From f08f3812f40322b6098d75573413ed83f358871f Mon Sep 17 00:00:00 2001
From: Kleidi Bujari <mail@4kb.net>
Date: Sun, 1 Dec 2024 22:30:26 -0500
Subject: Cleanup xnet module and add baseline modules

With these changes, the xnet module is useable as a system builder. At
this point, it is still undecided whether all configuration will be
generalized into this module, rather than keeping mini-modules local to
the machine they will run on.
---
 modules/xnet/net/sshd.nix | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 modules/xnet/net/sshd.nix

(limited to 'modules/xnet/net/sshd.nix')

diff --git a/modules/xnet/net/sshd.nix b/modules/xnet/net/sshd.nix
new file mode 100644
index 0000000..ef225db
--- /dev/null
+++ b/modules/xnet/net/sshd.nix
@@ -0,0 +1,46 @@
+{ config, lib, ... }:
+let
+  cfg = config.xnet.net.sshd;
+  inherit (lib) mkOption mkIf types;
+in
+{
+  options.xnet.net.sshd = {
+    enable = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Enable hardened SSH service.";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    services.openssh = {
+      enable = true;
+      startWhenNeeded = true;
+      openFirewall = true;
+      hostKeys = [{
+        path = "/persist/certs/ssh/ssh_host_ed25519_key";
+        type = "ed25519";
+      }];
+      settings = {
+        UsePAM = true;
+        X11Forwarding = false;
+        PermitRootLogin = "no";
+        PasswordAuthentication = false;
+        Ciphers = [ "chacha20-poly1305@openssh.com" ];
+        Macs = [ "hmac-sha2-512-etm@openssh.com" ];
+        KexAlgorithms = [ "curve25519-sha256@libssh.org" ];
+      };
+      sftpServerExecutable = "internal-sftp";
+      sftpFlags = [ "-f AUTHPRIV" "-l INFO" ];
+      extraConfig =
+        let
+          pubkeyTypes = lib.strings.concatStringsSep "," [
+            "sk-ssh-ed25519-cert-v01@openssh.com"
+            "ssh-ed25519-cert-v01@openssh.com"
+            "ssh-ed25519"
+          ];
+        in
+        "PubkeyAcceptedKeyTypes ${pubkeyTypes}";
+    };
+  };
+}
-- 
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