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This is the Chroot-BIND 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.
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
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.
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-BIND.html.
BIND is available from the Internet Software Consortium at http://www.isc.org/bind.html. As of this writing, the current version of BIND8 is 8.2.3. BIND 9.x has now been released, but I haven't had time to look at it in depth yet, so I don't know how much of this document will be applicable. Some administrators are now putting BIND9 into production use, but it still requires a taste for living on the bleeding edge (and upgrading every couple weeks), so you may be better off staying with BIND8 for now.
Keep in mind that there are known security holes in all versions of BIND8 less than 8.2.3, so make very sure that you're running the latest version!
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.
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.
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