Bug 2112001

Summary:	cron should not be using pam_systemd, leading to CRED failed in audit
Product:	Red Hat Enterprise Linux 9	Reporter:	Welterlen Benoit <bwelterl>
Component:	systemd	Assignee:	Michal Sekletar <msekleta>
Status:	CLOSED MIGRATED	QA Contact:	Frantisek Sumsal <fsumsal>
Severity:	high	Docs Contact:
Priority:	unspecified
Version:	9.0	CC:	brian, bwelterl, jstanek, lionel.cons, msekleta, opohorel, pbrezina, qguo, rhel-cs-apps-subsystem-qe, systemd-maint-list
Target Milestone:	rc	Keywords:	MigratedToJIRA
Target Release:	---	Flags:	pm-rhel: mirror+
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:	2053750	Environment:
Last Closed:	2023-09-21 11:52:52 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2053750
Bug Blocks:

Description Welterlen Benoit 2022-07-28 15:15:52 UTC

+++ This bug was initially created as a clone of Bug #2053750 +++

Description of problem:
Every user cron job is spamming the logs with systemd session messages.

In RHEL9, we also have an CRED error in audit:

type=CRED_ACQ msg=audit(07/18/22 14:34:01.335:375) : pid=4429 uid=root auid=unset ses=unset subj=system_u:system_r:crond_t:s0-s0:c0.c1023 msg='op=PAM:setcred grantors=pam_env,pam_unix acct=test exe=/usr/sbin/crond hostname=? addr=? terminal=cron res=success' 
type=CRED_ACQ msg=audit(07/18/22 14:34:01.478:379) : pid=4432 uid=root auid=unset ses=unset subj=system_u:system_r:init_t:s0 msg='op=PAM:setcred grantors=? acct=test exe=/usr/lib/systemd/systemd hostname=? addr=? terminal=? res=failed'  

Version-Release number of selected component (if applicable):
cronie-1.5.7-5.el9.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Create a cron job for a user at some reasonably high frequency, say every 5 minutes
2. Wait for cron job to fire

Actual results:
For every job, messages file is spammed with the like of:

04:06:01 systemd Created slice User Slice of UID 1001.
04:06:01 systemd Starting User runtime directory /run/user/1001...
04:06:01 systemd Started User runtime directory /run/user/1001.
04:06:01 systemd Starting User Manager for UID 1001...
04:06:02 systemd Starting D-Bus User Message Bus Socket.
04:06:02 systemd Started Mark boot as successful after the user session has run 2 minutes.
04:06:02 systemd Reached target Timers.
04:06:02 systemd Reached target Paths.
04:06:02 systemd Listening on D-Bus User Message Bus Socket.
04:06:02 systemd Reached target Sockets.
04:06:02 systemd Reached target Basic System.
04:06:02 systemd Started User Manager for UID 1001.
04:06:02 systemd Reached target Default.
04:06:02 systemd Startup finished in 65ms.
04:06:02 systemd pam_unix(systemd-user:session): session opened for user brian by (uid=0)
04:06:06 systemd session-2180.scope: Succeeded.
04:06:13 systemd session-2177.scope: Succeeded.
04:06:16 systemd Stopping User Manager for UID 1001...
04:06:16 systemd Stopped target Default.
04:06:16 systemd Stopped target Basic System.
04:06:16 systemd Stopped target Timers.
04:06:16 systemd Stopped Mark boot as successful after the user session has run 2 minutes.
04:06:16 systemd Stopped target Paths.
04:06:16 systemd Stopped target Sockets.
04:06:16 systemd Closed D-Bus User Message Bus Socket.
04:06:16 systemd Reached target Shutdown.
04:06:16 systemd Starting Exit the Session...
04:06:16 systemd user: Succeeded.
04:06:16 systemd Stopped User Manager for UID 1001.
04:06:16 systemd Stopping User runtime directory /run/user/1001...
04:06:16 systemd run-user-1001.mount: Succeeded.
04:06:16 systemd user-runtime-dir: Succeeded.
04:06:16 systemd Stopped User runtime directory /run/user/1001.
04:06:16 systemd Removed slice User Slice of UID 1001.
04:06:16 systemd pam_unix(systemd-user:session): session closed for user brian

in audit:

type=CRED_ACQ msg=audit(07/18/22 14:34:01.478:379) : pid=4432 uid=root auid=unset ses=unset subj=system_u:system_r:init_t:s0 msg='op=PAM:setcred grantors=? acct=test exe=/usr/lib/systemd/systemd hostname=? addr=? terminal=? res=failed'  

Expected results:
No landslide of systemd spam for each and every cron job run
No CRED fail in audit

Additional info:

I workaround that with this pam system-auth config:

---
#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authselect is run.
auth        required      pam_env.so
auth        sufficient    pam_unix.so try_first_pass nullok
auth        required      pam_deny.so

account     required      pam_unix.so

password    requisite     pam_pwquality.so try_first_pass local_users_only retry=3 authtok_type=
password    sufficient    pam_unix.so try_first_pass use_authtok nullok sha512 shadow
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
-session     optional      pam_systemd.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so
---

Comment 1 Iker Pedrosa 2022-09-01 13:34:08 UTC

I guess your proposal would be to change system-auth. More specifically to move the following one line above:
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid

From:
session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
-session     optional      pam_systemd.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so

To:
session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
-session     optional      pam_systemd.so
session     required      pam_unix.so

Comment 2 Welterlen Benoit 2022-09-01 13:49:46 UTC

My proposal is to not use pam_systemd in case of crond, thus add "session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid" before "-session     optional      pam_systemd.so"

This line is currently before "session     required      pam_unix.so"
I don't know if pam_unix is required in case of crond or not ...

Tx

Comment 3 Pavel Březina 2022-09-09 09:22:38 UTC

I would like to hear opinions from systemd developers. It sounds like pam_systemd shouldn't be run for session of automated services, but perhaps this is something to implement directly in pam_systemd? Iker will check.

Comment 4 Iker Pedrosa 2022-09-09 13:37:48 UTC

Michal do you think it would be possible to bypass services requests in pam_systemd? They wouldn't need to run all the pam_systemd workflow and we would avoid all this noise.

Comment 5 Michal Sekletar 2022-10-10 15:59:51 UTC

Hello, if pam_systemd.so is invoked as part of the session setup then generally speaking users get two main "side effects". First is associated .scope unit and ability to do resource management of this session through systemd and second is systemd --user instance for the user (if it isn't running yet). We want to introduce ability to avoid starting the --user instance for some sessions (e.g. cron sessions). Couple months ago I've posted the PR to add this https://github.com/systemd/systemd/pull/23569 however latter we reverted the change because Lennart had some reservations regarding the overall design. Since then I haven't spent more time on this but this BZ is a good reminder I need to get back to it.

Comment 6 Iker Pedrosa 2022-10-11 06:59:32 UTC

Thanks for the information. It seems like this bugzilla belongs to systemd, so I'm assigning it to you. I hope it helps you drive this effort forward.

Comment 7 RHEL Program Management 2023-09-21 11:47:46 UTC

Issue migration from Bugzilla to Jira is in process at this time. This will be the last message in Jira copied from the Bugzilla bug.

Comment 8 RHEL Program Management 2023-09-21 11:52:52 UTC

This BZ has been automatically migrated to the issues.redhat.com Red Hat Issue Tracker. All future work related to this report will be managed there.

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