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| author | vorlon <vorlon@alioth.debian.org> | 2007-11-21 17:29:21 +0000 |
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| committer | vorlon <vorlon@alioth.debian.org> | 2007-11-21 17:29:21 +0000 |
| commit | 58b37572718ed65d1b143f44de16aa5efb512f11 (patch) | |
| tree | 96694e5871586bd21d9b2b91f9a277111ace0812 /docs/htmldocs/Samba3-ByExample/kerberos.html | |
| parent | f24db2434a26f04e1761c6dbde69d4be999a1cfc (diff) | |
| download | samba-58b37572718ed65d1b143f44de16aa5efb512f11.tar.gz | |
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diff --git a/docs/htmldocs/Samba3-ByExample/kerberos.html b/docs/htmldocs/Samba3-ByExample/kerberos.html new file mode 100644 index 0000000000..f5085f4a98 --- /dev/null +++ b/docs/htmldocs/Samba3-ByExample/kerberos.html @@ -0,0 +1,826 @@ +<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 11. Active Directory, Kerberos, and Security</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.71.0"><link rel="start" href="index.html" title="Samba-3 by Example"><link rel="up" href="RefSection.html" title="Part III. Reference Section"><link rel="prev" href="RefSection.html" title="Part III. Reference Section"><link rel="next" href="DomApps.html" title="Chapter 12. Integrating Additional Services"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 11. Active Directory, Kerberos, and Security</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="RefSection.html">Prev</a> </td><th width="60%" align="center">Part III. Reference Section</th><td width="20%" align="right"> <a accesskey="n" href="DomApps.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="kerberos"></a>Chapter 11. Active Directory, Kerberos, and Security</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="kerberos.html#id372607">Introduction</a></span></dt><dd><dl><dt><span class="sect2"><a href="kerberos.html#id373189">Assignment Tasks</a></span></dt></dl></dd><dt><span class="sect1"><a href="kerberos.html#id373203">Dissection and Discussion</a></span></dt><dd><dl><dt><span class="sect2"><a href="kerberos.html#id373574">Technical Issues</a></span></dt></dl></dd><dt><span class="sect1"><a href="kerberos.html#ch10expl">Implementation</a></span></dt><dd><dl><dt><span class="sect2"><a href="kerberos.html#id375060">Share Access Controls</a></span></dt><dt><span class="sect2"><a href="kerberos.html#id375395">Share Definition Controls</a></span></dt><dt><span class="sect2"><a href="kerberos.html#id375952">Share Point Directory and File Permissions</a></span></dt><dt><span class="sect2"><a href="kerberos.html#id376321">Managing Windows 200x ACLs</a></span></dt><dt><span class="sect2"><a href="kerberos.html#id377005">Key Points Learned</a></span></dt></dl></dd><dt><span class="sect1"><a href="kerberos.html#id377127">Questions and Answers</a></span></dt></dl></div><p><a class="indexterm" name="id372556"></a> + 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. + </p><p><a class="indexterm" name="id372570"></a> + 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 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. + </p><p> + 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. + </p><p><a class="indexterm" name="id372594"></a> + 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. + </p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id372607"></a>Introduction</h2></div></div></div><p><a class="indexterm" name="id372613"></a><a class="indexterm" name="id372621"></a><a class="indexterm" name="id372629"></a><a class="indexterm" name="id372637"></a><a class="indexterm" name="id372645"></a> + 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. + </p><p><a class="indexterm" name="id372662"></a> + 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-3 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 “<span class="quote">an island of broken + technologies.</span>” This comment was made by one of Christine's staff as they were installing a new + Samba-3 server at the new business. + </p><p><a class="indexterm" name="id372681"></a><a class="indexterm" name="id372689"></a> + 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<sup>[<a name="id372701" href="#ftn.id372701">12</a>]</sup> on his unit's operations + and to investigate the role of Samba at his site. Here are key extracts from this hypothetical + report: + </p><div class="blockquote"><blockquote class="blockquote"><p><a class="indexterm" name="id372710"></a><a class="indexterm" name="id372718"></a><a class="indexterm" name="id372726"></a><a class="indexterm" name="id372733"></a> + ... 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. + </p><p> + ... + </p><p><a class="indexterm" name="id372751"></a><a class="indexterm" name="id372763"></a><a class="indexterm" name="id372774"></a><a class="indexterm" name="id372782"></a><a class="indexterm" name="id372790"></a><a class="indexterm" name="id372798"></a> + 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. + </p><p><a class="indexterm" name="id372811"></a><a class="indexterm" name="id372819"></a><a class="indexterm" name="id372827"></a> + Your staff are justifiably concerned that the use of Samba may compromise their good efforts to maintain + a secure network. + </p><p><a class="indexterm" name="id372843"></a><a class="indexterm" name="id372850"></a><a class="indexterm" name="id372858"></a><a class="indexterm" name="id372866"></a> + The recently installed Linux file and application server uses a tool called <code class="literal">winbind</code> + 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. + </p><p><a class="indexterm" name="id372892"></a><a class="indexterm" name="id372900"></a><a class="indexterm" name="id372908"></a> + 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. + </p><p> + ... + </p><p><a class="indexterm" name="id372927"></a><a class="indexterm" name="id372935"></a><a class="indexterm" name="id372943"></a><a class="indexterm" name="id372951"></a> + 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. + </p><p><a class="indexterm" name="id372968"></a><a class="indexterm" name="id372976"></a><a class="indexterm" name="id372984"></a><a class="indexterm" name="id372992"></a><a class="indexterm" name="id373000"></a><a class="indexterm" name="id373007"></a><a class="indexterm" name="id373015"></a> + 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. + </p><p><a class="indexterm" name="id373029"></a><a class="indexterm" name="id373037"></a><a class="indexterm" name="id373044"></a> + 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. + </p></blockquote></div><p><a class="indexterm" name="id373057"></a><a class="indexterm" name="id373065"></a> + 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: + </p><p> + Good afternoon, + </p><div class="blockquote"><table border="0" width="100%" cellspacing="0" cellpadding="0" class="blockquote" summary="Block quote"><tr><td width="10%" valign="top"> </td><td width="80%" valign="top"><p> + 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. + </p><p> + 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. + </p><p><a class="indexterm" name="id373096"></a><a class="indexterm" name="id373104"></a><a class="indexterm" name="id373111"></a><a class="indexterm" name="id373119"></a> + 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. + </p><p><a class="indexterm" name="id373134"></a><a class="indexterm" name="id373142"></a><a class="indexterm" name="id373150"></a><a class="indexterm" name="id373158"></a><a class="indexterm" name="id373166"></a><a class="indexterm" name="id373173"></a> + 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. + </p></td><td width="10%" valign="top"> </td></tr><tr><td width="10%" valign="top"> </td><td colspan="2" align="right" valign="top">--<span class="attribution">Stan</span></td></tr></table></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id373189"></a>Assignment Tasks</h3></div></div></div><p> + 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. + </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id373203"></a>Dissection and Discussion</h2></div></div></div><p><a class="indexterm" name="id373209"></a><a class="indexterm" name="id373217"></a><a class="indexterm" name="id373225"></a><a class="indexterm" name="id373233"></a><a class="indexterm" name="id373241"></a><a class="indexterm" name="id373249"></a><a class="indexterm" name="id373257"></a> + Samba-3 is a tool. No one is pounding your door to make you use Samba. That is a choice that you are free to + 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. + </p><p><a class="indexterm" name="id373273"></a><a class="indexterm" name="id373281"></a><a class="indexterm" name="id373289"></a><a class="indexterm" name="id373297"></a><a class="indexterm" name="id373305"></a> + 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. + </p><p><a class="indexterm" name="id373320"></a><a class="indexterm" name="id373328"></a><a class="indexterm" name="id373336"></a><a class="indexterm" name="id373343"></a> + 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. + </p><p><a class="indexterm" name="id373357"></a><a class="indexterm" name="id373365"></a><a class="indexterm" name="id373373"></a><a class="indexterm" name="id373381"></a><a class="indexterm" name="id373392"></a><a class="indexterm" name="id373400"></a><a class="indexterm" name="id373408"></a><a class="indexterm" name="id373416"></a><a class="indexterm" name="id373424"></a><a class="indexterm" name="id373432"></a><a class="indexterm" name="id373439"></a> + 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. + </p><p><a class="indexterm" name="id373462"></a><a class="indexterm" name="id373470"></a><a class="indexterm" name="id373477"></a><a class="indexterm" name="id373485"></a><a class="indexterm" name="id373493"></a><a class="indexterm" name="id373501"></a> + 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? + </p><p><a class="indexterm" name="id373516"></a><a class="indexterm" name="id373523"></a><a class="indexterm" name="id373531"></a><a class="indexterm" name="id373539"></a><a class="indexterm" name="id373547"></a><a class="indexterm" name="id373555"></a><a class="indexterm" name="id373562"></a> + 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. + </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id373574"></a>Technical Issues</h3></div></div></div><p> + Each issue is now discussed and, where appropriate, example implementation steps are + provided. + </p><div class="variablelist"><dl><dt><span class="term">Winbind and Security</span></dt><dd><p><a class="indexterm" name="id373594"></a><a class="indexterm" name="id373601"></a><a class="indexterm" name="id373609"></a><a class="indexterm" name="id373621"></a><a class="indexterm" name="id373628"></a><a class="indexterm" name="id373636"></a><a class="indexterm" name="id373644"></a><a class="indexterm" name="id373652"></a><a class="indexterm" name="id373660"></a><a class="indexterm" name="id373668"></a> + Windows network administrators may be dismayed to find that <code class="literal">winbind</code> + 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. + </p><p><a class="indexterm" name="id373688"></a><a class="indexterm" name="id373696"></a><a class="indexterm" name="id373704"></a><a class="indexterm" name="id373712"></a> + <code class="literal">winbind</code> 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. + </p><p><a class="indexterm" name="id373734"></a><a class="indexterm" name="id373742"></a><a class="indexterm" name="id373750"></a><a class="indexterm" name="id373758"></a><a class="indexterm" name="id373766"></a><a class="indexterm" name="id373777"></a> + Windows network administrators need to recognize that <code class="literal">winbind</code> does + not, and cannot, override account controls set using the Active Directory management + tools. The control is the same. Have no fear. + </p><p><a class="indexterm" name="id373796"></a><a class="indexterm" name="id373804"></a><a class="indexterm" name="id373815"></a><a class="indexterm" name="id373823"></a><a class="indexterm" name="id373831"></a><a class="indexterm" name="id373839"></a><a class="indexterm" name="id373847"></a><a class="indexterm" name="id373855"></a><a class="indexterm" name="id373862"></a><a class="indexterm" name="id373870"></a> + Where Samba and the ADS domain account information obtained through the use of + <code class="literal">winbind</code> 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: + </p><div class="itemizedlist"><ul type="disc"><li><p>Shares themselves (i.e., the logical share itself)</p></li><li><p>The share definition in <code class="filename">smb.conf</code></p></li><li><p>The shared directories and files using UNIX permissions</p></li><li><p>Using Windows 2000 ACLs if the file system is POSIX enabled</p></li></ul></div><p> + Examples of each are given in <a href="kerberos.html#ch10expl" title="Implementation">???</a>. + </p></dd><dt><span class="term">User and Group Controls</span></dt><dd><p><a class="indexterm" name="id373940"></a><a class="indexterm" name="id373947"></a><a class="indexterm" name="id373959"></a><a class="indexterm" name="id373970"></a><a class="indexterm" name="id373978"></a><a class="indexterm" name="id373986"></a><a class="indexterm" name="id373993"></a><a class="indexterm" name="id374001"></a><a class="indexterm" name="id374009"></a> + 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. + </p><p><a class="indexterm" name="id374029"></a><a class="indexterm" name="id374037"></a><a class="indexterm" name="id374045"></a><a class="indexterm" name="id374053"></a><a class="indexterm" name="id374064"></a><a class="indexterm" name="id374072"></a><a class="indexterm" name="id374080"></a> + 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. + </p><p><a class="indexterm" name="id374096"></a><a class="indexterm" name="id374104"></a> + 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. + </p></dd><dt><span class="term">Security Overall</span></dt><dd><p><a class="indexterm" name="id374124"></a> + 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. + </p><p><a class="indexterm" name="id374138"></a><a class="indexterm" name="id374146"></a><a class="indexterm" name="id374154"></a><a class="indexterm" name="id374162"></a> + 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. + </p><p><a class="indexterm" name="id374178"></a><a class="indexterm" name="id374186"></a><a class="indexterm" name="id374193"></a><a class="indexterm" name="id374201"></a><a class="indexterm" name="id374209"></a><a class="indexterm" name="id374217"></a><a class="indexterm" name="id374225"></a> + 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. + </p><p><a class="indexterm" name="id374239"></a><a class="indexterm" name="id374247"></a><a class="indexterm" name="id374255"></a><a class="indexterm" name="id374263"></a><a class="indexterm" name="id374271"></a> + 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. + </p><p><a class="indexterm" name="id374289"></a><a class="indexterm" name="id374297"></a><a class="indexterm" name="id374309"></a><a class="indexterm" name="id374320"></a><a class="indexterm" name="id374328"></a><a class="indexterm" name="id374336"></a><a class="indexterm" name="id374343"></a> + 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. + </p></dd><dt><span class="term">Cryptographic Controls (schannel, sign'n'seal)</span></dt><dd><p><a class="indexterm" name="id374368"></a><a class="indexterm" name="id374376"></a><a class="indexterm" name="id374383"></a> + The report correctly mentions that Samba did not support the most recent + <code class="constant">schannel</code> and <code class="constant">digital sign'n'seal</code> 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 they reflect accurately (at best) status at a snapshot in time. + Meanwhile, the world moves on. + </p><p><a class="indexterm" name="id374409"></a><a class="indexterm" name="id374416"></a><a class="indexterm" name="id374424"></a><a class="indexterm" name="id374432"></a><a class="indexterm" name="id374440"></a><a class="indexterm" name="id374455"></a><a class="indexterm" name="id374463"></a> + 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. + </p><p><a class="indexterm" name="id374478"></a><a class="indexterm" name="id374486"></a> + 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 <code class="constant">digital sign'n'seal</code> support + often dismiss the problems that Microsoft has + <a href="http://support.microsoft.com/default.aspx?kbid=321733" target="_top">acknowledged</a> + and for which a fix was provided. In fact, + <a href="http://www.tangent-systems.com/support/delayedwrite.html" target="_top">Tangent Systems</a> + 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. + </p><p><a class="indexterm" name="id374519"></a><a class="indexterm" name="id374527"></a><a class="indexterm" name="id374535"></a><a class="indexterm" name="id374543"></a><a class="indexterm" name="id374551"></a><a class="indexterm" name="id374558"></a><a class="indexterm" name="id374566"></a><a class="indexterm" name="id374574"></a><a class="indexterm" name="id374582"></a> + 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. + </p></dd><dt><span class="term">Active Directory Replacement with Kerberos, LDAP, and Samba</span></dt><dd><p> + </p><div class="literallayout"><p> </p></div><p> + 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. + </p><p><a class="indexterm" name="id374664"></a><a class="indexterm" name="id374675"></a><a class="indexterm" name="id374683"></a><a class="indexterm" name="id374691"></a><a class="indexterm" name="id374699"></a> + 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. + </p><p><a class="indexterm" name="id374715"></a><a class="indexterm" name="id374723"></a><a class="indexterm" name="id374731"></a><a class="indexterm" name="id374742"></a><a class="indexterm" name="id374750"></a> + 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. + </p></dd></dl></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id374766"></a>Kerberos Exposed</h4></div></div></div><p><a class="indexterm" name="id374772"></a><a class="indexterm" name="id374780"></a><a class="indexterm" name="id374788"></a> + 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. + </p><p><a class="indexterm" name="id374802"></a><a class="indexterm" name="id374810"></a><a class="indexterm" name="id374818"></a> + 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. + </p><p><a class="indexterm" name="id374833"></a><a class="indexterm" name="id374841"></a><a class="indexterm" name="id374849"></a><a class="indexterm" name="id374857"></a><a class="indexterm" name="id374868"></a> + 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. + </p><p> + <a class="indexterm" name="id374884"></a> + <a class="indexterm" name="id374891"></a> + <a class="indexterm" name="id374898"></a> + 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 <a href="http://www.pdc.kth.se/heimdal/" target="_top">Royal Institute</a> 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. + </p><p> + <a class="indexterm" name="id374920"></a> + A storm has broken out concerning interoperability between MIT Kerberos and Microsofts' implementation + of it. For example, a 2002 + <a href="http://www.idg.com.sg/idgwww.nsf/0/5DDA8D153A7505A748256BAB000D992A?OpenDocument" target="_top">IDG</a> + report<sup>[<a name="id374937" href="#ftn.id374937">13</a>]</sup> by + states: + </p><div class="blockquote"><blockquote class="blockquote"><p> + 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. + </p><p> + <a class="indexterm" name="id374958"></a> + 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. + </p></blockquote></div><p> + <a class="indexterm" name="id374976"></a> + <a class="indexterm" name="id374983"></a> + It so happens that Microsoft Windows clients depend on and expect the contents of the <span class="emphasis"><em>unspecified + fields</em></span> 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. + </p><p> + Microsoft makes the following comment in a reference in a + <a href="http://www.microsoft.com/technet/itsolutions/interop/mgmt/kerberos.asp" target="_top"> + technet</a> article: + </p><div class="blockquote"><blockquote class="blockquote"><p><a class="indexterm" name="id375016"></a><a class="indexterm" name="id375028"></a> + 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. + </p></blockquote></div></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="ch10expl"></a>Implementation</h2></div></div></div><p> + The following procedures outline the implementation of the security measures discussed so far. + </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375060"></a>Share Access Controls</h3></div></div></div><p><a class="indexterm" name="id375067"></a><a class="indexterm" name="id375075"></a><a class="indexterm" name="id375082"></a> + 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. + </p><div class="procedure"><a name="id375094"></a><p class="title"><b>Procedure 11.1. Create/Edit/Delete Share ACLs</b></p><ol type="1"><li><p><a class="indexterm" name="id375104"></a><a class="indexterm" name="id375112"></a> + 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 <code class="constant">root</code>). + </p></li><li><p> + Click + <span class="guimenu">Start</span> → <span class="guimenuitem">Settings</span> → <span class="guimenuitem">Control Panel</span> → <span class="guimenuitem">Administrative Tools</span> → <span class="guimenuitem">Computer Management</span>. + </p></li><li><p> + In the left panel, + <span class="guimenu">[Right mouse menu item] Computer Management (Local)</span> → <span class="guimenuitem">Connect to another computer ...</span> → <span class="guimenuitem">Browse...</span> → <span class="guimenuitem">Advanced</span> → <span class="guimenuitem">Find Now</span>. In the lower panel, click on the name of the server you wish to + administer. Click <span class="guimenu">OK</span> → <span class="guimenuitem">OK</span> → <span class="guimenuitem">OK</span>.<a class="indexterm" name="id375232"></a> + In the left panel, the entry <span class="guimenu">Computer Management (Local)</span> should now reflect + the change made. For example, if the server you are administering is called <code class="constant">FRODO</code>, + the Computer Management entry should now say <span class="guimenu">Computer Management (FRODO)</span>. + </p></li><li><p> + In the left panel, click <span class="guimenu">Computer Management (FRODO)</span> → <span class="guimenuitem">[+] Shared Folders</span> → <span class="guimenuitem">Shares</span>. + </p></li><li><p><a class="indexterm" name="id375293"></a><a class="indexterm" name="id375301"></a> + 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 <span class="guimenu">Share Permissions</span> tab. + </p></li><li><p><a class="indexterm" name="id375323"></a><a class="indexterm" name="id375331"></a><a class="indexterm" name="id375339"></a><a class="indexterm" name="id375347"></a><a class="indexterm" name="id375354"></a><a class="indexterm" name="id375362"></a> + 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 <code class="constant">Everyone</code>, which therefore overrules any permissions + set for the permitted group. + </p></li><li><p> + When you are done with editing, close all panels by clicking through the <span class="guimenu">OK</span> + buttons. + </p></li></ol></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375395"></a>Share Definition Controls</h3></div></div></div><p><a class="indexterm" name="id375401"></a><a class="indexterm" name="id375413"></a><a class="indexterm" name="id375421"></a><a class="indexterm" name="id375428"></a><a class="indexterm" name="id375436"></a><a class="indexterm" name="id375444"></a> + 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. + </p><p><a class="indexterm" name="id375460"></a><a class="indexterm" name="id375468"></a><a class="indexterm" name="id375476"></a><a class="indexterm" name="id375484"></a> + 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: + </p><div class="orderedlist"><ol type="1"><li><p>Share-level ACLs</p></li><li><p>Share-definition controls</p></li><li><p>Directory and file permissions</p></li><li><p>Directory and file POSIX ACLs</p></li></ol></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id375528"></a>Checkpoint Controls</h4></div></div></div><p><a class="indexterm" name="id375535"></a> + Consider the following extract from a <code class="filename">smb.conf</code> file defining the share called <code class="constant">Apps</code>: +</p><pre class="screen"> +[Apps] + comment = Application Share + path = /data/apps + read only = Yes + valid users = @Employees +</pre><p> + This definition permits only those who are members of the group called <code class="constant">Employees</code> to + access the share. + </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p><a class="indexterm" name="id375568"></a><a class="indexterm" name="id375579"></a><a class="indexterm" name="id375587"></a><a class="indexterm" name="id375595"></a><a class="indexterm" name="id375603"></a> + On domain member servers and clients, even when the <em class="parameter"><code>winbind use default domain</code></em> has + been specified, the use of domain accounts in security controls requires fully qualified domain specification, + for example, <a class="indexterm" name="id375620"></a>valid users = @"MEGANET\Northern Engineers". + Note the necessity to use the double quotes to avoid having the space in the Windows group name interpreted as a + delimiter. + </p></div><p><a class="indexterm" name="id375630"></a><a class="indexterm" name="id375638"></a><a class="indexterm" name="id375646"></a> + If there is an ACL on the share itself to permit read/write access for all <code class="constant">Employees</code> + as well as read/write for the group <code class="constant">Doctors</code>, 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 <code class="constant">Doctors</code>, who is not also a member of the group <code class="constant">Employees</code>, + would immediately fail to validate. + </p><p><a class="indexterm" name="id375674"></a> + Consider another example. In this case, you want to permit all members of the group <code class="constant">Employees</code> + except the user <code class="constant">patrickj</code> to access the <code class="constant">Apps</code> share. This can be + easily achieved by setting a share-level ACL permitting only <code class="constant">Employees</code> to access the share, + and then in the share definition controls excluding just <code class="constant">patrickj</code>. Here is how that might + be done: +</p><pre class="screen"> +[Apps] + comment = Application Share + path = /data/apps + read only = Yes + invalid users = patrickj +</pre><p> + <a class="indexterm" name="id375711"></a> + Let us assume that you want to permit the user <code class="constant">gbshaw</code> to manage any file in the + UNIX/Linux file system directory <code class="filename">/data/apps</code>, but you do not want to grant any write + permissions beyond that directory tree. Here is one way this can be done: +</p><pre class="screen"> +[Apps] + comment = Application Share + path = /data/apps + read only = Yes + invalid users = patrickj + admin users = gbshaw +</pre><p> + <a class="indexterm" name="id375738"></a> + Now we have a set of controls that permits only <code class="constant">Employees</code> who are also members of + the group <code class="constant">Doctors</code>, excluding the user <code class="constant">patrickj</code>, to have + read-only privilege, but the user <code class="constant">gbshaw</code> is granted administrative rights. + The administrative rights conferred upon the user <code class="constant">gbshaw</code> permit operation as + if that user has logged in as the user <code class="constant">root</code> 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. + </p><p> + There are additional checkpoint controls that may be used. For example, if for the same share we now + want to provide the user <code class="constant">peters</code> 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: +</p><pre class="screen"> +[Apps] + comment = Application Share + path = /data/apps + read only = Yes + invalid users = patrickj + admin users = gbshaw + write list = peters +</pre><p> + <a class="indexterm" name="id375789"></a> + 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 <code class="filename">smb.conf</code> file for more information regarding + the checkpoint controls that Samba implements. + </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id375808"></a>Override Controls</h4></div></div></div><p><a class="indexterm" name="id375815"></a> + 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 <code class="filename">smb.conf</code> file for more information regarding + the override controls that Samba implements. + </p><p> + 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 <code class="constant">billc</code> + and member of the group <code class="constant">Mentors</code> read/write the files. Here is one way this + can be done: +</p><pre class="screen"> +[someshare] + comment = Some Files Everyone May Overwrite + path = /data/somestuff + read only = No + force user = billc + force group = Mentors +</pre><p> + <a class="indexterm" name="id375852"></a><a class="indexterm" name="id375860"></a> + 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. + </p><p><a class="indexterm" name="id375876"></a><a class="indexterm" name="id375884"></a><a class="indexterm" name="id375892"></a><a class="indexterm" name="id375903"></a><a class="indexterm" name="id375911"></a> + The use of the <em class="parameter"><code>force user</code></em> or the <em class="parameter"><code>force group</code></em> 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 <code class="constant">oplock break</code> 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, <code class="constant">oplock breaks</code> + 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 <code class="constant">oplock break</code>, or time-out. + </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375952"></a>Share Point Directory and File Permissions</h3></div></div></div><p><a class="indexterm" name="id375958"></a><a class="indexterm" name="id375966"></a><a class="indexterm" name="id375974"></a><a class="indexterm" name="id375982"></a> + 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. + </p><p><a class="indexterm" name="id375999"></a><a class="indexterm" name="id376007"></a><a class="indexterm" name="id376015"></a> + 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: + </p><div class="orderedlist"><ol type="1"><li><p> + A user opens a Work document from a network drive. The file was owned by user <code class="constant">janetp</code> + and [users], and was set read/write-enabled for everyone. + </p></li><li><p> + File changes and edits are made. + </p></li><li><p> + The file is saved, and MS Word is closed. + </p></li><li><p> + The file is now owned by the user <code class="constant">billc</code> and group <code class="constant">doctors</code>, + and is set read/write by <code class="constant">billc</code>, read-only by <code class="constant">doctors</code>, and + no access by everyone. + </p></li><li><p> + The original owner cannot now access her own file and is “<span class="quote">justifiably</span>” upset. + </p></li></ol></div><p> + There have been many postings over the years that report the same basic problem. Frequently Samba users + want to know when this “<span class="quote">bug</span>” will be fixed. The fact is, this is not a bug in Samba at all. + Here is the real sequence of what happens in this case. + </p><p><a class="indexterm" name="id376099"></a><a class="indexterm" name="id376107"></a><a class="indexterm" name="id376115"></a> + 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 (<code class="constant">billc</code>) 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. + </p><p> + 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. + </p><p> + The question is, “<span class="quote">How can we solve the problem?</span>” + </p><p> + 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: + </p><div class="procedure"><a name="id376152"></a><p class="title"><b>Procedure 11.2. Using Directory Permissions to Force File User and Group Ownership</b></p><ol type="1"><li><p> + Change your share definition so that it matches this pattern: +</p><pre class="screen"> +[finance] + path = /usr/data/finance + browseable = Yes + read only = No +</pre><p> + </p></li><li><p><a class="indexterm" name="id376176"></a><a class="indexterm" name="id376187"></a> + Set consistent user and group permissions recursively down the directory tree as shown here: +</p><pre class="screen"> +<code class="prompt">root# </code> chown -R janetp.users /usr/data/finance +</pre><p> + </p></li><li><p><a class="indexterm" name="id376218"></a> + Set the files and directory permissions to be read/write for owner and group, and not accessible + to others (everyone), using the following command: +</p><pre class="screen"> +<code class="prompt">root# </code> chmod ug+rwx,o-rwx /usr/data/finance +</pre><p> + </p></li><li><p><a class="indexterm" name="id376245"></a> + 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 <code class="constant">finance</code> can read and write all files in + the directory. The directory is not readable or writable by anyone who is not in the + <code class="constant">finance</code> group. Simply follow this example: +</p><pre class="screen"> +<code class="prompt">root# </code> find /usr/data/finance -type d -exec chmod ug+s {}\; +</pre><p> + + </p></li><li><p><a class="indexterm" name="id376282"></a><a class="indexterm" name="id376290"></a><a class="indexterm" name="id376298"></a> + Make sure all users that must have read/write access to the directory have + <code class="constant">finance</code> group membership as their primary group, + for example, the group they belong to in <code class="filename">/etc/passwd</code>. + </p></li></ol></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id376321"></a>Managing Windows 200x ACLs</h3></div></div></div><p><a class="indexterm" name="id376328"></a><a class="indexterm" name="id376335"></a><a class="indexterm" name="id376343"></a><a class="indexterm" name="id376351"></a> + 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. + </p><p> + 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. + </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id376370"></a>Using the MMC Computer Management Interface</h4></div></div></div><div class="procedure"><ol type="1"><li><p> + 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 <code class="constant">root</code>). + </p></li><li><p> + Click + <span class="guimenu">Start</span> → <span class="guimenuitem">Settings</span> → <span class="guimenuitem">Control Panel</span> → <span class="guimenuitem">Administrative Tools</span> → <span class="guimenuitem">Computer Management</span>. + </p></li><li><p> + In the left panel, + <span class="guimenu">[Right mouse menu item] Computer Management (Local)</span> → <span class="guimenuitem">Connect to another computer ...</span> → <span class="guimenuitem">Browse...</span> → <span class="guimenuitem">Advanced</span> → <span class="guimenuitem">Find Now</span>. In the lower panel, click on the name of the server you wish to + administer. Click <span class="guimenu">OK</span> → <span class="guimenuitem">OK</span> → <span class="guimenuitem">OK</span>. + In the left panel, the entry <span class="guimenu">Computer Management (Local)</span> should now reflect + the change made. For example, if the server you are administering is called <code class="constant">FRODO</code>, + the Computer Management entry should now say: <span class="guimenu">Computer Management (FRODO)</span>. + </p></li><li><p> + In the left panel, click <span class="guimenu">Computer Management (FRODO)</span> → <span class="guimenuitem">[+] Shared Folders</span> → <span class="guimenuitem">Shares</span>. + </p></li><li><p><a class="indexterm" name="id376547"></a><a class="indexterm" name="id376555"></a><a class="indexterm" name="id376562"></a><a class="indexterm" name="id376570"></a> + 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 <span class="guimenu">Security</span> tab. It is best + to edit ACLs using the <code class="constant">Advanced</code> editing features. Click the + <span class="guimenu">Advanced</span> button. This opens a panel that has four tabs. Only the + functionality under the <code class="constant">Permissions</code> tab can be utilized with respect + to a Samba domain server. + </p></li><li><p><a class="indexterm" name="id376607"></a><a class="indexterm" name="id376615"></a> + 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 <code class="constant">Everyone</code>, which therefore overrules any permissions + set for the permitted group. + </p></li><li><p> + When you are done with editing, close all panels by clicking through the <span class="guimenu">OK</span> + buttons until the last panel closes. + </p></li></ol></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id376647"></a>Using MS Windows Explorer (File Manager)</h4></div></div></div><p> + The following alternative method may be used from a Windows workstation. In this example we work + with a domain called <code class="constant">MEGANET</code>, a server called <code class="constant">MASSIVE</code>, and a + share called <code class="constant">Apps</code>. The underlying UNIX/Linux share point for this share is + <code class="filename">/data/apps</code>. + </p><div class="procedure"><ol type="1"><li><p> + Click <span class="guimenu">Start</span> → <span class="guimenuitem">[right-click] My Computer</span> → <span class="guimenuitem">Explore</span> → <span class="guimenuitem">[left panel] [+] My Network Places</span> → <span class="guimenuitem">[+] Entire Network</span> → <span class="guimenuitem">[+] Microsoft Windows Network</span> → <span class="guimenuitem">[+] Meganet</span> → <span class="guimenuitem">[+] Massive</span> → <span class="guimenuitem">[right-click] Apps</span> → <span class="guimenuitem">Properties</span> → <span class="guimenuitem">Security</span> → <span class="guimenuitem">Advanced</span>. This opens a panel that has four tabs. Only the functionality under the + <code class="constant">Permissions</code> tab can be utilized for a Samba domain server. + </p></li><li><p><a class="indexterm" name="id376768"></a><a class="indexterm" name="id376775"></a> + 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 <code class="constant">Everyone</code>, which therefore overrules any permissions + set for the permitted group. + </p></li><li><p> + When you are done with editing, close all panels by clicking through the <span class="guimenu">OK</span> + buttons until the last panel closes. + </p></li></ol></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id376809"></a>Setting Posix ACLs in UNIX/Linux</h4></div></div></div><p><a class="indexterm" name="id376816"></a><a class="indexterm" name="id376824"></a> + 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: + </p><div class="procedure"><ol type="1"><li><p> + Log into the Linux system as the user <code class="constant">root</code>. + </p></li><li><p> + Change directory to the location of the exported (shared) Windows file share (Apps), which is in + the directory <code class="filename">/data</code>. Execute the following: +</p><pre class="screen"> +<code class="prompt">root# </code> cd /data +</pre><p> + Retrieve the existing POSIX ACLs entry by executing: +</p><pre class="screen"> +<code class="prompt">root# </code> getfacl apps +# file: apps +# owner: root +# group: root +user::rwx +group::rwx +other::r-x +</pre><p> + </p></li><li><p><a class="indexterm" name="id376892"></a> + You want to add permission for <code class="constant">AppsMgrs</code> 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 <code class="constant">-R</code> option as shown. + Execute the following: +</p><pre class="screen"> +<code class="prompt">root# </code> setfacl -m -R group:AppsMgrs:rwx /data/apps +</pre><p> + Because setting an ACL does not provide a response, you immediately validate the command executed + as follows: +</p><pre class="screen"> +<code class="prompt">root# </code> getfacl /data/apps +# file: apps +# owner: root +# group: root +user::rwx +group::rwx +group:AppsMgrs:rwx +mask::rwx +other::r-x +</pre><p> + This confirms that the change of POSIX ACL permissions has been effective. + </p></li><li><p><a class="indexterm" name="id376942"></a><a class="indexterm" name="id376950"></a><a class="indexterm" name="id376958"></a><a class="indexterm" name="id376965"></a><a class="indexterm" name="id376973"></a> + It is highly recommended that you read the online manual page for the <code class="literal">setfacl</code> + and <code class="literal">getfacl</code> 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 <code class="constant">inheritance</code> properties. + </p></li></ol></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id377005"></a>Key Points Learned</h3></div></div></div><p> + 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: + </p><div class="itemizedlist"><ul type="disc"><li><p><a class="indexterm" name="id377020"></a><a class="indexterm" name="id377028"></a><a class="indexterm" name="id377036"></a><a class="indexterm" name="id377043"></a> + 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. + </p></li><li><p><a class="indexterm" name="id377059"></a><a class="indexterm" name="id377067"></a> + 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. + </p></li><li><p><a class="indexterm" name="id377081"></a><a class="indexterm" name="id377089"></a><a class="indexterm" name="id377097"></a><a class="indexterm" name="id377104"></a> + 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. + </p></li><li><p> + 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. + </p></li></ul></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id377127"></a>Questions and Answers</h2></div></div></div><p> + </p><div class="qandaset"><dl><dt> <a href="kerberos.html#id377142"> + Does Samba-3 require the Sign'n'seal registry hacks needed by Samba-2? + </a></dt><dt> <a href="kerberos.html#id377210"> + Does Samba-3 support Active Directory? + </a></dt><dt> <a href="kerberos.html#id377238"> + When Samba-3 is used with Active Directory, is it necessary to run mixed-mode operation, as was + necessary with Samba-2? + </a></dt><dt> <a href="kerberos.html#id377273"> + Is it safe to set share-level access controls in Samba? + </a></dt><dt> <a href="kerberos.html#id377300"> + Is it mandatory to set share ACLs to get a secure Samba-3 server? + </a></dt><dt> <a href="kerberos.html#id377372"> + The valid users did not work on the [homes]. + Has this functionality been restored yet? + </a></dt><dt> <a href="kerberos.html#id377431"> + Is the bias against use of the force user and force group + really warranted? + </a></dt><dt> <a href="kerberos.html#id377492"> + 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? + </a></dt><dt> <a href="kerberos.html#id377536"> + In the book, “The Official Samba-3 HOWTO and Reference Guide”, you recommended use + of the Windows NT4 Server Manager (part of the SRVTOOLS.EXE) utility. Why + have you mentioned only the use of the Windows 200x/XP MMC Computer Management utility? + </a></dt><dt> <a href="kerberos.html#id377596"> + I tried to set valid users = @Engineers, but it does not work. My Samba + server is an Active Directory domain member server. Has this been fixed now? + </a></dt></dl><table border="0" summary="Q and A Set"><col align="left" width="1%"><tbody><tr class="question"><td align="left" valign="top"><a name="id377142"></a><a name="id377144"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id377147"></a><a class="indexterm" name="id377155"></a> + Does Samba-3 require the <code class="constant">Sign'n'seal</code> registry hacks needed by Samba-2? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id377174"></a><a class="indexterm" name="id377182"></a><a class="indexterm" name="id377190"></a> + No. Samba-3 fully supports <code class="constant">Sign'n'seal</code> as well as <code class="constant">schannel</code> + operation. The registry change should not be applied when Samba-3 is used as a domain controller. + </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id377210"></a><a name="id377212"></a></td><td align="left" valign="top"><p> + Does Samba-3 support Active Directory? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id377222"></a> + 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. + </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id377238"></a><a name="id377240"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id377243"></a> + When Samba-3 is used with Active Directory, is it necessary to run mixed-mode operation, as was + necessary with Samba-2? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id377259"></a> + 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, + because Samba-3 can join a native Windows 2003 Server ADS domain. + </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id377273"></a><a name="id377275"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id377278"></a> + Is it safe to set share-level access controls in Samba? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> + 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. + </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id377300"></a><a name="id377302"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id377305"></a> + Is it mandatory to set share ACLs to get a secure Samba-3 server? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id377320"></a><a class="indexterm" name="id377328"></a><a class="indexterm" name="id377336"></a><a class="indexterm" name="id377344"></a><a class="indexterm" name="id377352"></a> + 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 <code class="filename">smb.conf</code> file. The additional + support for share-level ACLs is like frosting on the cake. It adds to security but is not essential + to it. + </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id377372"></a><a name="id377374"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id377378"></a> + The <em class="parameter"><code>valid users</code></em> did not work on the <em class="parameter"><code>[homes]</code></em>. + Has this functionality been restored yet? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id377404"></a> + Yes. This was fixed in Samba-3.0.2. The use of this parameter is strongly recommended as a safeguard + on the <em class="parameter"><code>[homes]</code></em> meta-service. The correct way to specify this is: + <a class="indexterm" name="id377421"></a>valid users = %S. + </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id377431"></a><a name="id377433"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id377436"></a><a class="indexterm" name="id377444"></a><a class="indexterm" name="id377452"></a> + Is the bias against use of the <em class="parameter"><code>force user</code></em> and <em class="parameter"><code>force group</code></em> + really warranted? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id377479"></a> + 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? + </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id377492"></a><a name="id377494"></a></td><td align="left" valign="top"><p> + 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? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id377506"></a> + 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: +</p><pre class="screen"> +<code class="prompt">root# </code> find /usr/data/finance -type d -exec chmod g+s {}\; +</pre><p> + Note that this required no more than removing the <code class="constant">u</code> argument so that the + SUID bit is not set for the owner. + </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id377536"></a><a name="id377538"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id377541"></a> + In the book, “<span class="quote">The Official Samba-3 HOWTO and Reference Guide</span>”, you recommended use + of the Windows NT4 Server Manager (part of the <code class="filename">SRVTOOLS.EXE</code>) utility. Why + have you mentioned only the use of the Windows 200x/XP MMC Computer Management utility? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p><a class="indexterm" name="id377567"></a><a class="indexterm" name="id377575"></a> + 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 <code class="filename">SRVTOOLS.EXE</code> utility. + </p></td></tr><tr class="question"><td align="left" valign="top"><a name="id377596"></a><a name="id377599"></a></td><td align="left" valign="top"><p><a class="indexterm" name="id377602"></a><a class="indexterm" name="id377610"></a><a class="indexterm" name="id377618"></a> + I tried to set <em class="parameter"><code>valid users = @Engineers</code></em>, but it does not work. My Samba + server is an Active Directory domain member server. Has this been fixed now? + </p></td></tr><tr class="answer"><td align="left" valign="top"></td><td align="left" valign="top"><p> + The use of this parameter has always required the full specification of the domain account, for + example, <em class="parameter"><code>valid users = @"MEGANET2\Domain Admins"</code></em>. + </p></td></tr></tbody></table></div></div><div class="footnotes"><br><hr width="100" align="left"><div class="footnote"></div><div class="footnote"><a href="http://199.105.191.226/Man/2699/020430msdoj/" target="_top"><sup>[<a name="ftn.id374937" href="#id374937">13</a>] </sup>ITWorld.com</a></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="RefSection.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="RefSection.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="DomApps.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part III. Reference Section </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 12. Integrating Additional Services</td></tr></table></div></body></html> |