Launchpad Bug Tracker <1296...@bugs.launchpad.net> writes:

> So what is happening is that on the initial login, I get a valid ticket
> cache, owned by my logging-in user, and showing my UID in the file name.
> This ticket works fine.  However, once I lock the screen and then unlock
> it, I get a ticket cache owned by root, with "_pam_" in the filename,
> and of course I can't use it because I am not logged in as root.

The _pam_ ticket cache is created during the authenticate step of the PAM
interaction, and is then written to the user's actual ticket cache during
either setcred or open_session.  (setcred is the appropriate thing for a
screen saver to call.)  It's deleted on pam_end.

This sounds like a screen saver that isn't using PAM properly.  It looks
like it's starting a PAM interaction and then only calling authenticate,
never calling setcred, and never ending the PAM interaction, so it leaks a
root-owned ticket cache and never renews your cache.

There used to be widespread problems of this sort due to the number of
people writing screen savers who didn't really understand how PAM worked,
but I thought most of them had been fixed.

You can confirm that it's a problem with this program rather than with
your system configuration by running xscreensaver, locking the screen,
unlocking with your Kerberos password, and seeing if that properly
refreshes your credentials.  I know that xscreensaver does PAM properly.

-- 
Russ Allbery (r...@debian.org)               <http://www.eyrie.org/~eagle/>

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https://bugs.launchpad.net/bugs/1296276

Title:
  light-locker fails to properly renew kerberos tickets with pam-krb5

Status in “light-locker” package in Ubuntu:
  New
Status in “lightdm” package in Ubuntu:
  New

Bug description:
  I am using the pam-krb5 module to log into a Kerberos realm using
  lightdm.  This works the initial time I log in, when I come in through
  lightdm.  However, once I am logged in, and I lock the screen using
  light-locker, when I unlock the screen I no longer get renewed
  tickets.

  The problem seems to be this:

  -rw------- 1 me       me     504 Mar 23 08:37 krb5cc_1000_sjkfhagfg
  -rw------- 1 root   root    504 Mar 23 08:38 krb5cc_pam_lsdkjhfsdk

  So what is happening is that on the initial login, I get a valid
  ticket cache, owned by my logging-in user, and showing my UID in the
  file name.  This ticket works fine.  However, once I lock the screen
  and then unlock it, I get a ticket cache owned by root, with "_pam_"
  in the filename, and of course I can't use it because I am not logged
  in as root.

  This problem did not occur in 12.04 LTS, probably because it did not
  use light-locker.  The pam-krb5 module works in all other cases in my
  installations, so I do not believe this is any kind of problem with
  the pam_krb5 module.

  Thanks,
  Brian

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: light-locker 1.2.1-0ubuntu1
  ProcVersionSignature: Ubuntu 3.13.0-18.38-generic 3.13.6
  Uname: Linux 3.13.0-18-generic x86_64
  ApportVersion: 2.13.3-0ubuntu1
  Architecture: amd64
  Date: Sun Mar 23 08:40:38 2014
  InstallationDate: Installed on 2014-03-22 (0 days ago)
  InstallationMedia: Ubuntu-Server 14.04 LTS "Trusty Tahr" - Alpha amd64 
(20140320)
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: light-locker
  UpgradeStatus: No upgrade log present (probably fresh install)

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