fs.stat() and fs.lstat() cannot read the stats of a file with denied permissions on Windows

[aleksey-hoffman]

• Version: 14.5.0
• Platform: Win10 x64
• Subsystem: fs

What is the expected behavior?

A similar issue #22577 has been closed 2 years ago, but the issue hasn't been fixed.

Node.js cannot read the stats of immutable files (files with all permissions denied) on Windows. I'm not talking about the contents, just the stats.

Example:

After you deny all permissions to a file (to protect it from being deleted or modified), the default Windows File Explorer can still read the file's stats (name, size, etc) but Node.js throws EPERM: operation not permitted, lstat:

> icacls E:\test.txt /deny *S-1-1-0:(F)

This command effectively denies all modification permissions (delete, rename, write) for Everyone (*S-1-1-0).

What do you see instead?

Windows 10:

> icacls E:\test.txt /deny *S-1-1-0:(D)
> node
> fs.lstatSync('E:\\test.txt')
Uncaught Error: EPERM: operation not permitted, lstat 'E:/test.txt'
    at Object.lstatSync (fs.js:1033:3) {
  errno: -4048,
  syscall: 'lstat',
  code: 'EPERM',
  path: 'E:/test.txt'
}

Linux ubuntu 20.01:

> sudo chattr +i /home/user/Desktop/test.txt
> node
> fs.lstatSync('/home/user/Desktop/test.txt')
Stats {
  dev: 2053,
  mode: 33206,
  nlink: 1,
  uid: 1000,
  gid: 1000,
  rdev: 0,
  blksize: 4096,
  ino: 263860,
  size: 39881,
  blocks: 80,
  atimeMs: 1603884853571.3228,
  mtimeMs: 1602542159686.156,
  ctimeMs: 1603894615058.1975,
  birthtimeMs: 1603842167648.6978,
  atime: 2020-10-28T11:34:13.571Z,
  mtime: 2020-10-12T22:35:59.686Z,
  ctime: 2020-10-28T14:16:55.058Z,
  birthtime: 2020-10-27T23:42:47.649Z 
}

MacOS:

Haven't tested

[mmomtchev]

I am not a Windows expert, but I just noticed that your command will also make a type E:\test.txt fail - which it shouldn't do according to what I understood from its inline help page. So maybe this questions belongs to a Windows forum.
Otherwise, on Windows, libuv, which implements the lstat, will actually open the file (the infamous Windows CreateFileW call) and it will read the information from the file handle - which is not the only way to get the information on Windows, but it allows for a UNIX-like experience.

[peZhmanParsaee]

I succeeded in reading the read-only file stats in Windows 10.

First, I unset all inherited file permissions, then set file to read-only using these commands:

C:> icacls E:\test.txt /inheritance:r
C:> icacls E:\test.txt /grant "everyone":R

It makes our file only readable without any other inherited permissions.

Then read the file stats using:

C:> node
> fs.lstatSync('E:\\test.txt')
Stats {
  dev: 2553312950,
  mode: 33206,
  nlink: 1,
  uid: 0,
  gid: 0,
  rdev: 0,
  blksize: undefined,
  ino: 1125899909076950,
  size: 0,
  blocks: undefined,
  atimeMs: 1603975767956.215,
  mtimeMs: 1603975767956.215,
  ctimeMs: 1603975807848.567,
  birthtimeMs: 1603974615273.7944,
  atime: 2020-10-29T12:49:27.956Z,
  mtime: 2020-10-29T12:49:27.956Z,
  ctime: 2020-10-29T12:50:07.849Z,
  birthtime: 2020-10-29T12:30:15.274Z }

[aleksey-hoffman]

@mmomtchev hmm, for me the type /? (help) command says that it allows you to read the contents of a file, but that's not the problem, I only need the attributes (size, path, dates, etc). Even if all permissions are denied, Node.js should still be able to read the attributes (meta data) of the file.

The default file managers (File Explorer on Windows and Files on Ubuntu) can still read the attributes of a file that has all permissions denied for Everyone (all users, even for the admin).

I'm specifically trying to remove all permissions from a file for all users to protect it form editing / modification / renaming / deletion. But the problem is, when I do that, Node.js can no longer read the stats of the file on Windows specifically.

On Ubuntu it works properly - even if all permissions denied for all users (even admin) - Node.js can still read the stats:

> sudo chattr +i test.txt
> sudo rm -f test.txt
rm: cannot remove 'test.txt': Operation not permitted
> node
> fs.lstatSync('test.txt')
Stats {
  dev: 932753616,
  mode: 33206,
  nlink: 1,
  uid: 0,
  gid: 0,
  rdev: 0,
  blksize: 4096,
  ino: 11821949022255224,
  size: 0,
  ...
}

[aleksey-hoffman]

@peZhmanParsaee for some reason. your solution doesn't work for me - if I remove all permissions except READ, Node still cannot read the stats on Windows (even though, on Ubuntu it can):

1. Protect file from modification:

> icacls E:\test.txt /deny *S-1-1-0:(F)

2. Try to read protected file's stats:

> node
> fs.lstatSync('E:\\test.txt')
Uncaught Error: EPERM: operation not permitted, lstat 'E:/test.txt'
    at Object.lstatSync (fs.js:1033:3) {
  errno: -4048,
  syscall: 'lstat',
  code: 'EPERM',
  path: 'E:/test.txt'
}

• File Explorer can still read the attributes (size, path, etc.), but Node.js cannot.

3. Grant read permissions and try to read stats again (same result):

> icacls E:\test.txt /inheritance:r
> icacls E:\test.txt /grant *S-1-1-0:R
> node
> fs.lstatSync('E:\\test.txt')
Uncaught Error: EPERM: operation not permitted, lstat 'E:/test.txt'
    at Object.lstatSync (fs.js:1033:3) {
  errno: -4048,
  syscall: 'lstat',
  code: 'EPERM',
  path: 'E:/test.txt'
}

4. Give the file all permissions back and try to read stats again (only now it can read it):

> icacls E:\test.txt /grant *S-1-1-0:(F)
> node
> fs.lstatSync('E:\\test.txt')
Stats {
  dev: 932753616,
  mode: 33206,
  nlink: 1,
  uid: 0,
  gid: 0,
  rdev: 0,
  blksize: 4096,
  ino: 11821949022255224,
  size: 0,
  ...
}

[aleksey-hoffman]

@Trott @addaleax @targos Guys can this issue be solved, theoretically? This is a blocking issue in my file manager app.
Languages like C#, C++ have no problems reading read-only files, surely there's got to be a way to do this in Node, right?

[Trott]

@Trott @addaleax @targos Guys can this issue be solved, theoretically? This is a blocking issue in my file manager app.

(Not all of us are guys. Consider using everyone, people, friends, folks, or something like that.)

I imagine this would need to be solved by in libuv.

Languages like C#, C++ have no problems reading read-only files, surely there's got to be a way to do this in Node, right?

Short of finding a fix for libuv and having them land it, maybe a native extension using https://nodejs.org/api/n-api.html?

[Trott]

@nodejs/platform-windows @nodejs/libuv

[aleksey-hoffman]

@Trott thanks for the reply. I will open an issue there.
I might have to resort to creating a custom N-API plugin for this, indeed.

Not all of us are guys. Consider using everyone, people, friends, folks, or something like that

Sorry, I thought "guys" was a gender neutral word, I'm not a native English speaker.