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# Write this machine's USB policy before anything enforces one. |
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# |
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# The reasoning is all in usr/bin/alloy-usb-seed; this file is only what runs |
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# it. The short version: the image ships an empty rules.conf on purpose, and |
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# an empty policy plus ImplicitPolicyTarget=block is "deny every USB device on |
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# this machine". The seeder turns that into "allow what this machine already |
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# had", which is the only policy the machine itself can honestly assert. |
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# |
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# Ordering is the whole point of the unit. Before=usbguard.service, so the |
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# daemon never sees the empty file; After=systemd-udevd.service, so the bus has |
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# been enumerated and generate-policy has something to read. Without the second |
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# the policy would be written from a half-populated /sys and would deny whatever |
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# had not appeared yet. |
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# |
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# Not Wants=usbguard.service, and never Requires=. This must not be a reason for |
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# enforcement to start; it prepares the ground for a daemon that is armed |
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# somewhere else, and on the majority of machines — usbguard installed and not |
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# enabled — it writes a policy nothing reads. That is deliberate: it means the |
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# day a person arms enforcement from `alloy usb`, the policy is already there. |
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# |
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# The seeder is idempotent against a written policy, so this is enabled on every |
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# install rather than gated on a stamp. See the script for why the policy file |
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# itself is the state. |
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|
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[Unit] |
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Description=Seed the USB device policy from this machine's own devices |
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Documentation=https://makenot.work/git/max/alloy |
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After=systemd-udevd.service |
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Wants=systemd-udevd.service |
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Before=usbguard.service |
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# On a machine with no usbguard the script exits saying so, which is harmless |
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# and pointless. The condition says it out loud instead. |
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ConditionPathExists=/usr/bin/usbguard |
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|
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[Service] |
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Type=oneshot |
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RemainAfterExit=yes |
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ExecStart=/usr/bin/alloy-usb-seed |
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# The script returns 0 on every path it means to take, including the ones where |
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# it decides not to write anything, so a non-zero here is a real fault. It must |
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# not be fatal to the boot: a seeder that failed leaves the policy empty, and an |
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# empty policy is refused by usbguard's own drop-in rather than enforced. |
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|
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[Install] |
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WantedBy=multi-user.target |
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|