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Merged
amannocci merged 1 commit into from
Oct 24, 2026
Merged

feat(fix-perms): add OnRootMismatch change policy #6

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16 changes: 16 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,22 @@
- Drop-in replacements for the original execlineb scripts
- Single package replacing `ignity-utils` (`.deb` and `.rpm`)

## :wrench: Configuration

`fix-perms` reads the following environment variables:

| Variable | Default | Description |
|--------------------|----------|-----------------------------------------------------------------|
| `USERMAP_UID` | `0` | Substituted for `{{USERMAP_UID}}` in spec lines. |
| `USERMAP_GID` | `0` | Substituted for `{{USERMAP_GID}}` in spec lines. |
| `FIX_PERMS_POLICY` | `Always` | `Always` or `OnRootMismatch` (case-insensitive), see below. |

`FIX_PERMS_POLICY` mirrors Kubernetes' `fsGroupChangePolicy`:

- `Always` walks the whole tree of every spec path.
- `OnRootMismatch` skips a spec path entirely when its root already has the expected owner and mode, which avoids a full traversal of large trees on every start.
Entries below a matching root that have drifted are **not** fixed.

## :dart: Motivation

- ignity's built-in scripts fork `find`, `xargs`, `chown`, and `chmod` for every path spec.
Expand Down
183 changes: 166 additions & 17 deletions crates/fix-perms/src/main.rs
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Expand Up @@ -18,10 +18,18 @@
//! 2. `chmod fmode` every non-directory entry whose mode differs.
//! 3. `chmod dmode` every directory entry whose mode differs.
//!
//! The `FIX_PERMS_POLICY` environment variable mirrors Kubernetes'
//! `fsGroupChangePolicy` (case-insensitive):
//! - `Always` (default): walk the whole tree for every spec.
//! - `OnRootMismatch`: skip the spec entirely when the root path already has
//! the expected owner and mode. Entries below a matching root that have
//! drifted are *not* fixed.
//!
//! The implementation is fully in-process (no `find`, `xargs`, `chown` or
//! `chmod` child processes), making it significantly faster than the original
//! execlineb pipeline for large trees.

use std::fs::Metadata;
use std::io::{self, BufRead};
use std::os::unix::fs::{MetadataExt, PermissionsExt};
use std::path::Path;
Expand Down Expand Up @@ -140,12 +148,67 @@ fn parse_env_u32(name: &str) -> u32 {
}
}

// ---------------------------------------------------------------------------
// Change policy
// ---------------------------------------------------------------------------

/// When to traverse a spec path, mirroring Kubernetes' `fsGroupChangePolicy`.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum ChangePolicy {
/// Always walk the whole tree.
Always,
/// Skip the tree when its root already matches the spec.
OnRootMismatch,
}

/// Parse a `FIX_PERMS_POLICY` value, defaulting to `Always`.
///
/// An invalid value emits a warning and falls back to `Always` — the safe
/// choice, since it never skips a fix.
fn parse_policy(value: Option<&str>) -> ChangePolicy {
match value {
None => ChangePolicy::Always,
Some(v) if v.eq_ignore_ascii_case("Always") => ChangePolicy::Always,
Some(v) if v.eq_ignore_ascii_case("OnRootMismatch") => ChangePolicy::OnRootMismatch,
Some(v) => {
eprintln!(
"fix-perms: warning: FIX_PERMS_POLICY={v:?} is not one of Always, OnRootMismatch; defaulting to Always"
);
ChangePolicy::Always
}
}
}

/// Read the change policy from the `FIX_PERMS_POLICY` environment variable.
fn policy_from_env() -> ChangePolicy {
parse_policy(std::env::var("FIX_PERMS_POLICY").ok().as_deref())
}

// ---------------------------------------------------------------------------
// Core logic
// ---------------------------------------------------------------------------

/// Compare an entry's metadata against the spec.
///
/// Returns `(owner_matches, target_perm_bits)` where `target_perm_bits` is
/// `Some(bits)` when the permission bits differ and must be changed.
fn check_entry(metadata: &Metadata, spec: &PermSpec) -> (bool, Option<u32>) {
let owner_matches = metadata.uid() == spec.uid && metadata.gid() == spec.gid;
let target_mode = if metadata.is_dir() {
spec.dir_mode
} else {
spec.file_mode
};
// Compare only the permission bits (mask out file-type bits).
let current_perm_bits = metadata.mode() & 0o7777;
// `mode_t` is u16 on macOS and u32 on Linux; `as _` avoids an unnecessary-cast lint on Linux.
let target_perm_bits: u32 = target_mode.bits() as _;
let mode_change = (current_perm_bits != target_perm_bits).then_some(target_perm_bits);
(owner_matches, mode_change)
}

/// Apply the permission spec to all entries under `spec.path`.
fn apply_spec(spec: &PermSpec) -> Result<()> {
fn apply_spec(spec: &PermSpec, policy: ChangePolicy) -> Result<()> {
let root = Path::new(&spec.path);
if root.is_symlink() {
eprintln!(
Expand All @@ -162,6 +225,18 @@ fn apply_spec(spec: &PermSpec) -> Result<()> {
return Ok(());
}

if policy == ChangePolicy::OnRootMismatch {
// The root is known not to be a symlink, so lstat == stat here.
let metadata = std::fs::symlink_metadata(root)?;
if let (true, None) = check_entry(&metadata, spec) {
eprintln!(
"fix-perms: info: skipping '{}': root already matches (OnRootMismatch)",
root.display()
);
return Ok(());
}
}

let target_uid = Uid::from_raw(spec.uid);
let target_gid = Gid::from_raw(spec.gid);
let mut had_entry_error = false;
Expand Down Expand Up @@ -198,30 +273,19 @@ fn apply_spec(spec: &PermSpec) -> Result<()> {
};

let path = entry.path();
let current_uid = metadata.uid();
let current_gid = metadata.gid();
let (owner_matches, mode_change) = check_entry(&metadata, spec);

// ── 1. chown if owner differs ──────────────────────────────────────
if current_uid != spec.uid || current_gid != spec.gid {
if !owner_matches {
if let Err(err) = chown(path, Some(target_uid), Some(target_gid)) {
eprintln!("fix-perms: warning: chown {}: {err}", path.display());
had_entry_error = true;
}
}

// ── 2. chmod according to entry type ──────────────────────────────
let is_dir = metadata.is_dir();
let target_mode = if is_dir {
spec.dir_mode
} else {
spec.file_mode
};
// Compare only the permission bits (mask out file-type bits).
// chown(2) does not modify mode bits, so cached metadata is still valid here.
let current_perm_bits = metadata.mode() & 0o7777;
let target_perm_bits = target_mode.bits() as u32;

if current_perm_bits != target_perm_bits {
if let Some(target_perm_bits) = mode_change {
let new_perms = std::fs::Permissions::from_mode(target_perm_bits);
if let Err(err) = std::fs::set_permissions(path, new_perms) {
eprintln!("fix-perms: warning: chmod {}: {err}", path.display());
Expand Down Expand Up @@ -250,6 +314,7 @@ fn main() {
// to the operator.
let usermap_uid: u32 = parse_env_u32("USERMAP_UID");
let usermap_gid: u32 = parse_env_u32("USERMAP_GID");
let policy = policy_from_env();

let stdin = io::stdin();
let mut had_error = false;
Expand Down Expand Up @@ -277,7 +342,7 @@ fn main() {
}
};

if let Err(err) = apply_spec(&spec) {
if let Err(err) = apply_spec(&spec, policy) {
eprintln!("fix-perms: error applying spec for '{}': {err}", spec.path);
had_error = true;
}
Expand All @@ -295,6 +360,7 @@ fn main() {
#[cfg(test)]
mod tests {
use super::*;
use std::path::PathBuf;

// ── parse helpers ───────────────────────────────────────────────────────

Expand Down Expand Up @@ -421,7 +487,7 @@ mod tests {
file_mode: Mode::from_bits(0o644).unwrap(),
dir_mode: Mode::from_bits(0o755).unwrap(),
};
apply_spec(&spec).unwrap();
apply_spec(&spec, ChangePolicy::Always).unwrap();

let file_mode = std::fs::metadata(&file).unwrap().permissions().mode() & 0o777;
let dir_mode = std::fs::metadata(&real).unwrap().permissions().mode() & 0o777;
Expand All @@ -430,4 +496,87 @@ mod tests {
assert_eq!(file_mode, 0o600, "target file must not be touched");
assert_eq!(dir_mode, 0o700, "target dir must not be touched");
}

// ── change policy ───────────────────────────────────────────────────────

#[test]
fn test_parse_policy() {
assert_eq!(parse_policy(None), ChangePolicy::Always);
assert_eq!(parse_policy(Some("Always")), ChangePolicy::Always);
assert_eq!(
parse_policy(Some("OnRootMismatch")),
ChangePolicy::OnRootMismatch
);
assert_eq!(
parse_policy(Some("onrootmismatch")),
ChangePolicy::OnRootMismatch
);
assert_eq!(parse_policy(Some("bogus")), ChangePolicy::Always);
}

/// Create `<tmp>/<name>/root/child` with the given modes and return
/// `(base, root, child)`.
fn make_tree(name: &str, root_mode: u32, child_mode: u32) -> (PathBuf, PathBuf, PathBuf) {
let base = std::env::temp_dir().join(format!("fix-perms-{name}-{}", std::process::id()));
let _ = std::fs::remove_dir_all(&base);
let root = base.join("root");
std::fs::create_dir_all(&root).unwrap();
let child = root.join("child");
std::fs::write(&child, b"x").unwrap();
std::fs::set_permissions(&child, std::fs::Permissions::from_mode(child_mode)).unwrap();
std::fs::set_permissions(&root, std::fs::Permissions::from_mode(root_mode)).unwrap();
(base, root, child)
}

fn spec_for(path: &Path) -> PermSpec {
let meta = std::fs::metadata(path).unwrap();
PermSpec {
path: path.to_string_lossy().into_owned(),
uid: meta.uid(),
gid: meta.gid(),
file_mode: Mode::from_bits(0o644).unwrap(),
dir_mode: Mode::from_bits(0o755).unwrap(),
}
}

fn mode_of(path: &Path) -> u32 {
std::fs::metadata(path).unwrap().permissions().mode() & 0o7777
}

#[test]
fn test_on_root_mismatch_skips_matching_root() {
let (base, root, child) = make_tree("orm-skip", 0o755, 0o600);
apply_spec(&spec_for(&root), ChangePolicy::OnRootMismatch).unwrap();
let child_mode = mode_of(&child);
let _ = std::fs::remove_dir_all(&base);
assert_eq!(child_mode, 0o600, "child must not be touched");
}

#[test]
fn test_always_fixes_below_matching_root() {
let (base, root, child) = make_tree("always", 0o755, 0o600);
apply_spec(&spec_for(&root), ChangePolicy::Always).unwrap();
let child_mode = mode_of(&child);
let _ = std::fs::remove_dir_all(&base);
assert_eq!(child_mode, 0o644);
}

#[test]
fn test_on_root_mismatch_walks_mismatching_root() {
let (base, root, child) = make_tree("orm-walk", 0o700, 0o600);
apply_spec(&spec_for(&root), ChangePolicy::OnRootMismatch).unwrap();
let (root_mode, child_mode) = (mode_of(&root), mode_of(&child));
let _ = std::fs::remove_dir_all(&base);
assert_eq!(root_mode, 0o755);
assert_eq!(child_mode, 0o644);
}

#[test]
fn test_on_root_mismatch_matching_file_root() {
let (base, _root, child) = make_tree("orm-file", 0o755, 0o644);
apply_spec(&spec_for(&child), ChangePolicy::OnRootMismatch).unwrap();
let child_mode = mode_of(&child);
let _ = std::fs::remove_dir_all(&base);
assert_eq!(child_mode, 0o644);
}
}
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