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Filename : samba_spnupdate
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#!/usr/bin/python3
#
# update our servicePrincipalName names from spn_update_list
#
# Copyright (C) Andrew Tridgell 2010
# Copyright (C) Matthieu Patou <mat@matws.net> 2012
#
# 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 os, sys, re

# ensure we get messages out immediately, so they get in the samba logs,
# and don't get swallowed by a timeout
os.environ['PYTHONUNBUFFERED'] = '1'

# forcing GMT avoids a problem in some timezones with kerberos. Both MIT
# heimdal can get mutual authentication errors due to the 24 second difference
# between UTC and GMT when using some zone files (eg. the PDT zone from
# the US)
os.environ["TZ"] = "GMT"

# Find right directory when running from source tree


import samba, ldb
import optparse
from samba import Ldb
from samba import getopt as options
from samba.auth import system_session
from samba.samdb import SamDB
from samba.credentials import Credentials, DONT_USE_KERBEROS
from samba.common import get_string

parser = optparse.OptionParser("samba_spnupdate")
sambaopts = options.SambaOptions(parser)
parser.add_option_group(sambaopts)
parser.add_option_group(options.VersionOptions(parser))
parser.add_option("--verbose", action="store_true")

credopts = options.CredentialsOptions(parser)
parser.add_option_group(credopts)

ccachename = None

opts, args = parser.parse_args()

if len(args) != 0:
    parser.print_usage()
    sys.exit(1)

lp = sambaopts.get_loadparm()
creds = credopts.get_credentials(lp)

domain = lp.get("realm")
host = lp.get("netbios name")


# get the list of substitution vars
def get_subst_vars(samdb):
    global lp
    vars = {}

    vars['DNSDOMAIN'] = samdb.domain_dns_name()
    vars['DNSFOREST'] = samdb.forest_dns_name()
    vars['HOSTNAME']  = samdb.host_dns_name()
    vars['NETBIOSNAME'] = lp.get('netbios name').upper()
    vars['WORKGROUP'] = lp.get('workgroup')
    vars['NTDSGUID']  = samdb.get_ntds_GUID()
    res = samdb.search(base=samdb.get_default_basedn(), scope=ldb.SCOPE_BASE, attrs=["objectGUID"])
    guid = samdb.schema_format_value("objectGUID", res[0]['objectGUID'][0])
    vars['DOMAINGUID'] = get_string(guid)
    return vars

try:
    private_dir = lp.get("private dir")
    secrets_path = os.path.join(private_dir, "secrets.ldb")

    secrets_db = Ldb(url=secrets_path, session_info=system_session(),
                     credentials=creds, lp=lp)
    res = secrets_db.search(base=None,
                            expression="(&(objectclass=ldapSecret)(cn=SAMDB Credentials))",
                            attrs=["samAccountName", "secret"])

    if len(res) == 1:
        credentials = Credentials()
        credentials.set_kerberos_state(DONT_USE_KERBEROS)

        if "samAccountName" in res[0]:
            credentials.set_username(res[0]["samAccountName"][0])

        if "secret" in res[0]:
            credentials.set_password(res[0]["secret"][0])

    else:
        credentials = None

    samdb = SamDB(url=lp.samdb_url(), session_info=system_session(), credentials=credentials, lp=lp)
except ldb.LdbError as e:
    (num, msg) = e.args
    print("Unable to open sam database %s : %s" % (lp.samdb_url(), msg))
    sys.exit(1)


# get the substitution dictionary
sub_vars = get_subst_vars(samdb)

# get the list of SPN entries we should have
spn_update_list = lp.private_path('spn_update_list')

file = open(spn_update_list, "r")

spn_list = []

has_forest_dns = False
has_domain_dns = False
# check if we "are DNS server"
res = samdb.search(base=samdb.get_config_basedn(),
                   expression='(objectguid=%s)' % sub_vars['NTDSGUID'],
                   attrs=["msDS-hasMasterNCs"])

basedn = str(samdb.get_default_basedn())
if len(res) == 1:
    if "msDS-hasMasterNCs" in res[0]:
        for e in res[0]["msDS-hasMasterNCs"]:
            if str(e) == "DC=DomainDnsZones,%s" % basedn:
                has_domain_dns = True
            if str(e) == "DC=ForestDnsZones,%s" % basedn:
                has_forest_dns = True


# build the spn list
for line in file:
    line = line.strip()
    if line == '' or line[0] == "#":
        continue
    if re.match(r".*/DomainDnsZones\..*", line) and not has_domain_dns:
        continue
    if re.match(r".*/ForestDnsZones\..*", line) and not has_forest_dns:
        continue
    line = samba.substitute_var(line, sub_vars)
    spn_list.append(line)

# get the current list of SPNs in our sam
res = samdb.search(base=samdb.get_default_basedn(),
                   expression='(&(objectClass=computer)(samaccountname=%s$))' % sub_vars['NETBIOSNAME'],
                   attrs=["servicePrincipalName"])
if not res or len(res) != 1:
    print("Failed to find computer object for %s$" % sub_vars['NETBIOSNAME'])
    sys.exit(1)

machine_dn = res[0]["dn"]

old_spns = []
if "servicePrincipalName" in res[0]:
    for s in res[0]["servicePrincipalName"]:
        old_spns.append(str(s))

if opts.verbose:
    print("Existing SPNs: %s" % old_spns)

add_list = []

# work out what needs to be added
for s in spn_list:
    in_list = False
    for s2 in old_spns:
        if s2.upper() == s.upper():
            in_list = True
            break
    if not in_list:
        add_list.append(s)

if opts.verbose:
    print("New SPNs: %s" % add_list)

if add_list == []:
    if opts.verbose:
        print("Nothing to add")
    sys.exit(0)

def local_update(add_list):
    '''store locally'''
    global res
    msg = ldb.Message()
    msg.dn = res[0]['dn']
    msg[""] = ldb.MessageElement(add_list,
                                 ldb.FLAG_MOD_ADD, "servicePrincipalName")
    res = samdb.modify(msg)

def call_rodc_update(d):
    '''RODCs need to use the writeSPN DRS call'''
    global lp, sub_vars
    from samba import drs_utils
    from samba.dcerpc import drsuapi, nbt
    from samba.net import Net

    if opts.verbose:
        print("Using RODC SPN update")

    creds = credopts.get_credentials(lp)
    creds.set_machine_account(lp)

    net = Net(creds=creds, lp=lp)
    try:
        cldap_ret = net.finddc(domain=domain, flags=nbt.NBT_SERVER_DS | nbt.NBT_SERVER_WRITABLE)
    except Exception as reason:
        print("Unable to find writeable DC for domain '%s' to send DRS writeSPN to : %s" % (domain, reason))
        sys.exit(1)
    server = cldap_ret.pdc_dns_name
    try:
        binding_options = "seal"
        if lp.log_level() >= 5:
            binding_options += ",print"
        drs = drsuapi.drsuapi('ncacn_ip_tcp:%s[%s]' % (server, binding_options), lp, creds)
        (drs_handle, supported_extensions) = drs_utils.drs_DsBind(drs)
    except Exception as reason:
        print("Unable to connect to DC '%s' for domain '%s' : %s" % (server, domain, reason))
        sys.exit(1)
    req1 = drsuapi.DsWriteAccountSpnRequest1()
    req1.operation = drsuapi.DRSUAPI_DS_SPN_OPERATION_ADD
    req1.object_dn = str(machine_dn)
    req1.count = 0
    spn_names = []
    for n in add_list:
        if n.find('E3514235-4B06-11D1-AB04-00C04FC2DCD2') != -1:
            # this one isn't allowed for RODCs, but we don't know why yet
            continue
        ns = drsuapi.DsNameString()
        ns.str = n
        spn_names.append(ns)
        req1.count = req1.count + 1
    if spn_names == []:
        return
    req1.spn_names = spn_names
    (level, res) = drs.DsWriteAccountSpn(drs_handle, 1, req1)
    if (res.status != (0, 'WERR_OK')):
        print("WriteAccountSpn has failed with error %s" % str(res.status))

if samdb.am_rodc():
    call_rodc_update(add_list)
else:
    local_update(add_list)