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diff --git a/docs/htmldocs/Samba3-HOWTO/AccessControls.html b/docs/htmldocs/Samba3-HOWTO/AccessControls.html new file mode 100644 index 0000000000..0f2e0dc064 --- /dev/null +++ b/docs/htmldocs/Samba3-HOWTO/AccessControls.html @@ -0,0 +1,913 @@ +<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 16. File, Directory, and Share Access Controls</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="The Official Samba-3 HOWTO and Reference Guide"><link rel="up" href="optional.html" title="Part III. Advanced Configuration"><link rel="prev" href="rights.html" title="Chapter 15. User Rights and Privileges"><link rel="next" href="locking.html" title="Chapter 17. File and Record Locking"></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 16. File, Directory, and Share Access Controls</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="rights.html">Prev</a> </td><th width="60%" align="center">Part III. Advanced Configuration</th><td width="20%" align="right"> <a accesskey="n" href="locking.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="AccessControls"></a>Chapter 16. File, Directory, and Share Access Controls</h2></div><div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="othername">H.</span> <span class="surname">Terpstra</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><code class="email"><<a href="mailto:jht@samba.org">jht@samba.org</a>></code></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Jeremy</span> <span class="surname">Allison</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><code class="email"><<a href="mailto:jra@samba.org">jra@samba.org</a>></code></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Jelmer</span> <span class="othername">R.</span> <span class="surname">Vernooij</span></h3><span class="contrib">drawing</span><div class="affiliation"><span class="orgname">The Samba Team<br></span><div class="address"><p><code class="email"><<a href="mailto:jelmer@samba.org">jelmer@samba.org</a>></code></p></div></div></div></div><div><p class="pubdate">May 10, 2003</p></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="AccessControls.html#id373022">Features and Benefits</a></span></dt><dt><span class="sect1"><a href="AccessControls.html#id373190">File System Access Controls</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id373202">MS Windows NTFS Comparison with UNIX File Systems</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id373499">Managing Directories</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id373620">File and Directory Access Control</a></span></dt></dl></dd><dt><span class="sect1"><a href="AccessControls.html#id374219">Share Definition Access Controls</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id374250">User- and Group-Based Controls</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id374546">File and Directory Permissions-Based Controls</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id374820">Miscellaneous Controls</a></span></dt></dl></dd><dt><span class="sect1"><a href="AccessControls.html#id375089">Access Controls on Shares</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id375225">Share Permissions Management</a></span></dt></dl></dd><dt><span class="sect1"><a href="AccessControls.html#id375547">MS Windows Access Control Lists and UNIX Interoperability</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id375553">Managing UNIX Permissions Using NT Security Dialogs</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id375592">Viewing File Security on a Samba Share</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id375657">Viewing File Ownership</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id375783">Viewing File or Directory Permissions</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id375970">Modifying File or Directory Permissions</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id376107">Interaction with the Standard Samba “<span class="quote">create mask</span>” Parameters</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id376409">Interaction with the Standard Samba File Attribute Mapping</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id376473">Windows NT/200X ACLs and POSIX ACLs Limitations</a></span></dt></dl></dd><dt><span class="sect1"><a href="AccessControls.html#id376834">Common Errors</a></span></dt><dd><dl><dt><span class="sect2"><a href="AccessControls.html#id376844">Users Cannot Write to a Public Share</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id377152">File Operations Done as <span class="emphasis"><em>root</em></span> with <span class="emphasis"><em>force user</em></span> Set</a></span></dt><dt><span class="sect2"><a href="AccessControls.html#id377189">MS Word with Samba Changes Owner of File</a></span></dt></dl></dd></dl></div><p> +<a class="indexterm" name="id372870"></a> +<a class="indexterm" name="id372877"></a> +<a class="indexterm" name="id372884"></a> +<a class="indexterm" name="id372891"></a> +Advanced MS Windows users are frequently perplexed when file, directory, and share manipulation of +resources shared via Samba do not behave in the manner they might expect. MS Windows network +administrators are often confused regarding network access controls and how to +provide users with the access they need while protecting resources from unauthorized access. +</p><p> +<a class="indexterm" name="id372904"></a> +<a class="indexterm" name="id372911"></a> +Many UNIX administrators are unfamiliar with the MS Windows environment and in particular +have difficulty in visualizing what the MS Windows user wishes to achieve in attempts to set file +and directory access permissions. +</p><p> +<a class="indexterm" name="id372923"></a> +<a class="indexterm" name="id372930"></a> +<a class="indexterm" name="id372937"></a> +<a class="indexterm" name="id372943"></a> +The problem lies in the differences in how file and directory permissions and controls work +between the two environments. This difference is one that Samba cannot completely hide, even +though it does try to bridge the chasm to a degree. +</p><p> +<a class="indexterm" name="id372954"></a> +<a class="indexterm" name="id372961"></a> +<a class="indexterm" name="id372970"></a> +<a class="indexterm" name="id372977"></a> +POSIX Access Control List technology has been available (along with extended attributes) +for UNIX for many years, yet there is little evidence today of any significant use. This +explains to some extent the slow adoption of ACLs into commercial Linux products. MS Windows +administrators are astounded at this, given that ACLs were a foundational capability of the now +decade-old MS Windows NT operating system. +</p><p> +<a class="indexterm" name="id372991"></a> +The purpose of this chapter is to present each of the points of control that are possible with +Samba-3 in the hope that this will help the network administrator to find the optimum method +for delivering the best environment for MS Windows desktop users. +</p><p> +<a class="indexterm" name="id373003"></a> +<a class="indexterm" name="id373010"></a> +This is an opportune point to mention that Samba was created to provide a means of interoperability +and interchange of data between differing operating environments. Samba has no intent to change +UNIX/Linux into a platform like MS Windows. Instead the purpose was and is to provide a sufficient +level of exchange of data between the two environments. What is available today extends well +beyond early plans and expectations, yet the gap continues to shrink. +</p><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id373022"></a>Features and Benefits</h2></div></div></div><p> + Samba offers much flexibility in file system access management. These are the key access control + facilities present in Samba today: + </p><div class="itemizedlist"><p class="title"><b>Samba Access Control Facilities</b></p><ul type="disc"><li><p> + <a class="indexterm" name="id373041"></a> + <span class="emphasis"><em>UNIX File and Directory Permissions</em></span> + </p><p> +<a class="indexterm" name="id373057"></a> +<a class="indexterm" name="id373064"></a> +<a class="indexterm" name="id373070"></a> + Samba honors and implements UNIX file system access controls. Users + who access a Samba server will do so as a particular MS Windows user. + This information is passed to the Samba server as part of the logon or + connection setup process. Samba uses this user identity to validate + whether or not the user should be given access to file system resources + (files and directories). This chapter provides an overview for those + to whom the UNIX permissions and controls are a little strange or unknown. + </p></li><li><p> + <span class="emphasis"><em>Samba Share Definitions</em></span> + </p><p> +<a class="indexterm" name="id373094"></a> + In configuring share settings and controls in the <code class="filename">smb.conf</code> file, + the network administrator can exercise overrides to native file + system permissions and behaviors. This can be handy and convenient + to effect behavior that is more like what MS Windows NT users expect, + but it is seldom the <span class="emphasis"><em>best</em></span> way to achieve this. + The basic options and techniques are described herein. + </p></li><li><p> + <span class="emphasis"><em>Samba Share ACLs</em></span> + <a class="indexterm" name="id373122"></a> + </p><p> +<a class="indexterm" name="id373134"></a> + Just as it is possible in MS Windows NT to set ACLs on shares + themselves, so it is possible to do in Samba. + Few people make use of this facility, yet it remains one of the + easiest ways to affect access controls (restrictions) and can often + do so with minimum invasiveness compared with other methods. + </p></li><li><p> + <a class="indexterm" name="id373149"></a> + <a class="indexterm" name="id373159"></a> + <span class="emphasis"><em>MS Windows ACLs through UNIX POSIX ACLs</em></span> + </p><p> +<a class="indexterm" name="id373175"></a> + The use of POSIX ACLs on UNIX/Linux is possible only if the underlying + operating system supports them. If not, then this option will not be + available to you. Current UNIX technology platforms have native support + for POSIX ACLs. There are patches for the Linux kernel that also provide + this support. Sadly, few Linux platforms ship today with native ACLs and + extended attributes enabled. This chapter has pertinent information + for users of platforms that support them. + </p></li></ul></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id373190"></a>File System Access Controls</h2></div></div></div><p> +Perhaps the most important recognition to be made is the simple fact that MS Windows NT4/200x/XP +implement a totally divergent file system technology from what is provided in the UNIX operating system +environment. First we consider what the most significant differences are, then we look +at how Samba helps to bridge the differences. +</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id373202"></a>MS Windows NTFS Comparison with UNIX File Systems</h3></div></div></div><p> + <a class="indexterm" name="id373210"></a> + <a class="indexterm" name="id373217"></a> + <a class="indexterm" name="id373223"></a> + <a class="indexterm" name="id373233"></a> + Samba operates on top of the UNIX file system. This means it is subject to UNIX file system conventions + and permissions. It also means that if the MS Windows networking environment requires file system + behavior, that differs from UNIX file system behavior then somehow Samba is responsible for emulating + that in a transparent and consistent manner. + </p><p> + It is good news that Samba does this to a large extent, and on top of that, provides a high degree + of optional configuration to override the default behavior. We look at some of these overrides, + but for the greater part we stay within the bounds of default behavior. Those wishing to explore + the depths of control ability should review the <code class="filename">smb.conf</code> man page. + </p><p>The following compares file system features for UNIX with those of MS Windows NT/200x: + <a class="indexterm" name="id373261"></a> + + </p><div class="variablelist"><dl><dt><span class="term">Name Space</span></dt><dd><p> + MS Windows NT4/200x/XP file names may be up to 254 characters long, and UNIX file names + may be 1023 characters long. In MS Windows, file extensions indicate particular file types; + in UNIX this is not so rigorously observed because all names are considered arbitrary. + </p><p> + What MS Windows calls a folder, UNIX calls a directory. + </p></dd><dt><span class="term">Case Sensitivity</span></dt><dd><p> + <a class="indexterm" name="id373303"></a> + <a class="indexterm" name="id373310"></a> + MS Windows file names are generally uppercase if made up of 8.3 (8-character file name + and 3 character extension. File names that are longer than 8.3 are case preserving and case + insensitive. + </p><p> + UNIX file and directory names are case sensitive and case preserving. Samba implements the + MS Windows file name behavior, but it does so as a user application. The UNIX file system + provides no mechanism to perform case-insensitive file name lookups. MS Windows does this + by default. This means that Samba has to carry the processing overhead to provide features + that are not native to the UNIX operating system environment. + </p><p> + Consider the following. All are unique UNIX names but one single MS Windows file name: + </p><pre class="screen"> + MYFILE.TXT + MyFile.txt + myfile.txt + </pre><p> + So clearly, in an MS Windows file namespace these three files cannot co-exist, but in UNIX + they can. + </p><p> + So what should Samba do if all three are present? That which is lexically first will be + accessible to MS Windows users; the others are invisible and unaccessible any + other solution would be suicidal. The Windows client will ask for a case-insensitive file + lookup, and that is the reason for which Samba must offer a consistent selection in the + event that the UNIX directory contains multiple files that would match a case insensitive + file listing. + </p></dd><dt><span class="term">Directory Separators</span></dt><dd><p> + <a class="indexterm" name="id373362"></a> + MS Windows and DOS use the backslash <code class="constant">\</code> as a directory delimiter, and UNIX uses + the forward-slash <code class="constant">/</code> as its directory delimiter. This is handled transparently by Samba. + </p></dd><dt><span class="term">Drive Identification</span></dt><dd><p> + <a class="indexterm" name="id373388"></a> + MS Windows products support a notion of drive letters, like <code class="literal">C:</code>, to represent + disk partitions. UNIX has no concept of separate identifiers for file partitions; each + such file system is mounted to become part of the overall directory tree. + The UNIX directory tree begins at <code class="constant">/</code> just as the root of a DOS drive is specified as + <code class="constant">C:\</code>. + </p></dd><dt><span class="term">File Naming Conventions</span></dt><dd><p> + <a class="indexterm" name="id373421"></a> + MS Windows generally never experiences file names that begin with a dot (<code class="constant">.</code>), while in UNIX these + are commonly found in a user's home directory. Files that begin with a dot (<code class="constant">.</code>) are typically + startup files for various UNIX applications, or they may be files that contain + startup configuration data. + </p></dd><dt><span class="term">Links and Short-Cuts</span></dt><dd><p> + <a class="indexterm" name="id373448"></a> + <a class="indexterm" name="id373457"></a> + <a class="indexterm" name="id373466"></a> + MS Windows make use of <span class="emphasis"><em>links and shortcuts</em></span> that are actually special types of files that will + redirect an attempt to execute the file to the real location of the file. UNIX knows of file and directory + links, but they are entirely different from what MS Windows users are used to. + </p><p> + Symbolic links are files in UNIX that contain the actual location of the data (file or directory). An + operation (like read or write) will operate directly on the file referenced. Symbolic links are also + referred to as “<span class="quote">soft links.</span>” A hard link is something that MS Windows is not familiar with. It allows + one physical file to be known simultaneously by more than one file name. + </p></dd></dl></div><p> + There are many other subtle differences that may cause the MS Windows administrator some temporary discomfort + in the process of becoming familiar with UNIX/Linux. These are best left for a text that is dedicated to the + purpose of UNIX/Linux training and education. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id373499"></a>Managing Directories</h3></div></div></div><p> +<a class="indexterm" name="id373507"></a> +<a class="indexterm" name="id373514"></a> +<a class="indexterm" name="id373520"></a> + There are three basic operations for managing directories: <code class="literal">create</code>, <code class="literal">delete</code>, + <code class="literal">rename</code>. <a href="AccessControls.html#TOSH-Accesstbl" title="Table 16.1. Managing Directories with UNIX and Windows">Managing Directories with UNIX and + Windows</a> compares the commands in Windows and UNIX that implement these operations. + </p><div class="table"><a name="TOSH-Accesstbl"></a><p class="title"><b>Table 16.1. Managing Directories with UNIX and Windows</b></p><div class="table-contents"><table summary="Managing Directories with UNIX and Windows" border="1"><colgroup><col><col><col></colgroup><thead><tr><th align="center">Action</th><th align="center">MS Windows Command</th><th align="center">UNIX Command</th></tr></thead><tbody><tr><td align="center">create</td><td align="center">md folder</td><td align="center">mkdir folder</td></tr><tr><td align="center">delete</td><td align="center">rd folder</td><td align="center">rmdir folder</td></tr><tr><td align="center">rename</td><td align="center">rename oldname newname</td><td align="center">mv oldname newname</td></tr></tbody></table></div></div><br class="table-break"></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id373620"></a>File and Directory Access Control</h3></div></div></div><p> + <a class="indexterm" name="id373628"></a> +<a class="indexterm" name="id373637"></a> +<a class="indexterm" name="id373644"></a> + The network administrator is strongly advised to read basic UNIX training manuals and reference materials + regarding file and directory permissions maintenance. Much can be achieved with the basic UNIX permissions + without having to resort to more complex facilities like POSIX ACLs or extended attributes (EAs). + </p><p> + UNIX/Linux file and directory access permissions involves setting three primary sets of data and one control set. + A UNIX file listing looks as follows: +</p><pre class="screen"> +<code class="prompt">$ </code><strong class="userinput"><code>ls -la</code></strong> +total 632 +drwxr-xr-x 13 maryo gnomes 816 2003-05-12 22:56 . +drwxrwxr-x 37 maryo gnomes 3800 2003-05-12 22:29 .. +dr-xr-xr-x 2 maryo gnomes 48 2003-05-12 22:29 muchado02 +drwxrwxrwx 2 maryo gnomes 48 2003-05-12 22:29 muchado03 +drw-rw-rw- 2 maryo gnomes 48 2003-05-12 22:29 muchado04 +d-w--w--w- 2 maryo gnomes 48 2003-05-12 22:29 muchado05 +dr--r--r-- 2 maryo gnomes 48 2003-05-12 22:29 muchado06 +drwsrwsrwx 2 maryo gnomes 48 2003-05-12 22:29 muchado08 +---------- 1 maryo gnomes 1242 2003-05-12 22:31 mydata00.lst +--w--w--w- 1 maryo gnomes 7754 2003-05-12 22:33 mydata02.lst +-r--r--r-- 1 maryo gnomes 21017 2003-05-12 22:32 mydata04.lst +-rw-rw-rw- 1 maryo gnomes 41105 2003-05-12 22:32 mydata06.lst +<code class="prompt">$ </code> +</pre><p> + </p><p> + The columns represent (from left to right) permissions, number of hard links to file, owner, group, size + (bytes), access date, time of last modification, and file name. + </p><p> + An overview of the permissions field is shown in <a href="AccessControls.html#access1" title="Figure 16.1. Overview of UNIX permissions field.">Overview of UNIX permissions + field</a>. + </p><div class="figure"><a name="access1"></a><p class="title"><b>Figure 16.1. Overview of UNIX permissions field.</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/access1.png" width="216" alt="Overview of UNIX permissions field."></div></div></div><br class="figure-break"><p> + Any bit flag may be unset. An unset bit flag is the equivalent of "cannot" and is represented + as a “<span class="quote">-</span>” character (see <a href="AccessControls.html#access2" title="Example 16.1. Example File">???</a>) +<a class="indexterm" name="id373764"></a> +<a class="indexterm" name="id373770"></a> +<a class="indexterm" name="id373777"></a> +<a class="indexterm" name="id373784"></a> +<a class="indexterm" name="id373791"></a> +<a class="indexterm" name="id373798"></a> + </p><div class="example"><a name="access2"></a><p class="title"><b>Example 16.1. Example File</b></p><div class="example-contents"><pre class="programlisting"> +-rwxr-x--- Means: + ^^^ The owner (user) can read, write, execute + ^^^ the group can read and execute + ^^^ everyone else cannot do anything with it. +</pre></div></div><br class="example-break"><p> +<a class="indexterm" name="id373825"></a> +<a class="indexterm" name="id373832"></a> +<a class="indexterm" name="id373839"></a> +<a class="indexterm" name="id373845"></a> + Additional possibilities in the [type] field are c = character device, b = block device, p = pipe device, + s = UNIX Domain Socket. + </p><p> +<a class="indexterm" name="id373857"></a> +<a class="indexterm" name="id373863"></a> +<a class="indexterm" name="id373870"></a> +<a class="indexterm" name="id373877"></a> +<a class="indexterm" name="id373884"></a> + The letters <code class="constant">rwxXst</code> set permissions for the user, group, and others as read (r), write (w), + execute (or access for directories) (x), execute only if the file is a directory or already has execute + permission for some user (X), set user (SUID) or group ID (SGID) on execution (s), sticky (t). + </p><p> +<a class="indexterm" name="id373900"></a> +<a class="indexterm" name="id373907"></a> +<a class="indexterm" name="id373914"></a> +<a class="indexterm" name="id373920"></a> + When the sticky bit is set on a directory, files in that directory may be unlinked (deleted) or renamed only by root or their owner. + Without the sticky bit, anyone able to write to the directory can delete or rename files. The sticky bit is commonly found on + directories, such as <code class="filename">/tmp</code>, that are world-writable. + </p><p> +<a class="indexterm" name="id373939"></a> +<a class="indexterm" name="id373946"></a> +<a class="indexterm" name="id373953"></a> +<a class="indexterm" name="id373960"></a> +<a class="indexterm" name="id373969"></a> + When the set user or group ID bit (s) is set on a directory, then all files created within it will be owned by the user and/or + group whose `set user or group' bit is set. This can be helpful in setting up directories for which it is desired that + all users who are in a group should be able to write to and read from a file, particularly when it is undesirable for that file + to be exclusively owned by a user whose primary group is not the group that all such users belong to. + </p><p> + When a directory is set <code class="constant">d-wx--x---</code>, the owner can read and create (write) files in it, but because + the (r) read flags are not set, files cannot be listed (seen) in the directory by anyone. The group can read files in the + directory but cannot create new files. If files in the directory are set to be readable and writable for the group, then + group members will be able to write to (or delete) them. + </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id373993"></a>Protecting Directories and Files from Deletion</h4></div></div></div><p> +<a class="indexterm" name="id374001"></a> +<a class="indexterm" name="id374008"></a> +<a class="indexterm" name="id374015"></a> +<a class="indexterm" name="id374022"></a> + People have asked on the Samba mailing list how is it possible to protect files or directories from deletion by users. + For example, Windows NT/2K/XP provides the capacity to set access controls on a directory into which people can + write files but not delete them. It is possible to set an ACL on a Windows file that permits the file to be written to + but not deleted. Such concepts are foreign to the UNIX operating system file space. Within the UNIX file system + anyone who has the ability to create a file can write to it. Anyone who has write permission on the + directory that contains a file and has write permission for it has the capability to delete it. + </p><p> +<a class="indexterm" name="id374038"></a> +<a class="indexterm" name="id374044"></a> +<a class="indexterm" name="id374051"></a> + For the record, in the UNIX environment the ability to delete a file is controlled by the permissions on + the directory that the file is in. In other words, a user can delete a file in a directory to which that + user has write access, even if that user does not own the file. + </p><p> +<a class="indexterm" name="id374064"></a> +<a class="indexterm" name="id374070"></a> +<a class="indexterm" name="id374077"></a> +<a class="indexterm" name="id374084"></a> + Of necessity, Samba is subject to the file system semantics of the host operating system. Samba is therefore + limited in the file system capabilities that can be made available through Windows ACLs, and therefore performs + a "best fit" translation to POSIX ACLs. Some UNIX file systems do, however support, a feature known + as extended attributes. Only the Windows concept of <span class="emphasis"><em>inheritance</em></span> is implemented by Samba through + the appropriate extended attribute. + </p><p> +<a class="indexterm" name="id374102"></a> +<a class="indexterm" name="id374108"></a> +<a class="indexterm" name="id374115"></a> +<a class="indexterm" name="id374122"></a> + The specific semantics of the extended attributes are not consistent across UNIX and UNIX-like systems such as Linux. + For example, it is possible on some implementations of the extended attributes to set a flag that prevents the directory + or file from being deleted. The extended attribute that may achieve this is called the <code class="constant">immutible</code> bit. + Unfortunately, the implementation of the immutible flag is NOT consistent with published documentation. For example, the + man page for the <code class="literal">chattr</code> on SUSE Linux 9.2 says: +</p><pre class="screen"> +A file with the i attribute cannot be modified: it cannot be deleted +or renamed, no link can be created to this file and no data can be +written to the file. Only the superuser or a process possessing the +CAP_LINUX_IMMUTABLE capability can set or clear this attribute. +</pre><p> + A simple test can be done to check if the immutible flag is supported on files in the file system of the Samba host + server. + </p><div class="procedure"><a name="id374153"></a><p class="title"><b>Procedure 16.1. Test for File Immutibility Support</b></p><ol type="1"><li><p> + Create a file called <code class="filename">filename</code>. + </p></li><li><p> + Login as the <code class="constant">root</code> user, then set the immutibile flag on a test file as follows: +</p><pre class="screen"> +<code class="prompt">root# </code> chatter +i `filename' +</pre><p> + </p></li><li><p> + Login as the user who owns the file (not root) and attempt to remove the file as follows: +</p><pre class="screen"> +mystic:/home/hannibal > rm filename +</pre><p> + It will not be possible to delete the file if the immutible flag is correctly honored. + </p></li></ol></div><p> + On operating systems and file system types that support the immutible bit, it is possible to create directories + that cannot be deleted. Check the man page on your particular host system to determine whether or not + immutable directories are writable. If they are not, then the entire directory and its contents will effectively + be protected from writing (file creation also) and deletion. + </p></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id374219"></a>Share Definition Access Controls</h2></div></div></div><p> + <a class="indexterm" name="id374227"></a> + The following parameters in the <code class="filename">smb.conf</code> file sections define a share control or affect access controls. + Before using any of the following options, please refer to the man page for <code class="filename">smb.conf</code>. + </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id374250"></a>User- and Group-Based Controls</h3></div></div></div><p> + User- and group-based controls can prove quite useful. In some situations it is distinctly desirable to + force all file system operations as if a single user were doing so. The use of the + <a class="indexterm" name="id374260"></a>force user and <a class="indexterm" name="id374267"></a>force group behavior will achieve this. + In other situations it may be necessary to use a paranoia level of control to ensure that only particular + authorized persons will be able to access a share or its contents. Here the use of the + <a class="indexterm" name="id374276"></a>valid users or the <a class="indexterm" name="id374283"></a>invalid users parameter may be useful. + </p><p> + As always, it is highly advisable to use the easiest to maintain and the least ambiguous method for + controlling access. Remember, when you leave the scene, someone else will need to provide assistance, and + if he or she finds too great a mess or does not understand what you have done, there is risk of + Samba being removed and an alternative solution being adopted. + </p><p> + <a href="AccessControls.html#ugbc" title="Table 16.2. User- and Group-Based Controls">User and Group Based Controls</a> enumerates these controls. + </p><div class="table"><a name="ugbc"></a><p class="title"><b>Table 16.2. User- and Group-Based Controls</b></p><div class="table-contents"><table summary="User- and Group-Based Controls" border="1"><colgroup><col align="left"><col align="justify"></colgroup><thead><tr><th align="center">Control Parameter</th><th align="center">Description, Action, Notes</th></tr></thead><tbody><tr><td align="left"><a class="indexterm" name="id374360"></a>admin users</td><td align="justify"><p> + List of users who will be granted administrative privileges on the share. + They will do all file operations as the superuser (root). + Users in this list will be able to do anything they like on the share, + irrespective of file permissions. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374378"></a>force group</td><td align="justify"><p> + Specifies a UNIX group name that will be assigned as the default primary group + for all users connecting to this service. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374396"></a>force user</td><td align="justify"><p> + Specifies a UNIX username that will be assigned as the default user for all users connecting to this service. + This is useful for sharing files. Incorrect use can cause security problems. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374415"></a>guest ok</td><td align="justify"><p> + If this parameter is set for a service, then no password is required to connect to the service. Privileges will be + those of the guest account. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374433"></a>invalid users</td><td align="justify"><p> + List of users that should not be allowed to login to this service. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374450"></a>only user</td><td align="justify"><p> + Controls whether connections with usernames not in the user list will be allowed. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374468"></a>read list</td><td align="justify"><p> + List of users that are given read-only access to a service. Users in this list + will not be given write access, no matter what the read-only option is set to. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374486"></a>username</td><td align="justify"><p> + Refer to the <code class="filename">smb.conf</code> man page for more information; this is a complex and potentially misused parameter. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374510"></a>valid users</td><td align="justify"><p> + List of users that should be allowed to login to this service. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374527"></a>write list</td><td align="justify"><p> + List of users that are given read-write access to a service. + </p></td></tr></tbody></table></div></div><br class="table-break"></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id374546"></a>File and Directory Permissions-Based Controls</h3></div></div></div><p> + Directory permission-based controls, if misused, can result in considerable difficulty in diagnosing the causes of + misconfiguration. Use them sparingly and carefully. By gradually introducing each, one at a time, undesirable side + effects may be detected. In the event of a problem, always comment all of them out and then gradually reintroduce + them in a controlled way. + </p><p> + Refer to <a href="AccessControls.html#fdpbc" title="Table 16.3. File and Directory Permission-Based Controls">File and Directory Permission Based Controls</a> for information + regarding the parameters that may be used to set file and directory permission-based access controls. + </p><div class="table"><a name="fdpbc"></a><p class="title"><b>Table 16.3. File and Directory Permission-Based Controls</b></p><div class="table-contents"><table summary="File and Directory Permission-Based Controls" border="1"><colgroup><col align="left"><col align="justify"></colgroup><thead><tr><th align="center">Control Parameter</th><th align="center">Description, Action, Notes</th></tr></thead><tbody><tr><td align="left"><a class="indexterm" name="id374619"></a>create mask</td><td align="justify"><p> + Refer to the <code class="filename">smb.conf</code> man page. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374642"></a>directory mask</td><td align="justify"><p> + The octal modes used when converting DOS modes to UNIX modes when creating UNIX directories. + See also directory security mask. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374659"></a>dos filemode</td><td align="justify"><p> + Enabling this parameter allows a user who has write access to the file to modify the permissions on it. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374677"></a>force create mode</td><td align="justify"><p> + This parameter specifies a set of UNIX-mode bit permissions that will always be set on a file created by Samba. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374694"></a>force directory mode</td><td align="justify"><p> + This parameter specifies a set of UNIX-mode bit permissions that will always be set on a directory created by Samba. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374712"></a>force directory security mode</td><td align="justify"><p> + Controls UNIX permission bits modified when a Windows NT client is manipulating UNIX permissions on a directory. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374730"></a>force security mode</td><td align="justify"><p> + Controls UNIX permission bits modified when a Windows NT client manipulates UNIX permissions. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374748"></a>hide unreadable</td><td align="justify"><p> + Prevents clients from seeing the existence of files that cannot be read. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374765"></a>hide unwriteable files</td><td align="justify"><p> + Prevents clients from seeing the existence of files that cannot be written to. Unwritable directories are shown as usual. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374783"></a>nt acl support</td><td align="justify"><p> + This parameter controls whether smbd will attempt to map UNIX permissions into Windows NT ACLs. + </p></td></tr><tr><td align="left"><a class="indexterm" name="id374801"></a>security mask</td><td align="justify"><p> + Controls UNIX permission bits modified when a Windows NT client is manipulating the UNIX permissions on a file. + </p></td></tr></tbody></table></div></div><br class="table-break"></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id374820"></a>Miscellaneous Controls</h3></div></div></div><p> + The parameter documented in <a href="AccessControls.html#mcoc" title="Table 16.4. Other Controls">Other Controls</a> are often used by administrators + in ways that create inadvertent barriers to file access. Such are the consequences of not understanding the + full implications of <code class="filename">smb.conf</code> file settings. + </p><div class="table"><a name="mcoc"></a><p class="title"><b>Table 16.4. Other Controls</b></p><div class="table-contents"><table summary="Other Controls" border="1"><colgroup><col align="justify"><col align="justify"></colgroup><thead><tr><th align="center">Control Parameter</th><th align="center">Description, Action, Notes</th></tr></thead><tbody><tr><td align="justify"> + <a class="indexterm" name="id374896"></a>case sensitive, + <a class="indexterm" name="id374903"></a>default case, + <a class="indexterm" name="id374910"></a>short preserve case + </td><td align="justify"><p> + This means that all file name lookup will be done in a case-sensitive manner. + Files will be created with the precise file name Samba received from the MS Windows client. + </p></td></tr><tr><td align="justify"><a class="indexterm" name="id374928"></a>csc policy</td><td align="justify"><p> + Client-side caching policy parallels MS Windows client-side file caching capabilities. + </p></td></tr><tr><td align="justify"><a class="indexterm" name="id374946"></a>dont descend</td><td align="justify"><p> + Allows specifying a comma-delimited list of directories that the server should always show as empty. + </p></td></tr><tr><td align="justify"><a class="indexterm" name="id374964"></a>dos filetime resolution</td><td align="justify"><p> + This option is mainly used as a compatibility option for Visual C++ when used against Samba shares. + </p></td></tr><tr><td align="justify"><a class="indexterm" name="id374981"></a>dos filetimes</td><td align="justify"><p> + DOS and Windows allow users to change file timestamps if they can write to the file. POSIX semantics prevent this. + This option allows DOS and Windows behavior. + </p></td></tr><tr><td align="justify"><a class="indexterm" name="id375000"></a>fake oplocks</td><td align="justify"><p> + Oplocks are the way that SMB clients get permission from a server to locally cache file operations. If a server grants an + oplock, the client is free to assume that it is the only one accessing the file, and it will aggressively cache file data. + </p></td></tr><tr><td align="justify"> + <a class="indexterm" name="id375020"></a>hide dot files, + <a class="indexterm" name="id375027"></a>hide files, + <a class="indexterm" name="id375034"></a>veto files + </td><td align="justify"><p> + Note: MS Windows Explorer allows override of files marked as hidden so they will still be visible. + </p></td></tr><tr><td align="justify"><a class="indexterm" name="id375051"></a>read only</td><td align="justify"><p> + If this parameter is yes, then users of a service may not create or modify files in the service's directory. + </p></td></tr><tr><td align="justify"><a class="indexterm" name="id375069"></a>veto files</td><td align="justify"><p> + List of files and directories that are neither visible nor accessible. + </p></td></tr></tbody></table></div></div><br class="table-break"></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id375089"></a>Access Controls on Shares</h2></div></div></div><p> +<a class="indexterm" name="id375097"></a> +<a class="indexterm" name="id375104"></a> +<a class="indexterm" name="id375110"></a> +<a class="indexterm" name="id375117"></a> + <a class="indexterm" name="id375124"></a> + This section deals with how to configure Samba per-share access control restrictions. + By default, Samba sets no restrictions on the share itself. Restrictions on the share itself + can be set on MS Windows NT4/200x/XP shares. This can be an effective way to limit who can + connect to a share. In the absence of specific restrictions, the default setting is to allow + the global user <code class="constant">Everyone - Full Control</code> (full control, change and read). + </p><p> +<a class="indexterm" name="id375144"></a> +<a class="indexterm" name="id375150"></a> +<a class="indexterm" name="id375157"></a> + At this time Samba does not provide a tool for configuring access control settings on the share + itself the only way to create those settings is to use either the NT4 Server Manager or the Windows 200x + Microsoft Management Console (MMC) for Computer Management. There are currently no plans to provide + this capability in the Samba command-line tool set. + </p><p> +<a class="indexterm" name="id375170"></a> +<a class="indexterm" name="id375177"></a> +<a class="indexterm" name="id375184"></a> +<a class="indexterm" name="id375190"></a> + Samba stores the per-share access control settings in a file called <code class="filename">share_info.tdb</code>. + The location of this file on your system will depend on how Samba was compiled. The default location + for Samba's tdb files is under <code class="filename">/usr/local/samba/var</code>. If the <code class="filename">tdbdump</code> + utility has been compiled and installed on your system, then you can examine the contents of this file + by executing <code class="literal">tdbdump share_info.tdb</code> in the directory containing the tdb files. + </p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375225"></a>Share Permissions Management</h3></div></div></div><p> + The best tool for share permissions management is platform-dependent. Choose the best tool for your environment. + </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id375235"></a>Windows NT4 Workstation/Server</h4></div></div></div><p> +<a class="indexterm" name="id375243"></a> +<a class="indexterm" name="id375250"></a> +<a class="indexterm" name="id375257"></a> +<a class="indexterm" name="id375263"></a> + The tool you need to manage share permissions on a Samba server from a Windows NT4 Workstation or Server + is the NT Server Manager. Server Manager is shipped with Windows NT4 Server products but not with Windows + NT4 Workstation. You can obtain the NT Server Manager for MS Windows NT4 Workstation from the Microsoft + web site <a href="http://support.microsoft.com/default.aspx?scid=kb;en-us;173673" target="_top">support</a> section. + </p><div class="procedure"><a name="id375281"></a><p class="title"><b>Procedure 16.2. Instructions</b></p><ol type="1"><li><p> + Launch the <span class="application">NT4 Server Manager</span> and click on the Samba server you want to + administer. From the menu select <span class="guimenu">Computer</span>, then click on + <span class="guimenuitem">Shared Directories</span>. + </p></li><li><p> + Click on the share that you wish to manage and click the <span class="guilabel">Properties</span> tab, then click + the <span class="guilabel">Permissions</span> tab. Now you can add or change access control settings as you wish. + </p></li></ol></div></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id375334"></a>Windows 200x/XP</h4></div></div></div><p> +<a class="indexterm" name="id375341"></a> +<a class="indexterm" name="id375348"></a> +<a class="indexterm" name="id375355"></a> +<a class="indexterm" name="id375362"></a> + On <span class="application">MS Windows NT4/200x/XP</span> system, ACLs on the share itself are set using native + tools, usually from File Manager. For example, in Windows 200x, right-click on the shared folder, + then select <span class="guimenuitem">Sharing</span>, then click on <span class="guilabel">Permissions</span>. The default + Windows NT4/200x permission allows "Everyone" full control on the share. + </p><p> +<a class="indexterm" name="id375392"></a> +<a class="indexterm" name="id375399"></a> +<a class="indexterm" name="id375405"></a> + MS Windows 200x and later versions come with a tool called the <span class="application">Computer Management</span> + snap-in for the MMC. This tool is located by clicking on <span class="guimenu">Control Panel -> + Administrative Tools -> Computer Management</span>. + </p><div class="procedure"><a name="id375427"></a><p class="title"><b>Procedure 16.3. Instructions</b></p><ol type="1"><li><p> + After launching the MMC with the Computer Management snap-in, click the menu item <span class="guimenuitem">Action</span> + and select <span class="guilabel">Connect to another computer</span>. If you are not logged onto a domain you will be prompted + to enter a domain login user identifier and a password. This will authenticate you to the domain. + If you are already logged in with administrative privilege, this step is not offered. + </p></li><li><p> + If the Samba server is not shown in the <span class="guilabel">Select Computer</span> box, type in the name of the target + Samba server in the field <span class="guilabel">Name:</span>. Now click the on <span class="guibutton">[+]</span> next to + <span class="guilabel">System Tools</span>, then on the <span class="guibutton">[+]</span> next to + <span class="guilabel">Shared Folders</span> in the left panel. + </p></li><li><p> +<a class="indexterm" name="id375502"></a> + In the right panel, double-click on the share on which you wish to set access control permissions. + Then click the tab <span class="guilabel">Share Permissions</span>. It is now possible to add access control entities + to the shared folder. Remember to set what type of access (full control, change, read) you + wish to assign for each entry. + </p></li></ol></div><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p> + Be careful. If you take away all permissions from the <code class="constant">Everyone</code> user without removing + this user, effectively no user will be able to access the share. This is a result of what is known as + ACL precedence. Everyone with <span class="emphasis"><em>no access</em></span> means that <code class="constant">MaryK</code> who is + part of the group <code class="constant">Everyone</code> will have no access even if she is given explicit full + control access. + </p></div></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id375547"></a>MS Windows Access Control Lists and UNIX Interoperability</h2></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375553"></a>Managing UNIX Permissions Using NT Security Dialogs</h3></div></div></div><p> + <a class="indexterm" name="id375561"></a> + Windows NT clients can use their native security settings dialog box to view and modify the + underlying UNIX permissions. + </p><p> + This ability is careful not to compromise the security of the UNIX host on which Samba is running and + still obeys all the file permission rules that a Samba administrator can set. + </p><p> + Samba does not attempt to go beyond POSIX ACLs, so the various finer-grained access control + options provided in Windows are actually ignored. + </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> + All access to UNIX/Linux system files via Samba is controlled by the operating system file access controls. + When trying to figure out file access problems, it is vitally important to find the identity of the Windows + user as it is presented by Samba at the point of file access. This can best be determined from the + Samba log files. + </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375592"></a>Viewing File Security on a Samba Share</h3></div></div></div><p> + From an NT4/2000/XP client, right-click on any file or directory in a Samba-mounted drive letter + or UNC path. When the menu pops up, click on the <span class="guilabel">Properties</span> entry at the bottom + of the menu. This brings up the file <code class="constant">Properties</code> dialog box. Click on the + <span class="guilabel">Security</span> tab and you will see three buttons: <span class="guibutton">Permissions</span>, + <span class="guibutton">Auditing</span>, and <span class="guibutton">Ownership</span>. The <span class="guibutton">Auditing</span> + button will cause either an error message <span class="errorname">"A requested privilege is not held by the client"</span> + to appear if the user is not the NT administrator, or a dialog intended to allow an administrator + to add auditing requirements to a file if the user is logged on as the NT administrator. This dialog is + nonfunctional with a Samba share at this time, because the only useful button, the <span class="guibutton">Add</span> + button, will not currently allow a list of users to be seen. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375657"></a>Viewing File Ownership</h3></div></div></div><p> + Clicking on the <span class="guibutton">Ownership</span> button brings up a dialog box telling you who owns + the given file. The owner name will be displayed like this: + </p><pre class="screen"> + <code class="constant">SERVER\user (Long name)</code> + </pre><p> + <em class="replaceable"><code>SERVER</code></em> is the NetBIOS name of the Samba server, <em class="replaceable"><code>user</code></em> + is the username of the UNIX user who owns the file, and <em class="replaceable"><code>(Long name)</code></em> is the + descriptive string identifying the user (normally found in the GECOS field of the UNIX password database). + Click on the <span class="guibutton">Close</span> button to remove this dialog. + </p><p> + If the parameter <a class="indexterm" name="id375703"></a>nt acl support is set to <code class="constant">false</code>, + the file owner will be shown as the NT user <span class="emphasis"><em>Everyone</em></span>. + </p><p> +<a class="indexterm" name="id375721"></a> + The <span class="guibutton">Take Ownership</span> button will not allow you to change the ownership of this file to + yourself (clicking it will display a dialog box complaining that the user as whom you are currently logged onto + the NT client cannot be found). The reason for this is that changing the ownership of a file is a privileged + operation in UNIX, available only to the <span class="emphasis"><em>root</em></span> user. Because clicking on this button causes + NT to attempt to change the ownership of a file to the current user logged into the NT client, this will + not work with Samba at this time. + </p><p> +<a class="indexterm" name="id375745"></a> +<a class="indexterm" name="id375752"></a> +<a class="indexterm" name="id375759"></a> + There is an NT <code class="literal">chown</code> command that will work with Samba and allow a user with administrator + privilege connected to a Samba server as root to change the ownership of files on both a local NTFS file system + or remote mounted NTFS or Samba drive. This is available as part of the <span class="application">Seclib</span> NT + security library written by Jeremy Allison of the Samba Team and is downloadable from the main Samba FTP site. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375783"></a>Viewing File or Directory Permissions</h3></div></div></div><p> + The third button is the <span class="guibutton">Permissions</span> button. Clicking on it brings up a dialog box + that shows both the permissions and the UNIX owner of the file or directory. The owner is displayed like this: + </p><p><code class="literal"><em class="replaceable"><code>SERVER</code></em>\ + <em class="replaceable"><code>user</code></em> + <em class="replaceable"><code>(Long name)</code></em></code></p><p><em class="replaceable"><code>SERVER</code></em> is the NetBIOS name of the Samba server, + <em class="replaceable"><code>user</code></em> is the username of the UNIX user who owns the file, and + <em class="replaceable"><code>(Long name)</code></em> is the descriptive string identifying the user (normally found in the + GECOS field of the UNIX password database).</p><p> + If the parameter <a class="indexterm" name="id375832"></a>nt acl support is set to <code class="constant">false</code>, + the file owner will be shown as the NT user <code class="constant">Everyone</code>, and the permissions will be + shown as NT <span class="emphasis"><em>Full Control</em></span>. + </p><p> + The permissions field is displayed differently for files and directories. Both are discussed next. + </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id375856"></a>File Permissions</h4></div></div></div><p> + The standard UNIX user/group/world triplet and the corresponding <code class="constant">read, write, + execute</code> permissions triplets are mapped by Samba into a three-element NT ACL with the + “<span class="quote">r</span>”, “<span class="quote">w</span>”, and “<span class="quote">x</span>” bits mapped into the corresponding NT + permissions. The UNIX world permissions are mapped into the global NT group <code class="constant">Everyone</code>, followed + by the list of permissions allowed for the UNIX world. The UNIX owner and group permissions are displayed as an NT + <span class="guiicon">user</span> icon and an NT <span class="guiicon">local group</span> icon, respectively, followed by the list + of permissions allowed for the UNIX user and group. + </p><p> + Because many UNIX permission sets do not map into common NT names such as <code class="constant">read</code>, + <code class="constant">change</code>, or <code class="constant">full control</code>, usually the permissions will be prefixed + by the words <code class="constant">Special Access</code> in the NT display list. + </p><p> + But what happens if the file has no permissions allowed for a particular UNIX user group or world component? + In order to allow <span class="emphasis"><em>no permissions</em></span> to be seen and modified, Samba then overloads the NT + <code class="constant">Take Ownership</code> ACL attribute (which has no meaning in UNIX) and reports a component with + no permissions as having the NT <code class="literal">O</code> bit set. This was chosen, of course, to make it look + like a zero, meaning zero permissions. More details on the decision behind this action are given below. + </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id375939"></a>Directory Permissions</h4></div></div></div><p> + Directories on an NT NTFS file system have two different sets of permissions. The first set is the ACL set on the + directory itself, which is usually displayed in the first set of parentheses in the normal <code class="constant">RW</code> + NT style. This first set of permissions is created by Samba in exactly the same way as normal file permissions are, described + above, and is displayed in the same way. + </p><p> + The second set of directory permissions has no real meaning in the UNIX permissions world and represents the <code class="constant"> + inherited</code> permissions that any file created within this directory would inherit. + </p><p> + Samba synthesizes these inherited permissions for NT by returning as an NT ACL the UNIX permission mode that a new file + created by Samba on this share would receive. + </p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id375970"></a>Modifying File or Directory Permissions</h3></div></div></div><p> + Modifying file and directory permissions is as simple as changing the displayed permissions in the dialog box + and clicking on <span class="guibutton">OK</span>. However, there are limitations that a user needs to be aware of, + and also interactions with the standard Samba permission masks and mapping of DOS attributes that also need to + be taken into account. + </p><p> + If the parameter <a class="indexterm" name="id375990"></a>nt acl support is set to <code class="constant">false</code>, any attempt to + set security permissions will fail with an <span class="errorname">"Access Denied" </span> message. + </p><p> + The first thing to note is that the <span class="guibutton">Add</span> button will not return a list of users in Samba + (it will give an error message saying <span class="errorname">"The remote procedure call failed and did not + execute"</span>). This means that you can only manipulate the current user/group/world permissions listed + in the dialog box. This actually works quite well because these are the only permissions that UNIX actually + has. + </p><p> + If a permission triplet (either user, group, or world) is removed from the list of permissions in the NT + dialog box, then when the <span class="guibutton">OK</span> button is pressed, it will be applied as <span class="emphasis"><em>no + permissions</em></span> on the UNIX side. If you view the permissions again, the <span class="emphasis"><em>no + permissions</em></span> entry will appear as the NT <code class="literal">O</code> flag, as described above. This allows + you to add permissions back to a file or directory once you have removed them from a triplet component. + </p><p> + Because UNIX supports only the “<span class="quote">r</span>”, “<span class="quote">w</span>”, and “<span class="quote">x</span>” bits of an NT ACL, if + other NT security attributes such as <code class="constant">Delete Access</code> are selected, they will be ignored + when applied on the Samba server. + </p><p> + When setting permissions on a directory, the second set of permissions (in the second set of parentheses) is + by default applied to all files within that directory. If this is not what you want, you must uncheck the + <span class="guilabel">Replace permissions on existing files</span> checkbox in the NT dialog before clicking on + <span class="guibutton">OK</span>. + </p><p> + If you wish to remove all permissions from a user/group/world component, you may either highlight the + component and click on the <span class="guibutton">Remove</span> button or set the component to only have the special + <code class="constant">Take Ownership</code> permission (displayed as <code class="literal">O</code>) highlighted. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id376107"></a>Interaction with the Standard Samba “<span class="quote">create mask</span>” Parameters</h3></div></div></div><p>There are four parameters that control interaction with the standard Samba <em class="parameter"><code>create mask</code></em> parameters: + + + </p><div class="itemizedlist"><ul type="disc"><li><p><a class="indexterm" name="id376129"></a>security mask</p></li><li><p><a class="indexterm" name="id376139"></a>force security mode</p></li><li><p><a class="indexterm" name="id376149"></a>directory security mask</p></li><li><p><a class="indexterm" name="id376160"></a>force directory security mode</p></li></ul></div><p> + + </p><p> + When a user clicks on <span class="guibutton">OK</span> to apply the + permissions, Samba maps the given permissions into a user/group/world + r/w/x triplet set, and then checks the changed permissions for a + file against the bits set in the + <a class="indexterm" name="id376180"></a>security mask parameter. Any bits that + were changed that are not set to <span class="emphasis"><em>1</em></span> in this parameter are left alone + in the file permissions.</p><p> + Essentially, zero bits in the <a class="indexterm" name="id376195"></a>security mask + may be treated as a set of bits the user is <span class="emphasis"><em>not</em></span> + allowed to change, and one bits are those the user is allowed to change. + </p><p> + If not explicitly set, this parameter defaults to the same value as + the <a class="indexterm" name="id376210"></a>create mask parameter. To allow a user to modify all the + user/group/world permissions on a file, set this parameter to 0777. + </p><p> + Next Samba checks the changed permissions for a file against the bits set in the + <a class="indexterm" name="id376222"></a>force security mode parameter. Any bits + that were changed that correspond to bits set to <span class="emphasis"><em>1</em></span> in this parameter + are forced to be set.</p><p> + Essentially, bits set in the <em class="parameter"><code>force security mode</code></em> parameter + may be treated as a set of bits that, when modifying security on a file, the user + has always set to be <span class="emphasis"><em>on</em></span>.</p><p> + If not explicitly set, this parameter defaults to the same value + as the <a class="indexterm" name="id376251"></a>force create mode parameter. + To allow a user to modify all the user/group/world permissions on a file + with no restrictions, set this parameter to 000. The + <a class="indexterm" name="id376260"></a>security mask and <em class="parameter"><code>force + security mode</code></em> parameters are applied to the change + request in that order.</p><p> + For a directory, Samba performs the same operations as + described above for a file except it uses the parameter <em class="parameter"><code> + directory security mask</code></em> instead of <em class="parameter"><code>security + mask</code></em>, and <em class="parameter"><code>force directory security mode + </code></em> parameter instead of <em class="parameter"><code>force security mode + </code></em>.</p><p> + The <a class="indexterm" name="id376305"></a>directory security mask parameter + by default is set to the same value as the <em class="parameter"><code>directory mask + </code></em> parameter and the <em class="parameter"><code>force directory security + mode</code></em> parameter by default is set to the same value as + the <a class="indexterm" name="id376325"></a>force directory mode parameter. + In this way Samba enforces the permission restrictions that + an administrator can set on a Samba share, while still allowing users + to modify the permission bits within that restriction.</p><p> + If you want to set up a share that allows users full control + in modifying the permission bits on their files and directories and + does not force any particular bits to be set <span class="emphasis"><em>on</em></span>, + then set the following parameters in the <code class="filename">smb.conf</code> file in that + share-specific section: + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id376358"></a><em class="parameter"><code>security mask = 0777</code></em></td></tr><tr><td><a class="indexterm" name="id376370"></a><em class="parameter"><code>force security mode = 0</code></em></td></tr><tr><td><a class="indexterm" name="id376383"></a><em class="parameter"><code>directory security mask = 0777</code></em></td></tr><tr><td><a class="indexterm" name="id376395"></a><em class="parameter"><code>force directory security mode = 0</code></em></td></tr></table></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id376409"></a>Interaction with the Standard Samba File Attribute Mapping</h3></div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> + Samba maps some of the DOS attribute bits (such as “<span class="quote">read-only</span>”) + into the UNIX permissions of a file. This means there can + be a conflict between the permission bits set via the security + dialog and the permission bits set by the file attribute mapping. + </p></div><p> + If a file has no UNIX read access for the owner, it will show up + as “<span class="quote">read-only</span>” in the standard file attributes tabbed dialog. + Unfortunately, this dialog is the same one that contains the security information + in another tab. + </p><p> + What this can mean is that if the owner changes the permissions + to allow himself or herself read access using the security dialog, clicks on + <span class="guibutton">OK</span> to get back to the standard attributes tab + dialog, and clicks on <span class="guibutton">OK</span> on that dialog, then + NT will set the file permissions back to read-only (as that is what + the attributes still say in the dialog). This means that after setting + permissions and clicking on <span class="guibutton">OK</span> to get back to the + attributes dialog, you should always press <span class="guibutton">Cancel</span> + rather than <span class="guibutton">OK</span> to ensure that your changes + are not overridden. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id376473"></a>Windows NT/200X ACLs and POSIX ACLs Limitations</h3></div></div></div><p> + Windows administrators are familiar with simple ACL controls, and they typically + consider that UNIX user/group/other (ugo) permissions are inadequate and not + sufficiently fine-grained. + </p><p> + Competing SMB implementations differ in how they handle Windows ACLs. Samba handles + Windows ACLs from the perspective of UNIX file system administration and thus adopts + the limitations of POSIX ACLs. Therefore, where POSIX ACLs lack a capability of the + Windows NT/200X ACLs, the POSIX semantics and limitations are imposed on the Windows + administrator. + </p><p> + POSIX ACLs present an interesting challenge to the UNIX administrator and therefore + force a compromise to be applied to Windows ACLs administration. POSIX ACLs are not + covered by an official standard; rather, the latest standard is a draft standard + 1003.1e revision 17. This is the POSIX document on which the Samba implementation has + been implemented. + </p><p> + UNIX vendors differ in the manner in which POSIX ACLs are implemented. There are a + number of Linux file systems that support ACLs. Samba has to provide a way to make + transparent all the differences between the various implementations of POSIX ACLs. + The pressure for ACLs support in Samba has noticeably increased the pressure to + standardize ACLs support in the UNIX world. + </p><p> + Samba has to deal with the complicated matter of handling the challenge of the Windows + ACL that implements <span class="emphasis"><em>inheritance</em></span>, a concept not anticipated by POSIX + ACLs as implemented in UNIX file systems. Samba provides support for <span class="emphasis"><em>masks</em></span> + that permit normal ugo and ACLs functionality to be overrided. This further complicates + the way in which Windows ACLs must be implemented. + </p><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id376517"></a>UNIX POSIX ACL Overview</h4></div></div></div><p> + In examining POSIX ACLs we must consider the manner in which they operate for + both files and directories. File ACLs have the following significance: +</p><pre class="screen"> +# file: testfile <- the file name +# owner: jeremy <-- the file owner +# group: users <-- the POSIX group owner +user::rwx <-- perms for the file owner (user) +user:tpot:r-x <-- perms for the additional user `tpot' +group::r-- <-- perms for the file group owner (group) +group:engrs:r-- <-- perms for the additonal group `engineers' +mask:rwx <-- the mask that is `ANDed' with groups +other::--- <-- perms applied to everyone else (other) +</pre><p> + Directory ACLs have the following signficance: +</p><pre class="screen"> +# file: testdir <-- the directory name +# owner: jeremy <-- the directory owner +# group: jeremy <-- the POSIX group owner +user::rwx <-- directory perms for owner (user) +group::rwx <-- directory perms for owning group (group) +mask::rwx <-- the mask that is `ANDed' with group perms +other:r-x <-- perms applied to everyone else (other) +default:user::rwx <-- inherited owner perms +default:user:tpot:rwx <-- inherited extra perms for user `tpot' +default:group::r-x <-- inherited group perms +default:mask:rwx <-- inherited default mask +default:other:--- <-- inherited permissions for everyone (other) +</pre><p> + </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id376558"></a>Mapping of Windows File ACLs to UNIX POSIX ACLs</h4></div></div></div><p> + Microsoft Windows NT4/200X ACLs must of necessity be mapped to POSIX ACLs. + The mappings for file permissions are shown in <a href="AccessControls.html#fdsacls" title="Table 16.5. How Windows File ACLs Map to UNIX POSIX File ACLs">How + Windows File ACLs Map to UNIX POSIX File ACLs</a>. + The # character means this flag is set only when the Windows administrator + sets the <code class="constant">Full Control</code> flag on the file. + </p><div class="table"><a name="fdsacls"></a><p class="title"><b>Table 16.5. How Windows File ACLs Map to UNIX POSIX File ACLs</b></p><div class="table-contents"><table summary="How Windows File ACLs Map to UNIX POSIX File ACLs" border="1"><colgroup><col align="left"><col align="center"></colgroup><thead><tr><th align="left">Windows ACE</th><th align="center">File Attribute Flag</th></tr></thead><tbody><tr><td align="left"><p>Full Control</p></td><td align="center"><p>#</p></td></tr><tr><td align="left"><p>Traverse Folder/Execute File</p></td><td align="center"><p>x</p></td></tr><tr><td align="left"><p>List Folder/Read Data</p></td><td align="center"><p>r</p></td></tr><tr><td align="left"><p>Read Attributes</p></td><td align="center"><p>r</p></td></tr><tr><td align="left"><p>Read Extended Attribures</p></td><td align="center"><p>r</p></td></tr><tr><td align="left"><p>Create Files/Write Data</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Create Folders/Append Data</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Write Attributes</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Write Extended Attributes</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Delete Subfolders and Files</p></td><td align="center"><p>w</p></td></tr><tr><td align="left"><p>Delete</p></td><td align="center"><p>#</p></td></tr><tr><td align="left"><p>Read Permissions</p></td><td align="center"><p>all</p></td></tr><tr><td align="left"><p>Change Permissions</p></td><td align="center"><p>#</p></td></tr><tr><td align="left"><p>Take Ownership</p></td><td align="center"><p>#</p></td></tr></tbody></table></div></div><br class="table-break"><p> + As can be seen from the mapping table, there is no one-to-one mapping capability, and therefore + Samba must make a logical mapping that will permit Windows to operate more-or-less the way + that is intended by the administrator. + </p><p> + In general the mapping of UNIX POSIX user/group/other permissions will be mapped to + Windows ACLs. This has precedence over the creation of POSIX ACLs. POSIX ACLs are necessary + to establish access controls for users and groups other than the user and group that + own the file or directory. + </p><p> + The UNIX administrator can set any directory permission from within the UNIX environment. + The Windows administrator is more restricted in that it is not possible from within + Windows Explorer to remove read permission for the file owner. + </p></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="id376814"></a>Mapping of Windows Directory ACLs to UNIX POSIX ACLs</h4></div></div></div><p> + Interesting things happen in the mapping of UNIX POSIX directory permissions and + UNIX POSIX ACLs to Windows ACEs (Access Control Entries, the discrete components of + an ACL) are mapped to Windows directory ACLs. + </p><p> + Directory permissions function in much the same way as shown for file permissions, but + there are some notable exceptions and a few peculiarities that the astute administrator + will want to take into account in the setting up of directory permissions. + </p></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id376834"></a>Common Errors</h2></div></div></div><p> +File, directory, and share access problems are common topics on the mailing list. The following +are examples recently taken from the mailing list. +</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id376844"></a>Users Cannot Write to a Public Share</h3></div></div></div><p> + The following complaint has frequently been voiced on the Samba mailing list: + “<span class="quote"> + We are facing some troubles with file/directory permissions. I can log on the domain as admin user (root), + and there's a public share on which everyone needs to have permission to create/modify files, but only + root can change the file, no one else can. We need to constantly go to the server to + <strong class="userinput"><code>chgrp -R users *</code></strong> and <strong class="userinput"><code>chown -R nobody *</code></strong> to allow + other users to change the file. + </span>” + </p><p> + Here is one way the problem can be solved: + </p><div class="procedure"><ol type="1"><li><p> + Go to the top of the directory that is shared. + </p></li><li><p> + Set the ownership to whatever public user and group you want +</p><pre class="screen"> +<code class="prompt">$ </code>find `directory_name' -type d -exec chown user:group {}\; +<code class="prompt">$ </code>find `directory_name' -type d -exec chmod 2775 {}\; +<code class="prompt">$ </code>find `directory_name' -type f -exec chmod 0775 {}\; +<code class="prompt">$ </code>find `directory_name' -type f -exec chown user:group {}\; +</pre><p> + </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p> + The above will set the <code class="constant">SGID bit</code> on all directories. Read your + UNIX/Linux man page on what that does. This ensures that all files and directories + that are created in the directory tree will be owned by the current user and will + be owned by the group that owns the directory in which it is created. + </p></div></li><li><p> + Directory is <em class="replaceable"><code>/foodbar</code></em>: +</p><pre class="screen"> +<code class="prompt">$ </code><strong class="userinput"><code>chown jack:engr /foodbar</code></strong> +</pre><p> + </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>This is the same as doing:</p><pre class="screen"> +<code class="prompt">$ </code><strong class="userinput"><code>chown jack /foodbar</code></strong> +<code class="prompt">$ </code><strong class="userinput"><code>chgrp engr /foodbar</code></strong> +</pre></div></li><li><p>Now type: + +</p><pre class="screen"> +<code class="prompt">$ </code><strong class="userinput"><code>chmod 2775 /foodbar</code></strong> +<code class="prompt">$ </code><strong class="userinput"><code>ls -al /foodbar/..</code></strong> +</pre><p> + </p><p>You should see: +</p><pre class="screen"> +drwxrwsr-x 2 jack engr 48 2003-02-04 09:55 foodbar +</pre><p> + </p></li><li><p>Now type: +</p><pre class="screen"> +<code class="prompt">$ </code><strong class="userinput"><code>su - jill</code></strong> +<code class="prompt">$ </code><strong class="userinput"><code>cd /foodbar</code></strong> +<code class="prompt">$ </code><strong class="userinput"><code>touch Afile</code></strong> +<code class="prompt">$ </code><strong class="userinput"><code>ls -al</code></strong> +</pre><p> + </p><p> + You should see that the file <code class="filename">Afile</code> created by Jill will have ownership + and permissions of Jack, as follows: +</p><pre class="screen"> +-rw-r--r-- 1 jill engr 0 2007-01-18 19:41 Afile +</pre><p> + </p></li><li><p> + If the user that must have write permission in the directory is not a member of the group + <span class="emphasis"><em>engr</em></span> set in the <code class="filename">smb.conf</code> entry for the share: + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id377136"></a><em class="parameter"><code>force group = engr</code></em></td></tr></table><p> + </p></li></ol></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id377152"></a>File Operations Done as <span class="emphasis"><em>root</em></span> with <span class="emphasis"><em>force user</em></span> Set</h3></div></div></div><p> + When you have a user in <a class="indexterm" name="id377168"></a>admin users, Samba will always do file operations for + this user as <span class="emphasis"><em>root</em></span>, even if <a class="indexterm" name="id377179"></a>force user has been set. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id377189"></a>MS Word with Samba Changes Owner of File</h3></div></div></div><p> + <span class="emphasis"><em>Question:</em></span> “<span class="quote">When user B saves a word document that is owned by user A, + the updated file is now owned by user B. Why is Samba doing this? How do I fix this?</span>” + </p><p> + <span class="emphasis"><em>Answer:</em></span> Word does the following when you modify/change a Word document: MS Word creates a new document with + a temporary name. Word then closes the old document and deletes it, then renames the new document to the original document name. + There is no mechanism by which Samba can in any way know that the new document really should be owned by the owners + of the original file. Samba has no way of knowing that the file will be renamed by MS Word. As far as Samba is able + to tell, the file that gets created is a new file, not one that the application (Word) is updating. + </p><p> + There is a workaround to solve the permissions problem. It involves understanding how you can manage file + system behavior from within the <code class="filename">smb.conf</code> file, as well as understanding how UNIX file systems work. Set on the directory + in which you are changing Word documents: <code class="literal">chmod g+s `directory_name'.</code> This ensures that all files will + be created with the group that owns the directory. In <code class="filename">smb.conf</code> share declaration section set: + </p><p> + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id377254"></a><em class="parameter"><code>force create mode = 0660</code></em></td></tr><tr><td><a class="indexterm" name="id377267"></a><em class="parameter"><code>force directory mode = 0770</code></em></td></tr></table><p> + </p><p> + These two settings will ensure that all directories and files that get created in the share will be readable/writable by the + owner and group set on the directory itself. + </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="rights.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="optional.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="locking.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 15. 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