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81 lines
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ReStructuredText
81 lines
4.1 KiB
ReStructuredText
====================
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How to edit a policy
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====================
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There are three ways to edit a :term:`policy <policies>`:
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* with :program:`Qubes OS Global Config`, the **recommended way** for the most common policies
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* with :program:`Qubes Policy Editor`, a graphical text editor dedicated to this task
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* with :program:`qubes-policy-editor`, a command-line text editor that will validate the file
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before saving it.
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In this how-to, we will restrict the clipboard policy to prevent an *untrusted* qube from pasting something in a *vault* qube, **as an example**.
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.. _edit-a-policy-with-qubes-os-global-config:
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Edit a policy with :program:`Qubes OS Global Config`
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----------------------------------------------------
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:program:`Qubes OS Global Config` allows you to edit the most common policies. Following our clipboard example:
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1. you need to go to the :guilabel:`Clipboard` tab.
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2. Under :guilabel:`Custom policy`, select :guilabel:`Add`
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3. Change the drop-down items to get this: ":guilabel:`untrusted` will :guilabel:`never` be allowed to paste into the clipboard of :guilabel:`vault`"
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.. note:: if there is any inconsistency, a pop-up will warn you about that
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4. Click on :guilabel:`Accept` and at the bottom of the window, select either :guilabel:`OK` or :guilabel:`Apply`.
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Edit a policy with :program:`Qubes Policy Editor`
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-------------------------------------------------
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1. Open :program:`Qubes Policy Editor`
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2. You have to either:
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* open an existing file using :menuselection:`&File --> &Open` or :kbd:`Ctrl` + :kbd:`O`
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* or create a new file using :menuselection:`&File --> &New` or :kbd:`Ctrl` + :kbd:`N`
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In that case, you need to choose a filename. The filename can only contain alphanumeric characters, underscores and hyphens. The common practice is to use a name like :file:`{30}-{user}.policy` where:
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* :samp:`{30}` indicates the priority (i.e. the default policies start with ``90`` while the policies from :program:`Qubes OS Global Config` start with ``50``)
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* :samp:`{user}` could be any name
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In order to override some clipboard policy, :file:`30-clipboard` could be a good name. Starting with ``30`` makes sure that the file will be read before any file starting with ``31`` or more, especially :file:`50-config-clipboard.policy` (this file is automatically created if you :ref:`edit-a-policy-with-qubes-os-global-config`). If you want to create a policy that will never override the policies from :program:`Qubes OS Global Config`, use a name starting with a number between ``51`` and ``89``. The default policies from Qubes OS start with ``90``, so using a number equal or superior might be useless.
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3. Add a line to the file. In order to prevent the *untrusted* qube from pasting to the *vault* qube, the line should be:
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.. code:: text
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qubes.ClipboardPaste * untrusted vault deny
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4. If you have made any edits and if the format is correct, you will be able to select :guilabel:`Save Changes` and :guilabel:`Save and Exit`, or to press :kbd:`Ctrl` + :kbd:`S`.
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Edit a policy with :program:`qubes-policy-editor`
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-------------------------------------------------
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:program:`qubes-policy-editor` is a command-line tool that ensures that the syntax of the policy is valid. You have to run it as root:
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.. code:: console
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[root@dom0] # qubes-policy-editor
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An editor will open; it will be your default editor if you have set the environment variable ``$EDITOR`` or ``$VISUAL``, otherwise it will fall back to :program:`vi`. After saving the file, :program:`qubes-policy-editor` will check the content and tell you if there is something wrong with the syntax.
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It will open :file:`30-user.policy` by default but you can invoke the program with any valid filename (only alphanumeric characters, underscores and hyphens), without the ``.policy`` extension:
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.. code:: console
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[root@dom0] # qubes-policy-editor 30-clipboard
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In that case, :program:`qubes-policy-editor` will also check that the filename of the policy is correct.
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See also
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--------
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* :doc:`/developer/services/qrexec`
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* `qubes-core-qrexec's documentation <https://dev.qubes-os.org/projects/qubes-core-qrexec/en/latest/>`__
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