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nixpkgs/nixos/modules/config/users-groups.nix
Symphorien Gibol 7a87973b4c nixos/users: require one of users.users.name.{isSystemUser,isNormalUser}
As the only consequence of isSystemUser is that if the uid is null then
it's allocated below 500, if a user has uid = something below 500 then
we don't require isSystemUser to be set.

Motivation: https://github.com/NixOS/nixpkgs/issues/112647
2021-04-14 20:40:00 +02:00

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{ config, lib, utils, pkgs, ... }:
with lib;
let
ids = config.ids;
cfg = config.users;
# Check whether a password hash will allow login.
allowsLogin = hash:
hash == "" # login without password
|| !(lib.elem hash
[ null # password login disabled
"!" # password login disabled
"!!" # a variant of "!"
"*" # password unset
]);
passwordDescription = ''
The options <option>hashedPassword</option>,
<option>password</option> and <option>passwordFile</option>
controls what password is set for the user.
<option>hashedPassword</option> overrides both
<option>password</option> and <option>passwordFile</option>.
<option>password</option> overrides <option>passwordFile</option>.
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 <option>users.mutableUsers</option> 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
<option>users.mutableUsers</option> is false, you cannot change
user passwords, they will always be set according to the password
options.
'';
hashedPasswordDescription = ''
To generate a hashed password run <literal>mkpasswd -m sha-512</literal>.
If set to an empty string (<literal>""</literal>), this user will
be able to log in without being asked for a password (but not via remote
services such as SSH, or indirectly via <command>su</command> or
<command>sudo</command>). This should only be used for e.g. bootable
live systems. Note: this is different from setting an empty password,
which ca be achieved using <option>users.users.&lt;name?&gt;.password</option>.
If set to <literal>null</literal> (default) this user will not
be able to log in using a password (i.e. via <command>login</command>
command).
'';
userOpts = { name, config, ... }: {
options = {
name = mkOption {
type = types.str;
apply = x: assert (builtins.stringLength x < 32 || abort "Username '${x}' is longer than 31 characters which is not allowed!"); x;
description = ''
The name of the user account. If undefined, the name of the
attribute set will be used.
'';
};
description = mkOption {
type = types.str;
default = "";
example = "Alice Q. User";
description = ''
A short description of the user account, typically the
user's full name. This is actually the GECOS or comment
field in <filename>/etc/passwd</filename>.
'';
};
uid = mkOption {
type = with types; nullOr int;
default = null;
description = ''
The account UID. If the UID is null, a free UID is picked on
activation.
'';
};
isSystemUser = mkOption {
type = types.bool;
default = false;
description = ''
Indicates if the user is a system user or not. This option
only has an effect if <option>uid</option> is
<option>null</option>, in which case it determines whether
the user's UID is allocated in the range for system users
(below 500) or in the range for normal users (starting at
1000).
Exactly one of <literal>isNormalUser</literal> and
<literal>isSystemUser</literal> must be true.
'';
};
isNormalUser = mkOption {
type = types.bool;
default = false;
description = ''
Indicates whether this is an account for a real user. This
automatically sets <option>group</option> to
<literal>users</literal>, <option>createHome</option> to
<literal>true</literal>, <option>home</option> to
<filename>/home/<replaceable>username</replaceable></filename>,
<option>useDefaultShell</option> to <literal>true</literal>,
and <option>isSystemUser</option> to
<literal>false</literal>.
Exactly one of <literal>isNormalUser</literal> and
<literal>isSystemUser</literal> must be true.
'';
};
group = mkOption {
type = types.str;
apply = x: assert (builtins.stringLength x < 32 || abort "Group name '${x}' is longer than 31 characters which is not allowed!"); x;
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.path;
default = "/var/empty";
description = "The user's home directory.";
};
cryptHomeLuks = mkOption {
type = with types; nullOr str;
default = null;
description = ''
Path to encrypted luks device that contains
the user's home directory.
'';
};
pamMount = mkOption {
type = with types; attrsOf str;
default = {};
description = ''
Attributes for user's entry in
<filename>pam_mount.conf.xml</filename>.
Useful attributes might include <code>path</code>,
<code>options</code>, <code>fstype</code>, and <code>server</code>.
See <link
xlink:href="http://pam-mount.sourceforge.net/pam_mount.conf.5.html" />
for more information.
'';
};
shell = mkOption {
type = types.nullOr (types.either types.shellPackage types.path);
default = pkgs.shadow;
defaultText = "pkgs.shadow";
example = literalExample "pkgs.bashInteractive";
description = ''
The path to the user's shell. Can use shell derivations,
like <literal>pkgs.bashInteractive</literal>. Dont
forget to enable your shell in
<literal>programs</literal> if necessary,
like <code>programs.zsh.enable = true;</code>.
'';
};
subUidRanges = mkOption {
type = with types; listOf (submodule subordinateUidRange);
default = [];
example = [
{ startUid = 1000; count = 1; }
{ startUid = 100001; count = 65534; }
];
description = ''
Subordinate user ids that user is allowed to use.
They are set into <filename>/etc/subuid</filename> and are used
by <literal>newuidmap</literal> for user namespaces.
'';
};
subGidRanges = mkOption {
type = with types; listOf (submodule subordinateGidRange);
default = [];
example = [
{ startGid = 100; count = 1; }
{ startGid = 1001; count = 999; }
];
description = ''
Subordinate group ids that user is allowed to use.
They are set into <filename>/etc/subgid</filename> and are used
by <literal>newgidmap</literal> for user namespaces.
'';
};
createHome = mkOption {
type = types.bool;
default = false;
description = ''
Whether to create the home directory and ensure ownership as well as
permissions to match the user.
'';
};
useDefaultShell = mkOption {
type = types.bool;
default = false;
description = ''
If true, the user's shell will be set to
<option>users.defaultUserShell</option>.
'';
};
hashedPassword = mkOption {
type = with types; nullOr str;
default = null;
description = ''
Specifies the hashed password for the user.
${passwordDescription}
${hashedPasswordDescription}
'';
};
password = mkOption {
type = with types; 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; nullOr str;
default = null;
description = ''
The full 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}
'';
};
initialHashedPassword = mkOption {
type = with types; nullOr str;
default = null;
description = ''
Specifies the initial hashed password for the user, i.e. the
hashed password assigned if the user does not already
exist. If <option>users.mutableUsers</option> is true, the
password can be changed subsequently using the
<command>passwd</command> command. Otherwise, it's
equivalent to setting the <option>hashedPassword</option> option.
${hashedPasswordDescription}
'';
};
initialPassword = mkOption {
type = with types; nullOr str;
default = null;
description = ''
Specifies the initial password for the user, i.e. the
password assigned if the user does not already exist. If
<option>users.mutableUsers</option> is true, the password
can be changed subsequently using the
<command>passwd</command> command. Otherwise, it's
equivalent to setting the <option>password</option>
option. The same caveat applies: the password specified here
is world-readable in the Nix store, so it should only be
used for guest accounts or passwords that will be changed
promptly.
'';
};
packages = mkOption {
type = types.listOf types.package;
default = [];
example = literalExample "[ pkgs.firefox pkgs.thunderbird ]";
description = ''
The set of packages that should be made available to the user.
This is in contrast to <option>environment.systemPackages</option>,
which adds packages to all users.
'';
};
};
config = mkMerge
[ { name = mkDefault name;
shell = mkIf config.useDefaultShell (mkDefault cfg.defaultUserShell);
}
(mkIf config.isNormalUser {
group = mkDefault "users";
createHome = mkDefault true;
home = mkDefault "/home/${config.name}";
useDefaultShell = mkDefault true;
isSystemUser = mkDefault false;
})
# If !mutableUsers, setting initialPassword is equivalent to
# setting password (and similarly for hashed passwords).
(mkIf (!cfg.mutableUsers && config.initialPassword != null) {
password = mkDefault config.initialPassword;
})
(mkIf (!cfg.mutableUsers && config.initialHashedPassword != null) {
hashedPassword = mkDefault config.initialHashedPassword;
})
];
};
groupOpts = { name, ... }: {
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 GID is null, a free GID is picked on
activation.
'';
};
members = mkOption {
type = with types; listOf str;
default = [];
description = ''
The user names of the group members, added to the
<literal>/etc/group</literal> file.
'';
};
};
config = {
name = mkDefault name;
};
};
subordinateUidRange = {
options = {
startUid = mkOption {
type = types.int;
description = ''
Start of the range of subordinate user ids that user is
allowed to use.
'';
};
count = mkOption {
type = types.int;
default = 1;
description = "Count of subordinate user ids";
};
};
};
subordinateGidRange = {
options = {
startGid = mkOption {
type = types.int;
description = ''
Start of the range of subordinate group ids that user is
allowed to use.
'';
};
count = mkOption {
type = types.int;
default = 1;
description = "Count of subordinate group ids";
};
};
};
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.users) "uid";
gidsAreUnique = idsAreUnique (filterAttrs (n: g: g.gid != null) cfg.groups) "gid";
spec = pkgs.writeText "users-groups.json" (builtins.toJSON {
inherit (cfg) mutableUsers;
users = mapAttrsToList (_: u:
{ inherit (u)
name uid group description home createHome isSystemUser
password passwordFile hashedPassword
isNormalUser subUidRanges subGidRanges
initialPassword initialHashedPassword;
shell = utils.toShellPath u.shell;
}) cfg.users;
groups = mapAttrsToList (n: g:
{ inherit (g) name gid;
members = g.members ++ (mapAttrsToList (n: u: u.name) (
filterAttrs (n: u: elem g.name u.extraGroups) cfg.users
));
}) cfg.groups;
});
systemShells =
let
shells = mapAttrsToList (_: u: u.shell) cfg.users;
in
filter types.shellPackage.check shells;
in {
imports = [
(mkAliasOptionModule [ "users" "extraUsers" ] [ "users" "users" ])
(mkAliasOptionModule [ "users" "extraGroups" ] [ "users" "groups" ])
(mkChangedOptionModule
[ "security" "initialRootPassword" ]
[ "users" "users" "root" "initialHashedPassword" ]
(cfg: if cfg.security.initialRootPassword == "!"
then null
else cfg.security.initialRootPassword))
];
###### interface
options = {
users.mutableUsers = mkOption {
type = types.bool;
default = true;
description = ''
If set to <literal>true</literal>, 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.users</literal> and
<literal>users.groups</literal> options.
The initial password for a user will be set
according to <literal>users.users</literal>, but existing passwords
will not be changed.
<warning><para>
If set to <literal>false</literal>, the contents of the user and
group files will simply be replaced on system activation. This also
holds for the user passwords; all changed
passwords will be reset according to the
<literal>users.users</literal> configuration on activation.
</para></warning>
'';
};
users.enforceIdUniqueness = mkOption {
type = types.bool;
default = true;
description = ''
Whether to require that no two users/groups share the same uid/gid.
'';
};
users.users = mkOption {
default = {};
type = with types; attrsOf (submodule userOpts);
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.
'';
};
users.groups = mkOption {
default = {};
example =
{ students.gid = 1001;
hackers = { };
};
type = with types; attrsOf (submodule groupOpts);
description = ''
Additional groups to be created automatically by the system.
'';
};
};
###### implementation
config = {
users.users = {
root = {
uid = ids.uids.root;
description = "System administrator";
home = "/root";
shell = mkDefault cfg.defaultUserShell;
group = "root";
};
nobody = {
uid = ids.uids.nobody;
isSystemUser = true;
description = "Unprivileged account (don't use!)";
group = "nogroup";
};
};
users.groups = {
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;
input.gid = ids.gids.input;
kvm.gid = ids.gids.kvm;
render.gid = ids.gids.render;
shadow.gid = ids.gids.shadow;
};
system.activationScripts.users = stringAfter [ "stdio" ]
''
install -m 0700 -d /root
install -m 0755 -d /home
${pkgs.perl.withPackages (p: [ p.FileSlurp p.JSON ])}/bin/perl \
-w ${./update-users-groups.pl} ${spec}
'';
# for backwards compatibility
system.activationScripts.groups = stringAfter [ "users" ] "";
# Install all the user shells
environment.systemPackages = systemShells;
environment.etc = (mapAttrs' (_: { packages, name, ... }: {
name = "profiles/per-user/${name}";
value.source = pkgs.buildEnv {
name = "user-environment";
paths = packages;
inherit (config.environment) pathsToLink extraOutputsToInstall;
inherit (config.system.path) ignoreCollisions postBuild;
};
}) (filterAttrs (_: u: u.packages != []) cfg.users));
environment.profiles = [
"$HOME/.nix-profile"
"/etc/profiles/per-user/$USER"
];
assertions = [
{ assertion = !cfg.enforceIdUniqueness || (uidsAreUnique && gidsAreUnique);
message = "UIDs and GIDs must be unique!";
}
{ # If mutableUsers is false, to prevent users creating a
# configuration that locks them out of the system, ensure that
# there is at least one "privileged" account that has a
# password or an SSH authorized key. Privileged accounts are
# root and users in the wheel group.
assertion = !cfg.mutableUsers ->
any id ((mapAttrsToList (_: cfg:
(cfg.name == "root"
|| cfg.group == "wheel"
|| elem "wheel" cfg.extraGroups)
&&
(allowsLogin cfg.hashedPassword
|| cfg.password != null
|| cfg.passwordFile != null
|| cfg.openssh.authorizedKeys.keys != []
|| cfg.openssh.authorizedKeys.keyFiles != [])
) cfg.users) ++ [
config.security.googleOsLogin.enable
]);
message = ''
Neither the root account nor any wheel user has a password or SSH authorized key.
You must set one to prevent being locked out of your system.'';
}
] ++ flatten (flip mapAttrsToList cfg.users (name: user:
[
{
assertion = (user.hashedPassword != null)
-> (builtins.match ".*:.*" user.hashedPassword == null);
message = ''
The password hash of user "${user.name}" contains a ":" character.
This is invalid and would break the login system because the fields
of /etc/shadow (file where hashes are stored) are colon-separated.
Please check the value of option `users.users."${user.name}".hashedPassword`.'';
}
{
assertion = let
xor = a: b: a && !b || b && !a;
isEffectivelySystemUser = user.isSystemUser || (user.uid != null && user.uid < 500);
in xor isEffectivelySystemUser user.isNormalUser;
message = ''
Exactly one of users.users.${user.name}.isSystemUser and users.users.${user.name}.isNormalUser must be set.
'';
}
]
));
warnings =
builtins.filter (x: x != null) (
flip mapAttrsToList cfg.users (_: user:
# This regex matches a subset of the Modular Crypto Format (MCF)[1]
# informal standard. Since this depends largely on the OS or the
# specific implementation of crypt(3) we only support the (sane)
# schemes implemented by glibc and BSDs. In particular the original
# DES hash is excluded since, having no structure, it would validate
# common mistakes like typing the plaintext password.
#
# [1]: https://en.wikipedia.org/wiki/Crypt_(C)
let
sep = "\\$";
base64 = "[a-zA-Z0-9./]+";
id = "[a-z0-9-]+";
value = "[a-zA-Z0-9/+.-]+";
options = "${id}(=${value})?(,${id}=${value})*";
scheme = "${id}(${sep}${options})?";
content = "${base64}${sep}${base64}";
mcf = "^${sep}${scheme}${sep}${content}$";
in
if (allowsLogin user.hashedPassword
&& user.hashedPassword != "" # login without password
&& builtins.match mcf user.hashedPassword == null)
then ''
The password hash of user "${user.name}" may be invalid. You must set a
valid hash or the user will be locked out of their account. Please
check the value of option `users.users."${user.name}".hashedPassword`.''
else null
));
};
}