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Bug 1855770 - auditd cannot write into reply cache (/var/tmp/krb5_0.rcache2) due to security context
Summary: auditd cannot write into reply cache (/var/tmp/krb5_0.rcache2) due to securit...
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 8
Classification: Red Hat
Component: selinux-policy
Version: 8.3
Hardware: All
OS: Linux
medium
medium
Target Milestone: rc
: 8.3
Assignee: Zdenek Pytela
QA Contact: Milos Malik
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2020-07-10 12:59 UTC by Ondrej Moriš
Modified: 2020-11-04 01:58 UTC (History)
5 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2020-11-04 01:57:16 UTC
Type: Bug
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Bugzilla 1841488 0 medium CLOSED sshd cannot write into reply cache (/var/tmp/krb5_0.rcache2) due to security context 2021-02-22 00:41:40 UTC
Red Hat Product Errata RHBA-2020:4528 0 None None None 2020-11-04 01:57:27 UTC

Description Ondrej Moriš 2020-07-10 12:59:42 UTC 
Description of problem:

After recent rebase of krb5 (1.17 -> 1.18) in RHEL-8.3.0 audit remote logging using securing communication via KRB5 stopped working with the following AVC:

time->Fri Jul 10 07:36:37 2020
type=PROCTITLE msg=audit(1594380997.750:3561): proctitle="/sbin/auditd"
type=SYSCALL msg=audit(1594380997.750:3561): arch=c000003e syscall=257 success=no exit=-13 a0=ffffff9c a1=560e5c73cf70 a2=20042 a3=180 items=0 ppid=1 pid=28528 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="auditd" exe="/usr/sbin/auditd" subj=system_u:system_r:auditd_t:s0 key=(null)
type=AVC msg=audit(1594380997.750:3561): avc:  denied  { write } for  pid=28528 comm="auditd" name="krb5_0.rcache2" dev="vda1" ino=6916127 scontext=system_u:system_r:auditd_t:s0 tcontext=system_u:object_r:kadmind_tmp_t:s0 tclass=file permissive=0

Version-Release number of selected component (if applicable):

selinux-policy-3.14.3-48.el8
krb5-server-1.18.2-3.el8

How reproducible:

100%

Steps to Reproduce:

1. Enable audit remote logging using KRB5 to secure communication.

Actual results:

Remote logging does not work, AVC produced.

Expected results:

Remote logging works, no AVC.

Additional info:

Works fine with krb5-server-1.17, see also BZ#1841488 for wider context.
Comment 1 Ondrej Moriš 2020-07-10 13:02:40 UTC 
KRB5 is the only way to secure communication between server and clients in audit remote logging (see e.g. [1]). We have automated test case (linked) and I can help with verification of this bug.

[1] https://access.redhat.com/articles/3975971
Comment 4 Zdenek Pytela 2020-07-29 15:25:07 UTC 
I've submitted a Fedora PR to address the issue:
https://github.com/fedora-selinux/selinux-policy/pull/400
Comment 11 Ondrej Moriš 2020-08-17 19:03:48 UTC 
There is still some selinux-related bug I am not able to investigate. I do not see any AVC - not even in permissive mode but even with selinux-policy-3.14.3-51.el8.noarch audit remote logging using KRB5 still works ONLY when both client and server are in permissive mode. File /var/tmp/krb5_0.rcache2 is krb5_host_rcache_t but it seems not to be enough. Are there any tricks how to investigate this?

In enforcing mode I see the following in the journal:

SERVER:

Aug 17 14:53:41 ci-vm-10-0-139-99.hosted.upshift.rdu2.redhat.com auditd[62901]: TCP session from ::ffff:10.0.139.243:56008 will be closed, error ignored

CLIENT:

Aug 17 14:53:40 ci-vm-10-0-139-243.hosted.upshift.rdu2.redhat.com kcm[165210]: Starting up
Aug 17 14:53:40 ci-vm-10-0-139-243.hosted.upshift.rdu2.redhat.com audisp-remote[165188]: GSS error: initializing context: Unspecified GSS failure.  Minor code may provide more information
Aug 17 14:53:40 ci-vm-10-0-139-243.hosted.upshift.rdu2.redhat.com audisp-remote[165188]: GSS error: initializing context: No Kerberos credentials available (default cache: KCM:)
Aug 17 14:53:40 ci-vm-10-0-139-243.hosted.upshift.rdu2.redhat.com audisp-remote[165188]: startup network failure, First attempt at connecting to server unsuccessful
Aug 17 14:53:40 ci-vm-10-0-139-243.hosted.upshift.rdu2.redhat.com audisp-remote[165188]: socket already setup
Aug 17 14:53:40 ci-vm-10-0-139-243.hosted.upshift.rdu2.redhat.com audisp-remote[165188]: GSS error: encrypting message: A required input parameter could not be read
Aug 17 14:53:40 ci-vm-10-0-139-243.hosted.upshift.rdu2.redhat.com audisp-remote[165188]: GSS error: encrypting message: No context has been established
Aug 17 14:53:40 ci-vm-10-0-139-243.hosted.upshift.rdu2.redhat.com audisp-remote[165188]: kerberos principal: auditd/ci-vm-10-0-139-243.hosted.upshift.rdu2.redhat.com.COM

When I switch both server and client to permissive and restard auditd on both sides, it work just fine but I do not see any AVC (even with disabled dontaudit rules).
Comment 12 Zdenek Pytela 2020-08-19 10:07:25 UTC 
Ondrej,

Disabling dontaudit rules is the only way how to disclose any hidden denials:

  # semodule -DB

I'd rather try it first in enforcing mode as in permissive subsequent denials are not audited.
Comment 15 errata-xmlrpc 2020-11-04 01:57:16 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 (selinux-policy bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:4528
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