nixos/postsrsd: migrate to rfc42 settings

Allow a freeform configuration approach to satisfy different
configuration complexities.

Remove confinement options and make its hardening options more explicit
and removed the deprecated PermissionStartOnly= option.
This commit is contained in:
Martin Weinelt 2025-07-14 00:58:45 +02:00
parent dab3a6e781
commit 83af4a9aed
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@ -7,32 +7,59 @@
let
cfg = config.services.postsrsd;
runtimeDirectoryName = "postsrsd";
runtimeDirectory = "/run/${runtimeDirectoryName}";
# TODO: follow RFC 42, but we need a libconfuse format first:
# https://github.com/NixOS/nixpkgs/issues/401565
# Arrays in `libconfuse` look like this: {"Life", "Universe", "Everything"}
# See https://www.nongnu.org/confuse/tutorial-html/ar01s03.html.
#
# Note: We're using `builtins.toJSON` to escape strings, but JSON strings
# don't have exactly the same semantics as libconfuse strings. For example,
# "${F}" gets treated as an env var reference, see above issue for details.
libconfuseDomains = "{ " + lib.concatMapStringsSep ", " builtins.toJSON cfg.domains + " }";
configFile = pkgs.writeText "postsrsd.conf" ''
secrets-file = "''${CREDENTIALS_DIRECTORY}/secrets-file"
domains = ${libconfuseDomains}
separator = "${cfg.separator}"
socketmap = "unix:${cfg.socketPath}"
# Disable postsrsd's jailing in favor of confinement with systemd.
unprivileged-user = ""
chroot-dir = ""
'';
inherit (lib)
concatMapStringsSep
concatMapAttrsStringSep
isBool
isFloat
isInt
isPath
isString
isList
mkRemovedOptionModule
mkRenamedOptionModule
;
# This is a implementation of a simple libconfuse config renderer sufficient
# for the postsrsd configuration file complexity.
# TODO: Replace with pkgs.formats.libconfuse, once implemented (https://github.com/NixOS/nixpkgs/issues/401565)
renderValue =
value:
if isBool value then
if value then "true" else "false"
else if isString value || isPath value then
builtins.toJSON value # for escaping
else if isInt value || isFloat value then
toString value
else if isList value then
"{${concatMapStringsSep "," renderValue value}}"
else
throw "postsrsd: unsupported value type in settings option";
renderAttr =
attrs: concatMapAttrsStringSep "\n" (name: value: "${name} = ${renderValue value}") attrs;
configFile = pkgs.writeText "postsrsd.conf" (
renderAttr (lib.filterAttrsRecursive (_: v: v != null) cfg.settings)
);
in
{
imports =
map
[
(mkRemovedOptionModule [ "services" "postsrsd" "socketPath" ] ''
Configure/reference `services.postsrsd.settings.socketmap` instead. Note that its now required to start with the `inet:` or `unix:` prefix.
'')
(mkRenamedOptionModule
[ "services" "postsrsd" "domains" ]
[ "services" "postsrsd" "settings" "domains" ]
)
(mkRenamedOptionModule
[ "services" "postsrsd" "separator" ]
[ "services" "postsrsd" "settings" "separator" ]
)
]
++ map
(
name:
lib.mkRemovedOptionModule [ "services" "postsrsd" name ] ''
@ -62,24 +89,125 @@ in
secretsFile = lib.mkOption {
type = lib.types.path;
default = "/var/lib/postsrsd/postsrsd.secret";
description = "Secret keys used for signing and verification";
description = ''
Secret keys used for signing and verification.
::: {.note}
The secret will be generated, if it does not exist at the given path.
:::
'';
};
domains = lib.mkOption {
type = lib.types.listOf lib.types.str;
description = "Domain names for rewrite";
default = [ config.networking.hostName ];
defaultText = lib.literalExpression "[ config.networking.hostName ]";
};
settings = lib.mkOption {
type = lib.types.submodule {
freeformType =
with lib.types;
attrsOf (oneOf [
bool
float
int
path
str
(listOf str)
]);
separator = lib.mkOption {
type = lib.types.enum [
"-"
"="
"+"
];
default = "=";
description = "First separator character in generated addresses";
options = {
domains = lib.mkOption {
type = with lib.types; listOf str;
default = [ ];
example = [ "example.com" ];
description = ''
List of local domains, that do not require rewriting.
'';
};
secrets-file = lib.mkOption {
type = lib.types.str;
default = "\${CREDENTIALS_DIRECTORY}/secrets-file";
readOnly = true;
description = ''
Path to the file containing the secret keys.
::: {.note}
Secrets are passed using `LoadCredential=` on the systemd unit,
so this options is read-only.
Configure {option}`services.postsrsd.secretsFile` instead.
'';
};
separator = lib.mkOption {
type = lib.types.enum [
"-"
"="
"+"
];
default = "=";
description = ''
SRS tag separator used in generated sender addresses.
Unless you have a very good reason, you should leave this
setting at its default.
'';
};
srs-domain = lib.mkOption {
type = with lib.types; nullOr str;
default = null;
example = "srs.example.com";
description = ''
Dedicated mail domain used for ephemeral SRS envelope addresses.
Recommended to configure, when hosting multiple unrelated mail
domains (e.g. for different customers), to prevent privacy
issues.
Set to `null` to not configure any `srs-domain`.
'';
};
socketmap = lib.mkOption {
type = lib.types.strMatching "^(unix|inet):.+";
default = "unix:/run/postsrsd/socket";
example = "inet:localhost:10003";
description = ''
Listener configuration in socket map format native to Postfix configuration.
'';
};
chroot-dir = lib.mkOption {
type = lib.types.str;
default = "";
readOnly = true;
description = ''
Path to chroot into at runtime as an additional layer of protection.
::: {.note}
We confine the runtime environment through systemd hardening instead, so this option is read-only.
:::
'';
};
unprivileged-user = lib.mkOption {
type = lib.types.str;
default = "";
readOnly = true;
description = ''
Unprivileged user to drop privileges to.
::: {.note}
Our systemd unit never runs postsrsd as a privileged process, so this option is read-only.
:::
'';
};
};
};
default = { };
description = ''
Configuration options for the postsrsd.conf file.
See the [example configuration](https://github.com/roehling/postsrsd/blob/main/doc/postsrsd.conf) for possible values.
'';
};
user = lib.mkOption {
@ -93,15 +221,6 @@ in
default = "postsrsd";
description = "Group for the daemon";
};
socketPath = lib.mkOption {
type = lib.types.path;
default = "${runtimeDirectory}/socket";
readOnly = true;
description = ''
Path to the Unix socket for connecting to postsrsd.
Read-only, intended for usage when integrating postsrsd into other NixOS config.'';
};
};
};
@ -143,15 +262,21 @@ in
before = [ "postfix.service" ];
wantedBy = [ "multi-user.target" ];
requires = [ "postsrsd-generate-secrets.service" ];
confinement.enable = true;
serviceConfig = {
ExecStart = "${lib.getExe pkgs.postsrsd} -C ${configFile}";
User = cfg.user;
Group = cfg.group;
PermissionsStartOnly = true;
RuntimeDirectory = runtimeDirectoryName;
RuntimeDirectory = "postsrsd";
LoadCredential = "secrets-file:${cfg.secretsFile}";
PrivateDevices = true;
PrivateMounts = true;
PrivateTmp = true;
PrivateUsers = true;
ProtectControlGroups = true;
ProtectKernelModules = true;
ProtectKernelTunables = true;
};
};
};