Accept safe overlay work residue after unmount

crates/lazaret-state-anchor/src/lib.rs

@@ -34,10 +34,11 @@ use rustix::io::dup;
 use rustix::thread::{ThreadNameSpaceType, move_into_thread_name_spaces};
 use storage::{
     atomic_replace_at, create_directory, create_regular_file, descriptor_child_path,
-    descriptor_path, directory_has_entries, host_path, inspect_directory, move_all_entries,
-    move_selected_entries, open_directory, open_exact_directory_path, open_mounted_directory,
-    open_or_create_quarantine, open_regular_file, path_from_host, remove_directory_contents,
-    require_directory_descriptor_identity, require_same_descriptor, validate_relative_path,
+    descriptor_path, host_path, inspect_directory, move_all_entries, move_selected_entries,
+    open_directory, open_exact_directory_path, open_mounted_directory, open_or_create_quarantine,
+    open_regular_file, path_from_host, remove_directory_contents,
+    require_directory_descriptor_identity, require_maintenance_work_shape, require_same_descriptor,
+    validate_relative_path,
 };
 
 const MOUNT_TIMEOUT: Duration = Duration::from_secs(5);
@@ -394,12 +395,7 @@ impl<'configuration> StateAnchorLayout<'configuration> {
 
     fn require_maintenance_ready_allowing_quarantine(&self) -> Result<(), StateAnchorError> {
         self.require_unmounted()?;
-        if directory_has_entries(&self.work_descriptor)? {
-            return Err(StateAnchorError::InvalidLayout(
-                "State Anchor work directory is not empty",
-            ));
-        }
-        Ok(())
+        require_maintenance_work_shape(&self.work_descriptor)
     }
 }
 

crates/lazaret-state-anchor/src/lib/storage.rs

@@ -210,7 +210,14 @@ pub(super) fn remove_directory_contents(directory: impl AsFd) -> Result<(), Stat
 }
 
 fn directory_names(directory: impl AsFd) -> Result<Vec<OsString>, StateAnchorError> {
-    let descriptor = rustix::io::dup(directory.as_fd()).map_err(io::Error::from)?;
+    let descriptor = openat2(
+        directory.as_fd(),
+        ".",
+        OFlags::RDONLY | OFlags::DIRECTORY | OFlags::CLOEXEC,
+        Mode::empty(),
+        confined_resolve_flags(),
+    )
+    .map_err(io::Error::from)?;
     let mut buffer = [std::mem::MaybeUninit::uninit(); 8192];
     let mut raw = RawDir::new(descriptor, &mut buffer);
     let mut names = Vec::new();
@@ -228,6 +235,31 @@ pub(super) fn directory_has_entries(directory: impl AsFd) -> Result<bool, StateA
     Ok(!directory_names(directory)?.is_empty())
 }
 
+pub(super) fn require_maintenance_work_shape(directory: impl AsFd) -> Result<(), StateAnchorError> {
+    let names = directory_names(&directory)?;
+    if names.is_empty() {
+        return Ok(());
+    }
+    if names.as_slice() != [OsString::from("work")] {
+        return Err(StateAnchorError::InvalidLayout(
+            "State Anchor work directory has unsupported entries",
+        ));
+    }
+    let nested = open_directory(&directory, Path::new("work"))?;
+    let parent = rustix::fs::fstat(&directory).map_err(io::Error::from)?;
+    let child = rustix::fs::fstat(&nested).map_err(io::Error::from)?;
+    if child.st_mode & 0o7777 != 0o700
+        || child.st_uid != parent.st_uid
+        || child.st_gid != parent.st_gid
+        || directory_has_entries(&nested)?
+    {
+        return Err(StateAnchorError::InvalidLayout(
+            "State Anchor work directory has unsupported entries",
+        ));
+    }
+    Ok(())
+}
+
 pub(super) fn validate_relative_path(path: &Path) -> Result<(), StateAnchorError> {
     if path.as_os_str().is_empty()
         || path

crates/lazaret-state-anchor/tests/authority.rs

@@ -2,7 +2,7 @@ use std::collections::BTreeMap;
 use std::ffi::OsString;
 use std::fs::{self, File};
 use std::os::unix::ffi::OsStringExt;
-use std::os::unix::fs::MetadataExt;
+use std::os::unix::fs::{MetadataExt, PermissionsExt};
 use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicU64, Ordering};
 
@@ -21,6 +21,45 @@ use lazaret_state_anchor::{
 
 static SEQUENCE: AtomicU64 = AtomicU64::new(0);
 
+#[test]
+fn maintenance_accepts_exact_empty_fuse_overlayfs_work_shape() {
+    let tree = TestTree::new();
+    let configuration = configuration(&tree);
+    let layout = StateAnchorLayout::create(&configuration).unwrap();
+    let nested = domain_path(&configuration).join("state-anchor/work/work");
+    fs::create_dir(&nested).unwrap();
+    fs::set_permissions(&nested, fs::Permissions::from_mode(0o700)).unwrap();
+
+    layout.inspect_state().unwrap();
+}
+
+#[test]
+fn maintenance_refuses_mutated_fuse_overlayfs_work_shapes() {
+    let tree = TestTree::new();
+    let configuration = configuration(&tree);
+    let layout = StateAnchorLayout::create(&configuration).unwrap();
+    let work = domain_path(&configuration).join("state-anchor/work");
+    let nested = work.join("work");
+    fs::create_dir(&nested).unwrap();
+    fs::set_permissions(&nested, fs::Permissions::from_mode(0o755)).unwrap();
+    assert!(layout.inspect_state().is_err());
+
+    fs::set_permissions(&nested, fs::Permissions::from_mode(0o700)).unwrap();
+    fs::write(nested.join("unexpected"), b"").unwrap();
+    assert!(layout.inspect_state().is_err());
+
+    fs::remove_file(nested.join("unexpected")).unwrap();
+    fs::write(work.join("unexpected"), b"").unwrap();
+    assert!(layout.inspect_state().is_err());
+
+    fs::remove_file(work.join("unexpected")).unwrap();
+    fs::remove_dir(&nested).unwrap();
+    let foreign = tree.path.join("foreign-work");
+    fs::create_dir(&foreign).unwrap();
+    std::os::unix::fs::symlink(foreign, nested).unwrap();
+    assert!(layout.inspect_state().is_err());
+}
+
 #[test]
 fn selected_reset_removes_exact_state_and_whiteout_without_touching_siblings() {
     let tree = TestTree::new();

crates/lazaret-state-anchor/tests/state-anchor-lifecycle.rs

@@ -191,6 +191,7 @@ fn run() -> io::Result<()> {
         ));
     }
     first.unmount().map_err(io::Error::other)?;
+    layout.inspect_state().map_err(io::Error::other)?;
 
     let second = acquire(&layout, &artifact)?;
     if fs::read(layout.merged().join("usr/bin/installed-tool"))? != b"persistent"