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diff --git a/docs/docbook/projdoc/NT_Security.xml b/docs/docbook/projdoc/NT_Security.xml new file mode 100644 index 0000000000..9bff25337c --- /dev/null +++ b/docs/docbook/projdoc/NT_Security.xml @@ -0,0 +1,335 @@ +<chapter id="unix-permissions"> +<chapterinfo> + &author.jeremy; + <pubdate>12 Apr 1999</pubdate> +</chapterinfo> + +<title>UNIX Permission Bits and Windows NT Access Control Lists</title> + +<sect1> + <title>Viewing and changing UNIX permissions using the NT + security dialogs</title> + + <para>Windows NT clients can use their native security settings + dialog box to view and modify the underlying UNIX permissions.</para> + + <para>Note that this ability is careful not to compromise + the security of the UNIX host Samba is running on, and + still obeys all the file permission rules that a Samba + administrator can set.</para> + + <note> + <para> + All access to Unix/Linux system file via Samba is controlled at + the operating system file access control level. When trying to + figure out file access problems it is vitally important to identify + 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. + </para> + </note> +</sect1> + +<sect1> + <title>How to view file security on a Samba share</title> + + <para>From an NT4/2000/XP client, single-click with the right + mouse button on any file or directory in a Samba mounted + drive letter or UNC path. When the menu pops-up, click + on the <emphasis>Properties</emphasis> entry at the bottom of + the menu. This brings up the file properties dialog + box. Click on the tab <emphasis>Security</emphasis> and you + will see three buttons, <emphasis>Permissions</emphasis>, + <emphasis>Auditing</emphasis>, and <emphasis>Ownership</emphasis>. + The <emphasis>Auditing</emphasis> button will cause either + an error message <errorname>A requested privilege is not held + by the client</errorname> to appear if the user is not the + NT Administrator, or a dialog which is 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 + non-functional with a Samba share at this time, as the only + useful button, the <command>Add</command> button will not currently + allow a list of users to be seen.</para> + +</sect1> + +<sect1> + <title>Viewing file ownership</title> + + <para>Clicking on the <command>"Ownership"</command> button + brings up a dialog box telling you who owns the given file. The + owner name will be of the form :</para> + + <para><command>"SERVER\user (Long name)"</command></para> + + <para>Where <replaceable>SERVER</replaceable> is the NetBIOS name of + the Samba server, <replaceable>user</replaceable> is the user name of + the UNIX user who owns the file, and <replaceable>(Long name)</replaceable> + is the descriptive string identifying the user (normally found in the + GECOS field of the UNIX password database). Click on the <command>Close + </command> button to remove this dialog.</para> + + <para>If the parameter <parameter>nt acl support</parameter> + is set to <constant>false</constant> then the file owner will + be shown as the NT user <command>"Everyone"</command>.</para> + + <para>The <command>Take Ownership</command> button will not allow + you to change the ownership of this file to yourself (clicking on + it will display a dialog box complaining that the user 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 <emphasis>root</emphasis> + user. As 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.</para> + + <para>There is an NT chown 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 filesystem or remote mounted NTFS + or Samba drive. This is available as part of the <emphasis>Seclib + </emphasis> NT security library written by Jeremy Allison of + the Samba Team, available from the main Samba ftp site.</para> + +</sect1> + +<sect1> + <title>Viewing file or directory permissions</title> + + <para>The third button is the <command>"Permissions"</command> + button. Clicking on this brings up a dialog box that shows both + the permissions and the UNIX owner of the file or directory. + The owner is displayed in the form :</para> + + <para><command>"SERVER\user (Long name)"</command></para> + + <para>Where <replaceable>SERVER</replaceable> is the NetBIOS name of + the Samba server, <replaceable>user</replaceable> is the user name of + the UNIX user who owns the file, and <replaceable>(Long name)</replaceable> + is the descriptive string identifying the user (normally found in the + GECOS field of the UNIX password database).</para> + + <para>If the parameter <parameter>nt acl support</parameter> + is set to <constant>false</constant> then the file owner will + be shown as the NT user <command>"Everyone"</command> and the + permissions will be shown as NT "Full Control".</para> + + + <para>The permissions field is displayed differently for files + and directories, so I'll describe the way file permissions + are displayed first.</para> + + <sect2> + <title>File Permissions</title> + + <para>The standard UNIX user/group/world triple and + the corresponding "read", "write", "execute" permissions + triples are mapped by Samba into a three element NT ACL + with the 'r', 'w', and 'x' bits mapped into the corresponding + NT permissions. The UNIX world permissions are mapped into + the global NT group <command>Everyone</command>, followed + by the list of permissions allowed for UNIX world. The UNIX + owner and group permissions are displayed as an NT + <command>user</command> icon and an NT <command>local + group</command> icon respectively followed by the list + of permissions allowed for the UNIX user and group.</para> + + <para>As many UNIX permission sets don't map into common + NT names such as <command>"read"</command>, <command> + "change"</command> or <command>"full control"</command> then + usually the permissions will be prefixed by the words <command> + "Special Access"</command> in the NT display list.</para> + + <para>But what happens if the file has no permissions allowed + for a particular UNIX user group or world component ? In order + to allow "no permissions" to be seen and modified then Samba + overloads the NT <command>"Take Ownership"</command> ACL attribute + (which has no meaning in UNIX) and reports a component with + no permissions as having the NT <command>"O"</command> bit set. + This was chosen of course to make it look like a zero, meaning + zero permissions. More details on the decision behind this will + be given below.</para> + </sect2> + + <sect2> + <title>Directory Permissions</title> + + <para>Directories on an NT NTFS file system have two + different sets of permissions. The first set of permissions + is the ACL set on the directory itself, this is usually displayed + in the first set of parentheses in the normal <command>"RW"</command> + 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.</para> + + <para>The second set of directory permissions has no real meaning + in the UNIX permissions world and represents the <command> + "inherited"</command> permissions that any file created within + this directory would inherit.</para> + + <para>Samba synthesises 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.</para> + </sect2> +</sect1> + +<sect1> + <title>Modifying file or directory permissions</title> + + <para>Modifying file and directory permissions is as simple + as changing the displayed permissions in the dialog box, and + clicking the <command>OK</command> button. 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 need to also be taken into account.</para> + + <para>If the parameter <parameter>nt acl support</parameter> + is set to <constant>false</constant> then any attempt to set + security permissions will fail with an <command>"Access Denied" + </command> message.</para> + + <para>The first thing to note is that the <command>"Add"</command> + button will not return a list of users in Samba (it will give + an error message of <command>"The remote procedure call failed + and did not execute"</command>). This means that you can only + manipulate the current user/group/world permissions listed in + the dialog box. This actually works quite well as these are the + only permissions that UNIX actually has.</para> + + <para>If a permission triple (either user, group, or world) + is removed from the list of permissions in the NT dialog box, + then when the <command>"OK"</command> button is pressed it will + be applied as "no permissions" on the UNIX side. If you then + view the permissions again the "no permissions" entry will appear + as the NT <command>"O"</command> flag, as described above. This + allows you to add permissions back to a file or directory once + you have removed them from a triple component.</para> + + <para>As UNIX supports only the "r", "w" and "x" bits of + an NT ACL then if other NT security attributes such as "Delete + access" are selected then they will be ignored when applied on + the Samba server.</para> + + <para>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 <command>"Replace + permissions on existing files"</command> checkbox in the NT + dialog before clicking <command>"OK"</command>.</para> + + <para>If you wish to remove all permissions from a + user/group/world component then you may either highlight the + component and click the <command>"Remove"</command> button, + or set the component to only have the special <command>"Take + Ownership"</command> permission (displayed as <command>"O" + </command>) highlighted.</para> +</sect1> + +<sect1> + <title>Interaction with the standard Samba create mask + parameters</title> + + <para>There are four parameters + to control interaction with the standard Samba create mask parameters. + These are :</para> + + <para><parameter>security mask</parameter></para> + <para><parameter>force security mode</parameter></para> + <para><parameter>directory security mask</parameter></para> + <para><parameter>force directory security mode</parameter></para> + + <para>Once a user clicks <command>"OK"</command> to apply the + permissions Samba maps the given permissions into a user/group/world + r/w/x triple set, and then will check the changed permissions for a + file against the bits set in the <ulink url="smb.conf.5.html#SECURITYMASK"> + <parameter>security mask</parameter></ulink> parameter. Any bits that + were changed that are not set to '1' in this parameter are left alone + in the file permissions.</para> + + <para>Essentially, zero bits in the <parameter>security mask</parameter> + mask may be treated as a set of bits the user is <emphasis>not</emphasis> + allowed to change, and one bits are those the user is allowed to change. + </para> + + <para>If not set explicitly this parameter is set to the same value as + the <ulink url="smb.conf.5.html#CREATEMASK"><parameter>create mask + </parameter></ulink> parameter. To allow a user to modify all the + user/group/world permissions on a file, set this parameter + to 0777.</para> + + <para>Next Samba checks the changed permissions for a file against + the bits set in the <ulink url="smb.conf.5.html#FORCESECURITYMODE"> + <parameter>force security mode</parameter></ulink> parameter. Any bits + that were changed that correspond to bits set to '1' in this parameter + are forced to be set.</para> + + <para>Essentially, bits set in the <parameter>force security mode + </parameter> parameter may be treated as a set of bits that, when + modifying security on a file, the user has always set to be 'on'.</para> + + <para>If not set explicitly this parameter is set to the same value + as the <ulink url="smb.conf.5.html#FORCECREATEMODE"><parameter>force + create mode</parameter></ulink> parameter. + To allow a user to modify all the user/group/world permissions on a file + with no restrictions set this parameter to 000.</para> + + <para>The <parameter>security mask</parameter> and <parameter>force + security mode</parameter> parameters are applied to the change + request in that order.</para> + + <para>For a directory Samba will perform the same operations as + described above for a file except using the parameter <parameter> + directory security mask</parameter> instead of <parameter>security + mask</parameter>, and <parameter>force directory security mode + </parameter> parameter instead of <parameter>force security mode + </parameter>.</para> + + <para>The <parameter>directory security mask</parameter> parameter + by default is set to the same value as the <parameter>directory mask + </parameter> parameter and the <parameter>force directory security + mode</parameter> parameter by default is set to the same value as + the <parameter>force directory mode</parameter> parameter. </para> + + <para>In this way Samba enforces the permission restrictions that + an administrator can set on a Samba share, whilst still allowing users + to modify the permission bits within that restriction.</para> + + <para>If you want to set up a share that allows users full control + in modifying the permission bits on their files and directories and + doesn't force any particular bits to be set 'on', then set the following + parameters in the &smb.conf; file in that share specific section :</para> + + <para><parameter>security mask = 0777</parameter></para> + <para><parameter>force security mode = 0</parameter></para> + <para><parameter>directory security mask = 0777</parameter></para> + <para><parameter>force directory security mode = 0</parameter></para> +</sect1> + +<sect1> + <title>Interaction with the standard Samba file attribute + mapping</title> + + <para>Samba maps some of the DOS attribute bits (such as "read + only") 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. + </para> + + <para>One way this can show up is if a file has no UNIX read access + for the owner it will show up as "read only" in the standard + file attributes tabbed dialog. Unfortunately this dialog is + the same one that contains the security info in another tab.</para> + + <para>What this can mean is that if the owner changes the permissions + to allow themselves read access using the security dialog, clicks + <command>"OK"</command> to get back to the standard attributes tab + dialog, and then clicks <command>"OK"</command> 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 <command>"OK"</command> to get back to the + attributes dialog you should always hit <command>"Cancel"</command> + rather than <command>"OK"</command> to ensure that your changes + are not overridden.</para> +</sect1> + +</chapter> |