[Bug 1336663] Re: lightdm uses wrong ccache name on pam_krb5 credentials refresh

[Craig G]

FWIW, this issue is also present using gdm3 in Ubuntu 16.04.  With
pam_krb5's debug option set, I see the following during initial login
(with successful credential cache construction):

gdm-password]: pam_krb5(gdm-password:auth): pam_sm_authenticate: entry
gdm-password]: pam_krb5(gdm-password:auth): (user cgallek) attempting authentication as cgallek at XXXX.COM
gdm-password]: pam_krb5(gdm-password:auth): user cgallek authenticated as cgallek at XXXX.COM
gdm-password]: pam_krb5(gdm-password:auth): (user cgallek) temporarily storing credentials in /tmp/krb5cc_pam_LB8CeL
gdm-password]: pam_krb5(gdm-password:auth): pam_sm_authenticate: exit (success)
gdm-password]: pam_krb5(gdm-password:setcred): pam_sm_setcred: entry (establish)
gdm-password]: pam_krb5(gdm-password:setcred): (user cgallek) initializing ticket cache FILE:/tmp/krb5cc_1000_3BiTY0
gdm-password]: pam_krb5(gdm-password:setcred): pam_sm_setcred: exit (success)


When unlocking the screen, I see the following successful credential refresh, but to the wrong cache filename (/tmp/krb5cc_0):

gdm-password]: pam_krb5(gdm-password:auth): pam_sm_authenticate: entry
gdm-password]: pam_krb5(gdm-password:auth): (user cgallek) attempting authentication as cgallek at ANGRYDOUGHNUTS.COM
gdm-password]: pam_krb5(gdm-password:auth): user cgallek authenticated as cgallek at XXXX.COM
gdm-password]: pam_krb5(gdm-password:auth): (user cgallek) temporarily storing credentials in /tmp/krb5cc_pam_Dkg5Ip
gdm-password]: pam_krb5(gdm-password:auth): pam_sm_authenticate: exit (success)
gdm-password]: pam_krb5(gdm-password:setcred): pam_sm_setcred: entry (reinit)
gdm-password]: pam_krb5(gdm-password:setcred): (user cgallek) refreshing ticket cache /tmp/krb5cc_0
gdm-password]: pam_krb5(gdm-password:setcred): pam_sm_setcred: exit (success)

The _0 cache that is created has the correct new credential in it, but
is obviously not known by any other process as it does not match the
earlier version of $KRB5CCNAME.  I imagine this is the same issue
described above where the $KRB5CCNAME environment variable is not
available in the gdm context which unlocks the screen.

It's worth noting that in the GDM case, there appears to be a per-
session helper process (gdm-session-worker) used to communicate with the
GDM service.  This process _does not_ have the $KRB5CCNAME variable set
in its environment.  Would storing the value in this processes
environment fix the problem?

~: ps -ef | grep gdm-session-worker
root     11364 11203  0 Jun25 ?        00:00:00 gdm-session-worker [pam/gdm-password]

~: cat /proc/11364/environ 
LANG=en_US.UTF-8PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/binGDM_SESSION_DBUS_ADDRESS=unix:abstract=/tmp/dbus-oTnmcExV


** Also affects: gdm
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1336663

Title:
  lightdm uses wrong ccache name on pam_krb5 credentials refresh

Status in gdm:
  New
Status in Light Display Manager:
  Triaged
Status in libpam-krb5 package in Ubuntu:
  Confirmed
Status in lightdm package in Ubuntu:
  Triaged

Bug description:
  As already noted by Brian Knoll in https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1296276/comments/24
  lightdm 1.10.1-0ubuntu1 uses an inappropriate credentials cache, /tmp/krb5cc_0, when refreshing Kerberos credentials on screen unlock.

  I couldn't find the new bug Robert Ancell called for in
  https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1296276/comments/27
  so I'm opening one now.

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