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nixpkgs/nixos/modules/config/users-groups.nix
Austin Seipp 172dc1336f nixos: add grsecurity module (#1875)
This module implements a significant refactoring in grsecurity
configuration for NixOS, making it far more usable by default and much
easier to configure.

 - New security.grsecurity NixOS attributes.
   - All grsec kernels supported
   - Allows default 'auto' grsec configuration, or custom config
   - Supports custom kernel options through kernelExtraConfig
   - Defaults to high-security - user must choose kernel, server/desktop
     mode, and any virtualisation software. That's all.
   - kptr_restrict is fixed under grsecurity (it's unwriteable)
 - grsecurity patch creation is now significantly abstracted
   - only need revision, version, and SHA1
   - kernel version requirements are asserted for sanity
   - built kernels can have the uname specify the exact grsec version
     for development or bug reports. Off by default (requires
     `security.grsecurity.config.verboseVersion = true;`)
 - grsecurity sysctl support
   - By default, disabled.
   - For people who enable it, NixOS deploys a 'grsec-lock' systemd
     service which runs at startup. You are expected to configure sysctl
     through NixOS like you regularly would, which will occur before the
     service is started. As a result, changing sysctl settings requires
     a reboot.
 - New default group: 'grsecurity'
   - Root is a member by default
   - GRKERNSEC_PROC_GID is implicitly set to the 'grsecurity' GID,
     making it possible to easily add users to this group for /proc
     access
 - AppArmor is now automatically enabled where it wasn't before, despite
   implying features.apparmor = true

The most trivial example of enabling grsecurity in your kernel is by
specifying:

    security.grsecurity.enable          = true;
    security.grsecurity.testing         = true;      # testing 3.13 kernel
    security.grsecurity.config.system   = "desktop"; # or "server"

This specifies absolutely no virtualisation support. In general, you
probably at least want KVM host support, which is a little more work.
So:

    security.grsecurity.enable = true;
    security.grsecurity.stable = true; # enable stable 3.2 kernel
    security.grsecurity.config = {
      system   = "server";
      priority = "security";
      virtualisationConfig   = "host";
      virtualisationSoftware = "kvm";
      hardwareVirtualisation = true;
    }

This module has primarily been tested on Hetzner EX40 & VQ7 servers
using NixOps.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
2014-04-11 22:43:51 -05:00

508 lines
16 KiB
Nix

{pkgs, config, ...}:
with pkgs.lib;
let
ids = config.ids;
cfg = config.users;
nonUidUsers = filterAttrs (n: u: u.createUser && u.uid == null) cfg.extraUsers;
nonGidGroups = filterAttrs (n: g: g.gid == null) cfg.extraGroups;
passwordDescription = ''
The options <literal>hashedPassword</literal>,
<literal>password</literal> and <literal>passwordFile</literal>
controls what password is set for the user.
<literal>hashedPassword</literal> overrides both
<literal>password</literal> and <literal>passwordFile</literal>.
<literal>password</literal> overrides <literal>passwordFile</literal>.
If none of these three options are set, no password is assigned to
the user, and the user will not be able to do password logins.
If the option <literal>users.mutableUsers</literal> is true, the
password defined in one of the three options will only be set when
the user is created for the first time. After that, you are free to
change the password with the ordinary user management commands. If
<literal>users.mutableUsers</literal> is false, you cannot change
user passwords, they will always be set according to the password
options.
'';
userOpts = { name, config, ... }: {
options = {
name = mkOption {
type = types.str;
description = ''
The name of the user account. If undefined, the name of the
attribute set will be used.
'';
};
description = mkOption {
type = types.str;
default = "";
example = "Alice Q. User";
description = ''
A short description of the user account, typically the
user's full name. This is actually the GECOS or comment
field in <filename>/etc/passwd</filename>.
'';
};
uid = mkOption {
type = with types; nullOr int;
default = null;
description = ''
The account UID. If the <literal>mutableUsers</literal> option
is false, the UID cannot be null. Otherwise, the UID might be
null, in which case a free UID is picked on activation (by the
useradd command).
'';
};
group = mkOption {
type = types.str;
default = "nogroup";
description = "The user's primary group.";
};
extraGroups = mkOption {
type = types.listOf types.str;
default = [];
description = "The user's auxiliary groups.";
};
home = mkOption {
type = types.str;
default = "/var/empty";
description = "The user's home directory.";
};
shell = mkOption {
type = types.str;
default = "/run/current-system/sw/sbin/nologin";
description = "The path to the user's shell.";
};
createHome = mkOption {
type = types.bool;
default = false;
description = ''
If true, the home directory will be created automatically. If this
option is true and the home directory already exists but is not
owned by the user, directory owner and group will be changed to
match the user.
'';
};
useDefaultShell = mkOption {
type = types.bool;
default = false;
description = ''
If true, the user's shell will be set to
<literal>cfg.defaultUserShell</literal>.
'';
};
hashedPassword = mkOption {
type = with types; uniq (nullOr str);
default = null;
description = ''
Specifies the (hashed) password for the user.
${passwordDescription}
'';
};
password = mkOption {
type = with types; uniq (nullOr str);
default = null;
description = ''
Specifies the (clear text) password for the user.
Warning: do not set confidential information here
because it is world-readable in the Nix store. This option
should only be used for public accounts.
${passwordDescription}
'';
};
passwordFile = mkOption {
type = with types; uniq (nullOr string);
default = null;
description = ''
The path to a file that contains the user's password. The password
file is read on each system activation. The file should contain
exactly one line, which should be the password in an encrypted form
that is suitable for the <literal>chpasswd -e</literal> command.
${passwordDescription}
'';
};
createUser = mkOption {
type = types.bool;
default = true;
description = ''
Indicates if the user should be created automatically as a local user.
Set this to false if the user for instance is an LDAP user. NixOS will
then not modify any of the basic properties for the user account.
'';
};
};
config = {
name = mkDefault name;
shell = mkIf config.useDefaultShell (mkDefault cfg.defaultUserShell);
};
};
groupOpts = { name, config, ... }: {
options = {
name = mkOption {
type = types.str;
description = ''
The name of the group. If undefined, the name of the attribute set
will be used.
'';
};
gid = mkOption {
type = with types; nullOr int;
default = null;
description = ''
The group GID. If the <literal>mutableUsers</literal> option
is false, the GID cannot be null. Otherwise, the GID might be
null, in which case a free GID is picked on activation (by the
groupadd command).
'';
};
members = mkOption {
type = with types; listOf string;
default = [];
description = ''
The user names of the group members, added to the
<literal>/etc/group</literal> file.
'';
};
};
config = {
name = mkDefault name;
};
};
getGroup = gname:
let
groups = mapAttrsToList (n: g: g) (
filterAttrs (n: g: g.name == gname) cfg.extraGroups
);
in
if length groups == 1 then head groups
else if groups == [] then throw "Group ${gname} not defined"
else throw "Group ${gname} has multiple definitions";
getUser = uname:
let
users = mapAttrsToList (n: u: u) (
filterAttrs (n: u: u.name == uname) cfg.extraUsers
);
in
if length users == 1 then head users
else if users == [] then throw "User ${uname} not defined"
else throw "User ${uname} has multiple definitions";
mkGroupEntry = gname:
let
g = getGroup gname;
users = mapAttrsToList (n: u: u.name) (
filterAttrs (n: u: elem g.name u.extraGroups) cfg.extraUsers
);
in concatStringsSep ":" [
g.name "x" (toString g.gid)
(concatStringsSep "," (users ++ (filter (u: !(elem u users)) g.members)))
];
mkPasswdEntry = uname: let u = getUser uname; in
concatStringsSep ":" [
u.name "x" (toString u.uid)
(toString (getGroup u.group).gid)
u.description u.home u.shell
];
sortOn = a: sort (as1: as2: lessThan (getAttr a as1) (getAttr a as2));
groupFile = pkgs.writeText "group" (
concatStringsSep "\n" (map (g: mkGroupEntry g.name) (
let f = g: g.gid != null; in
sortOn "gid" (filter f (attrValues cfg.extraGroups))
))
);
passwdFile = pkgs.writeText "passwd" (
concatStringsSep "\n" (map (u: mkPasswdEntry u.name) (
let f = u: u.createUser && (u.uid != null); in
sortOn "uid" (filter f (attrValues cfg.extraUsers))
))
);
# If mutableUsers is true, this script adds all users/groups defined in
# users.extra{Users,Groups} to /etc/{passwd,group} iff there isn't any
# existing user/group with the same name in those files.
# If mutableUsers is false, the /etc/{passwd,group} files will simply be
# replaced with the users/groups defined in the NixOS configuration.
# The merging procedure could certainly be improved, and instead of just
# keeping the lines as-is from /etc/{passwd,group} they could be combined
# in some way with the generated content from the NixOS configuration.
merger = src: pkgs.writeScript "merger" ''
#!${pkgs.bash}/bin/bash
PATH=${pkgs.gawk}/bin:${pkgs.gnugrep}/bin:$PATH
${if !cfg.mutableUsers
then ''cp ${src} $1.tmp''
else ''awk -F: '{ print "^"$1":.*" }' $1 | egrep -vf - ${src} | cat $1 - > $1.tmp''
}
# set mtime to +1, otherwise change might go unnoticed (vipw/vigr only looks at mtime)
touch -m -t $(date -d @$(($(stat -c %Y $1)+1)) +%Y%m%d%H%M.%S) $1.tmp
mv -f $1.tmp $1
'';
idsAreUnique = set: idAttr: !(fold (name: args@{ dup, acc }:
let
id = builtins.toString (builtins.getAttr idAttr (builtins.getAttr name set));
exists = builtins.hasAttr id acc;
newAcc = acc // (builtins.listToAttrs [ { name = id; value = true; } ]);
in if dup then args else if exists
then builtins.trace "Duplicate ${idAttr} ${id}" { dup = true; acc = null; }
else { dup = false; acc = newAcc; }
) { dup = false; acc = {}; } (builtins.attrNames set)).dup;
uidsAreUnique = idsAreUnique (filterAttrs (n: u: u.uid != null) cfg.extraUsers) "uid";
gidsAreUnique = idsAreUnique (filterAttrs (n: g: g.gid != null) cfg.extraGroups) "gid";
in {
###### interface
options = {
users.mutableUsers = mkOption {
type = types.bool;
default = true;
description = ''
If true, you are free to add new users and groups to the system
with the ordinary <literal>useradd</literal> and
<literal>groupadd</literal> commands. On system activation, the
existing contents of the <literal>/etc/passwd</literal> and
<literal>/etc/group</literal> files will be merged with the
contents generated from the <literal>users.extraUsers</literal> and
<literal>users.extraGroups</literal> options. If
<literal>mutableUsers</literal> is false, the contents of the user and
group files will simply be replaced on system activation. This also
holds for the user passwords; if this option is false, all changed
passwords will be reset according to the
<literal>users.extraUsers</literal> configuration on activation. If
this option is true, the initial password for a user will be set
according to <literal>users.extraUsers</literal>, but existing passwords
will not be changed.
'';
};
users.enforceIdUniqueness = mkOption {
type = types.bool;
default = true;
description = ''
Whether to require that no two users/groups share the same uid/gid.
'';
};
users.extraUsers = mkOption {
default = {};
type = types.loaOf types.optionSet;
example = {
alice = {
uid = 1234;
description = "Alice Q. User";
home = "/home/alice";
createHome = true;
group = "users";
extraGroups = ["wheel"];
shell = "/bin/sh";
};
};
description = ''
Additional user accounts to be created automatically by the system.
This can also be used to set options for root.
'';
options = [ userOpts ];
};
users.extraGroups = mkOption {
default = {};
example =
{ students.gid = 1001;
hackers = { };
};
type = types.loaOf types.optionSet;
description = ''
Additional groups to be created automatically by the system.
'';
options = [ groupOpts ];
};
security.initialRootPassword = mkOption {
type = types.str;
default = "";
example = "!";
description = ''
The (hashed) password for the root account set on initial
installation. The empty string denotes that root can login
locally without a password (but not via remote services such
as SSH, or indirectly via <command>su</command> or
<command>sudo</command>). The string <literal>!</literal>
prevents root from logging in using a password.
Note, setting this option sets
<literal>users.extraUsers.root.hashedPassword</literal>.
Note, if <literal>users.mutableUsers</literal> is false
you cannot change the root password manually, so in that case
the name of this option is a bit misleading, since it will define
the root password beyond the user initialisation phase.
'';
};
};
###### implementation
config = {
users.extraUsers = {
root = {
uid = ids.uids.root;
description = "System administrator";
home = "/root";
shell = cfg.defaultUserShell;
group = "root";
extraGroups = [ "grsecurity" ];
hashedPassword = mkDefault config.security.initialRootPassword;
};
nobody = {
uid = ids.uids.nobody;
description = "Unprivileged account (don't use!)";
group = "nogroup";
};
};
users.extraGroups = {
root.gid = ids.gids.root;
wheel.gid = ids.gids.wheel;
disk.gid = ids.gids.disk;
kmem.gid = ids.gids.kmem;
tty.gid = ids.gids.tty;
floppy.gid = ids.gids.floppy;
uucp.gid = ids.gids.uucp;
lp.gid = ids.gids.lp;
cdrom.gid = ids.gids.cdrom;
tape.gid = ids.gids.tape;
audio.gid = ids.gids.audio;
video.gid = ids.gids.video;
dialout.gid = ids.gids.dialout;
nogroup.gid = ids.gids.nogroup;
users.gid = ids.gids.users;
nixbld.gid = ids.gids.nixbld;
utmp.gid = ids.gids.utmp;
adm.gid = ids.gids.adm;
grsecurity.gid = ids.gids.grsecurity;
};
system.activationScripts.users =
let
mkhomeUsers = filterAttrs (n: u: u.createHome) cfg.extraUsers;
setpwUsers = filterAttrs (n: u: u.createUser) cfg.extraUsers;
pwFile = u: if !(isNull u.hashedPassword)
then pkgs.writeTextFile { name = "password-file"; text = u.hashedPassword; }
else if !(isNull u.password)
then pkgs.runCommand "password-file" { pw = u.password; } ''
echo -n "$pw" | ${pkgs.mkpasswd}/bin/mkpasswd -s > $out
'' else u.passwordFile;
setpw = n: u: ''
setpw=yes
${optionalString cfg.mutableUsers ''
test "$(getent shadow '${u.name}' | cut -d: -f2)" != "x" && setpw=no
''}
if [ "$setpw" == "yes" ]; then
${if !(isNull (pwFile u))
then ''
echo -n "${u.name}:" | cat - "${pwFile u}" | \
${pkgs.shadow}/sbin/chpasswd -e
''
else "passwd -l '${u.name}' &>/dev/null"
}
fi
'';
mkhome = n: u: ''
uid="$(id -u ${u.name})"
gid="$(id -g ${u.name})"
h="${u.home}"
test -a "$h" || mkdir -p "$h" || true
test "$(stat -c %u "$h")" = $uid || chown $uid "$h" || true
test "$(stat -c %g "$h")" = $gid || chgrp $gid "$h" || true
'';
groupadd = n: g: ''
if [ -z "$(getent group "${g.name}")" ]; then
echo "Adding group ${g.name}"
${pkgs.shadow}/sbin/groupadd "${g.name}"
fi
'';
useradd = n: u: ''
if ! id "${u.name}" &>/dev/null; then
echo "Adding user ${u.name}"
${pkgs.shadow}/sbin/useradd \
-g "${u.group}" \
-s "${u.shell}" \
-d "${u.home}" \
"${u.name}"
echo "${u.name}:x" | ${pkgs.shadow}/sbin/chpasswd -e
fi
'';
in stringAfter [ "etc" ] ''
touch /etc/group
touch /etc/passwd
VISUAL=${merger groupFile} ${pkgs.shadow}/sbin/vigr &>/dev/null
VISUAL=${merger passwdFile} ${pkgs.shadow}/sbin/vipw &>/dev/null
${pkgs.shadow}/sbin/grpconv
${pkgs.shadow}/sbin/pwconv
${concatStrings (mapAttrsToList groupadd nonGidGroups)}
${concatStrings (mapAttrsToList useradd nonUidUsers)}
${concatStrings (mapAttrsToList mkhome mkhomeUsers)}
${concatStrings (mapAttrsToList setpw setpwUsers)}
'';
# for backwards compatibility
system.activationScripts.groups = stringAfter [ "users" ] "";
assertions = [
{ assertion = !cfg.enforceIdUniqueness || (uidsAreUnique && gidsAreUnique);
message = "uids and gids must be unique!";
}
{ assertion = cfg.mutableUsers || (nonUidUsers == {});
message = "When mutableUsers is false, no uid can be null";
}
{ assertion = cfg.mutableUsers || (nonGidGroups == {});
message = "When mutableUsers is false, no gid can be null";
}
];
};
}