From: "nagachika (Tomoyuki Chikanaga) via ruby-core" <ruby-core@...>
Date: 2026-09-23T04:32:34+00:00
Subject: [ruby-core:126839] [Ruby Bug#22340] Win32: File.stat succeeds on symbolic-link loops on Windows

Issue #22340 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 3.3: REQUIRED, 3.4: REQUIRED, 4.0: REQUIRED to 3.3: REQUIRED, 3.4: DONE, 4.0: REQUIRED

ruby_3_4 commit:7bbe8e88007f8283a421cb31db86da32076126a6 merged revision(s) commit:ad23fd4a519fde4fc96c7326fb9b0347cbc347b8.

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Bug #22340: Win32: File.stat succeeds on symbolic-link loops on Windows
https://bugs.ruby-lang.org/issues/22340#change-119183

* Author: nobu (Nobuyoshi Nakada)
* Status: Closed
* Backport: 3.3: REQUIRED, 3.4: DONE, 4.0: REQUIRED
----------------------------------------
On Windows, `File.stat` succeeds on a self-referential symbolic link instead of raising `Errno::ELOOP`, and `File.exist?` returns `true`.  Opening the same link raises `Errno::ELOOP`.

I noticed this while adding symbolic-link tests to FileUtils, whose Windows CI reported the unexpected `File.exist?` result.

## Reproduction

````ruby
require 'tmpdir'

Dir.mktmpdir do |dir|
  Dir.chdir(dir) do
    File.symlink('a', 'a')
    p File.readlink('a') # => "a"
    p File.exist?('a')  # => true; expected false
    p File.stat('a')    # succeeds; expected Errno::ELOOP
    File.open('a')      # raises Errno::ELOOP
  ensure
    File.unlink('a') if File.symlink?('a')
  end
end
````

`File.lstat('a')` should continue to succeed and identify the entry as a symbolic link.

## Cause

In `winnt_stat`, failure to open the resolved path falls back to `stat_by_find` unless `open_error` matches one of the listed errors.  The symbolic-link-following implementation introduced in f5b96e594c769cf309b70fd7736caaf90372a3b6 retained this fallback, which was intended to handle sharing violations for files such as `pagefile.sys`.

`ERROR_CANT_RESOLVE_FILENAME` is not listed, so a symbolic-link loop also reaches the fallback, which retrieves information about the link itself and reports success.




-- 
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