Date: Sat, 26 Sep 2020 13:44:57 -0500
From: Winston Weinert <winston@ml1.net>
To: ~alpine/users@lists.alpinelinux.org
Subject: umask 0022 creating directories with setgid?
Message-ID: <20200926184457.le4pu5gp6ukgi45c@ml1.net>
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On some of my alpine boxes setting the umask to 0077 and subsequently running
mkdir creates a directory with permissions 2700.  Has anybody noticed this
strange behavior?  It appears fixed in the repository, but I'd like to
understand the cause of the issue.

In short I see the following output when running this script:

    umask 0077
    mkdir thing
    ls -ld thing

outputs:

    drwx--S---    2 vagrant  vagrant       4096 Sep 26 18:01 thing

All the machines run 3.12.0, though the affected ones were last updated several
months ago.  In case anybody wants to reproduce the issue I found this will do
it.  This example uses a vagrant box from about two months ago:

1. Create a Vagrantfile with the following contents

    Vagrant.configure("2") do |config|
      config.vm.box = "generic/alpine312"
      config.vm.box_version = '3.0.14'
    end

2. run vagrant up && vagrant ssh

3. in the ssh session run the reproducer

    umask 0077
    mkdir thing
    ls -ld thing

Thanks in advance.
Winston Weinert
https://winny.tech/