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861a1cec60
Noted by @Infinisil on IRC:
infinisil: Question regarding the confinement PR
infinisil: On line 136 you do different things depending on
RootDirectoryStartOnly
infinisil: But on line 157 you have an assertion that disallows that
option being true
infinisil: Is there a reason behind this or am I missing something
I originally left this in so that once systemd supports that, we can
just flip a switch and remove the assertion and thus support
RootDirectoryStartOnly for our confinement module.
However, this doesn't seem to be on the roadmap for systemd in the
foreseeable future, so I'll just remove this, especially because it's
very easy to add it again, once it is supported.
Signed-off-by: aszlig <aszlig@nix.build>
199 lines
8.4 KiB
Nix
199 lines
8.4 KiB
Nix
{ config, pkgs, lib, ... }:
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let
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toplevelConfig = config;
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inherit (lib) types;
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inherit (import ../system/boot/systemd-lib.nix {
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inherit config pkgs lib;
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}) mkPathSafeName;
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in {
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options.systemd.services = lib.mkOption {
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type = types.attrsOf (types.submodule ({ name, config, ... }: {
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options.confinement.enable = lib.mkOption {
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type = types.bool;
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default = false;
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description = ''
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If set, all the required runtime store paths for this service are
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bind-mounted into a <literal>tmpfs</literal>-based <citerefentry>
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<refentrytitle>chroot</refentrytitle>
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<manvolnum>2</manvolnum>
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</citerefentry>.
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'';
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};
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options.confinement.fullUnit = lib.mkOption {
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type = types.bool;
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default = false;
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description = ''
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Whether to include the full closure of the systemd unit file into the
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chroot, instead of just the dependencies for the executables.
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<warning><para>While it may be tempting to just enable this option to
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make things work quickly, please be aware that this might add paths
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to the closure of the chroot that you didn't anticipate. It's better
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to use <option>confinement.packages</option> to <emphasis
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role="strong">explicitly</emphasis> add additional store paths to the
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chroot.</para></warning>
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'';
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};
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options.confinement.packages = lib.mkOption {
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type = types.listOf (types.either types.str types.package);
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default = [];
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description = let
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mkScOption = optName: "<option>serviceConfig.${optName}</option>";
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in ''
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Additional packages or strings with context to add to the closure of
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the chroot. By default, this includes all the packages from the
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${lib.concatMapStringsSep ", " mkScOption [
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"ExecReload" "ExecStartPost" "ExecStartPre" "ExecStop"
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"ExecStopPost"
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]} and ${mkScOption "ExecStart"} options. If you want to have all the
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dependencies of this systemd unit, you can use
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<option>confinement.fullUnit</option>.
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<note><para>The store paths listed in <option>path</option> are
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<emphasis role="strong">not</emphasis> included in the closure as
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well as paths from other options except those listed
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above.</para></note>
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'';
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};
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options.confinement.binSh = lib.mkOption {
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type = types.nullOr types.path;
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default = toplevelConfig.environment.binsh;
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defaultText = "config.environment.binsh";
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example = lib.literalExample "\${pkgs.dash}/bin/dash";
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description = ''
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The program to make available as <filename>/bin/sh</filename> inside
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the chroot. If this is set to <literal>null</literal>, no
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<filename>/bin/sh</filename> is provided at all.
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This is useful for some applications, which for example use the
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<citerefentry>
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<refentrytitle>system</refentrytitle>
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<manvolnum>3</manvolnum>
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</citerefentry> library function to execute commands.
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'';
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};
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options.confinement.mode = lib.mkOption {
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type = types.enum [ "full-apivfs" "chroot-only" ];
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default = "full-apivfs";
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description = ''
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The value <literal>full-apivfs</literal> (the default) sets up
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private <filename class="directory">/dev</filename>, <filename
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class="directory">/proc</filename>, <filename
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class="directory">/sys</filename> and <filename
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class="directory">/tmp</filename> file systems in a separate user
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name space.
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If this is set to <literal>chroot-only</literal>, only the file
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system name space is set up along with the call to <citerefentry>
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<refentrytitle>chroot</refentrytitle>
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<manvolnum>2</manvolnum>
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</citerefentry>.
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<note><para>This doesn't cover network namespaces and is solely for
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file system level isolation.</para></note>
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'';
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};
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config = let
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rootName = "${mkPathSafeName name}-chroot";
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inherit (config.confinement) binSh fullUnit;
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wantsAPIVFS = lib.mkDefault (config.confinement.mode == "full-apivfs");
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in lib.mkIf config.confinement.enable {
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serviceConfig = {
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RootDirectory = pkgs.runCommand rootName {} "mkdir \"$out\"";
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TemporaryFileSystem = "/";
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MountFlags = lib.mkDefault "private";
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# https://github.com/NixOS/nixpkgs/issues/14645 is a future attempt
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# to change some of these to default to true.
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#
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# If we run in chroot-only mode, having something like PrivateDevices
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# set to true by default will mount /dev within the chroot, whereas
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# with "chroot-only" it's expected that there are no /dev, /proc and
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# /sys file systems available.
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#
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# However, if this suddenly becomes true, the attack surface will
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# increase, so let's explicitly set these options to true/false
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# depending on the mode.
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MountAPIVFS = wantsAPIVFS;
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PrivateDevices = wantsAPIVFS;
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PrivateTmp = wantsAPIVFS;
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PrivateUsers = wantsAPIVFS;
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ProtectControlGroups = wantsAPIVFS;
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ProtectKernelModules = wantsAPIVFS;
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ProtectKernelTunables = wantsAPIVFS;
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};
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confinement.packages = let
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execOpts = [
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"ExecReload" "ExecStart" "ExecStartPost" "ExecStartPre" "ExecStop"
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"ExecStopPost"
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];
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execPkgs = lib.concatMap (opt: let
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isSet = config.serviceConfig ? ${opt};
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in lib.optional isSet config.serviceConfig.${opt}) execOpts;
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unitAttrs = toplevelConfig.systemd.units."${name}.service";
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allPkgs = lib.singleton (builtins.toJSON unitAttrs);
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unitPkgs = if fullUnit then allPkgs else execPkgs;
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in unitPkgs ++ lib.optional (binSh != null) binSh;
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};
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}));
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};
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config.assertions = lib.concatLists (lib.mapAttrsToList (name: cfg: let
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whatOpt = optName: "The 'serviceConfig' option '${optName}' for"
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+ " service '${name}' is enabled in conjunction with"
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+ " 'confinement.enable'";
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in lib.optionals cfg.confinement.enable [
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{ assertion = !cfg.serviceConfig.RootDirectoryStartOnly or false;
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message = "${whatOpt "RootDirectoryStartOnly"}, but right now systemd"
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+ " doesn't support restricting bind-mounts to 'ExecStart'."
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+ " Please either define a separate service or find a way to run"
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+ " commands other than ExecStart within the chroot.";
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}
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{ assertion = !cfg.serviceConfig.DynamicUser or false;
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message = "${whatOpt "DynamicUser"}. Please create a dedicated user via"
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+ " the 'users.users' option instead as this combination is"
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+ " currently not supported.";
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}
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]) config.systemd.services);
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config.systemd.packages = lib.concatLists (lib.mapAttrsToList (name: cfg: let
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rootPaths = let
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contents = lib.concatStringsSep "\n" cfg.confinement.packages;
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in pkgs.writeText "${mkPathSafeName name}-string-contexts.txt" contents;
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chrootPaths = pkgs.runCommand "${mkPathSafeName name}-chroot-paths" {
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closureInfo = pkgs.closureInfo { inherit rootPaths; };
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serviceName = "${name}.service";
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excludedPath = rootPaths;
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} ''
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mkdir -p "$out/lib/systemd/system"
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serviceFile="$out/lib/systemd/system/$serviceName"
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echo '[Service]' > "$serviceFile"
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# /bin/sh is special here, because the option value could contain a
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# symlink and we need to properly resolve it.
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${lib.optionalString (cfg.confinement.binSh != null) ''
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binsh=${lib.escapeShellArg cfg.confinement.binSh}
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realprog="$(readlink -e "$binsh")"
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echo "BindReadOnlyPaths=$realprog:/bin/sh" >> "$serviceFile"
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''}
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while read storePath; do
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if [ -L "$storePath" ]; then
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# Currently, systemd can't cope with symlinks in Bind(ReadOnly)Paths,
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# so let's just bind-mount the target to that location.
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echo "BindReadOnlyPaths=$(readlink -e "$storePath"):$storePath"
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elif [ "$storePath" != "$excludedPath" ]; then
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echo "BindReadOnlyPaths=$storePath"
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fi
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done < "$closureInfo/store-paths" >> "$serviceFile"
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'';
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in lib.optional cfg.confinement.enable chrootPaths) config.systemd.services);
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}
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