====================
Files access control
====================

Nextcloud's File Access Control app enables administrators to create and
manage a set of rule groups. Each of the rule groups consists of one or more
rules. If all rules of a group hold true, the group matches the request and
access is being denied. The rules criteria range from IP address, to user
groups, collaborative tags and :ref:`some more <available-rules-label>`.

Denied access
-------------

If access to a file has been denied for a user, the user can not:

* Create/upload the file
* Modify the files
* Delete the file
* Download the file
* Synchronize the file with clients, such as the Nextcloud desktop and mobile clients

Examples
--------
After installing the File Access Control app as described in :doc:`../apps_management`
navigate to the configuration and locate the settings for the Flow application.

    .. figure:: images/files_access_control_sample_rules.png
       :alt: Sample rules to block on user group, time and IP base.

The first rule group ``Support only 9-5`` denies any access to files for users
of the Support user group, between 5pm and 9am.

The second rule group ``Internal testing`` prevents users of the Internal
testers group to access files from outside of the local network.

Denying access to folders
-------------------------

The easiest way to block access to a folder, is to use a collaborative tag. As
mentioned in the :ref:`Available rules <available-rules-label>` section below,
either the file itself or one of the parents needs to have the given tag
assigned.

So you just need to assign the tag to the folder or file, and then block the
tag with a rule group. The check is independent of the user's permissions for
the tag. Therefore restricted and invisible tags are recommended, otherwise a
user could remove and reassign the tag.

This example blocks access to any folder with the tag ``Confidential``.

    .. figure:: images/files_access_control_collaborative_tags.png
       :alt: Deny access based on collaborative tag

Prevent uploading of specific files
-----------------------------------

It's possible to prevent specific files from being uploaded to Nextcloud. You
simply need to define a rule based on the mimetype and our powerful access control
engine will block any attempt to upload the file. The safest way to define the rule
is to use a regular expression, as it will help you cover all the known media types
used for the type of file you're trying to block.

The following example prevents zip files from being uploaded by using the regular
expression: ``/^application\/(zip|x-zip-compressed)$/i``

    .. figure:: images/files_access_control_block_mimetype.png
       :alt: Prevent upload based on mimetype

Common misconfigurations
------------------------

Blocking user groups
^^^^^^^^^^^^^^^^^^^^

When trying to deny access to a group of users, make sure that sharing does not
allow them to create a way back in. When users are able to create a public link,
the users can log themselves out and visit their own public link to access the
files. Since at this point they are no user and therefore no member of the
blocked group, they will be able to read and change the file.

The recommended work around is to create the same rule again, and deny access
for all users that are ``not member of`` a group, that contains all users of
your installation.

External storage
^^^^^^^^^^^^^^^^

While access to files in external storages is not possible via Nextcloud, users
that have direct access to the external storage, can of course change files
there directly. Therefore it is recommended to disable the ``Allow users to mount
external storage`` option, when trying to to completely lock out users.

.. _available-rules-label:

Available rules
---------------

All rules can also be inverted (from ``is`` to ``is not``) using the operator
option.

* **File collaborative tag:** Either the file itself, or any of the file
  owner's parent folders needs to be tagged with the tag.

  .. note:: Tags used in access control rules should be restricted tags,
            otherwise any user can remove the tag to access the file again.
            The best way to do this is with the :doc:`automated_tagging`.

* **File MIME type:** The MIME type of the file, e.g. ``text/plain`` for a text file or ``httpd/unix-directory`` for a folder.

  .. note:: see `mimetypealiases.dist.json <https://github.com/nextcloud/server/blob/master/resources/config/mimetypealiases.dist.json>`_ for a full list of possible MIME types.

* **File name:** The name of the file (``is`` and ``is not`` are case-insensitive)
* **File size:** The size of the file (*Only available on upload*)

* **Request remote address:** An IP range (either v4 or v6) for the accessing user
* **Request time:** Time span and timezone when the request happens
* **Request URL:** The URL which requests the file. (*This is the URL the file
  is served from, not the URL the user is currently looking at.*)
* **Request user agent:** The user agent of the users browser or client.
  Nextcloud desktop, Android and iOS clients are available as preconfigured
  options.

* **User group membership:** Whether the user is a member of the given group.
