_, proc_stat) = proc()?;
-
- // Don't use `NOATIME`, because it [requires us to own the file], and when
- // a process sets itself non-dumpable Linux changes the user:group of its
- // `/proc/<pid>` files [to root:root].
- //
- // [requires us to own the file]: https://man7.org/linux/man-pages/man2/openat.2.html
- // [to root:root]: https://man7.org/linux/man-pages/man5/proc.5.html
- let mut oflags = OFlags::RDONLY | OFlags::CLOEXEC | OFlags::NOFOLLOW | OFlags::NOCTTY;
- if let Kind::Symlink = kind {
- // Open symlinks with `O_PATH`.
- oflags |= OFlags::PATH;
- }
- let file = openat(dir, name, oflags, Mode::empty()).map_err(|_err| io::Errno::NOTSUP)?;
- let file_stat = fstat(&file)?;
-
- // `is_mountpoint` only works on directory mount points, not file mount
- // points. To detect file mount points, scan the parent directory to see if
- // we can find a regular file with an inode and name that matches the file
- // we just opened. If we can't find it, there could be a file bind mount on
- // top of the file we want.
- //
- // TODO: With Linux 5.8 we might be able to use `statx` and
- // `STATX_ATTR_MOUNT_ROOT` to detect mountpoints directly instead of doing
- // this scanning.
-
- let expected_type = match kind {
- Kind::File => FileType::RegularFile,
- Kind::Symlink => FileType::Symlink,
- _ => unreachable!(),
- };
-
- let mut found_file = false;
- let mut found_dot = false;
-
- let mut buf = [MaybeUninit::uninit(); 2048];
- let mut iter = RawDir::new(dir, &mut buf);
- while let Some(entry) = iter.next() {
- let entry = entry.map_err(|_err| io::Errno::NOTSUP)?;
- if entry.ino() == file_stat.st_ino
- && entry.file_type() == expected_type
- && entry.file_name() == name
- {
- // We found the file. Proceed to check the file handle.
- let _ = check_proc_entry_with_stat(kind, file.as_fd(), file_stat, Some(proc_stat))?;
-
- found_file = true;
- } else if entry.ino() == dir_stat.st_ino
- && entry.file_type() == FileType::Directory
- && entry.file_name() == cstr!(".")
- {
- // We found ".", and it's the right ".".
- found_dot = true;
- }
- }
-
- if found_file && found_dot {
- Ok(file)
- } else {
- Err(io::Errno::NOTSUP)
- }
-}