documentation: avoid recommending --user nobody

Recommend to create an user dedicated to openvpn
so that there is no priviledge escalation between
different services using that user.

cf. https://wiki.ubuntu.com/nobody

Trac: #1335
CC: tincantech <tincantech@protonmail.com>
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20221129144731.35105-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg25573.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

doc/man-sections/generic-options.rst

@@ -294,7 +294,7 @@ which mode OpenVPN is configured as.
 --persist-key
   Don't re-read key files across :code:`SIGUSR1` or ``--ping-restart``.
 
-  This option can be combined with ``--user nobody`` to allow restarts
+  This option can be combined with ``--user`` to allow restarts
   triggered by the :code:`SIGUSR1` signal. Normally if you drop root
   privileges in OpenVPN, the daemon cannot be restarted since it will now
   be unable to re-read protected key files.
@@ -491,7 +491,7 @@ which mode OpenVPN is configured as.
   able to gain control of an OpenVPN session. Though OpenVPN's security
   features make this unlikely, it is provided as a second line of defense.
 
-  By setting ``user`` to :code:`nobody` or somebody similarly unprivileged,
+  By setting ``user`` to an unprivileged user dedicated to run openvpn,
   the hostile party would be limited in what damage they could cause. Of
   course once you take away privileges, you cannot return them to an
   OpenVPN session. This means, for example, that if you want to reset an
@@ -501,5 +501,10 @@ which mode OpenVPN is configured as.
   operations in order to restart (such as re-reading key files or running
   ``ifconfig`` on the TUN device).
 
+  NOTE: Previous versions of openvpn used :code:`nobody` as the example
+  unpriviledged user. It is not recommended to actually use that user
+  since it is usually used by other system services already. Always
+  create a dedicated user for openvpn.
+
 --writepid file
   Write OpenVPN's main process ID to ``file``.

sample/sample-config-files/client.conf

@@ -58,8 +58,8 @@ resolv-retry infinite
 nobind
 
 # Downgrade privileges after initialization (non-Windows only)
-;user nobody
-;group nobody
+;user openvpn
+;group openvpn
 
 # Try to preserve some state across restarts.
 persist-key

sample/sample-config-files/server.conf

@@ -269,10 +269,10 @@ cipher AES-256-CBC
 # It's a good idea to reduce the OpenVPN
 # daemon's privileges after initialization.
 #
-# You can uncomment this out on
-# non-Windows systems.
-;user nobody
-;group nobody
+# You can uncomment this on non-Windows
+# systems after creating a dedicated user.
+;user openvpn
+;group openvpn
 
 # The persist options will try to avoid
 # accessing certain resources on restart

sample/sample-config-files/tls-home.conf

@@ -47,11 +47,11 @@ cipher AES-256-GCM
 # for local and remote.
 ; port 1194
 
-# Downgrade UID and GID to
-# "nobody" after initialization
+# Downgrade UID and GID to an
+# unpriviledged user after initialization
 # for extra security.
-; user nobody
-; group nobody
+; user openvpn
+; group openvpn
 
 # If you built OpenVPN with
 # LZO compression, uncomment

sample/sample-config-files/tls-office.conf

@@ -50,11 +50,11 @@ cipher AES-256-GCM
 # for local and remote.
 ; port 1194
 
-# Downgrade UID and GID to
-# "nobody" after initialization
+# Downgrade UID and GID to an
+# unpriviledged user after initialization
 # for extra security.
-; user nobody
-; group nobody
+; user openvpn
+; group openvpn
 
 # If you built OpenVPN with
 # LZO compression, uncomment

src/openvpn/init.c

@@ -2020,7 +2020,7 @@ do_close_tun(struct context *c, bool force)
         }
 
         /* Run the down script -- note that it will run at reduced
-         * privilege if, for example, "--user nobody" was used. */
+         * privilege if, for example, "--user" was used. */
         run_up_down(c->options.down_script,
                     c->plugins,
                     OPENVPN_PLUGIN_DOWN,