vfs: renaming a directory through a symlink into its descendant detaches the subtree

[trivikr]

Version

main

Platform

All

Subsystem

vfs

What steps will reproduce the bug?

import { create } from 'node:vfs';

const fs = create();

fs.mkdirSync('/a/b', { recursive: true });
fs.writeFileSync('/a/keep.txt', 'keep');
fs.symlinkSync('/a/b', '/alias');

try {
  fs.renameSync('/a', '/alias/moved');
  console.log('rename succeeded');
} catch (error) {
  console.log('rename threw:', error.code);
}

console.log('/a exists:', fs.existsSync('/a'));
console.log('original data exists:', fs.existsSync('/a/keep.txt'));
console.log('/alias exists:', fs.existsSync('/alias'));

How often does it reproduce? Is there a required condition?

Always

What is the expected behavior? Why is that the expected behavior?

The rename should throw EINVAL and leave the directory tree unchanged, matching native fs. /alias/moved resolves to /a/b/moved, so this attempts to move /a into its own descendant.

What do you see instead?

rename succeeded
/a exists: false
original data exists: false
/alias exists: false

The operation detaches /a and its contents from the filesystem root. /alias remains a symlink but becomes dangling.

Additional information

fs equivalent

import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';

const root = fs.mkdtempSync(path.join(os.tmpdir(), 'rename-repro-'));
const p = (name) => path.join(root, name);

try {
  fs.mkdirSync(p('a/b'), { recursive: true });
  fs.writeFileSync(p('a/keep.txt'), 'keep');
  fs.symlinkSync(p('a/b'), p('alias'), 'dir');

  try {
    fs.renameSync(p('a'), p('alias/moved'));
    console.log('rename succeeded');
  } catch (error) {
    console.log('rename threw:', error.code);
  }

  console.log('/a exists:', fs.existsSync(p('a')));
  console.log('original data exists:', fs.existsSync(p('a/keep.txt')));
  console.log('/alias exists:', fs.existsSync(p('alias')));
} finally {
  fs.rmSync(root, { recursive: true, force: true });
}

Output

rename threw: EINVAL
/a exists: true
original data exists: true
/alias exists: true