1
<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter�11.�Active Directory, Kerberos, and Security</title><link rel="stylesheet" href="../samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.74.0"><link rel="home" href="index.html" title="Samba-3 by Example"><link rel="up" href="RefSection.html" title="Part�III.�Reference Section"><link rel="prev" href="RefSection.html" title="Part�III.�Reference Section"><link rel="next" href="DomApps.html" title="Chapter�12.�Integrating Additional Services"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter�11.�Active Directory, Kerberos, and Security</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="RefSection.html">Prev</a>�</td><th width="60%" align="center">Part�III.�Reference Section</th><td width="20%" align="right">�<a accesskey="n" href="DomApps.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="kerberos"></a>Chapter�11.�Active Directory, Kerberos, and Security</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="kerberos.html#id2610586">Introduction</a></span></dt><dd><dl><dt><span class="sect2"><a href="kerberos.html#id2611237">Assignment Tasks</a></span></dt></dl></dd><dt><span class="sect1"><a href="kerberos.html#id2611253">Dissection and Discussion</a></span></dt><dd><dl><dt><span class="sect2"><a href="kerberos.html#id2611650">Technical Issues</a></span></dt></dl></dd><dt><span class="sect1"><a href="kerberos.html#ch10expl">Implementation</a></span></dt><dd><dl><dt><span class="sect2"><a href="kerberos.html#id2613280">Share Access Controls</a></span></dt><dt><span class="sect2"><a href="kerberos.html#id2613629">Share Definition Controls</a></span></dt><dt><span class="sect2"><a href="kerberos.html#id2614242">Share Point Directory and File Permissions</a></span></dt><dt><span class="sect2"><a href="kerberos.html#id2614655">Managing Windows 200x ACLs</a></span></dt><dt><span class="sect2"><a href="kerberos.html#id2615382">Key Points Learned</a></span></dt></dl></dd><dt><span class="sect1"><a href="kerberos.html#id2615516">Questions and Answers</a></span></dt></dl></div><p><a class="indexterm" name="id2610522"></a>
2
By this point in the book, you have been exposed to many Samba-3 features and capabilities.
3
More importantly, if you have implemented the examples given, you are well on your way to becoming
4
a Samba-3 networking guru who knows a lot about Microsoft Windows. If you have taken the time to
5
practice, you likely have thought of improvements and scenarios with which you can experiment. You
6
are rather well plugged in to the many flexible ways Samba can be used.
7
</p><p><a class="indexterm" name="id2610541"></a>
8
This is a book about Samba-3. Understandably, its intent is to present it in a positive light.
9
The casual observer might conclude that this book is one-eyed about Samba. It is what
10
would you expect? This chapter exposes some criticisms that have been raised concerning
11
the use of Samba. For each criticism, there are good answers and appropriate solutions.
13
Some criticism always comes from deep inside ranks that one would expect to be supportive of a particular
14
decision. Criticism can be expected from the outside. Let's see how the interesting dynamic of
15
criticism develops with respect to Abmas.
16
</p><p><a class="indexterm" name="id2610569"></a>
17
This chapter provides a shameless self-promotion of Samba-3. The objections raised were not pulled
18
out of thin air. They were drawn from comments made by Samba users and from criticism during
19
discussions with Windows network administrators. The tone of the objections reflects as closely
20
as possible that of the original. The case presented is a straw-man example that is designed to
21
permit each objection to be answered as it might occur in real life.
22
</p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2610586"></a>Introduction</h2></div></div></div><p><a class="indexterm" name="id2610593"></a><a class="indexterm" name="id2610601"></a><a class="indexterm" name="id2610609"></a><a class="indexterm" name="id2610616"></a><a class="indexterm" name="id2610624"></a>
23
Abmas is continuing its meteoric growth with yet further acquisitions. The investment community took
24
note of the spectacular projection of Abmas onto the global business stage. Abmas is building an
25
interesting portfolio of companies that includes accounting services, financial advice, investment
26
portfolio management, property insurance, risk assessment, and the recent addition of a a video rental
27
business. The pieces do not always appear to fit together, but Mr. Meany is certainly executing an
28
interesting business growth and development plan. Abmas Video Rentals was recently acquired.
29
During the time that the acquisition was closing, the Video Rentals business upgraded its Windows
30
NT4-based network to Windows 2003 Server and Active Directory.
31
</p><p><a class="indexterm" name="id2610649"></a>
32
You have accepted the fact that Abmas Video Rentals will use Microsoft Active Directory.
33
The IT team, led by Stan Soroka, is committed to Samba-3 and to maintaining a uniform technology platform.
34
Stan Soroka's team voiced its disapproval over the decision to permit this business to continue to
35
operate with a solution that is viewed by Christine and her group as “<span class="quote">an island of broken
36
technologies.</span>” This comment was made by one of Christine's staff as they were installing a new
37
Samba-3 server at the new business.
38
</p><p><a class="indexterm" name="id2610672"></a><a class="indexterm" name="id2610680"></a>
39
Abmas Video Rentals' head of IT heard of this criticism. He was offended that a junior engineer
40
should make such a comment. He felt that he had to prepare in case he might be criticized for his
41
decision to use Active Directory. He decided he would defend his decision by hiring the services
42
of an outside security systems consultant to report<sup>[<a name="id2610695" href="#ftn.id2610695" class="footnote">12</a>]</sup> on his unit's operations
43
and to investigate the role of Samba at his site. Here are key extracts from this hypothetical
45
</p><div class="blockquote"><blockquote class="blockquote"><p><a class="indexterm" name="id2610706"></a><a class="indexterm" name="id2610714"></a><a class="indexterm" name="id2610721"></a><a class="indexterm" name="id2610729"></a>
46
... the implementation of Microsoft Active Directory at the Abmas Video Rentals, Bamingsham site,
47
has been examined. We find no evidence to support a notion that vulnerabilities exist at your site.
48
... we took additional steps to validate the integrity of the installation and operation of Active
49
Directory and are pleased that your staff are following sound practices.
52
</p><p><a class="indexterm" name="id2610750"></a><a class="indexterm" name="id2610762"></a><a class="indexterm" name="id2610773"></a><a class="indexterm" name="id2610781"></a><a class="indexterm" name="id2610789"></a><a class="indexterm" name="id2610797"></a>
53
User and group accounts, and respective privileges, have been well thought out. File system shares are
54
appropriately secured. Backup and disaster recovery plans are well managed and validated regularly, and
55
effective off-site storage practices are considered to exceed industry norms.
56
</p><p><a class="indexterm" name="id2610813"></a><a class="indexterm" name="id2610821"></a><a class="indexterm" name="id2610829"></a>
57
Your staff are justifiably concerned that the use of Samba may compromise their good efforts to maintain
59
</p><p><a class="indexterm" name="id2610846"></a><a class="indexterm" name="id2610853"></a><a class="indexterm" name="id2610861"></a><a class="indexterm" name="id2610869"></a>
60
The recently installed Linux file and application server uses a tool called <code class="literal">winbind</code>
61
that is indiscriminate about security. All user accounts in Active Directory can be used to access data
62
stored on the Linux system. We are alarmed that secure information is accessible to staff who should
63
not even be aware that it exists. We share the concerns of your network management staff who have gone
64
to great lengths to set fine-grained controls that limit information access to those who need access.
65
It seems incongruous to us that Samba winbind should be permitted to be used considering that it voids this fine work.
66
</p><p><a class="indexterm" name="id2610909"></a><a class="indexterm" name="id2610917"></a><a class="indexterm" name="id2610925"></a>
67
Graham Judd [head of network administration] has locked down the security of all systems and is following
68
the latest Microsoft guidelines. ... null session connections have been disabled ... the internal network
69
is isolated from the outside world, the [product name removed] firewall is under current contract
70
maintenance support from [the manufacturer]. ... our attempts to penetrate security of your systems
71
failed to find problems common to Windows networking sites. We commend your staff on their attention to
72
detail and for following Microsoft recommended best practices.
75
</p><p><a class="indexterm" name="id2610949"></a><a class="indexterm" name="id2610957"></a><a class="indexterm" name="id2610965"></a><a class="indexterm" name="id2610973"></a>
76
Regarding the use of Samba, we offer the following comments: Samba is in use in nearly half of
77
all sites we have surveyed. ... It is our opinion that Samba offers no better security than Microsoft
78
... what worries us regarding Samba is the need to disable essential Windows security features such as
79
secure channel support, digital sign'n'seal on all communication traffic, and running Active Directory in
80
mixed mode so that Samba clients and servers can authenticate all of it. Additionally, we are concerned that
81
Samba is not at the full capabilities of Microsoft Windows NT4 server. Microsoft has moved well beyond that
82
with trusted computing initiatives that the Samba developers do not participate in.
83
</p><p><a class="indexterm" name="id2610996"></a><a class="indexterm" name="id2611004"></a><a class="indexterm" name="id2611012"></a><a class="indexterm" name="id2611020"></a><a class="indexterm" name="id2611028"></a><a class="indexterm" name="id2611036"></a><a class="indexterm" name="id2611044"></a>
84
One wonders about the integrity of an open source program that is developed by a team of hackers
85
who cannot be held accountable for the flaws in their code. The sheer number of updates and bug
86
fixes they have released should ring alarm bells in any business.
87
</p><p><a class="indexterm" name="id2611059"></a><a class="indexterm" name="id2611067"></a><a class="indexterm" name="id2611075"></a>
88
Another factor that should be considered is that buying Microsoft products and services helps to
89
provide employment in the IT industry. Samba and Open Source software place those jobs at risk.
90
</p></blockquote></div><p><a class="indexterm" name="id2611089"></a><a class="indexterm" name="id2611097"></a>
91
This is also a challenge to rise above the trouble spot. You call Stan's team together for a simple
92
discussion, but it gets further out of hand. When you return to your office, you find the following
96
</p><div class="blockquote"><table border="0" width="100%" cellspacing="0" cellpadding="0" class="blockquote" summary="Block quote"><tr><td width="10%" valign="top">�</td><td width="80%" valign="top"><p>
97
I apologize for the leak of internal discussions to the new business. It reflects poorly on our
98
professionalism and has put you in an unpleasant position. I regret the incident.
100
I also wish to advise that two of the recent recruits want to implement Kerberos authentication
101
across all systems. I concur with the desire to improve security. One of the new guys who is championing
102
the move to Kerberos was responsible for the comment that caused the embarrassment.
103
</p><p><a class="indexterm" name="id2611134"></a><a class="indexterm" name="id2611142"></a><a class="indexterm" name="id2611150"></a><a class="indexterm" name="id2611158"></a>
104
I am experiencing difficulty in handling the sharp push for Kerberos. He claims that Kerberos, OpenLDAP,
105
plus Samba-3 will seamlessly replace Microsoft Active Directory. I am a little out of my depth with respect
106
to the feasibility of such a move, but have taken steps to pull both of them into line. With your consent,
107
I would like to hire the services of a well-known Samba consultant to set the record straight.
108
</p><p><a class="indexterm" name="id2611176"></a><a class="indexterm" name="id2611184"></a><a class="indexterm" name="id2611192"></a><a class="indexterm" name="id2611200"></a><a class="indexterm" name="id2611208"></a><a class="indexterm" name="id2611216"></a>
109
I intend to use this report to answer the criticism raised and would like to establish a policy that we
110
will approve the use of Microsoft Windows Servers (and Active Directory) subject to all costs being covered
111
out of the budget of the division that wishes to go its own way. I propose that dissenters will still remain
112
responsible to meet the budgeted contribution to IT operations as a whole. I believe we should not coerce
113
use of any centrally proposed standards, but make all noncompliance the financial responsibility of the
114
out-of-step division. Hopefully, this will encourage all divisions to walk with us and not alone.
115
</p></td><td width="10%" valign="top">�</td></tr><tr><td width="10%" valign="top">�</td><td colspan="2" align="right" valign="top">--<span class="attribution">Stan</span></td></tr></table></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2611237"></a>Assignment Tasks</h3></div></div></div><p>
116
You agreed with Stan's recommendations and hired a consultant to help defuse the powder
117
keg. The consultant's task is to provide a tractable answer to each of the issues raised. The consultant must be able
118
to support his or her claims, keep emotions to the side, and answer technically.
119
</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2611253"></a>Dissection and Discussion</h2></div></div></div><p><a class="indexterm" name="id2611260"></a><a class="indexterm" name="id2611268"></a><a class="indexterm" name="id2611276"></a><a class="indexterm" name="id2611284"></a><a class="indexterm" name="id2611291"></a><a class="indexterm" name="id2611299"></a><a class="indexterm" name="id2611307"></a>
120
Samba-3 is a tool. No one is pounding your door to make you use Samba. That is a choice that you are free to
121
make or reject. It is likely that your decision to use Samba can greatly benefit your company.
122
The Samba Team obviously believes that the Samba software is a worthy choice.
123
If you hire a consultant to assist with the installation and/or deployment of Samba, or if you hire
124
someone to help manage your Samba installation, you can create income and employment. Alternately,
125
money saved by not spending in the IT area can be spent elsewhere in the business. All money saved
126
or spent creates employment.
127
</p><p><a class="indexterm" name="id2611329"></a><a class="indexterm" name="id2611337"></a><a class="indexterm" name="id2611345"></a><a class="indexterm" name="id2611353"></a><a class="indexterm" name="id2611361"></a>
128
In the long term, the use of Samba must be economically sustainable. In some situations, Samba is adopted
129
purely to provide file and print service interoperability on platforms that otherwise cannot provide
130
access to data and to printers for Microsoft Windows clients. Samba is used by some businesses to
131
effect a reduction in the cost of providing IT services. Obviously, it is also used by some as an
132
alternative to the use of a Microsoft file and print serving platforms with no consideration of costs.
133
</p><p><a class="indexterm" name="id2611381"></a><a class="indexterm" name="id2611389"></a><a class="indexterm" name="id2611397"></a><a class="indexterm" name="id2611405"></a>
134
It would be foolish to adopt a technology that might put any data or users at risk. Security affects
135
everyone. The Samba-Team is fully cognizant of the responsibility they have to their users.
136
The Samba documentation clearly reveals that full responsibility is accepted to fix anything
138
</p><p><a class="indexterm" name="id2611421"></a><a class="indexterm" name="id2611429"></a><a class="indexterm" name="id2611437"></a><a class="indexterm" name="id2611445"></a><a class="indexterm" name="id2611456"></a><a class="indexterm" name="id2611464"></a><a class="indexterm" name="id2611472"></a><a class="indexterm" name="id2611480"></a><a class="indexterm" name="id2611488"></a><a class="indexterm" name="id2611496"></a><a class="indexterm" name="id2611504"></a>
139
There is a mistaken perception in the IT industry that commercial software providers are fully
140
accountable for the defects in products. Open Source software comes with no warranty, so it is
141
often assumed that its use confers a higher degree of risk. Everyone should read commercial software
142
End User License Agreements (EULAs). You should determine what real warranty is offered and the
143
extent of liability that is accepted. Doing so soon dispels the popular notion that
144
commercial software vendors are willingly accountable for product defects. In many cases, the
145
commercial vendor accepts liability only to reimburse the price paid for the software.
146
</p><p><a class="indexterm" name="id2611526"></a><a class="indexterm" name="id2611534"></a><a class="indexterm" name="id2611542"></a><a class="indexterm" name="id2611550"></a><a class="indexterm" name="id2611558"></a><a class="indexterm" name="id2611566"></a>
147
The real issues that a consumer (like you) needs answered are What is the way of escape from technical
148
problems, and how long will it take? The average problem turnaround time in the Open Source community is
149
approximately 48 hours. What does the EULA offer? What is the track record in the commercial software
150
industry? What happens when your commercial vendor decides to cease providing support?
151
</p><p><a class="indexterm" name="id2611591"></a><a class="indexterm" name="id2611598"></a><a class="indexterm" name="id2611606"></a><a class="indexterm" name="id2611614"></a><a class="indexterm" name="id2611622"></a><a class="indexterm" name="id2611630"></a><a class="indexterm" name="id2611638"></a>
152
Open Source software at least puts you in possession of the source code. This means that when
153
all else fails, you can hire a programmer to solve the problem.
154
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2611650"></a>Technical Issues</h3></div></div></div><p>
155
Each issue is now discussed and, where appropriate, example implementation steps are
157
</p><div class="variablelist"><dl><dt><span class="term">Winbind and Security</span></dt><dd><p><a class="indexterm" name="id2611671"></a><a class="indexterm" name="id2611679"></a><a class="indexterm" name="id2611687"></a><a class="indexterm" name="id2611698"></a><a class="indexterm" name="id2611706"></a><a class="indexterm" name="id2611714"></a><a class="indexterm" name="id2611722"></a><a class="indexterm" name="id2611730"></a><a class="indexterm" name="id2611738"></a><a class="indexterm" name="id2611746"></a>
158
Windows network administrators may be dismayed to find that <code class="literal">winbind</code>
159
exposes all domain users so that they may use their domain account credentials to
160
log on to a UNIX/Linux system. The fact that all users in the domain can see the
161
UNIX/Linux server in their Network Neighborhood and can browse the shares on the
162
server seems to excite them further.
163
</p><p><a class="indexterm" name="id2611770"></a><a class="indexterm" name="id2611778"></a><a class="indexterm" name="id2611786"></a><a class="indexterm" name="id2611794"></a>
164
<code class="literal">winbind</code> provides for the UNIX/Linux domain member server or
165
client, the same as one would obtain by adding a Microsoft Windows server or
166
client to the domain. The real objection is the fact that Samba is not MS Windows
167
and therefore requires handling a little differently from the familiar Windows systems.
168
One must recognize fear of the unknown.
169
</p><p><a class="indexterm" name="id2611817"></a><a class="indexterm" name="id2611825"></a><a class="indexterm" name="id2611833"></a><a class="indexterm" name="id2611841"></a><a class="indexterm" name="id2611848"></a><a class="indexterm" name="id2611860"></a>
170
Windows network administrators need to recognize that <code class="literal">winbind</code> does
171
not, and cannot, override account controls set using the Active Directory management
172
tools. The control is the same. Have no fear.
173
</p><p><a class="indexterm" name="id2611881"></a><a class="indexterm" name="id2611888"></a><a class="indexterm" name="id2611900"></a><a class="indexterm" name="id2611908"></a><a class="indexterm" name="id2611916"></a><a class="indexterm" name="id2611923"></a><a class="indexterm" name="id2611931"></a><a class="indexterm" name="id2611939"></a><a class="indexterm" name="id2611947"></a><a class="indexterm" name="id2611955"></a>
174
Where Samba and the ADS domain account information obtained through the use of
175
<code class="literal">winbind</code> permits access, by browsing or by the drive mapping to
176
a share, to data that should be better protected. This can only happen when security
177
controls have not been properly implemented. Samba permits access controls to be set
179
</p><div class="itemizedlist"><ul type="disc"><li><p>Shares themselves (i.e., the logical share itself)</p></li><li><p>The share definition in <code class="filename">smb.conf</code></p></li><li><p>The shared directories and files using UNIX permissions</p></li><li><p>Using Windows 2000 ACLs if the file system is POSIX enabled</p></li></ul></div><p>
180
Examples of each are given in <a class="link" href="kerberos.html#ch10expl" title="Implementation">“Implementation”</a>.
181
</p></dd><dt><span class="term">User and Group Controls</span></dt><dd><p><a class="indexterm" name="id2612029"></a><a class="indexterm" name="id2612037"></a><a class="indexterm" name="id2612049"></a><a class="indexterm" name="id2612060"></a><a class="indexterm" name="id2612068"></a><a class="indexterm" name="id2612075"></a><a class="indexterm" name="id2612083"></a><a class="indexterm" name="id2612091"></a><a class="indexterm" name="id2612099"></a>
182
User and group management facilities as known in the Windows ADS environment may be
183
used to provide equivalent access control constraints or to provide equivalent
184
permissions and privileges on Samba servers. Samba offers greater flexibility in the
185
use of user and group controls because it has additional layers of control compared to
186
Windows 200x/XP. For example, access controls on a Samba server may be set within
187
the share definition in a manner for which Windows has no equivalent.
188
</p><p><a class="indexterm" name="id2612119"></a><a class="indexterm" name="id2612127"></a><a class="indexterm" name="id2612135"></a><a class="indexterm" name="id2612143"></a><a class="indexterm" name="id2612154"></a><a class="indexterm" name="id2612162"></a><a class="indexterm" name="id2612170"></a>
189
In any serious analysis of system security, it is important to examine the safeguards
190
that remain when all other protective measures fail. An administrator may inadvertently
191
set excessive permissions on the file system of a shared resource, or he may set excessive
192
privileges on the share itself. If that were to happen in a Windows 2003 Server environment,
193
the data would indeed be laid bare to abuse. Yet, within a Samba share definition, it is
194
possible to guard against that by enforcing controls on the share definition itself. You
195
see a practical example of this a little later in this chapter.
196
</p><p><a class="indexterm" name="id2612192"></a><a class="indexterm" name="id2612200"></a>
197
The report that is critical of Samba really ought to have exercised greater due
198
diligence: the real weakness is on the side of a Microsoft Windows environment.
199
</p></dd><dt><span class="term">Security Overall</span></dt><dd><p><a class="indexterm" name="id2612222"></a>
200
Samba is designed in such a manner that weaknesses inherent in the design of
201
Microsoft Windows networking ought not to expose the underlying UNIX/Linux file
202
system in any way. All software has potential defects, and Samba is no exception.
203
What matters more is how defects that are discovered get dealt with.
204
</p><p><a class="indexterm" name="id2612238"></a><a class="indexterm" name="id2612246"></a><a class="indexterm" name="id2612254"></a><a class="indexterm" name="id2612262"></a>
205
The Samba Team totally agrees with the necessity to observe and fully implement
206
every security facility to provide a level of protection and security that is necessary
207
and that the end user (or network administrator) needs. Never would the Samba Team
208
recommend a compromise to system security, nor would deliberate defoliation of
209
security be publicly condoned; yet this is the practice by many Windows network
210
administrators just to make happy users who have no notion of consequential risk.
211
</p><p><a class="indexterm" name="id2612282"></a><a class="indexterm" name="id2612290"></a><a class="indexterm" name="id2612298"></a><a class="indexterm" name="id2612306"></a><a class="indexterm" name="id2612314"></a><a class="indexterm" name="id2612322"></a><a class="indexterm" name="id2612330"></a>
212
The report condemns Samba for releasing updates and security fixes, yet Microsoft
213
online updates need to be applied almost weekly. The answer to the criticism
214
lies in the fact that Samba development is continuing, documentation is improving,
215
user needs are being increasingly met or exceeded, and security updates are issued
216
with a short turnaround time.
217
</p><p><a class="indexterm" name="id2612347"></a><a class="indexterm" name="id2612355"></a><a class="indexterm" name="id2612363"></a><a class="indexterm" name="id2612371"></a><a class="indexterm" name="id2612379"></a>
218
The release of Samba-4 is expected around late 2004 to early 2005 and involves a near
219
complete rewrite to permit extensive modularization and to prepare Samba for new
220
functionality planned for addition during the next-generation series. The Samba Team
221
is responsible and can be depended upon; the history to date suggests a high
222
degree of dependability and on charter development consistent with published
224
</p><p><a class="indexterm" name="id2612409"></a><a class="indexterm" name="id2612417"></a><a class="indexterm" name="id2612429"></a><a class="indexterm" name="id2612440"></a><a class="indexterm" name="id2612448"></a><a class="indexterm" name="id2612456"></a><a class="indexterm" name="id2612464"></a>
225
Not well published is the fact that Microsoft was a foundation member of
226
the Common Internet File System (CIFS) initiative, together with the participation
227
of the network attached storage (NAS) industry. Unfortunately, for the past few years,
228
Microsoft has been absent from active involvement at CIFS conferences and has
229
not exercised the leadership expected of a major force in the networking technology
230
space. The Samba Team has maintained consistent presence and leadership at all
231
CIFS conferences and at the interoperability laboratories run concurrently with
233
</p></dd><dt><span class="term">Cryptographic Controls (schannel, sign'n'seal)</span></dt><dd><p><a class="indexterm" name="id2612494"></a><a class="indexterm" name="id2612502"></a><a class="indexterm" name="id2612510"></a>
234
The report correctly mentions that Samba did not support the most recent
235
<code class="constant">schannel</code> and <code class="constant">digital sign'n'seal</code> features
236
of Microsoft Windows NT/200x/XPPro products. This is one of the key features
237
of the Samba-3 release. Market research reports take so long to generate that they are
238
seldom a reflection of current practice, and in many respects reports are like a
239
pathology report they reflect accurately (at best) status at a snapshot in time.
240
Meanwhile, the world moves on.
241
</p><p><a class="indexterm" name="id2612540"></a><a class="indexterm" name="id2612548"></a><a class="indexterm" name="id2612555"></a><a class="indexterm" name="id2612563"></a><a class="indexterm" name="id2612571"></a><a class="indexterm" name="id2612586"></a><a class="indexterm" name="id2612594"></a>
242
It should be pointed out that had clear public specifications for the protocols
243
been published, it would have been much easier to implement these features and would have
244
taken less time to do. The sole mechanism used to find an algorithm that is compatible
245
with the methods used by Microsoft has been based on observation of network traffic
246
and trial-and-error implementation of potential techniques. The real value of public
247
and defensible standards is obvious to all and would have enabled more secure networking
249
</p><p><a class="indexterm" name="id2612614"></a><a class="indexterm" name="id2612622"></a>
250
Critics of Samba often ignore fundamental problems that may plague (or may have plagued)
251
the users of Microsoft's products also. Those who are first to criticize Samba
252
for not rushing into release of <code class="constant">digital sign'n'seal</code> support
253
often dismiss the problems that Microsoft has
254
<a class="ulink" href="http://support.microsoft.com/default.aspx?kbid=321733" target="_top">acknowledged</a>
255
and for which a fix was provided. In fact,
256
<a class="ulink" href="http://www.tangent-systems.com/support/delayedwrite.html" target="_top">Tangent Systems</a>
257
have documented a significant problem with delays writes that can be connected with the
258
implementation of sign'n'seal. They provide a work-around that is not trivial for many
259
Windows networking sites. From notes such as this it is clear that there are benefits
260
from not rushing new technology out of the door too soon.
261
</p><p><a class="indexterm" name="id2612662"></a><a class="indexterm" name="id2612670"></a><a class="indexterm" name="id2612678"></a><a class="indexterm" name="id2612686"></a><a class="indexterm" name="id2612694"></a><a class="indexterm" name="id2612702"></a><a class="indexterm" name="id2612710"></a><a class="indexterm" name="id2612718"></a><a class="indexterm" name="id2612726"></a>
262
One final comment is warranted. If companies want more secure networking protocols,
263
the most effective method by which this can be achieved is by users seeking
264
and working together to help define open and publicly refereed standards. The
265
development of closed source, proprietary methods that are developed in a
266
clandestine framework of secrecy, under claims of digital rights protection, does
267
not favor the diffusion of safe networking protocols and certainly does not
268
help the consumer to make a better choice.
269
</p></dd><dt><span class="term">Active Directory Replacement with Kerberos, LDAP, and Samba</span></dt><dd><p>
270
</p><div class="literallayout"><p>����</p></div><p>
271
The Microsoft networking protocols extensively make use of remote procedure call (RPC)
272
technology. Active Directory is not a simple mixture of LDAP and Kerberos together
273
with file and print services, but rather is a complex, intertwined implementation
274
of them that uses RPCs that are not supported by any of these component technologies
275
and yet by which they are made to interoperate in ways that the components do not
277
</p><p><a class="indexterm" name="id2612814"></a><a class="indexterm" name="id2612825"></a><a class="indexterm" name="id2612833"></a><a class="indexterm" name="id2612841"></a><a class="indexterm" name="id2612849"></a>
278
In order to make the popular request for Samba to be an Active Directory Server a
279
reality, it is necessary to add to OpenLDAP, Kerberos, as well as Samba, RPC calls
280
that are not presently supported. The Samba Team has not been able to gain critical
281
overall support for all project maintainers to work together on the complex
282
challenge of developing and integrating the necessary technologies. Therefore, if
283
the Samba Team does not make it a priority to absorb Kerberos and LDAP functionality
284
into the Samba project, this dream request cannot become a reality.
285
</p><p><a class="indexterm" name="id2612880"></a><a class="indexterm" name="id2612888"></a><a class="indexterm" name="id2612896"></a><a class="indexterm" name="id2612907"></a><a class="indexterm" name="id2612914"></a>
286
At this time, the integration of LDAP, Kerberos, and the missing RPCs is not on the
287
Samba development roadmap. If it is not on the published roadmap, it cannot be delivered
288
anytime soon. Ergo, ADS server support is not a current goal for Samba development.
289
The Samba Team is most committed to permitting Samba to be a full ADS domain member
290
that is increasingly capable of being managed using Microsoft Windows MMC tools.
291
</p></dd></dl></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2612934"></a>Kerberos Exposed</h4></div></div></div><p><a class="indexterm" name="id2612941"></a><a class="indexterm" name="id2612949"></a><a class="indexterm" name="id2612957"></a>
292
Kerberos is a network authentication protocol that provides secure authentication for
293
client-server applications by using secret-key cryptography. Firewalls are an insufficient
294
barrier mechanism in today's networking world; at best they only restrict incoming network
295
traffic but cannot prevent network traffic that comes from authorized locations from
296
performing unauthorized activities.
297
</p><p><a class="indexterm" name="id2612975"></a><a class="indexterm" name="id2612983"></a><a class="indexterm" name="id2612991"></a>
298
Kerberos was created by MIT as a solution to network security problems. The Kerberos protocol uses
299
strong cryptography so that a client can prove its identity to a server (and vice versa) across an
300
insecure network connection. After a client and server has used Kerberos to prove their identity,
301
they can also encrypt all of their communications to assure privacy and data integrity as they go
302
about their business.
303
</p><p><a class="indexterm" name="id2613009"></a><a class="indexterm" name="id2613017"></a><a class="indexterm" name="id2613025"></a><a class="indexterm" name="id2613033"></a><a class="indexterm" name="id2613044"></a>
304
Kerberos is a trusted third-party service. That means that there is a third party (the kerberos
305
server) that is trusted by all the entities on the network (users and services, usually called
306
principals). All principals share a secret password (or key) with the kerberos server and this
307
enables principals to verify that the messages from the kerberos server are authentic. Therefore,
308
trusting the kerberos server, users and services can authenticate each other.
310
<a class="indexterm" name="id2613064"></a>
311
<a class="indexterm" name="id2613071"></a>
312
<a class="indexterm" name="id2613078"></a>
313
Kerberos was, until recently, a technology that was restricted from being exported from the United States.
314
For many years that hindered global adoption of more secure networking technologies both within the United States
315
and abroad. A free and unencumbered implementation of MIT Kerberos has been produced in Europe
316
and is available from the <a class="ulink" href="http://www.pdc.kth.se/heimdal/" target="_top">Royal Institute</a> of
317
Technology (KTH), Sweden. It is known as the Heimdal Kerberos project. In recent times the U.S. government
318
has removed sanctions affecting the global distribution of MIT Kerberos. It is likely that there will be a
319
significant surge forward in the development of Kerberos-enabled applications and in the general deployment
320
and use of Kerberos across the spectrum of the information technology industry.
322
<a class="indexterm" name="id2613107"></a>
323
A storm has broken out concerning interoperability between MIT Kerberos and Microsofts' implementation
324
of it. For example, a 2002
325
<a class="ulink" href="http://www.idg.com.sg/idgwww.nsf/0/5DDA8D153A7505A748256BAB000D992A?OpenDocument" target="_top">IDG</a>
326
report<sup>[<a name="id2613126" href="#ftn.id2613126" class="footnote">13</a>]</sup> by
328
</p><div class="blockquote"><blockquote class="blockquote"><p>
329
A Microsoft Corp. executive testified at the software giant's remedy hearing that the company goes to
330
great lengths to disclose interfaces and protocols that allow third-party software products to interact
331
with Windows. But a lawyer with the states suing Microsoft pointed out that when it comes to the company's
332
use of the Kerberos authentication specification, not everyone agrees.
334
<a class="indexterm" name="id2613152"></a>
335
Robert Short, vice president of Windows core technology at Microsoft, wrote in his direct testimony prepared
336
before his appearance that non-Microsoft operating systems can disregard the portion of the Kerberos version
337
5 specification that Windows clients use for proprietary purposes and still achieve interoperability with
338
the Microsoft OS. Microsoft takes advantage of unspecified fields in the Kerberos specification for storing
339
Windows-specific authorization data, Short wrote. The designers of Kerberos left these fields undefined so
340
that software developers could add their own authorization information, he said.
341
</p></blockquote></div><p>
342
<a class="indexterm" name="id2613176"></a>
343
<a class="indexterm" name="id2613182"></a>
344
It so happens that Microsoft Windows clients depend on and expect the contents of the <span class="emphasis"><em>unspecified
345
fields</em></span> in the Kerberos 5 communications data stream for their Windows interoperability,
346
particularly when Samba is expected to emulate a Windows Server 200x domain controller. But the interoperability
347
issue goes far deeper than this. In the domain control protocols that are used by MS Windows XP Professional,
348
there is a tight interdependency between the Kerberos protocols and the Microsoft distributed computing environment
349
(DCE) RPCs that themselves are an integral part of the SMB/CIFS protocols as used by
352
Microsoft makes the following comment in a reference in a
353
<a class="ulink" href="http://www.microsoft.com/technet/itsolutions/interop/mgmt/kerberos.asp" target="_top">
355
</p><div class="blockquote"><blockquote class="blockquote"><p><a class="indexterm" name="id2613217"></a><a class="indexterm" name="id2613229"></a>
356
The DCE Security Services are also layered on the Kerberos protocol. DCE authentication services use RPC
357
representation of Kerberos protocol messages. In addition, DCE uses the authorization data field in Kerberos
358
tickets to convey Privilege Attribute Certificates (PACs) that define user identity and group membership.
359
The DCE PAC is used in a similar manner as Windows NT Security IDs for user authorization and access control.
360
Windows NT services will not be able to translate DCE PACs into Windows NT user and group identifiers. This
361
is not an issue with Kerberos interoperability, but rather an issue of interoperability between DCE and
362
Windows NT access control information.
363
</p></blockquote></div></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ch10expl"></a>Implementation</h2></div></div></div><p>
364
The following procedures outline the implementation of the security measures discussed so far.
365
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2613280"></a>Share Access Controls</h3></div></div></div><p><a class="indexterm" name="id2613287"></a><a class="indexterm" name="id2613295"></a><a class="indexterm" name="id2613303"></a>
366
Access control entries placed on the share itself act as a filter at the time a when CIFS/SMB client (such as
367
Windows XP Pro) attempts to make a connection to the Samba server.
368
</p><div class="procedure"><a name="id2613316"></a><p class="title"><b>Procedure�11.1.�Create/Edit/Delete Share ACLs</b></p><ol type="1"><li><p><a class="indexterm" name="id2613327"></a><a class="indexterm" name="id2613335"></a>
369
From a Windows 200x/XP Professional workstation, log on to the domain using the Domain Administrator
370
account (on Samba domains, this is usually the account called <code class="constant">root</code>).
373
<span class="guimenu">Start</span> → <span class="guimenuitem">Settings</span> → <span class="guimenuitem">Control Panel</span> → <span class="guimenuitem">Administrative Tools</span> → <span class="guimenuitem">Computer Management</span>.
376
<span class="guimenu">[Right mouse menu item] Computer Management (Local)</span> → <span class="guimenuitem">Connect to another computer ...</span> → <span class="guimenuitem">Browse...</span> → <span class="guimenuitem">Advanced</span> → <span class="guimenuitem">Find Now</span>. In the lower panel, click on the name of the server you wish to
377
administer. Click <span class="guimenu">OK</span> → <span class="guimenuitem">OK</span> → <span class="guimenuitem">OK</span>.<a class="indexterm" name="id2613458"></a>
378
In the left panel, the entry <span class="guimenu">Computer Management (Local)</span> should now reflect
379
the change made. For example, if the server you are administering is called <code class="constant">FRODO</code>,
380
the Computer Management entry should now say <span class="guimenu">Computer Management (FRODO)</span>.
382
In the left panel, click <span class="guimenu">Computer Management (FRODO)</span> → <span class="guimenuitem">[+] Shared Folders</span> → <span class="guimenuitem">Shares</span>.
383
</p></li><li><p><a class="indexterm" name="id2613522"></a><a class="indexterm" name="id2613530"></a>
384
In the right panel, double-click on the share on which you wish to set/edit ACLs. This
385
will bring up the Properties panel. Click the <span class="guimenu">Share Permissions</span> tab.
386
</p></li><li><p><a class="indexterm" name="id2613553"></a><a class="indexterm" name="id2613561"></a><a class="indexterm" name="id2613569"></a><a class="indexterm" name="id2613577"></a><a class="indexterm" name="id2613585"></a><a class="indexterm" name="id2613593"></a>
387
You may now edit/add/remove access control settings. Be very careful. Many problems have been
388
created by people who decided that everyone should be rejected but one particular group should
389
have full control. This is a catch-22 situation because members of that particular group also
390
belong to the group <code class="constant">Everyone</code>, which therefore overrules any permissions
391
set for the permitted group.
393
When you are done with editing, close all panels by clicking through the <span class="guimenu">OK</span>
395
</p></li></ol></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2613629"></a>Share Definition Controls</h3></div></div></div><p><a class="indexterm" name="id2613636"></a><a class="indexterm" name="id2613648"></a><a class="indexterm" name="id2613655"></a><a class="indexterm" name="id2613663"></a><a class="indexterm" name="id2613671"></a><a class="indexterm" name="id2613679"></a>
396
Share-definition-based access controls can be used like a checkpoint or like a pile-driver. Just as a
397
checkpoint can be used to require someone who wants to get through to meet certain requirements, so
398
it is possible to require the user (or group the user belongs to) to meet specified credential-related
399
objectives. It can be likened to a pile-driver by overriding default controls in that having met the
400
credential-related objectives, the user can be granted powers and privileges that would not normally be
401
available under default settings.
402
</p><p><a class="indexterm" name="id2613699"></a><a class="indexterm" name="id2613707"></a><a class="indexterm" name="id2613715"></a><a class="indexterm" name="id2613723"></a>
403
It must be emphasized that the controls discussed here can act as a filter or give rights of passage
404
that act as a superstructure over normal directory and file access controls. However, share-level
405
ACLs act at a higher level than do share definition controls because the user must filter through the
406
share-level controls to get to the share-definition controls. The proper hierarchy of controls implemented
407
by Samba and Windows networking consists of:
408
</p><div class="orderedlist"><ol type="1"><li><p>Share-level ACLs</p></li><li><p>Share-definition controls</p></li><li><p>Directory and file permissions</p></li><li><p>Directory and file POSIX ACLs</p></li></ol></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2613769"></a>Checkpoint Controls</h4></div></div></div><p><a class="indexterm" name="id2613775"></a>
409
Consider the following extract from a <code class="filename">smb.conf</code> file defining the share called <code class="constant">Apps</code>:
410
</p><pre class="screen">
412
comment = Application Share
415
valid users = @Employees
417
This definition permits only those who are members of the group called <code class="constant">Employees</code> to
419
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p><a class="indexterm" name="id2613811"></a><a class="indexterm" name="id2613822"></a><a class="indexterm" name="id2613831"></a><a class="indexterm" name="id2613839"></a><a class="indexterm" name="id2613846"></a>
420
On domain member servers and clients, even when the <em class="parameter"><code>winbind use default domain</code></em> has
421
been specified, the use of domain accounts in security controls requires fully qualified domain specification,
422
for example, <a class="link" href="smb.conf.5.html#VALIDUSERS" target="_top">valid users = @"MEGANET\Northern Engineers"</a>.
423
Note the necessity to use the double quotes to avoid having the space in the Windows group name interpreted as a
425
</p></div><p><a class="indexterm" name="id2613882"></a><a class="indexterm" name="id2613889"></a><a class="indexterm" name="id2613897"></a>
426
If there is an ACL on the share itself to permit read/write access for all <code class="constant">Employees</code>
427
as well as read/write for the group <code class="constant">Doctors</code>, both groups are permitted through
428
to the share. However, at the moment an attempt is made to set up a connection to the share, a member of
429
the group <code class="constant">Doctors</code>, who is not also a member of the group <code class="constant">Employees</code>,
430
would immediately fail to validate.
431
</p><p><a class="indexterm" name="id2613928"></a>
432
Consider another example. In this case, you want to permit all members of the group <code class="constant">Employees</code>
433
except the user <code class="constant">patrickj</code> to access the <code class="constant">Apps</code> share. This can be
434
easily achieved by setting a share-level ACL permitting only <code class="constant">Employees</code> to access the share,
435
and then in the share definition controls excluding just <code class="constant">patrickj</code>. Here is how that might
437
</p><pre class="screen">
439
comment = Application Share
442
invalid users = patrickj
444
<a class="indexterm" name="id2613969"></a>
445
Let us assume that you want to permit the user <code class="constant">gbshaw</code> to manage any file in the
446
UNIX/Linux file system directory <code class="filename">/data/apps</code>, but you do not want to grant any write
447
permissions beyond that directory tree. Here is one way this can be done:
448
</p><pre class="screen">
450
comment = Application Share
453
invalid users = patrickj
456
<a class="indexterm" name="id2613999"></a>
457
Now we have a set of controls that permits only <code class="constant">Employees</code> who are also members of
458
the group <code class="constant">Doctors</code>, excluding the user <code class="constant">patrickj</code>, to have
459
read-only privilege, but the user <code class="constant">gbshaw</code> is granted administrative rights.
460
The administrative rights conferred upon the user <code class="constant">gbshaw</code> permit operation as
461
if that user has logged in as the user <code class="constant">root</code> on the UNIX/Linux system and thus,
462
for access to the directory tree that has been shared (exported), permit the user to override controls
463
that apply to all other users on that resource.
465
There are additional checkpoint controls that may be used. For example, if for the same share we now
466
want to provide the user <code class="constant">peters</code> with the ability to write to one directory to
467
which he has write privilege in the UNIX file system, you can specifically permit that with the
469
</p><pre class="screen">
471
comment = Application Share
474
invalid users = patrickj
478
<a class="indexterm" name="id2614059"></a>
479
This is a particularly complex example at this point, but it begins to demonstrate the possibilities.
480
You should refer to the online manual page for the <code class="filename">smb.conf</code> file for more information regarding
481
the checkpoint controls that Samba implements.
482
</p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2614081"></a>Override Controls</h4></div></div></div><p><a class="indexterm" name="id2614088"></a>
483
Override controls implemented by Samba permit actions like the adoption of a different identity
484
during file system operations, the forced overwriting of normal file and directory permissions,
485
and so on. You should refer to the online manual page for the <code class="filename">smb.conf</code> file for more information regarding
486
the override controls that Samba implements.
488
In the following example, you want to create a Windows networking share that any user can access.
489
However, you want all read and write operations to be performed as if the user <code class="constant">billc</code>
490
and member of the group <code class="constant">Mentors</code> read/write the files. Here is one way this
492
</p><pre class="screen">
494
comment = Some Files Everyone May Overwrite
495
path = /data/somestuff
498
force group = Mentors
500
<a class="indexterm" name="id2614132"></a><a class="indexterm" name="id2614140"></a>
501
That is all there is to it. Well, it is almost that simple. The downside of this method is that
502
users are logged onto the Windows client as themselves, and then immediately before accessing the
503
file, Samba makes system calls to change the effective user and group to the forced settings
504
specified, completes the file transaction, and then reverts to the actually logged-on identity.
505
This imposes significant overhead on Samba. The alternative way to effectively achieve the same result
506
(but with lower system CPU overheads) is described next.
507
</p><p><a class="indexterm" name="id2614160"></a><a class="indexterm" name="id2614168"></a><a class="indexterm" name="id2614176"></a><a class="indexterm" name="id2614187"></a><a class="indexterm" name="id2614195"></a>
508
The use of the <em class="parameter"><code>force user</code></em> or the <em class="parameter"><code>force group</code></em> may
509
also have a severe impact on system (particularly on Windows client) performance. If opportunistic
510
locking is enabled on the share (the default), it causes an <code class="constant">oplock break</code> to be
511
sent to the client even if the client has not opened the file. On networks that have high traffic
512
density, or on links that are routed to a remote network segment, <code class="constant">oplock breaks</code>
513
can be lost. This results in possible retransmission of the request, or the client may time-out while
514
waiting for the file system transaction (read or write) to complete. The result can be a profound
515
apparent performance degradation as the client continually attempts to reconnect to overcome the
516
effect of the lost <code class="constant">oplock break</code>, or time-out.
517
</p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2614242"></a>Share Point Directory and File Permissions</h3></div></div></div><p><a class="indexterm" name="id2614250"></a><a class="indexterm" name="id2614257"></a><a class="indexterm" name="id2614265"></a><a class="indexterm" name="id2614273"></a>
518
Samba has been designed and implemented so that it respects as far as is feasible the security and
519
user privilege controls that are built into the UNIX/Linux operating system. Samba does nothing
520
with respect to file system access that violates file system permission settings, unless it is
521
explicitly instructed to do otherwise through share definition controls. Given that Samba obeys
522
UNIX file system controls, this chapter does not document simple information that can be obtained
523
from a basic UNIX training guide. Instead, one common example of a typical problem is used
524
to demonstrate the most effective solution referred to in the immediately preceding paragraph.
525
</p><p><a class="indexterm" name="id2614296"></a><a class="indexterm" name="id2614304"></a><a class="indexterm" name="id2614312"></a>
526
One of the common issues that repeatedly pops up on the Samba mailing lists involves the saving of
527
Microsoft Office files (Word and Excel) to a network drive. Here is the typical sequence:
528
</p><div class="orderedlist"><ol type="1"><li><p>
529
A user opens a Word document from a network drive. The file was owned by user <code class="constant">janetp</code>
530
and [users], and was set read/write-enabled for everyone.
531
A user opens a Word document from a network drive. The file was owned by user <code class="constant">janetp</code>
532
and <code class="constant">users</code>, and was set read/write-enabled for everyone.
534
File changes and edits are made.
536
The file is saved, and MS Word is closed.
538
The file is now owned by the user <code class="constant">billc</code> and group <code class="constant">doctors</code>,
539
and is set read/write by <code class="constant">billc</code>, read-only by <code class="constant">doctors</code>, and
540
no access by everyone.
542
The original owner cannot now access her own file and is “<span class="quote">justifiably</span>” upset.
543
</p></li></ol></div><p>
544
There have been many postings over the years that report the same basic problem. Frequently Samba users
545
want to know when this “<span class="quote">bug</span>” will be fixed. The fact is, this is not a bug in Samba at all.
546
Here is the real sequence of what happens in this case.
547
</p><p><a class="indexterm" name="id2614413"></a><a class="indexterm" name="id2614421"></a><a class="indexterm" name="id2614429"></a>
548
When the user saves a file, MS Word creates a new (temporary) file. This file is naturally owned
549
by the user who creates the file (<code class="constant">billc</code>) and has the permissions that follow
550
that user's default settings within the operating system (UNIX/Linux). When MS Word has finished writing
551
the file to disk, it then renames the new (temporary) file to the name of the old one. MS Word does not
552
change the ownership or permissions to what they were on the original file. The file is thus a totally
553
new file, and the old one has been deleted in the process.
555
Samba received a request to create a new file, and then to rename the file to a new name. The old file that
556
has the same name is now automatically deleted. Samba has no way of knowing that the new file should
557
perhaps have the same ownership and permissions as the old file. To Samba, these are entirely independent
560
The question is, “<span class="quote">How can we solve the problem?</span>”
562
The solution is simple. Use UNIX file system permissions and controls to your advantage. Follow these
563
simple steps to create a share in which all files will consistently be owned by the same user and the
565
</p><div class="procedure"><a name="id2614475"></a><p class="title"><b>Procedure�11.2.�Using Directory Permissions to Force File User and Group Ownership</b></p><ol type="1"><li><p>
566
Change your share definition so that it matches this pattern:
567
</p><pre class="screen">
569
path = /usr/data/finance
573
</p></li><li><p><a class="indexterm" name="id2614501"></a><a class="indexterm" name="id2614513"></a>
574
Set consistent user and group permissions recursively down the directory tree as shown here:
575
</p><pre class="screen">
576
<code class="prompt">root# </code> chown -R janetp.users /usr/data/finance
578
</p></li><li><p><a class="indexterm" name="id2614544"></a>
579
Set the files and directory permissions to be read/write for owner and group, and not accessible
580
to others (everyone), using the following command:
581
</p><pre class="screen">
582
<code class="prompt">root# </code> chmod ug+rwx,o-rwx /usr/data/finance
584
</p></li><li><p><a class="indexterm" name="id2614574"></a>
585
Set the SGID (supergroup) bit on all directories from the top down. This means all files
586
can be created with the permissions of the group set on the directory. It means all users
587
who are members of the group <code class="constant">finance</code> can read and write all files in
588
the directory. The directory is not readable or writable by anyone who is not in the
589
<code class="constant">finance</code> group. Simply follow this example:
590
</p><pre class="screen">
591
<code class="prompt">root# </code> find /usr/data/finance -type d -exec chmod ug+s {}\;
594
</p></li><li><p><a class="indexterm" name="id2614614"></a><a class="indexterm" name="id2614622"></a><a class="indexterm" name="id2614630"></a>
595
Make sure all users that must have read/write access to the directory have
596
<code class="constant">finance</code> group membership as their primary group,
597
for example, the group they belong to in <code class="filename">/etc/passwd</code>.
598
</p></li></ol></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2614655"></a>Managing Windows 200x ACLs</h3></div></div></div><p><a class="indexterm" name="id2614662"></a><a class="indexterm" name="id2614670"></a><a class="indexterm" name="id2614678"></a><a class="indexterm" name="id2614686"></a>
599
Samba must translate Windows 2000 ACLs to UNIX POSIX ACLs. This has some interesting side effects because
600
there is not a one-to-one equivalence between them. The as-close-as-possible ACLs match means
601
that some transactions are not possible from MS Windows clients. One of these is to reset the ownership
602
of directories and files. If you want to reset ownership, this must be done from a UNIX/Linux login.
604
There are two possible ways to set ACLs on UNIX/Linux file systems from a Windows network workstation,
605
either via File Manager or via the Microsoft Management Console (MMC) Computer Management interface.
606
</p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2614709"></a>Using the MMC Computer Management Interface</h4></div></div></div><div class="procedure"><ol type="1"><li><p>
607
From a Windows 200x/XP Professional workstation, log on to the domain using the Domain Administrator
608
account (on Samba domains, this is usually the account called <code class="constant">root</code>).
611
<span class="guimenu">Start</span> → <span class="guimenuitem">Settings</span> → <span class="guimenuitem">Control Panel</span> → <span class="guimenuitem">Administrative Tools</span> → <span class="guimenuitem">Computer Management</span>.
614
<span class="guimenu">[Right mouse menu item] Computer Management (Local)</span> → <span class="guimenuitem">Connect to another computer ...</span> → <span class="guimenuitem">Browse...</span> → <span class="guimenuitem">Advanced</span> → <span class="guimenuitem">Find Now</span>. In the lower panel, click on the name of the server you wish to
615
administer. Click <span class="guimenu">OK</span> → <span class="guimenuitem">OK</span> → <span class="guimenuitem">OK</span>.
616
In the left panel, the entry <span class="guimenu">Computer Management (Local)</span> should now reflect
617
the change made. For example, if the server you are administering is called <code class="constant">FRODO</code>,
618
the Computer Management entry should now say: <span class="guimenu">Computer Management (FRODO)</span>.
620
In the left panel, click <span class="guimenu">Computer Management (FRODO)</span> → <span class="guimenuitem">[+] Shared Folders</span> → <span class="guimenuitem">Shares</span>.
621
</p></li><li><p><a class="indexterm" name="id2614892"></a><a class="indexterm" name="id2614900"></a><a class="indexterm" name="id2614908"></a><a class="indexterm" name="id2614916"></a>
622
In the right panel, double-click on the share on which you wish to set/edit ACLs. This
623
brings up the Properties panel. Click the <span class="guimenu">Security</span> tab. It is best
624
to edit ACLs using the <code class="constant">Advanced</code> editing features. Click the
625
<span class="guimenu">Advanced</span> button. This opens a panel that has four tabs. Only the
626
functionality under the <code class="constant">Permissions</code> tab can be utilized with respect
627
to a Samba domain server.
628
</p></li><li><p><a class="indexterm" name="id2614956"></a><a class="indexterm" name="id2614964"></a>
629
You may now edit/add/remove access control settings. Be very careful. Many problems have been
630
created by people who decided that everyone should be rejected but one particular group should
631
have full control. This is a catch-22 situation because members of that particular group also
632
belong to the group <code class="constant">Everyone</code>, which therefore overrules any permissions
633
set for the permitted group.
635
When you are done with editing, close all panels by clicking through the <span class="guimenu">OK</span>
636
buttons until the last panel closes.
637
</p></li></ol></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2615000"></a>Using MS Windows Explorer (File Manager)</h4></div></div></div><p>
638
The following alternative method may be used from a Windows workstation. In this example we work
639
with a domain called <code class="constant">MEGANET</code>, a server called <code class="constant">MASSIVE</code>, and a
640
share called <code class="constant">Apps</code>. The underlying UNIX/Linux share point for this share is
641
<code class="filename">/data/apps</code>.
642
</p><div class="procedure"><ol type="1"><li><p>
643
Click <span class="guimenu">Start</span> → <span class="guimenuitem">[right-click] My Computer</span> → <span class="guimenuitem">Explore</span> → <span class="guimenuitem">[left panel] [+] My Network Places</span> → <span class="guimenuitem">[+] Entire Network</span> → <span class="guimenuitem">[+] Microsoft Windows Network</span> → <span class="guimenuitem">[+] Meganet</span> → <span class="guimenuitem">[+] Massive</span> → <span class="guimenuitem">[right-click] Apps</span> → <span class="guimenuitem">Properties</span> → <span class="guimenuitem">Security</span> → <span class="guimenuitem">Advanced</span>. This opens a panel that has four tabs. Only the functionality under the
644
<code class="constant">Permissions</code> tab can be utilized for a Samba domain server.
645
</p></li><li><p><a class="indexterm" name="id2615125"></a><a class="indexterm" name="id2615133"></a>
646
You may now edit/add/remove access control settings. Be very careful. Many problems have been
647
created by people who decided that everyone should be rejected but one particular group should
648
have full control. This is a catch-22 situation because members of that particular group also
649
belong to the group <code class="constant">Everyone</code>, which therefore overrules any permissions
650
set for the permitted group.
652
When you are done with editing, close all panels by clicking through the <span class="guimenu">OK</span>
653
buttons until the last panel closes.
654
</p></li></ol></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id2615172"></a>Setting Posix ACLs in UNIX/Linux</h4></div></div></div><p><a class="indexterm" name="id2615179"></a><a class="indexterm" name="id2615187"></a>
655
Yet another alternative method for setting desired security settings on the shared resource files and
656
directories can be achieved by logging into UNIX/Linux and setting POSIX ACLs directly using command-line
657
tools. Here is an example session on the same resource as in the immediately preceding example on a SUSE 9
659
</p><div class="procedure"><ol type="1"><li><p>
660
Log into the Linux system as the user <code class="constant">root</code>.
662
Change directory to the location of the exported (shared) Windows file share (Apps), which is in
663
the directory <code class="filename">/data</code>. Execute the following:
664
</p><pre class="screen">
665
<code class="prompt">root# </code> cd /data
667
Retrieve the existing POSIX ACLs entry by executing:
668
</p><pre class="screen">
669
<code class="prompt">root# </code> getfacl apps
677
</p></li><li><p><a class="indexterm" name="id2615261"></a>
678
You want to add permission for <code class="constant">AppsMgrs</code> to enable them to
679
manage the applications (apps) share. It is important to set the ACL recursively
680
so that the AppsMgrs have this capability throughout the directory tree that is
681
being shared. This is done using the <code class="constant">-R</code> option as shown.
682
Execute the following:
683
</p><pre class="screen">
684
<code class="prompt">root# </code> setfacl -m -R group:AppsMgrs:rwx /data/apps
686
Because setting an ACL does not provide a response, you immediately validate the command executed
688
</p><pre class="screen">
689
<code class="prompt">root# </code> getfacl /data/apps
699
This confirms that the change of POSIX ACL permissions has been effective.
700
</p></li><li><p><a class="indexterm" name="id2615316"></a><a class="indexterm" name="id2615324"></a><a class="indexterm" name="id2615332"></a><a class="indexterm" name="id2615340"></a><a class="indexterm" name="id2615348"></a>
701
It is highly recommended that you read the online manual page for the <code class="literal">setfacl</code>
702
and <code class="literal">getfacl</code> commands. This provides information regarding how to set/read the default
703
ACLs and how that may be propagated through the directory tree. In Windows ACLs terms, this is the equivalent
704
of setting <code class="constant">inheritance</code> properties.
705
</p></li></ol></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2615382"></a>Key Points Learned</h3></div></div></div><p>
706
The mish-mash of issues were thrown together into one chapter because it seemed like a good idea.
707
Looking back, this chapter could be broken into two, but it's too late now. It has been done.
708
The highlights covered are as follows:
709
</p><div class="itemizedlist"><ul type="disc"><li><p><a class="indexterm" name="id2615399"></a><a class="indexterm" name="id2615407"></a><a class="indexterm" name="id2615415"></a><a class="indexterm" name="id2615423"></a>
710
Winbind honors and does not override account controls set in Active Directory.
711
This means that password change, logon hours, and so on, are (or soon will be) enforced
712
by Samba winbind. At this time, an out-of-hours login is denied and password
713
change is enforced. At this time, if logon hours expire, the user is not forcibly
714
logged off. That may be implemented at some later date.
715
</p></li><li><p><a class="indexterm" name="id2615442"></a><a class="indexterm" name="id2615450"></a>
716
Sign'n'seal (plus schannel support) has been implemented in Samba-3. Beware of potential
717
problems acknowledged by Microsoft as having been fixed but reported by some as still
718
possibly an open issue.
719
</p></li><li><p><a class="indexterm" name="id2615466"></a><a class="indexterm" name="id2615473"></a><a class="indexterm" name="id2615481"></a><a class="indexterm" name="id2615489"></a>
720
The combination of Kerberos 5, plus OpenLDAP, plus Samba, cannot replace Microsoft
721
Active Directory. The possibility to do this is not planned in the current Samba-3
722
roadmap. Samba-3 does aim to provide further improvements in interoperability so that
723
UNIX/Linux systems may be fully integrated into Active Directory domains.
725
This chapter reviewed mechanisms by which Samba servers may be kept secure. Each of
726
the four key methodologies was reviewed with specific reference to example deployment
728
</p></li></ul></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2615516"></a>Questions and Answers</h2></div></div></div><p>
729
</p><div class="qandaset"><dl><dt> <a href="kerberos.html#id2615532">
730
Does Samba-3 require the Sign'n'seal registry hacks needed by Samba-2?
731
</a></dt><dt> <a href="kerberos.html#id2615602">
732
Does Samba-3 support Active Directory?
733
</a></dt><dt> <a href="kerberos.html#id2615633">
734
When Samba-3 is used with Active Directory, is it necessary to run mixed-mode operation, as was
735
necessary with Samba-2?
736
</a></dt><dt> <a href="kerberos.html#id2615672">
737
Is it safe to set share-level access controls in Samba?
738
</a></dt><dt> <a href="kerberos.html#id2615701">
739
Is it mandatory to set share ACLs to get a secure Samba-3 server?
740
</a></dt><dt> <a href="kerberos.html#id2615778">
741
The valid users did not work on the [homes].
742
Has this functionality been restored yet?
743
</a></dt><dt> <a href="kerberos.html#id2615844">
744
Is the bias against use of the force user and force group
746
</a></dt><dt> <a href="kerberos.html#id2615907">
747
The example given for file and directory access control forces all files to be owned by one
748
particular user. I do not like that. Is there any way I can see who created the file?
749
</a></dt><dt> <a href="kerberos.html#id2615955">
750
In the book, “The Official Samba-3 HOWTO and Reference Guide”, you recommended use
751
of the Windows NT4 Server Manager (part of the SRVTOOLS.EXE) utility. Why
752
have you mentioned only the use of the Windows 200x/XP MMC Computer Management utility?
753
</a></dt><dt> <a href="kerberos.html#id2616022">
754
I tried to set valid users = @Engineers, but it does not work. My Samba
755
server is an Active Directory domain member server. Has this been fixed now?
756
</a></dt></dl><table border="0" summary="Q and A Set"><col align="left" width="1%"><tbody><tr class="question"><td align="left" valign="top"><a name="id2615532"></a><a name="id2615534"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id2615537"></a><a class="indexterm" name="id2615545"></a>
757
Does Samba-3 require the <code class="constant">Sign'n'seal</code> registry hacks needed by Samba-2?
758
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id2615564"></a><a class="indexterm" name="id2615572"></a><a class="indexterm" name="id2615580"></a>
759
No. Samba-3 fully supports <code class="constant">Sign'n'seal</code> as well as <code class="constant">schannel</code>
760
operation. The registry change should not be applied when Samba-3 is used as a domain controller.
761
</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2615602"></a><a name="id2615604"></a></td><td align="left" valign="top"><p>
762
Does Samba-3 support Active Directory?
763
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id2615615"></a>
764
Yes. Samba-3 can be a fully participating native mode Active Directory client. Samba-3 does not
765
provide Active Directory services. It cannot be used to replace a Microsoft Active Directory
766
server implementation. Samba-3 can function as an Active Directory client (workstation) toolkit,
767
and it can function as an Active Directory domain member server.
768
</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2615633"></a><a name="id2615635"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id2615639"></a>
769
When Samba-3 is used with Active Directory, is it necessary to run mixed-mode operation, as was
770
necessary with Samba-2?
771
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id2615655"></a>
772
No. Samba-3 can be used with NetBIOS over TCP/IP disabled, just as can be done with Windows 200x
773
Server and 200x/XPPro client products. It is no longer necessary to run mixed-mode operation,
774
because Samba-3 can join a native Windows 2003 Server ADS domain.
775
</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2615672"></a><a name="id2615674"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id2615677"></a>
776
Is it safe to set share-level access controls in Samba?
777
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
778
Yes. Share-level access controls have been supported since early versions of Samba-2. This is
779
very mature technology. Not enough sites make use of this powerful capability, neither on
780
Windows server or with Samba servers.
781
</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2615701"></a><a name="id2615703"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id2615706"></a>
782
Is it mandatory to set share ACLs to get a secure Samba-3 server?
783
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id2615722"></a><a class="indexterm" name="id2615730"></a><a class="indexterm" name="id2615738"></a><a class="indexterm" name="id2615746"></a><a class="indexterm" name="id2615754"></a>
784
No. Samba-3 honors UNIX/Linux file system security, supports Windows 200x ACLs, and provides
785
means of securing shares through share definition controls in the <code class="filename">smb.conf</code> file. The additional
786
support for share-level ACLs is like frosting on the cake. It adds to security but is not essential
788
</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2615778"></a><a name="id2615780"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id2615783"></a>
789
The <em class="parameter"><code>valid users</code></em> did not work on the <em class="parameter"><code>[homes]</code></em>.
790
Has this functionality been restored yet?
791
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id2615810"></a>
792
Yes. This was fixed in Samba-3.0.2. The use of this parameter is strongly recommended as a safeguard
793
on the <em class="parameter"><code>[homes]</code></em> meta-service. The correct way to specify this is:
794
<a class="link" href="smb.conf.5.html#VALIDUSERS" target="_top">valid users = %S</a>.
795
</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2615844"></a><a name="id2615846"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id2615849"></a><a class="indexterm" name="id2615856"></a><a class="indexterm" name="id2615864"></a>
796
Is the bias against use of the <em class="parameter"><code>force user</code></em> and <em class="parameter"><code>force group</code></em>
798
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id2615892"></a>
799
There is no bias. There is a determination to recommend the right tool for the task at hand.
800
After all, it is better than putting users through performance problems, isn't it?
801
</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2615907"></a><a name="id2615909"></a></td><td align="left" valign="top"><p>
802
The example given for file and directory access control forces all files to be owned by one
803
particular user. I do not like that. Is there any way I can see who created the file?
804
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id2615922"></a>
805
Sure. You do not have to set the SUID bit on the directory. Simply execute the following command
806
to permit file ownership to be retained by the user who created it:
807
</p><pre class="screen">
808
<code class="prompt">root# </code> find /usr/data/finance -type d -exec chmod g+s {}\;
810
Note that this required no more than removing the <code class="constant">u</code> argument so that the
811
SUID bit is not set for the owner.
812
</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2615955"></a><a name="id2615957"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id2615960"></a>
813
In the book, “<span class="quote">The Official Samba-3 HOWTO and Reference Guide</span>”, you recommended use
814
of the Windows NT4 Server Manager (part of the <code class="filename">SRVTOOLS.EXE</code>) utility. Why
815
have you mentioned only the use of the Windows 200x/XP MMC Computer Management utility?
816
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id2615988"></a><a class="indexterm" name="id2615996"></a>
817
Either tool can be used with equal effect. There is no benefit of one over the other, except that
818
the MMC utility is present on all Windows 200x/XP systems and does not require additional software
819
to be downloaded and installed. Note that if you want to manage user and group accounts in your
820
Samba-controlled domain, the only tool that permits that is the NT4 Domain User Manager, which
821
is provided as part of the <code class="filename">SRVTOOLS.EXE</code> utility.
822
</p></td></tr><tr class="question"><td align="left" valign="top"><a name="id2616022"></a><a name="id2616024"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id2616027"></a><a class="indexterm" name="id2616035"></a><a class="indexterm" name="id2616043"></a>
823
I tried to set <em class="parameter"><code>valid users = @Engineers</code></em>, but it does not work. My Samba
824
server is an Active Directory domain member server. Has this been fixed now?
825
</p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p>
826
The use of this parameter has always required the full specification of the domain account, for
827
example, <em class="parameter"><code>valid users = @"MEGANET2\Domain Admins"</code></em>.
828
</p></td></tr></tbody></table></div></div><div class="footnotes"><br><hr width="100" align="left"><div class="footnote"></div><div class="footnote"><a class="ulink" href="http://199.105.191.226/Man/2699/020430msdoj/" target="_top"><sup>[<a name="ftn.id2613126" href="#id2613126" class="ulink">13</a>] </sup>ITWorld.com</a></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="RefSection.html">Prev</a>�</td><td width="20%" align="center"><a accesskey="u" href="RefSection.html">Up</a></td><td width="40%" align="right">�<a accesskey="n" href="DomApps.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part�III.�Reference Section�</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">�Chapter�12.�Integrating Additional Services</td></tr></table></div></body></html>
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