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{ config, pkgs, ... }:
with pkgs.lib;
let
sysctlOption = mkOptionType {
name = "sysctl option value";
check = x: builtins.isBool x || builtins.isString x || builtins.isInt x;
merge = xs: last xs; # FIXME: hacky way to allow overriding in configuration.nix.
};
in
{
options = {
boot.kernel.sysctl = mkOption {
default = {};
example = {
"net.ipv4.tcp_syncookies" = false;
"vm.swappiness" = 60;
};
type = types.attrsOf sysctlOption;
description = ''
Runtime parameters of the Linux kernel, as set by
<citerefentry><refentrytitle>sysctl</refentrytitle>
<manvolnum>8</manvolnum></citerefentry>. Note that sysctl
parameters names must be enclosed in quotes
(e.g. <literal>"vm.swappiness"</literal> instead of
<literal>vm.swappiness</literal>). The value of each parameter
may be a string, integer or Boolean.
'';
};
};
config = {
environment.etc."sysctl.d/nixos.conf".text =
concatStrings (mapAttrsToList (n: v: "${n}=${if v == false then "0" else toString v}\n") config.boot.kernel.sysctl);
systemd.services.systemd-sysctl =
{ description = "Apply Kernel Variables";
before = [ "sysinit.target" "shutdown.target" ];
wantedBy = [ "sysinit.target" "multi-user.target" ];
restartTriggers = [ config.environment.etc."sysctl.d/nixos.conf".source ];
unitConfig.DefaultDependencies = false; # needed to prevent a cycle
serviceConfig = {
Type = "oneshot";
RemainAfterExit = true;
ExecStart = "${config.systemd.package}/lib/systemd/systemd-sysctl";
};
};
# Enable hardlink and symlink restrictions. See
# https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=800179c9b8a1e796e441674776d11cd4c05d61d7
# for details.
boot.kernel.sysctl."fs.protected_hardlinks" = true;
boot.kernel.sysctl."fs.protected_symlinks" = true;
# Hide kernel pointers (e.g. in /proc/modules) for unprivileged
# users as these make it easier to exploit kernel vulnerabilities.
boot.kernel.sysctl."kernel.kptr_restrict" = 1;
};
}