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1 <?xml version="1.0" encoding="iso-8859-1"?>
2 <!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
3 <chapter id="pam">
4 <chapterinfo>
5 &author.jht;
6 <author>
7 <firstname>Stephen</firstname><surname>Langasek</surname>
8 <affiliation>
9 <address><email>vorlon@netexpress.net</email></address>
10 </affiliation>
11 </author>
12 <pubdate>May 31, 2003</pubdate>
13 </chapterinfo>
15 <title>PAM-Based Distributed Authentication</title>
17 <para>
18 <indexterm><primary>PAM-enabled</primary></indexterm>
19 <indexterm><primary>Winbind</primary></indexterm>
20 <indexterm><primary>ADS</primary></indexterm>
21 <indexterm><primary>Winbind-based authentication</primary></indexterm>
22 This chapter should help you to deploy Winbind-based authentication on any PAM-enabled
23 UNIX/Linux system. Winbind can be used to enable user-level application access authentication
24 from any MS Windows NT domain, MS Windows 200x Active Directory-based
25 domain, or any Samba-based domain environment. It will also help you to configure PAM-based local host access
26 controls that are appropriate to your Samba configuration.
27 </para>
29 <para>
30 <indexterm><primary>PAM management</primary></indexterm>
31 <indexterm><primary>pam_smbpass.so</primary></indexterm>
32 In addition to knowing how to configure Winbind into PAM, you will learn generic PAM management
33 possibilities and in particular how to deploy tools like <filename>pam_smbpass.so</filename> to your advantage.
34 </para>
36 <note><para>
37 The use of Winbind requires more than PAM configuration alone.
38 Please refer to <link linkend="winbind">Winbind: Use of Domain Accounts</link>, for further information regarding Winbind.
39 </para></note>
41 <sect1>
42 <title>Features and Benefits</title>
44 <para>
45 <indexterm><primary>Sun Solaris</primary></indexterm>
46 <indexterm><primary>xxxxBSD</primary></indexterm>
47 <indexterm><primary>Linux</primary></indexterm>
48 <indexterm><primary>Pluggable Authentication Modules</primary><see>PAM</see></indexterm>
49 <indexterm><primary>/etc/passwd</primary></indexterm>
50 <indexterm><primary>login</primary></indexterm>
51 <indexterm><primary>passwd</primary></indexterm>
52 <indexterm><primary>chown</primary></indexterm>
53 A number of UNIX systems (e.g., Sun Solaris), as well as the xxxxBSD family and Linux,
54 now utilize the Pluggable Authentication Modules (PAM) facility to provide all authentication,
55 authorization, and resource control services. Prior to the introduction of PAM, a decision
56 to use an alternative to the system password database (<filename>/etc/passwd</filename>)
57 would require the provision of alternatives for all programs that provide security services.
58 Such a choice would involve provision of alternatives to programs such as <command>login</command>,
59 <command>passwd</command>, <command>chown</command>, and so on.
60 </para>
62 <para>
63 <indexterm><primary>PAM</primary></indexterm>
64 <indexterm><primary>/etc/pam.conf</primary></indexterm>
65 <indexterm><primary>Solaris</primary></indexterm>
66 <indexterm><primary>/etc/pam.d</primary></indexterm>
67 PAM provides a mechanism that disconnects these security programs from the underlying
68 authentication/authorization infrastructure. PAM is configured by making appropriate modifications to one file,
69 <filename>/etc/pam.conf</filename> (Solaris), or by editing individual control files that are
70 located in <filename>/etc/pam.d</filename>.
71 </para>
73 <para>
74 <indexterm><primary>PAM-enabled</primary></indexterm>
75 <indexterm><primary>dynamically loadable library modules</primary></indexterm>
76 On PAM-enabled UNIX/Linux systems, it is an easy matter to configure the system to use any
77 authentication backend so long as the appropriate dynamically loadable library modules
78 are available for it. The backend may be local to the system or may be centralized on a
79 remote server.
80 </para>
82 <para>
83 PAM support modules are available for:
84 </para>
86 <variablelist>
87 <varlistentry><term><filename>/etc/passwd</filename></term><listitem>
88 <para>
89 <indexterm><primary>/etc/passwd</primary></indexterm>
90 <indexterm><primary>PAM modules</primary></indexterm>
91 <indexterm><primary>pam_unix.so</primary></indexterm>
92 <indexterm><primary>pam_unix2.so</primary></indexterm>
93 <indexterm><primary>pam_pwdb.so</primary></indexterm>
94 <indexterm><primary>pam_userdb.so</primary></indexterm>
95 There are several PAM modules that interact with this standard UNIX user database. The most common are called
96 <filename>pam_unix.so</filename>, <filename>pam_unix2.so</filename>, <filename>pam_pwdb.so</filename> and
97 <filename>pam_userdb.so</filename>.
98 </para>
99 </listitem></varlistentry>
101 <varlistentry><term>Kerberos</term><listitem>
102 <para>
103 <indexterm><primary>pam_krb5.so</primary></indexterm>
104 <indexterm><primary>Kerberos</primary></indexterm>
105 <indexterm><primary>Heimdal</primary></indexterm>
106 <indexterm><primary>MIT Kerberos</primary></indexterm>
107 <indexterm><primary>ADS</primary></indexterm>
108 The <filename>pam_krb5.so</filename> module allows the use of any Kerberos-compliant server.
109 This tool is used to access MIT Kerberos, Heimdal Kerberos, and potentially
110 Microsoft Active Directory (if enabled).
111 </para>
112 </listitem></varlistentry>
114 <varlistentry><term>LDAP</term><listitem>
115 <para>
116 <indexterm><primary>LDAP</primary></indexterm>
117 <indexterm><primary>pam_ldap.so</primary></indexterm>
118 <indexterm><primary>OpenLDAP</primary></indexterm>
119 <indexterm><primary>Sun ONE iDentity server</primary></indexterm>
120 <indexterm><primary>Novell eDirectory server</primary></indexterm>
121 <indexterm><primary>Microsoft Active Directory</primary></indexterm>
122 The <filename>pam_ldap.so</filename> module allows the use of any LDAP v2- or v3-compatible backend
123 server. Commonly used LDAP backend servers include OpenLDAP v2.0 and v2.1,
124 Sun ONE iDentity server, Novell eDirectory server, and Microsoft Active Directory.
125 </para>
126 </listitem></varlistentry>
128 <varlistentry><term>NetWare Bindery</term><listitem>
129 <para>
130 <indexterm><primary>NetWare Bindery</primary></indexterm>
131 <indexterm><primary>pam_ncp_auth.so</primary></indexterm>
132 <indexterm><primary>bindery-enabled</primary></indexterm>
133 <indexterm><primary>NetWare Core Protocol-based server</primary></indexterm>
134 The <filename>pam_ncp_auth.so</filename> module allows authentication off any bindery-enabled
135 NetWare Core Protocol-based server.
136 </para>
137 </listitem></varlistentry>
139 <varlistentry><term>SMB Password</term><listitem>
140 <para>
141 <indexterm><primary>SMB Password</primary></indexterm>
142 <indexterm><primary>pam_smbpass.so</primary></indexterm>
143 <indexterm><primary>passdb backend</primary></indexterm>
144 This module, called <filename>pam_smbpass.so</filename>, allows user authentication of
145 the passdb backend that is configured in the Samba &smb.conf; file.
146 </para>
147 </listitem></varlistentry>
149 <varlistentry><term>SMB Server</term><listitem>
150 <para>
151 <indexterm><primary>SMB Server</primary></indexterm>
152 <indexterm><primary>pam_smb_auth.so</primary></indexterm>
153 The <filename>pam_smb_auth.so</filename> module is the original MS Windows networking authentication
154 tool. This module has been somewhat outdated by the Winbind module.
155 </para>
156 </listitem></varlistentry>
158 <varlistentry><term>Winbind</term><listitem>
159 <para>
160 <indexterm><primary>Winbind</primary></indexterm>
161 <indexterm><primary>pam_winbind.so</primary></indexterm>
162 <indexterm><primary>domain controller</primary></indexterm>
163 <indexterm><primary>authentication</primary></indexterm>
164 The <filename>pam_winbind.so</filename> module allows Samba to obtain authentication from any
165 MS Windows domain controller. It can just as easily be used to authenticate
166 users for access to any PAM-enabled application.
167 </para>
168 </listitem></varlistentry>
170 <varlistentry><term>RADIUS</term><listitem>
171 <para>
172 <indexterm><primary>Remote Access Dial-In User Service</primary><see>RADIUS</see></indexterm>
173 There is a PAM RADIUS (Remote Access Dial-In User Service) authentication
174 module. In most cases, administrators need to locate the source code
175 for this tool and compile and install it themselves. RADIUS protocols are
176 used by many routers and terminal servers.
177 </para>
178 </listitem></varlistentry>
179 </variablelist>
181 <para>
182 <indexterm><primary>pam_smbpasswd.so</primary></indexterm>
183 <indexterm><primary>pam_winbind.so</primary></indexterm>
184 Of the modules listed, Samba provides the <filename>pam_smbpasswd.so</filename> and the
185 <filename>pam_winbind.so</filename> modules alone.
186 </para>
188 <para>
189 <indexterm><primary>wide-area network bandwidth</primary></indexterm>
190 <indexterm><primary>efficient authentication</primary></indexterm>
191 <indexterm><primary>PAM-capable</primary></indexterm>
192 <indexterm><primary>centrally managed</primary></indexterm>
193 Once configured, these permit a remarkable level of flexibility in the location and use
194 of distributed Samba domain controllers that can provide wide-area network bandwidth,
195 efficient authentication services for PAM-capable systems. In effect, this allows the
196 deployment of centrally managed and maintained distributed authentication from a
197 single-user account database.
198 </para>
200 </sect1>
202 <sect1>
203 <title>Technical Discussion</title>
205 <para>
206 <indexterm><primary>PAM</primary></indexterm>
207 <indexterm><primary>privilege-granting applications</primary></indexterm>
208 <indexterm><primary>/etc/pam.conf</primary></indexterm>
209 <indexterm><primary>/etc/pam.d/</primary></indexterm>
210 PAM is designed to provide system administrators with a great deal of flexibility in
211 configuration of the privilege-granting applications of their system. The local
212 configuration of system security controlled by PAM is contained in one of two places:
213 either the single system file <filename>/etc/pam.conf</filename> or the
214 <filename>/etc/pam.d/</filename> directory.
215 </para>
217 <sect2>
218 <title>PAM Configuration Syntax</title>
220 <para>
221 <indexterm><primary>PAM-specific tokens</primary></indexterm>
222 <indexterm><primary>case sensitivity</primary></indexterm>
223 In this section we discuss the correct syntax of and generic options respected by entries to these files.
224 PAM-specific tokens in the configuration file are case insensitive. The module paths, however, are case
225 sensitive, since they indicate a file's name and reflect the case dependence of typical file systems. The
226 case sensitivity of the arguments to any given module is defined for each module in turn.
227 </para>
229 <para>
230 In addition to the lines described below, there are two special characters provided for the convenience
231 of the system administrator: comments are preceded by a <quote>#</quote> and extend to the next end-of-line; also,
232 module specification lines may be extended with a <quote>\</quote>-escaped newline.
233 </para>
235 <para>
236 <indexterm><primary>PAM authentication module</primary></indexterm>
237 <indexterm><primary>/lib/security</primary></indexterm>
238 If the PAM authentication module (loadable link library file) is located in the
239 default location, then it is not necessary to specify the path. In the case of
240 Linux, the default location is <filename>/lib/security</filename>. If the module
241 is located outside the default, then the path must be specified as:
242 <programlisting>
243 auth required /other_path/pam_strange_module.so
244 </programlisting>
245 </para>
247 <sect3>
248 <title>Anatomy of <filename>/etc/pam.d</filename> Entries</title>
250 <para>
251 The remaining information in this subsection was taken from the documentation of the Linux-PAM
252 project. For more information on PAM, see
253 <ulink url="http://ftp.kernel.org/pub/linux/libs/pam/">the Official Linux-PAM home page</ulink>.
254 </para>
256 <para>
257 <indexterm><primary>/etc/pam.conf</primary></indexterm>
258 A general configuration line of the <filename>/etc/pam.conf</filename> file has the following form:
259 <programlisting>
260 service-name module-type control-flag module-path args
261 </programlisting>
262 </para>
264 <para>
265 We explain the meaning of each of these tokens. The second (and more recently adopted)
266 way of configuring Linux-PAM is via the contents of the <filename>/etc/pam.d/</filename> directory.
267 Once we have explained the meaning of the tokens, we describe this method.
268 </para>
270 <variablelist>
271 <varlistentry><term>service-name</term><listitem>
272 <para>
273 <indexterm><primary>ftpd</primary></indexterm>
274 <indexterm><primary>rlogind</primary></indexterm>
275 <indexterm><primary>su</primary></indexterm>
276 The name of the service associated with this entry. Frequently, the service-name is the conventional
277 name of the given application &smbmdash; for example, <command>ftpd</command>, <command>rlogind</command> and
278 <command>su</command>, and so on.
279 </para>
281 <para>
282 There is a special service-name reserved for defining a default authentication mechanism. It has
283 the name <parameter>OTHER</parameter> and may be specified in either lower- or uppercase characters.
284 Note, when there is a module specified for a named service, the <parameter>OTHER</parameter>
285 entries are ignored.
286 </para>
287 </listitem>
288 </varlistentry>
290 <varlistentry><term>module-type</term><listitem>
291 <para>
292 One of (currently) four types of module. The four types are as follows:
293 </para>
295 <itemizedlist>
296 <listitem><para>
297 <indexterm><primary>auth</primary></indexterm>
298 <indexterm><primary>/etc/groups</primary></indexterm>
299 <parameter>auth:</parameter> This module type provides two aspects of authenticating the user.
300 It establishes that the user is who he or she claims to be by instructing the application
301 to prompt the user for a password or other means of identification. Second, the module can
302 grant group membership (independently of the <filename>/etc/groups</filename> file)
303 or other privileges through its credential-granting properties.
304 </para></listitem>
306 <listitem><para>
307 <indexterm><primary>account</primary></indexterm>
308 <indexterm><primary>non-authentication-based account management</primary></indexterm>
309 <parameter>account:</parameter> This module performs non-authentication-based account management.
310 It is typically used to restrict/permit access to a service based on the time of day, currently
311 available system resources (maximum number of users), or perhaps the location of the user
312 login. For example, the <quote>root</quote> login may be permitted only on the console.
313 </para></listitem>
315 <listitem><para>
316 <indexterm><primary>session</primary></indexterm>
317 <parameter>session:</parameter> Primarily, this module is associated with doing things that need
318 to be done for the user before and after he or she can be given service. Such things include logging
319 information concerning the opening and closing of some data exchange with a user, mounting
320 directories, and so on.
321 </para></listitem>
323 <listitem><para>
324 <indexterm><primary>password</primary></indexterm>
325 <parameter>password:</parameter> This last module type is required for updating the authentication
326 token associated with the user. Typically, there is one module for each
327 <quote>challenge/response</quote> authentication <parameter>(auth)</parameter> module type.
328 </para></listitem>
329 </itemizedlist>
330 </listitem>
331 </varlistentry>
333 <varlistentry><term>control-flag</term><listitem>
334 <para>
335 The control-flag is used to indicate how the PAM library will react to the success or failure of the
336 module it is associated with. Since modules can be stacked (modules of the same type execute in series,
337 one after another), the control-flags determine the relative importance of each module. The application
338 is not made aware of the individual success or failure of modules listed in the
339 <filename>/etc/pam.conf</filename> file. Instead, it receives a summary success or fail response from
340 the Linux-PAM library. The order of execution of these modules is that of the entries in the
341 <filename>/etc/pam.conf</filename> file; earlier entries are executed before later ones.
342 As of Linux-PAM v0.60, this control-flag can be defined with one of two syntaxes.
343 </para>
345 <para>
346 <indexterm><primary>required</primary></indexterm>
347 <indexterm><primary>requisite</primary></indexterm>
348 <indexterm><primary>sufficient</primary></indexterm>
349 <indexterm><primary>optional</primary></indexterm>
350 The simpler (and historical) syntax for the control-flag is a single keyword defined to indicate the
351 severity of concern associated with the success or failure of a specific module. There are four such
352 keywords: <parameter>required</parameter>, <parameter>requisite</parameter>,
353 <parameter>sufficient</parameter>, and <parameter>optional</parameter>.
354 </para>
356 <para>
357 The Linux-PAM library interprets these keywords in the following manner:
358 </para>
360 <itemizedlist>
361 <listitem><para>
362 <parameter>required:</parameter> This indicates that the success of the module is required for the
363 module-type facility to succeed. Failure of this module will not be apparent to the user until all
364 of the remaining modules (of the same module-type) have been executed.
365 </para></listitem>
367 <listitem><para>
368 <parameter>requisite:</parameter> Like required, except that if such a module returns a
369 failure, control is directly returned to the application. The return value is that associated with
370 the first required or requisite module to fail. This flag can be used to protect against the
371 possibility of a user getting the opportunity to enter a password over an unsafe medium. It is
372 conceivable that such behavior might inform an attacker of valid accounts on a system. This
373 possibility should be weighed against the not insignificant concerns of exposing a sensitive
374 password in a hostile environment.
375 </para></listitem>
377 <listitem><para>
378 <parameter>sufficient:</parameter> The success of this module is deemed <parameter>sufficient</parameter> to satisfy
379 the Linux-PAM library that this module-type has succeeded in its purpose. In the event that no
380 previous required module has failed, no more <quote>stacked</quote> modules of this type are invoked.
381 (In this case, subsequent required modules are not invoked). A failure of this module is not deemed
382 as fatal to satisfying the application that this module-type has succeeded.
383 </para></listitem>
385 <listitem><para>
386 <parameter>optional:</parameter> As its name suggests, this control-flag marks the module as not
387 being critical to the success or failure of the user's application for service. In general,
388 Linux-PAM ignores such a module when determining if the module stack will succeed or fail.
389 However, in the absence of any definite successes or failures of previous or subsequent stacked
390 modules, this module will determine the nature of the response to the application. One example of
391 this latter case is when the other modules return something like PAM_IGNORE.
392 </para></listitem>
393 </itemizedlist>
395 <para>
396 The more elaborate (newer) syntax is much more specific and gives the administrator a great deal of control
397 over how the user is authenticated. This form of the control-flag is delimited with square brackets and
398 consists of a series of <parameter>value=action</parameter> tokens:
399 </para>
401 <para><programlisting>
402 [value1=action1 value2=action2 ...]
403 </programlisting></para>
405 <para>
406 Here, <parameter>value1</parameter> is one of the following return values:
407 <screen>
408 <parameter>success; open_err; symbol_err; service_err; system_err; buf_err;</parameter>
409 <parameter>perm_denied; auth_err; cred_insufficient; authinfo_unavail;</parameter>
410 <parameter>user_unknown; maxtries; new_authtok_reqd; acct_expired; session_err;</parameter>
411 <parameter>cred_unavail; cred_expired; cred_err; no_module_data; conv_err;</parameter>
412 <parameter>authtok_err; authtok_recover_err; authtok_lock_busy;</parameter>
413 <parameter>authtok_disable_aging; try_again; ignore; abort; authtok_expired;</parameter>
414 <parameter>module_unknown; bad_item;</parameter> and <parameter>default</parameter>.
415 </screen>
416 </para>
418 <para>
419 The last of these (<parameter>default</parameter>) can be used to set the action for those return values that are not explicitly defined.
420 </para>
422 <para>
423 The <parameter>action1</parameter> can be a positive integer or one of the following tokens:
424 <parameter>ignore</parameter>; <parameter>ok</parameter>; <parameter>done</parameter>;
425 <parameter>bad</parameter>; <parameter>die</parameter>; and <parameter>reset</parameter>.
426 A positive integer, J, when specified as the action, can be used to indicate that the next J modules of the
427 current module-type will be skipped. In this way, the administrator can develop a moderately sophisticated
428 stack of modules with a number of different paths of execution. Which path is taken can be determined by the
429 reactions of individual modules.
430 </para>
432 <itemizedlist>
433 <listitem><para>
434 <parameter>ignore:</parameter> When used with a stack of modules, the module's return status will not
435 contribute to the return code the application obtains.
436 </para></listitem>
438 <listitem><para>
439 <parameter>bad:</parameter> This action indicates that the return code should be thought of as indicative
440 of the module failing. If this module is the first in the stack to fail, its status value will be used
441 for that of the whole stack.
442 </para></listitem>
444 <listitem><para>
445 <parameter>die:</parameter> Equivalent to bad with the side effect of terminating the module stack and
446 PAM immediately returning to the application.
447 </para></listitem>
449 <listitem><para>
450 <parameter>ok:</parameter> This tells PAM that the administrator thinks this return code should
451 contribute directly to the return code of the full stack of modules. In other words, if the former
452 state of the stack would lead to a return of PAM_SUCCESS, the module's return code will override
453 this value. Note, if the former state of the stack holds some value that is indicative of a module's
454 failure, this <parameter>ok</parameter> value will not be used to override that value.
455 </para></listitem>
457 <listitem><para>
458 <parameter>done:</parameter> Equivalent to <parameter>ok</parameter> with the side effect of terminating the module stack and
459 PAM immediately returning to the application.
460 </para></listitem>
462 <listitem><para>
463 <parameter>reset:</parameter> Clears all memory of the state of the module stack and starts again with
464 the next stacked module.
465 </para></listitem>
466 </itemizedlist>
468 <para>
469 Each of the four keywords, <parameter>required</parameter>; <parameter>requisite</parameter>;
470 <parameter>sufficient</parameter>; and <parameter>optional</parameter>, have an equivalent expression in terms
471 of the [...] syntax. They are as follows:
472 </para>
474 <para>
475 <itemizedlist>
476 <listitem><para>
477 <parameter>required</parameter> is equivalent to <parameter>[success=ok new_authtok_reqd=ok ignore=ignore default=bad]</parameter>.
478 </para></listitem>
480 <listitem><para>
481 <parameter>requisite</parameter> is equivalent to <parameter>[success=ok new_authtok_reqd=ok ignore=ignore default=die]</parameter>.
482 </para></listitem>
484 <listitem><para>
485 <parameter>sufficient</parameter> is equivalent to <parameter>[success=done new_authtok_reqd=done default=ignore]</parameter>.
486 </para></listitem>
488 <listitem><para>
489 <parameter>optional</parameter> is equivalent to <parameter>[success=ok new_authtok_reqd=ok default=ignore]</parameter>.
490 </para></listitem>
491 </itemizedlist>
492 </para>
494 <para>
495 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,
496 the notion of client plug-in agents was introduced. This makes it possible for PAM to support
497 machine-machine authentication using the transport protocol inherent to the client/server application. With the
498 <parameter>[ ... value=action ... ]</parameter> control syntax, it is possible for an application to be configured
499 to support binary prompts with compliant clients, but to gracefully fail over into an alternative authentication
500 mode for legacy applications.
501 </para>
502 </listitem>
503 </varlistentry>
505 <varlistentry><term>module-path</term><listitem>
506 <para>
507 The pathname of the dynamically loadable object file; the pluggable module itself. If the first character of the
508 module path is <quote>/</quote>, it is assumed to be a complete path. If this is not the case, the given module path is appended
509 to the default module path: <filename>/lib/security</filename> (but see the previous notes).
510 </para>
512 <para>
513 The arguments are a list of tokens that are passed to the module when it is invoked, much like arguments to a typical
514 Linux shell command. Generally, valid arguments are optional and are specific to any given module. Invalid arguments
515 are ignored by a module; however, when encountering an invalid argument, the module is required to write an error
516 to syslog(3). For a list of generic options, see the next section.
517 </para>
519 <para>
520 If you wish to include spaces in an argument, you should surround that argument with square brackets. For example:
521 </para>
523 <para><programlisting>
524 squid auth required pam_mysql.so user=passwd_query passwd=mada \
525 db=eminence [query=select user_name from internet_service where \
526 user_name=<quote>%u</quote> and password=PASSWORD(<quote>%p</quote>) and service=<quote>web_proxy</quote>]
527 </programlisting></para>
529 <para>
530 When using this convention, you can include <quote>[</quote> characters inside the string, and if you wish to have a <quote>]</quote>
531 character inside the string that will survive the argument parsing, you should use <quote>\[</quote>. In other words,
532 </para>
534 <para><programlisting>
535 [..[..\]..] --> ..[..]..
536 </programlisting></para>
538 <para>
539 Any line in one of the configuration files that is not formatted correctly will generally tend (erring on the
540 side of caution) to make the authentication process fail. A corresponding error is written to the system log files
541 with a call to syslog(3).
542 </para>
543 </listitem>
544 </varlistentry>
545 </variablelist>
547 </sect3>
549 </sect2>
551 <sect2>
552 <title>Example System Configurations</title>
554 <para>
555 The following is an example <filename>/etc/pam.d/login</filename> configuration file.
556 This example had all options uncommented and is probably not usable
557 because it stacks many conditions before allowing successful completion
558 of the login process. Essentially, all conditions can be disabled
559 by commenting them out, except the calls to <filename>pam_pwdb.so</filename>.
560 </para>
562 <sect3>
563 <title>PAM: Original Login Config</title>
565 <para>
566 <programlisting>
567 #%PAM-1.0
568 # The PAM configuration file for the <quote>login</quote> service
569 #
570 auth required pam_securetty.so
571 auth required pam_nologin.so
572 # auth required pam_dialup.so
573 # auth optional pam_mail.so
574 auth required pam_pwdb.so shadow md5
575 # account requisite pam_time.so
576 account required pam_pwdb.so
577 session required pam_pwdb.so
578 # session optional pam_lastlog.so
579 # password required pam_cracklib.so retry=3
580 password required pam_pwdb.so shadow md5
581 </programlisting>
582 </para>
584 </sect3>
586 <sect3>
587 <title>PAM: Login Using <filename>pam_smbpass</filename></title>
589 <para>
590 PAM allows use of replaceable modules. Those available on a sample system include:
591 </para>
593 <para><prompt>$</prompt><userinput>/bin/ls /lib/security</userinput>
594 <programlisting>
595 pam_access.so pam_ftp.so pam_limits.so
596 pam_ncp_auth.so pam_rhosts_auth.so pam_stress.so
597 pam_cracklib.so pam_group.so pam_listfile.so
598 pam_nologin.so pam_rootok.so pam_tally.so
599 pam_deny.so pam_issue.so pam_mail.so
600 pam_permit.so pam_securetty.so pam_time.so
601 pam_dialup.so pam_lastlog.so pam_mkhomedir.so
602 pam_pwdb.so pam_shells.so pam_unix.so
603 pam_env.so pam_ldap.so pam_motd.so
604 pam_radius.so pam_smbpass.so pam_unix_acct.so
605 pam_wheel.so pam_unix_auth.so pam_unix_passwd.so
606 pam_userdb.so pam_warn.so pam_unix_session.so
607 </programlisting></para>
609 <para>
610 The following example for the login program replaces the use of
611 the <filename>pam_pwdb.so</filename> module that uses the system
612 password database (<filename>/etc/passwd</filename>,
613 <filename>/etc/shadow</filename>, <filename>/etc/group</filename>) with
614 the module <filename>pam_smbpass.so</filename>, which uses the Samba
615 database containing the Microsoft MD4 encrypted password
616 hashes. This database is stored either in
617 <filename>/usr/local/samba/private/smbpasswd</filename>,
618 <filename>/etc/samba/smbpasswd</filename> or in
619 <filename>/etc/samba.d/smbpasswd</filename>, depending on the
620 Samba implementation for your UNIX/Linux system. The
621 <filename>pam_smbpass.so</filename> module is provided by
622 Samba version 2.2.1 or later. It can be compiled by specifying the
623 <option>--with-pam_smbpass</option> options when running Samba's
624 <command>configure</command> script. For more information
625 on the <filename>pam_smbpass</filename> module, see the documentation
626 in the <filename>source/pam_smbpass</filename> directory of the Samba
627 source distribution.
628 </para>
630 <para>
631 <programlisting>
632 #%PAM-1.0
633 # The PAM configuration file for the <quote>login</quote> service
634 #
635 auth required pam_smbpass.so nodelay
636 account required pam_smbpass.so nodelay
637 session required pam_smbpass.so nodelay
638 password required pam_smbpass.so nodelay
639 </programlisting></para>
641 <para>
642 The following is the PAM configuration file for a particular
643 Linux system. The default condition uses <filename>pam_pwdb.so</filename>.
644 </para>
646 <para>
647 <programlisting>
648 #%PAM-1.0
649 # The PAM configuration file for the <quote>samba</quote> service
650 #
651 auth required pam_pwdb.so nullok nodelay shadow audit
652 account required pam_pwdb.so audit nodelay
653 session required pam_pwdb.so nodelay
654 password required pam_pwdb.so shadow md5
655 </programlisting></para>
657 <para>
658 In the following example, the decision has been made to use the
659 <command>smbpasswd</command> database even for basic Samba authentication. Such a
660 decision could also be made for the <command>passwd</command> program and would
661 thus allow the <command>smbpasswd</command> passwords to be changed using the
662 <command>passwd</command> program:
663 </para>
665 <para>
666 <programlisting>
667 #%PAM-1.0
668 # The PAM configuration file for the <quote>samba</quote> service
669 #
670 auth required pam_smbpass.so nodelay
671 account required pam_pwdb.so audit nodelay
672 session required pam_pwdb.so nodelay
673 password required pam_smbpass.so nodelay smbconf=/etc/samba.d/smb.conf
674 </programlisting>
675 </para>
677 <note><para>PAM allows stacking of authentication mechanisms. It is
678 also possible to pass information obtained within one PAM module through
679 to the next module in the PAM stack. Please refer to the documentation for
680 your particular system implementation for details regarding the specific
681 capabilities of PAM in this environment. Some Linux implementations also
682 provide the <filename>pam_stack.so</filename> module that allows all
683 authentication to be configured in a single central file. The
684 <filename>pam_stack.so</filename> method has some devoted followers
685 on the basis that it allows for easier administration. As with all issues in
686 life, though, every decision has trade-offs, so you may want to examine the
687 PAM documentation for further helpful information.
688 </para></note>
690 </sect3>
692 </sect2>
694 <sect2>
695 <title>&smb.conf; PAM Configuration</title>
697 <para>
698 There is an option in &smb.conf; called <smbconfoption name="obey pam restrictions"/>.
699 The following is from the online help for this option in SWAT:
700 </para>
702 <blockquote>
703 <para>
704 When Samba is configured to enable PAM support (i.e., <option>--with-pam</option>), this parameter will
705 control whether or not Samba should obey PAM's account and session management directives. The default behavior
706 is to use PAM for clear-text authentication only and to ignore any account or session management. Samba always
707 ignores PAM for authentication in the case of <smbconfoption name="encrypt passwords">yes</smbconfoption>.
708 The reason is that PAM modules cannot support the challenge/response authentication mechanism needed in the presence of SMB
709 password encryption.
710 </para>
712 <para>Default: <smbconfoption name="obey pam restrictions">no</smbconfoption></para>
713 </blockquote>
715 </sect2>
717 <sect2>
718 <title>Remote CIFS Authentication Using <filename>winbindd.so</filename></title>
720 <para>
721 All operating systems depend on the provision of user credentials acceptable to the platform.
722 UNIX requires the provision of a user identifier (UID) as well as a group identifier (GID).
723 These are both simple integer numbers that are obtained from a password backend such
724 as <filename>/etc/passwd</filename>.
725 </para>
727 <para>
728 Users and groups on a Windows NT server are assigned a relative ID (RID) which is unique for
729 the domain when the user or group is created. To convert the Windows NT user or group into
730 a UNIX user or group, a mapping between RIDs and UNIX user and group IDs is required. This
731 is one of the jobs that winbind performs.
732 </para>
734 <para>
735 As winbind users and groups are resolved from a server, user and group IDs are allocated
736 from a specified range. This is done on a first come, first served basis, although all
737 existing users and groups will be mapped as soon as a client performs a user or group
738 enumeration command. The allocated UNIX IDs are stored in a database file under the Samba
739 lock directory and will be remembered.
740 </para>
742 <para>
743 The astute administrator will realize from this that the combination of <filename>pam_smbpass.so</filename>,
744 <command>winbindd</command>, and a distributed <smbconfoption name="passdb backend"></smbconfoption>
745 such as <parameter>ldap</parameter> will allow the establishment of a centrally managed, distributed user/password
746 database that can also be used by all PAM-aware (e.g., Linux) programs and applications. This arrangement can have
747 particularly potent advantages compared with the use of Microsoft Active Directory Service (ADS) insofar as
748 the reduction of wide-area network authentication traffic.
749 </para>
751 <warning><para>
752 The RID to UNIX ID database is the only location where the user and group mappings are
753 stored by <command>winbindd</command>. If this file is deleted or corrupted, there is no way for <command>winbindd</command>
754 to determine which user and group IDs correspond to Windows NT user and group RIDs.
755 </para></warning>
757 </sect2>
759 <sect2>
760 <title>Password Synchronization Using <filename>pam_smbpass.so</filename></title>
762 <para>
763 <filename>pam_smbpass</filename> is a PAM module that can be used on conforming systems to
764 keep the <filename>smbpasswd</filename> (Samba password) database in sync with the UNIX
765 password file. PAM is an API supported
766 under some UNIX operating systems, such as Solaris, HPUX, and Linux, that provides a
767 generic interface to authentication mechanisms.
768 </para>
770 <para>
771 This module authenticates a local <filename>smbpasswd</filename> user database. If you require
772 support for authenticating against a remote SMB server, or if you are
773 concerned about the presence of SUID root binaries on your system, it is
774 recommended that you use <filename>pam_winbind</filename> instead.
775 </para>
777 <para>
778 Options recognized by this module are shown in <link linkend="smbpassoptions">next table</link>.
779 <table frame="all" id="smbpassoptions">
780 <title>Options recognized by <parameter>pam_smbpass</parameter></title>
781 <tgroup cols="2" align="left">
782 <colspec align="left"/>
783 <colspec align="justify" colwidth="1*"/>
784 <tbody>
785 <row><entry>debug</entry><entry>Log more debugging info.</entry></row>
786 <row><entry>audit</entry><entry>Like debug, but also logs unknown usernames.</entry></row>
787 <row><entry>use_first_pass</entry><entry>Do not prompt the user for passwords; take them from PAM_ items instead.</entry></row>
788 <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>
789 <row><entry>use_authtok</entry>
790 <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>
791 <row><entry>not_set_pass</entry><entry>Do not make passwords used by this module available to other modules.</entry></row>
792 <row><entry>nodelay</entry><entry>dDo not insert ~1-second delays on authentication failure.</entry></row>
793 <row><entry>nullok</entry><entry>Null passwords are allowed.</entry></row>
794 <row><entry>nonull</entry><entry>Null passwords are not allowed. Used to override the Samba configuration.</entry></row>
795 <row><entry>migrate</entry><entry>Only meaningful in an <quote>auth</quote> context; used to update smbpasswd file with a password used for successful authentication.</entry></row>
796 <row><entry>smbconf=<replaceable>file</replaceable></entry><entry>Specify an alternate path to the &smb.conf; file.</entry></row>
797 </tbody>
798 </tgroup>
799 </table>
800 </para>
802 <para>
803 The following are examples of the use of <filename>pam_smbpass.so</filename> in the format of the Linux
804 <filename>/etc/pam.d/</filename> files structure. Those wishing to implement this
805 tool on other platforms will need to adapt this appropriately.
806 </para>
808 <sect3>
809 <title>Password Synchronization Configuration</title>
811 <para>
812 The following is a sample PAM configuration that shows the use of pam_smbpass to make
813 sure <filename>private/smbpasswd</filename> is kept in sync when <filename>/etc/passwd (/etc/shadow)</filename>
814 is changed. It is useful when an expired password might be changed by an
815 application (such as <command>ssh</command>).
816 </para>
818 <para>
819 <programlisting>
820 #%PAM-1.0
821 # password-sync
822 #
823 auth requisite pam_nologin.so
824 auth required pam_unix.so
825 account required pam_unix.so
826 password requisite pam_cracklib.so retry=3
827 password requisite pam_unix.so shadow md5 use_authtok try_first_pass
828 password required pam_smbpass.so nullok use_authtok try_first_pass
829 session required pam_unix.so
830 </programlisting></para>
831 </sect3>
833 <sect3>
834 <title>Password Migration Configuration</title>
836 <para>
837 The following PAM configuration shows the use of <filename>pam_smbpass</filename> to migrate
838 from plaintext to encrypted passwords for Samba. Unlike other methods,
839 this can be used for users who have never connected to Samba shares:
840 password migration takes place when users <command>ftp</command> in, login using <command>ssh</command>, pop
841 their mail, and so on.
842 </para>
844 <para>
845 <programlisting>
846 #%PAM-1.0
847 # password-migration
848 #
849 auth requisite pam_nologin.so
850 # pam_smbpass is called IF pam_unix succeeds.
851 auth requisite pam_unix.so
852 auth optional pam_smbpass.so migrate
853 account required pam_unix.so
854 password requisite pam_cracklib.so retry=3
855 password requisite pam_unix.so shadow md5 use_authtok try_first_pass
856 password optional pam_smbpass.so nullok use_authtok try_first_pass
857 session required pam_unix.so
858 </programlisting></para>
859 </sect3>
861 <sect3>
862 <title>Mature Password Configuration</title>
864 <para>
865 The following is a sample PAM configuration for a mature <filename>smbpasswd</filename> installation.
866 <filename>private/smbpasswd</filename> is fully populated, and we consider it an error if
867 the SMB password does not exist or does not match the UNIX password.
868 </para>
870 <para>
871 <programlisting>
872 #%PAM-1.0
873 # password-mature
874 #
875 auth requisite pam_nologin.so
876 auth required pam_unix.so
877 account required pam_unix.so
878 password requisite pam_cracklib.so retry=3
879 password requisite pam_unix.so shadow md5 use_authtok try_first_pass
880 password required pam_smbpass.so use_authtok use_first_pass
881 session required pam_unix.so
882 </programlisting></para>
883 </sect3>
885 <sect3>
886 <title>Kerberos Password Integration Configuration</title>
888 <para>
889 The following is a sample PAM configuration that shows <parameter>pam_smbpass</parameter> used together with
890 <parameter>pam_krb5</parameter>. This could be useful on a Samba PDC that is also a member of
891 a Kerberos realm.
892 </para>
894 <para>
895 <programlisting>
896 #%PAM-1.0
897 # kdc-pdc
898 #
899 auth requisite pam_nologin.so
900 auth requisite pam_krb5.so
901 auth optional pam_smbpass.so migrate
902 account required pam_krb5.so
903 password requisite pam_cracklib.so retry=3
904 password optional pam_smbpass.so nullok use_authtok try_first_pass
905 password required pam_krb5.so use_authtok try_first_pass
906 session required pam_krb5.so
907 </programlisting></para>
909 </sect3>
911 </sect2>
913 </sect1>
915 <sect1>
916 <title>Common Errors</title>
918 <para>
919 PAM can be fickle and sensitive to configuration glitches. Here we look at a few cases from
920 the Samba mailing list.
921 </para>
923 <sect2>
924 <title>pam_winbind Problem</title>
926 <para>
927 A user reported, <emphasis>I have the following PAM configuration</emphasis>:
928 </para>
930 <para>
931 <programlisting>
932 auth required /lib/security/pam_securetty.so
933 auth sufficient /lib/security/pam_winbind.so
934 auth sufficient /lib/security/pam_unix.so use_first_pass nullok
935 auth required /lib/security/pam_stack.so service=system-auth
936 auth required /lib/security/pam_nologin.so
937 account required /lib/security/pam_stack.so service=system-auth
938 account required /lib/security/pam_winbind.so
939 password required /lib/security/pam_stack.so service=system-auth
940 </programlisting>
941 </para>
943 <para>
944 <emphasis>When I open a new console with [ctrl][alt][F1], I can't log in with my user <quote>pitie.</quote>
945 I have tried with user <quote>scienceu\pitie</quote> also.</emphasis>
946 </para>
948 <para>
949 The problem may lie with the inclusion of <parameter>pam_stack.so
950 service=system-auth</parameter>. That file often contains a lot of stuff that may
951 duplicate what you are already doing. Try commenting out the <parameter>pam_stack</parameter> lines
952 for <parameter>auth</parameter> and <parameter>account</parameter> and see if things work. If they do, look at
953 <filename>/etc/pam.d/system-auth</filename> and copy only what you need from it into your
954 <filename>/etc/pam.d/login</filename> file. Alternatively, if you want all services to use
955 Winbind, you can put the Winbind-specific stuff in <filename>/etc/pam.d/system-auth</filename>.
956 </para>
958 </sect2>
960 <sect2>
961 <title>Winbind Is Not Resolving Users and Groups</title>
963 <para>
964 <quote>
965 My &smb.conf; file is correctly configured. I have specified
966 <smbconfoption name="idmap uid">12000</smbconfoption>
967 and <smbconfoption name="idmap gid">3000-3500,</smbconfoption>
968 and <command>winbind</command> is running. When I do the following it all works fine.
969 </quote>
970 </para>
972 <para><screen>
973 &rootprompt;<userinput>wbinfo -u</userinput>
974 MIDEARTH\maryo
975 MIDEARTH\jackb
976 MIDEARTH\ameds
977 ...
978 MIDEARTH\root
980 &rootprompt;<userinput>wbinfo -g</userinput>
981 MIDEARTH\Domain Users
982 MIDEARTH\Domain Admins
983 MIDEARTH\Domain Guests
984 ...
985 MIDEARTH\Accounts
987 &rootprompt;<userinput>getent passwd</userinput>
988 root:x:0:0:root:/root:/bin/bash
989 bin:x:1:1:bin:/bin:/bin/bash
990 ...
991 maryo:x:15000:15003:Mary Orville:/home/MIDEARTH/maryo:/bin/false
992 </screen></para>
994 <para>
995 <quote>
996 But this command fails:
997 </quote>
998 <screen>
999 &rootprompt;<userinput>chown maryo a_file</userinput>
1000 chown: 'maryo': invalid user
1001 </screen>
1002 <quote>This is driving me nuts! What can be wrong?</quote>
1003 </para>
1005 <para>
1006 Your system is likely running <command>nscd</command>, the name service
1007 caching daemon. Shut it down, do not restart it! You will find your problem resolved.
1008 </para>
1010 </sect2>
1011 </sect1>
1013 </chapter>