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authorJohn Terpstra <jht@samba.org>2005-04-13 02:26:17 +0000
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+<?xml version="1.0" encoding="iso-8859-1"?>
+<!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
+<chapter id="kerberos">
+ <title>Active Directory, Kerberos, and Security</title>
+
+ <para><indexterm>
+ <primary>experiment</primary>
+ </indexterm>
+ By this point in the book, you have been exposed to many Samba-3 features and capabilities.
+ More importantly, if you have implemented the examples given, you are well on your way to becoming
+ a Samba-3 networking guru who knows a lot about Microsoft Windows. If you have taken the time to
+ practice, you likely have thought of improvements and scenarios with which you can experiment. You
+ are rather well plugged in to the many flexible ways Samba can be used.
+ </para>
+
+ <para><indexterm>
+ <primary>criticism</primary>
+ </indexterm>
+ This is a book about Samba-3. Understandably, its intent is to present it in a positive light.
+ The casual observer might conclude that this book is one-eyed about Samba. It is &smbmdash; what
+ would you expect? This chapter exposes some criticisms that have been raised concerning
+ the use of Samba. For each criticism, there are good answers and appropriate solutions.
+ </para>
+
+ <para>
+ Some criticism always comes from deep inside ranks that one would expect to be supportive of a particular
+ decision. Criticism can be expected from the outside. Let's see how the interesting dynamic of
+ criticism develops with respect to Abmas.
+ </para>
+
+ <para><indexterm>
+ <primary>straw-man</primary>
+ </indexterm>
+ This chapter provides a shameless self-promotion of Samba-3. The objections raised were not pulled
+ out of thin air. They were drawn from comments made by Samba users and from criticism during
+ discussions with Windows network administrators. The tone of the objections reflects as closely
+ as possible that of the original. The case presented is a straw-man example that is designed to
+ permit each objection to be answered as it might occur in real life.
+ </para>
+
+<sect1>
+ <title>Introduction</title>
+
+ <para><indexterm>
+ <primary>acquisitions</primary>
+ </indexterm><indexterm>
+ <primary>risk</primary>
+ </indexterm><indexterm>
+ <primary>assessment</primary>
+ </indexterm><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm><indexterm>
+ <primary>Windows 2003 Serve</primary>
+ </indexterm>
+ Abmas is continuing its meteoric growth with yet further acquisitions. The investment community took
+ note of the spectacular projection of Abmas onto the global business stage. Abmas is building an
+ interesting portfolio of companies that includes accounting services, financial advice, investment
+ portfolio management, property insurance, risk assessment, and the recent addition of a a video rental
+ business. The pieces do not always appear to fit together, but Mr. Meany is certainly executing an
+ interesting business growth and development plan. Abmas Video Rentals has been recently acquired.
+ During the time that the acquisition was closing, the Video Rentals business upgraded their Windows
+ NT4-based network to Windows 2003 Server and Active Directory.
+ </para>
+
+ <para><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm>
+ Bob Jordan has been accepting of the fact that Abmas Video Rentals will use Microsoft Active Directory.
+ The IT team led by Stan Soroka is committed to Samba-3 and to maintaining a uniform technology platform.
+ Stan Soroka's team voiced their disapproval over the decision to permit this business to continue to
+ operate with a solution that is viewed by Christine and her group as <quote>an island of broken
+ technologies.</quote> This comment was made by one of Christine's staff as they were installing a new
+ Samba-3 server at the new business.
+ </para>
+
+
+ <para><indexterm>
+ <primary>consultant</primary>
+ </indexterm><indexterm>
+ <primary>hypothetical</primary>
+ </indexterm>
+ Abmas Video Rentals' head of IT heard of this criticism. He was offended that a junior engineer
+ should make such a comment. He felt that he had to prepare in case he might be criticized for his
+ decision to use Active Directory. He decided he would defend his decision by hiring the services
+ of an outside security systems consultant to report<footnote>This report is entirely fictitious.
+ Any resemblance to a factual report is purely coincidental.</footnote> on his unit's operations
+ and to investigate the role of Samba at his site. Here are key extracts from this hypothetical
+ report:
+ </para>
+
+ <blockquote><para><indexterm>
+ <primary>vulnerabilities</primary>
+ </indexterm><indexterm>
+ <primary>integrity</primary>
+ </indexterm><indexterm>
+ <primary>practices</primary>
+ </indexterm><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm>
+ ... the implementation of Microsoft Active Directory at the Abmas Video Rentals, Bamingsham site,
+ has been examined. We find no evidence to support a notion that vulnerabilities exist at your site.
+ ... we took additional steps to validate the integrity of the installation and operation of Active
+ Directory and are pleased that your staff are following sound practices.
+ </para>
+
+ <para>
+ ...
+ </para>
+
+ <para><indexterm>
+ <primary>accounts</primary>
+ <secondary>user</secondary>
+ </indexterm><indexterm>
+ <primary>accounts</primary>
+ <secondary>group</secondary>
+ </indexterm><indexterm>
+ <primary>Backup</primary>
+ </indexterm><indexterm>
+ <primary>disaster recovery</primary>
+ </indexterm><indexterm>
+ <primary>validated</primary>
+ </indexterm><indexterm>
+ <primary>off-site storage</primary>
+ </indexterm>
+ User and Group accounts, and respective privileges, have been well thought out. File system shares are
+ appropriately secured. Backup and disaster recovery plans are well managed and validated regularly, and
+ effective off-site storage practices are considered to exceed industry norms.
+ </para>
+
+ <para><indexterm>
+ <primary>compromise</primary>
+ </indexterm><indexterm>
+ <primary>secure</primary>
+ </indexterm><indexterm>
+ <primary>network</primary>
+ <secondary>secure</secondary>
+ </indexterm>
+ Your staff are justifiably concerned that the use of Samba may compromise their good efforts to maintain
+ a secure network.
+ </para>
+
+ <para><indexterm>
+ <primary>winbind</primary>
+ </indexterm><indexterm>
+ <primary>security</primary>
+ </indexterm><indexterm>
+ <primary>secure</primary>
+ </indexterm><indexterm>
+ <primary>network</primary>
+ <secondary>management</secondary>
+ </indexterm>
+ The recently installed Linux file and application server uses a tool called <command>winbind</command>
+ that is indiscriminate about security. All user accounts in Active Directory can be used to access data
+ stored on the Linux system. We are alarmed that secure information is accessible to staff who should
+ not even be aware that it exists. We share the concerns of your network management staff who have gone
+ to great lengths to set fine-grained controls that limit information access to those who need access.
+ It seems incongruous to us that Samba winbind should be permitted to be used as it voids this fine work.
+ </para>
+
+ <para><indexterm>
+ <primary>isolated</primary>
+ </indexterm><indexterm>
+ <primary>firewall</primary>
+ </indexterm><indexterm>
+ <primary>best practices</primary>
+ </indexterm>
+ Graham Judd [head of network administration] has locked down the security of all systems and is following
+ the latest Microsoft guidelines. ... null session connections have been disabled ... the internal network
+ is isolated from the outside world, the [product name removed] firewall is under current contract
+ maintenance support from [the manufacturer]. ... our attempts to penetrate security of your systems
+ failed to find problems common to Windows networking sites. We commend your staff on their attention to
+ detail and for following Microsoft recommended best practices.
+ </para>
+
+ <para>
+ ...
+ </para>
+
+ <para><indexterm>
+ <primary>security</primary>
+ </indexterm><indexterm>
+ <primary>disable</primary>
+ </indexterm><indexterm>
+ <primary>essential</primary>
+ </indexterm><indexterm>
+ <primary>trusted computing</primary>
+ </indexterm>
+ In respect of the use of Samba, we offer the following comments: Samba is in use in nearly half of
+ all sites we have surveyed. ... It is our opinion that Samba offers no better security than Microsoft
+ ... what worries us regarding Samba is the need to disable essential Windows security features such as
+ secure channel support, digital sign'n'seal on all communication traffic, running Active Directory in
+ mixed mode so that Samba clients and servers can authenticate all of it. Additionally, we are concerned that
+ Samba is not at the full capabilites of Microsoft Windows NT4 server. Microsoft has moved well beyond that
+ with trusted computing initiatives that the Samba developers do not participate in.
+ </para>
+
+ <para><indexterm>
+ <primary>integrity</primary>
+ </indexterm><indexterm>
+ <primary>hackers</primary>
+ </indexterm><indexterm>
+ <primary>accountable</primary>
+ </indexterm><indexterm>
+ <primary>flaws</primary>
+ </indexterm><indexterm>
+ <primary>updates</primary>
+ </indexterm><indexterm>
+ <primary>bug fixes</primary>
+ </indexterm><indexterm>
+ <primary>alarm</primary>
+ </indexterm>
+ One wonders about the integrity of an open source program that is developed by a team of hackers
+ who cannot be held accountable for the flaws in their code. The sheer number of updates and bug
+ fixes they have released should ring alarm bells in any business.
+ </para>
+
+ <para><indexterm>
+ <primary>employment</primary>
+ </indexterm><indexterm>
+ <primary>jobs</primary>
+ </indexterm><indexterm>
+ <primary>risk</primary>
+ </indexterm>
+ Another factor that should be considered is that buying Microsoft products and services helps to
+ provide employment in the IT industry. Samba and Open Source software place those jobs at risk.
+ </para></blockquote>
+
+ <para><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm><indexterm>
+ <primary>independent expert</primary>
+ </indexterm>
+ This is also a challenge to rise above the trouble spot. Bob calls Stan's team together for a simple
+ discussion, but it gets further out of hand. When he returns to his office, he finds the following
+ email in his in-box:
+ </para>
+
+ <para>
+ Bob,
+ </para>
+
+ <blockquote><attribution>Stan</attribution><para>
+ I apologize for the leak of internal discussions to the new business. It reflects poorly on our
+ professionalism and has put you in an unpleasant position. I regret the incident.
+ </para>
+
+ <para>
+ I also wish to advise that two of the recent recruits want to implement Kerberos authentication
+ across all systems. I concur with the desire to improve security. One of the new guys who is championing
+ the move to Kerberos was responsible for the comment that caused the embarrassment.
+ </para>
+
+ <para><indexterm>
+ <primary>Kerberos</primary>
+ </indexterm><indexterm>
+ <primary>OpenLDAP</primary>
+ </indexterm><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm><indexterm>
+ <primary>consultant</primary>
+ </indexterm>
+ I am experiencing difficulty in handling the sharp push for Kerberos. He claims that Kerberos, OpenLDAP,
+ plus Samba-3 will seamlessly replace Microsoft Active Directory. I am a little out of my depth with respect
+ to the feasibility of such a move, but have taken steps to pull both of them into line. With your consent,
+ I would like to hire the services of a well-known Samba consultant to set the record straight.
+ </para>
+
+ <para><indexterm>
+ <primary>criticism</primary>
+ </indexterm><indexterm>
+ <primary>policy</primary>
+ </indexterm><indexterm>
+ <primary>Windows Servers</primary>
+ </indexterm><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm><indexterm>
+ <primary>budgetted</primary>
+ </indexterm><indexterm>
+ <primary>financial responsibility</primary>
+ </indexterm>
+ I intend to use this report to answer the criticism raised and would like to establish a policy that we
+ will approve the use of Microsoft Windows Servers (and Active Directory) subject to all costs being covered
+ out of the budget of the division that wishes to go its own way. I propose that dissenters will still remain
+ responsible to meet the budgeted contribution to IT operations as a whole. I believe we should not coerce
+ use of any centrally proposed standards, but make all non-compliance the financial responsibility of the
+ out-of-step division. Hopefully, this will encourage all divisions to walk with us and not alone.
+ </para></blockquote>
+
+ <sect2>
+ <title>Assignment Tasks</title>
+
+ <para>
+ Bob agreed with Stan's recommendations and has hired your services to help defuse the powder
+ keg. Your task is to answer each of the issues raised with a tractable answer. You must be able
+ to support your claims, keep emotions to a side, and answer technically.
+ </para>
+
+ </sect2>
+</sect1>
+
+<sect1>
+ <title>Dissection and Discussion</title>
+
+ <para><indexterm>
+ <primary>tool</primary>
+ </indexterm><indexterm>
+ <primary>benefit</primary>
+ </indexterm><indexterm>
+ <primary>choice</primary>
+ </indexterm><indexterm>
+ <primary>consultant</primary>
+ </indexterm><indexterm>
+ <primary>installation</primary>
+ </indexterm><indexterm>
+ <primary>income</primary>
+ </indexterm><indexterm>
+ <primary>employment</primary>
+ </indexterm>
+ Samba-3 is a tool. No one pounding your door to use Samba. That is a choice that you are free to
+ make or reject. It is likely that your decision to use Samba can benefit your company more than
+ anyone else. The Samba Team obviously believes that the Samba software is a worthy choice.
+ If you hire a consultant to assist with the installation and/or deployment of Samba, or if you hire
+ someone to help manage your Samba installation, you can create income and employment. Alternately,
+ money saved by not spending in the IT area can be spent elsewhere in the business. All money saved
+ or spent creates employment.
+ </para>
+
+ <para><indexterm>
+ <primary>economically sustainable</primary>
+ </indexterm><indexterm>
+ <primary>inter-operability</primary>
+ </indexterm><indexterm>
+ <primary>file and print service</primary>
+ </indexterm><indexterm>
+ <primary>cost</primary>
+ </indexterm><indexterm>
+ <primary>alternative</primary>
+ </indexterm>
+ In the long term, the use of Samba must be economically sustainable. In some situations, Samba is adopted
+ purely to provide file and print service interoperability on platforms that otherwise cannot provide
+ access to data and to printers for Microsoft Windows clients. Samba is used by some businesses to
+ effect a reduction in the cost of providing IT services. Obviously, it is also used by some as an
+ alternative to the use of a Microsoft file and print serving platforms with no consideration of costs.
+ </para>
+
+ <para><indexterm>
+ <primary>documentation</primary>
+ </indexterm><indexterm>
+ <primary>responsibility</primary>
+ </indexterm><indexterm>
+ <primary>fix</primary>
+ </indexterm><indexterm>
+ <primary>broken</primary>
+ </indexterm>
+ It would be foolish to adopt a technology that might put any data or users at risk. Security affects
+ everyone. The Samba Team are fully cognizant of the responsibility they have to their users.
+ The Samba documentation clearly reveals the fact that full responsibility is accepted to fix anything
+ that is broken.
+ </para>
+
+ <para><indexterm>
+ <primary>commercial</primary>
+ </indexterm><indexterm>
+ <primary>software</primary>
+ </indexterm><indexterm>
+ <primary>commercial software</primary>
+ </indexterm><indexterm>
+ <primary>End User License Agreement</primary>
+ <see>EULA</see>
+ </indexterm><indexterm>
+ <primary>accountable</primary>
+ </indexterm><indexterm>
+ <secondary>liability</secondary>
+ </indexterm><indexterm>
+ <primary>accepts liability</primary>
+ </indexterm><indexterm>
+ <primary>price paid</primary>
+ </indexterm><indexterm>
+ <primary>product defects</primary>
+ </indexterm><indexterm>
+ <primary>reimburse</primary>
+ </indexterm><indexterm>
+ <primary>extent</primary>
+ </indexterm>
+ There is a mistaken perception in the IT industry that commercial software providers are fully
+ accountable for the defects in products. Open Source software comes with no warranty, so it is
+ often assumed that its use confers a higher degree of risk. Everyone should read commercial software
+ End User License Agreements (EULAs). You should determine what real warranty is offered and the
+ extent of liability that is accepted. Doing so soon dispels the popular notion that
+ commercial software vendors are willingly accountable for product defects. In many cases, the
+ commercial vendor accepts liability only to reimburse the price paid for the software.
+ </para>
+
+ <para><indexterm>
+ <primary>consumer</primary>
+ </indexterm><indexterm>
+ <primary>EULA</primary>
+ </indexterm><indexterm>
+ <primary>track record</primary>
+ </indexterm><indexterm>
+ <primary>commercial software</primary>
+ </indexterm><indexterm>
+ <primary>support</primary>
+ </indexterm><indexterm>
+ <primary>vendor</primary>
+ </indexterm>
+ The real issues that a consumer (like you) needs answered is what is the way of escape from technical
+ problems and how long will it take? The average problem turnaround time in the Open Source community is
+ approximately 48 hours. What does the EULA offer? What is the track record in the commercial software
+ industry? What happens when your commercial vendor decides to cease providing support?
+ </para>
+
+ <para><indexterm>
+ <primary>source code</primary>
+ </indexterm><indexterm>
+ <primary>Open Source</primary>
+ </indexterm><indexterm>
+ <primary>hire</primary>
+ </indexterm><indexterm>
+ <primary>programmer</primary>
+ </indexterm><indexterm>
+ <primary>solve</primary>
+ </indexterm><indexterm>
+ <primary>fix</primary>
+ </indexterm><indexterm>
+ <secondary>problem</secondary>
+ </indexterm>
+ Open Source software at least puts you in possession of the source code. This means that when
+ all else fails, you can hire a programmer to solve/fix the problem.
+ </para>
+
+ <sect2>
+ <title>Technical Issues</title>
+
+ <para>
+ Each issue is now discussed and, where appropriate, example implementation steps are
+ provided.
+ </para>
+
+ <variablelist>
+ <varlistentry>
+ <term>Winbind and Security</term>
+ <listitem><para><indexterm>
+ <primary>Winbind</primary>
+ </indexterm><indexterm>
+ <primary>Security</primary>
+ </indexterm><indexterm>
+ <primary>network</primary>
+ <secondary>administrators</secondary>
+ </indexterm><indexterm>
+ <primary>Domain users</primary>
+ </indexterm><indexterm>
+ <secondary>Domain account</secondary>
+ </indexterm><indexterm>
+ <primary>credentials</primary>
+ </indexterm><indexterm>
+ <primary>Network Neighborhood</primary>
+ </indexterm><indexterm>
+ <primary>UNIX/Linux server</primary>
+ </indexterm><indexterm>
+ <primary>browse</primary>
+ </indexterm><indexterm>
+ <primary>shares</primary>
+ </indexterm>
+ Windows network administrators may be dismayed to find that <command>winbind</command>
+ exposes all Domain users so that they may use their Domain account credentials to
+ log onto a UNIX/Linux system. The fact that all users in the Domain can see the
+ UNIX/Linux server in their Network Neighborhood and can browse the shares on the
+ server seems to excite them further.
+ </para>
+
+ <para><indexterm>
+ <primary>Domain Member server</primary>
+ </indexterm><indexterm>
+ <primary>familiar</primary>
+ </indexterm><indexterm>
+ <primary>fear</primary>
+ </indexterm><indexterm>
+ <primary>unknown</primary>
+ </indexterm>
+ <command>winbind</command> provides for the UNIX/Linux Domain Member server or
+ client, the same as one would obtain by adding a Microsoft Windows server or
+ client to the Domain. The real objection is the fact that Samba is not MS Windows
+ and, therefore, requires handling a little differently from the familiar Windows systems.
+ One must recognize fear of the unknown.
+ </para>
+
+ <para><indexterm>
+ <primary>network administrators</primary>
+ </indexterm><indexterm>
+ <primary>recognize</primary>
+ </indexterm><indexterm>
+ <primary>winbind</primary>
+ </indexterm><indexterm>
+ <primary>over-ride</primary>
+ </indexterm><indexterm>
+ <primary>Active Directory</primary>
+ <secondary>management tools</secondary>
+ </indexterm><indexterm>
+ <primary>fears</primary>
+ </indexterm>
+ Windows network administrators need to recognize that <command>winbind</command> does
+ not, and cannot, override account controls set using the Active Directory management
+ tools. The control is the same. Have no fear.
+ </para>
+
+ <para><indexterm>
+ <primary>ADS Domain</primary>
+ </indexterm><indexterm>
+ <primary>account</primary>
+ <secondary>ADS Domain</secondary>
+ </indexterm><indexterm>
+ <primary>winbind</primary>
+ </indexterm><indexterm>
+ <primary>browsing</primary>
+ </indexterm><indexterm>
+ <primary>permits</primary>
+ </indexterm><indexterm>
+ <primary>access</primary>
+ </indexterm><indexterm>
+ <primary>drive mapping</primary>
+ </indexterm><indexterm>
+ <primary>protected</primary>
+ </indexterm><indexterm>
+ <primary>security controls</primary>
+ </indexterm><indexterm>
+ <primary>access controls</primary>
+ </indexterm>
+ Where Samba and the ADS Domain account information obtained through the use of
+ <command>winbind</command> permits access, by browsing or by the drive mapping to
+ a share, to data that should be better protected. This can only happen when security
+ controls have not been properly implemented. Samba permits access controls to be set
+ on:
+ </para>
+
+ <itemizedlist>
+ <listitem><para>Shares themselves (i.e., the logical share itself)</para></listitem>
+ <listitem><para>The share definition in &smb.conf;</para></listitem>
+ <listitem><para>The shared directories and files using UNIX permissions</para></listitem>
+ <listitem><para>Using Windows 2000 ACLs &smbmdash; if the file system is Posix enabled</para></listitem>
+ </itemizedlist>
+
+ <para>
+ Examples of each are given in <link linkend="ch10expl"/>.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>User and Group Controls</term>
+ <listitem><para><indexterm>
+ <primary>User and Group Controls</primary>
+ </indexterm><indexterm>
+ <primary>management</primary>
+ <secondary>User</secondary>
+ </indexterm><indexterm>
+ <primary>management</primary>
+ <secondary>group</secondary>
+ </indexterm><indexterm>
+ <primary>ADS</primary>
+ </indexterm><indexterm>
+ <primary>permissions</primary>
+ </indexterm><indexterm>
+ <primary>privileges</primary>
+ </indexterm><indexterm>
+ <primary>flexibility</primary>
+ </indexterm><indexterm>
+ <primary>access controls</primary>
+ </indexterm><indexterm>
+ <primary>share definition</primary>
+ </indexterm>
+ User and group management facilities as known in the Windows ADS environment may be
+ used to provide equivalent access control constraints or to provide equivalent
+ permissions and privileges on Samba servers. Samba offers greater flexibility in the
+ use of user and group controls because it has additional layers of control compared to
+ Windows 200x/XP. For example, access controls on a Samba server may be set within
+ the share definition in a manner for which Windows has no equivalent.
+ </para>
+
+ <para><indexterm>
+ <primary>analysis</primary>
+ </indexterm><indexterm>
+ <primary>system security</primary>
+ </indexterm><indexterm>
+ <primary>safe-guards</primary>
+ </indexterm><indexterm>
+ <primary>permissions</primary>
+ <secondary>excessive</secondary>
+ </indexterm><indexterm>
+ <primary>file system</primary>
+ </indexterm><indexterm>
+ <primary>shared resource</primary>
+ </indexterm><indexterm>
+ <primary>share definition</primary>
+ </indexterm>
+ In any serious analysis of system security, it is important to examine the safeguards
+ that remain when all other protective measures fail. An administrator may inadvertently
+ set excessive permissions on the file system of a shared resource, or he may set excessive
+ privileges on the share itself. If that were to happen in a Windows 2003 Server environment,
+ the data would indeed be laid bare to abuse. Yet, within a Samba share definition, it is
+ possible to guard against that by enforcing controls on the share definition itself. You
+ see a practical example of this a little later in this chapter.
+ </para>
+
+ <para><indexterm>
+ <primary>diligence</primary>
+ </indexterm><indexterm>
+ <primary>weakness</primary>
+ </indexterm>
+ The report that is critical of Samba really ought to have exercised greater due
+ diligence, as the real weakness is on the side of a Microsoft Windows environment.
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Security Overall</term>
+ <listitem><para><indexterm>
+ <primary>defects</primary>
+ </indexterm>
+ Samba has been designed in such a manner that weaknesses inherent in the design of
+ Microsoft Windows networking ought not to expose the underlying UNIX/Linux file
+ system in any way. All software has potential defects, and Samba is no exception.
+ What matters more is how defects that are discovered get dealt with.
+ </para>
+
+ <para><indexterm>
+ <primary>security</primary>
+ </indexterm><indexterm>
+ <primary>protection</primary>
+ </indexterm><indexterm>
+ <primary>compromise</primary>
+ </indexterm><indexterm>
+ <primary>consequential risk</primary>
+ </indexterm>
+ The Samba Team totally agrees with the necessity to observe and fully implement
+ every security facility to provide a level of protection and security that is necessary
+ and that the end user (or network administrator) needs. Never would the Samba Team
+ recommend a compromise to system security, nor would deliberate defoliation of
+ security be publicly condoned; yet this is the practice by many Windows network
+ administrators just to make happy users who have no notion of consequential risk.
+ </para>
+
+ <para><indexterm>
+ <primary>condemns</primary>
+ </indexterm><indexterm>
+ <primary>security fixes</primary>
+ </indexterm><indexterm>
+ <primary>updates</primary>
+ </indexterm><indexterm>
+ <primary>development</primary>
+ </indexterm><indexterm>
+ <primary>documentation</primary>
+ </indexterm><indexterm>
+ <primary>security updates</primary>
+ </indexterm><indexterm>
+ <primary>turn-around time</primary>
+ </indexterm>
+ The report condemns Samba for releasing updates and security fixes, yet Microsoft
+ on-line updates need to be applied almost weekly. The answer to the criticism made
+ lies in the fact that Samba development is continuing, documentation is improving,
+ user needs are being increasingly met or exceeded, and security updates are issued
+ with a short turnaround time.
+ </para>
+
+ <para><indexterm>
+ <primary>modularization</primary>
+ </indexterm><indexterm>
+ <primary>next generation</primary>
+ </indexterm><indexterm>
+ <primary>responsible</primary>
+ </indexterm><indexterm>
+ <primary>dependability</primary>
+ </indexterm><indexterm>
+ <primary>road-map</primary>
+ <secondary>published</secondary>
+ </indexterm>
+ The release of Samba-4 is expected around late 2004 to early 2005 and involves a near
+ complete rewrite to permit extensive modularization and to prepare Samba for new
+ functionality planned for addition during the next generation series. The Samba Team
+ is responsible and can be depended upon; the history to date would suggest a high
+ degree of dependability as well as on charter development consistent with published
+ road-map projections.
+ </para>
+
+ <para><indexterm>
+ <primary>foundation members</primary>
+ </indexterm><indexterm>
+ <primary>Common Internet File System</primary>
+ <see>CIFS</see>
+ </indexterm><indexterm>
+ <primary>network attached storage</primary>
+ <see>NAS</see>
+ </indexterm><indexterm>
+ <primary>conferences</primary>
+ </indexterm><indexterm>
+ <primary>presence and leadership</primary>
+ </indexterm><indexterm>
+ <primary>leadership</primary>
+ </indexterm><indexterm>
+ <primary>inter-operability</primary>
+ </indexterm>
+ Not well published is the fact that Microsoft was a foundation member of
+ the Common Internet File System (CIFS) initiative, together with the participation
+ of the network attached storage (NAS) industry. Unfortunately, for the past few years,
+ Microsoft has been absent from active involvement at CIFS conferences and has
+ not exercised the leadership expected of a major force in the networking technology
+ space. The Samba Team has maintained consistent presence and leadership at all
+ CIFS conferences and at the interoperability laboratories run concurrently with
+ them.
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Cryptographic Controls (schannel, sign'n'seal)</term>
+ <listitem><para><indexterm>
+ <primary>Cryptographic</primary>
+ </indexterm><indexterm>
+ <primary>schannel</primary>
+ </indexterm><indexterm>
+ <primary>digital sign'n'seal</primary>
+ </indexterm>
+ The report correctly mentions the fact that Samba did not support the most recent
+ <constant>schannel</constant> and <constant>digital sign'n'seal</constant> features
+ of Microsoft Windows NT/200x/XPPro products. This is one of the key features
+ of the Samba-3 release. Market research reports take so long to generate that they are
+ seldom a reflection of current practice, and in many respects reports are like a
+ pathology report &smbmdash; they reflect accurately (at best) status at a snap-shot in time.
+ Meanwhile, the world moves on.
+ </para>
+
+ <para><indexterm>
+ <primary>public specifications</primary>
+ </indexterm><indexterm>
+ <primary>protocols</primary>
+ </indexterm><indexterm>
+ <primary>algorithm</primary>
+ </indexterm><indexterm>
+ <primary>compatible</primary>
+ </indexterm><indexterm>
+ <primary>network</primary>
+ <secondary>traffic</secondary>
+ <tertiary>observation</tertiary>
+ </indexterm><indexterm>
+ <primary>defensible standards</primary>
+ </indexterm><indexterm>
+ <primary>secure networking</primary>
+ </indexterm>
+ It should be pointed out that had clear public specifications for the protocols
+ been published, it would have been much easier to implement this and would have
+ taken less time to do. The sole mechanism used to find an algorithm that is compatible
+ with the methods used by Microsoft has been based on observation of network traffic
+ and trial-and-error implementation of potential techniques. The real value of public
+ and defensible standards is obvious to all, and would have enabled more secure networking
+ for everyone.
+ </para>
+
+ <para><indexterm>
+ <primary>Critics</primary>
+ </indexterm><indexterm>
+ <primary>digital sign'n'seal</primary>
+ </indexterm>
+ Critics of Samba often ignore fundamental problems that may plague (or may have plagued)
+ the users of Microsoft's products also. Those who are first to criticize Samba
+ for not rushing into release of <constant>digital sign'n'seal</constant> support
+ often dismiss the problems that Microsoft has
+ <ulink url="http://support.microsoft.com/default.aspx?kbid=321733">acknowledged</ulink>
+ and for which a fix was provided. In fact,
+ <ulink url="http://www.tangent-systems.com/support/delayedwrite.html">Tangent Systems</ulink>
+ appears even today<footnote>January 2004</footnote> to not be sure that the problem has been resolved.
+ So it is evident that some delay in release of new functionality may have
+ fortuitous consequences.
+ </para>
+
+ <para><indexterm>
+ <primary>secure networking protocols</primary>
+ </indexterm><indexterm>
+ <primary>refereed standards</primary>
+ </indexterm><indexterm>
+ <primary>proprietary</primary>
+ </indexterm><indexterm>
+ <primary>digital rights</primary>
+ </indexterm><indexterm>
+ <primary>protection</primary>
+ </indexterm><indexterm>
+ <primary>networking protocols</primary>
+ </indexterm><indexterm>
+ <primary>diffusion</primary>
+ </indexterm><indexterm>
+ <primary>consumer</primary>
+ </indexterm><indexterm>
+ <primary>choice</primary>
+ </indexterm>
+ One final comment is warranted. If companies want more secure networking protocols,
+ the most effective method by which this can be achieved is by users seeking
+ and working together to help define open and publicly refereed standards. The
+ development of closed source, proprietary methods that are developed in a
+ clandestine framework of secrecy, under claims of digital rights protection, does
+ not favor the diffusion of safe networking protocols, and certainly does not
+ help the consumer to make a better choice.
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Active Directory Replacement with Kerberos, LDAP, and Samba</term>
+ <indexterm>
+ <primary>Active Directory</primary>
+ <secondary>Replacement</secondary>
+ </indexterm><indexterm>
+ <primary>Kerberos</primary>
+ </indexterm><indexterm>
+ <primary>LDAP</primary>
+ </indexterm><indexterm>
+ <primary>remote procedure call</primary>
+ <see>RPC</see>
+ </indexterm>
+ <listitem><para>
+ <literallayout> </literallayout>
+ The Microsoft networking protocols extensively make use of remote procedure call (RPC)
+ technology. Active Directory is not a simple mixture of LDAP and Kerberos together
+ with file and print services, but rather is a complex intertwined implementation
+ of them that uses RPCs that are not supported by any of these component technologies
+ and yet by which they are made to interoperate in ways that the components do not
+ support.
+ </para>
+
+ <para><indexterm>
+ <primary>Active Directory</primary>
+ <secondary>Server</secondary>
+ </indexterm><indexterm>
+ <primary>OpenLDAP</primary>
+ </indexterm><indexterm>
+ <primary>Kerberos</primary>
+ </indexterm><indexterm>
+ <primary>project maintainers</primary>
+ </indexterm><indexterm>
+ <primary>LDAP</primary>
+ </indexterm>
+ In order to make the popular request for Samba to be an Active Directory Server a
+ reality, it is necessary to add to OpenLDAP, Kerberos, as well as Samba, RPC calls
+ that are not presently supported. The Samba Team has not been able to gain critical
+ overall support for all project maintainers to work together on the complex
+ challenge of developing and integrating the necessary technologies. Therefore, if
+ the Samba Team does not make it a priority to absorb Kerberos and LDAP functionality
+ into the Samba project, this dream request can not become a reality.
+ </para>
+
+ <para><indexterm>
+ <primary>missing RPC's</primary>
+ </indexterm><indexterm>
+ <primary>road-map</primary>
+ </indexterm><indexterm>
+ <primary>ADS</primary>
+ <secondary>server</secondary>
+ </indexterm><indexterm>
+ <primary>MMC</primary>
+ </indexterm><indexterm>
+ <primary>managed</primary>
+ </indexterm>
+ At this time, the integration of LDAP, Kerberos, and the missing RPCs is not on the
+ Samba development roadmap. If it is not on the published roadmap, it cannot be delivered
+ anytime soon. Ergo, ADS server support is not a current goal for Samba development.
+ The Samba Team is most committed to permitting Samba to be a full ADS Domain member
+ that is increasingly capable of being managed using Microsoft Windows MMC tools.
+ </para></listitem>
+ </varlistentry>
+ </variablelist>
+
+ <sect3>
+ <title>Kerberos Exposed</title>
+
+ <para><indexterm>
+ <primary>kerberos</primary>
+ </indexterm><indexterm>
+ <primary>unauthorized activities</primary>
+ </indexterm><indexterm>
+ <primary>authorized location</primary>
+ </indexterm>
+ Kerberos is a network authentication protocol that provides secure authentication for
+ client-server applications by using secret-key cryptography. Firewalls are an insufficient
+ barrier mechanism in todays networking world as at best they only restrict incoming network
+ traffic but can not prevent network traffic that comes from authorized locations from
+ performing unauthorized activities.
+ </para>
+
+ <para><indexterm>
+ <primary>strong cryptography</primary>
+ </indexterm><indexterm>
+ <primary>identity</primary>
+ </indexterm><indexterm>
+ <primary>integrity</primary>
+ </indexterm>
+ Kerberos was created by MIT as a solution to network security problems. The Kerberos protocol uses
+ strong cryptography so that a client can prove its identity to a server (and vice versa) across an
+ insecure network connection. After a client and server has used Kerberos to prove their identity,
+ they can also encrypt all of their communications to assure privacy and data integrity as they go
+ about their business.
+ </para>
+
+ <para><indexterm>
+ <primary>trusted third-party</primary>
+ </indexterm><indexterm>
+ <primary>principals</primary>
+ </indexterm><indexterm>
+ <primary>trusting</primary>
+ </indexterm><indexterm>
+ <primary>kerberos</primary>
+ <secondary>server</secondary>
+ </indexterm><indexterm>
+ <primary>secret</primary>
+ </indexterm>
+ Kerberos is a trusted third-party service. That means that there is a third party (the kerberos
+ server) that is trusted by all the entities on the network (users and services, usually called
+ principals). All principals share a secret password (or key) with the kerberos server and this
+ enables principals to verify that the messages from the kerberos server are authentic. Thus
+ trusting the kerberos server, users and services can authenticate each other.
+ </para>
+
+ <para><indexterm>
+ <primary>restricted export</primary>
+ </indexterm><indexterm>
+ <primary>MIT Kerberos</primary>
+ </indexterm><indexterm>
+ <primary>Heimdal Kerberos</primary>
+ </indexterm>
+ Kerberos was until recently a technology that was restricted from being exported from the United States.
+ For many years that hindered global adoption of more secure networking technologies both within the USA
+ as well as outside it. A free an unencumbered implementation of MIT Kerberos has been produced in Europe
+ and is available from the University of Paderborn, Sweden. It is known as the Heimdal Kerberos project.
+ In recent times the USA government has removed sanctions affecting the global distribution of MIT Kerberos.
+ It is likely that there will be a significant surge forward in the development of Kerberos enabled applications
+ and in the general deployment and use of Kerberos across the spectrum of the information technology industry.
+ </para>
+
+ <para><indexterm>
+ <primary>Kerberos</primary>
+ <secondary>interoperability</secondary>
+ </indexterm>
+ A storm has broken out concerning interoperability between MIT Kerberos and Microsofts' implementation
+ of it. For example, a 2002 new report by <ulink url="http://www.idg.com.sg/idgwww.nsf/0/5DDA8D153A7505A748256BAB000D992A?OpenDocument">IDG</ulink>
+ states:
+ </para>
+
+ <blockquote><para>
+ A Microsoft Corp. executive testified at the software giant's remedy hearing that the company goes to
+ great lengths to disclose interfaces and protocols that allow third-party software products to interact
+ with Windows. But a lawyer with the states suing Microsoft pointed out that when it comes to the company's
+ use of the Kerberos authentication specification, not everyone agrees.
+ </para>
+
+ <para><indexterm>
+ <primary>Kerberos</primary>
+ <secondary>unspecified fields</secondary>
+ </indexterm>
+ Robert Short, vice president of Windows core technology at Microsoft, wrote in his direct testimony prepared
+ before his appearance that non-Microsoft operating systems can disregard the portion of the Kerberos version
+ 5 specification that Windows clients use for proprietary purposes and still achieve interoperability with
+ the Microsoft OS. Microsoft takes advantage of unspecified fields in the Kerberos specification for storing
+ Windows-specific authorization data, Short wrote. The designers of Kerberos left these fields undefined so
+ that software developers could add their own authorization information, he said.
+ </para></blockquote>
+
+ <para><indexterm>
+ <primary>DCE</primary>
+ </indexterm><indexterm>
+ <primary>RPC</primary>
+ </indexterm>
+ It so happens that Microsoft Windows clients depend on and expect the contents of the <emphasis>unspecified
+ fields</emphasis> in the Kerberos 5 communications data stream for their Windows interoperability, in
+ particular when Samba is being expected to emulate a Windows Server 200x Domain Controller. But the interoperability
+ issue goes far deeper than this. In the Domain control protocols that are used by MS Windows XP Professional
+ there is a tight interdependency between the Kerberos protocols and the Microsoft distributed computing environment
+ (DCE) remote procedure calls (RPCs) that themselves are an integral part of the SMB/CIFS protocols as used by
+ Microsoft.
+ </para>
+
+ <para>
+ Microsoft makes the following comment in a reference in a <ulink url="http://www.microsoft.com/technet/itsolutions/interop/mgmt/kerberos.asp">
+ technet</ulink> article:
+ </para>
+
+ <blockquote><para><indexterm>
+ <primary>Privilege Attribute Certificates</primary>
+ <see>PAC</see>
+ </indexterm><indexterm>
+ <primary>access control</primary>
+ </indexterm>
+ The DCE Security Services are also layered on the Kerberos protocol. DCE authentication services use RPC
+ representation of Kerberos protocol messages. In addition, DCE uses the authorization data field in Kerberos
+ tickets to convey Privilege Attribute Certificates (PACs) that define user identity and group membership.
+ The DCE PAC is used in a similar manner as Windows NT Security IDs for user authorization and access control.
+ Windows NT services will not be able to translate DCE PACs into Windows NT user and group identifiers. This
+ is not an issue with Kerberos interoperability, but rather an issue of interoperability between DCE and
+ Windows NT access control information.
+ </para></blockquote>
+
+ </sect3>
+
+ </sect2>
+
+</sect1>
+
+<sect1 id="ch10expl">
+ <title>Implementation</title>
+
+ <para>
+ The following procedures outline the implementation of the security measures discussed so far.
+ </para>
+
+ <sect2>
+ <title>Share Access Controls</title>
+
+ <para><indexterm>
+ <primary>Share Access Controls</primary>
+ </indexterm><indexterm>
+ <primary>filter</primary>
+ </indexterm><indexterm>
+ <primary>connection</primary>
+ </indexterm>
+ Access control entries placed on the share itself act as a filter at the time a when CIFS/SMB client (such as
+ Windows XP Pro) attempts to make a connection to the Samba server.
+ </para>
+
+ <procedure>
+ <title>Create/Edit/Delete Share ACLs</title>
+ <step><para><indexterm>
+ <primary>Domain Administrator</primary>
+ </indexterm><indexterm>
+ <primary>account</primary>
+ </indexterm>
+ From a Windows 200x/XP Professional workstation, log onto the Domain using the Domain Administrator
+ account (on Samba Domains, this is usually the account called <constant>root</constant>).
+ </para></step>
+
+ <step><para>
+ Click
+ <menuchoice>
+ <guimenu>Start</guimenu>
+ <guimenuitem>Settings</guimenuitem>
+ <guimenuitem>Control Panel</guimenuitem>
+ <guimenuitem>Administrative Tools</guimenuitem>
+ <guimenuitem>Computer Management</guimenuitem>
+ </menuchoice>.
+ </para></step>
+
+ <step><para>
+ In the left panel,
+ <menuchoice>
+ <guimenu>[Right mouse menu item] Computer Management (Local)</guimenu>
+ <guimenuitem>Connect to another computer ...</guimenuitem>
+ <guimenuitem>Browse...</guimenuitem>
+ <guimenuitem>Advanced</guimenuitem>
+ <guimenuitem>Find Now</guimenuitem>
+ </menuchoice>. In the lower panel, click on the name of the server you wish to
+ administer. Click <menuchoice>
+ <guimenu>OK</guimenu>
+ <guimenuitem>OK</guimenuitem>
+ <guimenuitem>OK</guimenuitem>
+ </menuchoice>.<indexterm>
+ <primary>Computer Management</primary>
+ </indexterm>
+ In the left panel, the entry <guimenu>Computer Management (Local)</guimenu> should now reflect
+ the change made. For example, if the server you are administering is called <constant>FRODO</constant>,
+ the Computer Management entry should now say: <guimenu>Computer Management (FRODO)</guimenu>.
+ </para></step>
+
+ <step><para>
+ In the left panel, click <menuchoice>
+ <guimenu>Computer Management (FRODO)</guimenu>
+ <guimenuitem>[+] Shared Folders</guimenuitem>
+ <guimenuitem>Shares</guimenuitem>
+ </menuchoice>.
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>ACLs</primary>
+ </indexterm><indexterm>
+ <primary>Share Permissions</primary>
+ </indexterm>
+ In the right panel, double-click on the share on which you wish to set/edit ACLs. This
+ will bring up the Properties panel. Click the <guimenu>Share Permissions</guimenu> tab.
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>access control settings</primary>
+ </indexterm><indexterm>
+ <primary>Everyone</primary>
+ </indexterm><indexterm>
+ <primary>full control</primary>
+ </indexterm><indexterm>
+ <primary>over-rule</primary>
+ </indexterm><indexterm>
+ <primary>permissions</primary>
+ </indexterm><indexterm>
+ <primary>rejected</primary>
+ </indexterm>
+ You may now edit/add/remove access control settings. Be very careful. Many problems have been
+ created by people who decided that Everyone should be rejected but one particular group should
+ have full control. This is a catch-22 situation because members of that particular group also
+ belong to the group <constant>Everyone</constant>, which therefore overrules any permissions
+ set for the permitted group.
+ </para></step>
+
+ <step><para>
+ When you are done with editing, close all panels by clicking through the <guimenu>OK</guimenu>
+ buttons.
+ </para></step>
+ </procedure>
+
+ </sect2>
+
+ <sect2>
+ <title>Share Definition Controls</title>
+
+ <para><indexterm>
+ <primary>Share Definition</primary>
+ <secondary>Controls</secondary>
+ </indexterm><indexterm>
+ <primary>check-point</primary>
+ </indexterm><indexterm>
+ <primary>pile-driver</primary>
+ </indexterm><indexterm>
+ <primary>credential</primary>
+ </indexterm><indexterm>
+ <primary>powers</primary>
+ </indexterm><indexterm>
+ <primary>privileges</primary>
+ </indexterm>
+ Share-definition-based access controls can be used like a check-point or like a pile-driver. Just as a
+ check-point can be used to require someone who wants to get through to meet certain requirements, so
+ it is possible to require the user (or group the user belongs to) to meet specified credential-related
+ objectives. It can be likened to a pile-driver by overriding default controls, in that having met the
+ credential-related objectives, the user can be granted powers and privileges that would not normally be
+ available under default settings.
+ </para>
+
+ <para><indexterm>
+ <primary>access controls</primary>
+ </indexterm><indexterm>
+ <primary>ACLs</primary>
+ </indexterm><indexterm>
+ <primary>share definition controls</primary>
+ </indexterm><indexterm>
+ <primary>hierarchy of control</primary>
+ </indexterm>
+ It must be emphasized that the controls here discussed can act as a filter, or give rights of passage,
+ that act as a super-structure over normal directory and file access controls. However, share level
+ ACLs act at a higher level than to share definition controls because the user must filter through the
+ share level controls to get to the share definition controls. The proper hierarchy of controls implemented
+ by Samba and Windows networking consists of:
+ </para>
+
+ <orderedlist>
+ <listitem><para>Share Level ACLs</para></listitem>
+ <listitem><para>Share Definition Controls</para></listitem>
+ <listitem><para>Directory and File Permissions</para></listitem>
+ <listitem><para>Directory and File Posix ACLs</para></listitem>
+ </orderedlist>
+
+ <sect3>
+ <title>Check-point Controls</title>
+
+ <para><indexterm>
+ <primary>Check-point Controls</primary>
+ </indexterm>
+ Consider the following extract from a &smb.conf; file defining the share called <constant>Apps</constant>:
+<screen>
+[Apps]
+ comment = Application Share
+ path = /data/apps
+ read only = Yes
+ valid users = @Employees
+</screen>
+ This definition permits only those who are members of the group called <constant>Employees</constant> to
+ access the share.
+ </para>
+
+ <note><para><indexterm>
+ <primary>Domain Member</primary>
+ <secondary>servers</secondary>
+ </indexterm><indexterm>
+ <primary>winbind use default domain</primary>
+ </indexterm><indexterm>
+ <primary>fully qualified</primary>
+ </indexterm><indexterm>
+ <primary>valid users</primary>
+ </indexterm><indexterm>
+ <primary>delimiter</primary>
+ </indexterm>
+ On Domain Member servers and clients, even when the <parameter>winbind use default domain</parameter> has
+ been specified, the use of Domain accounts in security controls requires fully qualified Domain specification,
+ for example, <smbconfoption name="valid users">@"MEGANET\Northern Engineers"</smbconfoption>.
+ Note the necessity to use the double quotes to avoid having the space in the Windows group name interpreted as a
+ delimiter.
+ </para></note>
+
+ <para><indexterm>
+ <primary>ACL</primary>
+ </indexterm><indexterm>
+ <primary>access</primary>
+ </indexterm><indexterm>
+ <primary>validate</primary>
+ </indexterm>
+ If there is an ACL on the share itself to permit read/write access for all <constant>Employees</constant>
+ as well as read/write for the group <constant>Doctors</constant>, both groups are permitted through
+ to the share. However, at the moment an attempt is made to set up a connection to the share, a member of
+ the group <constant>Doctors</constant>, who is not also a member of the group <constant>Employees</constant>,
+ would immediately fail to validate.
+ </para>
+
+ <para><indexterm>
+ <primary>share definition controls</primary>
+ </indexterm>
+ Consider another example. In this case, you want to permit all members of the group <constant>Employees</constant>
+ to access the <constant>Apps</constant> share, except the user <constant>patrickj</constant>. This can be
+ easily achieved by setting a share level ACL permitting only <constant>Employees</constant> to access the share,
+ and then in the share definition controls excluding just <constant>patrickj</constant>. Here is how that might
+ be done:
+<screen>
+[Apps]
+ comment = Application Share
+ path = /data/apps
+ read only = Yes
+ invalid users = patrickj
+</screen>
+ <indexterm>
+ <primary>permissions</primary>
+ </indexterm>
+ Let us assume that you want to permit the user <constant>gbshaw</constant>, to manage any file in the
+ UNIX/Linux file system directory <filename>/data/apps</filename>, but you do not want to grant any write
+ permissions beyond that directory tree. Here is one way this can be done:
+<screen>
+[Apps]
+ comment = Application Share
+ path = /data/apps
+ read only = Yes
+ invalid users = patrickj
+ admin users = gbshaw
+</screen>
+ <indexterm>
+ <primary>administrative rights</primary>
+ </indexterm>
+ Now we have a set of controls that permits only <constant>Employees</constant> who are also members of
+ the group <constant>Doctors</constant>, excluding the user <constant>patrickj</constant>, to have
+ read-only privilege, but the user <constant>gbshaw</constant> is granted administrative rights.
+ The administrative rights conferred upon the user <constant>gbshaw</constant> permit operation as
+ if that user has logged in as the user <constant>root</constant> on the UNIX/Linux system, and thus
+ for access to the directory tree that has been shared (exported) permit the user to override controls
+ that apply to all other users on that resource.
+ </para>
+
+ <para>
+ There are additional check-point controls that may be used. For example, if for the same share we now
+ want to provide the user <constant>peters</constant> with the ability to write to one directory to
+ which he has write privilege in the UNIX file system, you can specifically permit that with the
+ following settings:
+<screen>
+[Apps]
+ comment = Application Share
+ path = /data/apps
+ read only = Yes
+ invalid users = patrickj
+ admin users = gbshaw
+ write list = peters
+</screen>
+ <indexterm>
+ <primary>check-point controls</primary>
+ </indexterm>
+ This is a particularly complex example at this point, but it begins to demonstrate the possibilities.
+ You should refer to the on-line manual page for the &smb.conf; file for more information regarding
+ the check-point controls that Samba implements.
+ </para>
+
+ </sect3>
+
+ <sect3>
+ <title>Override Controls</title>
+
+ <para><indexterm>
+ <primary>over-ride controls</primary>
+ </indexterm>
+ Override controls implemented by Samba permit actions like the adoption of a different identity
+ during file system operations, the forced overwriting of normal file and directory permissions,
+ and so on. You should refer to the on-line manual page for the &smb.conf; file for more information regarding
+ the override controls that Samba implements.
+ </para>
+
+ <para>
+ In the following example, you want to create a Windows networking share that any user can access.
+ However, you want all read and write operations to be performed as if the user <constant>billc</constant>
+ and member of the group <constant>Mentors</constant> read/write the files. Here is one way this
+ can be done:
+<screen>
+[someshare]
+ comment = Some Files Everyone May Overwrite
+ path = /data/somestuff
+ read only = No
+ force user = billc
+ force group = Mentors
+</screen>
+ <indexterm>
+ <primary>forced settings</primary>
+ </indexterm><indexterm>
+ <primary>overheads</primary>
+ </indexterm>
+ That is all there is to it. Well, it is almost that simple. The downside of this method is that
+ users are logged onto the Windows client as themselves, and then immediately before accessing the
+ file, Samba makes system calls to change the effective user and group to the forced settings
+ specified, completes the file transaction, and then reverts to the actually logged on identity.
+ This imposes significant overhead on Samba. The alternative way that effectively the same result
+ can be achieved (but with lower system CPU overheads) is described next.
+ </para>
+
+ <para><indexterm>
+ <primary>force user</primary>
+ </indexterm><indexterm>
+ <primary>force group</primary>
+ </indexterm><indexterm>
+ <primary>opportunistic</primary>
+ <secondary>locking</secondary>
+ </indexterm><indexterm>
+ <primary>oplock break</primary>
+ </indexterm><indexterm>
+ <primary>performance degradation</primary>
+ </indexterm>
+ The use of the <parameter>force user</parameter>, or the <parameter>force group</parameter>, may
+ also have a severe impact on system (and in particular Windows client) performance. If opportunistic
+ locking is enabled on the share (the default), it causes an <constant>oplock break</constant> to be
+ sent to the client, even if the client has not opened the file. On networks that have high traffic
+ density, or on links that are routed to a remote network segment, <constant>oplock breaks</constant>
+ can be lost. This results in possible retransmission of the request, or the client may time-out while
+ waiting for the file system transaction (read or write) to complete. The result can be a profound
+ apparent performance degradation as the client continually attempts to reconnect to overcome the
+ effect of the lost <constant>oplock break</constant>, or time-out.
+ </para>
+
+ </sect3>
+
+ </sect2>
+
+ <sect2>
+ <title>Share Point Directory and File Permissions</title>
+
+ <para><indexterm>
+ <primary>security</primary>
+ </indexterm><indexterm>
+ <primary>privilege controls</primary>
+ </indexterm><indexterm>
+ <primary>permission</primary>
+ </indexterm><indexterm>
+ <primary>share definition controls</primary>
+ </indexterm>
+ Samba has been designed and implemented so that it respects as far as is feasible the security and
+ user privilege controls that are built into the UNIX/Linux operating system. Samba does nothing
+ with respect to file system access that violates file system permission settings, unless it is
+ explicitly instructed to do otherwise through share definition controls. Given that Samba obeys
+ UNIX file system controls, this chapter does not document simple information that can be obtained
+ from a basic UNIX training guide. Instead, one common example of a typical problem is used
+ to demonstrate the most effective solution referred to in the immediately preceding paragraph.
+ </para>
+
+ <para><indexterm>
+ <primary>Microsoft Office</primary>
+ </indexterm><indexterm>
+ <primary>Word</primary>
+ </indexterm><indexterm>
+ <primary>Excel</primary>
+ </indexterm>
+ One of the common issues that repeatedly pops up on the Samba mailing lists involves the saving of
+ Microsoft Office files (Word and Excel) to a network drive. Here is the typical sequence:
+ </para>
+
+ <orderedlist>
+ <listitem><para>
+ A user opens a Work document from a network drive. The file was owned by user <constant>janetp</constant>
+ and <group>users</group>, and was set read/write enabled for everyone.
+ </para></listitem>
+
+ <listitem><para>
+ File changes and edits are made.
+ </para></listitem>
+
+ <listitem><para>
+ The file is saved, and MS Word is closed.
+ </para></listitem>
+
+ <listitem><para>
+ The file is now owned by the user <constant>billc</constant> and group <constant>doctors</constant>,
+ and is set read/write by <constant>billc</constant>, read only by <constant>doctors</constant>, and
+ no access by everyone.
+ </para></listitem>
+
+ <listitem><para>
+ The original owner can not now access her own file and is <quote>justifiably</quote> upset.
+ </para></listitem>
+ </orderedlist>
+
+ <para>
+ There have been many postings over the years that report the same basic problem. Frequently Samba users
+ want to know when this <quote>bug</quote> will be fixed. The fact is, this is not a bug in Samba at all.
+ Here is the real sequence of what happens in the case mentioned above.
+ </para>
+
+ <para><indexterm>
+ <primary>MS Word</primary>
+ </indexterm><indexterm>
+ <primary>ownership</primary>
+ </indexterm><indexterm>
+ <primary>permissions</primary>
+ </indexterm>
+ When the user saves a file, MS Word creates a new (temporary) file. This file is naturally owned
+ by the user who creates the file (<constant>billc</constant>) and has the permissions that follow
+ that user's default settings within the operating system (UNIX/Linux). When MS Word has finished writing
+ the file to disk, it then renames the new (temporary) file to the name of the old one. MS Word does not
+ change the ownership or permissions to what they were on the original file. The file is thus a totally
+ new file, and the old one has been deleted in the process.
+ </para>
+
+ <para>
+ Samba received a request to create a new file, and then to rename the file to a new name. The old file that
+ has the same name is now automatically deleted. Samba has no way of knowing that the new file should
+ perhaps have the same ownership and permissions as the old file. To Samba, these are entirely independent
+ operations.
+ </para>
+
+ <para>
+ The question is: <quote>How can we solve the problem?</quote>
+ </para>
+
+ <para>
+ The solution is simple. Use UNIX file system permissions and controls to your advantage. Follow these
+ simple steps to create a share in which all files will consistently be owned by the same user and the
+ same group:
+ </para>
+
+
+ <procedure>
+ <title>Using Directory Permissions to Force File User and Group Ownership</title>
+ <step><para>
+ Change your share definition so that it matches this pattern:
+<screen>
+[finance]
+ path = /usr/data/finance
+ browseable = Yes
+ read only = No
+</screen>
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>permissions</primary>
+ <secondary>user</secondary>
+ </indexterm><indexterm>
+ <primary>permissions</primary>
+ <secondary>group</secondary>
+ </indexterm>
+ Set consistent user and group permissions recursively down the directory tree as shown here:
+<screen>
+&rootprompt; chown -R janetp.users /usr/data/finance
+</screen>
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>accessible</primary>
+ </indexterm>
+ Set the files and directory permissions to be read/write for owner and group, and not accessible
+ to others (everyone) using the following command:
+<screen>
+&rootprompt; chmod ug+rwx,o-rwx /usr/data/finance
+</screen>
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>SGID</primary>
+ </indexterm>
+ Set the SGID (super-group) bit on all directories from the top down. This means all files
+ can be created with the permissions of the group set on the directory. It means all users
+ who are members of the group <constant>finance</constant> can read and write all files in
+ the directory. The directory is not readable or writable by anyone who is not in the
+ <constant>finance</constant> group. Simply follow this example:
+<screen>
+&rootprompt; find /usr/data/finance -type d -exec chmod ug+s {}\;
+</screen>
+
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>group membership</primary>
+ </indexterm><indexterm>
+ <primary>primary group</primary>
+ </indexterm><indexterm>
+ <primary>/etc/passwd</primary>
+ </indexterm>
+ Make sure all users that must have read/write access to the directory have
+ <constant>finance</constant> group membership as their primary group,
+ for example, the group they belong to in <filename>/etc/passwd</filename>.
+ </para></step>
+ </procedure>
+
+ </sect2>
+
+ <sect2>
+ <title>Managing Windows 200x ACLs</title>
+
+ <para><indexterm>
+ <primary>translate</primary>
+ </indexterm><indexterm>
+ <primary>Windows 2000 ACLs</primary>
+ </indexterm><indexterm>
+ <primary>Posix ACLs</primary>
+ </indexterm><indexterm>
+ <primary>side effects</primary>
+ </indexterm>
+ Samba must translate Windows 2000 ACLs to UNIX Posix ACLs. This has some interesting side effects because
+ of the fact that there is not a 1:1 equivalence between them. The as-close-as-possible ACLs match means
+ that some transactions are not possible from MS Windows clients. One of these is to reset the ownership
+ of directories and files. If you want to reset ownership, this must be done from a UNIX/Linux login.
+ </para>
+
+ <para>
+ There are two possible ways to set ACLs on UNIX/Linux file systems from a Windows network workstation,
+ either via File Manager or via the Microsoft Management Console (MMC) Computer Management interface.
+ </para>
+
+ <sect3>
+ <title>Using the MMC Computer Management Interface</title>
+
+ <procedure>
+ <step><para>
+ From a Windows 200x/XP Professional workstation, log onto the Domain using the Domain Administrator
+ account (on Samba Domains, this is usually the account called <constant>root</constant>).
+ </para></step>
+
+ <step><para>
+ Click
+ <menuchoice>
+ <guimenu>Start</guimenu>
+ <guimenuitem>Settings</guimenuitem>
+ <guimenuitem>Control Panel</guimenuitem>
+ <guimenuitem>Administrative Tools</guimenuitem>
+ <guimenuitem>Computer Management</guimenuitem>
+ </menuchoice>.
+ </para></step>
+
+ <step><para>
+ In the left panel,
+ <menuchoice>
+ <guimenu>[Right mouse menu item] Computer Management (Local)</guimenu>
+ <guimenuitem>Connect to another computer ...</guimenuitem>
+ <guimenuitem>Browse...</guimenuitem>
+ <guimenuitem>Advanced</guimenuitem>
+ <guimenuitem>Find Now</guimenuitem>
+ </menuchoice>. In the lower panel, click on the name of the server you wish to
+ administer. Click <menuchoice>
+ <guimenu>OK</guimenu>
+ <guimenuitem>OK</guimenuitem>
+ <guimenuitem>OK</guimenuitem>
+ </menuchoice>.
+ In the left panel, the entry <guimenu>Computer Management (Local)</guimenu> should now reflect
+ the change made. For example, if the server you are administering is called <constant>FRODO</constant>,
+ the Computer Management entry should now say: <guimenu>Computer Management (FRODO)</guimenu>.
+ </para></step>
+
+ <step><para>
+ In the left panel, click <menuchoice>
+ <guimenu>Computer Management (FRODO)</guimenu>
+ <guimenuitem>[+] Shared Folders</guimenuitem>
+ <guimenuitem>Shares</guimenuitem>
+ </menuchoice>.
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>Security</primary>
+ </indexterm><indexterm>
+ <primary>Properties</primary>
+ </indexterm><indexterm>
+ <primary>Permissions</primary>
+ </indexterm><indexterm>
+ <primary>Samba Domain server</primary>
+ </indexterm>
+ In the right panel, double-click on the share on which you wish to set/edit ACLs. This
+ brings up the Properties panel. Click the <guimenu>Security</guimenu> tab. It is best
+ to edit ACLs using the <constant>Advanced</constant> editing features. Click the
+ <guimenu>Advanced</guimenu> button. This opens a panel that has four tabs. Only the
+ functionality under the <constant>Permissions</constant> tab can be utilized with respect
+ to a Samba Domain server.
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>access control</primary>
+ </indexterm><indexterm>
+ <primary>permitted group</primary>
+ </indexterm>
+ You may now edit/add/remove access control settings. Be very careful. Many problems have been
+ created by people who decided that Everyone should be rejected but one particular group should
+ have full control. This is a catch-22 situation because members of that particular group also
+ belong to the group <constant>Everyone</constant>, which therefore overrules any permissions
+ set for the permitted group.
+ </para></step>
+
+ <step><para>
+ When you are done with editing, close all panels by clicking through the <guimenu>OK</guimenu>
+ buttons until the last panel closes.
+ </para></step>
+ </procedure>
+
+ </sect3>
+
+ <sect3>
+ <title>Using MS Windows Explorer (File Manager)</title>
+
+ <para>
+ The following alternative method may be used from a Windows workstation. In this example we work
+ with a Domain called <constant>MEGANET</constant>, a server called <constant>MASSIVE</constant>, and a
+ share called <constant>Apps</constant>. The underlying UNIX/Linux share point for this share is
+ <filename>/data/apps</filename>.
+ </para>
+
+ <procedure>
+ <step><para>
+ Click <menuchoice>
+ <guimenu>Start</guimenu>
+ <guimenuitem>[right-click] My Computer</guimenuitem>
+ <guimenuitem>Explore</guimenuitem>
+ <guimenuitem>[left panel] [+] My Network Places</guimenuitem>
+ <guimenuitem>[+] Entire Network</guimenuitem>
+ <guimenuitem>[+] Microsoft Windows Network</guimenuitem>
+ <guimenuitem>[+] Meganet</guimenuitem>
+ <guimenuitem>[+] Massive</guimenuitem>
+ <guimenuitem>[right-click] Apps</guimenuitem>
+ <guimenuitem>Properties</guimenuitem>
+ <guimenuitem>Security</guimenuitem>
+ <guimenuitem>Advanced</guimenuitem>
+ </menuchoice>. This opens a panel that has four tabs. Only the functionality under the
+ <constant>Permissions</constant> tab can be utilized in respect to a Samba Domain server.
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>full control</primary>
+ </indexterm><indexterm>
+ <primary>over-rule</primary>
+ </indexterm>
+ You may now edit/add/remove access control settings. Be very careful. Many problems have been
+ created by people who decided that Everyone should be rejected but one particular group should
+ have full control. This is a catch-22 situation because members of that particular group also
+ belong to the group <constant>Everyone</constant>, which therefore overrules any permissions
+ set for the permitted group.
+ </para></step>
+
+ <step><para>
+ When you are done with editing, close all panels by clicking through the <guimenu>OK</guimenu>
+ buttons until the last panel closes.
+ </para></step>
+ </procedure>
+
+ </sect3>
+
+ <sect3>
+ <title>Setting Posix ACLs in UNIX/Linux</title>
+
+ <para><indexterm>
+ <primary>desired security setting</primary>
+ </indexterm><indexterm>
+ <primary>shared resource</primary>
+ </indexterm>
+ Yet another alternative method for setting desired security settings on the shared resource files and
+ directories can be achieved by logging into UNIX/Linux and setting Posix ACLs directly using command-line
+ tools. Here is an example session on the same resource as in the immediately preceding example on a SUSE 9
+ Linux system:
+ </para>
+
+ <procedure>
+ <step><para>
+ Log into the Linux system as the user <constant>root</constant>.
+ </para></step>
+
+ <step><para>
+ Change directory to the location of the exported (shared) Windows file share (Apps), which is in
+ the directory <filename>/data</filename>. Execute the following:
+<screen>
+&rootprompt; cd /data
+</screen>
+ Retrieve the existing Posix ACLs entry by executing:
+<screen>
+&rootprompt; getfacl apps
+# file: apps
+# owner: root
+# group: root
+user::rwx
+group::rwx
+other::r-x
+</screen>
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>recursively</primary>
+ </indexterm>
+ You want to add permission for <constant>AppsMgrs</constant> to enable them to
+ manage the applications (apps) share. It is important to set the ACL recursively
+ so that the AppsMgrs have this capability throughout the directory tree that is
+ being shared. This is done using the <constant>-R</constant> option as shown.
+ Execute the following:
+<screen>
+&rootprompt; setfacl -m -R group:AppsMgrs:rwx /data/apps
+</screen>
+ Because setting an ACL does not provide a response, you immediately validate the command executed
+ as follows:
+<screen>
+&rootprompt; getfacl /data/apps
+# file: apps
+# owner: root
+# group: root
+user::rwx
+group::rwx
+group:AppsMgrs:rwx
+mask::rwx
+other::r-x
+</screen>
+ This confirms that the change of Posix ACL permissions has been effective.
+ </para></step>
+
+ <step><para><indexterm>
+ <primary>setfacl</primary>
+ </indexterm><indexterm>
+ <primary>getfacl</primary>
+ </indexterm><indexterm>
+ <primary>directory tree</primary>
+ </indexterm><indexterm>
+ <primary>Windows ACLs</primary>
+ </indexterm><indexterm>
+ <primary>inheritance</primary>
+ </indexterm>
+ It is highly recommend that you should read the on-line manual page for the <command>setfacl</command>
+ and <command>getfacl</command> commands. This provides information regarding how to set/read the default
+ ACLs and how that may be propagated through the directory tree. In Windows ACLs terms, this is the equivalent
+ of setting <constant>inheritance</constant> properties.
+ </para></step>
+ </procedure>
+
+ </sect3>
+
+ </sect2>
+
+ <sect2>
+ <title>Key Points Learned</title>
+
+ <para>
+ The mish-mash of issues were thrown together into one chapter because it seemed like a good idea.
+ Looking back, this chapter could be broken into two, but it's too late now. It has been done.
+ The highlights covered are:
+ </para>
+
+ <itemizedlist>
+ <listitem><para><indexterm>
+ <primary>Winbind</primary>
+ </indexterm><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm><indexterm>
+ <primary>password change</primary>
+ </indexterm><indexterm>
+ <primary>logon hours</primary>
+ </indexterm>
+ Winbind honors and does not override account controls set in Active Directory.
+ This means that password change, logon hours, and so on, are (or soon will be) enforced
+ by Samba Winbind. At this time, an out-of-hours login is denied and password
+ change is enforced. At this time, if logon hours expire, the user is not forcibly
+ logged off. That may be implemented at some later date.
+ </para></listitem>
+
+ <listitem><para><indexterm>
+ <primary>Sign'n'seal</primary>
+ </indexterm><indexterm>
+ <primary>schannel</primary>
+ </indexterm>
+ Sign'n'seal (plus schannel support) has been implemented in Samba-3. Beware of potential
+ problems acknowledged by Microsoft as having been fixed, but reported by some as still
+ possibly an open issue.
+ </para></listitem>
+
+ <listitem><para><indexterm>
+ <primary>Kerberos</primary>
+ </indexterm><indexterm>
+ <primary>OpenLDAP</primary>
+ </indexterm><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm><indexterm>
+ <primary>inter-operability</primary>
+ </indexterm>
+ The combination of Kerberos 5, plus OpenLDAP, plus Samba, cannot replace Microsoft
+ Active Directory. The possibility to do this is not planned in the current Samba-3
+ roadmap. Samba-3 does aim to provide further improvements in interoperability so that
+ UNIX/Linux systems may be fully integrated into Active Directory Domains.
+ </para></listitem>
+
+ <listitem><para>
+ This chapter reviewed mechanisms by which Samba servers may be kept secure. Each of
+ the four key methodologies was reviewed with specific reference to example deployment
+ techniques.
+ </para></listitem>
+ </itemizedlist>
+
+ </sect2>
+
+</sect1>
+
+<sect1>
+ <title>Questions and Answers</title>
+
+ <para>
+ </para>
+
+ <qandaset defaultlabel="chap10qa" type="number">
+ <qandaentry>
+ <question>
+
+ <para><indexterm>
+ <primary>Sign'n'seal</primary>
+ </indexterm><indexterm>
+ <primary>registry hacks</primary>
+ </indexterm>
+ Does Samba-3 require the <constant>Sign'n'seal</constant> registry hacks needed by Samba-2?
+ </para>
+
+ </question>
+ <answer>
+
+ <para><indexterm>
+ <primary>schannel</primary>
+ </indexterm><indexterm>
+ <primary>Sign'n'seal</primary>
+ </indexterm><indexterm>
+ <primary>registry change</primary>
+ </indexterm>
+ No. Samba-3 fully supports <constant>Sign'n'seal</constant> as well as <constant>schannel</constant>
+ operation. The registry change should not be applied when Samba-3 is used as a Domain Controller.
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
+ <question>
+
+ <para>
+ Does Samba-3 support Active Directory?
+ </para>
+
+ </question>
+ <answer>
+
+ <para><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm>
+ Yes. Samba-3 can be a fully participating native mode Active Directory client. Samba-3 does not
+ provide Active Directory services. It cannot be used to replace a Microsoft Active Directory
+ server implementation. Samba-3 can function as an Active Directory client (workstation) toolkit,
+ and it can function as an Active Directory Domain Member server.
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
+ <question>
+
+ <para><indexterm>
+ <primary>mixed-mode</primary>
+ </indexterm>
+ When Samba-3 is used with Active Directory, is it necessary to run mixed-mode operation, as was
+ necessary with Samba-2?
+ </para>
+
+ </question>
+ <answer>
+
+ <para><indexterm>
+ <primary>native</primary>
+ </indexterm>
+ No. Samba-3 can be used with NetBIOS over TCP/IP disabled, just as can be done with Windows 200x
+ Server and 200x/XPPro client products. It is no longer necessary to run mixed-mode operation,
+ as Samba-3 can join a native Windows 2003 Server ADS Domain.
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
+ <question>
+
+ <para><indexterm>
+ <primary>share level access controls</primary>
+ </indexterm>
+ Is it safe to set share level access controls in Samba?
+ </para>
+
+ </question>
+ <answer>
+
+ <para>
+ Yes. Share level access controls have been supported since early versions of Samba-2. This is
+ very mature technology. Not enough sites make use of this powerful capability, neither on
+ Windows server or with Samba servers.
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
+ <question>
+
+ <para><indexterm>
+ <primary>share ACLs</primary>
+ </indexterm>
+ Is it mandatory to set share ACLs to get a secure Samba-3 server?
+ </para>
+
+ </question>
+ <answer>
+
+ <para><indexterm>
+ <primary>file system security</primary>
+ </indexterm><indexterm>
+ <primary>Windows 200x ACLs</primary>
+ </indexterm><indexterm>
+ <primary>share definition controls</primary>
+ </indexterm><indexterm>
+ <primary>share level ACL</primary>
+ </indexterm><indexterm>
+ <primary>security</primary>
+ </indexterm>
+ No. Samba-3 honors UNIX/Linux file system security, supports Windows 200x ACLs, and provides
+ means of securing shares through share definition controls in the &smb.conf; file. The additional
+ support for share level ACLs is like frosting on the cake. It adds to security, but is not essential
+ to it.
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
+ <question>
+
+ <para><indexterm>
+ <primary>valid users</primary>
+ </indexterm>
+ The <parameter>valid users</parameter> did not work on the <smbconfsection name="[homes]"/>.
+ Has this functionality been restored yet?
+ </para>
+
+ </question>
+ <answer>
+
+ <para><indexterm>
+ <primary>meta-service</primary>
+ </indexterm>
+ Yes. This was fixed in Samba-3.0.2. The use of this parameter is strongly recommended as a safeguard
+ on the <smbconfsection name="[homes]"/> meta-service. The correct way to specify this is:
+ <smbconfoption name="valid users">%S</smbconfoption>.
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
+ <question>
+
+ <para><indexterm>
+ <primary>force user</primary>
+ </indexterm><indexterm>
+ <primary>force group</primary>
+ </indexterm><indexterm>
+ <primary>bias</primary>
+ </indexterm>
+ Is the bias against use of the <parameter>force user</parameter> and <parameter>force group</parameter>
+ really warranted?
+ </para>
+
+ </question>
+ <answer>
+
+ <para><indexterm>
+ <primary>performance</primary>
+ </indexterm>
+ There is no bias. There is a determination to recommend the right tool for the task at hand.
+ After all, it is better than putting users through performance problems, isn't it?
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
+ <question>
+
+ <para>
+ The example given for file and directory access control forces all files to be owned by one
+ particular user. I do not like that. Is there any way I can see who created the file?
+ </para>
+
+ </question>
+ <answer>
+
+ <para><indexterm>
+ <primary>SUID</primary>
+ </indexterm>
+ Sure. You do not have to set the SUID bit on the directory. Simply execute the following command
+ to permit file ownership to be retained by the user who created it:
+<screen>
+&rootprompt; find /usr/data/finance -type d -exec chmod g+s {}\;
+</screen>
+ Note that this required no more than removing the <constant>u</constant> argument so that the
+ SUID bit is not set for the owner.
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
+ <question>
+
+ <para><indexterm>
+ <primary>Computer Management</primary>
+ </indexterm>
+ In the book, <quote>The Official Samba-3 HOWTO and Reference Guide</quote>, you recommended use
+ of the Windows NT4 Server Manager (part of the <filename>SRVTOOLS.EXE</filename>) utility. Why
+ have you mentioned only the use of the Windows 200x/XP MMC Computer Management utility?
+ </para>
+
+ </question>
+ <answer>
+
+ <para><indexterm>
+ <primary>MMC</primary>
+ </indexterm><indexterm>
+ <primary>SRVTOOLS.EXE</primary>
+ </indexterm>
+ Either tool can be used with equal effect. There is no benefit of one over the other, except that
+ the MMC utility is present on all Windows 200x/XP systems and does not require additional software
+ to be downloaded and installed. Note that if you want to manage user and group accounts in your
+ Samba controlled Domain, the only tool that permits that is the NT4 Domain User Manager which
+ is provided as part of the <filename>SRVTOOLS.EXE</filename> utility.
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
+ <question>
+
+ <para><indexterm>
+ <primary>valid users</primary>
+ </indexterm><indexterm>
+ <primary>Active Directory</primary>
+ </indexterm><indexterm>
+ <primary>Domain Member server</primary>
+ </indexterm>
+ I tried to set <parameter>valid users = @Engineers</parameter>, but it does not work. My Samba
+ server is an Active Directory Domain Member server. Has this been fixed now?
+ </para>
+
+ </question>
+ <answer>
+
+ <para>
+ The use of this parameter has always required the full specification of the Domain account, for
+ example, <parameter>valid users = @"MEGANET2\Domain Admins"</parameter>.
+ </para>
+
+ </answer>
+ </qandaentry>
+
+ </qandaset>
+
+</sect1>
+
+</chapter>
+