harden: create rewind working-tree directories via os.Root

3417ff8→main·

Soph·1mo ago·3 files·+99 added/-6 removed

When entire checkpoint rewind restores files from a checkpoint tree, the file write already used os.Root (kernel-enforced containment), but the preceding directory creation used a raw os.MkdirAll(filepath.Join(repoRoot, f.Name)). A crafted tree entry name containing ".." from an untrusted checkpoint could thus create empty directories outside the repo before the guarded write refused to escape.

Add osroot.MkdirAll, which creates each level via os.Root.Mkdir so the kernel rejects any path that escapes the root, and use it in the restore loop. Both filesystem operations in that loop are now containment-safe.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

Sessions

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Changes

3

• cmd/entire/cli

• osroot

• Mosroot.go+31

• Mosroot_test.go+61

• strategy

• Mmanual_commit_rewind.go+7/-6

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package osroot

import (
    "errors"
    "io"
    "io/fs"
    "os"
    "path"
    "path/filepath"
    "strings"
)

// ReadFile reads the named file relative to root using os.Root for
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return nil
}

// MkdirAll creates the directory named by name, along with any necessary
// parents, relative to root. Each level is created with os.Root.Mkdir so the
// kernel enforces containment: unlike os.MkdirAll, it cannot create directories
// outside root. A name that escapes root (absolute, or containing ".." segments
// that climb above root) is rejected by os.Root and returns an error. Already-
// existing directories are tolerated. name may use either OS-native or forward
// slashes; an empty or "." name is a no-op.
func MkdirAll(root *os.Root, name string, perm os.FileMode) error {
    name = strings.Trim(filepath.ToSlash(name), "/")
    if name == "" || name == "." {
        return nil
    }

cur := ""
    for _, part := range strings.Split(name, "/") {
        if part == "" {
            continue
        }
        cur = path.Join(cur, part)
        if err := root.Mkdir(cur, perm); err != nil && !errors.Is(err, fs.ErrExist) {
            return err //nolint:wrapcheck // preserve original error (incl. traversal rejection) for callers
        }
    }
    return nil
}

// Remove removes the named file relative to root using os.Root for
// traversal-resistant access. Returns nil if the file doesn't exist.
func Remove(root *os.Root, name string) error {

Mcmd/entire/cli/osroot/osroot.go+31

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assert.Error(t, err)
}

func TestMkdirAll(t *testing.T) {
    t.Parallel()

dir := t.TempDir()
    root, err := os.OpenRoot(dir)
    require.NoError(t, err)
    defer root.Close()

require.NoError(t, osroot.MkdirAll(root, "a/b/c", 0o755))

info, err := os.Stat(filepath.Join(dir, "a", "b", "c"))
    require.NoError(t, err)
    assert.True(t, info.IsDir())
}

func TestMkdirAll_Idempotent(t *testing.T) {
    t.Parallel()

dir := t.TempDir()
    root, err := os.OpenRoot(dir)
    require.NoError(t, err)
    defer root.Close()

require.NoError(t, osroot.MkdirAll(root, "x/y", 0o755))
    // Creating an existing tree must not error.
    require.NoError(t, osroot.MkdirAll(root, "x/y", 0o755))
}

func TestMkdirAll_EmptyOrDotIsNoop(t *testing.T) {
    t.Parallel()

dir := t.TempDir()
    root, err := os.OpenRoot(dir)
    require.NoError(t, err)
    defer root.Close()

require.NoError(t, osroot.MkdirAll(root, "", 0o755))
    require.NoError(t, osroot.MkdirAll(root, ".", 0o755))
}

func TestMkdirAll_TraversalBlocked(t *testing.T) {
    t.Parallel()

dir := t.TempDir()
    outsideDir := t.TempDir()

root, err := os.OpenRoot(dir)
    require.NoError(t, err)
    defer root.Close()

for _, name := range []string{"../escape", "../../escape/deep", "a/../../escape"} {
        err := osroot.MkdirAll(root, name, 0o755)
        require.Error(t, err, "MkdirAll(%q) must be rejected", name)
    }

// Nothing must have been created outside the root.
    entries, err := os.ReadDir(outsideDir)
    require.NoError(t, err)
    assert.Empty(t, entries, "no directories should be created outside the root")
}

func TestWriteFile(t *testing.T) {
    t.Parallel()

Mcmd/entire/cli/osroot/osroot_test.go+61

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"fmt"
    "io"
    "os"
    "path"
    "path/filepath"
    "sort"
    "strings"
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return fmt.Errorf("failed to read file %s: %w", f.Name, err)
        }

// Ensure directory exists (MkdirAll not available on os.Root)
        absPath := filepath.Join(repoRoot, f.Name)
        dir := filepath.Dir(absPath)
        if dir != "." {
            //nolint:gosec // G301: Need 0o755 for user directories during rewind
            if err := os.MkdirAll(dir, 0o755); err != nil {
        // Ensure parent directories exist via os.Root so a crafted tree entry
        // name (e.g. containing "..") from an untrusted checkpoint cannot create
        // directories outside the repo. f.Name uses forward slashes (git tree).
        dir := path.Dir(f.Name)
        if dir != "." && dir != "" {
            if err := osroot.MkdirAll(repoRootHandle, dir, 0o755); err != nil {
                return fmt.Errorf("failed to create directory %s: %w", dir, err)
            }
        }