Managing Operation Policies

Managing Operation Policies

Operation policies are the rules used for each IPP operation in CUPS. These rules include things like "user must provide a password", "user must be in the system group", "allow only from the local system", and so forth. Until CUPS 1.2, these rules were largely hardcoded and could only be customized at a very basic level.

CUPS 1.2 and later provides a fine-grained policy layer which allows you to completely redefine the rules for each operation and/or printer. Each policy is named and defines access control rules for each IPP operation. This document describes how to manage policies and their rules.

The Basics

Operation policies are used for all IPP requests sent to the scheduler and are evaluated after the Location based access control rules. This means that operation policies can only add additional security restrictions to a request, never relax them. Use Location based access control rules for server-wide limits and operation policies for limits on individual printers, tasks, or services.

Policies are stored in the cupsd.conf file in Policy sections. Each policy has an alphanumeric name that is used to select it. Inside the policy section are one or more Limit subsections which list the operations that are affected by the rules inside it. Listing 1 shows the default operation policy, appropriately called "default", that is shipped with CUPS.

The easiest way to add a policy to the cupsd.conf file is to use the web interface. Click on the Administration tab and then the Edit Configuration File button to edit the current cupsd.conf file. Click on the Save Changes button to save the changes and restart the scheduler. If you edit the cupsd.conf file from the console, make sure to restart the cupsd process before trying to use the new policy.

Listing 1: Default Operation Policy

 1    <Policy default>
 2      # Job-related operations must be done by the owner or an
      administrator...
 3      <Limit Send-Document Send-URI Hold-Job Release-Job
      Restart-Job Purge-Jobs Set-Job-Attributes
      Create-Job-Subscription Renew-Subscription
      Cancel-Subscription Get-Notifications Reprocess-Job
      Cancel-Current-Job Suspend-Current-Job Resume-Job
      CUPS-Move-Job CUPS-Get-Document>
 4        Require user @OWNER @SYSTEM
 5        Order deny,allow
 6      </Limit>
 7
 8      # All administration operations require an administrator
      to authenticate...
 9      <Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class
      CUPS-Delete-Class CUPS-Set-Default>
10        AuthType Default
11        Require user @SYSTEM
12        Order deny,allow
13      </Limit>
14
15      # All printer operations require a printer operator
      to authenticate...
16      <Limit Pause-Printer Resume-Printer
      Set-Printer-Attributes Enable-Printer Disable-Printer
      Pause-Printer-After-Current-Job Hold-New-Jobs
      Release-Held-New-Jobs Deactivate-Printer Activate-Printer
      Restart-Printer Shutdown-Printer Startup-Printer
      Promote-Job Schedule-Job-After CUPS-Accept-Jobs
      CUPS-Reject-Jobs>
17        AuthType Default
18        Require user varies by OS
19        Order deny,allow
20      </Limit>
21
22      # Only the owner or an administrator can cancel or
      authenticate a job...
23      <Limit Cancel-Job CUPS-Authenticate-Job>
24        Require user @OWNER @SYSTEM
25        Order deny,allow
26      </Limit>
27
28      <Limit All>
29        Order deny,allow
30      </Limit>
31    </Policy>

The Default CUPS Operation Policy

The policy definition starts with an opening Policy directive:

 1    <Policy default>

The first Limit subsection defines the rules for IPP job operations:

 3      <Limit Send-Document Send-URI Hold-Job Release-Job
      Restart-Job Purge-Jobs Set-Job-Attributes
      Create-Job-Subscription Renew-Subscription
      Cancel-Subscription Get-Notifications Reprocess-Job
      Cancel-Current-Job Suspend-Current-Job Resume-Job
      CUPS-Move-Job CUPS-Get-Document>
 4        Require user @OWNER @SYSTEM
 5        Order deny,allow
 6      </Limit>

The operation names are listed on a single line with spaces separating them. Each name corresponds to the IPP operation described in any of the IETF or PWG standards documents for the Internet Printing Protocol. Table 1 lists all of the operations that have been defined along with their usage in CUPS.

The access control rules are listed after the Limit line and are the same as those used for Location sections. In this case, we require the owner of the job ("@OWNER") or a member of the SystemGroup ("@SYSTEM") to do the operation. Because we do not include an AuthType directive here, the user information can come from the IPP request itself or the authenticated username from the HTTP request. The administrative operations starting on line 9, however, do use the AuthType directive, and so administrative operations need to be authenticated:

 9      <Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class
      CUPS-Delete-Class CUPS-Set-Default>
10        AuthType Default
11        Require user @SYSTEM
12        Order deny,allow
13      </Limit>
14
15      # All printer operations require a printer operator
      to authenticate...
16      <Limit Pause-Printer Resume-Printer
      Set-Printer-Attributes Enable-Printer Disable-Printer
      Pause-Printer-After-Current-Job Hold-New-Jobs
      Release-Held-New-Jobs Deactivate-Printer Activate-Printer
      Restart-Printer Shutdown-Printer Startup-Printer
      Promote-Job Schedule-Job-After CUPS-Accept-Jobs
      CUPS-Reject-Jobs>
17        AuthType Default
18        Require user varies by OS
19        Order deny,allow
20      </Limit>

The "Order deny,allow" line at the end of both Limit subsections allows the request to come from any system allowed by the Location sections elsewhere in the cupsd.conf file.

The Cancel-Job and CUPS-Authenticate-Job operations are listed separately to allow the web interface to more easily edit their policy without disturbing the rest. Like the rest of the job operations, we want the job's owner ("@OWNER") or an administrator ("@SYSTEM") to do it:

16      <Limit Cancel-Job CUPS-Authenticate-Job>
17        Require user @OWNER @SYSTEM
18        Order deny,allow
19      </Limit>

The last Limit subsection in any policy uses the special operation name All. CUPS will use the rules in this subsection for any operation you don't list specifically in the policy. In this case, all other operations are allowed without a username or authentication:

21      <Limit All>
22        Order deny,allow
23      </Limit>
24    </Policy>
Table 1: IPP Operation Names
Name Used by CUPS? Description
Activate-Printer No Activates a printer or class.
Cancel-Current-Job No Cancels the current job on a printer or class.
Cancel-Job Yes Cancels a print job.
Cancel-Jobs Yes Cancels all print jobs.
Cancel-My-Jobs Yes Cancels a user's print job.
Cancel-Subscription Yes Cancels an event subscription.
Close-Job Yes Closes a user's print job so that it can be printed.
Create-Job Yes Creates a print job with no files or URIs.
Create-Job-Subscriptions Yes Creates one or more event subscriptions for a job.
Create-Printer-Subscriptions Yes Creates one or more event subscriptions for a printer or the server.
Deactivate-Printer No Deactivates a printer or class.
Disable-Printer Yes Stops a printer or class.
Enable-Printer Yes Starts a printer or class.
Get-Job-Attributes Yes Gets information and options associated with a job.
Get-Jobs Yes Gets a list of jobs.
Get-Notifications Yes Gets (pending) events for an event subscription.
Get-Printer-Attributes Yes Gets information and options associated with a printer or class.
Get-Printer-Supported-Values Yes Gets -supported attributes for a printer based on job options.
Get-Subscription-Attributes Yes Gets information for an event subscription.
Get-Subscriptions Yes Gets a list of event subscriptions.
Hold-Job Yes Holds a print job for printing.
Hold-New-Jobs Yes Holds new jobs submitted to a printer or class.
Pause-Printer Yes Stops a printer or class.
Pause-Printer-After-Current-Job No Stops a printer or class after the current job is finished.
Print-Job Yes Creates a print job with a single file.
Print-URI No Create a print job with a single URI.
Promote-Job No Prints a job before others.
Purge-Jobs Yes Cancels all jobs on the server or a printer or class and removes the job history information.
Release-Held-New-Jobs Yes Releases jobs that were held because of the Hold-New-Jobs operation.
Release-Job Yes Releases a print job for printing.
Renew-Subscription Yes Renews an event subscription that is about to expire.
Reprocess-Job No Reprints a job on a different printer or class; CUPS has the CUPS-Move-Job operation instead.
Restart-Job Yes Reprints a print job.
Restart-Printer No Restarts a printer or class, resuming print jobs as needed.
Resubmit-Job No Reprints a job with new options.
Resume-Job No Resumes printing of a stopped job.
Resume-Printer Yes Starts a printer or class.
Schedule-Job-After No Prints a job after others.
Send-Document Yes Adds a file to a print job.
Send-URI No Adds a URI to a print job.
Set-Printer-Attributes Yes Sets printer or class information; CUPS uses CUPS-Add-Modify-Printer and CUPS-Add-Modify-Class for most attributes instead.
Set-Job-Attributes Yes Changes job options.
Shutdown-Printer No Powers a printer or class off.
Startup-Printer No Powers a printer or class on.
Suspend-Current-Job No Stops the current job on a printer or class.
Validate-Document No Validates a document request before sending.
Validate-Job Yes Validates a print request before printing.
CUPS-Accept-Jobs Yes Sets a printer's or class' printer-is-accepting-jobs attribute to true.
CUPS-Add-Modify-Class Yes Adds or modifies a class.
CUPS-Add-Modify-Printer Yes Adds or modifies a printer.
CUPS-Authenticate-Job Yes Authenticates a job for printing.
CUPS-Delete-Class * Yes Removes a class.
CUPS-Delete-Printer * Yes Removes a printer.
CUPS-Get-Classes * Yes Gets a list of classes.
CUPS-Get-Default * Yes Gets the server/network default printer or class.
CUPS-Get-Devices * Yes Gets a list of printer devices.
CUPS-Get-Document Yes Retrieves a document file from a job.
CUPS-Get-PPDs * Yes Gets a list of printer drivers or manufacturers.
CUPS-Get-Printers * Yes Gets a list of printers and/or classes.
CUPS-Move-Job Yes Moves a job to a different printer or class.
CUPS-Reject-Jobs Yes Sets a printer's or class' printer-is-accepting-jobs attribute to false.
CUPS-Set-Default * Yes Sets the server/network default printer or class.

* = These operations only apply to the default policy.

Creating Your Own Policies

The easiest way to create a new policy is to start with the default policy and then make changes to the copy. The first change you'll make is to give the policy a new name. Policy names can use the same characters as a printer name, specifically all printable characters except space, slash (/), and pound (#):

<Policy mypolicy>

Then you need to decide exactly what limits you want for the policy. For example, if you want to allow any user to cancel any other users' jobs, you can change the Cancel-Job limits to:

<Limit Cancel-Job>
  Order deny,allow
</Limit>

The directives inside the Limit subsection can use any of the normal limiting directives: Allow, AuthType, Deny, Encryption, Require, and Satisfy. Table 2 lists some basic "recipes" for different access control rules.

Table 2: Access Control Recipes
Access Level Directives to Use
Allow Everyone
Order deny,allow
Allow from all
Allow Everyone on the Local Network
Order deny,allow
Allow from @LOCAL
Deny Everyone/Disable Operation(s)
Order deny,allow
Require Login (System) Password
AuthType Basic
Require CUPS (lppasswd) Password
AuthType BasicDigest
Require Kerberos
AuthType Negotiate
Require the Owner of a Job or Subscription
Require user @OWNER
Require an Administrative User
Require user @SYSTEM
Require Member of Group "foogroup"
Require user @foogroup
Require "john" or "mary"
Require user john mary
Require Encryption
Encryption Required

Creating a Policy for a Computer Lab

One common operating scenario is a computer lab. The lab is managed by one or more technicians that assist the users of the lab and handle the basic administration tasks. Listing 2 shows an operation policy that only allows access from the lab's subnet, 10.0.2.x, and allows the lab technicians, who are members of a special UNIX group for that lab called "lab999", to do job, printer, and subscription management operations.

Listing 2: Operation Policy for a Lab

 1    <Policy lab999>
 2      # Job- and subscription-related operations must be done
      by the owner, a lab technician, or an administrator...
 3      <Limit Send-Document Send-URI Hold-Job Release-Job
      Restart-Job Purge-Jobs Set-Job-Attributes
      Create-Job-Subscription Renew-Subscription
      Cancel-Subscription Get-Notifications Reprocess-Job
      Cancel-Current-Job Suspend-Current-Job Resume-Job
      CUPS-Move-Job Cancel-Job CUPS-Authenticate-Job CUPS-Get-Document>
 4        Require user @OWNER @lab999 @SYSTEM
 5        Order allow,deny
 6        Allow from 10.0.2.0/24
 7      </Limit>
 8
 9      # All administration operations require a lab technician
      or an administrator to authenticate...
10      <Limit Pause-Printer Resume-Printer
      Set-Printer-Attributes Enable-Printer Disable-Printer
      Pause-Printer-After-Current-Job Hold-New-Jobs
      Release-Held-New-Jobs Deactivate-Printer Activate-Printer
      Restart-Printer Shutdown-Printer Startup-Printer
      Promote-Job Schedule-Job-After CUPS-Accept-Jobs
      CUPS-Reject-Jobs CUPS-Set-Default>
11        AuthType Default
12        Require user @lab999 @SYSTEM
13        Order allow,deny
14        Allow from 10.0.2.0/24
15      </Limit>
16
17      # All other operations are allowed from the lab network...
18      <Limit All>
19        Order allow,deny
20        Allow from 10.0.2.0/24
21      </Limit>
22    </Policy>

Using Policies

Once you have created a policy, you can use it in two ways. The first way is to assign it as the default policy for the system using the DefaultPolicy directive in the cupsd.conf file. For example, add the following line to the cupsd.conf file to use the "lab999" policy from the previous section:

DefaultPolicy lab999

To associate the policy with one or more printers, use either the lpadmin(8) command or the web interface to change the operation policy for each printer. When using the lpadmin command, the -o printer-op-policy=name option sets the operation policy for a printer. For example, enter the following command to use the "lab999" policy from the previous section with a printer named "LaserJet4000":

lpadmin -p LaserJet4000 -o printer-op-policy=lab999

To make the same change in the web interface, go to the printer's web page, for example "http://localhost:631/printers/LaserJet4000", and choose Set Default Options from the Administration menu button. Click on the Policies link and choose the desired policy from the pull-down list. Click on Set Default Options to change the policy for the printer.