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If the /tmp directory of the target user was polyinstantiated, no credentials
cache was found on the remote machine.
Fix:
The cache is now recreated in a new /tmp after pam session is initiated.
DescriptionJan Pazdziora (Red Hat)
2013-06-13 12:15:59 UTC
Description of problem:
If the /tmp directory of the target user is polyinstantiated, even if
klist -f
reports the ticket is forwardable and
GSSAPIDelegateCredentials yes
GSSAPIAuthentication yes
is enabled and ssh -v will report
debug1: Authentication succeeded (gssapi-with-mic).
running klist on the remote machine will say
klist: No credentials cache found (ticket cache FILE:/tmp/krb5cc_501_nPsAJ11386)
The issue was first observed when setting up OpenShift Enterprise with IPA.
Version-Release number of selected component (if applicable):
openssh-server-5.3p1-84.1.el6.x86_64
How reproducible:
Deterministic.
Steps to Reproduce:
1. Have remote system with pam_namespace configured to polyinstantiate /tmp.
2. Have the system accept GSSAPI authentication -- the easiest way is to ipa-client-install both the remote and local system to some IPA server.
3. kinit and verify that you have forwardable ticket.
4. ssh to the remote system as a user for whom /tmp gets polyinstantiated (typically not root).
5. Run klist to see your ticket forwarded.
Actual results:
klist: No credentials cache found (ticket cache FILE:/tmp/krb5cc_501_nPsAJ11386)
Expected results:
Ticket cache: FILE:/tmp/krb5cc_501_ojsOB12112
Default principal: 51b6e6e0cd9a28d6fb000006
Valid starting Expires Service principal
06/13/13 07:54:16 06/14/13 07:52:15 krbtgt/TESTRELM.COM
Additional info:
If you check the /tmp/krb5cc_501_nPsAJ11386 in your remote user's session, it won't exist. If you check it in remote root's session, it will actually exist.
The problem seems to stem from the fact that the Kerberos cache file gets created before the /tmp gets polyinstantiated, so in user's bash, it cannot be accessed.
This bugzilla limits the possibility of OpenShift Enterprise and Identity Management integration.
Created attachment 760670[details]
fixed openssh-5.3p1-gsskex.patch
It's possible to store krb5 credentials after a pam session is created. This patch changes the order. Instead of ssh_gssapi_storecreds(); ssh_selinux_setup_exec_context(); do_pam_session() it has moved ssh_gssapi_storecreds(); to the end of chain.
There's a possible workaround using pam_exec which could be set to wrap up pam_namespace in the pam configuration. A script could copy the cache out of /tmp before pam_namespace is run, and copy back the cache after pam namespace set a new /tmp. Something similar to:
snip pam config:
session optional pam_exec.so /etc/security/namespace.d/kerberos
session required pam_namespace.so
session optional pam_exec.so /etc/security/namespace.d/kerberos 1
# cat /etc/security/namespace.d/kerberos
#!/bin/bash
if [ -z "$KRB5CCNAME" ]; then
exit 0
fi
CCNAME=${KRB5CCNAME#FILE:}
if [ ${CCNAME#/tmp} == ${CCNAME} ]; then
exit 0
fi
if [ $# -eq 0 ]; then
tar cvf /var/tmp/krbcc/${CCNAME//\//-}.tar $CCNAME
rm -rf ${CCNAME}
exit 0
fi
if [ $# -eq 1 ]; then
tar -C / -x -v -p -f /var/tmp/krbcc/${CCNAME//\//-}.tar
rm /var/tmp/krbcc/${CCNAME//\//-}.tar
exit 0
fi
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
http://rhn.redhat.com/errata/RHSA-2013-1591.html