From f0069d03cc6f587844fb59b716deb3e1262138c7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cyryl=20P=C5=82otnicki?= <cyplo@cyplo.net>
Date: Sat, 15 Jan 2022 10:18:49 +0000
Subject: [PATCH] update security options

---
 nixos/security.nix | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/nixos/security.nix b/nixos/security.nix
index 7490abca..f56ad957 100644
--- a/nixos/security.nix
+++ b/nixos/security.nix
@@ -1,4 +1,4 @@
-{ config, pkgs, ... }:
+{ config, pkgs, lib, ... }:
 {
   nix.allowedUsers = [ "@users" ];
   security.lockKernelModules = false;
@@ -6,16 +6,21 @@
   security.forcePageTableIsolation = true;
   security.virtualisation.flushL1DataCache = "always";
   security.apparmor.enable = true;
+  security.apparmor.killUnconfinedConfinables = true;
   services.haveged.enable = true;
   networking.firewall.enable = true;
   services.clamav.daemon.enable = true;
   services.clamav.updater.enable = true;
   security.chromiumSuidSandbox.enable = true;
   boot.kernelParams = [
+    "slub_debug=FZP"
     "page_poison=1"
     "page_alloc.shuffle=1"
   ];
 
+  environment.memoryAllocator.provider = "scudo";
+  environment.variables.SCUDO_OPTIONS = "ZeroContents=1";
+
   boot.blacklistedKernelModules = [
     # Obscure network protocols
     "ax25"
@@ -38,25 +43,47 @@
     "jfs"
     "minix"
     "nilfs2"
+    "omfs"
     "qnx4"
     "qnx6"
     "sysv"
     "ufs"
   ];
 
+  # Restrict ptrace() usage to processes with a pre-defined relationship
+  # (e.g., parent/child)
+  boot.kernel.sysctl."kernel.yama.ptrace_scope" = lib.mkOverride 500 1;
+
+  # Hide kptrs even for processes with CAP_SYSLOG
+  boot.kernel.sysctl."kernel.kptr_restrict" = lib.mkOverride 500 2;
+
+  # Disable bpf() JIT (to eliminate spray attacks)
   boot.kernel.sysctl."net.core.bpf_jit_enable" = false;
+
+  # Disable ftrace debugging
   boot.kernel.sysctl."kernel.ftrace_enabled" = false;
+
+  # Enable strict reverse path filtering (that is, do not attempt to route
+  # packets that "obviously" do not belong to the iface's network; dropped
+  # packets are logged as martians).
   boot.kernel.sysctl."net.ipv4.conf.all.log_martians" = true;
   boot.kernel.sysctl."net.ipv4.conf.all.rp_filter" = "1";
   boot.kernel.sysctl."net.ipv4.conf.default.log_martians" = true;
   boot.kernel.sysctl."net.ipv4.conf.default.rp_filter" = "1";
+
+  # Ignore broadcast ICMP (mitigate SMURF)
   boot.kernel.sysctl."net.ipv4.icmp_echo_ignore_broadcasts" = true;
+
+  # Ignore incoming ICMP redirects (note: default is needed to ensure that the
+  # setting is applied to interfaces added after the sysctls are set)
   boot.kernel.sysctl."net.ipv4.conf.all.accept_redirects" = false;
   boot.kernel.sysctl."net.ipv4.conf.all.secure_redirects" = false;
   boot.kernel.sysctl."net.ipv4.conf.default.accept_redirects" = false;
   boot.kernel.sysctl."net.ipv4.conf.default.secure_redirects" = false;
   boot.kernel.sysctl."net.ipv6.conf.all.accept_redirects" = false;
   boot.kernel.sysctl."net.ipv6.conf.default.accept_redirects" = false;
+
+  # Ignore outgoing ICMP redirects (this is ipv4 only)
   boot.kernel.sysctl."net.ipv4.conf.all.send_redirects" = false;
   boot.kernel.sysctl."net.ipv4.conf.default.send_redirects" = false;
 }