summaryrefslogtreecommitdiff
path: root/docs/htmldocs/securitylevels.html
blob: 256df33ce4f42bb49d0cbd87fbfa26d7cea4ce10 (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
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML
><HEAD
><TITLE
>Samba as Stand-Alone Server</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
REL="HOME"
TITLE="SAMBA Project Documentation"
HREF="samba-howto-collection.html"><LINK
REL="UP"
TITLE="Type of installation"
HREF="type.html"><LINK
REL="PREVIOUS"
TITLE="Nomenclature of Server Types"
HREF="servertype.html"><LINK
REL="NEXT"
TITLE="Samba as an NT4 or Win2k Primary Domain Controller"
HREF="samba-pdc.html"></HEAD
><BODY
CLASS="CHAPTER"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>SAMBA Project Documentation</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="servertype.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="samba-pdc.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="CHAPTER"
><H1
><A
NAME="SECURITYLEVELS"
></A
>Chapter 5. Samba as Stand-Alone Server</H1
><P
>In this section the function and purpose of Samba's <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>security</I
></SPAN
>
modes are described.</P
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN766"
>5.1. User and Share security level</A
></H1
><P
>A SMB server tells the client at startup what "security level" it is
running. There are two options "share level" and "user level". Which
of these two the client receives affects the way the client then tries
to authenticate itself. It does not directly affect (to any great
extent) the way the Samba server does security. I know this is
strange, but it fits in with the client/server approach of SMB. In SMB
everything is initiated and controlled by the client, and the server
can only tell the client what is available and whether an action is
allowed. </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN769"
>5.1.1. User Level Security</A
></H2
><P
>I'll describe user level security first, as its simpler. In user level
security the client will send a "session setup" command directly after
the protocol negotiation. This contains a username and password. The
server can either accept or reject that username/password
combination. Note that at this stage the server has no idea what
share the client will eventually try to connect to, so it can't base
the "accept/reject" on anything other than:</P
><P
></P
><OL
TYPE="1"
><LI
><P
>the username/password</P
></LI
><LI
><P
>the machine that the client is coming from</P
></LI
></OL
><P
>If the server accepts the username/password then the client expects to
be able to mount any share (using a "tree connection") without
specifying a password. It expects that all access rights will be as
the username/password specified in the "session setup". </P
><P
>It is also possible for a client to send multiple "session setup"
requests. When the server responds it gives the client a "uid" to use
as an authentication tag for that username/password. The client can
maintain multiple authentication contexts in this way (WinDD is an
example of an application that does this)</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN779"
>5.1.2. Share Level Security</A
></H2
><P
>Ok, now for share level security. In share level security the client
authenticates itself separately for each share. It will send a
password along with each "tree connection" (share mount). It does not
explicitly send a username with this operation. The client is
expecting a password to be associated with each share, independent of
the user. This means that samba has to work out what username the
client probably wants to use. It is never explicitly sent the
username. Some commercial SMB servers such as NT actually associate
passwords directly with shares in share level security, but samba
always uses the unix authentication scheme where it is a
username/password that is authenticated, not a "share/password".</P
><P
>Many clients send a "session setup" even if the server is in share
level security. They normally send a valid username but no
password. Samba records this username in a list of "possible
usernames". When the client then does a "tree connection" it also adds
to this list the name of the share they try to connect to (useful for
home directories) and any users listed in the <B
CLASS="COMMAND"
>user =</B
> <TT
CLASS="FILENAME"
>smb.conf</TT
>
line. The password is then checked in turn against these "possible
usernames". If a match is found then the client is authenticated as
that user.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN785"
>5.1.3. Server Level Security</A
></H2
><P
>Finally "server level" security. In server level security the samba
server reports to the client that it is in user level security. The
client then does a "session setup" as described earlier. The samba
server takes the username/password that the client sends and attempts
to login to the "password server" by sending exactly the same
username/password that it got from the client. If that server is in
user level security and accepts the password then samba accepts the
clients connection. This allows the samba server to use another SMB
server as the "password server". </P
><P
>You should also note that at the very start of all this, where the
server tells the client what security level it is in, it also tells
the client if it supports encryption. If it does then it supplies the
client with a random "cryptkey". The client will then send all
passwords in encrypted form. You have to compile samba with encryption
enabled to support this feature, and you have to maintain a separate
smbpasswd file with SMB style encrypted passwords. It is
cryptographically impossible to translate from unix style encryption
to SMB style encryption, although there are some fairly simple management
schemes by which the two could be kept in sync.</P
><P
>"security = server" means that Samba reports to clients that
it is running in "user mode" but actually passes off all authentication
requests to another "user mode" server. This requires an additional
parameter "password server =" that points to the real authentication server.
That real authentication server can be another Samba server or can be a
Windows NT server, the later natively capable of encrypted password support.</P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN790"
>5.1.3.1. Configuring Samba for Seemless Windows Network Integration</A
></H3
><P
>MS Windows clients may use encrypted passwords as part of a challenege/response
authentication model (a.k.a. NTLMv1) or alone, or clear text strings for simple
password based authentication. It should be realized that with the SMB protocol
the password is passed over the network either in plain text or encrypted, but
not both in the same authentication requests.</P
><P
>When encrypted passwords are used a password that has been entered by the user
is encrypted in two ways:</P
><P
></P
><UL
><LI
><P
>An MD4 hash of the UNICODE of the password
	string.  This is known as the NT hash.
	</P
></LI
><LI
><P
>The password is converted to upper case,
	and then padded or trucated to 14 bytes.  This string is 
	then appended with 5 bytes of NULL characters and split to
	form two 56 bit DES keys to encrypt a "magic" 8 byte value.
	The resulting 16 bytes for the LanMan hash.
	</P
></LI
></UL
><P
>MS Windows 95 pre-service pack 1, MS Windows NT versions 3.x and version 4.0
pre-service pack 3 will use either mode of password authentication. All
versions of MS Windows that follow these versions no longer support plain
text passwords by default.</P
><P
>MS Windows clients have a habit of dropping network mappings that have been idle
for 10 minutes or longer. When the user attempts to use the mapped drive
connection that has been dropped, the client re-establishes the connection using
a cached copy of the password.</P
><P
>When Microsoft changed the default password mode, support was dropped for caching
of the plain text password. This means that when the registry parameter is changed
to re-enable use of plain text passwords it appears to work, but when a dropped
service connection mapping attempts to revalidate it will fail if the remote
authentication server does not support encrypted passwords.  This means that it
is definitely not a good idea to re-enable plain text password support in such clients.</P
><P
>The following parameters can be used to work around the issue of Windows 9x client
upper casing usernames and password before transmitting them to the SMB server
when using clear text authentication.</P
><P
><PRE
CLASS="PROGRAMLISTING"
>	<A
HREF="smb.conf.5.html#PASSWORDLEVEL"
TARGET="_top"
>passsword level</A
> = <VAR
CLASS="REPLACEABLE"
>integer</VAR
>
	<A
HREF="smb.conf.5.html#USERNAMELEVEL"
TARGET="_top"
>username level</A
> = <VAR
CLASS="REPLACEABLE"
>integer</VAR
></PRE
></P
><P
>By default Samba will lower case the username before attempting to lookup the user
in the database of local system accounts.  Because UNIX usernames conventionally
only contain lower case character, the <VAR
CLASS="PARAMETER"
>username level</VAR
> parameter
is rarely needed.</P
><P
>However, passwords on UNIX systems often make use of mixed case characters. 
This means that in order for a user on a Windows 9x client to connect to a Samba
server using clear text authentication, the <VAR
CLASS="PARAMETER"
>password level</VAR
>
must be set to the maximum number of upper case letter which <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>could</I
></SPAN
>
appear is a password.  Note that is the server OS uses the traditional DES version
of crypt(), then a <VAR
CLASS="PARAMETER"
>password level</VAR
> of 8 will result in case
insensitive passwords as seen from Windows users.  This will also result in longer
login times as Samba hash to compute the permutations of the password string and 
try them one by one until a match is located (or all combinations fail).</P
><P
>The best option to adopt is to enable support for encrypted passwords 
where ever Samba is used. There are three configuration possibilities 
for support of encrypted passwords:</P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN816"
>5.1.3.2. Use MS Windows NT as an authentication server</A
></H3
><P
>This method involves the additions of the following parameters in the <TT
CLASS="FILENAME"
>smb.conf</TT
> file:</P
><P
><PRE
CLASS="PROGRAMLISTING"
>	encrypt passwords = Yes
	security = server
	password server = "NetBIOS_name_of_PDC"</PRE
></P
><P
>There are two ways of identifying whether or not a username and 
password pair was valid or not. One uses the reply information provided 
as part of the authentication messaging process, the other uses 
just and error code.</P
><P
>The down-side of this mode of configuration is the fact that 
for security reasons Samba will send the password server a bogus 
username and a bogus password and if the remote server fails to 
reject the username and password pair then an alternative mode 
of identification of validation is used. Where a site uses password 
lock out after a certain number of failed authentication attempts 
this will result in user lockouts.</P
><P
>Use of this mode of authentication does require there to be 
a standard Unix account for the user, this account can be blocked 
to prevent logons by other than MS Windows clients.</P
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN825"
>5.1.4. Domain Level Security</A
></H2
><P
>When samba is operating in <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>security = domain</I
></SPAN
> mode this means that
the Samba server has a domain security trust account (a machine account) and will cause
all authentication requests to be passed through to the domain controllers.</P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN829"
>5.1.4.1. Samba as a member of an MS Windows NT security domain</A
></H3
><P
>This method involves additon of the following paramters in the <TT
CLASS="FILENAME"
>smb.conf</TT
> file:</P
><P
><PRE
CLASS="PROGRAMLISTING"
>	encrypt passwords = Yes
	security = domain
	workgroup = "name of NT domain"
	password server = *</PRE
></P
><P
>The use of the "*" argument to <B
CLASS="COMMAND"
>password server</B
> will cause samba to locate the
domain controller in a way analogous to the way this is done within MS Windows NT.
This is the default behaviour.</P
><P
>In order for this method to work the Samba server needs to join the 
MS Windows NT security domain. This is done as follows:</P
><P
></P
><UL
><LI
><P
>On the MS Windows NT domain controller using 
	the Server Manager add a machine account for the Samba server.
	</P
></LI
><LI
><P
>Next, on the Linux system execute: 
	<B
CLASS="COMMAND"
>smbpasswd -r PDC_NAME -j DOMAIN_NAME</B
>
	</P
></LI
></UL
><P
>Use of this mode of authentication does require there to be a standard Unix account
for the user in order to assign a uid once the account has been authenticated by
the remote Windows DC.  This account can be blocked to prevent logons by other than
MS Windows clients by things such as setting an invalid shell in the
<TT
CLASS="FILENAME"
>/etc/passwd</TT
> entry. </P
><P
>An alternative to assigning UIDs to Windows users on a Samba member server is
presented in the <A
HREF="winbind.html"
TARGET="_top"
>Winbind Overview</A
> chapter
in this HOWTO collection.</P
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN848"
>5.1.5. ADS Level Security</A
></H2
><P
>For information about the configuration option please refer to the entire section entitled
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>Samba as an ADS Domain Member.</I
></SPAN
></P
></DIV
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="servertype.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="samba-howto-collection.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="samba-pdc.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Nomenclature of Server Types</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="type.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Samba as an NT4 or Win2k Primary Domain Controller</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>