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freeipa/ipalib/krb_utils.py
Simo Sorce 03fc5c3d73 Fix ticket checks when using either s4u2proxy or a delegated krbtgt 
When using s4u2proxy the only ticket we can access via direct krb5 calls is
the HTTP/ ticket which was saved in the ccache as evidence ticket.
This ticket is later used by GSSAPI as evidence to obtain an ldap ticket.

This works by chance, we shouldn't use calls to get_credentials just to
verify ticket expiration dates, but I realize this is a limitation of the
current krbV bindings and we have no other way around at the moment.

Checking the HTTP/ ticket will fail in case a krbtgt is fully delegated to
us. In that case the ccache will contain only a krbtgt, so as a fallback
we check that.

Checking the ldap/ ticket is never really useful. When s4u2proxy is used,
trying to check the ldap/ ticket will fail because we do not have it yet
on the first authentication before a session is estalished, and doing it
later is not useful.

When we have a krbtgt we could go and grap a ldap/ ticket directy, but
again that makes little sense. In general all tickets will have the same
expiration date (which deopends on the original krbtgt) so checking one
is sufficient.

Fixes: http://fedorahosted.org/freeipa/ticket/2472
2012-03-01 00:56:01 -05:00

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# Authors: John Dennis <jdennis@redhat.com>
#
# Copyright (C) 2012 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 krbV
import time
import re
from ipapython.ipa_log_manager import *
#-------------------------------------------------------------------------------
# Kerberos constants, should be defined in krbV, but aren't
KRB5_GC_CACHED = 0x2
# Kerberos error codes, should be defined in krbV, but aren't
KRB5_CC_NOTFOUND = -1765328243 # Matching credential not found
KRB5_FCC_NOFILE = -1765328189 # No credentials cache found
KRB5KDC_ERR_S_PRINCIPAL_UNKNOWN = -1765328377 # Server not found in Kerberos database
KRB5KRB_AP_ERR_TKT_EXPIRED = -1765328352 # Ticket expired
KRB5_FCC_PERM = -1765328190 # Credentials cache permissions incorrect
KRB5_CC_FORMAT = -1765328185 # Bad format in credentials cache
KRB5_REALM_CANT_RESOLVE = -1765328164 # Cannot resolve network address for KDC in requested realm
krb_ticket_expiration_threshold = 60*5 # number of seconds to accmodate clock skew
krb5_time_fmt = '%m/%d/%y %H:%M:%S'
ccache_name_re = re.compile(r'^((\w+):)?(.+)')
#-------------------------------------------------------------------------------
def krb5_parse_ccache(ccache_name):
'''
Given a Kerberos ccache name parse it into it's scheme and
location components. Currently valid values for the scheme
are:
* FILE
* MEMORY
The scheme is always returned as upper case. If the scheme
does not exist it defaults to FILE.
:parameters:
ccache_name
The name of the Kerberos ccache.
:returns:
A two-tuple of (scheme, ccache)
'''
match = ccache_name_re.search(ccache_name)
if match:
scheme = match.group(2)
location = match.group(3)
if scheme is None:
scheme = 'FILE'
else:
scheme = scheme.upper()
return scheme, location
else:
raise ValueError('Invalid ccache name = "%s"' % ccache_name)
def krb5_unparse_ccache(scheme, name):
return '%s:%s' % (scheme.upper(), name)
def krb5_format_principal_name(user, realm):
'''
Given a Kerberos user principal name and a Kerberos realm
return the Kerberos V5 user principal name.
:parameters:
user
User principal name.
realm
The Kerberos realm the user exists in.
:returns:
Kerberos V5 user principal name.
'''
return '%s@%s' % (user, realm)
def krb5_format_service_principal_name(service, host, realm):
'''
Given a Kerberos service principal name, the host where the
service is running and a Kerberos realm return the Kerberos V5
service principal name.
:parameters:
service
Service principal name.
host
The DNS name of the host where the service is located.
realm
The Kerberos realm the service exists in.
:returns:
Kerberos V5 service principal name.
'''
return '%s/%s@%s' % (service, host, realm)
def krb5_format_tgt_principal_name(realm):
'''
Given a Kerberos realm return the Kerberos V5 TGT name.
:parameters:
realm
The Kerberos realm the TGT exists in.
:returns:
Kerberos V5 TGT name.
'''
return krb5_format_service_principal_name('krbtgt', realm, realm)
def krb5_format_time(timestamp):
'''
Given a UNIX timestamp format it into a string in the same
manner the MIT Kerberos library does. Kerberos timestamps are
always in local time.
:parameters:
timestamp
Unix timestamp
:returns:
formated string
'''
return time.strftime(krb5_time_fmt, time.localtime(timestamp))
class KRB5_CCache(object):
'''
Kerberos stores a TGT (Ticket Granting Ticket) and the service
tickets bound to it in a ccache (credentials cache). ccaches are
bound to a Kerberos user principal. This class opens a Kerberos
ccache and allows one to manipulate it. Most useful is the
extraction of ticket entries (cred's) in the ccache and the
ability to examine their attributes.
'''
def __init__(self, ccache):
'''
:parameters:
ccache
The name of a Kerberos ccache used to hold Kerberos tickets.
:returns:
`KRB5_CCache` object encapsulting the ccache.
'''
log_mgr.get_logger(self, True)
self.context = None
self.scheme = None
self.name = None
self.ccache = None
self.principal = None
try:
self.context = krbV.default_context()
self.scheme, self.name = krb5_parse_ccache(ccache)
self.ccache = krbV.CCache(name=str(ccache), context=self.context)
self.principal = self.ccache.principal()
except krbV.Krb5Error, e:
error_code = e.args[0]
message = e.args[1]
if error_code == KRB5_FCC_NOFILE:
raise ValueError('"%s", ccache="%s"' % (message, ccache))
else:
raise e
def ccache_str(self):
'''
A Kerberos ccache is identified by a name comprised of a
scheme and location component. This function returns that
canonical name. See `krb5_parse_ccache()`
:returns:
The name of ccache with it's scheme and location components.
'''
return '%s:%s' % (self.scheme, self.name)
def __str__(self):
return 'cache="%s" principal="%s"' % (self.ccache_str(), self.principal.name)
def get_credentials(self, principal):
'''
Given a Kerberos principal return the krbV credentials
tuple describing the credential. If the principal does
not exist in the ccache a KeyError is raised.
:parameters:
principal
The Kerberos principal whose ticket is being retrieved.
The principal may be either a string formatted as a
Kerberos V5 principal or it may be a `krbV.Principal`
object.
:returns:
A krbV credentials tuple. If the principal is not in the
ccache a KeyError is raised.
'''
if isinstance(principal, krbV.Principal):
krbV_principal = principal
else:
try:
krbV_principal = krbV.Principal(str(principal), self.context)
except Exception, e:
self.error('could not create krbV principal from "%s", %s', principal, e)
raise e
creds_tuple = (self.principal,
krbV_principal,
(0, None), # keyblock: (enctype, contents)
(0, 0, 0, 0), # times: (authtime, starttime, endtime, renew_till)
0,0, # is_skey, ticket_flags
None, # addrlist
None, # ticket_data
None, # second_ticket_data
None) # adlist
try:
cred = self.ccache.get_credentials(creds_tuple, KRB5_GC_CACHED)
except krbV.Krb5Error, e:
error_code = e.args[0]
if error_code == KRB5_CC_NOTFOUND:
raise KeyError('"%s" credential not found in "%s" ccache' % \
(krbV_principal.name, self.ccache_str())) #pylint: disable=E1103
raise e
except Exception, e:
raise e
return cred
def get_credential_times(self, principal):
'''
Given a Kerberos principal return the ticket timestamps if the
principal's ticket in the ccache is valid. If the principal
does not exist in the ccache a KeyError is raised.
The return credential time values are Unix timestamps in
localtime.
The returned timestamps are:
authtime
The time when the ticket was issued.
starttime
The time when the ticket becomes valid.
endtime
The time when the ticket expires.
renew_till
The time when the ticket becomes no longer renewable (if renewable).
:parameters:
principal
The Kerberos principal whose ticket is being validated.
The principal may be either a string formatted as a
Kerberos V5 principal or it may be a `krbV.Principal`
object.
:returns:
return authtime, starttime, endtime, renew_till
'''
if isinstance(principal, krbV.Principal):
krbV_principal = principal
else:
try:
krbV_principal = krbV.Principal(str(principal), self.context)
except Exception, e:
self.error('could not create krbV principal from "%s", %s', principal, e)
raise e
try:
cred = self.get_credentials(krbV_principal)
authtime, starttime, endtime, renew_till = cred[3]
self.debug('get_credential_times: principal=%s, authtime=%s, starttime=%s, endtime=%s, renew_till=%s',
krbV_principal.name, #pylint: disable=E1103
krb5_format_time(authtime), krb5_format_time(starttime),
krb5_format_time(endtime), krb5_format_time(renew_till))
return authtime, starttime, endtime, renew_till
except KeyError, e:
raise e
except Exception, e:
self.error('get_credential_times failed, principal="%s" error="%s"', krbV_principal.name, e) #pylint: disable=E1103
raise e
def credential_is_valid(self, principal):
'''
Given a Kerberos principal return a boolean indicating if the
principal's ticket in the ccache is valid. If the ticket is
not in the ccache False is returned. If the ticket
exists in the ccache it's validity is checked and returned.
:parameters:
principal
The Kerberos principal whose ticket is being validated.
The principal may be either a string formatted as a
Kerberos V5 principal or it may be a `krbV.Principal`
object.
:returns:
True if the principal's ticket exists and is valid. False if
the ticket does not exist or if the ticket is not valid.
'''
try:
authtime, starttime, endtime, renew_till = self.get_credential_times(principal)
except KeyError, e:
return False
except Exception, e:
self.error('credential_is_valid failed, principal="%s" error="%s"', principal, e)
raise e
now = time.time()
if starttime > now:
return False
if endtime < now:
return False
return True
def valid(self, host, realm):
'''
Test to see if ldap service ticket or the TGT is valid.
:parameters:
host
ldap server
realm
kerberos realm
:returns:
True if either the ldap service ticket or the TGT is valid,
False otherwise.
'''
try:
principal = krb5_format_service_principal_name('HTTP', host, realm)
valid = self.credential_is_valid(principal)
if valid:
return True
except KeyError:
pass
try:
principal = krb5_format_tgt_principal_name(realm)
valid = self.credential_is_valid(principal)
return valid
except KeyError:
return False
def endtime(self, host, realm):
'''
Returns the minimum endtime for tickets of interest (ldap service or TGT).
:parameters:
host
ldap server
realm
kerberos realm
:returns:
UNIX timestamp value.
'''
result = 0
try:
principal = krb5_format_service_principal_name('HTTP', host, realm)
authtime, starttime, endtime, renew_till = self.get_credential_times(principal)
if result:
result = min(result, endtime)
else:
result = endtime
except KeyError:
pass
try:
principal = krb5_format_tgt_principal_name(realm)
authtime, starttime, endtime, renew_till = self.get_credential_times(principal)
if result:
result = min(result, endtime)
else:
result = endtime
except KeyError:
pass
self.debug('KRB5_CCache %s endtime=%s (%s)', self.ccache_str(), result, krb5_format_time(result))
return result
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