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magnetite: confine the builder account's key to the nix protocol #2887

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Merged
cameronraysmith merged 1 commit into from
Sep 1, 2026
Merged

magnetite: confine the builder account's key to the nix protocol #2887

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13 changes: 11 additions & 2 deletions modules/machines/nixos/magnetite/default.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -396,8 +396,17 @@ in
users.users.builder = {
isNormalUser = true;
description = "Remote nix build user";
openssh.authorizedKeys.keys = inputs.self.users.crs58.meta.sshKeys ++ [
inputs.self.darwinConfigurations.stibnite.config.clan.core.vars.generators.nix-remote-build.files."key.pub".value
# nix-daemon --stdio is exactly what an ssh-ng caller would otherwise
# invoke (`remote-program` defaults to nix-daemon), so forcing it serves
# the build protocol and discards anything else the client asks for.
# sshd runs the forced command through the account's login shell, so the
# shell must stay executable; a nologin shell would break the protocol
# rather than harden it. Mirrors the stibnite direction of this pair.
openssh.authorizedKeys.keys = [
''restrict,command="${config.nix.package}/bin/nix-daemon --stdio" ${
lib.removeSuffix "\n"
inputs.self.darwinConfigurations.stibnite.config.clan.core.vars.generators.nix-remote-build.files."key.pub".value
}''
];
};

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