[DSE-Dev] Bug#900782: selinux-policy-default: Systemd fails to set context for tmpfs mounts in enforcing mode
debian-bugs at ares-macrotechnology.com
Mon Jun 4 21:06:34 BST 2018
I tried setting up a tmpfs mount on a SELinux enabled system.
My fstab entry looks like this:
tmpfs /tmp rootcontext=system_u:object_r:tmp_t:s0 0 0
When I boot in permissive mode, this works as expected.
However, when I boot in enforcing mode, /tmp is labelled tmpfs_t,
instead of tmp_t.
This affects other mount points that /tmp and other labels than tmp_t as
well. The default tmpfs mount points (/run, ...) do get correct labels
even in enforcing mode.
(Note: In permissive mode systemd sets the correct label for /tmp even
when it is not explicitly specified in /etc/fstab, but this obviously
does not hold for arbitrary mount points.)
I set up a unit that runs "restorecon /tmp" on boot and it successfully
relabels /tmp, so this may not be a permission/policy issue after all.
Also, I do not see any (related) AVC denials in the log.
It does not seem to make a difference (to label or logs) whether Systemd
mounts /tmp on boot or if I trigger it later with
"systemctl restart tmp.mount".
I also tried the classical "mount /tmp" as unconfined root user and
this did set the label correctly. Unlike systemd, mount would also throw
an error when the label was invalid.
I noticed that "systemctl show tmp.mount" does not list rootcontext in
"Options". But it is listed as part of the "ExecMount" command.
I also tried the "context" and "fscontext" mount options to no avail.
I did not test if other filesystems than tmpfs show a similar behaviour.
I am filing this against selinux-policy-default, because my impression
is that it may a policy issue. But honestly this is just a guess and the
issue may be elsewhere entirely. Systemd would be my next guess.
The issue is easily reproducible for me in a freshly installed VM with
all the defaults plus SELinux.
Please let me know if you need any other information.
-- System Information:
Debian Release: 9.4
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)
Kernel: Linux 4.9.0-6-amd64 (SMP w/1 CPU core)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages selinux-policy-default depends on:
ii libselinux1 2.6-3+b3
ii libsemanage1 2.6-2
ii libsepol1 2.6-2
ii policycoreutils 2.6-3
ii selinux-utils 2.6-3+b3
Versions of packages selinux-policy-default recommends:
ii checkpolicy 2.6-2
ii setools 4.0.1-6
Versions of packages selinux-policy-default suggests:
pn logcheck <none>
pn syslog-summary <none>
-- no debconf information
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