nixos/security/wrappers: make well-typed
The security.wrappers option is morally a set of submodules but it's actually (un)typed as a generic attribute set. This is bad for several reasons: 1. Some of the "submodule" option are not document; 2. the default values are not documented and are chosen based on somewhat bizarre rules (issue #23217); 3. It's not possible to override an existing wrapper due to the dumb types.attrs.merge strategy; 4. It's easy to make mistakes that will go unnoticed, which is really bad given the sensitivity of this module (issue #47839). This makes the option a proper set of submodule and add strict types and descriptions to every sub-option. Considering it's not yet clear if the way the default values are picked is intended, this reproduces the current behavior, but it's now documented explicitly.
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rnhmjoj
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@ -5,23 +5,108 @@ let
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parentWrapperDir = dirOf wrapperDir;
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programs =
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(lib.mapAttrsToList
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(n: v: (if v ? program then v else v // {program=n;}))
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wrappers);
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securityWrapper = pkgs.callPackage ./wrapper.nix {
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inherit parentWrapperDir;
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};
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fileModeType =
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let
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# taken from the chmod(1) man page
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symbolic = "[ugoa]*([-+=]([rwxXst]*|[ugo]))+|[-+=][0-7]+";
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numeric = "[-+=]?[0-7]{0,4}";
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mode = "((${symbolic})(,${symbolic})*)|(${numeric})";
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in
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lib.types.strMatching mode
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// { description = "file mode string"; };
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wrapperType = lib.types.submodule ({ name, config, ... }: {
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options.source = lib.mkOption
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{ type = lib.types.path;
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description = "The absolute path to the program to be wrapped.";
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};
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options.program = lib.mkOption
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{ type = with lib.types; nullOr str;
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default = name;
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description = ''
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The name of the wrapper program. Defaults to the attribute name.
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'';
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};
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options.owner = lib.mkOption
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{ type = lib.types.str;
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default = with config;
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if (capabilities != "") || !(setuid || setgid || permissions != null)
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then "root"
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else "nobody";
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description = ''
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The owner of the wrapper program. Defaults to <literal>root</literal>
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if any capability is set and setuid/setgid/permissions are not, otherwise to
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<literal>nobody</litera>.
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'';
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};
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options.group = lib.mkOption
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{ type = lib.types.str;
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default = with config;
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if (capabilities != "") || !(setuid || setgid || permissions != null)
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then "root"
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else "nogroup";
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description = ''
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The group of the wrapper program. Defaults to <literal>root</literal>
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if any capability is set and setuid/setgid/permissions are not,
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otherwise to <literal>nogroup</litera>.
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'';
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};
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options.permissions = lib.mkOption
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{ type = lib.types.nullOr fileModeType;
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default = null;
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example = "u+rx,g+x,o+x";
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apply = x: if x == null then "u+rx,g+x,o+x" else x;
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description = ''
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The permissions of the wrapper program. The format is that of a
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symbolic or numeric file mode understood by <command>chmod</command>.
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'';
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};
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options.capabilities = lib.mkOption
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{ type = lib.types.commas;
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default = "";
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description = ''
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A comma-separated list of capabilities to be given to the wrapper
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program. For capabilities supported by the system check the
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<citerefentry>
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<refentrytitle>capabilities</refentrytitle>
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<manvolnum>7</manvolnum>
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</citerefentry>
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manual page.
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<note><para>
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<literal>cap_setpcap</literal>, which is required for the wrapper
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program to be able to raise caps into the Ambient set is NOT raised
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to the Ambient set so that the real program cannot modify its own
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capabilities!! This may be too restrictive for cases in which the
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real program needs cap_setpcap but it at least leans on the side
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security paranoid vs. too relaxed.
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</para></note>
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'';
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};
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options.setuid = lib.mkOption
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{ type = lib.types.bool;
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default = false;
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description = "Whether to add the setuid bit the wrapper program.";
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};
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options.setgid = lib.mkOption
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{ type = lib.types.bool;
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default = false;
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description = "Whether to add the setgid bit the wrapper program.";
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};
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});
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###### Activation script for the setcap wrappers
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mkSetcapProgram =
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{ program
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, capabilities
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, source
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, owner ? "nobody"
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, group ? "nogroup"
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, permissions ? "u+rx,g+x,o+x"
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, owner
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, group
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, permissions
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, ...
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}:
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assert (lib.versionAtLeast (lib.getVersion config.boot.kernelPackages.kernel) "4.3");
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@ -46,11 +131,11 @@ let
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mkSetuidProgram =
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{ program
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, source
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, owner ? "nobody"
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, group ? "nogroup"
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, setuid ? false
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, setgid ? false
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, permissions ? "u+rx,g+x,o+x"
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, owner
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, group
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, setuid
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, setgid
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, permissions
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, ...
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}:
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''
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@ -66,24 +151,11 @@ let
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mkWrappedPrograms =
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builtins.map
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(s: if (s ? capabilities)
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then mkSetcapProgram
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({ owner = "root";
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group = "root";
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} // s)
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else if
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(s ? setuid && s.setuid) ||
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(s ? setgid && s.setgid) ||
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(s ? permissions)
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then mkSetuidProgram s
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else mkSetuidProgram
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({ owner = "root";
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group = "root";
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setuid = true;
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setgid = false;
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permissions = "u+rx,g+x,o+x";
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} // s)
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) programs;
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(opts:
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if opts.capabilities != ""
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then mkSetcapProgram opts
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else mkSetuidProgram opts
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) (lib.attrValues wrappers);
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in
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{
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imports = [
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@ -95,7 +167,7 @@ in
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options = {
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security.wrappers = lib.mkOption {
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type = lib.types.attrs;
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type = lib.types.attrsOf wrapperType;
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default = {};
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example = lib.literalExample
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''
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@ -109,31 +181,11 @@ in
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}
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'';
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description = ''
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This option allows the ownership and permissions on the setuid
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wrappers for specific programs to be overridden from the
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default (setuid root, but not setgid root).
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<note>
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<para>The sub-attribute <literal>source</literal> is mandatory,
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it must be the absolute path to the program to be wrapped.
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</para>
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<para>The sub-attribute <literal>program</literal> is optional and
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can give the wrapper program a new name. The default name is the same
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as the attribute name itself.</para>
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<para>Additionally, this option can set capabilities on a
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wrapper program that propagates those capabilities down to the
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wrapped, real program.</para>
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<para>NOTE: cap_setpcap, which is required for the wrapper
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program to be able to raise caps into the Ambient set is NOT
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raised to the Ambient set so that the real program cannot
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modify its own capabilities!! This may be too restrictive for
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cases in which the real program needs cap_setpcap but it at
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least leans on the side security paranoid vs. too
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relaxed.</para>
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</note>
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This option effectively allows adding setuid/setgid bits, capabilities,
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changing file ownership and permissions of a program without directly
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modifying it. This works by creating a wrapper program under the
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<option>security.wrapperDir</option> directory, which is then added to
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the shell <literal>PATH</literal>.
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'';
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};
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@ -151,6 +203,16 @@ in
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###### implementation
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config = {
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assertions = lib.mapAttrsToList
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(name: opts:
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{ assertion = opts.setuid || opts.setgid -> opts.capabilities == "";
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message = ''
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The security.wrappers.${name} wrapper is not valid:
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setuid/setgid and capabilities are mutually exclusive.
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'';
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}
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) wrappers;
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security.wrappers = {
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# These are mount related wrappers that require the +s permission.
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fusermount.source = "${pkgs.fuse}/bin/fusermount";
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