Difference between revisions of "Setting up a Share Using POSIX ACLs"

m (Updated link)
m (/* Added warning)
 
(18 intermediate revisions by 4 users not shown)
Line 1: Line 1:
 
= Introduction =
 
= Introduction =
  
On every Samba host you can, as on any MS Windows OS, share a folder to make it accessible for other users. There's no difference if this host is a Samba [[Active_Directory_Domain_Controller|Active Directory Domain Controller]], a [[Setting_up_Samba_as_a_Domain_Member|Domain Member]] or a [[Setting_up_a_Samba_Standalone_Server|Standalone Server]]. File shares can be setup in two ways: To be [[Shares_with_Windows_ACLs|managed from Windows using Windows tools and ACLs]] or completely via smb.conf parameters and POSIX ACLs. The latter is described in this documentation.
+
Samba supports shares with POSIX access control lists (ACL) on Unix domain members, they enable you to manage permissions locally on the Samba host using UNIX utilities. The Unix file system must support extended attributes, this will enable you to use extended POSIX ACLs to set multiple users and groups in ACLs - similar to Windows ACLs. For details, see [[#Setting_Extended_ACLs|Setting Extended ACLs]].
  
'''Important note:''' Samba Active Directory Domain Controllers have extended ACL support enabled globally, to enable [[Shares_with_Windows_ACLs|management of share permissions and ACLs via Windows]]!
+
{{Imbox
 +
| type = note
 +
| text = You are advised that a better option is to use Windows ACLs, this will allow you to set up fine-granular ACLs. For details, see [[Setting_up_a_Share_Using_Windows_ACLs|Setting up a Share Using Windows ACLs]].
 +
}}
  
 +
{{Imbox
 +
| type = important
 +
| text = If you set share permissions with POSIX ACLs, then you must not use Windows ACLs, Never set the permissions from Windows.
 +
}}
  
  
 +
Samba supports shares with POSIX ACLs on:
 +
* Domain members
 +
* NT4 PDC and BDCs
 +
* Standalone hosts
  
  
= Execute bit on files =
+
{{Imbox
 +
| type = important
 +
| text = On a Samba Active Directory (AD) domain controller (DC), Windows ACL support is enabled globally, and therefore shares with POSIX ACLs are not supported. You must use Windows ACLs.
 +
}}
  
For details, see [[Updating_Samba#File_Execution_Permissions|File Execution Permissions]].
 
  
  
  
  
 +
= Preparing the Host =
  
= Adding a new share =
+
Before you are able to create a share, set up Samba. For details, see:
 +
* [[Setting_up_Samba_as_a_Domain_Member|Setting up Samba as a Domain Member]]
 +
* [[Setting_up_Samba_as_an_NT4_PDC_(Quick_Start)|Setting up Samba as an NT4 PDC (Quick Start)]]
 +
* [[Setting_up_Samba_as_an_NT4_BDC|Setting up Samba as an NT4 BDC]]
 +
* [[Setting_up_Samba_as_a_Standalone_Server|Setting up Samba as a Standalone Server]]
  
* Create a new folder, that should be shared, if it doesn't already exist
+
 
 +
 
 +
 
 +
 
 +
= Making Files Executable =
 +
 
 +
Using the default setting, users are only able to execute files, such as <code>*.exe</code> and <code>*.bat</code>, on a Samba share if they have the POSIX x-bit set. For example, the following file is executable for the <code>root</code> user and members of the <code>Domain Users</code> group:
 +
 
 +
-rw<u>x</u>r-<u>x</u>--- 1 root "Domain Users" 133160 1. Jan 00:00 /srv/samba/Demo/example.exe
 +
 
 +
In some scenarios it is necessary to enable users to execute all files on a share, regardless if the x-bit is set. To enable, set in the <code>[global]</code> or in a specific share section of your <code>smb.conf</code>:
 +
 
 +
acl allow execute always = yes
 +
 
 +
= Adding a Share =
 +
 
 +
To share the <code>/srv/samba/Demo/</code> directory using the <code>Demo</code> share name:
 +
 
 +
* Create the directory:
  
 
  # mkdir -p /srv/samba/Demo/
 
  # mkdir -p /srv/samba/Demo/
  
* Add a new share to your smb.conf. The following is the required minimum:
+
* Add the <code>[Demo]</code> share definition to your <code>smb.conf</code> file:
  
 
  [Demo]
 
  [Demo]
Line 29: Line 65:
 
         read only = no
 
         read only = no
  
* Reload Samba
+
: These are the minimum parameters required to set up a writeable share. Optionally, you can set share permissions. For details, see [[#Setting_Share_Permissions|Setting Share Permissions]].
 +
 
 +
* Reload the Samba configuration:
  
 
  # smbcontrol all reload-config
 
  # smbcontrol all reload-config
Line 36: Line 74:
  
  
= Setup share permissions (optional) =
 
  
As on MS Windows OS, you can define share permissions, which are validated directly when a user connects to a share. Share permissions are defined on each share individually. Samba needs to be reloaded/restarted if changes are made.
+
= Setting ACLs =
 +
 
 +
== Setting Standard UNIX ACLs ==
 +
 
 +
The standard access control lists (ACL) on a UNIX operating system supports setting permissions for one owner, one group, and everyone else (other). If you need to set multiple ACLs on a directory, see [[#Setting_Extended_ACLs|Setting Extended ACLs]].
 +
 
 +
For example, to set the owner of the <code>/srv/samba/Demo/</code> directory to <code>root</code>, grant read and write permissions to the owner and the <code>Domain Users</code> group, and deny access to all other users, enter:
 +
 
 +
# chmod 2770 /srv/samba/Demo/
 +
# chown root:"Domain Users" /srv/samba/Demo/
 +
 
 +
{{Imbox
 +
| type = note
 +
| text = Setting the SGID bit (<code><u>2</u>770</code>) automatically inherits the directory's group to all new files and directories created, instead setting it to the user's primary group.
 +
}}
  
 +
For further details about the permissions, see the <code>chmod(1)</code> and <code>chown(1)</code> man page.
  
  
== User/group based share access ==
 
  
 +
== Setting Extended ACLs ==
 +
 +
If your file system supports extended access control lists (ACL), you can use extended POSIX ACLs. They enable you to set permissions for multiple users and groups on a file or directory - similar to Windows ACLs. However, POSIX ACLs are limited to the following general permissions modes:
 +
* None
 +
* Read
 +
* Write
 +
* Full control
 +
 +
For example, to set read, write, and execute permissions for the <code>Domain Admins</code> group, read and execute permissions for the <code>Domain Users</code> group, and deny access to everyone else on the <code>/srv/samba/Demo/</code> directory:
 +
 +
* Add the <code>inherit acls = yes</code> parameter to the share's configuration. For example:
 
  [Demo]
 
  [Demo]
 
         path = /srv/samba/Demo/
 
         path = /srv/samba/Demo/
 
         read only = no
 
         read only = no
         valid users = +SAMDOM\"Domain Users"
+
         inherit acls = yes
        invalid users = +SAMDOM\"Demo Group" SAMDOM\foobar
+
: The <code>inherit acls = yes</code> parameter enables ACL inheritance of extended ACLs. For further details, see the parameter description in the <code>smb.conf</code> man page.
 +
 
 +
* Reload Samba:
 +
 
 +
# smbcontrol all reload-config
 +
 
 +
* Verify that the directory is stored on a file system that supports extended ACLs. For details, see [[File System Support]].
 +
 
 +
* Disable auto-granting permissions for the primary group of user accounts:
 +
# setfacl -m group::--- /srv/samba/Demo/
 +
# setfacl -m default:group::--- /srv/samba/Demo/
 +
: The primary group of the directory is additionally mapped to the dynamical <code>CREATOR GROUP</code> principal. If you use extended POSIX ACLs on a Samba share, this principal is automatically added and you cannot remove it. For further details about the <code>CREATOR GROUP</code> principal, see [https://support.microsoft.com/de-at/help/243330/well-known-security-identifiers-in-windows-operating-systems Well-known security identifiers in Windows operating systems].
 +
 
 +
* Set the permissions on the directory:
 +
 
 +
:* Grant read, write, and execute permissions to the <code>Domain Admins</code> group:
 +
# setfacl -m group:"SAMDOM\Domain Admins":rwx /srv/samba/Demo/
 +
 
 +
:* Grant read and execute permissions to the <code>Domain Users</code> group:
 +
# setfacl -m group:"SAMDOM\Domain Users":r-x /srv/samba/Demo/
 +
 
 +
:* Set permissions for the <code>other</code> ACL entry to deny access to users that do not match other ACL entries:
 +
# setfacl -R -m other::--- /srv/samba/Demo/
 +
 
 +
: These settings are only applied to the directory itself. In Windows, this is converted to <code>This folder only</code>.
 +
 
 +
* To configure that the same permissions set in the previous step are inherited to new file system objects created in this directory, enter:
 +
 
 +
# setfacl -m default:group:"SAMDOM\Domain Admins":rwx /srv/samba/Demo/
 +
# setfacl -m default:group:"SAMDOM\Domain Users":r-x /srv/samba/Demo/
 +
# setfacl -m default:other::--- /srv/samba/Demo/
 +
 
 +
: With this settings, the <code>This folder only</code> mode for the principals now changed to <code>This folder, subfolders, and files</code>.
 +
 
 +
The ACLs set in the previous steps are mapped to the following Windows ACLs:
 +
 
 +
{| class="wikitable"
 +
!Principal
 +
!Access
 +
!Applies to
 +
!Comments
 +
|-
 +
|SAMDOM\Domain Admins
 +
|Full control
 +
|This folder, subfolders, and files
 +
|
 +
|-
 +
|SAMDOM\Domain Users
 +
|Read & execute
 +
||This folder, subfolders, and files
 +
|
 +
|-
 +
|Everyone
 +
|None
 +
|This folder, subfolders, and files
 +
|Samba maps the permissions for this principal from the UNIX <code>other</code> ACL entry.
 +
|-
 +
|''directory_owner'' (Unix User\''directory_owner'') *
 +
|Full control
 +
|This folder only
 +
|Samba maps the owner of the directory to this entry.
 +
|-
 +
|''directory_primary_group'' (Unix User\''directory_primary_group'') *
 +
|None
 +
|This folder only
 +
|Samba maps the primary group of the directory to this entry.
 +
|-
 +
|CREATOR OWNER *
 +
|Full control
 +
|Subfolders and files only
 +
|On new file system objects, the creator inherits automatically the permissions of this principal.
 +
|-
 +
|CREATOR GROUP *
 +
|None
 +
|Subfolders and files only
 +
|On new file system objects, the creator's primary group inherits automatically the permissions of this principal.
 +
|}
 +
 
 +
<nowiki>*</nowiki> Configuring or removing these principals from the ACLs is only supported when using Windows ACLs. For details, see [[Setting up a Share Using Windows ACLs]].
 +
 
 +
For further details, see the <code>setfacl</code> man page.
  
The example above allows connection to the "Demo" share, if the user is member of the "Domain Users" group. Member of the "Demo Group" and user "foobar" are not allowed to connect, even if they are part of "Domain Users". Where the lists conflict, the "invalid users" parameter has precedence!
 
  
  
  
== Host based share access ==
 
  
Contrary to MS Windows hosts, Samba is able to limit the access to a share to a list of IPs, subnets or hostnames.
+
= Setting Share Permissions =
  
[Demo]
+
''Optional'': Samba enables you to set permissions on each share which are validated when a user connects.
        path = /srv/samba/Demo
 
        read only = no
 
        hosts allow = 127.0.0.1 10.99.0.0/24 GoodHost1
 
  
The above example allows access to the share only if the connection is initiated from 127.0.0.1, the subnet 10.99.0.0/24 or the host with name "GoodHost1". Alternatively it is possible to deny hosts via
+
Access to the content on a share, is controlled using file system access control lists (ACL). For details, see [[#Setting_POSIX_ACLs_on_a_Samba_Share|Setting POSIX ACLs on a Samba Share]]
  
        hosts deny = BadHost1
 
  
If both parameters (allow/deny) are defined and the lists conflict, the "allow" parameter has precedence! For further information and examples, see the smb.conf man page.
 
  
 +
== Configuring User and Group-based Share Access ==
  
 +
Share-based access control enables you to grant or deny access to a share for certain users and groups. For example, to enable all members of the <code>Domain Users</code> group to access a share while access is denied for the <code>example_user</code> account, add the following parameters to the share's configuration:
  
 +
        valid users = +SAMDOM\"Domain Users"
 +
        invalid users = SAMDOM\example_user
  
 +
The <code>invalid users</code> parameter has a higher priority than the <code>valid users</code> parameter. For example, if the <code>example_user</code> account is a member of the <code>Domain Users</code> group, access is denied for this account in the previous example.
  
= File system ACLs =
+
For further details, see the parameter descriptions in the <code>smb.conf(5)</code> man page.
  
ACLs on POSIX enabled shares are set using the typical tools: "chmod", "chown" and "chgrp".
 
  
Example:
 
  
# mkdir /srv/samba/Demo/Example/
+
== Configuring Host-based Share Access ==
# chmod 2770 /srv/samba/Demo/Example/
 
# chown foobar:"Demo Group" /srv/samba/Demo/Example/
 
  
These commands create a new folder in the root of the "Demo" share. The permissions (2770) define that only the owner "foobar" and group "Demo Group" have read/write/execute permissions on the folder. You might have noticed the SGID (setgid) bit was set on the folder. This means that all files and subfolders that will be created, inherit the group ("Demo Group") instead setting it to the default group of the users doing the creation.
+
Host-based access control enables you to grant or deny access to a share based on host names, IP addresses, or IP ranges. For example, to enable the 127.0.0.1 IP address, the 10.99.0.0/24 IP range, and the <code>GoodHost</code> host name to access a share, and additionally deny access for the <code>BadHost</code> host name, add the following parameters to the share's configuration:
  
 +
        hosts allow = 127.0.0.1 10.99.0.0/24 GoodHost
 +
        hosts deny = BadHost
  
 +
The <code>hosts deny</code> parameter has a higher priority than the <code>hosts allow</code> parameter. For example, if <code>BadHost</code> resolves to an IP address that is listed in the <code>hosts allow</code> parameter, access to this host is denied.
  
 +
For further details, see the parameter descriptions in the <code>smb.conf(5)</code> man page.
  
  
= Related documentation =
 
  
The following documentation discusses related topics:
 
  
* [[User_home_drives|Setting up home drives]]
 
  
* [[Implementing_roaming_profiles|Implementing Windows roaming profiles]]
+
----
 +
[[Category:Active Directory]]
 +
[[Category:Domain Members]]
 +
[[Category:File Serving]]
 +
[[Category:NT4 Domains]]

Latest revision as of 10:36, 26 February 2021

Introduction

Samba supports shares with POSIX access control lists (ACL) on Unix domain members, they enable you to manage permissions locally on the Samba host using UNIX utilities. The Unix file system must support extended attributes, this will enable you to use extended POSIX ACLs to set multiple users and groups in ACLs - similar to Windows ACLs. For details, see Setting Extended ACLs.


Samba supports shares with POSIX ACLs on:

  • Domain members
  • NT4 PDC and BDCs
  • Standalone hosts




Preparing the Host

Before you are able to create a share, set up Samba. For details, see:



Making Files Executable

Using the default setting, users are only able to execute files, such as *.exe and *.bat, on a Samba share if they have the POSIX x-bit set. For example, the following file is executable for the root user and members of the Domain Users group:

-rwxr-x--- 1 root "Domain Users" 133160 1. Jan 00:00 /srv/samba/Demo/example.exe

In some scenarios it is necessary to enable users to execute all files on a share, regardless if the x-bit is set. To enable, set in the [global] or in a specific share section of your smb.conf:

acl allow execute always = yes

Adding a Share

To share the /srv/samba/Demo/ directory using the Demo share name:

  • Create the directory:
# mkdir -p /srv/samba/Demo/
  • Add the [Demo] share definition to your smb.conf file:
[Demo]
       path = /srv/samba/Demo/
       read only = no
These are the minimum parameters required to set up a writeable share. Optionally, you can set share permissions. For details, see Setting Share Permissions.
  • Reload the Samba configuration:
# smbcontrol all reload-config



Setting ACLs

Setting Standard UNIX ACLs

The standard access control lists (ACL) on a UNIX operating system supports setting permissions for one owner, one group, and everyone else (other). If you need to set multiple ACLs on a directory, see Setting Extended ACLs.

For example, to set the owner of the /srv/samba/Demo/ directory to root, grant read and write permissions to the owner and the Domain Users group, and deny access to all other users, enter:

# chmod 2770 /srv/samba/Demo/
# chown root:"Domain Users" /srv/samba/Demo/

For further details about the permissions, see the chmod(1) and chown(1) man page.


Setting Extended ACLs

If your file system supports extended access control lists (ACL), you can use extended POSIX ACLs. They enable you to set permissions for multiple users and groups on a file or directory - similar to Windows ACLs. However, POSIX ACLs are limited to the following general permissions modes:

  • None
  • Read
  • Write
  • Full control

For example, to set read, write, and execute permissions for the Domain Admins group, read and execute permissions for the Domain Users group, and deny access to everyone else on the /srv/samba/Demo/ directory:

  • Add the inherit acls = yes parameter to the share's configuration. For example:
[Demo]
       path = /srv/samba/Demo/
       read only = no
       inherit acls = yes
The inherit acls = yes parameter enables ACL inheritance of extended ACLs. For further details, see the parameter description in the smb.conf man page.
  • Reload Samba:
# smbcontrol all reload-config
  • Verify that the directory is stored on a file system that supports extended ACLs. For details, see File System Support.
  • Disable auto-granting permissions for the primary group of user accounts:
# setfacl -m group::--- /srv/samba/Demo/
# setfacl -m default:group::--- /srv/samba/Demo/
The primary group of the directory is additionally mapped to the dynamical CREATOR GROUP principal. If you use extended POSIX ACLs on a Samba share, this principal is automatically added and you cannot remove it. For further details about the CREATOR GROUP principal, see Well-known security identifiers in Windows operating systems.
  • Set the permissions on the directory:
  • Grant read, write, and execute permissions to the Domain Admins group:
# setfacl -m group:"SAMDOM\Domain Admins":rwx /srv/samba/Demo/
  • Grant read and execute permissions to the Domain Users group:
# setfacl -m group:"SAMDOM\Domain Users":r-x /srv/samba/Demo/
  • Set permissions for the other ACL entry to deny access to users that do not match other ACL entries:
# setfacl -R -m other::--- /srv/samba/Demo/
These settings are only applied to the directory itself. In Windows, this is converted to This folder only.
  • To configure that the same permissions set in the previous step are inherited to new file system objects created in this directory, enter:
# setfacl -m default:group:"SAMDOM\Domain Admins":rwx /srv/samba/Demo/
# setfacl -m default:group:"SAMDOM\Domain Users":r-x /srv/samba/Demo/
# setfacl -m default:other::--- /srv/samba/Demo/
With this settings, the This folder only mode for the principals now changed to This folder, subfolders, and files.

The ACLs set in the previous steps are mapped to the following Windows ACLs:

Principal Access Applies to Comments
SAMDOM\Domain Admins Full control This folder, subfolders, and files
SAMDOM\Domain Users Read & execute This folder, subfolders, and files
Everyone None This folder, subfolders, and files Samba maps the permissions for this principal from the UNIX other ACL entry.
directory_owner (Unix User\directory_owner) * Full control This folder only Samba maps the owner of the directory to this entry.
directory_primary_group (Unix User\directory_primary_group) * None This folder only Samba maps the primary group of the directory to this entry.
CREATOR OWNER * Full control Subfolders and files only On new file system objects, the creator inherits automatically the permissions of this principal.
CREATOR GROUP * None Subfolders and files only On new file system objects, the creator's primary group inherits automatically the permissions of this principal.

* Configuring or removing these principals from the ACLs is only supported when using Windows ACLs. For details, see Setting up a Share Using Windows ACLs.

For further details, see the setfacl man page.



Setting Share Permissions

Optional: Samba enables you to set permissions on each share which are validated when a user connects.

Access to the content on a share, is controlled using file system access control lists (ACL). For details, see Setting POSIX ACLs on a Samba Share


Configuring User and Group-based Share Access

Share-based access control enables you to grant or deny access to a share for certain users and groups. For example, to enable all members of the Domain Users group to access a share while access is denied for the example_user account, add the following parameters to the share's configuration:

       valid users = +SAMDOM\"Domain Users"
       invalid users = SAMDOM\example_user

The invalid users parameter has a higher priority than the valid users parameter. For example, if the example_user account is a member of the Domain Users group, access is denied for this account in the previous example.

For further details, see the parameter descriptions in the smb.conf(5) man page.


Configuring Host-based Share Access

Host-based access control enables you to grant or deny access to a share based on host names, IP addresses, or IP ranges. For example, to enable the 127.0.0.1 IP address, the 10.99.0.0/24 IP range, and the GoodHost host name to access a share, and additionally deny access for the BadHost host name, add the following parameters to the share's configuration:

       hosts allow = 127.0.0.1 10.99.0.0/24 GoodHost
       hosts deny = BadHost

The hosts deny parameter has a higher priority than the hosts allow parameter. For example, if BadHost resolves to an IP address that is listed in the hosts allow parameter, access to this host is denied.

For further details, see the parameter descriptions in the smb.conf(5) man page.