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freeipa/ipapython/dnsutil.py
Christian Heimes f90e137a17 Sort and shuffle SRV record by priority and weight 
On multiple occasions, SRV query answers were not properly sorted by
priority. Records with same priority weren't randomized and shuffled.
This caused FreeIPA to contact the same remote peer instead of
distributing the load across all available servers.

Two new helper functions now take care of SRV queries. sort_prio_weight()
sorts SRV and URI records. query_srv() combines SRV lookup with
sort_prio_weight().

Fixes: https://pagure.io/freeipa/issue/7475
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>
2018-06-19 08:56:46 +02:00

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# Authors: Martin Basti <mbasti@redhat.com>
#
# Copyright (C) 2007-2014 Red Hat
# see file 'COPYING' for use and warranty information
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
import copy
import logging
import operator
import random
import dns.name
import dns.exception
import dns.resolver
import dns.rdataclass
import dns.rdatatype
import six
from ipapython.ipautil import UnsafeIPAddress
if six.PY3:
unicode = str
logger = logging.getLogger(__name__)
@six.python_2_unicode_compatible
class DNSName(dns.name.Name):
labels = None # make pylint happy
@classmethod
def from_text(cls, labels, origin=None):
return cls(dns.name.from_text(labels, origin))
def __init__(self, labels, origin=None):
try:
if isinstance(labels, six.string_types):
#pylint: disable=E1101
labels = dns.name.from_text(unicode(labels), origin).labels
elif isinstance(labels, dns.name.Name):
labels = labels.labels
super(DNSName, self).__init__(labels)
except UnicodeError as e:
# dnspython bug, an invalid domain name returns the UnicodeError
# instead of a dns.exception
raise dns.exception.SyntaxError(e)
def __bool__(self):
#dns.name.from_text('@') is represented like empty tuple
#we need to acting '@' as nonzero value
return True
__nonzero__ = __bool__ # for Python 2
def __copy__(self):
return DNSName(self.labels)
def __deepcopy__(self, memo):
return DNSName(copy.deepcopy(self.labels, memo))
def __str__(self):
return self.to_unicode()
# method ToASCII named by RFC 3490 and python standard library
if six.PY2:
def ToASCII(self):
# must be unicode string in Py2
return self.to_text().decode('ascii')
else:
def ToASCII(self):
return self.to_text()
def canonicalize(self):
return DNSName(super(DNSName, self).canonicalize())
def concatenate(self, other):
return DNSName(super(DNSName, self).concatenate(other))
def relativize(self, origin):
return DNSName(super(DNSName, self).relativize(origin))
def derelativize(self, origin):
return DNSName(super(DNSName, self).derelativize(origin))
def choose_relativity(self, origin=None, relativize=True):
return DNSName(super(DNSName, self).choose_relativity(origin=origin,
relativize=relativize))
def make_absolute(self):
return self.derelativize(self.root)
def is_idn(self):
return any(label.startswith('xn--') for label in self.labels)
def is_ip4_reverse(self):
return self.is_subdomain(self.ip4_rev_zone)
def is_ip6_reverse(self):
return self.is_subdomain(self.ip6_rev_zone)
def is_reverse(self):
return self.is_ip4_reverse() or self.is_ip6_reverse()
def is_empty(self):
return len(self.labels) == 0
#DNS public constants
DNSName.root = DNSName(dns.name.root) # '.'
DNSName.empty = DNSName(dns.name.empty) # '@'
DNSName.ip4_rev_zone = DNSName(('in-addr', 'arpa', ''))
DNSName.ip6_rev_zone = DNSName(('ip6', 'arpa', ''))
# Empty zones are defined in various RFCs. BIND is by default serving them.
# This constat should contain everything listed in
# IANA registry "Locally-Served DNS Zones"
# URL: http://www.iana.org/assignments/locally-served-dns-zones
# + AS112 zone defined in RFC 7534. It is not in the registry for some
# reason but BIND 9.10 is serving it as automatic empty zones.
EMPTY_ZONES = [DNSName(aez).make_absolute() for aez in [
# RFC 1918
"10.IN-ADDR.ARPA", "16.172.IN-ADDR.ARPA", "17.172.IN-ADDR.ARPA",
"18.172.IN-ADDR.ARPA", "19.172.IN-ADDR.ARPA", "20.172.IN-ADDR.ARPA",
"21.172.IN-ADDR.ARPA", "22.172.IN-ADDR.ARPA", "23.172.IN-ADDR.ARPA",
"24.172.IN-ADDR.ARPA", "25.172.IN-ADDR.ARPA", "26.172.IN-ADDR.ARPA",
"27.172.IN-ADDR.ARPA", "28.172.IN-ADDR.ARPA", "29.172.IN-ADDR.ARPA",
"30.172.IN-ADDR.ARPA", "31.172.IN-ADDR.ARPA", "168.192.IN-ADDR.ARPA",
# RFC 6598
"64.100.IN-ADDR.ARPA", "65.100.IN-ADDR.ARPA", "66.100.IN-ADDR.ARPA",
"67.100.IN-ADDR.ARPA", "68.100.IN-ADDR.ARPA", "69.100.IN-ADDR.ARPA",
"70.100.IN-ADDR.ARPA", "71.100.IN-ADDR.ARPA", "72.100.IN-ADDR.ARPA",
"73.100.IN-ADDR.ARPA", "74.100.IN-ADDR.ARPA", "75.100.IN-ADDR.ARPA",
"76.100.IN-ADDR.ARPA", "77.100.IN-ADDR.ARPA", "78.100.IN-ADDR.ARPA",
"79.100.IN-ADDR.ARPA", "80.100.IN-ADDR.ARPA", "81.100.IN-ADDR.ARPA",
"82.100.IN-ADDR.ARPA", "83.100.IN-ADDR.ARPA", "84.100.IN-ADDR.ARPA",
"85.100.IN-ADDR.ARPA", "86.100.IN-ADDR.ARPA", "87.100.IN-ADDR.ARPA",
"88.100.IN-ADDR.ARPA", "89.100.IN-ADDR.ARPA", "90.100.IN-ADDR.ARPA",
"91.100.IN-ADDR.ARPA", "92.100.IN-ADDR.ARPA", "93.100.IN-ADDR.ARPA",
"94.100.IN-ADDR.ARPA", "95.100.IN-ADDR.ARPA", "96.100.IN-ADDR.ARPA",
"97.100.IN-ADDR.ARPA", "98.100.IN-ADDR.ARPA", "99.100.IN-ADDR.ARPA",
"100.100.IN-ADDR.ARPA", "101.100.IN-ADDR.ARPA",
"102.100.IN-ADDR.ARPA", "103.100.IN-ADDR.ARPA",
"104.100.IN-ADDR.ARPA", "105.100.IN-ADDR.ARPA",
"106.100.IN-ADDR.ARPA", "107.100.IN-ADDR.ARPA",
"108.100.IN-ADDR.ARPA", "109.100.IN-ADDR.ARPA",
"110.100.IN-ADDR.ARPA", "111.100.IN-ADDR.ARPA",
"112.100.IN-ADDR.ARPA", "113.100.IN-ADDR.ARPA",
"114.100.IN-ADDR.ARPA", "115.100.IN-ADDR.ARPA",
"116.100.IN-ADDR.ARPA", "117.100.IN-ADDR.ARPA",
"118.100.IN-ADDR.ARPA", "119.100.IN-ADDR.ARPA",
"120.100.IN-ADDR.ARPA", "121.100.IN-ADDR.ARPA",
"122.100.IN-ADDR.ARPA", "123.100.IN-ADDR.ARPA",
"124.100.IN-ADDR.ARPA", "125.100.IN-ADDR.ARPA",
"126.100.IN-ADDR.ARPA", "127.100.IN-ADDR.ARPA",
# RFC 5735 and RFC 5737
"0.IN-ADDR.ARPA", "127.IN-ADDR.ARPA", "254.169.IN-ADDR.ARPA",
"2.0.192.IN-ADDR.ARPA", "100.51.198.IN-ADDR.ARPA",
"113.0.203.IN-ADDR.ARPA", "255.255.255.255.IN-ADDR.ARPA",
# Local IPv6 Unicast Addresses
"0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA",
"1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA",
# LOCALLY ASSIGNED LOCAL ADDRESS SCOPE
"D.F.IP6.ARPA", "8.E.F.IP6.ARPA", "9.E.F.IP6.ARPA", "A.E.F.IP6.ARPA",
"B.E.F.IP6.ARPA",
# Example Prefix, RFC 3849.
"8.B.D.0.1.0.0.2.IP6.ARPA",
# RFC 7534
"EMPTY.AS112.ARPA",
]]
def assert_absolute_dnsname(name):
"""Raise AssertionError if name is not DNSName or is not absolute.
>>> assert_absolute_dnsname(DNSName('absolute.name.example.'))
>>> assert_absolute_dnsname(DNSName('relative.name.example'))
Traceback (most recent call last):
...
AssertionError: name must be absolute, ...
>>> assert_absolute_dnsname('absolute.string.example.')
Traceback (most recent call last):
...
AssertionError: name must be DNSName instance, ...
"""
assert isinstance(name, DNSName), ("name must be DNSName instance, "
"got '%s'" % type(name))
assert name.is_absolute(), "name must be absolute, got '%s'" % name
def is_auto_empty_zone(zone):
"""True if specified zone name exactly matches an automatic empty zone.
>>> is_auto_empty_zone(DNSName('in-addr.arpa.'))
False
>>> is_auto_empty_zone(DNSName('10.in-addr.arpa.'))
True
>>> is_auto_empty_zone(DNSName('1.10.in-addr.arpa.'))
False
>>> is_auto_empty_zone(DNSName('10.in-addr.arpa'))
Traceback (most recent call last):
...
AssertionError: ...
"""
assert_absolute_dnsname(zone)
return zone in EMPTY_ZONES
def inside_auto_empty_zone(name):
"""True if specified absolute name is a subdomain of an automatic empty
zone.
DNS domain is a subdomain of itself so this function
returns True for zone apexes, too.
>>> inside_auto_empty_zone(DNSName('in-addr.arpa.'))
False
>>> inside_auto_empty_zone(DNSName('10.in-addr.arpa.'))
True
>>> inside_auto_empty_zone(DNSName('1.10.in-addr.arpa.'))
True
>>> inside_auto_empty_zone(DNSName('1.10.in-addr.arpa'))
Traceback (most recent call last):
...
AssertionError: ...
"""
assert_absolute_dnsname(name)
for aez in EMPTY_ZONES:
if name.is_subdomain(aez):
return True
return False
def related_to_auto_empty_zone(name):
"""True if specified absolute name is a sub/superdomain of an automatic
empty zone.
DNS domain is a subdomain of itself so this function
returns True for zone apexes, too.
>>> related_to_auto_empty_zone(DNSName('.'))
True
>>> related_to_auto_empty_zone(DNSName('in-addr.arpa.'))
True
>>> related_to_auto_empty_zone(DNSName('10.in-addr.arpa.'))
True
>>> related_to_auto_empty_zone(DNSName('1.10.in-addr.arpa.'))
True
>>> related_to_auto_empty_zone(DNSName('unrelated.example.'))
False
>>> related_to_auto_empty_zone(DNSName('1.10.in-addr.arpa'))
Traceback (most recent call last):
...
AssertionError: ...
"""
assert_absolute_dnsname(name)
relations = {dns.name.NAMERELN_SUBDOMAIN,
dns.name.NAMERELN_EQUAL,
dns.name.NAMERELN_SUPERDOMAIN}
return any(name.fullcompare(aez)[0] in relations
for aez in EMPTY_ZONES)
def has_empty_zone_addresses(hostname):
"""Detect if given host is using IP address belonging to
an automatic empty zone.
Information from --ip-address option used in installed is lost by
the time when upgrade is run. Use IP addresses from DNS as best
approximation.
This is brain-dead and duplicates logic from DNS installer
but I did not find other way around.
"""
ip_addresses = resolve_ip_addresses(hostname)
return any(
inside_auto_empty_zone(DNSName(ip.reverse_dns))
for ip in ip_addresses
)
def resolve_rrsets(fqdn, rdtypes):
"""
Get Resource Record sets for given FQDN.
CNAME chain is followed during resolution
but CNAMEs are not returned in the resulting rrset.
:returns:
set of dns.rrset.RRset objects, can be empty
if the FQDN does not exist or if none of rrtypes exist
"""
# empty set of rdtypes would always return empty set of rrsets
assert rdtypes, "rdtypes must not be empty"
if not isinstance(fqdn, DNSName):
fqdn = DNSName(fqdn)
fqdn = fqdn.make_absolute()
rrsets = []
for rdtype in rdtypes:
try:
answer = dns.resolver.query(fqdn, rdtype)
logger.debug('found %d %s records for %s: %s',
len(answer),
rdtype,
fqdn,
' '.join(str(rr) for rr in answer))
rrsets.append(answer.rrset)
except dns.resolver.NXDOMAIN as ex:
logger.debug('%s', ex)
break # no such FQDN, do not iterate
except dns.resolver.NoAnswer as ex:
logger.debug('%s', ex) # record type does not exist for given FQDN
except dns.exception.DNSException as ex:
logger.error('DNS query for %s %s failed: %s', fqdn, rdtype, ex)
raise
return rrsets
def resolve_ip_addresses(fqdn):
"""Get IP addresses from DNS A/AAAA records for given host (using DNS).
:returns:
list of IP addresses as UnsafeIPAddress objects
"""
rrsets = resolve_rrsets(fqdn, ['A', 'AAAA'])
ip_addresses = set()
for rrset in rrsets:
ip_addresses.update({UnsafeIPAddress(ip) for ip in rrset})
return ip_addresses
def check_zone_overlap(zone, raise_on_error=True):
logger.info("Checking DNS domain %s, please wait ...", zone)
if not isinstance(zone, DNSName):
zone = DNSName(zone).make_absolute()
# automatic empty zones always exist so checking them is pointless,
# do not report them to avoid meaningless error messages
if is_auto_empty_zone(zone):
return
try:
containing_zone = dns.resolver.zone_for_name(zone)
except dns.exception.DNSException as e:
msg = ("DNS check for domain %s failed: %s." % (zone, e))
if raise_on_error:
raise ValueError(msg)
else:
logger.warning('%s', msg)
return
if containing_zone == zone:
try:
ns = [ans.to_text() for ans in dns.resolver.query(zone, 'NS')]
except dns.exception.DNSException as e:
logger.debug("Failed to resolve nameserver(s) for domain %s: %s",
zone, e)
ns = []
msg = u"DNS zone {0} already exists in DNS".format(zone)
if ns:
msg += u" and is handled by server(s): {0}".format(', '.join(ns))
raise ValueError(msg)
def _mix_weight(records):
"""Weighted population sorting for records with same priority
"""
# trivial case
if len(records) <= 1:
return records
# Optimization for common case: If all weights are the same (e.g. 0),
# just shuffle the records, which is about four times faster.
if all(rr.weight == records[0].weight for rr in records):
random.shuffle(records)
return records
noweight = 0.01 # give records with 0 weight a small chance
result = []
records = set(records)
while len(records) > 1:
# Compute the sum of the weights of those RRs. Then choose a
# uniform random number between 0 and the sum computed (inclusive).
urn = random.uniform(0, sum(rr.weight or noweight for rr in records))
# Select the RR whose running sum value is the first in the selected
# order which is greater than or equal to the random number selected.
acc = 0.
for rr in records.copy():
acc += rr.weight or noweight
if acc >= urn:
records.remove(rr)
result.append(rr)
if records:
result.append(records.pop())
return result
def sort_prio_weight(records):
"""RFC 2782 sorting algorithm for SRV and URI records
RFC 2782 defines a sorting algorithms for SRV records, that is also used
for sorting URI records. Records are sorted by priority and than randomly
shuffled according to weight.
This implementation also removes duplicate entries.
"""
# order records by priority
records = sorted(records, key=operator.attrgetter("priority"))
# remove duplicate entries
uniquerecords = []
seen = set()
for rr in records:
# A SRV record has target and port, URI just has target.
target = (rr.target, getattr(rr, "port", None))
if target not in seen:
uniquerecords.append(rr)
seen.add(target)
# weighted randomization of entries with same priority
result = []
sameprio = []
for rr in uniquerecords:
# add all items with same priority in a bucket
if not sameprio or sameprio[0].priority == rr.priority:
sameprio.append(rr)
else:
# got different priority, shuffle bucket
result.extend(_mix_weight(sameprio))
# start a new priority list
sameprio = [rr]
# add last batch of records with same priority
if sameprio:
result.extend(_mix_weight(sameprio))
return result
def query_srv(qname, resolver=None, **kwargs):
"""Query SRV records and sort reply according to RFC 2782
:param qname: query name, _service._proto.domain.
:return: list of dns.rdtypes.IN.SRV.SRV instances
"""
if resolver is None:
resolver = dns.resolver
answer = resolver.query(qname, rdtype=dns.rdatatype.SRV, **kwargs)
return sort_prio_weight(answer)
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