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mailinabox/setup/dns.sh

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#!/bin/bash
# DNS
# -----------------------------------------------
# This script installs packages, but the DNS zone files are only
# created by the /dns/update API in the management server because
# the set of zones (domains) hosted by the server depends on the
# mail users & aliases created by the user later.
source setup/functions.sh # load our functions
source /etc/mailinabox.conf # load global vars
# Install the packages.
#
# * nsd: The non-recursive nameserver that publishes our DNS records.
# * ldnsutils: Helper utilities for signing DNSSEC zones.
# * openssh-client: Provides ssh-keyscan which we use to create SSHFP records.
apt_install nsd ldnsutils openssh-client
# Prepare nsd's configuration.
mkdir -p /var/run/nsd
cat > /etc/nsd/nsd.conf << EOF;
# No not edit. Overwritten by Mail-in-a-Box setup.
server:
hide-version: yes
# identify the server (CH TXT ID.SERVER entry).
identity: ""
# The directory for zonefile: files.
zonesdir: "/etc/nsd/zones"
# Allows NSD to bind to IP addresses that are not (yet) added to the
# network interface. This allows nsd to start even if the network stack
# isn't fully ready, which apparently happens in some cases.
# See https://www.nlnetlabs.nl/projects/nsd/nsd.conf.5.html.
ip-transparent: yes
EOF
# Since we have bind9 listening on localhost for locally-generated
# DNS queries that require a recursive nameserver, and the system
# might have other network interfaces for e.g. tunnelling, we have
# to be specific about the network interfaces that nsd binds to.
for ip in $PRIVATE_IP $PRIVATE_IPV6; do
echo " ip-address: $ip" >> /etc/nsd/nsd.conf;
done
echo "include: /etc/nsd/zones.conf" >> /etc/nsd/nsd.conf;
# Create DNSSEC signing keys.
mkdir -p "$STORAGE_ROOT/dns/dnssec";
# TLDs don't all support the same algorithms, so we'll generate keys using a few
# different algorithms. RSASHA1-NSEC3-SHA1 was possibly the first widely used
# algorithm that supported NSEC3, which is a security best practice. However TLDs
# will probably be moving away from it to a a SHA256-based algorithm.
#
# Supports `RSASHA1-NSEC3-SHA1` (didn't test with `RSASHA256`):
#
# * .info
# * .me
#
# Requires `RSASHA256`
#
# * .email
# * .guide
#
# Supports `RSASHA256` (and defaulting to this)
#
# * .fund
FIRST=1 #NODOC
for algo in RSASHA1-NSEC3-SHA1 RSASHA256; do
if [ ! -f "$STORAGE_ROOT/dns/dnssec/$algo.conf" ]; then
if [ $FIRST == 1 ]; then
echo "Generating DNSSEC signing keys. This may take a few minutes..."
FIRST=0 #NODOC
fi
# Create the Key-Signing Key (KSK) (with `-k`) which is the so-called
# Secure Entry Point. The domain name we provide ("_domain_") doesn't
# matter -- we'll use the same keys for all our domains.
#
# `ldns-keygen` outputs the new key's filename to stdout, which
# we're capturing into the `KSK` variable.
KSK=$(umask 077; cd $STORAGE_ROOT/dns/dnssec; ldns-keygen -a $algo -b 2048 -k _domain_);
# Now create a Zone-Signing Key (ZSK) which is expected to be
# rotated more often than a KSK, although we have no plans to
# rotate it (and doing so would be difficult to do without
# disturbing DNS availability.) Omit `-k` and use a shorter key length.
ZSK=$(umask 077; cd $STORAGE_ROOT/dns/dnssec; ldns-keygen -a $algo -b 1024 _domain_);
# These generate two sets of files like:
#
# * `K_domain_.+007+08882.ds`: DS record normally provided to domain name registrar (but it's actually invalid with `_domain_`)
# * `K_domain_.+007+08882.key`: public key
# * `K_domain_.+007+08882.private`: private key (secret!)
# The filenames are unpredictable and encode the key generation
# options. So we'll store the names of the files we just generated.
# We might have multiple keys down the road. This will identify
# what keys are the current keys.
cat > $STORAGE_ROOT/dns/dnssec/$algo.conf << EOF;
KSK=$KSK
ZSK=$ZSK
EOF
fi
# And loop to do the next algorithm...
done
# Force the dns_update script to be run every day to re-sign zones for DNSSEC
# before they expire. When we sign zones (in `dns_update.py`) we specify a
# 30-day validation window, so we had better re-sign before then.
cat > /etc/cron.daily/mailinabox-dnssec << EOF;
#!/bin/bash
# Mail-in-a-Box
# Re-sign any DNS zones with DNSSEC because the signatures expire periodically.
`pwd`/tools/dns_update
EOF
chmod +x /etc/cron.daily/mailinabox-dnssec
# Permit DNS queries on TCP/UDP in the firewall.
ufw_allow domain