landlock/fs.rs
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use crate::compat::private::OptionCompatLevelMut;
use crate::{
uapi, Access, AddRuleError, AddRulesError, CompatError, CompatLevel, CompatResult, CompatState,
Compatible, HandleAccessError, HandleAccessesError, PathBeneathError, PathFdError,
PrivateAccess, PrivateRule, Rule, Ruleset, RulesetCreated, RulesetError, TailoredCompatLevel,
TryCompat, ABI,
};
use enumflags2::{bitflags, make_bitflags, BitFlags};
use std::fs::OpenOptions;
use std::io::Error;
use std::mem::zeroed;
use std::os::unix::fs::OpenOptionsExt;
use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, OwnedFd};
use std::path::Path;
#[cfg(test)]
use crate::{RulesetAttr, RulesetCreatedAttr};
#[cfg(test)]
use strum::IntoEnumIterator;
/// File system access right.
///
/// Each variant of `AccessFs` is an [access right](https://www.kernel.org/doc/html/latest/userspace-api/landlock.html#access-rights)
/// for the file system.
/// A set of access rights can be created with [`BitFlags<AccessFs>`](BitFlags).
///
/// # Example
///
/// ```
/// use landlock::{ABI, Access, AccessFs, BitFlags, make_bitflags};
///
/// let exec = AccessFs::Execute;
///
/// let exec_set: BitFlags<AccessFs> = exec.into();
///
/// let file_content = make_bitflags!(AccessFs::{Execute | WriteFile | ReadFile});
///
/// let fs_v1 = AccessFs::from_all(ABI::V1);
///
/// let without_exec = fs_v1 & !AccessFs::Execute;
///
/// assert_eq!(fs_v1 | AccessFs::Refer, AccessFs::from_all(ABI::V2));
/// ```
///
/// # Warning
///
/// To avoid unknown restrictions **don't use `BitFlags::<AccessFs>::all()` nor `BitFlags::ALL`**,
/// but use a version you tested and vetted instead,
/// for instance [`AccessFs::from_all(ABI::V1)`](Access::from_all).
/// Direct use of **the [`BitFlags`] API is deprecated**.
/// See [`ABI`] for the rationale and help to test it.
#[bitflags]
#[repr(u64)]
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[non_exhaustive]
pub enum AccessFs {
/// Execute a file.
Execute = uapi::LANDLOCK_ACCESS_FS_EXECUTE as u64,
/// Open a file with write access.
WriteFile = uapi::LANDLOCK_ACCESS_FS_WRITE_FILE as u64,
/// Open a file with read access.
ReadFile = uapi::LANDLOCK_ACCESS_FS_READ_FILE as u64,
/// Open a directory or list its content.
ReadDir = uapi::LANDLOCK_ACCESS_FS_READ_DIR as u64,
/// Remove an empty directory or rename one.
RemoveDir = uapi::LANDLOCK_ACCESS_FS_REMOVE_DIR as u64,
/// Unlink (or rename) a file.
RemoveFile = uapi::LANDLOCK_ACCESS_FS_REMOVE_FILE as u64,
/// Create (or rename or link) a character device.
MakeChar = uapi::LANDLOCK_ACCESS_FS_MAKE_CHAR as u64,
/// Create (or rename) a directory.
MakeDir = uapi::LANDLOCK_ACCESS_FS_MAKE_DIR as u64,
/// Create (or rename or link) a regular file.
MakeReg = uapi::LANDLOCK_ACCESS_FS_MAKE_REG as u64,
/// Create (or rename or link) a UNIX domain socket.
MakeSock = uapi::LANDLOCK_ACCESS_FS_MAKE_SOCK as u64,
/// Create (or rename or link) a named pipe.
MakeFifo = uapi::LANDLOCK_ACCESS_FS_MAKE_FIFO as u64,
/// Create (or rename or link) a block device.
MakeBlock = uapi::LANDLOCK_ACCESS_FS_MAKE_BLOCK as u64,
/// Create (or rename or link) a symbolic link.
MakeSym = uapi::LANDLOCK_ACCESS_FS_MAKE_SYM as u64,
/// Link or rename a file from or to a different directory.
Refer = uapi::LANDLOCK_ACCESS_FS_REFER as u64,
/// Truncate a file with `truncate(2)`, `ftruncate(2)`, `creat(2)`, or `open(2)` with `O_TRUNC`.
Truncate = uapi::LANDLOCK_ACCESS_FS_TRUNCATE as u64,
/// Send IOCL commands to a device file.
IoctlDev = uapi::LANDLOCK_ACCESS_FS_IOCTL_DEV as u64,
}
impl Access for AccessFs {
/// Union of [`from_read()`](AccessFs::from_read) and [`from_write()`](AccessFs::from_write).
fn from_all(abi: ABI) -> BitFlags<Self> {
// An empty access-right would be an error if passed to the kernel, but because the kernel
// doesn't support Landlock, no Landlock syscall should be called. try_compat() should
// also return RestrictionStatus::Unrestricted when called with unsupported/empty
// access-rights.
Self::from_read(abi) | Self::from_write(abi)
}
}
impl AccessFs {
// Roughly read (i.e. not all FS actions are handled).
/// Gets the access rights identified as read-only according to a specific ABI.
/// Exclusive with [`from_write()`](AccessFs::from_write).
pub fn from_read(abi: ABI) -> BitFlags<Self> {
match abi {
ABI::Unsupported => BitFlags::EMPTY,
ABI::V1 | ABI::V2 | ABI::V3 | ABI::V4 | ABI::V5 => make_bitflags!(AccessFs::{
Execute
| ReadFile
| ReadDir
}),
}
}
// Roughly write (i.e. not all FS actions are handled).
/// Gets the access rights identified as write-only according to a specific ABI.
/// Exclusive with [`from_read()`](AccessFs::from_read).
pub fn from_write(abi: ABI) -> BitFlags<Self> {
match abi {
ABI::Unsupported => BitFlags::EMPTY,
ABI::V1 => make_bitflags!(AccessFs::{
WriteFile
| RemoveDir
| RemoveFile
| MakeChar
| MakeDir
| MakeReg
| MakeSock
| MakeFifo
| MakeBlock
| MakeSym
}),
ABI::V2 => Self::from_write(ABI::V1) | AccessFs::Refer,
ABI::V3 | ABI::V4 => Self::from_write(ABI::V2) | AccessFs::Truncate,
ABI::V5 => Self::from_write(ABI::V4) | AccessFs::IoctlDev,
}
}
/// Gets the access rights legitimate for non-directory files.
pub fn from_file(abi: ABI) -> BitFlags<Self> {
Self::from_all(abi) & ACCESS_FILE
}
}
#[test]
fn consistent_access_fs_rw() {
for abi in ABI::iter() {
let access_all = AccessFs::from_all(abi);
let access_read = AccessFs::from_read(abi);
let access_write = AccessFs::from_write(abi);
assert_eq!(access_read, !access_write & access_all);
assert_eq!(access_read | access_write, access_all);
}
}
impl PrivateAccess for AccessFs {
fn ruleset_handle_access(
ruleset: &mut Ruleset,
access: BitFlags<Self>,
) -> Result<(), HandleAccessesError> {
// We need to record the requested accesses for PrivateRule::check_consistency().
ruleset.requested_handled_fs |= access;
ruleset.actual_handled_fs |= match access
.try_compat(
ruleset.compat.abi(),
ruleset.compat.level,
&mut ruleset.compat.state,
)
.map_err(HandleAccessError::Compat)?
{
Some(a) => a,
None => return Ok(()),
};
Ok(())
}
fn into_add_rules_error(error: AddRuleError<Self>) -> AddRulesError {
AddRulesError::Fs(error)
}
fn into_handle_accesses_error(error: HandleAccessError<Self>) -> HandleAccessesError {
HandleAccessesError::Fs(error)
}
}
// TODO: Make ACCESS_FILE a property of AccessFs.
// TODO: Add tests for ACCESS_FILE.
const ACCESS_FILE: BitFlags<AccessFs> = make_bitflags!(AccessFs::{
ReadFile | WriteFile | Execute | Truncate | IoctlDev
});
// XXX: What should we do when a stat call failed?
fn is_file<F>(fd: F) -> Result<bool, Error>
where
F: AsFd,
{
unsafe {
let mut stat = zeroed();
match libc::fstat(fd.as_fd().as_raw_fd(), &mut stat) {
0 => Ok((stat.st_mode & libc::S_IFMT) != libc::S_IFDIR),
_ => Err(Error::last_os_error()),
}
}
}
/// Landlock rule for a file hierarchy.
///
/// # Example
///
/// ```
/// use landlock::{AccessFs, PathBeneath, PathFd, PathFdError};
///
/// fn home_dir() -> Result<PathBeneath<PathFd>, PathFdError> {
/// Ok(PathBeneath::new(PathFd::new("/home")?, AccessFs::ReadDir))
/// }
/// ```
#[cfg_attr(test, derive(Debug))]
pub struct PathBeneath<F> {
attr: uapi::landlock_path_beneath_attr,
// Ties the lifetime of a file descriptor to this object.
parent_fd: F,
allowed_access: BitFlags<AccessFs>,
compat_level: Option<CompatLevel>,
}
impl<F> PathBeneath<F>
where
F: AsFd,
{
/// Creates a new `PathBeneath` rule identifying the `parent` directory of a file hierarchy,
/// or just a file, and allows `access` on it.
/// The `parent` file descriptor will be automatically closed with the returned `PathBeneath`.
pub fn new<A>(parent: F, access: A) -> Self
where
A: Into<BitFlags<AccessFs>>,
{
PathBeneath {
// Invalid access rights until as_ptr() is called.
attr: unsafe { zeroed() },
parent_fd: parent,
allowed_access: access.into(),
compat_level: None,
}
}
}
impl<F> TryCompat<AccessFs> for PathBeneath<F>
where
F: AsFd,
{
fn try_compat_children<L>(
mut self,
abi: ABI,
parent_level: L,
compat_state: &mut CompatState,
) -> Result<Option<Self>, CompatError<AccessFs>>
where
L: Into<CompatLevel>,
{
// Checks with our own compatibility level, if any.
self.allowed_access = match self.allowed_access.try_compat(
abi,
self.tailored_compat_level(parent_level),
compat_state,
)? {
Some(a) => a,
None => return Ok(None),
};
Ok(Some(self))
}
fn try_compat_inner(
&mut self,
_abi: ABI,
) -> Result<CompatResult<AccessFs>, CompatError<AccessFs>> {
// Gets subset of valid accesses according the FD type.
let valid_access =
if is_file(&self.parent_fd).map_err(|e| PathBeneathError::StatCall { source: e })? {
self.allowed_access & ACCESS_FILE
} else {
self.allowed_access
};
if self.allowed_access != valid_access {
let error = PathBeneathError::DirectoryAccess {
access: self.allowed_access,
incompatible: self.allowed_access ^ valid_access,
}
.into();
self.allowed_access = valid_access;
// Linux would return EINVAL.
Ok(CompatResult::Partial(error))
} else {
Ok(CompatResult::Full)
}
}
}
#[test]
fn path_beneath_try_compat_children() {
use crate::*;
// AccessFs::Refer is not handled by ABI::V1 and only for directories.
let access_file = AccessFs::ReadFile | AccessFs::Refer;
// Test error ordering with ABI::V1
let mut ruleset = Ruleset::from(ABI::V1).handle_access(access_file).unwrap();
// Do not actually perform any syscall.
ruleset.compat.state = CompatState::Dummy;
assert!(matches!(
RulesetCreated::new(ruleset, -1)
.set_compatibility(CompatLevel::HardRequirement)
.add_rule(PathBeneath::new(PathFd::new("/dev/null").unwrap(), access_file))
.unwrap_err(),
RulesetError::AddRules(AddRulesError::Fs(AddRuleError::Compat(
CompatError::PathBeneath(PathBeneathError::DirectoryAccess { access, incompatible })
))) if access == access_file && incompatible == AccessFs::Refer
));
// Test error ordering with ABI::V2
let mut ruleset = Ruleset::from(ABI::V2).handle_access(access_file).unwrap();
// Do not actually perform any syscall.
ruleset.compat.state = CompatState::Dummy;
assert!(matches!(
RulesetCreated::new(ruleset, -1)
.set_compatibility(CompatLevel::HardRequirement)
.add_rule(PathBeneath::new(PathFd::new("/dev/null").unwrap(), access_file))
.unwrap_err(),
RulesetError::AddRules(AddRulesError::Fs(AddRuleError::Compat(
CompatError::PathBeneath(PathBeneathError::DirectoryAccess { access, incompatible })
))) if access == access_file && incompatible == AccessFs::Refer
));
}
#[test]
fn path_beneath_try_compat() {
use crate::*;
let abi = ABI::V1;
for file in &["/etc/passwd", "/dev/null"] {
let mut compat_state = CompatState::Init;
let ro_access = AccessFs::ReadDir | AccessFs::ReadFile;
assert!(matches!(
PathBeneath::new(PathFd::new(file).unwrap(), ro_access)
.try_compat(abi, CompatLevel::HardRequirement, &mut compat_state)
.unwrap_err(),
CompatError::PathBeneath(PathBeneathError::DirectoryAccess { access, incompatible })
if access == ro_access && incompatible == AccessFs::ReadDir
));
let mut compat_state = CompatState::Init;
assert!(matches!(
PathBeneath::new(PathFd::new(file).unwrap(), BitFlags::EMPTY)
.try_compat(abi, CompatLevel::BestEffort, &mut compat_state)
.unwrap_err(),
CompatError::Access(AccessError::Empty)
));
}
let full_access = AccessFs::from_all(ABI::V1);
for compat_level in &[
CompatLevel::BestEffort,
CompatLevel::SoftRequirement,
CompatLevel::HardRequirement,
] {
let mut compat_state = CompatState::Init;
let mut path_beneath = PathBeneath::new(PathFd::new("/").unwrap(), full_access)
.try_compat(abi, *compat_level, &mut compat_state)
.unwrap()
.unwrap();
assert_eq!(compat_state, CompatState::Full);
// Without synchronization.
let raw_access = path_beneath.attr.allowed_access;
assert_eq!(raw_access, 0);
// Synchronize the inner attribute buffer.
let _ = path_beneath.as_ptr();
let raw_access = path_beneath.attr.allowed_access;
assert_eq!(raw_access, full_access.bits());
}
}
impl<F> OptionCompatLevelMut for PathBeneath<F> {
fn as_option_compat_level_mut(&mut self) -> &mut Option<CompatLevel> {
&mut self.compat_level
}
}
impl<F> OptionCompatLevelMut for &mut PathBeneath<F> {
fn as_option_compat_level_mut(&mut self) -> &mut Option<CompatLevel> {
&mut self.compat_level
}
}
impl<F> Compatible for PathBeneath<F> {}
impl<F> Compatible for &mut PathBeneath<F> {}
#[test]
fn path_beneath_compatibility() {
let mut path = PathBeneath::new(PathFd::new("/").unwrap(), AccessFs::from_all(ABI::V1));
let path_ref = &mut path;
let level = path_ref.as_option_compat_level_mut();
assert_eq!(level, &None);
assert_eq!(
<Option<CompatLevel> as Into<CompatLevel>>::into(*level),
CompatLevel::BestEffort
);
path_ref.set_compatibility(CompatLevel::SoftRequirement);
assert_eq!(
path_ref.as_option_compat_level_mut(),
&Some(CompatLevel::SoftRequirement)
);
path.set_compatibility(CompatLevel::HardRequirement);
}
// It is useful for documentation generation to explicitely implement Rule for every types, instead
// of doing it generically.
impl<F> Rule<AccessFs> for PathBeneath<F> where F: AsFd {}
impl<F> PrivateRule<AccessFs> for PathBeneath<F>
where
F: AsFd,
{
const TYPE_ID: uapi::landlock_rule_type = uapi::landlock_rule_type_LANDLOCK_RULE_PATH_BENEATH;
fn as_ptr(&mut self) -> *const libc::c_void {
self.attr.parent_fd = self.parent_fd.as_fd().as_raw_fd();
self.attr.allowed_access = self.allowed_access.bits();
&self.attr as *const _ as _
}
fn check_consistency(&self, ruleset: &RulesetCreated) -> Result<(), AddRulesError> {
// Checks that this rule doesn't contain a superset of the access-rights handled by the
// ruleset. This check is about requested access-rights but not actual access-rights.
// Indeed, we want to get a deterministic behavior, i.e. not based on the running kernel
// (which is handled by Ruleset and RulesetCreated).
if ruleset.requested_handled_fs.contains(self.allowed_access) {
Ok(())
} else {
Err(AddRuleError::UnhandledAccess {
access: self.allowed_access,
incompatible: self.allowed_access & !ruleset.requested_handled_fs,
}
.into())
}
}
}
#[test]
fn path_beneath_check_consistency() {
use crate::*;
let ro_access = AccessFs::ReadDir | AccessFs::ReadFile;
let rx_access = AccessFs::Execute | AccessFs::ReadFile;
assert!(matches!(
Ruleset::from(ABI::Unsupported)
.handle_access(ro_access)
.unwrap()
.create()
.unwrap()
.add_rule(PathBeneath::new(PathFd::new("/").unwrap(), rx_access))
.unwrap_err(),
RulesetError::AddRules(AddRulesError::Fs(AddRuleError::UnhandledAccess { access, incompatible }))
if access == rx_access && incompatible == AccessFs::Execute
));
}
/// Simple helper to open a file or a directory with the `O_PATH` flag.
///
/// This is the recommended way to identify a path
/// and manage the lifetime of the underlying opened file descriptor.
/// Indeed, using other [`AsFd`] implementations such as [`File`] brings more complexity
/// and may lead to unexpected errors (e.g., denied access).
///
/// [`File`]: std::fs::File
///
/// # Example
///
/// ```
/// use landlock::{AccessFs, PathBeneath, PathFd, PathFdError};
///
/// fn allowed_root_dir(access: AccessFs) -> Result<PathBeneath<PathFd>, PathFdError> {
/// let fd = PathFd::new("/")?;
/// Ok(PathBeneath::new(fd, access))
/// }
/// ```
#[cfg_attr(test, derive(Debug))]
pub struct PathFd {
fd: OwnedFd,
}
impl PathFd {
pub fn new<T>(path: T) -> Result<Self, PathFdError>
where
T: AsRef<Path>,
{
Ok(PathFd {
fd: OpenOptions::new()
.read(true)
// If the O_PATH is not supported, it is automatically ignored (Linux < 2.6.39).
.custom_flags(libc::O_PATH | libc::O_CLOEXEC)
.open(path.as_ref())
.map_err(|e| PathFdError::OpenCall {
source: e,
path: path.as_ref().into(),
})?
.into(),
})
}
}
impl AsFd for PathFd {
fn as_fd(&self) -> BorrowedFd<'_> {
self.fd.as_fd()
}
}
#[test]
fn path_fd() {
use std::fs::File;
use std::io::Read;
PathBeneath::new(PathFd::new("/").unwrap(), AccessFs::Execute);
PathBeneath::new(File::open("/").unwrap(), AccessFs::Execute);
let mut buffer = [0; 1];
// Checks that PathFd really returns an FD opened with O_PATH (Bad file descriptor error).
File::from(PathFd::new("/etc/passwd").unwrap().fd)
.read(&mut buffer)
.unwrap_err();
}
/// Helper to quickly create an iterator of PathBeneath rules.
///
/// Silently ignores paths that cannot be opened, and automatically adjust access rights according
/// to file types when possible.
///
/// # Example
///
/// ```
/// use landlock::{
/// ABI, Access, AccessFs, Ruleset, RulesetAttr, RulesetCreatedAttr, RulesetStatus, RulesetError,
/// path_beneath_rules,
/// };
///
/// fn restrict_thread() -> Result<(), RulesetError> {
/// let abi = ABI::V1;
/// let status = Ruleset::default()
/// .handle_access(AccessFs::from_all(abi))?
/// .create()?
/// // Read-only access to /usr, /etc and /dev.
/// .add_rules(path_beneath_rules(&["/usr", "/etc", "/dev"], AccessFs::from_read(abi)))?
/// // Read-write access to /home and /tmp.
/// .add_rules(path_beneath_rules(&["/home", "/tmp"], AccessFs::from_all(abi)))?
/// .restrict_self()?;
/// match status.ruleset {
/// // The FullyEnforced case must be tested by the developer.
/// RulesetStatus::FullyEnforced => println!("Fully sandboxed."),
/// RulesetStatus::PartiallyEnforced => println!("Partially sandboxed."),
/// // Users should be warned that they are not protected.
/// RulesetStatus::NotEnforced => println!("Not sandboxed! Please update your kernel."),
/// }
/// Ok(())
/// }
/// ```
pub fn path_beneath_rules<I, P, A>(
paths: I,
access: A,
) -> impl Iterator<Item = Result<PathBeneath<PathFd>, RulesetError>>
where
I: IntoIterator<Item = P>,
P: AsRef<Path>,
A: Into<BitFlags<AccessFs>>,
{
let access = access.into();
paths.into_iter().filter_map(move |p| match PathFd::new(p) {
Ok(f) => {
let valid_access = match is_file(&f) {
Ok(true) => access & ACCESS_FILE,
// If the stat call failed, let's blindly rely on the requested access rights.
Err(_) | Ok(false) => access,
};
Some(Ok(PathBeneath::new(f, valid_access)))
}
Err(_) => None,
})
}
#[test]
fn path_beneath_rules_iter() {
let _ = Ruleset::default()
.handle_access(AccessFs::from_all(ABI::V1))
.unwrap()
.create()
.unwrap()
.add_rules(path_beneath_rules(
&["/usr", "/opt", "/does-not-exist", "/root"],
AccessFs::Execute,
))
.unwrap();
}