974096 – Kerberos ticket forwarding does not work if /tmp is polyinstantiated

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Bug 974096 - Kerberos ticket forwarding does not work if /tmp is polyinstantiated

Summary: Kerberos ticket forwarding does not work if /tmp is polyinstantiated

Keywords:
Status:	CLOSED ERRATA
Alias:	None
Product:	Red Hat Enterprise Linux 6
Classification:	Red Hat
Component:	openssh
Sub Component:
Version:	6.4
Hardware:	All
OS:	Linux
Priority:	high
Severity:	high
Target Milestone:	rc
Target Release:	---
Assignee:	Petr Lautrbach
QA Contact:	Lukas "krteknet" Novy
Docs Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+	depends on / blocked

Reported:	2013-06-13 12:15 UTC by Jan Pazdziora (Red Hat)
Modified:	2014-02-18 23:56 UTC (History)
CC List:	6 users (show)
Fixed In Version:
Doc Type:	Bug Fix
Doc Text:	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.
Clone Of:
Clones:	1083495 (view as bug list)
Environment:
Last Closed:	2013-11-21 09:46:31 UTC
Target Upstream Version:
Embargoed:

Attachments	(Terms of Use)
fixed openssh-5.3p1-gsskex.patch (90.35 KB, patch) 2013-06-13 13:00 UTC, Petr Lautrbach	no flags	Details \| Diff
View All

Links
System	ID	Private	Priority	Status	Summary	Last Updated
Red Hat Product Errata	RHSA-2013:1591	0	normal	SHIPPED_LIVE	Low: openssh security, bug fix, and enhancement update	2013-11-20 21:39:30 UTC

Description Jan 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.

Comment 1 Petr Lautrbach 2013-06-13 13:00:11 UTC

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.

Comment 12 Petr Lautrbach 2013-07-31 15:22:31 UTC

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

Comment 13 Petr Lautrbach 2013-08-14 14:35:06 UTC

An update pushed with a fix based on https://bugzilla.redhat.com/show_bug.cgi?id=987792#c6 suggestion

Comment 16 errata-xmlrpc 2013-11-21 09:46:31 UTC

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

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