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   2 <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 11. UNIX Permission Bits and Windows NT Access Control Lists</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.59.1"><link rel="home" href="index.html" title="SAMBA Project Documentation"><link rel="up" href="optional.html" title="Part III. Advanced Configuration"><link rel="previous" href="passdb.html" title="Chapter 10. User information database"><link rel="next" href="groupmapping.html" title="Chapter 12. Configuring Group Mapping"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 11. UNIX Permission Bits and Windows NT Access Control Lists</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="passdb.html">Prev</a> </td><th width="60%" align="center">Part III. Advanced Configuration</th><td width="20%" align="right"> <a accesskey="n" href="groupmapping.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><h2 class="title"><a name="unix-permissions"></a>Chapter 11. UNIX Permission Bits and Windows NT Access Control Lists</h2></div><div><div class="author"><h3 class="author">Jeremy Allison</h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt>&lt;<a href="mailto:jra@samba.org">jra@samba.org</a>&gt;</tt></p></div></div></div></div><div><p class="pubdate">12 Apr 1999</p></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><a href="unix-permissions.html#id2881950">Viewing and changing UNIX permissions using the NT
   3         security dialogs</a></dt><dt><a href="unix-permissions.html#id2881832">How to view file security on a Samba share</a></dt><dt><a href="unix-permissions.html#id2885176">Viewing file ownership</a></dt><dt><a href="unix-permissions.html#id2885297">Viewing file or directory permissions</a></dt><dd><dl><dt><a href="unix-permissions.html#id2885379">File Permissions</a></dt><dt><a href="unix-permissions.html#id2885483">Directory Permissions</a></dt></dl></dd><dt><a href="unix-permissions.html#id2885533">Modifying file or directory permissions</a></dt><dt><a href="unix-permissions.html#id2885693">Interaction with the standard Samba create mask
   4         parameters</a></dt><dt><a href="unix-permissions.html#id2886008">Interaction with the standard Samba file attribute
   5         mapping</a></dt></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2881950"></a>Viewing and changing UNIX permissions using the NT
   6         security dialogs</h2></div></div><p>Windows NT clients can use their native security settings
   7         dialog box to view and modify the underlying UNIX permissions.</p><p>Note that this ability is careful not to compromise
   8         the security of the UNIX host Samba is running on, and
   9         still obeys all the file permission rules that a Samba
  10         administrator can set.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
  11         All access to Unix/Linux system file via Samba is controlled at
  12         the operating system file access control level. When trying to
  13         figure out file access problems it is vitally important to identify
  14         the identity of the Windows user as it is presented by Samba at
  15         the point of file access. This can best be determined from the
  16         Samba log files.
  17         </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2881832"></a>How to view file security on a Samba share</h2></div></div><p>From an NT4/2000/XP client, single-click with the right
  18         mouse button on any file or directory in a Samba mounted
  19         drive letter or UNC path. When the menu pops-up, click
  20         on the <span class="emphasis"><em>Properties</em></span> entry at the bottom of
  21         the menu. This brings up the file properties dialog
  22         box. Click on the tab <span class="emphasis"><em>Security</em></span> and you
  23         will see three buttons, <span class="emphasis"><em>Permissions</em></span>,
  24         <span class="emphasis"><em>Auditing</em></span>, and <span class="emphasis"><em>Ownership</em></span>.
  25         The <span class="emphasis"><em>Auditing</em></span> button will cause either
  26         an error message A requested privilege is not held
  27         by the client to appear if the user is not the
  28         NT Administrator, or a dialog which is intended to allow an
  29         Administrator to add auditing requirements to a file if the
  30         user is logged on as the NT Administrator. This dialog is
  31         non-functional with a Samba share at this time, as the only
  32         useful button, the <b>Add</b> button will not currently
  33         allow a list of users to be seen.</p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2885176"></a>Viewing file ownership</h2></div></div><p>Clicking on the <b>&quot;Ownership&quot;</b> button
  34         brings up a dialog box telling you who owns the given file. The
  35         owner name will be of the form :</p><p><b>&quot;SERVER\user (Long name)&quot;</b></p><p>Where <i><tt>SERVER</tt></i> is the NetBIOS name of
  36         the Samba server, <i><tt>user</tt></i> is the user name of
  37         the UNIX user who owns the file, and <i><tt>(Long name)</tt></i>
  38         is the descriptive string identifying the user (normally found in the
  39         GECOS field of the UNIX password database). Click on the <b>Close
  40         </b> button to remove this dialog.</p><p>If the parameter <i><tt>nt acl support</tt></i>
  41         is set to <tt>false</tt> then the file owner will
  42         be shown as the NT user <b>&quot;Everyone&quot;</b>.</p><p>The <b>Take Ownership</b> button will not allow
  43         you to change the ownership of this file to yourself (clicking on
  44         it will display a dialog box complaining that the user you are
  45         currently logged onto the NT client cannot be found). The reason
  46         for this is that changing the ownership of a file is a privileged
  47         operation in UNIX, available only to the <span class="emphasis"><em>root</em></span>
  48         user. As clicking on this button causes NT to attempt to change
  49         the ownership of a file to the current user logged into the NT
  50         client this will not work with Samba at this time.</p><p>There is an NT chown command that will work with Samba
  51         and allow a user with Administrator privilege connected
  52         to a Samba server as root to change the ownership of
  53         files on both a local NTFS filesystem or remote mounted NTFS
  54         or Samba drive. This is available as part of the <span class="emphasis"><em>Seclib
  55         </em></span> NT security library written by Jeremy Allison of
  56         the Samba Team, available from the main Samba ftp site.</p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2885297"></a>Viewing file or directory permissions</h2></div></div><p>The third button is the <b>&quot;Permissions&quot;</b>
  57         button. Clicking on this brings up a dialog box that shows both
  58         the permissions and the UNIX owner of the file or directory.
  59         The owner is displayed in the form :</p><p><b>&quot;SERVER\user (Long name)&quot;</b></p><p>Where <i><tt>SERVER</tt></i> is the NetBIOS name of
  60         the Samba server, <i><tt>user</tt></i> is the user name of
  61         the UNIX user who owns the file, and <i><tt>(Long name)</tt></i>
  62         is the descriptive string identifying the user (normally found in the
  63         GECOS field of the UNIX password database).</p><p>If the parameter <i><tt>nt acl support</tt></i>
  64         is set to <tt>false</tt> then the file owner will
  65         be shown as the NT user <b>&quot;Everyone&quot;</b> and the
  66         permissions will be shown as NT &quot;Full Control&quot;.</p><p>The permissions field is displayed differently for files
  67         and directories, so I'll describe the way file permissions
  68         are displayed first.</p><div class="sect2" lang="en"><div class="titlepage"><div><h3 class="title"><a name="id2885379"></a>File Permissions</h3></div></div><p>The standard UNIX user/group/world triple and
  69                 the corresponding &quot;read&quot;, &quot;write&quot;, &quot;execute&quot; permissions
  70                 triples are mapped by Samba into a three element NT ACL
  71                 with the 'r', 'w', and 'x' bits mapped into the corresponding
  72                 NT permissions. The UNIX world permissions are mapped into
  73                 the global NT group <b>Everyone</b>, followed
  74                 by the list of permissions allowed for UNIX world. The UNIX
  75                 owner and group permissions are displayed as an NT
  76                 <b>user</b> icon and an NT <b>local
  77                 group</b> icon respectively followed by the list
  78                 of permissions allowed for the UNIX user and group.</p><p>As many UNIX permission sets don't map into common
  79                 NT names such as <b>&quot;read&quot;</b>, <b>
  80                 &quot;change&quot;</b> or <b>&quot;full control&quot;</b> then
  81                 usually the permissions will be prefixed by the words <b>
  82                 &quot;Special Access&quot;</b> in the NT display list.</p><p>But what happens if the file has no permissions allowed
  83                 for a particular UNIX user group or world component ? In order
  84                 to  allow &quot;no permissions&quot; to be seen and modified then Samba
  85                 overloads the NT <b>&quot;Take Ownership&quot;</b> ACL attribute
  86                 (which has no meaning in UNIX) and reports a component with
  87                 no permissions as having the NT <b>&quot;O&quot;</b> bit set.
  88                 This was chosen of course to make it look like a zero, meaning
  89                 zero permissions. More details on the decision behind this will
  90                 be given below.</p></div><div class="sect2" lang="en"><div class="titlepage"><div><h3 class="title"><a name="id2885483"></a>Directory Permissions</h3></div></div><p>Directories on an NT NTFS file system have two
  91                 different sets of permissions. The first set of permissions
  92                 is the ACL set on the directory itself, this is usually displayed
  93                 in the first set of parentheses in the normal <b>&quot;RW&quot;</b>
  94                 NT style. This first set of permissions is created by Samba in
  95                 exactly the same way as normal file permissions are, described
  96                 above, and is displayed in the same way.</p><p>The second set of directory permissions has no real meaning
  97                 in the UNIX permissions world and represents the <b>
  98                 &quot;inherited&quot;</b> permissions that any file created within
  99                 this directory would inherit.</p><p>Samba synthesises these inherited permissions for NT by
 100                 returning as an NT ACL the UNIX permission mode that a new file
 101                 created by Samba on this share would receive.</p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2885533"></a>Modifying file or directory permissions</h2></div></div><p>Modifying file and directory permissions is as simple
 102         as changing the displayed permissions in the dialog box, and
 103         clicking the <b>OK</b> button. However, there are
 104         limitations that a user needs to be aware of, and also interactions
 105         with the standard Samba permission masks and mapping of DOS
 106         attributes that need to also be taken into account.</p><p>If the parameter <i><tt>nt acl support</tt></i>
 107         is set to <tt>false</tt> then any attempt to set
 108         security permissions will fail with an <b>&quot;Access Denied&quot;
 109         </b> message.</p><p>The first thing to note is that the <b>&quot;Add&quot;</b>
 110         button will not return a list of users in Samba (it will give
 111         an error message of <b>&quot;The remote procedure call failed
 112         and did not execute&quot;</b>). This means that you can only
 113         manipulate the current user/group/world permissions listed in
 114         the dialog box. This actually works quite well as these are the
 115         only permissions that UNIX actually has.</p><p>If a permission triple (either user, group, or world)
 116         is removed from the list of permissions in the NT dialog box,
 117         then when the <b>&quot;OK&quot;</b> button is pressed it will
 118         be applied as &quot;no permissions&quot; on the UNIX side. If you then
 119         view the permissions again the &quot;no permissions&quot; entry will appear
 120         as the NT <b>&quot;O&quot;</b> flag, as described above. This
 121         allows you to add permissions back to a file or directory once
 122         you have removed them from a triple component.</p><p>As UNIX supports only the &quot;r&quot;, &quot;w&quot; and &quot;x&quot; bits of
 123         an NT ACL then if other NT security attributes such as &quot;Delete
 124         access&quot; are selected then they will be ignored when applied on
 125         the Samba server.</p><p>When setting permissions on a directory the second
 126         set of permissions (in the second set of parentheses) is
 127         by default applied to all files within that directory. If this
 128         is not what you want you must uncheck the <b>&quot;Replace
 129         permissions on existing files&quot;</b> checkbox in the NT
 130         dialog before clicking <b>&quot;OK&quot;</b>.</p><p>If you wish to remove all permissions from a
 131         user/group/world  component then you may either highlight the
 132         component and click the <b>&quot;Remove&quot;</b> button,
 133         or set the component to only have the special <b>&quot;Take
 134         Ownership&quot;</b> permission (displayed as <b>&quot;O&quot;
 135         </b>) highlighted.</p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2885693"></a>Interaction with the standard Samba create mask
 136         parameters</h2></div></div><p>There are four parameters
 137         to control interaction with the standard Samba create mask parameters.
 138         These are :</p><p><i><tt>security mask</tt></i></p><p><i><tt>force security mode</tt></i></p><p><i><tt>directory security mask</tt></i></p><p><i><tt>force directory security mode</tt></i></p><p>Once a user clicks <b>&quot;OK&quot;</b> to apply the
 139         permissions Samba maps the given permissions into a user/group/world
 140         r/w/x triple set, and then will check the changed permissions for a
 141         file against the bits set in the <a href="smb.conf.5.html#SECURITYMASK" target="_top">
 142         <i><tt>security mask</tt></i></a> parameter. Any bits that
 143         were changed that are not set to '1' in this parameter are left alone
 144         in the file permissions.</p><p>Essentially, zero bits in the <i><tt>security mask</tt></i>
 145         mask may be treated as a set of bits the user is <span class="emphasis"><em>not</em></span>
 146         allowed to change, and one bits are those the user is allowed to change.
 147         </p><p>If not set explicitly this parameter is set to the same value as
 148         the <a href="smb.conf.5.html#CREATEMASK" target="_top"><i><tt>create mask
 149         </tt></i></a> parameter. To allow a user to modify all the
 150         user/group/world permissions on a file, set this parameter
 151         to 0777.</p><p>Next Samba checks the changed permissions for a file against
 152         the bits set in the <a href="smb.conf.5.html#FORCESECURITYMODE" target="_top">
 153         <i><tt>force security mode</tt></i></a> parameter. Any bits
 154         that were changed that correspond to bits set to '1' in this parameter
 155         are forced to be set.</p><p>Essentially, bits set in the <i><tt>force security mode
 156         </tt></i> parameter may be treated as a set of bits that, when
 157         modifying security on a file, the user has always set to be 'on'.</p><p>If not set explicitly this parameter is set to the same value
 158         as the <a href="smb.conf.5.html#FORCECREATEMODE" target="_top"><i><tt>force
 159         create mode</tt></i></a> parameter.
 160         To allow a user to modify all the user/group/world permissions on a file
 161         with no restrictions set this parameter to 000.</p><p>The <i><tt>security mask</tt></i> and <i><tt>force
 162         security mode</tt></i> parameters are applied to the change
 163         request in that order.</p><p>For a directory Samba will perform the same operations as
 164         described above for a file except using the parameter <i><tt>
 165         directory security mask</tt></i> instead of <i><tt>security
 166         mask</tt></i>, and <i><tt>force directory security mode
 167         </tt></i> parameter instead of <i><tt>force security mode
 168         </tt></i>.</p><p>The <i><tt>directory security mask</tt></i> parameter
 169         by default is set to the same value as the <i><tt>directory mask
 170         </tt></i> parameter and the <i><tt>force directory security
 171         mode</tt></i> parameter by default is set to the same value as
 172         the <i><tt>force directory mode</tt></i> parameter. </p><p>In this way Samba enforces the permission restrictions that
 173         an administrator can set on a Samba share, whilst still allowing users
 174         to modify the permission bits within that restriction.</p><p>If you want to set up a share that allows users full control
 175         in modifying the permission bits on their files and directories and
 176         doesn't force any particular bits to be set 'on', then set the following
 177         parameters in the <tt>smb.conf</tt> file in that share specific section :</p><p><i><tt>security mask = 0777</tt></i></p><p><i><tt>force security mode = 0</tt></i></p><p><i><tt>directory security mask = 0777</tt></i></p><p><i><tt>force directory security mode = 0</tt></i></p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2886008"></a>Interaction with the standard Samba file attribute
 178         mapping</h2></div></div><p>Samba maps some of the DOS attribute bits (such as &quot;read
 179         only&quot;) into the UNIX permissions of a file. This means there can
 180         be a conflict between the permission bits set via the security
 181         dialog and the permission bits set by the file attribute mapping.
 182         </p><p>One way this can show up is if a file has no UNIX read access
 183         for the owner it will show up as &quot;read only&quot; in the standard
 184         file attributes tabbed dialog. Unfortunately this dialog is
 185         the same one that contains the security info in another tab.</p><p>What this can mean is that if the owner changes the permissions
 186         to allow themselves read access using the security dialog, clicks
 187         <b>&quot;OK&quot;</b> to get back to the standard attributes tab
 188         dialog, and then clicks <b>&quot;OK&quot;</b> on that dialog, then
 189         NT will set the file permissions back to read-only (as that is what
 190         the attributes still say in the dialog). This means that after setting
 191         permissions and clicking <b>&quot;OK&quot;</b> to get back to the
 192         attributes dialog you should always hit <b>&quot;Cancel&quot;</b>
 193         rather than <b>&quot;OK&quot;</b> to ensure that your changes
 194         are not overridden.</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="passdb.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="groupmapping.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 10. User information database </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 12. Configuring Group Mapping</td></tr></table></div></body></html>