samba-mirror/docs/Samba3-HOWTO/TOSHARG-RightsAndPriviliges.xml

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<!DOCTYPE chapter PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
<chapter id="rights">
<chapterinfo>
        &author.jerry;
        &author.jht;
</chapterinfo>

<title>User Rights and Privileges</title>

<para>
The administration of Windows user, group, and machine accounts in the Samba
domain-controlled network necessitates interfacing between the MS Windows
networking environment and the UNIX operating system environment. The right
(permission) to add machines to the Windows security domain can be assigned
(set) to non-administrative users both in Windows NT4 domains and
Active Directory domains.
</para>

<para>
The addition of Windows NT4/2kX/XPPro machines to the domain necessitates the
creation of a machine account for each machine added. The machine account is
a necessity that is used to validate that the machine can be trusted to permit
user logons.
</para>

<para>
Machine accounts are analogous to user accounts, and thus in implementing them on a UNIX machine that is
hosting Samba (i.e., on which Samba is running) it is necessary to create a special type of user account.
Machine accounts differ from a normal user account in that the account name (login ID) is terminated with a
<literal>$</literal> sign. An additional difference is that this type of account should not ever be able to
log into the UNIX environment as a system user and therefore is set to have a shell of
<command>/bin/false</command> and a home directory of <command>/dev/null.</command>
</para>

<para>
The creation of UNIX system accounts has traditionally been the sole right of
the system administrator, better known as the <constant>root</constant> account.
It is possible in the UNIX environment to create multiple users who have the
same UID. Any UNIX user who has a UID=0 is inherently the same as the
<constant>root</constant> account.
</para>

<para>
All versions of Samba call system interface scripts that permit CIFS function
calls that are used to manage users, groups, and machine accounts
in the UNIX environment. All versions of Samba up to and including version 3.0.10
required the use of a Windows administrator account that unambiguously maps to
the UNIX <constant>root</constant> account to permit the execution of these
interface scripts. The requirement to do this has understandably met with some
disdain and consternation among Samba administrators, particularly where it became
necessary to permit people who should not possess <constant>root</constant>-level
access to the UNIX host system.
</para>

<sect1>
<title>Rights Management Capabilities</title>

<para>
Samba 3.0.11 introduces support for the Windows privilege model.  This model
allows certain rights to be assigned to a user or group SID.  In order to enable
this feature, <smbconfoption name="enable privileges">yes</smbconfoption>
must be defined in the <smbconfsection name="global"/> section of the &smb.conf; file.
</para>

<para>
Currently, the rights supported in Samba-3 are listed in <link linkend="rp-privs"/>.
The remainder of this chapter explains how to manage and use these privileges on Samba servers.
</para>

<table id="rp-privs">
        <title>Current Privilege Capabilities</title>
        <tgroup cols="2">
                <colspec align="right"/>
                <colspec align="left"/>
                <thead>
                        <row>
                                <entry align="center">Privilege</entry>
                                <entry align="center">Description</entry>
                        </row>
                </thead>
                <tbody>
                        <row>
                                <entry><para>SeMachineAccountPrivilege</para></entry>
                                <entry><para>Add machines to domain</para></entry>
                        </row>
                        <row>
                                <entry><para>SePrintOperatorPrivilege</para></entry>
                                <entry><para>Manage printers</para></entry>
                        </row>
                        <row>
                                <entry><para>SeAddUsersPrivilege</para></entry>
                                <entry><para>Add users and groups to the domain</para></entry>
                        </row>
                        <row>
                                <entry><para>SeRemoteShutdownPrivilege</para></entry>
                                <entry><para>Force shutdown from a remote system</para></entry>
                        </row>
                        <row>
                                <entry><para>SeDiskOperatorPrivilege</para></entry>
                                <entry><para>Manage disk share</para></entry>
                        </row>
                </tbody>
        </tgroup>
</table>

<sect2>
<title>Using the <quote>net rpc rights</quote> Utility</title>

<para>
There are two primary means of managing the rights assigned to users and groups
on a Samba server.  The <command>NT4 User Manager for Domains</command> may be
used from any Windows NT4, 2000, or XP Professional domain member client to
connect to a Samba domain controller and view/modify the rights assignments.
This application, however, appears to have bugs when run on a client running
Windows 2000 or later; therefore, Samba provides a command-line utility for
performing the necessary administrative actions.
</para>

<para>
The <command>net rpc rights</command> utility in Samba 3.0.11 has three new subcommands:
</para>

<variablelist>
	<varlistentry><term>list [name|accounts]</term>
		<listitem><para>
		When called with no arguments, <command>net rpc list</command>
		simply lists the available rights on the server.  When passed
		a specific user or group name, the tool lists the privileges
		currently assigned to the specified account.  When invoked using
		the special string <constant>accounts</constant>,
		<command>net rpc rights list</command> returns a list of all
		privileged accounts on the server and the assigned rights.
		</para></listitem>
	</varlistentry>

	<varlistentry><term>grant &lt;user&gt; &lt;right [right ...]&gt;</term>
		<listitem><para>
		When called with no arguments, this function is used to assign
		a list of rights to a specified user or group.  For example,
		to grant the members of the Domain Admins group on a Samba domain controller,
		the capability to add client machines to the domain, one would run:
<screen>
&rootprompt; net -S server -U domadmin rpc rights grant \
	 'DOMAIN\Domain Admins' SeMachineAccountPrivilege
</screen>
		More than one privilege can be assigned by specifying a
		list of rights separated by spaces. The parameter 'Domain\Domain Admins'
		must be quoted with single ticks or using double-quotes to prevent
		the backslash and the space from being interpreted by the system shell.
		</para></listitem>
	</varlistentry>

	<varlistentry><term>revoke &lt;user&gt; &lt;right [right ...]&gt;</term>
		<listitem><para>
		This command is similar in format to <command>net rpc rights grant</command>.  Its
		effect is to remove an assigned right (or list of rights) from a user or group.
		</para></listitem>
	</varlistentry>

</variablelist>

<note><para>
You must be connected as a member of the Domain Admins group to be able to
grant or revoke privileges assigned to an account.  This capability is
inherent to the Domain Admins group and is not configurable.
</para></note>

<para>
By default, no privileges are initially assigned to any
account because certain actions will
be performed as root once smbd determines that a user has
the necessary rights.  For example, when joining a client to
a Windows domain, the `add machine script' must be executed
with superuser rights in most cases.  For this reason, you
should be very careful about handing out privileges to
accounts.
</para>

<para>
Access as the root user (UID=0) bypasses all privilege checks.
</para>

</sect2>

<sect2>
<title>Description of Privileges</title>

<para>
The privileges that have been implemented in Samba-3.0.11 are shown below.
It is possible, and likely, that additional privileges may be implemented in
later releases of Samba. It is also likely that any privileges currently implemented
but not used may be removed from future releases, so it is important that
the successful as well as unsuccessful use of these facilities should be reported
on the Samba mailing lists.
</para>

<variablelist>
	<varlistentry><term>SeAddUsersPrivilege</term>
		<listitem><para>
		This right determines whether or not smbd will allow the
		user to create new user or group accounts via such tools
		as <command>net rpc user add</command> or 
		<command>NT4 User Manager for Domains.</command>
		</para></listitem>
	</varlistentry>

	<varlistentry><term>SeDiskOperatorPrivilege</term>
		<listitem><para>
		Accounts that possess this right will be able to execute
		scripts defined by the <command>add/delete/change</command>
		share command in &smb.conf; file as root.  Such users will
		also be able to modify the ACL associated with file shares
		on the Samba server.
		</para></listitem>
	</varlistentry>

	<varlistentry><term>SeMachineAccountPrivilege</term>
		<listitem><para>
		Controls whether or not the user can join client
		machines to a Samba-controlled domain.
		</para></listitem>
	</varlistentry>

	<varlistentry><term>SePrintOperatorPrivilege</term>
		<listitem><para>
		This privilege operates identically to the
		<smbconfoption name="printer admin"/>
		option in the &smb.conf; file (see section 5 man page for &smb.conf;)
		except that it is a global right (not on a per-printer basis). 
		Eventually the smb.conf option will be deprecated and administrative
		rights to printers will be controlled exclusively by this right and
		the security descriptor associated with the printer object in the
		<filename>ntprinters.tdb</filename> file.
		</para></listitem>
	</varlistentry>

	<varlistentry><term>SeRemoteShutdownPrivilege</term>
		<listitem><para>
		Samba provides two hooks for shutting down or rebooting
		the server and for aborting a previously issued shutdown
		command.  Since this is an operation normally limited by
		the operating system to the root user, an account must possess this
		right to be able to execute either of these hooks.
		</para></listitem>
	</varlistentry>

</variablelist>

</sect2>

</sect1>

<sect1>
<title>The Administrator Domain SID</title>

<para>
Please note that every Windows NT4 and later server requires a domain Adminsitrator account. Samba version
commencing with 3.0.11 permit the Administrative duties to be performed via assigned rights and privileges
(see <link linkend="rights">User Rights and Privileges</link>).  An account in the server's passdb backend can
be set to the domain SID of the default administrator account.  To obtain the domain SID on a Samba domain
controller, run the following command:
<screen>
&rootprompt; net getlocalsid
SID for domain FOO is: S-1-5-21-4294955119-3368514841-2087710299
</screen>
You may assign the domain administrator RID to an account using the <command>pdbedit</command>
command as shown here:
<screen>
&rootprompt; pdbedit -U S-1-5-21-4294955119-3368514841-2087710299-500 -u root -r
</screen>
</para>

<note><para>
The RID 500 is the well known standard value of the default Administrator account. It is the RID
that confers the rights and privileges that the Administrator account has on a Windows machine
or domain. Under UNIX/Linux the equivalent is UID=0 (the root account).
</para></note>

<para>
Releases of Samba version 3.0.11 and later make it possible to operate without an Administrator account
providing equivalent rights and privileges have been established for a Windows user or a Windows
group account. 
</para>

</sect1>

<sect1>
<title>Common Errors</title>

	<sect2>
	<title>What Rights and Privileges Will Permit Windows Client Administration?</title>

	<para>
	When a Windows NT4 (or later) client joins a domain, the domain global <literal>Domain Admins</literal> group
	is added to the membership of the local <literal>Administrators</literal> group on the client. Any user who is
	a member of the domain global <literal>Domain Admins</literal> group will have administrative rights on the
	Windows client.
	</para>

	<para>
	This is often not the most desirable solution because it means that the user will have administrative
	rights and privileges on domain servers also. The <literal>Power Users</literal> group on Windows client
	workstations permits local administration of the workstation alone. Any domain global user or domain global
	group can be added to the membership of the local workstation group <literal>Power Users</literal>.
	</para>

	<para>
	See <link linkend="nestedgrpmgmgt">Nested Group Support</link> for an example of how to add domain users
	and groups to a local group that is on a Windows workstation. The use of the <command>net</command>
	command permits this to be done from the Samba server.
	</para>

	<para>
	Another way this can be done is to log onto the Windows workstation as the user
	<literal>Administrator</literal>, then open a <command>cmd</command> shell, then execute:
<screen>
c:\ net localgroup administrators /add <userinput>domain_name\entity</userinput>
</screen>
	where <literal>entity</literal> is either a domain user or a domain group account name.
	</para>

	</sect2>

</sect1>

</chapter>