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Bug 1540956

Summary: In container, attempt to write to /dev/stdout in systemd service fails with AVC denial
Product: Red Hat Enterprise Linux 7 Reporter: Jan Pazdziora (Red Hat) <jpazdziora>
Component: dockerAssignee: Daniel Walsh <dwalsh>
Status: CLOSED WONTFIX QA Contact: atomic-bugs <atomic-bugs>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 7.5CC: amurdaca, anssi.hannula, jpazdziora, lsm5, pasik, tsweeney
Target Milestone: rcKeywords: Extras
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of:
: 1540963 (view as bug list) Environment:
Last Closed: 2020-06-09 21:37:24 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:

Description Jan Pazdziora (Red Hat) 2018-02-01 12:08:16 UTC
Description of problem:

In program which is run as systemd service in container, we try to write to stdout. For some reasons, the bash script is actually doing equivalent of

    echo Test > /dev/stdout

It fails.

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

docker-1.13.1-1.gitddee18e.el7.x86_64
selinux-policy-3.13.1-186.el7.noarch
container-selinux-2.40-1.gitdf0c335.el7.noarch

How reproducible:

Deterministic.

Steps to Reproduce:
1. Have Dockerfile:

FROM rhel7
ADD test-service /usr/bin/
ADD test-service.service /etc/systemd/system/
RUN systemctl enable test-service

2. Have test-service:

#!/bin/bash
echo This is test service.
ls -la /dev/std* /dev/console
( echo This is test service with stdout. ) > /dev/stdout

3. Run # chmod a+x test-service
4. Have test-service.service:

[Unit]
Description=Test proc AVC denials
[Service]
Type=oneshot
ExecStart=/usr/bin/test-service
[Install]
WantedBy=multi-user.target

5. Build container: docker build -t systemd .
6. Run the container: docker run --name systemd systemd /usr/sbin/init
7. Check audit.log.
8. From another terminal, run: docker exec systemd journalctl _COMM=test-service -l

Actual results:

type=AVC msg=audit(1517486803.253:7237): avc:  denied  { sendto } for  pid=28004 comm="test-service" path="socket:[1487457]" dev="sockfs" ino=1487457 scontext=system_u:system_r:svirt_lxc_net_t:s0:c734,c741 tcontext=system_u:system_r:svirt_lxc_net_t:s0:c734,c741 tclass=unix_stream_socket
type=AVC msg=audit(1517486803.253:7238): avc:  denied  { sendto } for  pid=28004 comm="test-service" path="socket:[1487457]" dev="sockfs" ino=1487457 scontext=system_u:system_r:svirt_lxc_net_t:s0:c734,c741 tcontext=system_u:system_r:svirt_lxc_net_t:s0:c734,c741 tclass=unix_stream_socket

-- Logs begin at Thu 2018-02-01 12:06:43 UTC, end at Thu 2018-02-01 12:06:43 UTC. --
Feb 01 12:06:43 f65e66d72159 test-service[26]: This is test service.
Feb 01 12:06:43 f65e66d72159 test-service[26]: ls: cannot access /dev/console: No such file or directory
Feb 01 12:06:43 f65e66d72159 test-service[26]: lrwxrwxrwx. 1 root root 15 Feb  1 12:06 /dev/stderr -> /proc/self/fd/2
Feb 01 12:06:43 f65e66d72159 test-service[26]: lrwxrwxrwx. 1 root root 15 Feb  1 12:06 /dev/stdin -> /proc/self/fd/0
Feb 01 12:06:43 f65e66d72159 test-service[26]: lrwxrwxrwx. 1 root root 15 Feb  1 12:06 /dev/stdout -> /proc/self/fd/1
Feb 01 12:06:43 f65e66d72159 test-service[26]: /usr/bin/test-service: line 5: /dev/stdout: Permission denied

Expected results:

No AVC denials.

-- Logs begin at Thu 2018-02-01 12:06:43 UTC, end at Thu 2018-02-01 12:06:43 UTC. --
Feb 01 12:06:43 f65e66d72159 test-service[26]: This is test service.
Feb 01 12:06:43 f65e66d72159 test-service[26]: ls: cannot access /dev/console: No such file or directory
Feb 01 12:06:43 f65e66d72159 test-service[26]: lrwxrwxrwx. 1 root root 15 Feb  1 12:06 /dev/stderr -> /proc/self/fd/2
Feb 01 12:06:43 f65e66d72159 test-service[26]: lrwxrwxrwx. 1 root root 15 Feb  1 12:06 /dev/stdin -> /proc/self/fd/0
Feb 01 12:06:43 f65e66d72159 test-service[26]: lrwxrwxrwx. 1 root root 15 Feb  1 12:06 /dev/stdout -> /proc/self/fd/1
Feb 01 12:06:43 f65e66d72159 test-service[26]: This is test service with stdout.

Additional info:

Comment 2 Jan Pazdziora (Red Hat) 2018-02-01 12:16:57 UTC
On Fedora 27, things fail as well but the AVC denial is different and the error is about No such device or address, not Permission denied -- see bug 1540963.

Comment 3 Daniel Walsh 2018-02-02 18:32:20 UTC
Does this work if you run in permissive mode?

Comment 4 Jan Pazdziora (Red Hat) 2018-02-23 14:41:33 UTC
Running in permissive changes the error message in journal from

Feb 23 14:39:19 1c5991a7a4e8 test-service[28]: /usr/bin/test-service: line 4: /dev/stdout: Permission denied

to

Feb 23 14:40:02 21b99de0e44d test-service[26]: /usr/bin/test-service: line 4: /dev/stdout: No such device or address

but things still do not work.

Tested with

docker-1.13.1-53.git774336d.el7.x86_64
container-selinux-2.42-1.gitad8f0f7.el7.noarch

Comment 5 Tom Sweeney 2020-06-09 21:37:24 UTC
We have no plans to ship another version of Docker at this time. RHEL7 is in final support stages where only security fixes will get released.  Customers should move to use Podman which is available starting in RHEL 7.6.