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

m (Added category)
(Added section "Setting Extended ACLs" + a few minor updates.)
Line 8: Line 8:
 
{{Imbox
 
{{Imbox
 
| type = important
 
| type = important
| text = On a Samba Active Directory (AD) domain controller (DC), extended ACL support is enabled globally and thus shares using POSIX ACLs are not supported. Samba AD DCs only support shares using Windows ACLs.
+
| text = On a Samba Active Directory (AD) domain controller (DC), Windows ACL support is enabled globally and thus shares using POSIX ACLs are not supported.
 
}}
 
}}
  
Line 45: Line 45:
 
= Adding a Share =
 
= Adding a Share =
  
To share the <code>/srv/samba/Demo/</code> folder using the <code>Demo</code> share name:
+
To share the <code>/srv/samba/Demo/</code> directory using the <code>Demo</code> share name:
  
* Create the folder:
+
* Create the directory:
  
 
  # mkdir -p /srv/samba/Demo/
 
  # mkdir -p /srv/samba/Demo/
Line 67: Line 67:
  
  
= Setting POSIX ACLs on a Samba Share =
+
= Setting ACLs =
  
To control access to folders on a share, use the operating system-specific tools. For example, to set the owner of the <code>/srv/samba/Demo/Example/</code> directory to <code>root</code>, grant read and write permissions to the owner and the <code>Domain User</code> group, and deny access to all other users, enter:
+
== Setting Standard UNIX ACLs ==
  
  # chmod 2770 /srv/samba/Demo/Example/
+
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]].
  # chown root:"Demo Group" /srv/samba/Demo/Example/
+
 
 +
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 User</code> group, and deny access to all other users, enter:
 +
 
 +
  # chmod 2770 /srv/samba/Demo/
 +
  # chown root:"Demo Group" /srv/samba/Demo/
  
 
{{Imbox
 
{{Imbox
Line 80: Line 84:
  
 
For further details about the permissions, see the <code>chmod(1)</code> and <code>chown(1)</code> man page.
 
For further details about the permissions, see the <code>chmod(1)</code> and <code>chown(1)</code> man page.
 +
 +
 +
 +
== Setting Extended ACLs ==
 +
 +
If your file system supports extended access control lists (ACL), you can use extended ACLs to set permissions for multiple users and groups on a directory.
 +
To set extended ACLs on a directory, use the <code>setfacl</code> utility.
 +
 +
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]
 +
        path = /srv/samba/Demo/
 +
        read only = no
 +
        inherit acls = yes
 +
: 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.
  
  

Revision as of 19:28, 11 April 2017

Introduction

Samba enables you to create file shares using POSIX access control lists (ACL) on:

  • Domain members
  • NT4 PDC and BDCs
  • Standalone hosts

As an alternative to POSIX ACLs, you can set up shares using Windows ACLs. For details, see Setting up a Share Using Windows ACLs.



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] 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 User group, and deny access to all other users, enter:

# chmod 2770 /srv/samba/Demo/
# chown root:"Demo Group" /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 ACLs to set permissions for multiple users and groups on a directory. To set extended ACLs on a directory, use the setfacl utility.

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 to the code>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 the 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.