doc/userguide: start on a security chapter

This is the start of a security consideration chapter, starting with
directions on how to run Suricata as a non-root user.

doc/userguide/Makefile.am

@@ -25,6 +25,7 @@ EXTRA_DIST = \
 	reputation \
 	rule-management \
 	rules \
+	security.rst \
 	setting-up-ipsinline-for-linux \
 	setting-up-ipsinline-for-linux.rst \
 	setting-up-ipsinline-for-windows.rst \

doc/userguide/index.rst

@@ -9,6 +9,7 @@ Suricata User Guide
    quickstart
    install.rst
    upgrade.rst
+   security.rst
    command-line-options
    rules/index.rst
    rule-management/index.rst

doc/userguide/security.rst

@@ -0,0 +1,145 @@
+Security Considerations
+=======================
+
+Suricata is a security tool that processes untrusted network data, as
+well as requiring elevated system privileges to acquire that
+data. This combination deserves extra security precautions that we
+discuss below.
+
+Additionally, supply chain attacks, particularly around rule
+distribution could potentially target Suricata installations.
+
+Running as a User Other Than Root
+---------------------------------
+
+.. note:: If using the Suricata RPMs, either from the OISF COPR repo,
+          or the EPEL repo the following is already configured for
+          you. The only thing you might want to do is add your
+          management user to the ``suricata`` group.
+
+Many Suricata examples and guides will show Suricata running as the
+*root* user, particularly when running on live traffic. As Suricata
+generally needs low level read (and in IPS write) access to network
+traffic, it is required that Suricata starts as root, however Suricata
+does have the ability to drop down to a non-root user after startup
+which could limit the impact of a security vulnerability in Suricata
+itself.
+
+.. note:: Currently the ability to drop root privileges after startup
+          is only available on Linux systems.
+
+Create User
+~~~~~~~~~~~
+
+Before running as a non-root user you have to choose, and possibly
+create the user and group that will Suricata will run as. Typically
+this user would be a sytem user with the name ``suricata``. Such a
+user can be created with the following command::
+
+  useradd --no-create-home --system --shell /sbin/nologin suricata
+
+This will create a user and group with the name ``suricata``.
+
+File System Permissions
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Before running Suricata as the user ``suricata``, some directory
+permissions will need to be updated to allow the ``suricata`` read and
+write access.
+
+Assuming your Suricata was installed from source using the recommended
+configuration of::
+
+  ./configure --prefix=/usr/ --sysconfdir=/etc/ --localstatedir=/var/
+
+the following directories will need their permissions updated:
+
++------------------+-----------+
+|Directory         |Permissions|
++==================+===========+
+|/etc/suricata     |Read       |
++------------------+-----------+
+|/var/log/suricata |Read, Write|
++------------------+-----------+
+|/var/lib/suricata |Read, Write|
++------------------+-----------+
+|/var/run/suricata |Read, Write|
++------------------+-----------+
+
+The following commands will setup the correct permissions:
+
+* ``/etc/suricata``::
+
+    chgrp -R suricata /etc/suricata
+    chmod -R g+r /etc/suricata
+
+* ``/var/log/suricata``::
+
+    chgrp -R suricata /var/log/suricata
+    chmod -R g+rw /var/log/suricata
+
+* ``/var/lib/suricata``::
+
+    chgrp -R suricata /var/lib/suricata
+    chmod -R g+srw /var/lib/suricata
+
+* ``/var/lib/suricata``::
+
+    chgrp -R suricata /var/run/suricata
+    chmod -R g+srw /var/run/suricata
+
+Configure Suricata to Run as ``Suricata``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Suricata can be configured to run as an alternate user by updating the
+configuration file or using command line arguments.
+
+* Using the configuration file, update the ``run-as`` section to look like::
+
+    run-as:
+      user: suricata
+      group: suricata
+
+* Or if using command line arguments, add the following to your command::
+
+    --user suricata --group suricata
+
+Starting Suricata
+~~~~~~~~~~~~~~~~~
+
+It is important to note that Suricata still needs to be started with
+**root** permissions in most cases. Starting as *root* allows Suricata
+to get access to the network interfaces and set the *capabilities*
+required during runtime before it switches down to the configured
+user.
+
+Other Commands: Suricata-Update, SuricataSC
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+With the previous permissions setup, ``suricata-update`` and
+``suricatasc`` can also be run without root or sudo. To allow a user
+to access these commands, add them to the ``suricata`` group.
+
+Containers
+----------
+
+Containers such as Docker and Podman are other methods to provide
+isolation between Suricata and host machine running Suricata, however
+we still recommend running as a non-root user even in containers.
+
+Capabilities
+~~~~~~~~~~~~
+
+For both Docker and Podman the following capabilities should be
+provided to the container running Suricata for proper operation::
+
+  --cap-add=net_admin --cap-add=net_raw --cap-add=sys_nice
+
+Podman
+~~~~~~
+
+Unfortunately Suricata will not work with *rootless* Podman, this is
+due to Suricata's requirement to start with root privileges to gain
+access to the network interfaces. However, if started with the above
+capabilities, and configured to run as a non-root user it will drop
+root privileges before processing network data.