From f9a9e18f15717e089e59cec86384a6fb9ecf1989 Mon Sep 17 00:00:00 2001 From: Andrew Bartlett Date: Tue, 3 Jun 2014 20:20:08 +1200 Subject: docs: Remove out of date Kerberos and security chapter Signed-off-by: Andrew Bartlett Reviewed-by: Jeremy Allison Autobuild-User(master): Jeremy Allison Autobuild-Date(master): Tue Jun 3 21:24:45 CEST 2014 on sn-devel-104 --- .../Samba3-ByExample/SBE-KerberosFastStart.xml | 2073 -------------------- docs-xml/Samba3-ByExample/index.xml | 14 +- 2 files changed, 6 insertions(+), 2081 deletions(-) delete mode 100644 docs-xml/Samba3-ByExample/SBE-KerberosFastStart.xml (limited to 'docs-xml') diff --git a/docs-xml/Samba3-ByExample/SBE-KerberosFastStart.xml b/docs-xml/Samba3-ByExample/SBE-KerberosFastStart.xml deleted file mode 100644 index 3bc301c96dc..00000000000 --- a/docs-xml/Samba3-ByExample/SBE-KerberosFastStart.xml +++ /dev/null @@ -1,2073 +0,0 @@ - - - - Active Directory, Kerberos, and Security - - - experiment - - 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. - - - - criticism - - 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. - - - - 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. - - - - straw-man - - 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. - - - - Introduction - - - acquisitions - - risk - - assessment - - Active Directory - - Windows 2003 Serve - - 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. - - - - Active Directory - - 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 an island of broken - technologies. This comment was made by one of Christine's staff as they were installing a new - Samba server at the new business. - - - - - consultant - - hypothetical - - 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 reportThis report is entirely fictitious. - Any resemblance to a factual report is purely coincidental. on his unit's operations - and to investigate the role of Samba at his site. Here are key extracts from this hypothetical - report: - - -
- vulnerabilities - - integrity - - practices - - Active Directory - - ... 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. - - - - ... - - - - accounts - user - - accounts - group - - Backup - - disaster recovery - - validated - - off-site storage - - 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. - - - - compromise - - secure - - network - secure - - Your staff are justifiably concerned that the use of Samba may compromise their good efforts to maintain - a secure network. - - - - winbind - - security - - secure - - network - management - - The recently installed Linux file and application server uses a tool called winbind - 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. - - - - isolated - - firewall - - best practices - - 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. - - - - ... - - - - security - - disable - - essential - - trusted computing - - 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. - - - - integrity - - hackers - - accountable - - flaws - - updates - - bug fixes - - alarm - - 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. - - - - employment - - jobs - - risk - - 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. -
- - - Active Directory - - independent expert - - 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: - - - - Good afternoon, - - -
Stan - 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. - - - - 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. - - - - Kerberos - - OpenLDAP - - Active Directory - - consultant - - 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. - - - - criticism - - policy - - Windows Servers - - Active Directory - - budgetted - - financial responsibility - - 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. -
- - - Assignment Tasks - - - 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. - - - - - - - Dissection and Discussion - - - tool - - benefit - - choice - - consultant - - installation - - income - - employment - - 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. - - - - economically sustainable - - inter-operability - - file and print service - - cost - - alternative - - 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. - - - - documentation - - responsibility - - fix - - broken - - 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. - - - - commercial - - software - - commercial software - - End User License Agreement - EULA - - accountable - - liability - - accepts liability - - price paid - - product defects - - reimburse - - extent - - 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. - - - - consumer - - EULA - - track record - - commercial software - - support - - vendor - - 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? - - - - source code - - Open Source - - hire - - programmer - - solve - - fix - - problem - - 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. - - - - Technical Issues - - - Each issue is now discussed and, where appropriate, example implementation steps are - provided. - - - - - Winbind and Security - - Winbind - - Security - - network - administrators - - Domain users - - Domain account - - credentials - - Network Neighborhood - - UNIX/Linux server - - browse - - shares - - Windows network administrators may be dismayed to find that winbind - 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. - - - - Domain Member server - - familiar - - fear - - unknown - - winbind 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. - - - - network administrators - - recognize - - winbind - - over-ride - - Active Directory - management tools - - fears - - Windows network administrators need to recognize that winbind does - not, and cannot, override account controls set using the Active Directory management - tools. The control is the same. Have no fear. - - - - ADS Domain - - account - ADS Domain - - winbind - - browsing - - permits - - access - - drive mapping - - protected - - security controls - - access controls - - Where Samba and the ADS domain account information obtained through the use of - winbind 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: - - - - Shares themselves (i.e., the logical share itself) - The share definition in &smb.conf; - The shared directories and files using UNIX permissions - Using Windows 2000 ACLs &smbmdash; if the file system is POSIX enabled - - - - Examples of each are given in . - - - - - - User and Group Controls - - User and Group Controls - - management - User - - management - group - - ADS - - permissions - - privileges - - flexibility - - access controls - - share definition - - 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. - - - - analysis - - system security - - safe-guards - - permissions - excessive - - file system - - shared resource - - share definition - - 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. - - - - diligence - - weakness - - 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. - - - - - Security Overall - - defects - - 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. - - - - security - - protection - - compromise - - consequential risk - - 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. - - - - condemns - - security fixes - - updates - - development - - documentation - - security updates - - turn-around time - - 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. - - - - modularization - - next generation - - responsible - - dependability - - road-map - published - - 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. - - - - foundation members - - Common Internet File System - CIFS - - network attached storage - NAS - - conferences - - presence and leadership - - leadership - - inter-operability - - 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. - - - - - Cryptographic Controls (schannel, sign'n'seal) - - Cryptographic - - schannel - - digital sign'n'seal - - The report correctly mentions that Samba did not support the most recent - schannel and digital sign'n'seal 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. - - - - public specifications - - protocols - - algorithm - - compatible - - network - traffic - observation - - defensible standards - - secure networking - - 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. - - - - Critics - - digital sign'n'seal - - 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 digital sign'n'seal support - often dismiss the problems that Microsoft has - acknowledged - and for which a fix was provided. In fact, - Tangent Systems - 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. - - - - secure networking protocols - - refereed standards - - proprietary - - digital rights - - protection - - networking protocols - - diffusion - - consumer - - choice - - 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. - - - - - Active Directory Replacement with Kerberos, LDAP, and Samba - - Active Directory - Replacement - - Kerberos - - LDAP - - remote procedure call - RPC - - - - - - 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. - - - - Active Directory - Server - - OpenLDAP - - Kerberos - - project maintainers - - LDAP - - 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. - - - - missing RPC's - - road-map - - ADS - server - - MMC - - managed - - 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. - - - - - - Kerberos Exposed - - - kerberos - - unauthorized activities - - authorized location - - 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. - - - - strong cryptography - - identity - - integrity - - 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. - - - - trusted third-party - - principals - - trusting - - kerberos - server - - secret - - 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. - - - - restricted export - MIT Kerberos - Heimdal Kerberos - 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 Royal Institute 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. - - - - Kerberosinteroperability - A storm has broken out concerning interoperability between MIT Kerberos and Microsofts' implementation - of it. For example, a 2002 - IDG - reportNote: This link is no longer active. The same article is still - available from ITWorld.com (July 5, 2005) by - states: - - -
- 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. - - - - Kerberosunspecified fields - 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. -
- - - DCE - RPC - It so happens that Microsoft Windows clients depend on and expect the contents of the unspecified - fields 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. - - - - Microsoft makes the following comment in a reference in a - - technet article: - - -
- Privilege Attribute Certificates - PAC - - access control - - 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. -
- - - - - - - - - Implementation - - - The following procedures outline the implementation of the security measures discussed so far. - - - - Share Access Controls - - - Share Access Controls - - filter - - connection - - 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. - - - - Create/Edit/Delete Share ACLs - - Domain Administrator - - account - - 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 root). - - - - Click - - Start - Settings - Control Panel - Administrative Tools - Computer Management - . - - - - In the left panel, - - [Right mouse menu item] Computer Management (Local) - Connect to another computer ... - Browse... - Advanced - Find Now - . In the lower panel, click on the name of the server you wish to - administer. Click - OK - OK - OK - . - Computer Management - - In the left panel, the entry Computer Management (Local) should now reflect - the change made. For example, if the server you are administering is called FRODO, - the Computer Management entry should now say Computer Management (FRODO). - - - - In the left panel, click - Computer Management (FRODO) - [+] Shared Folders - Shares - . - - - - ACLs - - Share Permissions - - 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 Share Permissions tab. - - - - access control settings - - Everyone - - full control - - over-rule - - permissions - - rejected - - 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 Everyone, which therefore overrules any permissions - set for the permitted group. - - - - When you are done with editing, close all panels by clicking through the OK - buttons. - - - - - - - Share Definition Controls - - - Share Definition - Controls - - check-point - - pile-driver - - credential - - powers - - privileges - - 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. - - - - access controls - - ACLs - - share definition controls - - hierarchy of control - - 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: - - - - Share-level ACLs - Share-definition controls - Directory and file permissions - Directory and file POSIX ACLs - - - - Checkpoint Controls - - - Checkpoint Controls - - Consider the following extract from a &smb.conf; file defining the share called Apps: - -[Apps] - comment = Application Share - path = /data/apps - read only = Yes - valid users = @Employees - - This definition permits only those who are members of the group called Employees to - access the share. - - - - Domain Member - servers - - winbind use default domain - - fully qualified - - valid users - - delimiter - - On domain member servers and clients, even when the winbind use default domain has - been specified, the use of domain accounts in security controls requires fully qualified domain specification, - for example, @"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. - - - - ACL - - access - - validate - - If there is an ACL on the share itself to permit read/write access for all Employees - as well as read/write for the group Doctors, 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 Doctors, who is not also a member of the group Employees, - would immediately fail to validate. - - - - share definition controls - - Consider another example. In this case, you want to permit all members of the group Employees - except the user patrickj to access the Apps share. This can be - easily achieved by setting a share-level ACL permitting only Employees to access the share, - and then in the share definition controls excluding just patrickj. Here is how that might - be done: - -[Apps] - comment = Application Share - path = /data/apps - read only = Yes - invalid users = patrickj - - - permissions - - Let us assume that you want to permit the user gbshaw to manage any file in the - UNIX/Linux file system directory /data/apps, but you do not want to grant any write - permissions beyond that directory tree. Here is one way this can be done: - -[Apps] - comment = Application Share - path = /data/apps - read only = Yes - invalid users = patrickj - admin users = gbshaw - - - administrative rights - - Now we have a set of controls that permits only Employees who are also members of - the group Doctors, excluding the user patrickj, to have - read-only privilege, but the user gbshaw is granted administrative rights. - The administrative rights conferred upon the user gbshaw permit operation as - if that user has logged in as the user root 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. - - - - There are additional checkpoint controls that may be used. For example, if for the same share we now - want to provide the user peters 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: - -[Apps] - comment = Application Share - path = /data/apps - read only = Yes - invalid users = patrickj - admin users = gbshaw - write list = peters - - - check-point controls - - 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. - - - - - - Override Controls - - - over-ride controls - - 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. - - - - 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 billc - and member of the group Mentors read/write the files. Here is one way this - can be done: - -[someshare] - comment = Some Files Everyone May Overwrite - path = /data/somestuff - read only = No - force user = billc - force group = Mentors - - - forced settings - - overheads - - 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. - - - - force user - - force group - - opportunistic - locking - - oplock break - - performance degradation - - The use of the force user or the force group 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 oplock break 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, oplock breaks - 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 oplock break, or time-out. - - - - - - - - Share Point Directory and File Permissions - - - security - - privilege controls - - permission - - share definition controls - - 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. - - - - Microsoft Office - - Word - - Excel - - 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: - - - - - A user opens a Word document from a network drive. The file was owned by user janetp - and users, and was set read/write-enabled for everyone. - - - - File changes and edits are made. - - - - The file is saved, and MS Word is closed. - - - - The file is now owned by the user billc and group doctors, - and is set read/write by billc, read-only by doctors, and - no access by everyone. - - - - The original owner cannot now access her own file and is justifiably upset. - - - - - There have been many postings over the years that report the same basic problem. Frequently Samba users - want to know when this bug 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. - - - - MS Word - - ownership - - permissions - - 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 (billc) 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. - - - - 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. - - - - The question is, How can we solve the problem? - - - - 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: - - - - - Using Directory Permissions to Force File User and Group Ownership - - Change your share definition so that it matches this pattern: - -[finance] - path = /usr/data/finance - browseable = Yes - read only = No - - - - - permissions - user - - permissions - group - - Set consistent user and group permissions recursively down the directory tree as shown here: - -&rootprompt; chown -R janetp.users /usr/data/finance - - - - - accessible - - Set the files and directory permissions to be read/write for owner and group, and not accessible - to others (everyone), using the following command: - -&rootprompt; chmod ug+rwx,o-rwx /usr/data/finance - - - - - SGID - - 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 finance can read and write all files in - the directory. The directory is not readable or writable by anyone who is not in the - finance group. Simply follow this example: - -&rootprompt; find /usr/data/finance -type d -exec chmod ug+s {}\; - - - - - - group membership - - primary group - - /etc/passwd - - Make sure all users that must have read/write access to the directory have - finance group membership as their primary group, - for example, the group they belong to in /etc/passwd. - - - - - - - Managing Windows 200x ACLs - - - translate - - Windows 2000 ACLs - - Posix ACLs - - side effects - - 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. - - - - 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. - - - - Using the MMC Computer Management Interface - - - - 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 root). - - - - Click - - Start - Settings - Control Panel - Administrative Tools - Computer Management - . - - - - In the left panel, - - [Right mouse menu item] Computer Management (Local) - Connect to another computer ... - Browse... - Advanced - Find Now - . In the lower panel, click on the name of the server you wish to - administer. Click - OK - OK - OK - . - In the left panel, the entry Computer Management (Local) should now reflect - the change made. For example, if the server you are administering is called FRODO, - the Computer Management entry should now say: Computer Management (FRODO). - - - - In the left panel, click - Computer Management (FRODO) - [+] Shared Folders - Shares - . - - - - Security - - Properties - - Permissions - - Samba Domain server - - 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 Security tab. It is best - to edit ACLs using the Advanced editing features. Click the - Advanced button. This opens a panel that has four tabs. Only the - functionality under the Permissions tab can be utilized with respect - to a Samba domain server. - - - - access control - - permitted group - - 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 Everyone, which therefore overrules any permissions - set for the permitted group. - - - - When you are done with editing, close all panels by clicking through the OK - buttons until the last panel closes. - - - - - - - Using MS Windows Explorer (File Manager) - - - The following alternative method may be used from a Windows workstation. In this example we work - with a domain called MEGANET, a server called MASSIVE, and a - share called Apps. The underlying UNIX/Linux share point for this share is - /data/apps. - - - - - Click - Start - [right-click] My Computer - Explore - [left panel] [+] My Network Places - [+] Entire Network - [+] Microsoft Windows Network - [+] Meganet - [+] Massive - [right-click] Apps - Properties - Security - Advanced - . This opens a panel that has four tabs. Only the functionality under the - Permissions tab can be utilized for a Samba domain server. - - - - full control - - over-rule - - 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 Everyone, which therefore overrules any permissions - set for the permitted group. - - - - When you are done with editing, close all panels by clicking through the OK - buttons until the last panel closes. - - - - - - - Setting Posix ACLs in UNIX/Linux - - - desired security setting - - shared resource - - 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: - - - - - Log into the Linux system as the user root. - - - - Change directory to the location of the exported (shared) Windows file share (Apps), which is in - the directory /data. Execute the following: - -&rootprompt; cd /data - - Retrieve the existing POSIX ACLs entry by executing: - -&rootprompt; getfacl apps -# file: apps -# owner: root -# group: root -user::rwx -group::rwx -other::r-x - - - - - recursively - - You want to add permission for AppsMgrs 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 -R option as shown. - Execute the following: - -&rootprompt; setfacl -m -R group:AppsMgrs:rwx /data/apps - - Because setting an ACL does not provide a response, you immediately validate the command executed - as follows: - -&rootprompt; getfacl /data/apps -# file: apps -# owner: root -# group: root -user::rwx -group::rwx -group:AppsMgrs:rwx -mask::rwx -other::r-x - - This confirms that the change of POSIX ACL permissions has been effective. - - - - setfacl - - getfacl - - directory tree - - Windows ACLs - - inheritance - - It is highly recommended that you read the online manual page for the setfacl - and getfacl 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 inheritance properties. - - - - - - - - - Key Points Learned - - - 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: - - - - - Winbind - - Active Directory - - password change - - logon hours - - 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. - - - - Sign'n'seal - - schannel - - 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. - - - - Kerberos - - OpenLDAP - - Active Directory - - inter-operability - - 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. - - - - 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. - - - - - - - - - Questions and Answers - - - - - - - - - - Sign'n'seal - - registry hacks - - Does Samba-3 require the Sign'n'seal registry hacks needed by Samba-2? - - - - - - - schannel - - Sign'n'seal - - registry change - - No. Samba fully supports Sign'n'seal as well as schannel - operation. The registry change should not be applied when Samba is used as a domain controller. - - - - - - - - - - Does Samba support Active Directory? - - - - - - - Active Directory - - 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. - - - - - - - - - - mixed-mode - - When Samba is used with Active Directory, is it necessary to run mixed-mode operation, as was - necessary with Samba-2? - - - - - - - native - - 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. - - - - - - - - - - share level access controls - - Is it safe to set share-level access controls in Samba? - - - - - - - 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. - - - - - - - - - - share ACLs - - Is it mandatory to set share ACLs to get a secure Samba server? - - - - - - - file system security - - Windows 200x ACLs - - share definition controls - - share level ACL - - security - - 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. - - - - - - - - - - valid users - - The valid users did not work on the . - Has this functionality been restored yet? - - - - - - - meta-service - - Yes. This was fixed in Samba-3.0.2. The use of this parameter is strongly recommended as a safeguard - on the meta-service. The correct way to specify this is: - %S. - - - - - - - - - - force user - - force group - - bias - - Is the bias against use of the force user and force group - really warranted? - - - - - - - performance - - 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? - - - - - - - - - - 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? - - - - - - - SUID - - 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: - -&rootprompt; find /usr/data/finance -type d -exec chmod g+s {}\; - - Note that this required no more than removing the u argument so that the - SUID bit is not set for the owner. - - - - - - - - - - Computer Management - - In the book, The Official Samba 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? - - - - - - - MMC - - SRVTOOLS.EXE - - 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 SRVTOOLS.EXE utility. - - - - - - - - - - valid users - - Active Directory - - Domain Member server - - 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? - - - - - - - The use of this parameter has always required the full specification of the domain account, for - example, valid users = @"MEGANET2\Domain Admins". - - - - - - - - - - - diff --git a/docs-xml/Samba3-ByExample/index.xml b/docs-xml/Samba3-ByExample/index.xml index 7650af82dc9..6b2b6071e4c 100644 --- a/docs-xml/Samba3-ByExample/index.xml +++ b/docs-xml/Samba3-ByExample/index.xml @@ -126,14 +126,12 @@ published regarding Samba, or just to gain a more broad understanding of how Sam play in a Windows networking world. - - - - - - - - + + + + + + -- cgit v1.2.1