You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
130 lines
6.2 KiB
ReStructuredText
130 lines
6.2 KiB
ReStructuredText
########
|
|
Security
|
|
########
|
|
|
|
The authors of this library tried their best to make sure that nothing bad happens, but they are only human. Thus:
|
|
|
|
.. warning:: Use this library at your own risk.
|
|
|
|
Running as root
|
|
***************
|
|
|
|
The library goes to great length to make sure everything passed to the operating system is safe. Due to the nature of
|
|
operating systems, many tasks can only be carried out with elevated privileges, commonly running with the privileges
|
|
of the user ``root``. This means that care must be taken when using it with elevated privileges!
|
|
|
|
Thankfully, ZFS allows to delegate permission to some extend, allowing a user or a group on the local system to carry
|
|
out administrative tasks. One exception is mounting, which is handled in the next paragraph.
|
|
|
|
It is suggested to take a look at the ``zfs(8)`` manpage, especially the part that covers ``zfs allow``.
|
|
|
|
.. _the_mount_problem:
|
|
|
|
The mount problem
|
|
*****************
|
|
On Linux, only root is allowed to manipulate the global namespace. This means that no amount of ``zfs allow`` will
|
|
allow any other user to mount a fileset. They can be created with the ``mountpoint`` property set, but can't be
|
|
mounted. One workaround is to specify ``legacy``, and using ``/etc/fstab`` to mount it, the other is to install and use
|
|
a special privilege escalation (PE) helper.
|
|
|
|
Elevated privileges are required for the following tasks:
|
|
|
|
* ``mount`` or ``unmount`` a fileset without the use of ``/etc/fstab`` and ``legacy`` mountpoints
|
|
* set or change the ``mountpoint`` property, which results in changing the mountpoint
|
|
* ZPool ``import`` or ``export``
|
|
|
|
Whether the helper is installed **setuid root** or uses **sudo** internally or any other way is up to the user. An
|
|
example helper script is provided that will allow creating and moving filesets in a subtree of the ZFS hierarchy and
|
|
local filesystem hierarchy.
|
|
|
|
.. note::
|
|
|
|
The helper is provided as an example, use at your own risk.
|
|
|
|
PE Helper protocol
|
|
******************
|
|
The PE helper will be called with different sets of parameters, depending on the action to perform. Its exit code
|
|
communicates the basic problem or success and output is captured and fed to the logger.
|
|
|
|
Calling convention
|
|
==================
|
|
The `first` parameter denotes the ``action``, followed by one or two parameters:
|
|
|
|
* ``create`` is used when creating a fileset. It receives the ``fileset`` name, and the ``mountpoint``. The PE helper
|
|
should then issue the equivalent to ``zfs create -o mountpoint=$mountpoint $fileset``.
|
|
* ``set_mountpoint`` sets or changes the mountpoint property of filesets, which usually results in remounting to the
|
|
new location. It receives the ``fileset`` name and the new ``mountpoint``.
|
|
* ``import``/``export`` imports or exports a pool. It takes a ``pool`` name as parameter.
|
|
|
|
Reporting
|
|
=========
|
|
If all went well, the helper shall return ``0`` as exit code. Otherwise, the exit code denotes the nature of the
|
|
problem. Text output to stdout/stderr is captured and logged as info (if the exit code is ``0``) or error (otherwise).
|
|
The logger is either called ``simplezfs.zfs.pe_helper`` or ``simplezfs.zpool.pe_helper``, depending on the usage.
|
|
|
|
+-------+------------------------------------------------------------------------+
|
|
| Exit | Meaning |
|
|
+-------+------------------------------------------------------------------------+
|
|
| ``0`` | Everything went well |
|
|
+-------+------------------------------------------------------------------------+
|
|
| ``1`` | Parameter or general error, such as missing utilities |
|
|
+-------+------------------------------------------------------------------------+
|
|
| ``2`` | The parent directory does not exist or is not a directory |
|
|
+-------+------------------------------------------------------------------------+
|
|
| ``3`` | The parent dataset does not exist |
|
|
+-------+------------------------------------------------------------------------+
|
|
| ``4`` | The target fileset is not in the hierarchy of the parent dataset |
|
|
+-------+------------------------------------------------------------------------+
|
|
| ``5`` | The mountpoint is not inside the parent directory or otherwise invalid |
|
|
+-------+------------------------------------------------------------------------+
|
|
| ``6`` | Calling the zfs utilities failed (when carrying out the command) |
|
|
+-------+------------------------------------------------------------------------+
|
|
|
|
When to use
|
|
===========
|
|
The helper is generally only required on Linux, where, according to the ``zfs(8)`` manpage on ``zfs allow``, the
|
|
``mount(8)`` "command restricts modifications of the global namespace to the root user".
|
|
|
|
The permissions that require ``root`` are:
|
|
|
|
* ``mount``
|
|
* ``unmount``
|
|
* ``canmount``
|
|
* ``rename``
|
|
* ``share``
|
|
|
|
As some commands manipulate the namespace, the following actions require root permission:
|
|
|
|
* ``clone``
|
|
* ``create`` (:func:`~simplezfs.ZFS.create_fileset` because it mounts it right away)
|
|
* ``destroy`` (:func:`~simplezfs.ZFS.destroy_dataset`)
|
|
* ``mount``
|
|
* ``promote``
|
|
* ``receive``
|
|
* ``rename``
|
|
* ``rollback``
|
|
* ``share``
|
|
* ``snapshot`` (:func:`~simplezfs.ZFS.create_snapshot`)
|
|
|
|
Additionally, changing the ``mountpoint`` property on filesets (:func:`~simplezfs.ZFS.set_mountpoint`)
|
|
|
|
When not to use
|
|
===============
|
|
The privilege escalation helper implements only the absolute minimum that is required. For everything else, the user
|
|
is expected to use ``zfs allow`` to delegate the permissions to the user. For example, it does not implement volume
|
|
creation, only filesets are handled.
|
|
|
|
Delegation (``zfs allow``)
|
|
**************************
|
|
Using ``zfs allow``, a lot of the required permissions can be delegated to the user. For example, to create volumes,
|
|
one needs the following permissions:
|
|
|
|
* ``create``
|
|
* ``volsize``
|
|
* ``refreservation``
|
|
|
|
``create`` is the command, and ``volsize`` and ``refreservation`` are properties set by ``zfs create -V <size>
|
|
<dataset>``. Some more may be required with other options (such as ``volblocksize`` etc.) Since it does not mount the
|
|
volume (as opposed to a fileset), the privilege escalation helper is not required and the permissions are expected to
|
|
be delegated to the user running the program using ``zfs allow``.
|