[cups] Odd cups/ldap interaction

Tue Jun 28 13:04:40 PDT 2016

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