helios64: fix fancontrol service on trixie

[Fil0sOFF]

Description

fancontrol.service was "hardened" in Debian trixie. See Debian bug #944808.
fancontrol can't access fans in /dev after that.
This change returns full access to /dev for fancontrol.service

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings

[coderabbitai]

Walkthrough

Adds a new systemd drop-in override for fancontrol on Helios64 to disable PrivateDevices. Introduces packages/bsp/helios64/fancontrol.service.noprivdev-override with [Service] PrivateDevices=no. Updates config/boards/helios64.conf to install this override to /etc/systemd/system/fancontrol.service.d/noprivdev.conf (mode 0644) during post_family_tweaks_bsp__helios64, positioned after the existing fancontrol.service.pid-override installation. No other changes.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested labels

Ready to merge, 05

Suggested reviewers

• Heisath

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (4)

packages/bsp/helios64/fancontrol.service.noprivdev-override (2)

1-2: Retain hardening where possible: consider binding only the needed /dev nodes instead of full de-sandboxing

PrivateDevices=no removes the /dev sandbox entirely. If the board only needs specific device nodes (e.g., /dev/i2c-0,/dev/i2c-1), a tighter alternative is to keep PrivateDevices=yes and bind just those nodes. That preserves most of the defense-in-depth.

Example alternative drop-in (adjust devices to what Helios64 actually uses):

[Service]
PrivateDevices=yes
BindPaths=/dev/i2c-0:/dev/i2c-0
BindPaths=/dev/i2c-1:/dev/i2c-1

If PWM is only via sysfs (/sys/class/hwmon or /sys/class/pwm), PrivateDevices should not matter; in that case, re-check what exactly requires /dev on Helios64 (e.g., an I²C fan controller).

Would you like me to open a follow-up to prototype a minimal-bind setup once we confirm the exact device nodes needed?

---

1-2: Add a short rationale comment for future maintainers

Add context so this override isn’t “mysterious” a year from now. Suggestion:

-[Service]
-PrivateDevices=no
+# Helios64: Debian trixie fancontrol hardening (see Debian#944808) isolates /dev and breaks access
+# to required device nodes on this board. Restore access here; consider minimal BindPaths in future.
+[Service]
+PrivateDevices=no

I can amend the PR with this comment if you agree.

config/boards/helios64.conf (2)

43-43: Install path is fine; consider quoting vars and deterministic drop-in ordering

• Quoting $SRC and $destination is a minor hardening against whitespace/expansion issues.
• Using a numeric prefix like 10-noprivdev.conf creates deterministic ordering if more drop-ins are added later (even though there’s no conflict today).

Proposed tweak:

-install -m 644 $SRC/packages/bsp/helios64/fancontrol.service.noprivdev-override $destination/etc/systemd/system/fancontrol.service.d/noprivdev.conf
+install -m 0644 "$SRC/packages/bsp/helios64/fancontrol.service.noprivdev-override" "$destination/etc/systemd/system/fancontrol.service.d/10-noprivdev.conf"

---

43-43: Ensure the drop-in is picked up on upgrades without requiring a reboot

If this file lands via a BSP package update on an already running system, systemd won’t notice new drop-ins until a daemon-reload (and fancontrol won’t pick it up until restart). Consider adding a daemon-reload + try-restart in the BSP postinst path.

Reference (from lib/functions/bsp/armbian-bsp-cli-deb.sh, board_side_bsp_cli_postinst_finish): it currently enables several services with --no-reload. You could append:

systemctl daemon-reload || true
systemctl try-restart fancontrol.service || true

This can be a separate, tiny follow-up PR if you prefer to keep this one scoped.

I can draft that follow-up change against armbian-bsp-cli postinst if you want.

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📥 Commits

Reviewing files that changed from the base of the PR and between 5eb8bd0 and dbb4a66.

📒 Files selected for processing (2)

• config/boards/helios64.conf (1 hunks)
• packages/bsp/helios64/fancontrol.service.noprivdev-override (1 hunks)

🧰 Additional context used

🧬 Code graph analysis (1)

config/boards/helios64.conf (1)

lib/functions/bsp/armbian-bsp-cli-deb.sh (2)

• board_side_bsp_cli_postinst_finish (448-471)
• board_side_bsp_cli_postrm (417-423)

🔇 Additional comments (1)

packages/bsp/helios64/fancontrol.service.noprivdev-override (1)

1-2: Functional fix: disabling PrivateDevices restores /dev access for fancontrol on trixie

This is a pragmatic drop-in that should immediately unblock Helios64 on Debian trixie where the hardened unit breaks access to device nodes. No syntax issues. Applies cleanly as a unit drop-in.

[leggewie]

am I correct to think that you are overriding the hardening feature? that sounds like a bad idea.

PrivateDevices was specifically and explicitly set to yes in the bug ticket you mentioned

[Fil0sOFF]

A more granular approach would be to allow access only to required devices. I.e.

[Service]
BindPaths=/dev/fan-p6
BindPaths=/dev/fan-p7
BindPaths=/dev/thermal-cpu

Does that look better?
I can update the PR.

[leggewie]

Certainly better, but I am not sure it addresses the issue properly. I haven't had the chance to look into it deeply.

You are circumventing an explicitly set security-policy. Just doesn't sound right.

[Fil0sOFF]

As far as i understand, 90-helios64-hwmon.rules in helios64 bsp symlinks path to fan and thermal controls into /dev/

user@helios64:~$ ls -l /dev/{fan,thermal}*
lrwxrwxrwx 1 root root 41 Aug 24 22:11 /dev/fan-p6 -> /sys/devices/platform/p6-fan/hwmon/hwmon6
lrwxrwxrwx 1 root root 41 Aug 24 22:11 /dev/fan-p7 -> /sys/devices/platform/p7-fan/hwmon/hwmon5
lrwxrwxrwx 1 root root 60 Aug 24 22:11 /dev/thermal-board -> /sys/devices/platform/ff120000.i2c/i2c-2/2-004c/hwmon/hwmon4
lrwxrwxrwx 1 root root 49 Aug 24 22:11 /dev/thermal-cpu -> /sys/devices/virtual/thermal/thermal_zone0/hwmon0

I guess those udev rules must be used to deal with devices inside /sys/devices changing paths sometimes.
It may be possible that those symlinks are not needed at all and we could use /sys/devices/ paths in /etc/fancontrol. But someone needs to confirm that.

Also, helios4 bsp has similar udev rules, so it must be suffering from this issue as well.

[leggewie]

Also, helios4 bsp has similar udev rules, so it must be suffering from this issue as well.

I see. I have a helios4 unit but won't have access to it for another 2 months.

[leggewie]

My reading of the PrivateDevices= section at https://www.freedesktop.org/software/systemd/man/latest/systemd.exec.html is that the correct thing to do is to set DeviceAllow=

What we probably need is a /etc/systemd/system/fancontrol.service file

[Unit]
Description=Fan Control Service

[Service]
Type=simple
ExecStart=/usr/sbin/fancontrol
DeviceAllow=/dev/fan rw
DeviceAllow=/dev/sensors rw

[Install]
WantedBy=multi-user.target

[Fil0sOFF]

That was my initial thought as well. But it doesn't work. I guess it works for only device files, not directories.BindPaths method works fine though.