myc

config_loader.rs (24167B)

---

 //! Secure descriptor-bound configuration loading and create-new initialization.
 
 use core::fmt;
 use std::{error::Error, path::Path};
 
 use crate::{
     MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES, MycConfigDocumentV1, MycConfigProfile, MycConfigV1Error,
     MycRuntimeContext, parse_myc_config_v1,
 };
 
 /// Stable source-free secure configuration I/O failure classification.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum MycConfigLoadErrorKind {
     InvalidPath,
     Missing,
     AlreadyExists,
     InsecureParent,
     InsecureArtifact,
     TooLarge,
     Io,
     InvalidDocument,
     UnsupportedPlatform,
 }
 
 /// One path- and content-free secure configuration failure.
 #[derive(Clone, Copy, PartialEq, Eq)]
 pub struct MycConfigLoadError {
     kind: MycConfigLoadErrorKind,
 }
 
 impl MycConfigLoadError {
     const fn new(kind: MycConfigLoadErrorKind) -> Self {
         Self { kind }
     }
 
     #[must_use]
     pub const fn kind(self) -> MycConfigLoadErrorKind {
         self.kind
     }
 }
 
 impl fmt::Debug for MycConfigLoadError {
     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
         formatter
             .debug_struct("MycConfigLoadError")
             .field("kind", &self.kind)
             .finish()
     }
 }
 
 impl fmt::Display for MycConfigLoadError {
     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
         formatter.write_str(match self.kind {
             MycConfigLoadErrorKind::InvalidPath => "configuration path is invalid",
             MycConfigLoadErrorKind::Missing => "configuration document is missing",
             MycConfigLoadErrorKind::AlreadyExists => "configuration document already exists",
             MycConfigLoadErrorKind::InsecureParent => "configuration parent is insecure",
             MycConfigLoadErrorKind::InsecureArtifact => "configuration artifact is insecure",
             MycConfigLoadErrorKind::TooLarge => "configuration document exceeds its size limit",
             MycConfigLoadErrorKind::Io => "configuration storage failed",
             MycConfigLoadErrorKind::InvalidDocument => "configuration document is invalid",
             MycConfigLoadErrorKind::UnsupportedPlatform => {
                 "secure configuration storage is unsupported"
             }
         })
     }
 }
 
 impl Error for MycConfigLoadError {}
 
 /// Loads one selected configuration through the governed descriptor boundary.
 pub fn load_myc_config_document(
     runtime: &MycRuntimeContext,
 ) -> Result<MycConfigDocumentV1, MycConfigLoadError> {
     load_myc_config_document_at(runtime.selected_config_path(), profile(runtime))
 }
 
 /// Loads one absolute candidate document without changing the selected path.
 pub fn load_myc_config_candidate(
     runtime: &MycRuntimeContext,
     candidate: &Path,
 ) -> Result<MycConfigDocumentV1, MycConfigLoadError> {
     load_myc_config_document_at(candidate, profile(runtime))
 }
 
 /// Validates and creates the selected non-secret configuration exactly once.
 pub fn initialize_myc_config_document(
     runtime: &MycRuntimeContext,
     bytes: &[u8],
 ) -> Result<MycConfigDocumentV1, MycConfigLoadError> {
     if bytes.len() > MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES {
         return Err(MycConfigLoadError::new(MycConfigLoadErrorKind::TooLarge));
     }
     let document = parse_myc_config_v1(bytes, profile(runtime)).map_err(map_document)?;
     persist_create_new(runtime.selected_config_path(), bytes)?;
     Ok(document)
 }
 
 fn profile(runtime: &MycRuntimeContext) -> MycConfigProfile {
     match runtime.profile() {
         crate::MycBootstrapProfileV1::RepoLocal => MycConfigProfile::RepoLocal,
         crate::MycBootstrapProfileV1::ServiceHost | crate::MycBootstrapProfileV1::Interactive => {
             MycConfigProfile::Production
         }
     }
 }
 
 fn map_document(_: MycConfigV1Error) -> MycConfigLoadError {
     MycConfigLoadError::new(MycConfigLoadErrorKind::InvalidDocument)
 }
 
 #[cfg(any(target_os = "linux", target_os = "macos"))]
 fn load_myc_config_document_at(
     path: &Path,
     profile: MycConfigProfile,
 ) -> Result<MycConfigDocumentV1, MycConfigLoadError> {
     let bytes = native::read_existing(path, MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES)?;
     parse_myc_config_v1(&bytes, profile).map_err(map_document)
 }
 
 #[cfg(not(any(target_os = "linux", target_os = "macos")))]
 fn load_myc_config_document_at(
     _path: &Path,
     _profile: MycConfigProfile,
 ) -> Result<MycConfigDocumentV1, MycConfigLoadError> {
     Err(MycConfigLoadError::new(
         MycConfigLoadErrorKind::UnsupportedPlatform,
     ))
 }
 
 #[cfg(any(target_os = "linux", target_os = "macos"))]
 fn persist_create_new(path: &Path, bytes: &[u8]) -> Result<(), MycConfigLoadError> {
     native::persist_create_new(path, bytes)
 }
 
 #[cfg(not(any(target_os = "linux", target_os = "macos")))]
 fn persist_create_new(_path: &Path, _bytes: &[u8]) -> Result<(), MycConfigLoadError> {
     Err(MycConfigLoadError::new(
         MycConfigLoadErrorKind::UnsupportedPlatform,
     ))
 }
 
 #[cfg(any(target_os = "linux", target_os = "macos"))]
 pub(crate) fn read_secure_bounded_file(
     path: &Path,
     maximum: usize,
 ) -> Result<Vec<u8>, MycConfigLoadError> {
     native::read_existing(path, maximum)
 }
 
 #[cfg(any(target_os = "linux", target_os = "macos"))]
 mod native {
     use std::ffi::OsString;
     use std::fs::File;
     use std::io::{Read, Write};
     use std::os::unix::ffi::OsStrExt;
     use std::path::{Component, Path, PathBuf};
 
     use rustix::fs::{FileType, Mode, OFlags, fchmod, fstat, open, openat, unlinkat};
     use rustix::process::geteuid;
 
     use super::{MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES, MycConfigLoadError, MycConfigLoadErrorKind};
 
     #[derive(Clone, Copy, PartialEq, Eq)]
     struct Identity {
         device: u64,
         inode: u64,
     }
 
     struct SelectedPath {
         parent: PathBuf,
         name: OsString,
     }
 
     impl SelectedPath {
         fn parse(path: &Path) -> Result<Self, MycConfigLoadError> {
             if !path.is_absolute()
                 || path.as_os_str().as_bytes().len() > 4_096
                 || path.components().any(|component| {
                     !matches!(component, Component::RootDir | Component::Normal(_))
                 })
             {
                 return Err(error(MycConfigLoadErrorKind::InvalidPath));
             }
             let name = match path.components().next_back() {
                 Some(Component::Normal(name)) if !name.as_bytes().is_empty() => name.to_os_string(),
                 _ => return Err(error(MycConfigLoadErrorKind::InvalidPath)),
             };
             let parent = path
                 .parent()
                 .filter(|parent| parent.is_absolute())
                 .ok_or_else(|| error(MycConfigLoadErrorKind::InvalidPath))?;
             Ok(Self {
                 parent: parent.to_path_buf(),
                 name,
             })
         }
     }
 
     pub(super) fn read_existing(
         path: &Path,
         maximum: usize,
     ) -> Result<Vec<u8>, MycConfigLoadError> {
         let selected = SelectedPath::parse(path)?;
         let parent = open_parent(&selected.parent)?;
         let parent_identity = directory_identity(&parent)?;
         let descriptor = openat(
             &parent,
             &selected.name,
             OFlags::RDONLY | OFlags::NOFOLLOW | OFlags::CLOEXEC | OFlags::NONBLOCK,
             Mode::empty(),
         )
         .map_err(|source| {
             error(if source == rustix::io::Errno::NOENT {
                 MycConfigLoadErrorKind::Missing
             } else {
                 MycConfigLoadErrorKind::InsecureArtifact
             })
         })?;
         let mut file = File::from(descriptor);
         let status = fstat(&file).map_err(|_| error(MycConfigLoadErrorKind::InsecureArtifact))?;
         let (identity, length) = file_identity(&status, maximum)?;
         let mut bytes = Vec::with_capacity(length);
         Read::by_ref(&mut file)
             .take(u64::try_from(length).unwrap_or(u64::MAX).saturating_add(1))
             .read_to_end(&mut bytes)
             .map_err(|_| error(MycConfigLoadErrorKind::Io))?;
         if bytes.len() != length {
             return Err(error(MycConfigLoadErrorKind::InsecureArtifact));
         }
         validate_current(
             &selected,
             &parent,
             parent_identity,
             &file,
             identity,
             length,
             maximum,
         )?;
         Ok(bytes)
     }
 
     pub(super) fn persist_create_new(path: &Path, bytes: &[u8]) -> Result<(), MycConfigLoadError> {
         let selected = SelectedPath::parse(path)?;
         let parent = open_parent(&selected.parent)?;
         let parent_identity = directory_identity(&parent)?;
         let descriptor = openat(
             &parent,
             &selected.name,
             OFlags::WRONLY
                 | OFlags::CREATE
                 | OFlags::EXCL
                 | OFlags::NOFOLLOW
                 | OFlags::CLOEXEC
                 | OFlags::NONBLOCK,
             Mode::RUSR | Mode::WUSR,
         )
         .map_err(|source| {
             error(if source == rustix::io::Errno::EXIST {
                 MycConfigLoadErrorKind::AlreadyExists
             } else {
                 MycConfigLoadErrorKind::Io
             })
         })?;
         let mut file = File::from(descriptor);
         let status = fstat(&file).map_err(|_| error(MycConfigLoadErrorKind::InsecureArtifact))?;
         let identity = status_identity(&status)?;
         let result = (|| {
             fchmod(&file, Mode::RUSR | Mode::WUSR)
                 .map_err(|_| error(MycConfigLoadErrorKind::Io))?;
             file.write_all(bytes)
                 .and_then(|()| file.sync_all())
                 .map_err(|_| error(MycConfigLoadErrorKind::Io))?;
             validate_current(
                 &selected,
                 &parent,
                 parent_identity,
                 &file,
                 identity,
                 bytes.len(),
                 MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES,
             )?;
             parent
                 .sync_all()
                 .map_err(|_| error(MycConfigLoadErrorKind::Io))?;
             validate_current(
                 &selected,
                 &parent,
                 parent_identity,
                 &file,
                 identity,
                 bytes.len(),
                 MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES,
             )
         })();
         if result.is_err() {
             cleanup(&parent, &selected.name, identity);
         }
         result
     }
 
     fn open_parent(path: &Path) -> Result<File, MycConfigLoadError> {
         let mut components = path.components();
         if !matches!(components.next(), Some(Component::RootDir)) {
             return Err(error(MycConfigLoadErrorKind::InvalidPath));
         }
         let flags = OFlags::RDONLY | OFlags::DIRECTORY | OFlags::NOFOLLOW | OFlags::CLOEXEC;
         let mut parent = File::from(
             open(Path::new("/"), flags, Mode::empty())
                 .map_err(|_| error(MycConfigLoadErrorKind::InsecureParent))?,
         );
         for component in components {
             let Component::Normal(name) = component else {
                 return Err(error(MycConfigLoadErrorKind::InvalidPath));
             };
             parent = File::from(
                 openat(&parent, name, flags, Mode::empty())
                     .map_err(|_| error(MycConfigLoadErrorKind::InsecureParent))?,
             );
         }
         directory_identity(&parent)?;
         Ok(parent)
     }
 
     fn directory_identity(directory: &File) -> Result<Identity, MycConfigLoadError> {
         let status = fstat(directory).map_err(|_| error(MycConfigLoadErrorKind::InsecureParent))?;
         let mode = normalize_mode(status.st_mode);
         if !FileType::from_raw_mode(status.st_mode).is_dir()
             || status.st_uid != geteuid().as_raw()
             || mode & 0o022 != 0
         {
             return Err(error(MycConfigLoadErrorKind::InsecureParent));
         }
         status_identity(&status)
     }
 
     fn file_identity(
         status: &rustix::fs::Stat,
         maximum: usize,
     ) -> Result<(Identity, usize), MycConfigLoadError> {
         let mode = normalize_mode(status.st_mode);
         let length =
             usize::try_from(status.st_size).map_err(|_| error(MycConfigLoadErrorKind::TooLarge))?;
         if !FileType::from_raw_mode(status.st_mode).is_file()
             || normalize_link_count(status.st_nlink) != 1
             || status.st_uid != geteuid().as_raw()
             || mode & 0o400 == 0
             || mode & 0o022 != 0
         {
             return Err(error(MycConfigLoadErrorKind::InsecureArtifact));
         }
         if length > maximum {
             return Err(error(MycConfigLoadErrorKind::TooLarge));
         }
         Ok((status_identity(status)?, length))
     }
 
     fn status_identity(status: &rustix::fs::Stat) -> Result<Identity, MycConfigLoadError> {
         Ok(Identity {
             device: normalize_device(status.st_dev)
                 .map_err(|_| error(MycConfigLoadErrorKind::InsecureArtifact))?,
             inode: status.st_ino,
         })
     }
 
     pub(super) fn normalize_mode<T: Into<u32>>(raw: T) -> u32 {
         raw.into()
     }
 
     pub(super) fn normalize_link_count<T: Into<u64>>(raw: T) -> u64 {
         raw.into()
     }
 
     pub(super) fn normalize_device<T: TryInto<u64>>(raw: T) -> Result<u64, T::Error> {
         raw.try_into()
     }
 
     fn validate_current(
         selected: &SelectedPath,
         parent: &File,
         parent_identity: Identity,
         held: &File,
         held_identity: Identity,
         length: usize,
         maximum: usize,
     ) -> Result<(), MycConfigLoadError> {
         if directory_identity(parent)? != parent_identity {
             return Err(error(MycConfigLoadErrorKind::InsecureParent));
         }
         let current_parent = open_parent(&selected.parent)?;
         if directory_identity(&current_parent)? != parent_identity {
             return Err(error(MycConfigLoadErrorKind::InsecureParent));
         }
         let held_status =
             fstat(held).map_err(|_| error(MycConfigLoadErrorKind::InsecureArtifact))?;
         let (current_held, current_length) = file_identity(&held_status, maximum)?;
         if current_held != held_identity || current_length != length {
             return Err(error(MycConfigLoadErrorKind::InsecureArtifact));
         }
         let current = File::from(
             openat(
                 &current_parent,
                 &selected.name,
                 OFlags::RDONLY | OFlags::NOFOLLOW | OFlags::CLOEXEC | OFlags::NONBLOCK,
                 Mode::empty(),
             )
             .map_err(|_| error(MycConfigLoadErrorKind::InsecureArtifact))?,
         );
         let status =
             fstat(&current).map_err(|_| error(MycConfigLoadErrorKind::InsecureArtifact))?;
         let (current_identity, current_length) = file_identity(&status, maximum)?;
         if current_identity != held_identity || current_length != length {
             return Err(error(MycConfigLoadErrorKind::InsecureArtifact));
         }
         Ok(())
     }
 
     fn cleanup(parent: &File, name: &std::ffi::OsStr, identity: Identity) {
         let current = openat(
             parent,
             name,
             OFlags::RDONLY | OFlags::NOFOLLOW | OFlags::CLOEXEC | OFlags::NONBLOCK,
             Mode::empty(),
         )
         .ok()
         .map(File::from);
         if current.as_ref().is_some_and(|file| {
             fstat(file)
                 .ok()
                 .and_then(|status| status_identity(&status).ok())
                 == Some(identity)
         }) {
             let _ = unlinkat(parent, name, rustix::fs::AtFlags::empty());
             let _ = parent.sync_all();
         }
     }
 
     const fn error(kind: MycConfigLoadErrorKind) -> MycConfigLoadError {
         MycConfigLoadError::new(kind)
     }
 
     #[cfg(test)]
     mod tests {
         use std::os::unix::fs::PermissionsExt as _;
 
         use super::*;
 
         #[test]
         fn validation_rejects_a_replaced_parent_path() {
             let root = tempfile::tempdir().expect("temporary root");
             let parent_path = root.path().join("selected");
             std::fs::create_dir(&parent_path).expect("selected parent");
             std::fs::set_permissions(&parent_path, std::fs::Permissions::from_mode(0o700))
                 .expect("secure selected parent");
             let path = parent_path.join("config.toml");
             std::fs::write(&path, b"config").expect("selected config");
             std::fs::set_permissions(&path, std::fs::Permissions::from_mode(0o600))
                 .expect("secure selected config");
 
             let selected = SelectedPath::parse(&path).expect("selected path");
             let parent = open_parent(&selected.parent).expect("held parent");
             let parent_identity = directory_identity(&parent).expect("parent identity");
             let held = File::from(
                 openat(
                     &parent,
                     &selected.name,
                     OFlags::RDONLY | OFlags::NOFOLLOW | OFlags::CLOEXEC | OFlags::NONBLOCK,
                     Mode::empty(),
                 )
                 .expect("held config"),
             );
             let status = fstat(&held).expect("held status");
             let (identity, length) = file_identity(&status, 16).expect("held identity");
 
             let moved = root.path().join("moved");
             std::fs::rename(&parent_path, &moved).expect("move held parent");
             std::fs::create_dir(&parent_path).expect("replacement parent");
             std::fs::set_permissions(&parent_path, std::fs::Permissions::from_mode(0o700))
                 .expect("secure replacement parent");
             std::fs::write(parent_path.join("config.toml"), b"config").expect("replacement config");
 
             assert_eq!(
                 validate_current(
                     &selected,
                     &parent,
                     parent_identity,
                     &held,
                     identity,
                     length,
                     16,
                 )
                 .expect_err("parent replacement")
                 .kind(),
                 MycConfigLoadErrorKind::InsecureParent
             );
         }
     }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
     #[test]
     fn errors_are_source_free_and_path_free() {
         for kind in [
             MycConfigLoadErrorKind::InvalidPath,
             MycConfigLoadErrorKind::Missing,
             MycConfigLoadErrorKind::AlreadyExists,
             MycConfigLoadErrorKind::InsecureParent,
             MycConfigLoadErrorKind::InsecureArtifact,
             MycConfigLoadErrorKind::TooLarge,
             MycConfigLoadErrorKind::Io,
             MycConfigLoadErrorKind::InvalidDocument,
             MycConfigLoadErrorKind::UnsupportedPlatform,
         ] {
             let error = MycConfigLoadError::new(kind);
             assert_eq!(error.kind(), kind);
             let rendered = format!("{error} {error:?}");
             assert!(!rendered.contains('/'));
             assert!(Error::source(&error).is_none());
         }
     }
 
     #[cfg(any(target_os = "linux", target_os = "macos"))]
     #[test]
     fn native_create_read_permissions_and_collision_are_exact() {
         use std::os::unix::fs::PermissionsExt as _;
 
         let directory = tempfile::tempdir().expect("temporary directory");
         std::fs::set_permissions(directory.path(), std::fs::Permissions::from_mode(0o700))
             .expect("secure directory");
         let path = directory.path().join("config.toml");
         let bytes = b"schema = \"radroots.myc.config\"\n";
         native::persist_create_new(&path, bytes).expect("create-new config");
         assert_eq!(
             std::fs::metadata(&path)
                 .expect("metadata")
                 .permissions()
                 .mode()
                 & 0o777,
             0o600
         );
         assert_eq!(
             native::read_existing(&path, MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES).expect("secure read"),
             bytes
         );
         assert_eq!(
             native::persist_create_new(&path, bytes)
                 .expect_err("collision")
                 .kind(),
             MycConfigLoadErrorKind::AlreadyExists
         );
     }
 
     #[cfg(any(target_os = "linux", target_os = "macos"))]
     #[test]
     fn native_reader_rejects_insecure_parent_artifact_links_and_oversize() {
         use std::os::unix::fs::{PermissionsExt as _, symlink};
 
         let directory = tempfile::tempdir().expect("temporary directory");
         std::fs::set_permissions(directory.path(), std::fs::Permissions::from_mode(0o700))
             .expect("secure directory");
         let path = directory.path().join("config.toml");
         std::fs::write(&path, b"config").expect("config");
         std::fs::set_permissions(&path, std::fs::Permissions::from_mode(0o620))
             .expect("insecure mode");
         assert_eq!(
             native::read_existing(&path, MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES)
                 .expect_err("group-write rejection")
                 .kind(),
             MycConfigLoadErrorKind::InsecureArtifact
         );
 
         std::fs::set_permissions(&path, std::fs::Permissions::from_mode(0o600))
             .expect("secure mode");
         let hardlink = directory.path().join("hardlink.toml");
         std::fs::hard_link(&path, &hardlink).expect("hard link");
         assert_eq!(
             native::read_existing(&path, MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES)
                 .expect_err("single-link rejection")
                 .kind(),
             MycConfigLoadErrorKind::InsecureArtifact
         );
         std::fs::remove_file(&hardlink).expect("remove link");
 
         let symlink_path = directory.path().join("symlink.toml");
         symlink(&path, &symlink_path).expect("symlink");
         assert_eq!(
             native::read_existing(&symlink_path, MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES)
                 .expect_err("no-follow rejection")
                 .kind(),
             MycConfigLoadErrorKind::InsecureArtifact
         );
 
         std::fs::write(&path, vec![b'x'; MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES + 1])
             .expect("oversize");
         assert_eq!(
             native::read_existing(&path, MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES)
                 .expect_err("oversize rejection")
                 .kind(),
             MycConfigLoadErrorKind::TooLarge
         );
 
         std::fs::set_permissions(directory.path(), std::fs::Permissions::from_mode(0o720))
             .expect("insecure parent");
         assert_eq!(
             native::read_existing(&path, MYC_CONFIG_DOCUMENT_MAX_UTF8_BYTES)
                 .expect_err("parent rejection")
                 .kind(),
             MycConfigLoadErrorKind::InsecureParent
         );
     }
 
     #[cfg(any(target_os = "linux", target_os = "macos"))]
     #[test]
     fn native_metadata_normalization_preserves_width_and_signed_device_rejection() {
         assert_eq!(native::normalize_mode(0o600_u16), 0o600);
         assert_eq!(native::normalize_mode(0o700_u32), 0o700);
         assert_eq!(native::normalize_link_count(1_u16), 1);
         assert_eq!(native::normalize_link_count(1_u64), 1);
         assert_eq!(native::normalize_device(7_i32), Ok(7));
         assert!(native::normalize_device(-1_i32).is_err());
     }
 
     #[cfg(any(target_os = "linux", target_os = "macos"))]
     #[test]
     fn generic_secure_reader_enforces_the_callers_exact_bound() {
         use std::os::unix::fs::PermissionsExt as _;
 
         let directory = tempfile::tempdir().expect("temporary directory");
         std::fs::set_permissions(directory.path(), std::fs::Permissions::from_mode(0o700))
             .expect("secure directory");
         let path = directory.path().join("artifact");
         std::fs::write(&path, b"four").expect("artifact");
         std::fs::set_permissions(&path, std::fs::Permissions::from_mode(0o600))
             .expect("secure artifact");
 
         assert_eq!(
             read_secure_bounded_file(&path, 4).expect("exact bound"),
             b"four"
         );
         assert_eq!(
             read_secure_bounded_file(&path, 3)
                 .expect_err("just over bound")
                 .kind(),
             MycConfigLoadErrorKind::TooLarge
         );
     }
 }