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# -*- mode: org-mode; truncate-lines: nil -*-
#+TITLE: Systems documentation
#+AUTHOR: The Free E-mail Association
#+DESCRIPTION: Systems documentation for The Free E-mail Association
#+KEYWORDS:
#+LANGUAGE: en
#+OPTIONS: H:3 num:t toc:t \n:nil @:t ::t |:t ^:t -:t f:t *:t <:t
#+OPTIONS: TeX:t LaTeX:nil skip:nil d:nil todo:t pri:nil tags:not-in-toc
#+INFOJS_OPT: view:nil toc:nil ltoc:t mouse:underline buttons:0 path:http://orgmode.org/org-info.js
#+EXPORT_SELECT_TAGS: export
#+EXPORT_EXCLUDE_TAGS: noexport
#+LINK_UP:
#+LINK_HOME:
#+XSLT:
#+DRAWERS: HIDDEN STATE PROPERTIES CONTENT
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License,
Version 1.3 or any later version published by the Free Software
Foundation; with no Invariant Sections, no Front-Cover Texts and
no Back-Cover Texts. A copy of the license is included in a
separate file called "COPYING".
This is documentation of the server configuration used by the free e-mail association, given here in general interest of transparency.
The complete documentation is the actual configuration files on the servers. This document intends to give a general idea of the setup and be of help if we need to recreate a crashed server. Also, if an administrator goes AWOL, it should be easy to pick up where he left of.
We welcome all critisism, suggestions for improvements, additions etc. Please send them to skangas@skangas.se.
* BASIC SETUP -- Checklist after having installed a new Debian GNU/Linux-server
NB! Do not install any "tasks" during installation (web server etc.).
Make sure to answer "yes" to shadow passwords and MD5.
** Uninstall a bunch of unecessary packages, among them:
sudo aptitude remove --purge openbsd-inetd portmap
** Install etckeeper
Used to keep track of /etc. Install ASAP after install!
- /etc/etckeeper/etckeeper.conf
AVOID_COMMIT_BEFORE_INSTALL=1
** Packages to install
*** Administrative
sudo aptitude install openssh-server ntp ntpdate screen
*** Security
sudo aptitude install logcheck harden-clients harden-servers
NB harden-clients conflicts with telnet, which as we know is very handy during configuration
** Configure sshd
- /etc/ssh/sshd_config
PermitRootLogin no
PasswordAuthentication no
X11Forwarding no
** Configure sudo
- Add relevant users to the sudo group
- sudo visudo
%sudo ALL= (ALL) ALL
** Configure logcheck
- sudo aptitude install logcheck syslog-summary
- /etc/logcheck/logcheck.conf
INTRO=0
SENDMAILTO="skangas@skangas.se"
- /etc/logcheck/ignore.d.server/ntpd
- ^\w{3} [ :0-9]{11} [._[:alnum:]-]+ ntpd\[[0-9]+\]: kernel time sync (disabled|enabled) [0-9]+$
+ ^\w{3} [ :0-9]{11} [._[:alnum:]-]+ ntpd\[[0-9]+\]: kernel time sync (disabled|enabled|status( change)?) [0-9]+$
- /etc/logcheck/ignore.d.server/ssh [until logcheck 1.3.7 hits stable]
+ ^\w{3} [ :[:digit:]]{11} [._[:alnum:]-]+ sshd\[[[:digit:]]+\]: Received disconnect from [:[:xdigit:].]+: [[:digit:]]+: disconnected by user$
** Configuring aptitude and friends
We're going for a setup where we install many security updates automatically using the package "unattended-upgrades". Automated upgrades are in general not a very good idea, but "unattended-upgrades" takes steps to minimize the issues with this kind of setup. Given the Debian security teams track record we believe the positives outweigh the negatives.
For the situations when unattended-upgrades fails (e.g. when there are configuration changes), we should e-mail the administrator. We will be using apticron to do this until the version of unattended-upgrades in stable supports mailing when an upgrade fails (the one in unstable does).
- sudo aptitude install apticron unattended-upgrades
- /etc/apt/apt.conf
:CONTENT:
// Limit download speed
//Acquire::http::Dl-Limit "70";
/* Unsupported in the version of unattended-upgrades that is in stable,
* but will later send an e-mail when an upgrade fails.
* Until this works in stable, we will use apticron. */
//Unattended-Upgrade::Mail "skangas@skangas.se";
APT
{
// Increase cache size to some arbitrary size.
// Remove this line completely once we have apt v0.7.26 in stable. (it defaults to no limit)
Cache-Limit "33554432";
// Configuration for /etc/cron.daily/apt
Periodic
{
// Do "apt-get update" automatically every n-days (0=disable)
Update-Package-Lists "1";
// Do "apt-get autoclean" every n-days (0=disable)
AutocleanInterval "1";
// Do "apt-get upgrade --download-only" every n-days (0=disable)
Download-Upgradeable-Packages "1";
// Run the "unattended-upgrade" security upgrade script every n days
Unattended-Upgrade "1"
}
};
Aptitude
{
UI
{
Autoclean-After-Update: true;
Auto-Fix-Broken: false;
Keep-Recommends: true;
Recommends-Important: true;
Description-Visible-By-Default: false;
HelpBar false;
Menubar-Autohide true;
Purge-Unused: true;
Prompt-On-Exit false;
}
}
:END:
- /etc/apticron/apticron.conf
EMAIL="skangas@skangas.se"
* NEXT STEPS
** Configuring the backup solution
General idea [[http://wikis.sun.com/display/BigAdmin/Using+rdist+rsync+with+sudo+for+remote+updating][from here]]. This is just a basic setup for now, will need to be changed to rsnapshot or perhaps something even more sophisticated like bacula.
1. Install rsync
- sudo aptitude install rsync
2. Create a key on the backup computer
- ssh-keygen -N "" -b 4096 -f ~/.ssh/backup_key
- cat .ssh/backup_key.pub
3. Create a user on the computer that will be backed up
- sudo adduser remupd
- turn of password using sudo vipw -s
- add the key to ~remupd/.ssh/authorized_keys2
prefix with: no-X11-forwarding,no-agent-forwarding,no-port-forwarding
- test the key:
ssh -i ~/.ssh/backup_key -l remupd host
- add remupd to sudo:
Cmnd_Alias RSYNCDIST=/usr/bin/rsync
remupd ALL=NOPASSWD:RSYNCDIST
3. Create a script on the backup computer to automatically backup
4. Add script to crontab
** Configuring the e-mail servers
We will be using one main mail storage server, accessible by users via IMAP. We will have two or more mail gateways that will relay e-mail to the main server over secure connections.
The main server will also be responsible for keeping all users in an MySQL database that will be replicated over
*** Configuring the MySQL replication
*** Configuring the SSH tunnel for SMTP
Steps to reproduce the configuration:
1. Create a user on the main e-mail server [if not done]
- sudo aptitude install openbsd-netcat
- sudo adduser smtptunnel
- echo "exit" > .bash_profile [to be sure]
We need bash, so we can not change the shell to something else.
- disable the password: sudo vipw -s
2. Create a key on the smarthost:
- sudo su
- ssh-keygen -N "" -b 4096 -f ~/.ssh/tunnel_key
- cat .ssh/tunnel_key.pub
3. Add this key to the "smtptunnel"-user on the smarthost
- echo "<thekey>" | sude tee .ssh/authorized_keys2
- Add this before "ssh-rsa" in authorized_keys2:
command="nc localhost 25",no-X11-forwarding,no-agent-forwarding,no-port-forwarding
4. Test the key on the client server:
- sudo ssh -l remupd -i /root/.ssh/tunnel_key smtptunnel@host
5. Configure openbsd-inetd:
(We use inetd instead of ssh -L because, among other things, ssh -L tends to hang.)
- sudo aptitude install openbsd-inetd
- /etc/inetd.conf
127.0.0.1:1917 stream tcp nowait root /usr/bin/ssh -q -T -i /root/.ssh/tunnel_key smtptunnel@example.com
- Make sure the tunnel works:
telnet localhost 1917
6. Configure postfix on the client server to relay emails through the tunnel
One quick-n-dirty example to try it out is:
- /etc/postfix/main.cf
relay_domains = fri-epost.dyndns.org
transport_maps = hash:/etc/postfix/transport
- /etc/postfix/transport
hostname.org smtp:localhost:1917
- sudo postmap hash:/etc/postfix/transport
# ssh tunnel to smarthost.com's SMTP server
127.0.0.1:smtp stream tcp nowait root /usr/bin/ssh -q -T -i /root/.ssh/tunnel_key utumno@smarthost.com
** Necessary stuff to fix for security
*** Firewall rules
** Ideas for improved security
*** Increased rate of backups when the IMAP server goes down
*** Bacula for backups
Also has tripwire-like capabilities.
*** Some kind of IDS
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