313 lines
9.9 KiB
Nix
313 lines
9.9 KiB
Nix
{ config, lib, pkgs, ... }:
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let
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inherit (config.security) wrapperDir wrappers;
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parentWrapperDir = dirOf wrapperDir;
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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 = lib.mdDoc "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 = lib.mdDoc ''
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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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description = lib.mdDoc "The owner of the wrapper program.";
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};
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options.group = lib.mkOption
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{ type = lib.types.str;
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description = lib.mdDoc "The group of the wrapper program.";
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};
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options.permissions = lib.mkOption
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{ type = fileModeType;
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default = "u+rx,g+x,o+x";
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example = "a+rx";
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description = lib.mdDoc ''
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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`.
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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 = lib.mdDoc ''
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A comma-separated list of capability clauses to be given to the
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wrapper program. The format for capability clauses is described in the
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“TEXTUAL REPRESENTATION” section of the {manpage}`cap_from_text(3)`
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manual page. For a list of capabilities supported by the system, check
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the {manpage}`capabilities(7)` manual page.
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::: {.note}
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`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 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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:::
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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 = lib.mdDoc "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 = lib.mdDoc "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
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, group
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, permissions
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, ...
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}:
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''
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cp ${securityWrapper}/bin/security-wrapper "$wrapperDir/${program}"
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echo -n "${source}" > "$wrapperDir/${program}.real"
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# Prevent races
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chmod 0000 "$wrapperDir/${program}"
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chown ${owner}:${group} "$wrapperDir/${program}"
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# Set desired capabilities on the file plus cap_setpcap so
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# the wrapper program can elevate the capabilities set on
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# its file into the Ambient set.
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${pkgs.libcap.out}/bin/setcap "cap_setpcap,${capabilities}" "$wrapperDir/${program}"
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# Set the executable bit
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chmod ${permissions} "$wrapperDir/${program}"
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'';
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###### Activation script for the setuid wrappers
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mkSetuidProgram =
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{ program
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, source
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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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cp ${securityWrapper}/bin/security-wrapper "$wrapperDir/${program}"
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echo -n "${source}" > "$wrapperDir/${program}.real"
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# Prevent races
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chmod 0000 "$wrapperDir/${program}"
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chown ${owner}:${group} "$wrapperDir/${program}"
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chmod "u${if setuid then "+" else "-"}s,g${if setgid then "+" else "-"}s,${permissions}" "$wrapperDir/${program}"
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'';
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mkWrappedPrograms =
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builtins.map
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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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(lib.mkRemovedOptionModule [ "security" "setuidOwners" ] "Use security.wrappers instead")
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(lib.mkRemovedOptionModule [ "security" "setuidPrograms" ] "Use security.wrappers instead")
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];
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###### interface
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options = {
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security.wrappers = lib.mkOption {
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type = lib.types.attrsOf wrapperType;
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default = {};
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example = lib.literalExpression
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''
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{
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# a setuid root program
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doas =
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{ setuid = true;
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owner = "root";
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group = "root";
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source = "''${pkgs.doas}/bin/doas";
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};
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# a setgid program
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locate =
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{ setgid = true;
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owner = "root";
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group = "mlocate";
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source = "''${pkgs.locate}/bin/locate";
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};
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# a program with the CAP_NET_RAW capability
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ping =
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{ owner = "root";
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group = "root";
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capabilities = "cap_net_raw+ep";
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source = "''${pkgs.iputils.out}/bin/ping";
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};
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}
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'';
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description = lib.mdDoc ''
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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` directory, which is then added to
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the shell `PATH`.
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'';
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};
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security.wrapperDirSize = lib.mkOption {
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default = "50%";
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example = "10G";
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type = lib.types.str;
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description = lib.mdDoc ''
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Size limit for the /run/wrappers tmpfs. Look at mount(8), tmpfs size option,
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for the accepted syntax. WARNING: don't set to less than 64MB.
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'';
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};
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security.wrapperDir = lib.mkOption {
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type = lib.types.path;
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default = "/run/wrappers/bin";
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internal = true;
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description = lib.mdDoc ''
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This option defines the path to the wrapper programs. It
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should not be overridden.
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'';
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};
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};
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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.${name} wrapper is not valid:
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setuid/setgid and capabilities are mutually exclusive.
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'';
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}
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) wrappers;
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security.wrappers =
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let
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mkSetuidRoot = source:
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{ setuid = true;
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owner = "root";
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group = "root";
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inherit source;
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};
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in
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{ # These are mount related wrappers that require the +s permission.
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fusermount = mkSetuidRoot "${pkgs.fuse}/bin/fusermount";
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fusermount3 = mkSetuidRoot "${pkgs.fuse3}/bin/fusermount3";
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mount = mkSetuidRoot "${lib.getBin pkgs.util-linux}/bin/mount";
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umount = mkSetuidRoot "${lib.getBin pkgs.util-linux}/bin/umount";
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};
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boot.specialFileSystems.${parentWrapperDir} = {
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fsType = "tmpfs";
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options = [ "nodev" "mode=755" "size=${config.security.wrapperDirSize}" ];
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};
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# Make sure our wrapperDir exports to the PATH env variable when
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# initializing the shell
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environment.extraInit = ''
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# Wrappers override other bin directories.
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export PATH="${wrapperDir}:$PATH"
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'';
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security.apparmor.includes."nixos/security.wrappers" = ''
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include "${pkgs.apparmorRulesFromClosure { name="security.wrappers"; } [
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securityWrapper
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]}"
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'';
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###### wrappers activation script
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system.activationScripts.wrappers =
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lib.stringAfter [ "specialfs" "users" ]
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''
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chmod 755 "${parentWrapperDir}"
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# We want to place the tmpdirs for the wrappers to the parent dir.
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wrapperDir=$(mktemp --directory --tmpdir="${parentWrapperDir}" wrappers.XXXXXXXXXX)
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chmod a+rx "$wrapperDir"
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${lib.concatStringsSep "\n" mkWrappedPrograms}
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if [ -L ${wrapperDir} ]; then
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# Atomically replace the symlink
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# See https://axialcorps.com/2013/07/03/atomically-replacing-files-and-directories/
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old=$(readlink -f ${wrapperDir})
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if [ -e "${wrapperDir}-tmp" ]; then
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rm --force --recursive "${wrapperDir}-tmp"
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fi
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ln --symbolic --force --no-dereference "$wrapperDir" "${wrapperDir}-tmp"
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mv --no-target-directory "${wrapperDir}-tmp" "${wrapperDir}"
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rm --force --recursive "$old"
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else
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# For initial setup
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ln --symbolic "$wrapperDir" "${wrapperDir}"
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fi
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'';
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###### wrappers consistency checks
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system.checks = lib.singleton (pkgs.runCommandLocal
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"ensure-all-wrappers-paths-exist" { }
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''
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# make sure we produce output
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mkdir -p $out
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echo -n "Checking that Nix store paths of all wrapped programs exist... "
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declare -A wrappers
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${lib.concatStringsSep "\n" (lib.mapAttrsToList (n: v:
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"wrappers['${n}']='${v.source}'") wrappers)}
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for name in "''${!wrappers[@]}"; do
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path="''${wrappers[$name]}"
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if [[ "$path" =~ /nix/store ]] && [ ! -e "$path" ]; then
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test -t 1 && echo -ne '\033[1;31m'
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echo "FAIL"
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echo "The path $path does not exist!"
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echo 'Please, check the value of `security.wrappers."'$name'".source`.'
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test -t 1 && echo -ne '\033[0m'
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exit 1
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fi
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done
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echo "OK"
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'');
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};
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}
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