summaryrefslogtreecommitdiff
path: root/docs/docbook/projdoc/PAM-Authentication-And-Samba.xml
blob: addd646057212c9dccdfbee7b8f814b07739feda (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
<chapter id="pam">
<chapterinfo>
	&author.jht;
	<author>
		<firstname>Stephen</firstname><surname>Langasek</surname>
		<affiliation>
			<address><email>vorlon@netexpress.net</email></address>
		</affiliation>
	</author>
    <pubdate>May 31, 2003</pubdate>
</chapterinfo>
 
<title>PAM based Distributed Authentication</title>

<para>
This chapter you should help you to deploy winbind based authentication on any PAM enabled
UNIX/Linux system. Winbind can be used to enable user level application access authentication
from any MS Windows NT Domain, MS Windows 200x Active Directory based domain, or any Samba
based domain environment. It will also help you to configure PAM based local host access
controls that are appropriate to your Samba configuration.
</para>

<para>
In addition to knowing how to configure winbind into PAM, you will learn generic PAM management
possibilities and in particular how to deploy tools like pam_smbpass.so to your advantage.
</para>

<note><para>
The use of Winbind require more than PAM configuration alone. Please refer to <link linkend="winbind">the Winbind chapter</link>.
</para></note>

<sect1>
<title>Features and Benefits</title>

<para>
A number of UNIX systems (eg: Sun Solaris), as well as the xxxxBSD family and Linux,
now utilize the Pluggable Authentication Modules (PAM) facility to provide all authentication, 
authorization and resource control services. Prior to the introduction of PAM, a decision
to use an alternative to the system password database (<filename>/etc/passwd</filename>) 
would require the provision of alternatives for all programs that provide security services.
Such a choice would involve provision of alternatives to such programs as: <command>login</command>, 
<command>passwd</command>, <command>chown</command>, etc.
</para>

<para>
PAM provides a mechanism that disconnects these security programs from the underlying
authentication/authorization infrastructure.  PAM is configured either through one file
<filename>/etc/pam.conf</filename> (Solaris), or by editing individual files that are
located in <filename>/etc/pam.d</filename>.
</para>

<para>
On PAM enabled UNIX/Linux systems it is an easy matter to configure the system to use any
authentication backend, so long as the appropriate dynamically loadable library modules
are available for it. The backend may be local to the system, or may be centralised on a
remote server.
</para>

<para>
PAM support modules are available for:
</para>

<variablelist>
	<varlistentry><term><filename>/etc/passwd</filename>:</term><listitem>
		<para>
		There are several PAM modules that interact with this standard UNIX user
		database. The most common are called: pam_unix.so, pam_unix2.so, pam_pwdb.so
		and pam_userdb.so.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>Kerberos:</term><listitem>
		<para>
		The pam_krb5.so module allows the use of any Kerberos compliant server.
		This tool is used to access MIT Kerberos, Heimdal Kerberos, and potentially
		Microsoft Active Directory (if enabled).
		</para>
	</listitem></varlistentry>

	<varlistentry><term>LDAP:</term><listitem>
		<para>
		The pam_ldap.so module allows the use of any LDAP v2 or v3 compatible backend
		server. Commonly used LDAP backend servers include: OpenLDAP v2.0 and v2.1,
		Sun ONE iDentity server, Novell eDirectory server, Microsoft Active Directory.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>NetWare Bindery:</term><listitem>
		<para>
		The pam_ncp_auth.so module allows authentication off any bindery enabled
		NetWare Core Protocol based server.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>SMB Password:</term><listitem>
		<para>
		This module, called pam_smbpass.so, will allow user authentication off
		the passdb backend that is configured in the Samba &smb.conf; file.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>SMB Server:</term><listitem>
		<para>
		The pam_smb_auth.so module is the original MS Windows networking authentication
		tool. This module has been somewhat outdated by the Winbind module.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>Winbind:</term><listitem>
		<para>
		The pam_winbind.so module allows Samba to obtain authentication from any
		MS Windows Domain Controller. It can just as easily be used to authenticate
		users for access to any PAM enabled application.
		</para>
	</listitem></varlistentry>

	<varlistentry><term>RADIUS:</term><listitem>
		<para>
		There is a PAM RADIUS (Remote Access Dial-In User Service) authentication
		module. In most cases the administrator will need to locate the source code
		for this tool and compile and install it themselves. RADIUS protocols are
		used by many routers and terminal servers.
		</para>
	</listitem></varlistentry>
</variablelist>

<para>
Of the above, Samba provides the pam_smbpasswd.so and the pam_winbind.so modules alone.
</para>

<para>
Once configured, these permit a remarkable level of flexibility in the location and use
of distributed samba domain controllers that can provide wide are network bandwidth
efficient authentication services for PAM capable systems. In effect, this allows the
deployment of centrally managed and maintained distributed authentication from a single
user account database.
</para>

</sect1>

<sect1>
<title>Technical Discussion</title>

<para>
PAM is designed to provide the system administrator with a great deal of flexibility in
configuration of the privilege granting applications of their system. The local
configuration of system security controlled by PAM is contained in one of two places:
either the single system file, /etc/pam.conf; or the /etc/pam.d/ directory.
</para>

<sect2>
<title>PAM Configuration Syntax</title>

<para>
In this section we discuss the correct syntax of and generic options respected by entries to these files.
PAM specific tokens in the configuration file are case insensitive. The module paths, however, are case
sensitive since they indicate a file's name and reflect the case dependence of typical file-systems.
The case-sensitivity of the arguments to any given module is defined for each module in turn.
</para>

<para>
In addition to the lines described below, there are two special characters provided for the convenience
of the system administrator: comments are preceded by a `#' and extend to the next end-of-line; also,
module specification lines may be extended with a `\' escaped newline. 
</para>

<para>
If the PAM authentication module (loadable link library file) is located in the
default location then it is not necessary to specify the path. In the case of
Linux, the default location is <filename>/lib/security</filename>. If the module
is located outside the default then the path must be specified as:
</para>

<para>
<programlisting>
auth  required  /other_path/pam_strange_module.so
</programlisting>
</para>

<sect3>
<title>Anatomy of <filename>/etc/pam.d</filename> Entries</title>

<para>
The remaining information in this subsection was taken from the documentation of the Linux-PAM
project. For more information on PAM, see 
<ulink url="http://ftp.kernel.org/pub/linux/libs/pam/">The Official Linux-PAM home page</ulink>
</para>

<para>
A general configuration line of the /etc/pam.conf file has the following form:
</para>

<para>
<programlisting>
service-name   module-type   control-flag   module-path   args
</programlisting>
</para>

<para>
Below, we explain the meaning of each of these tokens. The second (and more recently adopted)
way of configuring Linux-PAM is via the contents of the <filename>/etc/pam.d/</filename> directory.
Once we have explained the meaning of the above tokens, we will describe this method.
</para>

<variablelist>
	<varlistentry><term>service-name:</term><listitem>
		<para>
		The name of the service associated with this entry. Frequently the service name is the conventional
		name of the given application. For example, `ftpd', `rlogind' and `su', etc. .
		</para>

		<para>
		There is a special service-name, reserved for defining a default authentication mechanism. It has
		the name `OTHER' and may be specified in either lower or upper case characters. Note, when there
		is a module specified for a named service, the `OTHER' entries are ignored.
		</para>
		</listitem>
	</varlistentry>

	<varlistentry><term>module-type:</term><listitem>
                <para>
		One of (currently) four types of module. The four types are as follows:
		</para>

		<itemizedlist>
			<listitem><para>
			<emphasis>auth:</emphasis> this module type provides two aspects of authenticating the user.
			Firstly, it establishes that the user is who they claim to be, by instructing the application
			to prompt the user for a password or other means of identification. Secondly, the module can
			grant group membership (independently of the <filename>/etc/groups</filename> file discussed
			above) or other privileges through its credential granting properties.
			</para></listitem>

			<listitem><para>
			<emphasis>account:</emphasis> this module performs non-authentication based account management.
			It is typically used to restrict/permit access to a service based on the time of day, currently
		 	available system resources (maximum number of users) or perhaps the location of the applicant
			user `root' login only on the console.
			</para></listitem>

			<listitem><para>
			<emphasis>session:</emphasis> primarily, this module is associated with doing things that need
			to be done for the user before/after they can be given service. Such things include the logging
			of information concerning the opening/closing of some data exchange with a user, mounting
			directories, etc.
			</para></listitem>

			<listitem><para>
			<emphasis>password:</emphasis> this last module type is required for updating the authentication
			token associated with the user. Typically, there is one module for each `challenge/response'
			based authentication (auth) module-type.
			</para></listitem>
		</itemizedlist>
		</listitem>
	</varlistentry>

	<varlistentry><term>control-flag:</term><listitem>
                <para>
		The control-flag is used to indicate how the PAM library will react to the success or failure of the
		module it is associated with. Since modules can be stacked (modules of the same type execute in series,
		one after another), the control-flags determine the relative importance of each module. The application
		is not made aware of the individual success or failure of modules listed in the
		<filename>/etc/pam.conf</filename> file. Instead, it receives a summary success or fail response from
		the Linux-PAM library. The order of execution of these modules is that of the entries in the
		<filename>/etc/pam.conf</filename> file; earlier entries are executed before later ones.
		As of Linux-PAM v0.60, this control-flag can be defined with one of two syntaxes.
		</para>

		<para>
		The simpler (and historical) syntax for the control-flag is a single keyword defined to indicate the
		severity of concern associated with the success or failure of a specific module. There are four such
		<emphasis>keywords: required, requisite, sufficient and optional</emphasis>.
		</para>

		<para>
		The Linux-PAM library interprets these keywords in the following manner:
		</para>

		<itemizedlist>
			<listitem><para>
			<emphasis>required:</emphasis> this indicates that the success of the module is required for the
			module-type facility to succeed. Failure of this module will not be apparent to the user until all
			of the remaining modules (of the same module-type) have been executed.
			</para></listitem>

			<listitem><para>
			<emphasis>requisite:</emphasis> like required, however, in the case that such a module returns a
			failure, control is directly returned to the application. The return value is that associated with
			the first required or requisite module to fail. Note, this flag can be used to protect against the
			possibility of a user getting the opportunity to enter a password over an unsafe medium. It is
			conceivable that such behavior might inform an attacker of valid accounts on a system. This
			possibility should be weighed against the not insignificant concerns of exposing a sensitive
			password in a hostile environment.
			</para></listitem>

                        <listitem><para>
                        <emphasis>sufficient:</emphasis> the success of this module is deemed `sufficient' to satisfy
			the Linux-PAM library that this module-type has succeeded in its purpose. In the event that no
			previous required module has failed, no more `stacked' modules of this type are invoked. (Note,
			in this case subsequent required modules are not invoked.). A failure of this module is not deemed
			as fatal to satisfying the application that this module-type has succeeded.
			</para></listitem>

                        <listitem><para>
                        <emphasis>optional:</emphasis> as its name suggests, this control-flag marks the module as not
			being critical to the success or failure of the user's application for service. In general,
			Linux-PAM ignores such a module when determining if the module stack will succeed or fail.
			However, in the absence of any definite successes or failures of previous or subsequent stacked
			modules this module will determine the nature of the response to the application. One example of
			this latter case, is when the other modules return something like PAM_IGNORE.
			</para></listitem>
		</itemizedlist>

		<para>
		The more elaborate (newer) syntax is much more specific and gives the administrator a great deal of control
		over how the user is authenticated. This form of the control flag is delimited with square brackets and
		consists of a series of value=action tokens:
		</para>

<para><programlisting>
[value1=action1 value2=action2 ...]
</programlisting></para>

		<para>
		Here, value1 is one of the following return values: success; open_err; symbol_err; service_err;
		system_err; buf_err; perm_denied; auth_err; cred_insufficient; authinfo_unavail; user_unknown; maxtries;
		new_authtok_reqd; acct_expired; session_err; cred_unavail; cred_expired; cred_err; no_module_data; conv_err;
		authtok_err; authtok_recover_err; authtok_lock_busy; authtok_disable_aging; try_again; ignore; abort;
		authtok_expired; module_unknown; bad_item; and default. The last of these (default) can be used to set
		the action for those return values that are not explicitly defined.
		</para>

		<para>
		The action1 can be a positive integer or one of the following tokens: ignore; ok; done; bad; die; and reset.
		A positive integer, J, when specified as the action, can be used to indicate that the next J modules of the
		current module-type will be skipped. In this way, the administrator can develop a moderately sophisticated
		stack of modules with a number of different paths of execution. Which path is taken can be determined by the
		reactions of individual modules.
		</para>

		<itemizedlist>
			<listitem><para>
			<emphasis>ignore:</emphasis> when used with a stack of modules, the module's return status will not
			contribute to the return code the application obtains.
			</para></listitem>

			<listitem><para>
                        <emphasis>bad:</emphasis> this action indicates that the return code should be thought of as indicative
			of the module failing. If this module is the first in the stack to fail, its status value will be used
			for that of the whole stack.
			</para></listitem>

                        <listitem><para>
                        <emphasis>die:</emphasis> equivalent to bad with the side effect of terminating the module stack and
			PAM immediately returning to the application.
			</para></listitem>

                        <listitem><para>
                        <emphasis>ok:</emphasis> this tells PAM that the administrator thinks this return code should
			contribute directly to the return code of the full stack of modules. In other words, if the former
			state of the stack would lead to a return of PAM_SUCCESS, the module's return code will override
			this value. Note, if the former state of the stack holds some value that is indicative of a modules
			failure, this 'ok' value will not be used to override that value.
			</para></listitem>

                        <listitem><para>
                        <emphasis>done:</emphasis> equivalent to ok with the side effect of terminating the module stack and
			PAM immediately returning to the application.
                        </para></listitem>

                        <listitem><para>
                        <emphasis>reset:</emphasis> clear all memory of the state of the module stack and start again with
			the next stacked module.
			</para></listitem>
		</itemizedlist>

		<para>
		Each of the four keywords: required; requisite; sufficient; and optional, have an equivalent expression in
		terms of the [...] syntax. They are as follows:
		</para>

		<para>
		<itemizedlist>
			<listitem><para>
			required is equivalent to [success=ok new_authtok_reqd=ok ignore=ignore default=bad]
			</para></listitem>

			<listitem><para>
			requisite is equivalent to [success=ok new_authtok_reqd=ok ignore=ignore default=die]
			</para></listitem>

			<listitem><para>
			sufficient is equivalent to [success=done new_authtok_reqd=done default=ignore]
			</para></listitem>

			<listitem><para>
			optional is equivalent to [success=ok new_authtok_reqd=ok default=ignore]
			</para></listitem>
		</itemizedlist>
		</para>

		<para>
		Just to get a feel for the power of this new syntax, here is a taste of what you can do with it. With Linux-PAM-0.63,
		the notion of client plug-in agents was introduced. This is something that makes it possible for PAM to support
		machine-machine authentication using the transport protocol inherent to the client/server application. With the
		<emphasis>[ ... value=action ... ]</emphasis> control syntax, it is possible for an application to be configured
		to support binary prompts with compliant clients, but to gracefully fall over into an alternative authentication
		mode for older, legacy, applications.
		</para>
		</listitem>
	</varlistentry>

	<varlistentry><term>module-path:</term><listitem>
		<para>
		The path-name of the dynamically loadable object file; the pluggable module itself. If the first character of the
		module path is `/', it is assumed to be a complete path. If this is not the case, the given module path is appended
		to the default module path: <filename>/lib/security</filename> (but see the notes above).
		</para>

		<para>
		The args are a list of tokens that are passed to the module when it is invoked. Much like arguments to a typical
		Linux shell command. Generally, valid arguments are optional and are specific to any given module. Invalid arguments
		are ignored by a module, however, when encountering an invalid argument, the module is required to write an error
		to syslog(3). For a list of generic options see the next section.
		</para>

		<para>
		Note, if you wish to include spaces in an argument, you should surround that argument with square brackets. For example:
		</para>

<para><programlisting>
squid auth required pam_mysql.so user=passwd_query passwd=mada \
        db=eminence [query=select user_name from internet_service where \
                     user_name='%u' and password=PASSWORD('%p') and \
                     service='web_proxy']
</programlisting></para>

		<para>
		Note, when using this convention, you can include `[' characters inside the string, and if you wish to include a `]'
		character inside the string that will survive the argument parsing, you should use `\['. In other words:
		</para>

<para><programlisting><!--FIXME:Diagram-->
[..[..\]..]    -->   ..[..]..
</programlisting></para>

		<para>
		Any line in (one of) the configuration file(s), that is not formatted correctly, will generally tend (erring on the
		side of caution) to make the authentication process fail. A corresponding error is written to the system log files
		with a call to syslog(3). 
		</para>
		</listitem>
	</varlistentry>
</variablelist>

</sect3>

</sect2>

<sect2>
<title>Example System Configurations</title>

<para>
The following is an example <filename>/etc/pam.d/login</filename> configuration file. 
This example had all options been uncommented is probably not usable 
as it stacks many conditions before allowing successful completion 
of the login process. Essentially all conditions can be disabled 
by commenting them out except the calls to <filename>pam_pwdb.so</filename>.
</para>

<sect3>
<title>PAM: original login config</title>

<para><programlisting>
#%PAM-1.0
# The PAM configuration file for the `login' service
#
auth         required    pam_securetty.so
auth         required    pam_nologin.so
# auth       required    pam_dialup.so
# auth       optional    pam_mail.so
auth         required    pam_pwdb.so shadow md5
# account    requisite   pam_time.so
account      required    pam_pwdb.so
session      required    pam_pwdb.so
# session    optional    pam_lastlog.so
# password   required    pam_cracklib.so retry=3
password     required    pam_pwdb.so shadow md5
</programlisting></para>

</sect3>

<sect3>
<title>PAM: login using pam_smbpass</title>

<para>
PAM allows use of replaceable modules. Those available on a sample system include:
</para>

<para><prompt>$</prompt><userinput>/bin/ls /lib/security</userinput>
<programlisting>
pam_access.so    pam_ftp.so          pam_limits.so     
pam_ncp_auth.so  pam_rhosts_auth.so  pam_stress.so     
pam_cracklib.so  pam_group.so        pam_listfile.so   
pam_nologin.so   pam_rootok.so       pam_tally.so      
pam_deny.so      pam_issue.so        pam_mail.so       
pam_permit.so    pam_securetty.so    pam_time.so       
pam_dialup.so    pam_lastlog.so      pam_mkhomedir.so  
pam_pwdb.so      pam_shells.so       pam_unix.so       
pam_env.so       pam_ldap.so         pam_motd.so       
pam_radius.so    pam_smbpass.so      pam_unix_acct.so  
pam_wheel.so     pam_unix_auth.so    pam_unix_passwd.so
pam_userdb.so    pam_warn.so         pam_unix_session.so
</programlisting></para>

<para>
The following example for the login program replaces the use of 
the <filename>pam_pwdb.so</filename> module which uses the system 
password database (<filename>/etc/passwd</filename>,
<filename>/etc/shadow</filename>, <filename>/etc/group</filename>) with 
the module <filename>pam_smbpass.so</filename> which uses the Samba 
database which contains the Microsoft MD4 encrypted password 
hashes. This database is stored in either 
<filename>/usr/local/samba/private/smbpasswd</filename>, 
<filename>/etc/samba/smbpasswd</filename>, or in 
<filename>/etc/samba.d/smbpasswd</filename>, depending on the 
Samba implementation for your UNIX/Linux system. The 
<filename>pam_smbpass.so</filename> module is provided by 
Samba version 2.2.1 or later. It can be compiled by specifying the 
<option>--with-pam_smbpass</option> options when running Samba's
<command>configure</command> script.  For more information
on the <filename>pam_smbpass</filename> module, see the documentation
in the <filename>source/pam_smbpass</filename> directory of the Samba 
source distribution.
</para>

<para><programlisting>
#%PAM-1.0
# The PAM configuration file for the `login' service
#
auth        required    pam_smbpass.so nodelay
account     required    pam_smbpass.so nodelay
session     required    pam_smbpass.so nodelay
password    required    pam_smbpass.so nodelay
</programlisting></para>

<para>
The following is the PAM configuration file for a particular 
Linux system. The default condition uses <filename>pam_pwdb.so</filename>.
</para>

<para><programlisting>
#%PAM-1.0
# The PAM configuration file for the `samba' service
#
auth       required     pam_pwdb.so nullok nodelay shadow audit
account    required     pam_pwdb.so audit nodelay
session    required     pam_pwdb.so nodelay
password   required     pam_pwdb.so shadow md5
</programlisting></para>

<para>
In the following example the decision has been made to use the 
smbpasswd database even for basic samba authentication. Such a 
decision could also be made for the passwd program and would 
thus allow the smbpasswd passwords to be changed using the passwd 
program.
</para>

<para><programlisting>
#%PAM-1.0
# The PAM configuration file for the `samba' service
#
auth       required     pam_smbpass.so nodelay
account    required     pam_pwdb.so audit nodelay
session    required     pam_pwdb.so nodelay
password   required     pam_smbpass.so nodelay smbconf=/etc/samba.d/smb.conf
</programlisting></para>

<note><para>PAM allows stacking of authentication mechanisms. It is 
also possible to pass information obtained within one PAM module through 
to the next module in the PAM stack. Please refer to the documentation for 
your particular system implementation for details regarding the specific 
capabilities of PAM in this environment. Some Linux implementations also 
provide the <filename>pam_stack.so</filename> module that allows all 
authentication to be configured in a single central file. The 
<filename>pam_stack.so</filename> method has some very devoted followers 
on the basis that it allows for easier administration. As with all issues in 
life though, every decision makes trade-offs, so you may want examine the 
PAM documentation for further helpful information.
</para></note>

</sect3>

</sect2>

<sect2>
<title>smb.conf PAM Configuration</title>

<para>
	There is an option in smb.conf called <smbconfoption><name>obey pam restrictions</name></smbconfoption>.
The following is from the on-line help for this option in SWAT;
</para>

<para>
When Samba is configured to enable PAM support (i.e. 
<option>--with-pam</option>), this parameter will 
control whether or not Samba should obey PAM's account 
and session management directives. The default behavior 
is to use PAM for clear text authentication only and to 
ignore any account or session management. Note that Samba always 
ignores PAM for authentication in the case of 
<smbconfoption><name>encrypt passwords</name><value>yes</value></smbconfoption>. 
The reason is that PAM modules cannot support the challenge/response 
authentication mechanism needed in the presence of SMB 
password encryption. 
</para>

<para>Default: <smbconfoption><name>obey pam restrictions</name><value>no</value></smbconfoption></para>

</sect2>

<sect2>
<title>Remote CIFS Authentication using winbindd.so</title>

<para>
All operating systems depend on the provision of users credentials acceptable to the platform.
UNIX requires the provision of a user identifier (UID) as well as a group identifier (GID).
These are both simple integer type numbers that are obtained from a password backend such
as <filename>/etc/passwd</filename>.
</para>

<para>
Users and groups on a Windows NT server are assigned a relative id (rid) which is unique for
the domain when the user or group is created. To convert the Windows NT user or group into
a  unix user or group, a mapping between rids and unix user and group ids is required. This
is one of the jobs that winbind performs.
</para>

<para>
As winbind users and groups are resolved from a server, user and group ids are allocated
from a specified range. This is done on a first come, first served basis, although all
existing users and groups will be mapped as soon as a client performs a user or  group 
enumeration command.  The allocated unix ids are stored in a database file under the Samba
lock directory and will be remembered.
</para>

<para>
The astute administrator will realize from this that the combination of <filename>pam_smbpass.so</filename>, 
<command>winbindd</command>, and a distributed passdb backend, such as ldap, will allow the establishment of a
centrally managed, distributed user/password database that can also be used by all PAM (eg: Linux) aware
programs and applications. This arrangement can have particularly potent advantages compared with the use of
Microsoft Active Directory Service (ADS) in so far as reduction of wide area network authentication traffic.
</para>

<warning><para>
The rid to unix id database is the only location where the user and group  mappings are 
stored by winbindd.  If this file is deleted or corrupted, there is no way for winbindd
to determine which user and group ids correspond to Windows NT user and group rids.
</para></warning>

</sect2>

<sect2>
<title>Password Synchronization using pam_smbpass.so</title>

<para>
pam_smbpass is a PAM module which can be used on conforming systems to
keep the smbpasswd (Samba password) database in sync with the unix
password file. PAM (Pluggable Authentication Modules) is an API supported
under some Unices, such as Solaris, HPUX and Linux, that provides a
generic interface to authentication mechanisms.
</para>

<para>
This module authenticates a local smbpasswd user database.  If you require
support for authenticating against a remote SMB server, or if you're
concerned about the presence of suid root binaries on your system, it is
recommended that you use pam_winbind instead.
</para>

<para>
Options recognized by this module are as follows:
<table frame="all">
	<title>Options recognized by pam_smbpass</title>
	<tgroup cols="2" align="left">
		<colspec align="left"/>
		<colspec align="justify"/>
	<tbody>
		<row><entry>debug</entry><entry>log more debugging info</entry></row>
		<row><entry>audit</entry><entry>like debug, but also logs unknown usernames</entry></row>
		<row><entry>use_first_pass</entry><entry>don't prompt the user for passwords; take them from PAM_ items instead</entry></row>
		<row><entry>try_first_pass</entry><entry>try to get the password from a previous PAM module, fall back to prompting the user</entry></row>
		<row><entry>use_authtok</entry><entry>like try_first_pass, but *fail* if the new PAM_AUTHTOK has not been previously set. (intended for stacking password modules only)</entry></row>
		<row><entry>not_set_pass</entry><entry>don't make passwords used by this module available to other modules.</entry></row>
		<row><entry>nodelay</entry><entry>don't insert ~1 second delays on authentication failure.</entry></row>
		<row><entry>nullok</entry><entry>null passwords are allowed.</entry></row>
		<row><entry>nonull</entry><entry>null passwords are not allowed. Used to override the Samba configuration.</entry></row>
		<row><entry>migrate</entry><entry>only meaningful in an "auth" context; used to update smbpasswd file with a password used for successful authentication.</entry></row>
		<row><entry>smbconf=<replaceable>file</replaceable></entry><entry>specify an alternate path to the &smb.conf; file.</entry></row>
	</tbody>
</tgroup>
</table>
</para>

<para>
<itemizedlist>
	<listitem><para><ulink url="mailto:morgan@transmeta.com">Andrew Morgan</ulink>, for providing the Linux-PAM
			framework, without which none of this would have happened</para></listitem>

<listitem><para><ulink url="mailto:gafton@redhat.com">Christian Gafton</ulink> and Andrew Morgan again, for the
		pam_pwdb module upon which pam_smbpass was originally based</para></listitem>

<listitem><para><ulink url="mailto:lkcl@switchboard.net">Luke Leighton</ulink> for being receptive to the idea,
	and for the occasional good-natured complaint about the project's status
	that keep me working on it :)</para></listitem>
</itemizedlist>.
</para>

<para>
The following are examples of the use of pam_smbpass.so in the format of Linux
<filename>/etc/pam.d/</filename> files structure. Those wishing to implement this
tool on other platforms will need to adapt this appropriately.
</para>

<sect3>
<title>Password Synchronisation Configuration</title>

<para>
A sample PAM configuration that shows the use of pam_smbpass to make
sure private/smbpasswd is kept in sync when /etc/passwd (/etc/shadow)
is changed.  Useful when an expired password might be changed by an
application (such as ssh).
</para>

<para><programlisting>
#%PAM-1.0
# password-sync
#
auth       requisite    pam_nologin.so
auth       required     pam_unix.so
account    required     pam_unix.so
password   requisite    pam_cracklib.so retry=3
password   requisite    pam_unix.so shadow md5 use_authtok try_first_pass
password   required     pam_smbpass.so nullok use_authtok try_first_pass
session    required     pam_unix.so
</programlisting></para>
</sect3>

<sect3>
<title>Password Migration Configuration</title>

<para>
A sample PAM configuration that shows the use of pam_smbpass to migrate
from plaintext to encrypted passwords for Samba.  Unlike other methods,
this can be used for users who have never connected to Samba shares:
password migration takes place when users ftp in, login using ssh, pop
their mail, etc.
</para>

<para><programlisting>
#%PAM-1.0
# password-migration
#
auth       requisite   pam_nologin.so
# pam_smbpass is called IF pam_unix succeeds.
auth       requisite   pam_unix.so
auth       optional    pam_smbpass.so migrate
account    required    pam_unix.so
password   requisite   pam_cracklib.so retry=3
password   requisite   pam_unix.so shadow md5 use_authtok try_first_pass
password   optional    pam_smbpass.so nullok use_authtok try_first_pass
session    required    pam_unix.so
</programlisting></para>
</sect3>

<sect3>
<title>Mature Password Configuration</title>

<para>
A sample PAM configuration for a 'mature' smbpasswd installation.
private/smbpasswd is fully populated, and we consider it an error if
the smbpasswd doesn't exist or doesn't match the UNIX password.
</para>

<para><programlisting>
#%PAM-1.0
# password-mature
#
auth       requisite    pam_nologin.so
auth       required     pam_unix.so
account    required     pam_unix.so
password   requisite    pam_cracklib.so retry=3
password   requisite    pam_unix.so shadow md5 use_authtok try_first_pass
password   required     pam_smbpass.so use_authtok use_first_pass
session    required     pam_unix.so
</programlisting></para>
</sect3>

<sect3>
<title>Kerberos Password Integration Configuration</title>

<para>
A sample PAM configuration that shows pam_smbpass used together with
pam_krb5.  This could be useful on a Samba PDC that is also a member of
a Kerberos realm.
</para>

<para><programlisting>
#%PAM-1.0
# kdc-pdc
#
auth       requisite   pam_nologin.so
auth       requisite   pam_krb5.so
auth       optional    pam_smbpass.so migrate
account    required    pam_krb5.so
password   requisite   pam_cracklib.so retry=3
password   optional    pam_smbpass.so nullok use_authtok try_first_pass
password   required    pam_krb5.so use_authtok try_first_pass
session    required    pam_krb5.so
</programlisting></para>

</sect3>

</sect2>

</sect1>

<sect1>
<title>Common Errors</title>

<para>
PAM can be a very fickle and sensitive to configuration glitches. Here we look at a few cases from
the Samba mailing list.
</para>

	<sect2>
	<title>pam_winbind problem</title>

	<para>
		<quote>
			I have the following PAM configuration:
		</quote>
	</para>

	<para>
<programlisting>
auth required /lib/security/pam_securetty.so
auth sufficient /lib/security/pam_winbind.so
auth sufficient /lib/security/pam_unix.so use_first_pass nullok
auth required /lib/security/pam_stack.so service=system-auth
auth required /lib/security/pam_nologin.so
account required /lib/security/pam_stack.so service=system-auth
account required /lib/security/pam_winbind.so
password required /lib/security/pam_stack.so service=system-auth
</programlisting>
	</para>

	<para>
		<quote>
	When I open a new console with [ctrl][alt][F1], then I cant log in with my user "pitie".
	I've tried with user "scienceu+pitie" also.
</quote>
	</para>

	<para>
		The problem may lie with your inclusion of <parameter>pam_stack.so
	service=system-auth</parameter>. That file often contains a lot of stuff that may
	duplicate what you're already doing. Try commenting out the pam_stack lines
	for auth and account and see if things work. If they do, look at
	<filename>/etc/pam.d/system-auth</filename> and copy only what you need from it into your
	<filename>/etc/pam.d/login</filename> file.  Alternatively, if you want all services to use
	winbind, you can put the winbind-specific stuff in <filename>/etc/pam.d/system-auth</filename>.
	</para>

	</sect2>

	<sect2>
	<title>Winbind is not resolving users and groups</title>

	<para>
		<quote>
	My smb.conf file is correctly configured. I have specified 
	<smbconfoption><name>idmap uid</name><value>12000</value></smbconfoption>, 
	and <smbconfoption><name>idmap gid</name><value>3000-3500</value></smbconfoption>
	and <command>winbind</command> is running. When I do the following it all works fine.
</quote>
	</para>

<para><screen>
&rootprompt;<userinput>wbinfo -u</userinput>
MIDEARTH+maryo
MIDEARTH+jackb
MIDEARTH+ameds
...
MIDEARTH+root

&rootprompt;<userinput>wbinfo -g</userinput>
MIDEARTH+Domain Users
MIDEARTH+Domain Admins
MIDEARTH+Domain Guests
...
MIDEARTH+Accounts

&rootprompt;<userinput>getent passwd</userinput>
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/bin/bash
...
maryo:x:15000:15003:Mary Orville:/home/MIDEARTH/maryo:/bin/false
</screen></para>

<para>
	<quote>
	But the following command just fails:
</quote>
<screen>
&rootprompt;<userinput>chown 'maryo' a_file</userinput>
chown: `maryo': invalid user
</screen>
<quote>
This is driving me nuts! What can be wrong?
</quote>
	</para>

	<para>
	Your system is likely running <command>nscd</command>, the name service
	caching daemon. Shut it down, do NOT restart it! You will find your problem resolved.
	</para>

	</sect2>
</sect1>

</chapter>