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Bug 2126583 - systemd InaccessiblePaths triggers SELinux alerts
Summary: systemd InaccessiblePaths triggers SELinux alerts
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Red Hat Enterprise Linux 8
Classification: Red Hat
Component: selinux-policy
Version: 8.6
Hardware: All
OS: Linux
medium
medium
Target Milestone: rc
: ---
Assignee: Zdenek Pytela
QA Contact: Milos Malik
URL:
Whiteboard:
Depends On:
Blocks: 2127972
TreeView+ depends on / blocked
 
Reported: 2022-09-14 01:50 UTC by Etienne CHAMPETIER
Modified: 2022-09-19 13:55 UTC (History)
3 users (show)

Fixed In Version:
Doc Type: No Doc Update
Doc Text:
Clone Of:
: 2127972 (view as bug list)
Environment:
Last Closed: 2022-09-19 13:52:05 UTC
Type: Bug
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Issue Tracker RHELPLAN-133895 0 None None None 2022-09-14 07:28:12 UTC

Description Etienne CHAMPETIER 2022-09-14 01:50:57 UTC 
Description of problem:
I'm using systemd InaccessiblePaths directive to prevent firewalld from using iptables
this causes SELinux alerts

Version-Release number of selected component (if applicable):
selinux-policy-3.14.3-95.el8_6.4

How reproducible:
100%

Steps to Reproduce:
1. install firewalld

2. add the following systemd dropin
```
# /etc/systemd/system/firewalld.service.d/10-hide-iptables.conf
[Service]
# Hide iptables so firewalld doesn't flush tables on start/reload/stop
InaccessiblePaths=/usr/sbin/xtables-nft-multi
```

3. restart firewalld

Actual results:
type=AVC msg=audit(1663092286.961:27): avc:  denied  { getattr } for  pid=1889 comm="firewalld" path="/usr/sbin/xtables-nft-multi" dev="tmpfs" ino=16285 scontext=system_u:system_r:firewalld_t:s0 tcontext=system_u:object_r:init_var_run_t:s0 tclass=file permissive=1


Expected results:
No log spam, either allow the program to try accessing the inaccessible file, or block the access and make it silent


Additional info:

Haven't looked at the code but I think systemd does some bind mount to those inaccessible files

# ls -laZ /run/systemd/inaccessible/
total 0
d---------.  3 root root system_u:object_r:init_var_run_t:s0  160 Sep 13 20:04 .
drwxr-xr-x. 16 root root system_u:object_r:init_var_run_t:s0  420 Sep 13 20:05 ..
b---------.  1 root root system_u:object_r:init_var_run_t:s0 0, 0 Sep 13 20:04 blk
c---------.  1 root root system_u:object_r:init_var_run_t:s0 0, 0 Sep 13 20:04 chr
d---------.  2 root root system_u:object_r:init_var_run_t:s0   40 Sep 13 20:04 dir
p---------.  1 root root system_u:object_r:init_var_run_t:s0    0 Sep 13 20:04 fifo
----------.  1 root root system_u:object_r:init_var_run_t:s0    0 Sep 13 20:04 reg
s---------.  1 root root system_u:object_r:init_var_run_t:s0    0 Sep 13 20:04 sock
Comment 1 Milos Malik 2022-09-14 07:29:43 UTC 
Appears multiple times in enforcing mode:
----
type=PROCTITLE msg=audit(09/14/2022 09:23:34.399:707) : proctitle=/usr/libexec/platform-python -s /usr/sbin/firewalld --nofork --nopid 
type=PATH msg=audit(09/14/2022 09:23:34.399:707) : item=0 name=/usr/sbin/ebtables-restore inode=1333 dev=00:18 mode=file,000 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:init_var_run_t:s0 nametype=NORMAL cap_fp=none cap_fi=none cap_fe=0 cap_fver=0 cap_frootid=0 
type=CWD msg=audit(09/14/2022 09:23:34.399:707) : cwd=/ 
type=SYSCALL msg=audit(09/14/2022 09:23:34.399:707) : arch=x86_64 syscall=stat success=no exit=EACCES(Permission denied) a0=0x7efe609c8d50 a1=0x7ffe12af3990 a2=0x7ffe12af3990 a3=0x1 items=1 ppid=1 pid=20500 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=firewalld exe=/usr/libexec/platform-python3.6 subj=system_u:system_r:firewalld_t:s0 key=(null) 
type=AVC msg=audit(09/14/2022 09:23:34.399:707) : avc:  denied  { getattr } for  pid=20500 comm=firewalld path=/usr/sbin/xtables-nft-multi dev="tmpfs" ino=1333 scontext=system_u:system_r:firewalld_t:s0 tcontext=system_u:object_r:init_var_run_t:s0 tclass=file permissive=0 
----

But the file context does not change:

# ls -lZ /usr/sbin/xtables-*
lrwxrwxrwx. 1 root root system_u:object_r:bin_t:s0               17 Aug  5 17:31 /usr/sbin/xtables-monitor -> xtables-nft-multi
-rwxr-xr-x. 1 root root system_u:object_r:iptables_exec_t:s0 221784 Aug  5 17:31 /usr/sbin/xtables-nft-multi
#

The content of type=PATH records varies:

name=/usr/sbin/ebtables
name=/usr/sbin/ebtables-restore
name=/usr/sbin/ip6tables
name=/usr/sbin/ip6tables-restore
name=/usr/sbin/iptables
name=/usr/sbin/iptables-restore

# rpm -qa selinux\* firewalld\* | sort
firewalld-0.9.3-13.el8.noarch
firewalld-filesystem-0.9.3-13.el8.noarch
selinux-policy-3.14.3-108.el8.noarch
selinux-policy-devel-3.14.3-108.el8.noarch
selinux-policy-doc-3.14.3-108.el8.noarch
selinux-policy-minimum-3.14.3-108.el8.noarch
selinux-policy-mls-3.14.3-108.el8.noarch
selinux-policy-sandbox-3.14.3-108.el8.noarch
selinux-policy-targeted-3.14.3-108.el8.noarch
#
Comment 2 Milos Malik 2022-09-14 07:33:55 UTC 
Appears only once in permissive mode:
----
type=PROCTITLE msg=audit(09/14/2022 09:30:01.429:802) : proctitle=/usr/libexec/platform-python -s /usr/sbin/firewalld --nofork --nopid 
type=PATH msg=audit(09/14/2022 09:30:01.429:802) : item=0 name=/usr/sbin/iptables inode=1333 dev=00:18 mode=file,000 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:init_var_run_t:s0 nametype=NORMAL cap_fp=none cap_fi=none cap_fe=0 cap_fver=0 cap_frootid=0 
type=CWD msg=audit(09/14/2022 09:30:01.429:802) : cwd=/ 
type=SYSCALL msg=audit(09/14/2022 09:30:01.429:802) : arch=x86_64 syscall=stat success=yes exit=0 a0=0x7f06e61adf30 a1=0x7fff9e641760 a2=0x7fff9e641760 a3=0x1 items=1 ppid=1 pid=23059 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=firewalld exe=/usr/libexec/platform-python3.6 subj=system_u:system_r:firewalld_t:s0 key=(null) 
type=AVC msg=audit(09/14/2022 09:30:01.429:802) : avc:  denied  { getattr } for  pid=23059 comm=firewalld path=/usr/sbin/xtables-nft-multi dev="tmpfs" ino=1333 scontext=system_u:system_r:firewalld_t:s0 tcontext=system_u:object_r:init_var_run_t:s0 tclass=file permissive=1 
----

# mount | grep tmpfs
devtmpfs on /dev type devtmpfs (rw,nosuid,seclabel,size=907960k,nr_inodes=226990,mode=755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,seclabel)
tmpfs on /run type tmpfs (rw,nosuid,nodev,seclabel,mode=755)
tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,seclabel,mode=755)
tmpfs on /run/stratisd/keyfiles type tmpfs (rw,relatime,seclabel,size=1024k)
tmpfs on /run/user/42 type tmpfs (rw,nosuid,nodev,relatime,seclabel,size=185592k,mode=700,uid=42,gid=42)
tmpfs on /run/user/0 type tmpfs (rw,nosuid,nodev,relatime,seclabel,size=185592k,mode=700)
# find /run -xdev -inum 1333
/run/systemd/inaccessible/reg
# ls -ilZ /run/systemd/inaccessible/reg 
1333 ----------. 1 root root system_u:object_r:init_var_run_t:s0 0 Sep 14 08:29 /run/systemd/inaccessible/reg
#
Comment 3 Zdenek Pytela 2022-09-19 13:52:05 UTC 
Etienne,

As discussed with systemd developers, when directives like InaccessiblePaths are used, any access outside the scope should be reported since it may indicate an incorrect service behaviour or a security issue. This can be done both on systemd side as well as on selinux-policy, these layers are independent.

What we can do is to assign a different label to inaccessible files so that the issue is clear without additional audit data, but not in RHEL 8.

If you need a selinux support to your scenario, use a local policy module, e. g.

  # cat local_dontaudit_firewalld_inaccessible.cil
(dontaudit firewalld_t init_var_run_t (file (getattr)))
  # semodule -i local_dontaudit_firewalld_inaccessible.cil
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