[cups] Odd cups/ldap interaction

[Michael Sweet]

David,

This is likely a PAM bug of some kind - cupsd is a long-lived process on the server, so the PAM module we talk to for authentication also sticks around a long time.  My guess is that the LDAP server is disconnecting but the PAM module isn't retrying its connection to the server.


> On Jun 28, 2016, at 4:04 PM, LeFevre, David C <dlefevre at purdue.edu> wrote:
> 
> Hello!
> 
> I've got an odd problem going on with a new installation of cups on RHEL7 and I am
> having a weird interaction with ldap that I can't figure out.  The version of CUPS
> that RHEL7 packages is 1.6.3 right now.
> 
> First of all, I am *not* trying to set up CUPS to talk to ldap.  I have CUPS set up 
> as plain Basic Authentication.  I don't want any interaction at all between CUPS
> and ldap.
> 
> Second, we still use the older pam_ldap setup and nslcd, not the sssd that Redhat actually wants us to use. (long story)
> 
> What happens is that after a certain period of time (usually 8-12 hours) ldap stops 
> being able to do lookups for users logging in.  The log entry 
> when someone logs on looks  something like this:
> 
> Jun 28 15:20:14 cupshost nslcd[2438]: [695dec] <authc="**something**"> <something,something>,dc=edu: lookup failed: Invalid credentials
> 
> ldapsearch continues to work.
> 
> It took me a while to even think about CUPS while looking into this, but I've 
> found today that restarting the CUPS daemon actually solves the issue with 
> the logins.  Why would that be? I can't even figure out what to check.
> 
> I'll paste an obscured version of my cups.conf below.  I'm still kind of new 
> with administering a cups server, so maybe someone can give me an idea of 
> what to look for.  I've got a cronjob restarting cups to work around the issue, 
> but that is hardly an elegant solution.
> 
> --
> 
> ######################################
> ######################################
> 
> MaxLogSize 0
> #
> # "$Id: cupsd.conf.in 7888 2008-08-29 21:16:56Z mike $"
> #
> # Sample configuration file for the CUPS scheduler.  See "man cupsd.conf" for a
> # complete description of this file.
> #
> 
> # Log general information in error_log - change "warn" to "debug"
> # for troubleshooting...
> LogLevel debug
> 
> # Only listen for connections from the local machine.
> Listen *:631
> Listen /var/run/cups/cups.sock
> 
> # Show shared printers on the local network.
> Browsing off
> #BrowseOrder allow,deny
> #BrowseDeny all
> #BrowseAllow none
> 
> # Default authentication type, when authentication is required...
> DefaultAuthType Basic
> 
> # Web interface setting...
> WebInterface Yes
> 
> # turn this to on if in trouble
> PreserveJobFiles Off
> 
> # Restrict access to the server...
> <Location />
>   ##left out, don't need to know
> </Location>
> 
> <Location /admin>
>  ##left out, don't need to know    
> </Location>
> 
> # Restrict access to configuration files...
> <Location /admin/conf>
>  AuthType Default
>  Require user @SYSTEM
>  Order allow,deny
> </Location>
> 
> # Set the default printer/job policies...
> <Policy default>
>  # Job/subscription privacy...
>  JobPrivateAccess default
>  JobPrivateValues none
>  SubscriptionPrivateAccess default
>  SubscriptionPrivateValues default
> 
>  # Job-related operations must be done by the owner or an administrator...
>  <Limit Create-Job Print-Job Print-URI Validate-Job>
>    Order deny,allow
>  </Limit>
> 
>  <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 Cancel-My-Jobs Close-Job CUPS-Move-Job CUPS-Get-Document>
>    Require user @OWNER @SYSTEM
>    Order deny,allow
>  </Limit>
> 
>  # All administration operations require an administrator to authenticate...
>  <Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class CUPS-Delete-Class CUPS-Set-Default CUPS-Get-Devices>
>    AuthType Default
>    Require user @SYSTEM
>    Order deny,allow
>  </Limit>
> 
>  # All printer operations require a printer operator to authenticate...
>  <Limit Pause-Printer Resume-Printer 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 Cancel-Jobs CUPS-Accept-Jobs CUPS-Reject-Jobs>
>    AuthType Default
>    Require user @SYSTEM
>    Order deny,allow
>  </Limit>
> 
>  # Only the owner or an administrator can cancel or authenticate a job...
>  <Limit Cancel-Job CUPS-Authenticate-Job>
>    Require user @OWNER @SYSTEM
>    Order deny,allow
>  </Limit>
> 
>  <Limit All>
>    Order deny,allow
>  </Limit>
> </Policy>
> 
> # Set the authenticated printer/job policies...
> <Policy authenticated>
>  # Job/subscription privacy...
>  JobPrivateAccess default
>  JobPrivateValues default
>  SubscriptionPrivateAccess default
>  SubscriptionPrivateValues default
> 
>  # Job-related operations must be done by the owner or an administrator...
>  <Limit Create-Job Print-Job Print-URI Validate-Job>
>    AuthType Default
>    Order deny,allow
>  </Limit>
> 
>  <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 Cancel-My-Jobs Close-Job CUPS-Move-Job CUPS-Get-Document>
>    AuthType Default
>    Require user @OWNER @SYSTEM
>    Order deny,allow
>  </Limit>
> 
>  # All administration operations require an administrator to authenticate...
>  <Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class CUPS-Delete-Class CUPS-Set-Default>
>    AuthType Default
>    Require user @SYSTEM
>    Order deny,allow
>  </Limit>
> 
>  # All printer operations require a printer operator to authenticate...
>  <Limit Pause-Printer Resume-Printer 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 Cancel-Jobs CUPS-Accept-Jobs CUPS-Reject-Jobs>
>    AuthType Default
>    Require user @SYSTEM
>    Order deny,allow
>  </Limit>
> 
>  # Only the owner or an administrator can cancel or authenticate a job...
>  <Limit Cancel-Job CUPS-Authenticate-Job>
>    AuthType Default
>    Require user @OWNER @SYSTEM
>    Order deny,allow
>  </Limit>
> 
>  <Limit All>
>    Order deny,allow
>  </Limit>
> </Policy>
> 
> #
> # End of "$Id: cupsd.conf.in 7888 2008-08-29 21:16:56Z mike $".
> 
> 
> 
> 
> 
> Thanks!
> 
> -dcl
> Dave LeFevre
> _______________________________________________
> cups mailing list
> cups at cups.org
> https://www.cups.org/mailman/listinfo/cups

_________________________________________________________
Michael Sweet, Senior Printing System Engineer