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|
{ config, lib, pkgs, ... }:
let
inherit (config.security) wrapperDir wrappers setuidPrograms;
programs =
(map (x: { program = x; owner = "root"; group = "root"; setuid = true; }) setuidPrograms)
++
(lib.mapAttrsToList
(n: v: (if v ? "program" then v else v // {program=n;}))
wrappers);
mkWrapper = { program, source ? null, ...}: ''
if ! source=${if source != null then source else "$(readlink -f $(PATH=$WRAPPER_PATH type -tP ${program}))"}; then
# If we can't find the program, fall back to the
# system profile.
source=/nix/var/nix/profiles/default/bin/${program}
fi
gcc -Wall -O2 -DSOURCE_PROG=\"$source\" -DWRAPPER_DIR=\"${config.security.wrapperDir}\" \
-lcap-ng -lcap ${./wrapper.c} -o $out/bin/${program}.wrapper -L ${pkgs.libcap.lib}/lib -L ${pkgs.libcap_ng}/lib \
-I ${pkgs.libcap.dev}/include -I ${pkgs.libcap_ng}/include -I ${pkgs.linuxHeaders}/include
'';
wrappedPrograms = pkgs.stdenv.mkDerivation {
name = "permissions-wrapper";
unpackPhase = "true";
installPhase = ''
mkdir -p $out/bin
${lib.concatMapStrings mkWrapper programs}
'';
};
###### Activation script for the setcap wrappers
mkSetcapProgram =
{ program
, capabilities
, source ? null
, owner ? "nobody"
, group ? "nogroup"
, ...
}:
assert (lib.versionAtLeast (lib.getVersion config.boot.kernelPackages.kernel) "4.3");
''
cp ${wrappedPrograms}/bin/${program}.wrapper $wrapperDir/${program}
# Prevent races
chmod 0000 $wrapperDir/${program}
chown ${owner}.${group} $wrapperDir/${program}
# Set desired capabilities on the file plus cap_setpcap so
# the wrapper program can elevate the capabilities set on
# its file into the Ambient set.
${pkgs.libcap.out}/bin/setcap "cap_setpcap,${capabilities}" $wrapperDir/${program}
# Set the executable bit
chmod u+rx,g+x,o+x $wrapperDir/${program}
'';
###### Activation script for the setuid wrappers
mkSetuidProgram =
{ program
, source ? null
, owner ? "nobody"
, group ? "nogroup"
, setuid ? false
, setgid ? false
, permissions ? "u+rx,g+x,o+x"
, ...
}: ''
cp ${wrappedPrograms}/bin/${program}.wrapper $wrapperDir/${program}
# Prevent races
chmod 0000 $wrapperDir/${program}
chown ${owner}.${group} $wrapperDir/${program}
chmod "u${if setuid then "+" else "-"}s,g${if setgid then "+" else "-"}s,${permissions}" $wrapperDir/${program}
'';
mkWrappedPrograms =
builtins.map
(s: if (s ? "capabilities")
then mkSetcapProgram s
else if
(s ? "setuid" && s.setuid == true) ||
(s ? "setguid" && s.setguid == true) ||
(s ? "permissions")
then mkSetuidProgram s
else ""
) programs;
in
{
###### interface
options = {
security.setuidPrograms = lib.mkOption {
type = lib.types.listOf lib.types.str;
default = [];
example = ["passwd"];
description = ''
The Nix store cannot contain setuid/setgid programs directly.
For this reason, NixOS can automatically generate wrapper
programs that have the necessary privileges. This option
lists the names of programs in the system environment for
which setuid root wrappers should be created.
'';
};
security.wrappers = lib.mkOption {
type = lib.types.attrs;
default = {};
example = {
sendmail.source = "/nix/store/.../bin/sendmail";
ping = {
source = "${pkgs.iputils.out}/bin/ping";
owner = "nobody";
group = "nogroup";
capabilities = "cap_net_raw+ep";
};
};
description = ''
This option allows the ownership and permissions on the setuid
wrappers for specific programs to be overridden from the
default (setuid root, but not setgid root).
Additionally, this option can set capabilities on a wrapper
program that propagates those capabilities down to the
wrapped, real program.
The <literal>program</literal> attribute is the name of the
program to be wrapped. If no <literal>source</literal>
attribute is provided, specifying the absolute path to the
program, then the program will be searched for in the path
environment variable.
NOTE: cap_setpcap, which is required for the wrapper program
to be able to raise caps into the Ambient set is NOT raised to
the Ambient set so that the real program cannot modify its own
capabilities!! This may be too restrictive for cases in which
the real program needs cap_setpcap but it at least leans on
the side security paranoid vs. too relaxed.
'';
};
security.old-wrapperDir = lib.mkOption {
type = lib.types.path;
default = "/var/setuid-wrappers";
internal = true;
description = ''
This option defines the path to the wrapper programs. It
should not be overriden.
'';
};
security.wrapperDir = lib.mkOption {
type = lib.types.path;
default = "/run/wrappers";
internal = true;
description = ''
This option defines the path to the wrapper programs. It
should not be overriden.
'';
};
};
###### implementation
config = {
# Make sure our wrapperDir exports to the PATH env variable when
# initializing the shell
environment.extraInit = ''
# Wrappers override other bin directories.
export PATH="${wrapperDir}:$PATH"
'';
###### setcap activation script
system.activationScripts.wrappers =
lib.stringAfter [ "users" ]
''
# Look in the system path and in the default profile for
# programs to be wrapped.
WRAPPER_PATH=${config.system.path}/bin:${config.system.path}/sbin
mkdir -p ${wrapperDir}
wrapperDir=$(mktemp --directory --tmpdir=${wrapperDir} wrappers.XXXXXXXXXX)
chmod a+rx $wrapperDir
${lib.concatStringsSep "\n" mkWrappedPrograms}
'';
};
}
|