= Lab Exercise 5: The Art of OVAL Checks
:toc2:
:linkattrs:
:experimental:
:imagesdir: images

// Variables
:container_name: fedora_container


== Introduction

OVAL stands for Open Vulnerability and Assessment Language.
In a nutshell, it is an XML-based declarative language that is part of the SCAP standard.
This lab focuses on its ability to query and evaluate the state of a system.
Quoting from the link:http://ovalproject.github.io/getting-started/faqs/[OVAL FAQ^]:

__
The language standardizes the three main steps of the assessment process: representing configuration information of systems for testing; analyzing the system for the presence of the specified machine state (vulnerability, configuration, patch state, etc.); and reporting the results of this assessment.
__

The `ComplianceAsCode` project supports OVAL as the language for writing automated configurable checks.
It compiles OVAL snippets into checks that are understood by OVAL interpreters--for example, the OpenSCAP scanner.
The scanner evaluates the check, and determines whether the system passes.

In this lab exercise, you go through the OVAL snippet of the `accounts_tmout` rule.
You see how even simple checks can rapidly become complicated, and what you can do about it.
Finally, you discover that the check was written incorrectly and you fix it.

.*Goals*

* Learn about OVAL.
* Learn how `ComplianceAsCode` facilitates creation of new OVAL content.
* Learn how to test OVAL checks.
* Learn how to use tests and remediations to safely and gradually improve an OVAL check.


.*Preconfigured Lab Environment*

* The `ComplianceAsCode` repository was already cloned.
* The following dependencies required for the content build were installed using `yum install`:
** Generic build utilities: `cmake` and `make`,
** Utilities for generating SCAP content: `openscap-scanner`
** Python dependencies for putting content together: `python3-pyyaml` and `python3-jinja2`

* A `docker` `fedora_container` image was built using the `Dockerfiles/test_suite-fedora` files.
The SSH keys for lab user are authorized by the container's root user.
The steps for how to accomplish this are in the link:https://complianceascode.readthedocs.io/en/latest/tests/README.html[How to Test].
* The OVAL check for `accounts_tmout` was modified so you can improve it.

IMPORTANT: Content used in this lab has been altered to increase its educative potential, and is therefore different from the content in ComplianceAsCode upstream repository or the content in the scap-security-guide package shipped in Red Hat^(R)^ products.

== Hands-on Lab

The `ComplianceAsCode` project consists of human-readable files that are compiled into standard-compliant files that are difficult to read and edit directly.

For your convenience, the environment is already set up, so the content is built and ready to be used.
No worries, though--you get to rebuild it later in the exercise.

To start the hands-on section, take one of the following steps:

=== Github Codespaces
. Go to: link:https://github.com/codespaces/new?hide_repo_select=true&ref=master&repo=19279458&skip_quickstart=true[Github Codespaces]
. Select `ComplianceAsCode Workshop Exercise 5` in the `Dev container configuration` option.

=== Gitpod
. Go to: link:https://gitpod.io/#WORKSHOP=lab5_oval/https://github.com/ComplianceAsCode/content[Lab 5 Environment]
. Wait until all the steps being executed in the terminal are complete.

== Anatomy of an Existing Check-Remediation Pair

There is already a built HTML guide in the build directory.

. Navigate to the `build/guides` folder.:
. Right click the `ssg-rhel8-guide-ospp.html` file and select `Open with Live Server` to preview the file. Note: Your browser may block the pop-up. You must allow it when asked.
. A new tab opens and you can see your `OSPP` profile, which contains two rules.
. Check the "Set Interactive Session Timeout" rule.
. In this lab exercise, you focus on the `accounts_tmout` rule.
To find the rule entry in the guide, press `Ctrl+F` or use the `Edit -> Find in this page` menu item, and search for the `Set Interactive Session Timeout` string, which is the rule title.
+
The description says:
+
----

Setting the TMOUT option in /etc/profile ensures that all user sessions
will terminate based on inactivity. The TMOUT setting in /etc/profile
should read as follows:

TMOUT=600

----
+
When dealing with the rule check, there are additional aspects to keep in mind:

- Because the timeout is supposed to be set to 600 seconds, what is the consequence if the timeout value is set to 100?
Is it more or less secure?
+
Having a shorter time interval between inactivity and logout is more bothersome for the user, but it is a stricter requirement.
Therefore, you need to make sure that if the rule requires `TMOUT=600`, having `TMOUT=100` is also evaluated as correct.

- The rule description that the `TMOUT=...` statement is in a config file is accurate, but guides on the Internet often recommend that you have `export TMOUT=...` there.
The assignment form with the `export` keyword ensures that the variable is available to other programs.
Environmental variables such as `PATH` and `HOME` are commonly exported, so this probably is where the confusion comes from that `export` is needed for `TMOUT` to work.
+
In this case, you want to make sure that the rule's check allows both forms--with and without `export`, even though the `export` keyword is not required.


=== Bash Remediation

. Examine the Bash remediation by opening the following file in the text editor:
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/bash/shared.sh
----
+
The remediation body looks like this:
+
NOTE: The header of the remediation is processed by the build system, so the actual file contents and the remediation displayed in the HTML guide are different.
+
[source,sh]
----
if grep --silent ^TMOUT /etc/profile ; then
        sed -i "s/^TMOUT.*/TMOUT=$var_accounts_tmout/g" /etc/profile
else
        echo -e "\n# Set TMOUT to $var_accounts_tmout per security requirements" >> /etc/profile
        echo "TMOUT=$var_accounts_tmout" >> /etc/profile
fi
----
+
You do not need to make any changes to the file.
+
You can see that the remediation is in sync with the description--it handles the `/etc/profile` file, and it does one of the following:

- Adds the `TMOUT` assignment to the file if it is missing
- Modifies the `TMOUT` assignment so that the correct value is used if an assignment already exists


=== OVAL Check

In this section, you move on to the OVAL check.

. In the text editor, open the file that defines the check:
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/oval/shared.xml
----

. This file is much more complicated, so examine it piece by piece:

.. Note the leading `definition` element:
+
[source,xml]
----

  <definition class="compliance" id="accounts_tmout" version="2">
    <metadata>
      <title>Set Interactive Session Timeout</title>
      <affected family="unix">
        <platform>multi_platform_rhel</platform>
        <platform>multi_platform_fedora</platform>
        <platform>multi_platform_ol</platform>
      </affected>
      <description>Checks interactive shell timeout</description>
    </metadata>
    <criteria operator="OR">
      <criterion comment="TMOUT value in /etc/profile >= var_accounts_tmout" test_ref="test_etc_profile_tmout" />
      <criterion comment="TMOUT value in /etc/profile.d/*.sh >= var_accounts_tmout" test_ref="test_etc_profiled_tmout" />
    </criteria>
  </definition>
  ...
----
+
The `definition` specifies a `criteria` element.
Here is a close-up of those criteria:
+
[source,xml]
----
    ...
    <criteria operator="OR">
      <criterion comment="TMOUT value in /etc/profile >= var_accounts_tmout"
        test_ref="test_etc_profile_tmout" />
      <criterion comment="TMOUT value in /etc/profile.d/*.sh >= var_accounts_tmout"
        test_ref="test_etc_profiled_tmout" />
    </criteria>
  </definition>
  ...
----
+
You can see that each criterion references a test.
The first test checks for the `TMOUT` setting in the `/etc/profile` file, the other one checks all files in `/etc/profile.d/` that have the `sh` file extension.
If either test passes, the whole test passes as well, as the `operator="OR"` attribute of the `criteria` element imposes.
+
A test is typically composed of an object and state definitions.
The object defines what should be gathered on the tested system, the state defines expected properties of the object.
In order for the test to pass, the object has to exist, and it has to conform to the specified state.

. Now examine the test for the `/etc/profile` criterion and its dependencies:
+
[source,xml]
----
  ...
  <ind:textfilecontent54_test check="all" check_existence="all_exist"
      comment="TMOUT in /etc/profile" id="test_etc_profile_tmout" version="1">
    <ind:object object_ref="object_etc_profile_tmout" />
    <ind:state state_ref="state_etc_profile_tmout" />
  </ind:textfilecontent54_test>
  ...
----
+
The object definition associates a filename with a regular expression.
The filename is checked for the regular expression, and if there is a match, contents of the regular expression group become the object.

. Note the `instance` element that equals `1`. This indicates that it is the first match of the regular expression that defines the object:
+
[source,xml]
----
  ...
  <ind:textfilecontent54_object id="object_etc_profile_tmout" version="1">
    <ind:filepath>/etc/profile</ind:filepath>
    <ind:pattern operation="pattern match">^[\s]*TMOUT[\s]*=[\s]*(.*)[\s]*$</ind:pattern>
    <ind:instance datatype="int">1</ind:instance>
  </ind:textfilecontent54_object>
----

. The state is a specification that the object (the matched substring) should be an integer that equals the value of the `var_accounts_tmout` variable:
+
[source,xml]
----
  <ind:textfilecontent54_state id="state_etc_profile_tmout" version="1">
    <ind:subexpression datatype="int" operation="equals" var_check="all" var_ref="var_accounts_tmout" />
  </ind:textfilecontent54_state>

  <external_variable comment="external variable for TMOUT" datatype="int"
      id="var_accounts_tmout" version="1" />
  ...
----
+
There are two regular expressions that check for `TMOUT=...` in the `shared.xml` file: one for the `profile` test and one for the `profile.d/\*.sh` test.
As there are two types of locations that need to be examined, (the single `/etc/profile` file and `*.sh` files in the `/etc/profile.d` directory), there have to be two objects.
The `object_etc_profile_tmout` and `object_etc_profiled_tmout` objects have different file/path specifications, but the regular expression is the same.
The alternative form of the assignment `export TMOUT=...` is not handled in either of them.
+
Moreover, there is the `equals` operation used to perform the match.
As stated in the previous section, this looks wrong, as shorter timeouts are more secure, and therefore should be allowed.

. Now you can close the file.
As a reminder, you do not need to make any changes at this point.


== Tests Introduction

The `ComplianceAsCode` project features a test suite that is useful for defining which scenarios the check and remediation are supposed to handle.
It sets up a system to a certain state and runs the scan and possibly remediations.
Results are reported in the form of console output, and detailed reports are saved to a log directory.

Regarding scenarios, consider, for example, the `accounts_tmout` rule--the two simplest cases are handled using the following scenarios:

* `TMOUT=600` is present in `/etc/profile`. This test scenario should pass.
* `TMOUT=600` is not present in `/etc/profile` or `/etc/profile.d/*.sh`. This is more complicated because remediations become involved:
** This test scenario should fail the initial scan.
** If there is a remediation for the rule, it should apply without errors.
** The final scan after the remediation should pass.

The test suite has to prepare a system, scan it, and report results.
Due to practical considerations, the system under test should be isolated from the system running the test.
The test suite supports `libvirt` VMs, and `docker` or `podman` containers that satisfy this isolation requirement.
In this exercise, you are going to use a `docker` container with the Fedora image and Red Hat^(R)^ Enterprise Linux^(R)^ 8 (RHEL 8) SCAP content.

=== Tests Hands-on

. We need the RHEL 8 content to test the Fedora image.
As we have already seen earlier, the initial build of the content including build of the guide has already been done for us.

. You test the `accounts_tmout` rule included in the `ospp` profile of the RHEL 8 data stream.
With that in mind, execute the test suite:
+
[subs="attributes"]
----
[... ]$ SSH_ADDITIONAL_OPTIONS="-o IdentityFile=/workspace/content/.ssh/id_rsa" tests/automatus.py rule \
            --docker {container_name} \
            --datastream build/ssg-rhel8-ds.xml \
            --remediate-using bash \
            --make-applicable-in-containers \
            --remove-platforms \
            accounts_tmout
----
+
----
Setting console output to log level INFO
INFO - The base image option has been specified, choosing Docker-based test environment.
INFO - Logging into /workspace/content/logs/...
INFO - xccdf_org.ssgproject.content_rule_accounts_tmout
INFO - Script comment.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script correct_value.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script line_not_there.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script wrong_value.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
----
+
[NOTE]
====
The test suite is a Python script `tests/test_suite.py`.
You supplied the following arguments to it:

* You want to use the test suite in `rule` mode--you want to test a rule under all available rule test scenarios.
+
The alternative mode is `profile` mode, which is simpler--there are no test scenarios and the system is scanned.

* You want to use `docker` with the `fedora_container` image as the back end, so you supply the `--docker {container_name}` arguments.

* Of course you have to specify which data stream to use for testing--you use the built one, so you specify `--datastream build/ssg-rhel8-ds.xml` arguments.

* Finally, you specify what to test--a rule regular expression: `accounts_tmout` or `^accounts_tmout$`.

* Other parameters are also used for supporting running tests in this kind of environment. For example, you use `--remove-platforms` to make the RHEL8 content applicable to Fedora images.
====

The output tells you the following:

* The rule with full ID `xccdf_org.ssgproject.content_rule_accounts_tmout` was tested in the `OSPP` profile context.
* There were four test scenarios: `comment.fail.sh`, `line_not_there.fail.sh`, `correct_value.pass.sh` and `wrong_value.fail.sh`, all of which passed.
These scenarios test whether the rule can handle various situations correctly.
You examine these test scenarios later in this lab exercise.
For now, it is important to realize that all of the scenarios should still pass after you make any changes in the OVAL.
* More information about the test run is available in the respective log directory.
This is useful when a test breaks unexpectedly or the test suite suffers from internal issues.

Now when you have a reasonable amount of certainty about your rules, you can improve the OVAL content.

// This is probably not necessary in gitpod environment
// TIP: You repeat the (re)build of the content and subsequent test suite execution multiple times.
// Therefore, it may be practical to dedicate a terminal window for this purpose.
// You can browse the command history using `Up` and `Down` keyboard arrow keys, so if you want to rebuild after the test run finishes, tap the `Up` key until the `build_product` command shows up (typically you have to tap twice), and confirm the execution of the build command by pressing `Enter`.

== OVAL Optimization

In this section, you analyze the OVAL check for the `accounts_tmout` rule and perform the following steps:

. Analyze the OVAL and identify duplicated elements.
. Design a Jinja2 macro that deduplicates test definitions.
. Test changes.
. Design a Jinja2 macro that deduplicates test objects.
. Test changes again.

// This comment is here just to break the numbered list.


=== Code Duplication Analysis

The OVAL test repeats itself a bit--there are checks for the `/etc/profile` file as well as for other `/etc/profile.d/*.sh` files, but the tests and respective objects are very similar.
This makes editing tedious and prone to link:https://en.wikipedia.org/wiki/Copy_and_paste_programming#/media/File:Forgotten_edits_in_copypaste_programming.gif[copy-paste errors^].
Luckily, `ComplianceAsCode` supports the link:http://jinja.pocoo.org/docs/2.10/[Jinja2^] macro language that can be used to introduce templating, thus removing the duplication.

. Analyze the difference between the two tests:
+
There is a difference in name and comment, and test objects are also different.

.. Compare the following two excerpts:
+
[source,xml]
----
<ind:textfilecontent54_test check="all" check_existence="all_exist"
    comment="TMOUT in /etc/profile" id="test_etc_profile_tmout" version="1">
  <ind:object object_ref="object_etc_profile_tmout" />
  <ind:state state_ref="state_etc_profile_tmout" />
</ind:textfilecontent54_test>
...

<ind:textfilecontent54_test check="all" check_existence="all_exist"
    comment="TMOUT in /etc/profile.d/*.sh" id="test_etc_profiled_tmout" version="1">
  <ind:object object_ref="object_etc_profiled_tmout" />
  <ind:state state_ref="state_etc_profile_tmout" />
</ind:textfilecontent54_test>
...
----

You have `etc_profile_tmout` and `etc_profiled_tmout` (note the extra **d**) in the test ID and in the object reference.


=== Deduplication of Tests

Luckily, the Jinja2 language enables you to define link:http://jinja.pocoo.org/docs/2.10/templates/#macros[macros^] that can help you to remove the duplication.
You are going to define a macro that accepts the filename comment and the test stem as arguments.

Therefore, you remove both tests and add the new macro and its new invocations.

// This is probably not necessary in gitpod environment
// TIP: To delete a text section in `nano`, move the cursor to the start of the text you want to select.
// Press `Ctrl+6` to mark the start, then move the cursor to the end of the section you want to select.
// Finally, press `Ctrl+K` to erase the selection.
// Undo by pressing `Alt+U`, redo by pressing `Alt+E`.
// Also remember that if you paste to the terminal, you have to press `Ctrl+Shift+V`.

. Open the `oval/shared.xml` file in the editor:
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/oval/shared.xml
----

. Now, delete the two `textfilecontent54_test` XML elements, and then copy and paste the following content to replace it (between the `definition` and the first of the `textfilecontent54_object` elements):
+
[source,xml]
----

  {{% macro test_tmout(test_stem, files) %}}
  <ind:textfilecontent54_test check="all" check_existence="all_exist"
      comment="TMOUT in {{{ files }}}" id="test_{{{ test_stem }}}" version="1">
    <ind:object object_ref="object_{{{ test_stem }}}" />
    <ind:state state_ref="state_etc_profile_tmout" />
  </ind:textfilecontent54_test>
  {{% endmacro %}}

  {{{ test_tmout(  test_stem="etc_profile_tmout", files="/etc/profile") }}}
  {{{ test_tmout(  test_stem="etc_profiled_tmout", files="/etc/profile.d/*.sh") }}}
----

. Finish your edits as usual by pressing `Ctrl+S` to save the file.
+
NOTE: The delimiters are different than the link:https://jinja.pocoo.org/docs[Jinja2^] website shows--that is, instead of `{% macro ... %}`, you use the `{{% macro ... %}}` form and so on. There is always one curly bracket more than the website documentation shows.


=== Checking That You Are Safe

So, did you do everything correctly?

. Rebuild the data stream and execute the test suite again--the result should be exactly the same.
+
TIP: You can use the `Up` arrow key to browse the command history so you do not have to retype them every time.
+
----
[... ]$ ./build_product rhel8 --datastream-only
----
+
[subs="attributes"]
----
[... ]$ SSH_ADDITIONAL_OPTIONS="-o IdentityFile=/workspace/content/.ssh/id_rsa" tests/automatus.py rule \
            --docker {container_name} \
            --datastream build/ssg-rhel8-ds.xml \
            --remediate-using bash \
            --make-applicable-in-containers \
            --remove-platforms \
            accounts_tmout
----
+
----
Setting console output to log level INFO
INFO - The base image option has been specified, choosing Docker-based test environment.
INFO - Logging into /workspace/content/logs/...
INFO - xccdf_org.ssgproject.content_rule_accounts_tmout
INFO - Script comment.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script correct_value.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script line_not_there.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script wrong_value.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
----


=== Deduplication of Objects

Next, the test objects are very similar, as well--the only thing that differs is their name, and path + filename/filepath attributes.
So you define a macro that accepts the test name stem and `path`, `filename`, or `filepath` attributes.

You use the link:http://jinja.pocoo.org/docs/2.10/templates/#if[if-statement^] here--if, for example, `filepath` is not supplied, `{{% if filepath %}}` evaluates to `False` and the body of the condition is ignored.
Conversely, if the `filepath` is supplied, the `textfilecontent54_object` definition created by the macro includes the `ind:filepath` child element holding the respective value.

. Open the `oval/shared.xml` file in the editor, if it is not already open:
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/oval/shared.xml
----

. Remove the two `textfilecontent54_object` XML elements and then copy and paste the following block as a replacement (between the test creation and the `textfilecontent54_state` XML elements):
+
[source,xml]
----
  {{% macro object_tmout(test_stem, path, filename, filepath) %}}
  <ind:textfilecontent54_object id="object_{{{ test_stem }}}" version="1">
    {{% if path %}}
    <ind:path>{{{ path }}}</ind:path>
    {{% endif %}}
    {{% if filename %}}
    <ind:filename operation="pattern match">{{{ filename }}}</ind:filename>
    {{% endif %}}
    {{% if filepath %}}
    <ind:filepath>{{{ filepath }}}</ind:filepath>
    {{% endif %}}
    <ind:pattern operation="pattern match">^[\s]*TMOUT[\s]*=[\s]*(.*)[\s]*$</ind:pattern>
    <ind:instance datatype="int">1</ind:instance>
  </ind:textfilecontent54_object>
  {{% endmacro %}}

  {{{ object_tmout(test_stem="etc_profile_tmout", filepath="/etc/profile") }}}
  {{{ object_tmout(test_stem="etc_profiled_tmout", path="/etc/profile.d", filename="^.*\.sh$") }}}
----

. To actually create tests and objects, macros have to be called.
Therefore, do it and place the macro calls close to each other. Doing this emphasizes that there are two tests: `etc_profile_tmout` that examines the single file and `etc_profiled_tmout` that goes through the whole directory.

. Finish your edits as usual by pressing `Ctrl+S` to save the file.

. If you get errors during the build or during the tests and you do not know how to fix them, you are covered.
The snippet below represents the OVAL file after performing the deduplication described in the previous section.
To get back on track, copy and paste the text below to the `linux_os/guide/system/accounts/accounts-session/accounts_tmout/oval/shared.xml` file.
+
[source,xml]
----
<def-group>
  <definition class="compliance" id="accounts_tmout" version="2">
    <metadata>
      <title>Set Interactive Session Timeout</title>
      <affected family="unix">
        <platform>multi_platform_rhel</platform>
        <platform>multi_platform_fedora</platform>
        <platform>multi_platform_ol</platform>
      </affected>
      <description>Checks interactive shell timeout</description>
    </metadata>
    <criteria operator="OR">
      <criterion comment="TMOUT value in /etc/profile >= var_accounts_tmout"
        test_ref="test_etc_profile_tmout" />
      <criterion comment="TMOUT value in /etc/profile.d/*.sh >= var_accounts_tmout"
        test_ref="test_etc_profiled_tmout" />
    </criteria>
  </definition>

  {{% macro test_tmout(test_stem, files) %}}
  <ind:textfilecontent54_test check="all" check_existence="all_exist"
      comment="TMOUT in {{{ files }}}" id="test_{{{ test_stem }}}" version="1">
    <ind:object object_ref="object_{{{ test_stem }}}" />
    <ind:state state_ref="state_etc_profile_tmout" />
  </ind:textfilecontent54_test>
  {{% endmacro %}}

  {{{ test_tmout(  test_stem="etc_profile_tmout", files="/etc/profile") }}}
  {{{ test_tmout(  test_stem="etc_profiled_tmout", files="/etc/profile.d/*.sh") }}}

  {{% macro object_tmout(test_stem, path, filename, filepath) %}}
  <ind:textfilecontent54_object id="object_{{{ test_stem }}}" version="1">
    {{% if path %}}
    <ind:path>{{{ path }}}</ind:path>
    {{% endif %}}
    {{% if filename %}}
    <ind:filename operation="pattern match">{{{ filename }}}</ind:filename>
    {{% endif %}}
    {{% if filepath %}}
    <ind:filepath>{{{ filepath }}}</ind:filepath>
    {{% endif %}}
    <ind:pattern operation="pattern match">^[\s]*TMOUT[\s]*=[\s]*(.*)[\s]*$</ind:pattern>
    <ind:instance datatype="int">1</ind:instance>
  </ind:textfilecontent54_object>
  {{% endmacro %}}

  {{{ object_tmout(test_stem="etc_profile_tmout", filepath="/etc/profile") }}}
  {{{ object_tmout(test_stem="etc_profiled_tmout", path="/etc/profile.d", filename="^.*\.sh$") }}}

  <ind:textfilecontent54_state id="state_etc_profile_tmout" version="1">
    <ind:subexpression datatype="int" operation="equals" var_check="all"
      var_ref="var_accounts_tmout" />
  </ind:textfilecontent54_state>

  <external_variable comment="external variable for TMOUT" datatype="int" id="var_accounts_tmout" version="1" />
</def-group>
----
+
This way, you do not have to worry about possibly introducing those link:https://en.wikipedia.org/wiki/Copy_and_paste_programming#/media/File:Forgotten_edits_in_copypaste_programming.gif[copy-paste errors^].


=== Reassuring That You Are Safe

. Finally, run the rule's test again--it may be that a typo was introduced, and the OVAL is not actually correct:
+
----
[... ]$ ./build_product rhel8 --datastream-only
----
+
[subs="attributes"]
----
[... ]$ SSH_ADDITIONAL_OPTIONS="-o IdentityFile=/workspace/content/.ssh/id_rsa" tests/automatus.py rule \
            --docker {container_name} \
            --remediate-using bash \
            --make-applicable-in-containers \
            --remove-platforms \
            accounts_tmout
----
+
----
Setting console output to log level INFO
INFO - The base image option has been specified, choosing Docker-based test environment.
INFO - Logging into /workspace/content/logs/...
INFO - xccdf_org.ssgproject.content_rule_accounts_tmout
INFO - Script comment.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script correct_value.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script line_not_there.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script wrong_value.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
----
+

As there are no errors, this proves that your check-remediation combination works as expected.

TIP: You do not need to specify the parameter `--datastream` when there is data stream build for only one product, so our command this time is shorter.

== OVAL Development


=== Correct Handling of Supercompliance

. Examine the test scenarios--for example, the `wrong_value.fail.sh` scenario:
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/tests/wrong_value.fail.sh
----
+
As you can see, the test sets the `TMOUT` value to 1234.
The value is correctly considered to be noncompliant--the timeout should be 600, and 1234 is longer and therefore less secure.

.. What about the `correct_value.pass.sh` scenario?
Open it in the editor, as well:
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/tests/correct_value.pass.sh
----
+
As you can see, this one sets the `TMOUT` value to 600, which is the value defined by the profile.

. Add another check for a correct value--check for a timeout of 100.
In the case of a timeout, 100 seconds is more secure than 600 seconds.
Therefore, the scenario represents a *supercompliant* case, that is, the setting is stricter than necessary, but it is within the area of allowed values.
.. Copy that one, and make a new test scenario out of it.
Run this command in the terminal in the `tests` directory:
+
----
[... ]$ cp linux_os/guide/system/accounts/accounts-session/accounts_tmout/tests/{correct_value,supercompliant}.pass.sh
----

.. Then, open it in the editor, and change the value from 600 to 100.
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/tests/supercompliant.pass.sh
----

.. After you finish editing, press `Ctrl+S` to save the file.
For reference, the `supercompliant.pass.sh` file now looks like this:
+
[source,sh]
----
#!/bin/bash
#
# profiles = xccdf_org.ssgproject.content_profile_ospp

if grep -q "TMOUT" /etc/profile; then
        sed -i "s/.*TMOUT.*/TMOUT=100/" /etc/profile
else
        echo "TMOUT=100" >> /etc/profile
fi
----

. Now go back to the tests and run them:
+
[subs="attributes"]
----
[... ]$ SSH_ADDITIONAL_OPTIONS="-o IdentityFile=/workspace/content/.ssh/id_rsa" tests/automatus.py rule \
            --docker {container_name} \
            --remediate-using bash \
            --make-applicable-in-containers \
            --remove-platforms \
            accounts_tmout
----
+
----
Setting console output to log level INFO
INFO - The base image option has been specified, choosing Docker-based test environment.
INFO - Logging into /workspace/content/logs/...
INFO - xccdf_org.ssgproject.content_rule_accounts_tmout
INFO - Script comment.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script correct_value.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script line_not_there.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script wrong_value.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
ERROR - Script supercompliant.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp found issue:
ERROR - Rule evaluation resulted in fail, instead of expected pass during initial stage 
ERROR - The initial scan failed for rule 'xccdf_org.ssgproject.content_rule_accounts_tmout'.
----
+
The test output tells you that the `supercompliant.pass.sh` scenario has failed, which was not expected.

. Modify the OVAL snippet, so timeouts shorter than the threshold are allowed:
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/oval/shared.xml
----

. The modification should be easy--instead of checking that the timeout value `equals` the threshold, you use the `less than or equal` check as per the link:https://oval.mitre.org/language/version5.11/ovaldefinition/documentation/oval-common-schema.html#OperationEnumeration[OVAL specification^].
So just replace `equals` with `less than or equal` in the definition of the `textfilecontent54_state` like this:
+
[source,xml]
----
  <ind:textfilecontent54_state id="state_etc_profile_tmout" version="1">
    <ind:subexpression datatype="int" operation="less than or equal" var_check="all" var_ref="var_accounts_tmout" />
  </ind:textfilecontent54_state>
----

. After you are finished editing, press `Ctrl+S` to save the file.
This time, when rebuilt and executed again, the tests pass:
+
----
[... ]$ ./build_product rhel8 --datastream-only
----
+
[subs="attributes"]
----
[... ]$ SSH_ADDITIONAL_OPTIONS="-o IdentityFile=/workspace/content/.ssh/id_rsa" tests/automatus.py rule \
            --docker {container_name} \
            --remediate-using bash \
            --make-applicable-in-containers \
            --remove-platforms \
            accounts_tmout
----
+
----
Setting console output to log level INFO
INFO - The base image option has been specified, choosing Docker-based test environment.
INFO - Logging into /workspace/content/logs/...
INFO - xccdf_org.ssgproject.content_rule_accounts_tmout
INFO - Script comment.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script correct_value.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script line_not_there.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script wrong_value.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script supercompliant.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
----


=== Correct Handling of Export

As discussed at the beginning of this exercise, the `TMOUT` variable can be prefixed by the `export` keyword--this is allowed, but not required.

. Modify the passing `correct_value.pass.sh` test scenario to test a correct value in addition to the usage of the `export` keyword:
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/tests/correct_value.pass.sh
----
+
[source,sh]
----
#!/bin/bash
#
# profiles = xccdf_org.ssgproject.content_profile_ospp

if grep -q "TMOUT" /etc/profile; then
        sed -i "s/.*TMOUT.*/export TMOUT=600/" /etc/profile
else
        echo "export TMOUT=600" >> /etc/profile
fi
----

. After you are finished editing, press `Ctrl+S` to save the file.

. It is time to rerun those tests.
You do not have to rebuild the product, as you have changed only the test definition, and you can rerun the test suite without the prior rebuild.
Execute the test suite again and expect the `ERROR - Script correct_value.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp found issue:` line to appear in the output.
+
[subs="attributes"]
----
[... ]$ SSH_ADDITIONAL_OPTIONS="-o IdentityFile=/workspace/content/.ssh/id_rsa" tests/automatus.py rule \
            --docker {container_name} \
            --remediate-using bash \
            --make-applicable-in-containers \
            --remove-platforms \
            accounts_tmout
----
+
This confirms the theory that OVAL does not allow this configuration, although it is valid.
Therefore, in order to make tests pass, you have to edit the OVAL so that the occurrence of `export` is allowed.
Thanks to the OVAL optimization that you performed earlier, there is only one place that needs to be changed--the definition of the test object.

. Open the OVAL file again:
+
----
[... ]$ open linux_os/guide/system/accounts/accounts-session/accounts_tmout/oval/shared.xml
----

. Note that the current test object specifies the following:
+
[source,xml]
----
<ind:pattern operation="pattern match">^[\s]*TMOUT[\s]*=[\s]*(.*)[\s]*$</ind:pattern>
<ind:instance datatype="int">1</ind:instance>
----
+
It needs to be changed to ignore the `export` keyword followed by at least one whitespace.

. The best approach is to make this an optional group.
This means adding `(export[\s]+)?` to the regular expression, but as you do not want that group to be registered (stored in memory or captured), you have to link:https://oval.mitre.org/language/about/re_support_5.6.html[add some special syntax^]. Add `(?:export[\s]+)` and the section becomes this:
+
[source,xml]
----
<ind:pattern operation="pattern match">^[\s]*(?:export[\s]+)?TMOUT[\s]*=[\s]*(.*)[\s]*$</ind:pattern>
<ind:instance datatype="int">1</ind:instance>
----
+
The non-capturing group that consists of `export` followed by at least one whitespace can be either absent or present exactly once.

. It is time to save the OVAL. Press `Ctrl+S` to save the file, and then rebuild the product and run the tests again:
+
----
[... ]$ ./build_product rhel8 --datastream-only
----
+
[subs="attributes"]
----
[... ]$ SSH_ADDITIONAL_OPTIONS="-o IdentityFile=/workspace/content/.ssh/id_rsa" tests/automatus.py rule \
            --docker {container_name} \
            --remediate-using bash \
            --make-applicable-in-containers \
            --remove-platforms \
            accounts_tmout
----
+
----
Setting console output to log level INFO
INFO - The base image option has been specified, choosing Docker-based test environment.
INFO - Logging into /workspace/content/logs/...
INFO - xccdf_org.ssgproject.content_rule_accounts_tmout
INFO - Script comment.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script correct_value.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script line_not_there.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script wrong_value.fail.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
INFO - Script supercompliant.pass.sh using profile xccdf_org.ssgproject.content_profile_ospp OK
----
+
Everything passes, which means that your check can now handle a range of compliant values and it does not produce false positives when the `export` keyword is involved.

Congratulations--now you know how to use the `ComplianceAsCode` project to make OVAL creation less error-prone and how to make sure that OVAL checks are working according to expectations.

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link:README.adoc#table-of-contents[ Table of Contents ] | link:next_steps_with_complianceascode.adoc[Next Steps with ComplianceAsCode]
