add DNSSEC
* sign zones * in a cron job, periodically re-sign zones because they expire (not tested)
This commit is contained in:
Joshua Tauberer
parent
aaa735dbfe
commit
88709506f8
4 changed files with 234 additions and 18 deletions
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@ -53,7 +53,18 @@ def mail_domains():
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@app.route('/dns/update', methods=['POST'])
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def dns_update():
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from dns_update import do_dns_update
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return do_dns_update(env)
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try:
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return do_dns_update(env)
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except Exception as e:
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return (str(e), 500)
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@app.route('/dns/ds')
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def dns_get_ds_records():
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from dns_update import get_ds_records
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try:
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return get_ds_records(env)
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except Exception as e:
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return (str(e), 500)
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# System
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@ -2,12 +2,12 @@
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# and mail aliases and restarts nsd.
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########################################################################
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import os, os.path, urllib.parse, time, re
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import os, os.path, urllib.parse, datetime, re
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from mailconfig import get_mail_domains
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from utils import shell
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from utils import shell, load_env_vars_from_file
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def do_dns_update(env):
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def get_dns_domains(env):
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# What domains should we serve DNS for?
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domains = set()
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@ -16,20 +16,55 @@ def do_dns_update(env):
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# Add all domain names in use by email users and mail aliases.
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domains |= get_mail_domains(env)
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# Make a nice and safe filename for each domain.
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zonefiles = []
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for domain in domains:
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zonefiles.append((domain, urllib.parse.quote(domain, safe='') + ".txt" ))
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zonefiles.append([domain, urllib.parse.quote(domain, safe='') + ".txt"])
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return zonefiles
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def do_dns_update(env):
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# What domains (and their zone filenames) should we build?
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zonefiles = get_dns_domains(env)
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# Write zone files.
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os.makedirs('/etc/nsd/zones', exist_ok=True)
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updated_domains = []
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for domain, zonefile in zonefiles:
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for i, (domain, zonefile) in enumerate(zonefiles):
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# Build the records to put in the zone.
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records = build_zone(domain, env)
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if write_nsd_zone(domain, "/etc/nsd/zones/" + zonefile, records, env):
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# See if the zone has changed, and if so update the serial number
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# and write the zone file.
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if not write_nsd_zone(domain, "/etc/nsd/zones/" + zonefile, records, env):
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# Zone was not updated. There were no changes.
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continue
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# If this is a .justtesting.email domain, then post the update.
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try:
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justtestingdotemail(domain, records)
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updated_domains.append(domain)
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except:
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# Hmm. Might be a network issue. If we stop now, will we end
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# up in an inconsistent state? Let's just continue.
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pass
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# Mark that we just updated this domain.
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updated_domains.append(domain)
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# Sign the zone.
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#
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# Every time we sign the zone we get a new result, which means
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# we can't sign a zone without bumping the zone's serial number.
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# Thus we only sign a zone if write_nsd_zone returned True
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# indicating the zone changed, and thus it got a new serial number.
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# write_nsd_zone is smart enough to check if a zone's signature
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# is nearing experiation and if so it'll bump the serial number
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# and return True so we get a chance to re-sign it.
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#
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# Also update the zone's filename so nsd.conf uses the signed file.
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zonefiles[i][1] = sign_zone(domain, zonefile, env)
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# Write the main nsd.conf file.
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if write_nsd_conf(zonefiles):
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@ -94,8 +129,12 @@ def write_nsd_zone(domain, zonefile, records, env):
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# We set the administrative email address for every domain to domain_contact@[domain.com].
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# You should probably create an alias to your email address.
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# On the $ORIGIN line, there's typically a ';' comment at the end explaining
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# what the $ORIGIN line does. Any further data after the domain confuses
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# ldns-signzone, however. It used to say '; default zone domain'.
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zone = """
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$ORIGIN {domain}. ; default zone domain
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$ORIGIN {domain}.
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$TTL 86400 ; default time to live
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@ IN SOA ns1.{primary_domain}. hostmaster.{primary_domain}. (
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@ -117,8 +156,36 @@ $TTL 86400 ; default time to live
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zone += "\tIN\t" + querytype + "\t"
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zone += value + "\n"
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# DNSSEC requires re-signing a zone periodically. That requires
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# bumping the serial number even if no other records have changed.
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# We don't see the DNSSEC records yet, so we have to figure out
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# if a re-signing is necessary so we can prematurely bump the
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# serial number.
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force_bump = False
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if not os.path.exists(zonefile + ".signed"):
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# No signed file yet. Shouldn't normally happen unless a box
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# is going from not using DNSSEC to using DNSSEC.
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force_bump = True
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else:
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# We've signed the domain. Check if we are close to the expiration
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# time of the signature. If so, we'll force a bump of the serial
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# number so we can re-sign it.
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with open(zonefile + ".signed") as f:
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signed_zone = f.read()
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expiration_times = re.findall(r"\sRRSIG\s+SOA\s+\d+\s+\d+\s\d+\s+(\d{14})", signed_zone)
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if len(expiration_times) == 0:
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# weird
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force_bump = True
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else:
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# All of the times should be the same, but if not choose the soonest.
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expiration_time = min(expiration_times)
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expiration_time = datetime.datetime.strptime(expiration_time, "%Y%m%d%H%M%S")
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if expiration_time - datetime.datetime.now() < datetime.timedelta(days=3):
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# We're within three days of the expiration, so bump serial & resign.
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force_bump = True
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# Set the serial number.
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serial = time.strftime("%Y%m%d00")
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serial = datetime.datetime.now().strftime("%Y%m%d00")
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if os.path.exists(zonefile):
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# If the zone already exists, is different, and has a later serial number,
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# increment the number.
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@ -126,15 +193,20 @@ $TTL 86400 ; default time to live
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existing_zone = f.read()
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m = re.search(r"(\d+)\s*;\s*serial number", existing_zone)
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if m:
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# Clear out the serial number in the existing zone file for the
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# purposes of seeing if anything *else* in the zone has changed.
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existing_serial = m.group(1)
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existing_zone = existing_zone.replace(m.group(0), "__SERIAL__ ; serial number")
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# If the existing zone is the same as the new zone (modulo the serial number),
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# there is no need to update the file.
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if zone == existing_zone:
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# there is no need to update the file. Unless we're forcing a bump.
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if zone == existing_zone and not force_bump:
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return False
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# If the existing serial is not less than the new one, increment it.
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# If the existing serial is not less than a serial number
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# based on the current date plus 00, increment it. Otherwise,
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# the serial number is less than our desired new serial number
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# so we'll use the desired new number.
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if existing_serial >= serial:
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serial = str(int(existing_serial) + 1)
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@ -182,6 +254,89 @@ zone:
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########################################################################
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def sign_zone(domain, zonefile, env):
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dnssec_keys = load_env_vars_from_file(os.path.join(env['STORAGE_ROOT'], 'dns/dnssec/keys.conf'))
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# In order to use the same keys for all domains, we have to generate
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# a new .key file with a DNSSEC record for the specific domain. We
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# can reuse the same key, but it won't validate without a DNSSEC
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# record specifically for the domain.
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#
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# Copy the .key and .private files to /tmp to patch them up.
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#
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# Use os.umask and open().write() to securely create a copy that only
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# we (root) can read.
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files_to_kill = []
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for key in ("KSK", "ZSK"):
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if dnssec_keys.get(key, "").strip() == "": raise Exception("DNSSEC is not properly set up.")
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oldkeyfn = os.path.join(env['STORAGE_ROOT'], 'dns/dnssec/' + dnssec_keys[key])
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newkeyfn = '/tmp/' + dnssec_keys[key].replace("_domain_", domain)
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dnssec_keys[key] = newkeyfn
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for ext in (".private", ".key"):
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if not os.path.exists(oldkeyfn + ext): raise Exception("DNSSEC is not properly set up.")
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with open(oldkeyfn + ext, "r") as fr:
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keydata = fr.read()
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keydata = keydata.replace("_domain_", domain) # trick ldns-signkey into letting our generic key be used by this zone
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fn = newkeyfn + ext
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prev_umask = os.umask(0o77) # ensure written file is not world-readable
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try:
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with open(fn, "w") as fw:
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fw.write(keydata)
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finally:
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os.umask(prev_umask) # other files we write should be world-readable
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files_to_kill.append(fn)
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# Do the signing.
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expiry_date = (datetime.datetime.now() + datetime.timedelta(days=30)).strftime("%Y%m%d")
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shell('check_call', ["/usr/bin/ldns-signzone",
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# expire the zone after 30 days
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"-e", expiry_date,
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# use NSEC3
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"-n",
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# zonefile to sign
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"/etc/nsd/zones/" + zonefile,
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# keys to sign with (order doesn't matter -- it'll figure it out)
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dnssec_keys["KSK"],
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dnssec_keys["ZSK"],
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])
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# Create a DS record based on the patched-up key files. The DS record is specific to the
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# zone being signed, so we can't use the .ds files generated when we created the keys.
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# The DS record points to the KSK only. Write this next to the zone file so we can
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# get it later to give to the user with instructions on what to do with it.
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rr_ds = shell('check_output', ["/usr/bin/ldns-key2ds",
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"-n", # output to stdout
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"-2", # SHA256
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dnssec_keys["KSK"] + ".key"
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])
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with open("/etc/nsd/zones/" + zonefile + ".ds", "w") as f:
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f.write(rr_ds)
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# Remove our temporary file.
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for fn in files_to_kill:
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os.unlink(fn)
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# Update the zone's filename so nsd.conf uses the signed file.
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return zonefile + ".signed"
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########################################################################
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def get_ds_records(env):
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zonefiles = get_dns_domains(env)
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ret = ""
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for domain, zonefile in zonefiles:
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fn = "/etc/nsd/zones/" + zonefile + ".ds"
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if os.path.exists(fn):
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with open(fn, "r") as fr:
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ret += fr.read().strip() + "\n"
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return ret
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########################################################################
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def write_opendkim_tables(zonefiles, env):
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# Append a record to OpenDKIM's KeyTable and SigningTable for each domain.
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#
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@ -1,11 +1,16 @@
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def load_environment():
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# Load settings from /etc/mailinabox.conf.
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import os.path
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env = { }
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for line in open("/etc/mailinabox.conf"): env.setdefault(*line.strip().split("=", 1))
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env = load_env_vars_from_file("/etc/mailinabox.conf")
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env["CONF_DIR"] = os.path.join(os.path.dirname(__file__), "../conf")
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return env
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def load_env_vars_from_file(fn):
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# Load settings from a KEY=VALUE file.
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env = { }
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for line in open(fn): env.setdefault(*line.strip().split("=", 1))
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return env
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def exclusive_process(name):
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# Ensure that a process named `name` does not execute multiple
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# times concurrently.
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49
setup/dns.sh
49
setup/dns.sh
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@ -8,7 +8,8 @@
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source setup/functions.sh # load our functions
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# Install nsd, our DNS server software.
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# Install nsd, our DNS server software, and ldnsutils which helps
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# us sign zones for DNSSEC.
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# ...but first, we have to create the user because the
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# current Ubuntu forgets to do so in the .deb
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@ -21,12 +22,56 @@ fi
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# Okay now install the packages.
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apt_install nsd
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apt_install nsd ldnsutils
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# Prepare nsd's configuration.
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sudo mkdir -p /var/run/nsd
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# Create DNSSEC signing keys.
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mkdir -p "$STORAGE_ROOT/dns/dnssec";
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if [ ! -f "$STORAGE_ROOT/dns/dnssec/keys.conf" ]; then
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# These two steps take a while.
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# Create the Key-Signing Key (KSK) (-k) which is the so-called
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# Secure Entry Point. Use a NSEC3-compatible algorithm (best
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# practice), and a nice and long keylength. Use /dev/urandom
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# instead of /dev/random for noise or else we'll be waiting
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# a very long time. The domain name we provide ("_domain_")
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# doesn't matter -- we'll use the same keys for all our domains.
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KSK=$(umask 077; cd $STORAGE_ROOT/dns/dnssec; ldns-keygen -a RSASHA1-NSEC3-SHA1 -b 2048 -k -r /dev/urandom _domain_);
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# Now create a Zone-Signing Key (ZSK) which is expected to be
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# rotated more often than a KSK, although we have no plans to
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# rotate it (and doing so would be difficult to do without
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# disturbing DNS availability.) Omit '-k' and use a shorter key.
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ZSK=$(umask 077; cd $STORAGE_ROOT/dns/dnssec; ldns-keygen -a RSASHA1-NSEC3-SHA1 -b 1024 -r /dev/urandom _domain_);
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# These generate two sets of files like:
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# K_domain_.+007+08882.ds <- DS record for adding to NSD configuration files
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# K_domain_.+007+08882.key <- public key (goes into DS record & upstream DNS provider like your registrar)
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# K_domain_.+007+08882.private <- private key (secret!)
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# The filenames are unpredictable and encode the key generation
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# options. So we'll store the names of the files we just generated.
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# We might have multiple keys down the road. This will identify
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# what keys are the current keys.
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cat > $STORAGE_ROOT/dns/dnssec/keys.conf << EOF;
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KSK=$KSK
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ZSK=$ZSK
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EOF
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fi
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# Force the dns_update script to be run every day to re-sign zones for DNSSEC.
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cat > /etc/cron.daily/mailinabox-dnssec << EOF;
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#!/bin/bash
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# Mail-in-a-Box
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# Re-sign any DNS zones with DNSSEC because the signatures expire periodically.
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curl -d GO http://localhost:10222/dns/update
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EOF
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chmod +x /etc/cron.daily/mailinabox-dnssec
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# Permit DNS queries on TCP/UDP in the firewall.
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ufw_allow domain
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