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nixpkgs/nixos/modules/security/sudo.nix
2021-10-04 12:47:20 +02:00

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{ config, lib, pkgs, ... }:
with lib;
let
cfg = config.security.sudo;
inherit (pkgs) sudo;
toUserString = user: if (isInt user) then "#${toString user}" else "${user}";
toGroupString = group: if (isInt group) then "%#${toString group}" else "%${group}";
toCommandOptionsString = options:
"${concatStringsSep ":" options}${optionalString (length options != 0) ":"} ";
toCommandsString = commands:
concatStringsSep ", " (
map (command:
if (isString command) then
command
else
"${toCommandOptionsString command.options}${command.command}"
) commands
);
in
{
###### interface
options = {
security.sudo.enable = mkOption {
type = types.bool;
default = true;
description =
''
Whether to enable the <command>sudo</command> command, which
allows non-root users to execute commands as root.
'';
};
security.sudo.package = mkOption {
type = types.package;
default = pkgs.sudo;
defaultText = literalExpression "pkgs.sudo";
description = ''
Which package to use for `sudo`.
'';
};
security.sudo.wheelNeedsPassword = mkOption {
type = types.bool;
default = true;
description =
''
Whether users of the <code>wheel</code> group must
provide a password to run commands as super user via <command>sudo</command>.
'';
};
security.sudo.execWheelOnly = mkOption {
type = types.bool;
default = false;
description = ''
Only allow members of the <code>wheel</code> group to execute sudo by
setting the executable's permissions accordingly.
This prevents users that are not members of <code>wheel</code> from
exploiting vulnerabilities in sudo such as CVE-2021-3156.
'';
};
security.sudo.configFile = mkOption {
type = types.lines;
# Note: if syntax errors are detected in this file, the NixOS
# configuration will fail to build.
description =
''
This string contains the contents of the
<filename>sudoers</filename> file.
'';
};
security.sudo.extraRules = mkOption {
description = ''
Define specific rules to be in the <filename>sudoers</filename> file.
More specific rules should come after more general ones in order to
yield the expected behavior. You can use mkBefore/mkAfter to ensure
this is the case when configuration options are merged.
'';
default = [];
example = literalExpression ''
[
# Allow execution of any command by all users in group sudo,
# requiring a password.
{ groups = [ "sudo" ]; commands = [ "ALL" ]; }
# Allow execution of "/home/root/secret.sh" by user `backup`, `database`
# and the group with GID `1006` without a password.
{ users = [ "backup" "database" ]; groups = [ 1006 ];
commands = [ { command = "/home/root/secret.sh"; options = [ "SETENV" "NOPASSWD" ]; } ]; }
# Allow all users of group `bar` to run two executables as user `foo`
# with arguments being pre-set.
{ groups = [ "bar" ]; runAs = "foo";
commands =
[ "/home/baz/cmd1.sh hello-sudo"
{ command = '''/home/baz/cmd2.sh ""'''; options = [ "SETENV" ]; } ]; }
]
'';
type = with types; listOf (submodule {
options = {
users = mkOption {
type = with types; listOf (either str int);
description = ''
The usernames / UIDs this rule should apply for.
'';
default = [];
};
groups = mkOption {
type = with types; listOf (either str int);
description = ''
The groups / GIDs this rule should apply for.
'';
default = [];
};
host = mkOption {
type = types.str;
default = "ALL";
description = ''
For what host this rule should apply.
'';
};
runAs = mkOption {
type = with types; str;
default = "ALL:ALL";
description = ''
Under which user/group the specified command is allowed to run.
A user can be specified using just the username: <code>"foo"</code>.
It is also possible to specify a user/group combination using <code>"foo:bar"</code>
or to only allow running as a specific group with <code>":bar"</code>.
'';
};
commands = mkOption {
description = ''
The commands for which the rule should apply.
'';
type = with types; listOf (either str (submodule {
options = {
command = mkOption {
type = with types; str;
description = ''
A command being either just a path to a binary to allow any arguments,
the full command with arguments pre-set or with <code>""</code> used as the argument,
not allowing arguments to the command at all.
'';
};
options = mkOption {
type = with types; listOf (enum [ "NOPASSWD" "PASSWD" "NOEXEC" "EXEC" "SETENV" "NOSETENV" "LOG_INPUT" "NOLOG_INPUT" "LOG_OUTPUT" "NOLOG_OUTPUT" ]);
description = ''
Options for running the command. Refer to the <a href="https://www.sudo.ws/man/1.7.10/sudoers.man.html">sudo manual</a>.
'';
default = [];
};
};
}));
};
};
});
};
security.sudo.extraConfig = mkOption {
type = types.lines;
default = "";
description = ''
Extra configuration text appended to <filename>sudoers</filename>.
'';
};
};
###### implementation
config = mkIf cfg.enable {
# We `mkOrder 600` so that the default rule shows up first, but there is
# still enough room for a user to `mkBefore` it.
security.sudo.extraRules = mkOrder 600 [
{ groups = [ "wheel" ];
commands = [ { command = "ALL"; options = (if cfg.wheelNeedsPassword then [ "SETENV" ] else [ "NOPASSWD" "SETENV" ]); } ];
}
];
security.sudo.configFile =
''
# Don't edit this file. Set the NixOS options security.sudo.configFile
# or security.sudo.extraRules instead.
# Keep SSH_AUTH_SOCK so that pam_ssh_agent_auth.so can do its magic.
Defaults env_keep+=SSH_AUTH_SOCK
# "root" is allowed to do anything.
root ALL=(ALL:ALL) SETENV: ALL
# extraRules
${concatStringsSep "\n" (
lists.flatten (
map (
rule: if (length rule.commands != 0) then [
(map (user: "${toUserString user} ${rule.host}=(${rule.runAs}) ${toCommandsString rule.commands}") rule.users)
(map (group: "${toGroupString group} ${rule.host}=(${rule.runAs}) ${toCommandsString rule.commands}") rule.groups)
] else []
) cfg.extraRules
)
)}
${cfg.extraConfig}
'';
security.wrappers = let
owner = "root";
group = if cfg.execWheelOnly then "wheel" else "root";
setuid = true;
permissions = if cfg.execWheelOnly then "u+rx,g+x" else "u+rx,g+x,o+x";
in {
sudo = {
source = "${cfg.package.out}/bin/sudo";
inherit owner group setuid permissions;
};
sudoedit = {
source = "${cfg.package.out}/bin/sudoedit";
inherit owner group setuid permissions;
};
};
environment.systemPackages = [ sudo ];
security.pam.services.sudo = { sshAgentAuth = true; };
environment.etc.sudoers =
{ source =
pkgs.runCommand "sudoers"
{
src = pkgs.writeText "sudoers-in" cfg.configFile;
preferLocalBuild = true;
}
# Make sure that the sudoers file is syntactically valid.
# (currently disabled - NIXOS-66)
"${pkgs.buildPackages.sudo}/sbin/visudo -f $src -c && cp $src $out";
mode = "0440";
};
};
}