Does Landlock not work with eCryptfs?

["Günther Noack" <gnoack3000@gmail.com>]

Hello!

I have a machine where the home directory is encrypted with eCryptfs,
and it seems that Landlock is not working properly on eCryptfs files
(but the same program works as expected on other mounts)?


## Problem description

Steps to reproduce:

  * Create a directory "subdir" in the current directory
  * Enable Landlock but ask for "subdir" to be readable
  * os.ReadDir(dir)

Observed result:

* os.ReadDir function fails when trying to open the file (verified with strace)

Expected result:

* os.ReadDir should work, because we asked for it to work when enabling Landlock


## Reproduction code

I have uploaded a reproduction program in Go to Github,
which should be understandable also if you are primarily a C user:
https://github.com/gnoack/llecryptfsrepro/blob/main/repro.go

To build and run the reproduction code, run:

  git clone https://github.com/gnoack/llecryptfsrepro
  cd llecryptfsrepro
  go build
  ./llecryptfsrepro  # executes the three steps as above, check source code

You can invoke this binary in different file system types to see the difference.


I have admittedly only checked it with a distribution kernel on
Manjaro Linux: The Linux version is 6.2.2-1-MANJARO.

This looks like a bug to me?
Is this a known issue?

Thanks,
–Günther