549 lines
17 KiB
Groff
549 lines
17 KiB
Groff
.\"
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.\" Copyright (c) 2000, 2003 Robert N. M. Watson
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\"
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.\" ----------------------------------------------------------------------------
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.\" "THE BEER-WARE LICENSE" (Revision 42):
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.\" <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
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.\" can do whatever you want with this stuff. If we meet some day, and you think
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.\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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.\" ----------------------------------------------------------------------------
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.\"
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.\" $FreeBSD$
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.\"
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.Dd April 8, 2003
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.Dt JAIL 8
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.Os
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.Sh NAME
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.Nm jail
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.Nd "imprison process and its descendants"
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.Sh SYNOPSIS
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.Nm
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.Op Fl i
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.Op Fl u Ar username | Fl U Ar username
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.Ar path hostname ip-number command ...
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.Sh DESCRIPTION
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The
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.Nm
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utility imprisons a process and all future descendants.
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.Pp
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The options are as follows:
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.Bl -tag -width ".Fl u Ar username"
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.It Fl i
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Output the jail identifier of the newly created jail.
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.It Fl u Ar username
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The user name from host environment as whom the
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.Ar command
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should run.
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.It Fl U Ar username
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The user name from jailed environment as whom the
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.Ar command
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should run.
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.It Ar path
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Directory which is to be the root of the prison.
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.It Ar hostname
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Hostname of the prison.
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.It Ar ip-number
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IP number assigned to the prison.
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.It Ar command
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Pathname of the program which is to be executed.
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.El
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.Pp
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Jails are typically set up using one of two philosophies: either to
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constrain a specific application (possibly running with privilege), or
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to create a
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.Dq "virtual system image"
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running a variety of daemons and services.
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In both cases, a fairly complete file system install of
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.Fx
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is
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required, so as to provide the necessary command line tools, daemons,
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libraries, application configuration files, etc.
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However, for a virtual server configuration, a fair amount of
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additional work is required so as to configure the
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.Dq boot
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process.
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This manual page documents the configuration steps necessary to support
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either of these steps, although the configuration steps may be
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refined based on local requirements.
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.Pp
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Please see the
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.Xr jail 2
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man page for further details.
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.Sh EXAMPLES
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.Ss "Setting up a Jail Directory Tree"
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This example shows how to set up a jail directory tree
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containing an entire
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.Fx
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distribution:
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.Bd -literal
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D=/here/is/the/jail
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cd /usr/src
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mkdir -p $D
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make world DESTDIR=$D
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cd etc
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make distribution DESTDIR=$D
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mount_devfs devfs $D/dev
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cd $D
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ln -sf dev/null kernel
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.Ed
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.Pp
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NOTE: It is important that only appropriate device nodes in devfs be
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exposed to a jail; access to disk devices in the jail may permit processes
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in the jail to bypass the jail sandboxing by modifying files outside of
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the jail.
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See
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.Xr devfs 8
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for information on how to use devfs rules to limit access to entries
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in the per-jail devfs.
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.Pp
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In many cases this example would put far more in the jail than needed.
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In the other extreme case a jail might contain only one file:
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the executable to be run in the jail.
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.Pp
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We recommend experimentation and caution that it is a lot easier to
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start with a
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.Dq fat
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jail and remove things until it stops working,
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than it is to start with a
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.Dq thin
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jail and add things until it works.
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.Ss "Setting Up a Jail"
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Do what was described in
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.Sx "Setting Up a Jail Directory Tree"
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to build the jail directory tree.
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For the sake of this example, we will
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assume you built it in
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.Pa /data/jail/192.168.11.100 ,
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named for the jailed IP address.
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Substitute below as needed with your
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own directory, IP address, and hostname.
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.Ss "Setting up the Host Environment"
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First, you will want to set up your real system's environment to be
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.Dq jail-friendly .
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For consistency, we will refer to the parent box as the
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.Dq "host environment" ,
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and to the jailed virtual machine as the
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.Dq "jail environment" .
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Since jail is implemented using IP aliases, one of the first things to do
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is to disable IP services on the host system that listen on all local
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IP addresses for a service.
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If a network service is present in the host environment that binds all
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available IP addresses rather than specific IP addresses, it may service
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requests sent to jail IP addresses.
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This means changing
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.Xr inetd 8
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to only listen on the
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appropriate IP address, and so forth.
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Add the following to
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.Pa /etc/rc.conf
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in the host environment:
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.Bd -literal -offset indent
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sendmail_enable="NO"
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inetd_flags="-wW -a 192.168.11.23"
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rpcbind_enable="NO"
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.Ed
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.Pp
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.Li 192.168.11.23
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is the native IP address for the host system, in this example.
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Daemons that run out of
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.Xr inetd 8
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can be easily set to use only the specified host IP address.
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Other daemons
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will need to be manually configured\(emfor some this is possible through
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the
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.Xr rc.conf 5
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flags entries; for others it is necessary to modify per-application
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configuration files, or to recompile the applications.
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The following frequently deployed services must have their individual
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configuration files modified to limit the application to listening
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to a specific IP address:
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.Pp
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To configure
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.Xr sshd 8 ,
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it is necessary to modify
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.Pa /etc/ssh/sshd_config .
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.Pp
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To configure
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.Xr sendmail 8 ,
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it is necessary to modify
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.Pa /etc/mail/sendmail.cf .
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.Pp
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For
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.Xr named 8 ,
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it is necessary to modify
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.Pa /etc/namedb/named.conf .
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.Pp
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In addition, a number of services must be recompiled in order to run
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them in the host environment.
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This includes most applications providing services using
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.Xr rpc 3 ,
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such as
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.Xr rpcbind 8,
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.Xr nfsd 8 ,
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and
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.Xr mountd 8 .
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In general, applications for which it is not possible to specify which
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IP address to bind should not be run in the host environment unless they
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should also service requests sent to jail IP addresses.
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Attempting to serve
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NFS from the host environment may also cause confusion, and cannot be
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easily reconfigured to use only specific IPs, as some NFS services are
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hosted directly from the kernel.
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Any third-party network software running
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in the host environment should also be checked and configured so that it
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does not bind all IP addresses, which would result in those services' also
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appearing to be offered by the jail environments.
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.Pp
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Once
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these daemons have been disabled or fixed in the host environment, it is
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best to reboot so that all daemons are in a known state, to reduce the
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potential for confusion later (such as finding that when you send mail
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to a jail, and its sendmail is down, the mail is delivered to the host,
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etc.).
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.Ss "Configuring the Jail"
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Start any jail for the first time without configuring the network
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interface so that you can clean it up a little and set up accounts.
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As
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with any machine (virtual or not) you will need to set a root password, time
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zone, etc.
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Some of these steps apply only if you intend to run a full virtual server
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inside the jail; others apply both for constraining a particular application
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or for running a virtual server.
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.Pp
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Start a shell in the jail:
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.Pp
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.Dl "jail /data/jail/192.168.11.100 testhostname 192.168.11.100 /bin/sh"
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.Pp
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Assuming no errors, you will end up with a shell prompt within the jail.
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You can now run
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.Pa /usr/sbin/sysinstall
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and do the post-install configuration to set various configuration options,
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or perform these actions manually by editing
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.Pa /etc/rc.conf ,
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etc.
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.Pp
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.Bl -bullet -offset indent -compact
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.It
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Create an empty
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.Pa /etc/fstab
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to quell startup warnings about missing fstab (virtual server only)
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.It
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Disable the port mapper
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.Pa ( /etc/rc.conf :
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.Li rpcbind_enable="NO" )
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(virtual server only)
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.It
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Run
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.Xr newaliases 1
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to quell
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.Xr sendmail 8
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warnings.
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.It
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Disable interface configuration to quell startup warnings about
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.Xr ifconfig 8
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.Pq Li network_interfaces=""
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(virtual server only)
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.It
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Configure
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.Pa /etc/resolv.conf
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so that name resolution within the jail will work correctly
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.It
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Set a root password, probably different from the real host system
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.It
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Set the timezone
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.It
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Add accounts for users in the jail environment
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.It
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Install any packages the environment requires
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.El
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.Pp
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You may also want to perform any package-specific configuration (web servers,
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SSH servers, etc), patch up
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.Pa /etc/syslog.conf
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so it logs as you would like, etc.
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If you are not using a virtual server, you may wish to modify
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.Xr syslogd 8
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in the host environment to listen on the syslog socket in the jail
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environment; in this example, the syslog socket would be stored in
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.Pa /data/jail/192.168.11.100/var/run/log .
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.Pp
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Exit from the shell, and the jail will be shut down.
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.Ss "Starting the Jail"
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You are now ready to restart the jail and bring up the environment with
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all of its daemons and other programs.
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If you are running a single application in the jail, substitute the
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command used to start the application for
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.Pa /etc/rc
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in the examples below.
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To start a virtual server environment,
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.Pa /etc/rc
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is run to launch various daemons and services.
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To do this, first bring up the
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virtual host interface, and then start the jail's
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.Pa /etc/rc
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script from within the jail.
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.Pp
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NOTE: If you plan to allow untrusted users to have root access inside the
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jail, you may wish to consider setting the
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.Va security.jail.set_hostname_allowed
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sysctl variable to 0.
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Please see the management discussion later in this document as to why this
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may be a good idea.
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If you do decide to set this variable,
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it must be set before starting any jails, and once each boot.
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.Bd -literal -offset indent
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ifconfig ed0 inet alias 192.168.11.100/32
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mount -t procfs proc /data/jail/192.168.11.100/proc
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jail /data/jail/192.168.11.100 testhostname 192.168.11.100 \\
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/bin/sh /etc/rc
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.Ed
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.Pp
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A few warnings will be produced, because most
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.Xr sysctl 8
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configuration variables cannot be set from within the jail, as they are
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global across all jails and the host environment.
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However, it should all
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work properly.
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You should be able to see
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.Xr inetd 8 ,
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.Xr syslogd 8 ,
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and other processes running within the jail using
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.Xr ps 1 ,
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with the
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.Ql J
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flag appearing beside jailed processes.
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To see an active list of jails, use the
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.Xr jls 8
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utility.
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You should also be able to
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.Xr telnet 1
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to the hostname or IP address of the jailed environment, and log
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in using the accounts you created previously.
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.Ss "Managing the Jail"
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Normal machine shutdown commands, such as
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.Xr halt 8 ,
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.Xr reboot 8 ,
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and
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.Xr shutdown 8 ,
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cannot be used successfully within the jail.
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To kill all processes in a
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jail, you may log into the jail and, as root, use one of the following
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commands, depending on what you want to accomplish:
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.Pp
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.Bd -literal -offset indent
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kill -TERM -1
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kill -KILL -1
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.Ed
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.Pp
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This will send the
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.Dv SIGTERM
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or
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.Dv SIGKILL
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signals to all processes in the jail from within the jail.
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Depending on
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the intended use of the jail, you may also want to run
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.Pa /etc/rc.shutdown
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from within the jail.
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To kill processes from outside the jail, use the
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.Xr jexec 8
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utility in conjuction with the one of the
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.Xr kill 1
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commands above, or use the
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.Xr killall 1
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utility with the
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.Fl j
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option.
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.Pp
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The
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.Pa /proc/ Ns Ar pid Ns Pa /status
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file contains, as its last field, the hostname of the jail in which the
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process runs, or
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.Dq Li -
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to indicate that the process is not running within a jail.
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The
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.Xr ps 1
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command also shows a
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.Ql J
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flag for processes in a jail.
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However, the hostname for a jail may be, by
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default, modified from within the jail, so the
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.Pa /proc
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status entry is unreliable by default.
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To disable the setting of the hostname
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from within a jail, set the
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.Va security.jail.set_hostname_allowed
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sysctl variable in the host environment to 0, which will affect all jails.
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You can have this sysctl set on each boot using
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.Xr sysctl.conf 5 .
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Just add the following line to
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.Pa /etc/sysctl.conf :
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.Pp
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.Dl security.jail.set_hostname_allowed=0
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.Ss "Sysctl MIB Entries"
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Certain aspects of the jail containments environment may be modified from
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the host environment using
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.Xr sysctl 8
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MIB variables.
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Currently, these variables affect all jails on the system, although in
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the future this functionality may be finer grained.
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.Bl -tag -width XXX
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.It Va security.jail.allow_raw_sockets
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This MIB entry determines whether or not prison root is allowed to
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create raw sockets.
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Setting this MIB to 1 allows utilities like
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.Xr ping 8
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and
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.Xr traceroute 8
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to operate inside the prison.
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If this MIB
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is set, the source IP addresses are enforced to comply
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with the IP address bound to the jail, regardless of whether or not
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the
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.Dv IP_HDRINCL
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flag has been set on the socket.
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Since raw sockets can be used to configure
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and interact with various network subsystems, extra caution should be used
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where privileged access to jails is given out to untrusted parties.
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As such,
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by default this option is disabled.
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.It Va security.jail.getfsstatroot_only
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This MIB entry determines whether or not processes within a jail are able
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to see data for all mountpoints.
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When set to 1 (default), the
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.Xr getfsstat 2
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system call returns only (when called by jailed processes) the data for
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the file system on which the jail's root vnode is located.
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Note: this also has the effect of hiding other mounts inside a jail,
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such as
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.Pa /dev ,
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.Pa /tmp ,
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and
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.Pa /proc ,
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but errs on the side of leaking less information.
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.It Va security.jail.set_hostname_allowed
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This MIB entry determines whether or not processes within a jail are
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allowed to change their hostname via
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.Xr hostname 1
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or
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.Xr sethostname 3 .
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In the current jail implementation, the ability to set the hostname from
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within the jail can impact management tools relying on the accuracy of jail
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information in
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.Pa /proc .
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As such, this should be disabled in environments where privileged access to
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jails is given out to untrusted parties.
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.It Va security.jail.socket_unixiproute_only
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The jail functionality binds an IPv4 address to each jail, and limits
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access to other network addresses in the IPv4 space that may be available
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in the host environment.
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However, jail is not currently able to limit access to other network
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protocol stacks that have not had jail functionality added to them.
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As such, by default, processes within jails may only access protocols
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in the following domains:
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.Dv PF_LOCAL , PF_INET ,
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and
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.Dv PF_ROUTE ,
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permitting them access to
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.Ux
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domain sockets,
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IPv4 addresses, and routing sockets.
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To enable access to other domains, this MIB variable may be set to
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0.
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.It Va security.jail.sysvipc_allowed
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|
This MIB entry determines whether or not processes within a jail have access
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to System V IPC primitives.
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|
In the current jail implementation, System V primitives share a single
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namespace across the host and jail environments, meaning that processes
|
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within a jail would be able to communicate with (and potentially interfere
|
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with) processes outside of the jail, and in other jails.
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As such, this functionality is disabled by default, but can be enabled
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by setting this MIB entry to 1.
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.El
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.Pp
|
|
There are currently two MIB related variables that have per-jail settings.
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Changes to these variables by a jailed process do not effect the host
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environment, only the jail environment.
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The variables are
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.Va kern.securelevel
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and
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.Va kern.hostname .
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.Sh SEE ALSO
|
|
.Xr killall 1 ,
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|
.Xr newaliases 1 ,
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|
.Xr ps 1 ,
|
|
.Xr chroot 2 ,
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|
.Xr jail 2 ,
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.Xr jail_attach 2 ,
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|
.Xr procfs 5 ,
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|
.Xr rc.conf 5 ,
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|
.Xr sysctl.conf 5 ,
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.Xr devfs 8 ,
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.Xr halt 8 ,
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.Xr inetd 8 ,
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.Xr jexec 8 ,
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.Xr jls 8 ,
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.Xr mount_devfs 8 ,
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.Xr named 8 ,
|
|
.Xr reboot 8 ,
|
|
.Xr rpcbind 8 ,
|
|
.Xr sendmail 8 ,
|
|
.Xr shutdown 8 ,
|
|
.Xr sysctl 8 ,
|
|
.Xr syslogd 8
|
|
.Sh HISTORY
|
|
The
|
|
.Nm
|
|
utility appeared in
|
|
.Fx 4.0 .
|
|
.Sh AUTHORS
|
|
.An -nosplit
|
|
The jail feature was written by
|
|
.An Poul-Henning Kamp
|
|
for R&D Associates
|
|
.Pa http://www.rndassociates.com/
|
|
who contributed it to
|
|
.Fx .
|
|
.Pp
|
|
.An Robert Watson
|
|
wrote the extended documentation, found a few bugs, added
|
|
a few new features, and cleaned up the userland jail environment.
|
|
.Sh BUGS
|
|
Jail currently lacks the ability to allow access to
|
|
specific jail information via
|
|
.Xr ps 1
|
|
as opposed to
|
|
.Xr procfs 5 .
|
|
Similarly, it might be a good idea to add an
|
|
address alias flag such that daemons listening on all IPs
|
|
.Pq Dv INADDR_ANY
|
|
will not bind on that address, which would facilitate building a safe
|
|
host environment such that host daemons do not impose on services offered
|
|
from within jails.
|
|
Currently, the simplest answer is to minimize services
|
|
offered on the host, possibly limiting it to services offered from
|
|
.Xr inetd 8
|
|
which is easily configurable.
|