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| Newer page: | version 3 | Last edited on Thursday, October 21, 2004 5:19:54 pm | by AristotlePagaltzis | Revert |
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@@ -1,891 +1 @@
-
-
-
-Chroot-BIND8 HOWTO
-
-
-
-----
-
-!!!Chroot-BIND8 HOWTO
-
-!!Scott Wunsch, scott at wunsch.orgv1.4, 1 July 2001
-
-
-----
-''This document describes installing the BIND 8 nameserver to run in a chroot
-jail and as a non-root user, to provide added security and minimise the
-potential effects of a security compromise. This version of the document
-covers the old but still popular BIND 8; there is another document which
-provides similar information for BIND 9.''
-----
-
-
-
-
-!!1. Introduction
-
-
-*1.1 What?
-
-*1.2 Why?
-
-*1.3 Where?
-
-*1.4 How?
-
-*1.5 Disclaimer
-
-
-
-
-
-!!2. Preparing the Jail
-
-
-*2.1 Creating a User
-
-*2.2 Directory Structure
-
-*2.3 Placing the BIND Data
-
-*2.4 System Support Files
-
-*2.5 Logging
-
-
-
-
-
-!!3. Compiling BIND
-
-
-*3.1 Modifying Paths
-
-*3.2 Doing the Build
-
-
-
-
-
-!!4. Installing Your Shiny New BIND
-
-
-*4.1 Installing the Tools Outside the Jail
-
-*4.2 Installing the Binaries in the Jail
-
-*4.3 Setting up the Init Script
-
-*4.4 Configuration Changes
-
-
-
-
-
-!!5. The End
-
-
-*5.1 Launching BIND
-
-*5.2 That's It!
-
-
-
-
-
-!!6. Appendix - Upgrading BIND Later
-
-
-
-
-!!7. Appendix - Thanks
-
-
-
-
-!!8. Appendix - Document Distribution Policy
-----
-
-!!1. Introduction
-
-
-This is the Chroot-BIND8 HOWTO; see
-Where? for the
-master site, which contains the latest copy. It is assumed that you already
-know how to configure and use BIND (the Berkeley Internet Name Domain). If
-not, I would recommend that you read the DNS HOWTO first. It is also assumed
-that you have a basic familiarity with compiling and installing software on
-your UNIX-like system.
-
-
-
-
-!!1.1 What?
-
-
-
-This document describes some extra security precautions that you can take when
-you install BIND. It explains how to configure BIND so that it resides in a
-``chroot jail'', meaning that it cannot see or access files outside its own
-little directory tree. We shall also configure it to run as a non-root user.
-
-
-The idea behind chroot is fairly simple. When you run BIND (or any other
-process) in a chroot jail, the process is simply unable to see any part of the
-filesystem outside the jail. For example, in this document, we'll set BIND up
-to run chrooted to the directory /chroot/named. Well, to BIND, the
-contents of this directory will appear to be /, the root directory.
-Nothing outside this directory will be accessible to it. You've probably
-encounted a chroot jail before, if you've ever ftped into a public system.
-
-
-
-
-!!1.2 Why?
-
-
-
-The idea behind running BIND in a chroot jail is to limit the amount of access
-any malicious individual could gain by exploiting vulnerabilities in BIND. It
-is for the same reason that we run BIND as a non-root user.
-
-
-This should be considered as a supplement to the normal security precautions
-(running the latest version, using access control, etc.), not a replacement for
-them.
-
-
-If you're interested in DNS security, you might also be interested in a few
-other products. Building BIND with
-!StackGuard would
-probably be a good idea for even more protection. Using it is easy; it's
-just like using ordinary gcc. Also,
-DNScache is a secure replacement
-for BIND, written by Dan Bernstein. Dan is the author of qmail, and DNScache
-appears to follow a similar philosophy.
-
-
-
-
-!! 1.3 Where?
-
-
-
-The latest version of this document is always available from the web site of the
-Linux/Open Source Users of Regina, Sask., at
-http://www.losurs.org/docs/howto/Chroot-BIND8.html.
-
-
-There is now a Japanese translation of this document, maintained by nakano
-at apm.seikei.ac.jp. This is available at
-http://www.linux.or.jp/JF/JFdocs/Chroot-BIND8-HOWTO.html.
-
-
-BIND is available from
-the Internet Software Consortium at
-http://www.isc.org/bind.html. As of this
-writing, the current version of BIND 8 is 8.2.4. BIND 9.x has now been
-released, and has been around for a little while. You may consider upgrading
-to it; the chroot process is certainly much simpler and cleaner. If you are
-running BIND 9, then you want the Chroot-BIND HOWTO, which should be available
-from the same location as this document.
-
-
-Keep in mind that there are __known__ security holes in all
-versions of BIND 8 less than __8.2.3__, so make very sure that you're
-running the latest version!
-
-
-
-
-!!1.4 How?
-
-
-
-I wrote this document based on my experiences in setting BIND up in a chroot
-environment. In my case, I already had an existing BIND installation in the
-form of a package that came with my Linux distribution. I'll assume that most
-of you are probably in the same situation, and will simply be transferring over
-and modifying the configuration files from your existing BIND installation, and
-then removing the package before installing the new one. Don't remove the
-package yet, though; we may want some files from it first.
-
-
-If this is not the case for you, you should still be able to follow this
-document. The only difference is that, where I refer to copying an existing
-file, you first have to create it yourself. The DNS HOWTO may be helpful for
-this.
-
-
-
-
-!!1.5 Disclaimer
-
-
-
-These steps worked for me, on my system. Your mileage may vary. This is but
-one way to approach this; there are other ways to set the same thing up
-(although the general approach will be the same). It just happens that this
-was the first way that I tried that worked, so I wrote it down.
-
-
-My BIND experience to date has been installing on Linux servers. However, most
-of the instructions in this document should be easily applicable to other
-flavours of UNIX as well, and I shall try to point out differences of which I am
-aware.
-
-
-
-----
-
-!!2. Preparing the Jail
-
-!!2.1 Creating a User
-
-
-
-As mentioned in the introduction, it's not a good idea to run BIND as root. So,
-before we begin, let's create a separate user for BIND. Note that you should
-never use an existing generic user like nobody for this purpose.
-However, some distributions, such as SuSE and Linux Mandrake have started
-providing a specific user (generally called named); you can simply adapt
-this user for our purposes, if you like.
-
-
-This requires adding a line something like the following to /etc/passwd:
-
-
-named:x:200:200:Nameserver:/chroot/named:/bin/false
-
-
-And one like this to /etc/group:
-
-
-named:x:200:
-
-
-This creates a user and group called named for BIND. Make sure that the
-UID and GID (both 200 in this example) are unique on your system. The shell is
-set to /bin/false because this user will never need to log in.
-
-
-
-
-!!2.2 Directory Structure
-
-
-
-Now, we must set up the directory structure that we will use for the chroot jail
-in which BIND will live. This can be anywhere on your filesystem; the truly
-paranoid may even want to put it on a separate volume. I shall assume that you
-will use /chroot/named. Let's start by creating the following directory
-structure:
-
-
-
-
-
-/chroot
-+-- named
-+-- bin
-+-- dev
-+-- etc
-| +-- namedb
-+-- lib
-+-- var
-+-- run
-
-
-
-
-
-
-!!2.3 Placing the BIND Data
-
-
-
-Assuming that you have already done a conventional installation of BIND and are
-using it, you will already have an existing named.conf and zone files.
-These files must now be moved (or copied, to be safe) into the chroot jail, so
-that BIND can get at them. named.conf goes in /chroot/named/etc,
-and the zone files can go in /chroot/named/etc/namedb. For example:
-
-
-# cp -p /etc/named.conf /chroot/named/etc/
-# cp -a /var/named/* /chroot/named/etc/namedb/
-
-
-
-
-BIND will likely need to write to the namedb directory, and probably some
-of the files in it. For example, if your DNS serves as a slave for a zone, it
-will have to update that zone file. Also, BIND can dump statistical
-information, and does so in this directory. For that reason, you should
-probably make the named user the owner of this directory and its contents:
-
-
-# chown -R named:named /chroot/named/etc/namedb
-
-
-BIND will also need to write to the /var/run directory, to put its
-pidfile and ndc socket there, so let's allow it to do so:
-
-
-# chown named:named /chroot/named/var/run
-
-
-
-
-
-
-!!2.4 System Support Files
-
-
-
-Once BIND is running in the chroot jail, it will not be able to access files
-outside the jail __at all__. However, it needs to access a few key files, such
-as the system's C library. Exactly what libraries are required will depend on
-your flavour of UNIX. For most modern Linux systems, the following commands
-will be sufficient to put the necessary libraries in place:
-
-
-# cd /chroot/named/lib
-# cp -p /lib/libc-2.*.so .
-# ln -s libc-2.*.so libc.so.6
-# cp -p /lib/ld-2.*.so .
-# ln -s ld-2.*.so ld-linux.so.2
-
-
-As an alternative, you could simply build statically-linked versions of the BIND
-binaries to put in your chroot jail. You should also copy ldconfig into
-the jail, and run it to create an etc/ld.so.cache for the jail environment.
-The following commands could take care of this:
-
-
-# cp /sbin/ldconfig /chroot/named/bin/
-# chroot /chroot/named /bin/ldconfig -v
-
-
-
-
-BIND needs one more system file in its jail: good ol' /dev/null. Again,
-the exact command necessary to create this device node may vary from system to
-system; check your /dev/MAKEDEV script to be sure. Some systems may also
-require /dev/zero. For most Linux systems, we can use the following
-command:
-
-
-# mknod /chroot/named/dev/null c 1 3
-
-
-
-
-Finally, you need a couple extra files in the /etc directory inside the
-jail. In particular, you must copy /etc/localtime (this sometimes known
-as /usr/lib/zoneinfo/localtime on some systems) in there so that BIND
-logs things with the right time on them, and you must make a simple group
-file with the named group in it. The following two commands will take
-care of this:
-
-
-# cp /etc/localtime /chroot/named/etc/
-# echo 'named:x:200:' > /chroot/named/etc/group
-
-
-
-
-Keep in mind that the GID, 200 in this example, must match the one you defined
-in the real /etc/group above.
-
-
-
-
-!! 2.5 Logging
-
-
-
-Unlike a conventional jailbird, BIND can't just scribble its log entries on the
-walls :-). Normally, BIND logs through syslogd, the system logging daemon.
-However, this type of logging is performed by sending the log entries to the
-special socket /dev/log. Since this is outside the jail, BIND can't use
-it any more. Fortuantely, there are a couple options to work around this.
-
-
-
-
-!The Ideal Solution
-
-
-The ideal solution to this dilemma requires a reasonably recent version of
-syslogd which supports the -a switch introduced by OpenBSD.
-Check the manpage for your syslogd(8) to see if you have such a
-version.
-
-
-If you do, all you have to do is add the switch ``-a
-/chroot/named/dev/log'' to the command line when you launch syslogd.
-On systems which use a full SysV-init (which includes most Linux distributions),
-this is typically done in the file /etc/rc.d/init.d/syslog. For example,
-on my Red Hat Linux system, I changed the line
-
-
-daemon syslogd -m
-
-
-to
-
-
-daemon syslogd -m 0 -a /chroot/named/dev/log
-
-
-
-
-On Caldera !OpenLinux systems, they use a daemon launcher called ssd,
-which reads configuration from /etc/sysconfig/daemons/syslog. You
-simply need to modify the options line to look like this:
-
-
-OPTIONS_SYSLOGD="-m 0 -a /chroot/named/dev/log"
-
-
-
-
-Similarly, on SuSE systems, I'm told that the best place to add this switch
-is in the /etc/rc.config file. Changing the line
-
-
-SYSLOGD_PARAMS=""
-
-
-to read
-
-
-SYSLOGD_PARAMS="-a /chroot/named/dev/log"
-
-
-should do the trick.
-
-
-Once you've figured out how to make this change for your system, simply
-restart syslogd, either by killing it and launching it again (with
-the extra parameters), or by using the SysV-init script to do it for you:
-
-
-# /etc/rc.d/init.d/syslog stop
-# /etc/rc.d/init.d/syslog start
-
-
-
-
-Once it's been restarted, you should see a ``file'' in /chroot/named/dev
-called log, that looks something like this:
-
-
-
-
-srw-rw-rw- 1 root root 0 Mar 13 20:58 log
-
-
-
-
-
-!The Other Solutions
-
-
-If you have an older syslogd, then you'll have to find another way to do
-your logging. There are a couple programs out there, such as holelogd,
-which are designed to help by acting as a ``proxy'' and accepting log entries
-from the chrooted BIND and passing them out to the regular /dev/log
-socket.
-
-
-Alteratively, you can simply configure BIND to log to files instead of going
-through syslog. See the BIND documentation for more details if you choose to go
-this route.
-
-
-
-----
-
-!! 3. Compiling BIND
-
-
-You should be able to find the BIND source by visiting
-http://www.isc.org/bind.html. You need the bind-src.tar.gz
-package. Be sure to get the latest version!
-
-
-
-
-!!3.1 Modifying Paths
-
-
-
-Things can get a bit confusing at this point, because different parts of the
-BIND package will be referring to the same directories by different names
-(depending on whether or not they're running inside the jail). I'll try not to
-confuse you __too__ much :-).
-
-
-The main directory that we have to worry about here is /var/run, because
-its contents are required for both the main named daemon (inside the
-jail), and the ndc utility (on the outside). We'll start by setting
-everything up to find this directory from the outside world. To do this, we
-need to modify src/port/linux/Makefile.set (substitute your port's
-directory if you're not running Linux), and change the line
-
-
-DESTRUN=/var/run
-
-
-to
-
-
-DESTRUN=/chroot/named/var/run
-
-
-While you're in there, you may want to change the other destination paths from
-/usr to /usr/local.
-
-
-Now everything should be able to find that directory... except the named
-daemon itself, to which it's still just /var/run inside the jail. We can
-get around this by making a small change in the named source. In the file
-src/bin/named/named.h, find the line
-
-
-#include "pathnames.h"
-
-
-and add the following line immediately after it
-
-
-#define _PATH_NDCSOCK "/var/run/ndc"
-
-
-This way, named will ignore our definition of DESTRUN over in
-Makefile.set and use the correct location (from its perspective in the
-chroot jail). You will notice some warnings about redefinitions of
-_PATH_NDCSOCK when you do the build; just ignore them.
-
-
-
-
-!!3.2 Doing the Build
-
-
-
-You should now be able to compile BIND as normal, following the instructions in
-the INSTALL file. At this stage, we only want to compile BIND, not install
-it. Don't go too far when following the INSTALL file. Essentially, it's
-just make clean, make depend, and make.
-
-
-
-----
-
-!! 4. Installing Your Shiny New BIND
-
-
-I should mention that if you have an existing installation of BIND, such as from
-an RPM, you should probably remove it before installing the new one. On Red Hat
-systems, this probably means removing the packages bind and
-bind-utils, and possibly bind-devel and caching-nameserver, if
-you have them.
-
-
-You may want to save a copy of the init script (e.g.,
-/etc/rc.d/init.d/named), if any, before doing so; it'll be useful later
-on.
-
-
-
-
-!!4.1 Installing the Tools Outside the Jail
-
-
-
-This is the easy part :-). Just run make install and let it take care of
-it for you. You may want to chmod 000 /usr/local/sbin/named afterwards,
-to make sure you don't accidentally run the non-chrooted copy of BIND. (This
-is /usr/sbin/named if you didn't tell it to go in /usr/local/sbin
-like I suggested.)
-
-
-
-
-!!4.2 Installing the Binaries in the Jail
-
-
-
-Only two parts of the package have to live inside the chroot jail: the main
-named daemon itself, and named-xfer, which it uses for zone transfers.
-You can simply copy them in from the source tree:
-
-
-# cp src/bin/named/named /chroot/named/bin
-# cp src/bin/named-xfer/named-xfer /chroot/named/bin
-
-
-
-
-
-
-!!4.3 Setting up the Init Script
-
-
-
-If you have an existing init script from your distribution, it would probably be
-best simply to modify it to run /chroot/named/bin/named, with the
-appropriate switches. The switches are... ''(drumroll please...)''
-
-
-*-u named, which tells BIND to run as the user named, rather than
-root.
-*
-
-*-g named, to run BIND under the group named too, rather than
-root or wheel.
-*
-
-*-t /chroot/named, which tells BIND to chroot itself to the jail
-that we've set up.
-*
-
-
-
-The following is the init script I use with my Red Hat 6.0 system. As you can
-see, it is almost exactly the same as the way it shipped from Red Hat. I have
-also modified the ndc restart command so that it restarts the server
-properly, and keeps it chrooted. You should probably do the same in your init
-script, even if you don't copy this one.
-
-----
-
-#!/bin/sh
-#
-# named This shell script takes care of starting and stopping
-# named (BIND DNS server).
-#
-# chkconfig: 345 55 45
-# description: named (BIND) is a Domain Name Server (DNS) \
-# that is used to resolve host names to IP addresses.
-# probe: true
-# Source function library.
-. /etc/rc.d/init.d/functions
-# Source networking configuration.
-. /etc/sysconfig/network
-# Check that networking is up.
-[ ${NETWORKING} = "no"
] && exit
-[[ -f /chroot/named/bin/named ] || exit
-[[ -f /chroot/named/etc/named.conf ] || exit
-# See how we were called.
-case "$1" in
-start)
-# Start daemons.
-echo -n "Starting named: "
-daemon /chroot/named/bin/named -u named -g named -t /chroot/named
-echo
-touch /var/lock/subsys/named
-;;
-stop)
-# Stop daemons.
-echo -n "Shutting down named: "
-killproc named
-rm -f /var/lock/subsys/named
-echo
-;;
-status)
-/usr/local/sbin/ndc status
-exit $?
-;;
-restart)
-/usr/local/sbin/ndc -n /chroot/named/bin/named "restart -u named -g named -t /chroot/named"
-exit $?
-;;
-reload)
-/usr/local/sbin/ndc reload
-exit $?
-;;
-probe)
-# named knows how to reload intelligently; we don't want linuxconf
-# to offer to restart every time
-/usr/local/sbin/ndc reload >/dev/null 2>&1 || echo start
-exit
-;;
-*)
-echo "Usage: named {start|stop|status|restart}"
-exit 1
-esac
-exit
-
-----
-
-
-
-On Caldera !OpenLinux systems, you simply need to modify the variables defined
-at the top, and it will apparently take care of the rest for you:
-
-
-NAME=named
-DAEMON=/chroot/named/bin/$NAME
-OPTIONS="-t /chroot/named -u named -g named"
-
-
-
-
-
-
-!!4.4 Configuration Changes
-
-
-
-You will also have to add or change a few options in your named.conf to
-keep the various directories straight. In particular, you should add (or
-change, if you already have them) the following directives in the options
-section:
-
-
-directory "/etc/namedb";
-pid-file "/var/run/named.pid";
-named-xfer "/bin/named-xfer";
-
-
-Since this file is being read by the named daemon, all the paths are of
-course relative to the chroot jail.
-
-
-Some people have also reported having to add an extra block to their
-named.conf to get ndc working properly:
-
-
-controls {
-unix "/var/run/ndc" perm 0600 owner 0 group ;
-};
-
-
-
-
-
-----
-
-!!5. The End
-
-!!5.1 Launching BIND
-
-
-
-Everything should be set up, and you should be ready to put your new, more
-secure BIND into action. Assuming you set up a SysV-style init script, you can
-simply launch it as:
-
-
-# /etc/rc.d/init.d/named start
-
-
-Make sure you kill any old versions of BIND still running before doing this.
-
-
-If you take a look at your logs, you should find the initialisation messages
-that BIND spits out when it loads. (If not, there's a problem with your
-logging configuration that you need to fix.) Amongst those
-messages, BIND should tell you that it chrooted successfully, and that it is
-running as the user and group named. If not, you have a problem.
-
-
-
-
-!!5.2 That's It!
-
-
-
-You can go take a nap now ;-).
-
-
-
-----
-
-!! 6. Appendix - Upgrading BIND Later
-
-
-So, you had BIND 8.2.2_P7 all nicely chrooted and tweaked to your taste...
-and then you hear this nasty rumour that there's a remotely-exploitable root
-hole in that version too, and you need to upgrade to 8.2.3 right away. Do
-you have to go through this whole long process to install this new version?
-
-
-Nope. In fact, you really just need the section on
-Compiling BIND and the first two parts of the section on
-Installing BIND (installing the binaries outside and
-inside the jail, respectively).
-
-
-The rest of the HOWTO deals with setting up the jail and other things like
-that, which shouldn't need to be altered between versions of BIND. You can
-just dump the new binaries in over top of the old ones, and you're good to go.
-But don't forget to kill and restart BIND afterwards, or the old, vulnerable
-version will still be running!
-
-
-
-----
-
-!! 7. Appendix - Thanks
-
-
-I'd like to thank the following people for their assistance in the creation
-of this HOWTO:
-
-
-
-
-
-*Lonny Selinger <lonny at abyss.za.org> for "testing" the
-first version of this HOWTO and making sure that I didn't miss any steps.
-
-*
-
-*Chirik <chirik at !CastleFur.COM>, Dwayne Litzenberger
-<dlitz at dlitz.net>, Phil Bambridge <phil.b at
-cableinet.co.uk>, Robert Cole <rcole at metrum-datatape.com>,
-Colin !MacDonald <colinm at telus.net>, and others for pointing out
-errors, omissions, and providing other useful advice to make this HOWTO even
-better.
-
-*
-
-*Erik Wallin <erikw at sec.se> and Brian Cervenka
-<brian at zerobelow.org> for providing good suggestions for
-further tightening the jail.
-
-*
-
-
-
-And last but certainly not least, I'd like to thank Nakano Takeo <nakano
-at apm.seikei.ac.jp> for translating the Chroot-BIND HOWTO into
-Japanese. You can find his translation at
-http://www.linux.or.jp/JF/JFdocs/Chroot-BIND-HOWTO.html.
-
-
-
-----
-
-!! 8. Appendix - Document Distribution Policy
-
-
-Copyright (c) Scott Wunsch, 2000-2001. This document may be distributed only
-subject to the terms set forth in the LDP licence at
-http://metalab.unc.edu/LDP/COPYRIGHT.html.
-
-
-This HOWTO is free documentation; you can redistribute it and/or modify it under
-the terms of the LDP licence. It is distributed in the hope that it will be
-useful, but __without any warranty__; without even the impled warranty of
-merchantability or fitness for a particular purpose. See the LDP licence for
-more details
.
-
-
-
-----
+Describe
[HowToChrootBIND8HOWTO
] here
.
