Linux Server Security, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 9: Securing Internet Email

Running Postfix in a chroot Jail

One of the niftier things you can do to secure Postfix is to run selected parts of it

chrooted (see Chapter 6 for more information on the chroot technique). This usually

requires you to create copies of things needed by the chrooted process. For example,

if the process looks for /etc/mydaemon.conf on startup but is chrooted to /var/mydae-

mon, the process will actually look for mydaemon.conf in /var/mydaemon/etc/mydae-

mon.conf.

Happily, the preparations required to chroot Postfix are explained for a variety of

architectures, including Linux, in the examples/chroot-setup subdirectory of the Post-

fix source code. If you install Postfix from a binary package, the package may have

an installation script to make these preparations for you automatically after install-

ing Postfix. In SUSE, for example, the Postfix RPM package runs a script that creates

a complete directory tree for chrooted Postfix processes to use (etc, usr, lib,andso

forth). This directory tree then resides in /var/spool/postfix (the default Postfix home

directory and therefore the logical place to chroot its processes to), with the appro-

priate ownerships and permissions preset.

If your binary distribution doesn’t do this for you, simply download