smartctl_exporter already runs with SupplementaryGroups "disk", which
gives full access to SATA drives, but NVMe devices are owned by
root:root, resulting in no access:
[...] msg="Smartctl open device: /dev/nvme0 failed: Permission denied"
This patch introduces a "smartctl-exporter-access" supplementary
group, and an udev rule with setfacl to give the exporter access to NVMe
drives, without changing the base root:root ownership.
Fixes https://github.com/NixOS/nixpkgs/issues/210041
Fixes issues described in #208242 for this part of the nixpkgs tree.
There are no behavioral changes in this, it only adjusts the code so
that it is easier to understand.
these changes were generated with nixq 0.0.2, by running
nixq ">> lib.mdDoc[remove] Argument[keep]" --batchmode nixos/**.nix
nixq ">> mdDoc[remove] Argument[keep]" --batchmode nixos/**.nix
nixq ">> Inherit >> mdDoc[remove]" --batchmode nixos/**.nix
two mentions of the mdDoc function remain in nixos/, both of which
are inside of comments.
Since lib.mdDoc is already defined as just id, this commit is a no-op as
far as Nix (and the built manual) is concerned.
Setting up the DeviceAllow list with explicitly configured devices was a
nice idea, but sometimes a configured device (`/dev/nvme0n1` an NVMe
namespace) has a parent device (`/dev/nvme0`) that smartctl needs to
access to query metrics.
Falling back to the block and character definitions is probably a valid
fallback.
When no devices are given the exporter tries to autodiscover available
disks. The previous DevicePolicy was however preventing the exporter
from accessing any device at all, since only explicitly mentioned ones
were allowed.
This commit adds an allow rule for several device classes that I could
find on my machines, that gets set when no devices are explicitly
configured.
There is an existing problem with nvme devices, that expose a character
device at `/dev/nvme0`, and a (namespaced) block device at
`/dev/nvme0n1`. The character device does not come with permissions that
we could give to the exporter without further impacting the hardening.
crw------- 1 root root 247, 0 27. Jan 03:10 /dev/nvme0
brw-rw---- 1 root disk 259, 0 27. Jan 03:10 /dev/nvme0n1
The autodiscovery only finds the character device, which the exporter
unfortunately does not have access to.
However a simple udev rule can be used to resolve this:
services.udev.extraRules = ''
SUBSYSTEM=="nvme", KERNEL=="nvme[0-9]*", GROUP="disk"
'';
Unfortunately I'm not fully aware of the security implications this
change carries and we should question upstream (systemd) why they did
not include such a rule.
The disk group has no members on any of my machines.
❯ getent group disk
disk❌6:
