Network disabling does not always work

Originally created by @bertagaz on #11593 (Redmine)

The test suite has reported once that it found eth0 to be up while the network disabling option was selected in the greeter. There is probably a problem in this feature. Debug log and infos can be found in the 2016 June fragile test referencing ticket (#11087 (closed)).

  Scenario: The Tails Greeter "disable all networking" option disables networking within Tails      # features/checks.feature:99
calling as root: echo 'hello?'
call returned: [0, "hello?\n", ""]
[log] CLICK on (1024,384)
calling as root: /sbin/ifconfig eth0 | grep -q 'inet addr'
call returned: [1, "", "eth0: error fetching interface information: Device not found\n"]
calling as root: date -s '@1465635115'
call returned: [0, "Sat Jun 11 08:51:55 UTC 2016\n", ""]
    Given I have started Tails from DVD without network and stopped at Tails Greeter's login screen # features/step_definitions/snapshots.rb:199
[log] CLICK on (433,404)
    And I enable more Tails Greeter options                                                         # features/step_definitions/common_steps.rb:308
[log] CLICK on (643,447)
    And I disable all networking in the Tails Greeter                                               # features/step_definitions/checks.rb:240
[log] CLICK on (512,671)
[log] CLICK on (812,712)
calling as root: test -e '/etc/sudoers.d/tails-greeter' -o -e '/etc/sudoers.d/tails-greeter-no-password-lecture'
call returned: [1, "", ""]
calling as root: test -e '/etc/sudoers.d/tails-greeter' -o -e '/etc/sudoers.d/tails-greeter-no-password-lecture'
call returned: [0, "", ""]
calling as amnesia: gsettings set org.gnome.desktop.session idle-delay 0
call returned: [0, "", ""]
calling as amnesia: gsettings set org.gnome.desktop.interface toolkit-accessibility true
call returned: [0, "", ""]
calling as amnesia: xdotool search --all --onlyvisible --maxdepth 1 --classname 'Florence'
call returned: [1, "", ""]
    And I log in to a new session                                                                   # features/step_definitions/common_steps.rb:292
calling as root: . /usr/local/lib/tails-shell-library/hardware.sh && get_all_ethernet_nics
call returned: [0, "eth0\n", ""]
    Then no network interfaces are enabled                                                          # features/step_definitions/mac_spoofing.rb:75
      <0> expected but was
      <1>. (Test::Unit::AssertionFailedError)
      ./features/step_definitions/mac_spoofing.rb:79:in `/^(\d+|no) network interface(?:s)? (?:is|are) enabled$/'
      features/checks.feature:104:in `Then no network interfaces are enabled'
      Scenario failed at time 00:58:11

      Screenshot: https://jenkins.tails.boum.org/job/test_Tails_ISO_devel/400/artifact/build-artifacts/00:58:11_The_Tails_Greeter__disable_all_networking__option_disables_networking_within_Tails.png

      Video: https://jenkins.tails.boum.org/job/test_Tails_ISO_devel/400/artifact/build-artifacts/00:58:11_The_Tails_Greeter__disable_all_networking__option_disables_networking_within_Tails.mkv

Related issues

• Related to #6811 (closed)
• Related to #10774 (closed)