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# This module adds some extra configuration useful when running behid a Cloudflare Proxy.
# Mainly, it blocks all incomming conncections on relevant ports that aren't
# coming from an official CloudFlare domain.
{
config,
lib,
pkgs,
metadata,
...
}: let
# TODO: What happens when these get out of date??? Huh??? You little pissbaby
fileToList = x: lib.strings.splitString "\n" (builtins.readFile x);
cfipv4 = fileToList (pkgs.fetchurl {
url = "https://www.cloudflare.com/ips-v4";
hash = "sha256-8Cxtg7wBqwroV3Fg4DbXAMdFU1m84FTfiE5dfZ5Onns=";
});
cfipv6 = fileToList (pkgs.fetchurl {
url = "https://www.cloudflare.com/ips-v6";
hash = "sha256-np054+g7rQDE3sr9U8Y/piAp89ldto3pN9K+KCNMoKk=";
});
# Allow local IP addresses.
# See: https://en.wikipedia.org/wiki/Reserved_IP_addresses
IPv4Whitelist = [
"100.64.0.0/10 "
"10.0.0.0/8"
"127.0.0.0/8"
"172.16.0.0/12"
"192.0.0.0/24"
"192.168.0.0/16"
"198.18.0.0/15"
];
IPv6Whitelist = [
"64:ff9b:1::/48 "
"fc00::/7"
];
in {
config = {
# Teach NGINX how to extract the proxied IP from proxied requests.
#
# See: https://nixos.wiki/wiki/Nginx#Using_realIP_when_behind_CloudFlare_or_other_CDN
services.nginx.commonHttpConfig = let
realIpsFromList = lib.strings.concatMapStringsSep "\n" (x: "set_real_ip_from ${x};");
in ''
${realIpsFromList cfipv4}
${realIpsFromList cfipv6}
real_ip_header CF-Connecting-IP;
'';
# Block non-Cloudflare IP addresses.
networking.firewall = let
chain = "cloudflare-whitelist";
in {
extraCommands = let
allow-interface = lib.strings.concatMapStringsSep "\n" (i: ''ip46tables --append ${chain} --in-interface ${i} --jump RETURN'');
allow-ip = cmd: lib.strings.concatMapStringsSep "\n" (r: ''${cmd} --append ${chain} --source ${r} --jump RETURN'');
in ''
# Flush the old firewall rules. This behavior mirrors the default firewall service.
# See: https://github.com/NixOS/nixpkgs/blob/ac911bf685eecc17c2df5b21bdf32678b9f88c92/nixos/modules/services/networking/firewall-iptables.nix#L59-L66
ip46tables --delete INPUT --protocol tcp --destination-port 80 --syn --jump ${chain} 2>/dev/null || true
ip46tables --delete INPUT --protocol tcp --destination-port 443 --syn --jump ${chain} 2>/dev/null || true
ip46tables --flush ${chain} || true
ip46tables --delete-chain ${chain} || true
# Create a chain that only allows whitelisted IPs through.
ip46tables --new-chain ${chain}
# Allow trusted interfaces through.
${allow-interface config.networking.firewall.trustedInterfaces}
# Allow local whitelisted IPs through
${allow-ip "iptables" IPv4Whitelist}
${allow-ip "ip6tables" IPv6Whitelist}
# Allow Cloudflare's IP ranges through.
${allow-ip "iptables" cfipv4}
${allow-ip "ip6tables" cfipv6}
# Everything else is dropped.
#
# TODO: I would like to use `nixos-fw-log-refuse` here, but I keep
# running into weird issues when reloading the firewall.
# Something about the table not being deleted properly.
ip46tables --append ${chain} --jump DROP
# Inject our chain as the first check in INPUT (before nixos-fw).
# We want to capture any new incomming TCP connections.
ip46tables --insert INPUT 1 --protocol tcp --destination-port 80 --syn --jump ${chain}
ip46tables --insert INPUT 1 --protocol tcp --destination-port 443 --syn --jump ${chain}
'';
extraStopCommands = ''
# Clean up added rulesets (${chain}). This mirrors the behavior of the
# default firewall at the time of writing.
#
# See: https://github.com/NixOS/nixpkgs/blob/ac911bf685eecc17c2df5b21bdf32678b9f88c92/nixos/modules/services/networking/firewall-iptables.nix#L218-L219
ip46tables --delete INPUT --protocol tcp --destination-port 80 --syn --jump ${chain} 2>/dev/null || true
ip46tables --delete INPUT --protocol tcp --destination-port 443 --syn --jump ${chain} 2>/dev/null || true
'';
};
};
}
|
