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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 features and capabilities.
- More importantly, if you have implemented the examples given, you are well on your way to becoming
- a Samba 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. 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. 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 was recently acquired.
- During the time that the acquisition was closing, the Video Rentals business upgraded its Windows
- NT4-based network to Windows 2003 Server and Active Directory.
- </para>
-
- <para><indexterm>
- <primary>Active Directory</primary>
- </indexterm>
- You have accepted the fact that Abmas Video Rentals will use Microsoft Active Directory.
- The IT team, led by Stan Soroka, is committed to Samba and to maintaining a uniform technology platform.
- Stan Soroka's team voiced its 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 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><para>This report is entirely fictitious.
- Any resemblance to a factual report is purely coincidental.</para></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 considering that 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>
- Regarding 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, and 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 capabilities 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. You call Stan's team together for a simple
- discussion, but it gets further out of hand. When you return to your office, you find the following
- email in your in-box:
- </para>
-
- <para>
- Good afternoon,
- </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 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 noncompliance 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>
- You agreed with Stan's recommendations and hired a consultant to help defuse the powder
- keg. The consultant's task is to provide a tractable answer to each of the issues raised. The consultant must be able
- to support his or her claims, keep emotions to the 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 is a tool. No one is pounding your door to make you use Samba. That is a choice that you are free to
- make or reject. It is likely that your decision to use Samba can greatly benefit your company.
- 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 is fully cognizant of the responsibility they have to their users.
- The Samba documentation clearly reveals 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 are 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 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 on to 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: 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 is 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
- online updates need to be applied almost weekly. The answer to the criticism
- 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 suggests a high
- degree of dependability and on charter development consistent with published
- roadmap 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 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 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 snapshot 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 these features 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>
- have documented a significant problem with delays writes that can be connected with the
- implementation of sign'n'seal. They provide a work-around that is not trivial for many
- Windows networking sites. From notes such as this it is clear that there are benefits
- from not rushing new technology out of the door too soon.
- </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
- <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>
-
- </term>
- <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 cannot 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 today's networking world; at best they only restrict incoming network
- traffic but cannot 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. Therefore,
- 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 United States
- and abroad. A free and unencumbered implementation of MIT Kerberos has been produced in Europe
- and is available from the <ulink url="http://www.pdc.kth.se/heimdal/">Royal Institute</ulink> of
- Technology (KTH), Sweden. It is known as the Heimdal Kerberos project. In recent times the U.S. 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
- <ulink url="http://www.idg.com.sg/idgwww.nsf/0/5DDA8D153A7505A748256BAB000D992A?OpenDocument">IDG</ulink>
- report<footnote><para>Note: This link is no longer active. The same article is still
- available from <ulink url="http://199.105.191.226/Man/2699/020430msdoj/">ITWorld.com</ulink> (July 5, 2005)</para></footnote> by
- 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,
- particularly when Samba is 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) 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 on to 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 checkpoint or like a pile-driver. Just as a
- checkpoint 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 discussed here can act as a filter or give rights of passage
- that act as a superstructure over normal directory and file access controls. However, share-level
- ACLs act at a higher level than do 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>Checkpoint Controls</title>
-
- <para><indexterm>
- <primary>Checkpoint 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>
- except the user <constant>patrickj</constant> to access the <constant>Apps</constant> share. 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 checkpoint 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 online manual page for the &smb.conf; file for more information regarding
- the checkpoint 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 online 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 to effectively achieve the same result
- (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 (particularly on 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 Word document from a network drive. The file was owned by user <constant>janetp</constant>
- and <constant>users</constant>, 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 cannot 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 this case.
- </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 (supergroup) 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
- there is not a one-to-one 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 on to 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 for 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 recommended that you read the online 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 as follows:
- </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. 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
- roadmap. Samba 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 fully supports <constant>Sign'n'seal</constant> as well as <constant>schannel</constant>
- operation. The registry change should not be applied when Samba is used as a domain controller.
- </para>
-
- </answer>
- </qandaentry>
-
- <qandaentry>
- <question>
-
- <para>
- Does Samba support Active Directory?
- </para>
-
- </question>
- <answer>
-
- <para><indexterm>
- <primary>Active Directory</primary>
- </indexterm>
- Yes. Samba 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 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 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 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,
- because Samba 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 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 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 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>
-
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