nixpkgs/nixos/modules/security/audit.nix
pennae 2e751c0772 treewide: automatically md-convert option descriptions
the conversion procedure is simple:

 - find all things that look like options, ie calls to either `mkOption`
   or `lib.mkOption` that take an attrset. remember the attrset as the
   option
 - for all options, find a `description` attribute who's value is not a
   call to `mdDoc` or `lib.mdDoc`
 - textually convert the entire value of the attribute to MD with a few
   simple regexes (the set from mdize-module.sh)
 - if the change produced a change in the manual output, discard
 - if the change kept the manual unchanged, add some text to the
   description to make sure we've actually found an option. if the
   manual changes this time, keep the converted description

this procedure converts 80% of nixos options to markdown. around 2000
options remain to be inspected, but most of those fail the "does not
change the manual output check": currently the MD conversion process
does not faithfully convert docbook tags like <code> and <package>, so
any option using such tags will not be converted at all.
2022-07-30 15:16:34 +02:00

123 lines
3.7 KiB
Nix

{ config, lib, pkgs, ... }:
with lib;
let
cfg = config.security.audit;
enabled = cfg.enable == "lock" || cfg.enable;
failureModes = {
silent = 0;
printk = 1;
panic = 2;
};
disableScript = pkgs.writeScript "audit-disable" ''
#!${pkgs.runtimeShell} -eu
# Explicitly disable everything, as otherwise journald might start it.
auditctl -D
auditctl -e 0 -a task,never
'';
# TODO: it seems like people like their rules to be somewhat secret, yet they will not be if
# put in the store like this. At the same time, it doesn't feel like a huge deal and working
# around that is a pain so I'm leaving it like this for now.
startScript = pkgs.writeScript "audit-start" ''
#!${pkgs.runtimeShell} -eu
# Clear out any rules we may start with
auditctl -D
# Put the rules in a temporary file owned and only readable by root
rulesfile="$(mktemp)"
${concatMapStrings (x: "echo '${x}' >> $rulesfile\n") cfg.rules}
# Apply the requested rules
auditctl -R "$rulesfile"
# Enable and configure auditing
auditctl \
-e ${if cfg.enable == "lock" then "2" else "1"} \
-b ${toString cfg.backlogLimit} \
-f ${toString failureModes.${cfg.failureMode}} \
-r ${toString cfg.rateLimit}
'';
stopScript = pkgs.writeScript "audit-stop" ''
#!${pkgs.runtimeShell} -eu
# Clear the rules
auditctl -D
# Disable auditing
auditctl -e 0
'';
in {
options = {
security.audit = {
enable = mkOption {
type = types.enum [ false true "lock" ];
default = false;
description = lib.mdDoc ''
Whether to enable the Linux audit system. The special `lock' value can be used to
enable auditing and prevent disabling it until a restart. Be careful about locking
this, as it will prevent you from changing your audit configuration until you
restart. If possible, test your configuration using build-vm beforehand.
'';
};
failureMode = mkOption {
type = types.enum [ "silent" "printk" "panic" ];
default = "printk";
description = lib.mdDoc "How to handle critical errors in the auditing system";
};
backlogLimit = mkOption {
type = types.int;
default = 64; # Apparently the kernel default
description = lib.mdDoc ''
The maximum number of outstanding audit buffers allowed; exceeding this is
considered a failure and handled in a manner specified by failureMode.
'';
};
rateLimit = mkOption {
type = types.int;
default = 0;
description = lib.mdDoc ''
The maximum messages per second permitted before triggering a failure as
specified by failureMode. Setting it to zero disables the limit.
'';
};
rules = mkOption {
type = types.listOf types.str; # (types.either types.str (types.submodule rule));
default = [];
example = [ "-a exit,always -F arch=b64 -S execve" ];
description = lib.mdDoc ''
The ordered audit rules, with each string appearing as one line of the audit.rules file.
'';
};
};
};
config = {
systemd.services.audit = {
description = "Kernel Auditing";
wantedBy = [ "basic.target" ];
unitConfig = {
ConditionVirtualization = "!container";
ConditionSecurity = [ "audit" ];
};
path = [ pkgs.audit ];
serviceConfig = {
Type = "oneshot";
RemainAfterExit = true;
ExecStart = "@${if enabled then startScript else disableScript} audit-start";
ExecStop = "@${stopScript} audit-stop";
};
};
};
}