Patch for Ruby's Etc module to avoid using C-extensions on modern hosts in GCE with oslogin enabled. Provided as-is, without warranty, express or implied.

patch_etc.rb

# monkey patch Etc module to work around the segfault that occurs using when
# oslogin is enabled on newer systems (Debian 11+, Ubuntu 20.04+)
# https://github.com/chef/chef/issues/12993

module PatchedEtc
  def _getent(db, key, regex, schema, struct_klass, error_word = db)
    info = `getent #{db} #{key}`.chomp
    raise(ArgumentError, "can't find #{error_word} for #{key}") unless $?.success?
    fn_schema = schema.map { |k, v| v.class == Class ? [k, _to_class_fn(v)] : [k, v] }.to_h
    matches = info.match(regex)
    init_vars = fn_schema.map { |k, fn| fn.call(matches[k]) }
    struct_klass.new(*init_vars)
  end

  def _getent_passwd(key)
    r = /(?<name>.+):(?<passwd>.+):(?<uid>\d+):(?<gid>\d+):(?<gecos>.+)?:(?<dir>.+):(?<shell>.+)/
    schema = { name: String, passwd: String, uid: Integer, gid: Integer, gecos: String, dir: String, shell: String }
    _getent('passwd', key, r, schema, Etc::Passwd, 'user')
  end

  def _to_class_fn(klass)
    ->(v) { v.is_a?(klass) ? v : Object.send(klass.to_s.to_sym, v) }
  end

  def _getent_group(key)
    r = /(?<name>.+):(?<passwd>.+):(?<gid>\d+):(?<mem>.+)?/
    schema = {
      name: String, passwd: String, gid: Integer,
      mem: ->(v) { v ? v.split(',') : [] },
    }
    _getent('group', key, r, schema, Etc::Group)
  end

  def getgrgid(group_id)
    _getent_group(group_id)
  end

  def getgrnam(name)
    _getent_group(name)
  end

  def getlogin
    ENV['USER']
  end

  def getpwnam(name)
    _getent_passwd(name)
  end

  def getpwuid(user_id)
    _getent_passwd(user_id)
  end
end

# gce_metadata is just a helper function to query the instance's metadata
# implementation is left as an exercise for the reader 😉
def oslogin_enabled?
  r = gce_metadata('attributes/enable-oslogin')
  return false unless r
  r.downcase == 'true'
end

module Etc
  class << self
    prepend PatchedEtc if Kernel.send(:oslogin_enabled?)
  end
end