0033: the Flatpak network block writes the override file

ADR-0033: the Flatpak network block writes the override file

Status: accepted (spike S4-c done, 2026-11-03). Phase: F4.

Context

F4 must block a Flatpak app and revert it. flatpak override exists, but the core executes typed operations only (no shell, no free-form exec), and rollback must restore the exact bytes.

Decision

flatpak.override is a typed operation the core executes by writing the file Flatpak itself reads: /var/lib/flatpak/overrides/<app-id> (the default system-wide installation). It accepts exactly one change, --unshare=network, for a syntactically valid application id (three or more dot-separated elements of [A-Za-z0-9_-]). The engine snapshots the file like any other, so rollback restores the administrator’s bytes or removes the file we created. The plugin refuses apps that are not installed system-wide, so a typo cannot leave a stray file.

Findings (Flatpak 1.14.6, 1.16.6, 1.18.4 on the five distros)

• flatpak override --system --unshare=network <app> writes [Context]\nshared=!network;\n (27 bytes, 0644 root) in that directory.
• Merging into an existing file edits the shared= list. The order of the entries differs between versions (ipc;!network; on 1.18.4, !network;ipc; on 1.14.6 and 1.16.6); Flatpak reads both. Ours keeps the administrator’s entries and appends, so the result is valid everywhere.
• flatpak override --system --show <app> prints the merged view; the VM scenario uses it to prove Flatpak parses our file the same way.
• Documentation: https://docs.flatpak.org/en/latest/flatpak-command-reference.html (flatpak-override, consulted 2026-11-03).

Consequences

• Per-user installs (~/.local/share/flatpak) are out of reach: the core does not read home directories. The Apps screen must say so.
• Unblocking is the transaction’s rollback; there is no separate “allow” operation yet.
• The op carries no network risk flag: cutting one app cannot lock the machine out, so it needs no confirmation window.
• The F4 plugin is apps.flatpak-network. The specification reserves apps.flatpak_perms for the F7 audit plugin, and that id breaks the manifest rule [a-z0-9-] (the same spec lists system.session_lock and privacy.camera_mic). The spec and the rule need reconciling; reported to the maintainer, not decided here.