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This module implements a significant refactoring in grsecurity
configuration for NixOS, making it far more usable by default and much
easier to configure.
- New security.grsecurity NixOS attributes.
- All grsec kernels supported
- Allows default 'auto' grsec configuration, or custom config
- Supports custom kernel options through kernelExtraConfig
- Defaults to high-security - user must choose kernel, server/desktop
mode, and any virtualisation software. That's all.
- kptr_restrict is fixed under grsecurity (it's unwriteable)
- grsecurity patch creation is now significantly abstracted
- only need revision, version, and SHA1
- kernel version requirements are asserted for sanity
- built kernels can have the uname specify the exact grsec version
for development or bug reports. Off by default (requires
`security.grsecurity.config.verboseVersion = true;`)
- grsecurity sysctl support
- By default, disabled.
- For people who enable it, NixOS deploys a 'grsec-lock' systemd
service which runs at startup. You are expected to configure sysctl
through NixOS like you regularly would, which will occur before the
service is started. As a result, changing sysctl settings requires
a reboot.
- New default group: 'grsecurity'
- Root is a member by default
- GRKERNSEC_PROC_GID is implicitly set to the 'grsecurity' GID,
making it possible to easily add users to this group for /proc
access
- AppArmor is now automatically enabled where it wasn't before, despite
implying features.apparmor = true
The most trivial example of enabling grsecurity in your kernel is by
specifying:
security.grsecurity.enable = true;
security.grsecurity.testing = true; # testing 3.13 kernel
security.grsecurity.config.system = "desktop"; # or "server"
This specifies absolutely no virtualisation support. In general, you
probably at least want KVM host support, which is a little more work.
So:
security.grsecurity.enable = true;
security.grsecurity.stable = true; # enable stable 3.2 kernel
security.grsecurity.config = {
system = "server";
priority = "security";
virtualisationConfig = "host";
virtualisationSoftware = "kvm";
hardwareVirtualisation = true;
}
This module has primarily been tested on Hetzner EX40 & VQ7 servers
using NixOps.
Signed-off-by: Austin Seipp <aseipp@pobox.com>
77 lines
2.5 KiB
Nix
77 lines
2.5 KiB
Nix
{ config, pkgs, ... }:
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with pkgs.lib;
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let
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sysctlOption = mkOptionType {
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name = "sysctl option value";
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check = x: isBool x || isString x || isInt x || isNull x;
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merge = args: defs: (last defs).value; # FIXME: hacky way to allow overriding in configuration.nix.
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};
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in
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{
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options = {
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boot.kernel.sysctl = mkOption {
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default = {};
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example = {
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"net.ipv4.tcp_syncookies" = false;
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"vm.swappiness" = 60;
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};
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type = types.attrsOf sysctlOption;
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description = ''
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Runtime parameters of the Linux kernel, as set by
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<citerefentry><refentrytitle>sysctl</refentrytitle>
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<manvolnum>8</manvolnum></citerefentry>. Note that sysctl
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parameters names must be enclosed in quotes
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(e.g. <literal>"vm.swappiness"</literal> instead of
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<literal>vm.swappiness</literal>). The value of each
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parameter may be a string, integer, boolean, or null
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(signifying the option will not appear at all).
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'';
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};
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};
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config = {
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environment.etc."sysctl.d/nixos.conf".text =
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concatStrings (mapAttrsToList (n: v:
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optionalString (v != null) "${n}=${if v == false then "0" else toString v}\n"
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) config.boot.kernel.sysctl);
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systemd.services.systemd-sysctl =
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{ description = "Apply Kernel Variables";
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before = [ "sysinit.target" "shutdown.target" ];
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wantedBy = [ "sysinit.target" "multi-user.target" ];
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restartTriggers = [ config.environment.etc."sysctl.d/nixos.conf".source ];
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unitConfig = {
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DefaultDependencies = false; # needed to prevent a cycle
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ConditionPathIsReadWrite = "/proc/sys/"; # prevent systemd-sysctl in containers
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};
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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ExecStart = "${config.systemd.package}/lib/systemd/systemd-sysctl";
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};
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};
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# Enable hardlink and symlink restrictions. See
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# https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=800179c9b8a1e796e441674776d11cd4c05d61d7
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# for details.
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boot.kernel.sysctl."fs.protected_hardlinks" = true;
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boot.kernel.sysctl."fs.protected_symlinks" = true;
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# Hide kernel pointers (e.g. in /proc/modules) for unprivileged
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# users as these make it easier to exploit kernel vulnerabilities.
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#
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# Removed under grsecurity.
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boot.kernel.sysctl."kernel.kptr_restrict" =
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if config.security.grsecurity.enable then null else 1;
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};
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}
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