add restricted network nixos modules

See README.md for explanation

checks/flake-module.nix

@@ -49,6 +49,8 @@ in
             zt-tcp-relay = self.clanLib.test.containerTest ./zt-tcp-relay nixosTestArgs;
             matrix-synapse = self.clanLib.test.containerTest ./matrix-synapse nixosTestArgs;
             postgresql = self.clanLib.test.containerTest ./postgresql nixosTestArgs;
+            user-firewall-iptables = self.clanLib.test.containerTest ./user-firewall/iptables.nix nixosTestArgs;
+            user-firewall-nftables = self.clanLib.test.containerTest ./user-firewall/nftables.nix nixosTestArgs;
 
             dummy-inventory-test = import ./dummy-inventory-test nixosTestArgs;
             dummy-inventory-test-from-flake = import ./dummy-inventory-test-from-flake nixosTestArgs;

checks/user-firewall/common.nix

@@ -0,0 +1,100 @@
+# Shared configuration for user firewall tests
+{ self, pkgs, ... }:
+{
+  imports = [
+    self.nixosModules.user-firewall
+  ];
+
+  networking.firewall.enable = true;
+
+  # Configure the user firewall module
+  # Test with default allowedInterfaces (which includes wg*)
+  networking.user-firewall = {
+    # Use defaults for allowedInterfaces to test that wg* is included by default
+    exemptUsers = [
+      "root"
+      "alice"
+    ];
+  };
+
+  # Create test users
+  users.users = {
+    alice = {
+      isNormalUser = true;
+      uid = 1001;
+      initialPassword = "test";
+    };
+
+    bob = {
+      isNormalUser = true;
+      uid = 1002;
+      initialPassword = "test";
+    };
+  };
+
+  # Add tools for testing
+  environment.systemPackages = with pkgs; [
+    curl
+    netcat
+    iproute2
+  ];
+
+  # Add a local web server for testing
+  services.nginx = {
+    enable = true;
+    virtualHosts = {
+      "localhost" = {
+        listen = [
+          {
+            addr = "127.0.0.1";
+            port = 8080;
+          }
+        ];
+        locations."/" = {
+          return = "200 'test server response'";
+          extraConfig = "add_header Content-Type text/plain;";
+        };
+      };
+      "wg0-test" = {
+        listen = [
+          {
+            addr = "10.100.0.2";
+            port = 8081;
+          }
+          {
+            addr = "[fd00::2]";
+            port = 8081;
+          }
+        ];
+        locations."/" = {
+          return = "200 'wg0 interface test response'";
+          extraConfig = "add_header Content-Type text/plain;";
+        };
+      };
+    };
+  };
+
+  # Create a dummy interface to test allowed interface patterns
+  systemd.services.setup-wg0-interface = {
+    description = "Setup wg0 dummy interface";
+    after = [ "network-pre.target" ];
+    before = [ "network.target" ];
+    wantedBy = [ "multi-user.target" ];
+    serviceConfig = {
+      Type = "oneshot";
+      RemainAfterExit = true;
+    };
+    script = ''
+      ${pkgs.iproute2}/bin/ip link add wg0 type dummy || true
+      ${pkgs.iproute2}/bin/ip addr add 10.100.0.2/24 dev wg0 || true
+      ${pkgs.iproute2}/bin/ip addr add fd00::2/64 dev wg0 || true
+      ${pkgs.iproute2}/bin/ip link set wg0 up || true
+    '';
+  };
+
+  # Make nginx wait for the wg0 interface
+  systemd.services.nginx = {
+    after = [ "setup-wg0-interface.service" ];
+    requires = [ "setup-wg0-interface.service" ];
+  };
+}

checks/user-firewall/iptables.nix

@@ -0,0 +1,82 @@
+{
+  name = "user-firewall-iptables";
+
+  nodes = {
+    router =
+      { ... }:
+      {
+        imports = [ ./router.nix ];
+      };
+
+    machine =
+      { ... }:
+      {
+        imports = [ ./common.nix ];
+
+        # Force iptables backend
+        networking.nftables.enable = false;
+      };
+  };
+
+  testScript = ''
+    start_all()
+    router.wait_for_unit("multi-user.target")
+    router.wait_for_unit("nginx.service")
+    machine.wait_for_unit("multi-user.target")
+    machine.wait_for_unit("nginx.service")
+
+    # Get router IPs (both IPv4 and IPv6)
+    router_ip = router.succeed("ip -4 addr show eth1 | grep -oP '(?<=inet\\s)\\d+(\\.\\d+){3}'").strip()
+    router_ip6 = router.succeed("ip -6 addr show eth1 | grep -oP '(?<=inet6\\s)[0-9a-f:]+' | grep -v '^fe80' | head -1").strip()
+    print(f"Router IPv4: {router_ip}")
+    print(f"Router IPv6: {router_ip6}")
+
+    # Test firewall restart
+    machine.succeed("systemctl restart firewall")
+    machine.wait_for_unit("firewall.service")
+
+    # Verify rules are loaded
+    machine.succeed("iptables -L user-firewall-output >&2")
+
+    # Test alice (exempt user) - should succeed both locally and to router
+    machine.wait_until_succeeds("runuser -u alice -- curl -s http://127.0.0.1:8080")
+    machine.succeed(f"runuser -u alice -- curl -s http://{router_ip}")
+    machine.succeed(f"runuser -u alice -- curl -s http://[{router_ip6}]")
+
+    # Test bob (restricted user) - localhost should work, external should fail
+    machine.succeed("runuser -u bob -- curl -s http://127.0.0.1:8080")
+    # This should be blocked by firewall - IPv4
+    result = machine.succeed(f"runuser -u bob -- curl -s --connect-timeout 2 http://{router_ip} 2>&1 || echo 'EXIT_CODE='$?")
+    assert "EXIT_CODE=7" in result, f"Bob should be blocked from external IPv4 access (expected EXIT_CODE=7) but got: {result}"
+    # This should be blocked by firewall - IPv6
+    result6 = machine.succeed(f"runuser -u bob -- curl -s --connect-timeout 2 http://[{router_ip6}] 2>&1 || echo 'EXIT_CODE='$?")
+    assert "EXIT_CODE=7" in result6, f"Bob should be blocked from external IPv6 access (expected EXIT_CODE=7) but got: {result6}"
+
+    # Verify the rules are actually present for both IPv4 and IPv6
+    rules4 = machine.succeed("iptables -L user-firewall-output -n -v")
+    assert "REJECT" in rules4, "REJECT rule not found in iptables"
+    rules6 = machine.succeed("ip6tables -L user-firewall-output -n -v")
+    assert "REJECT" in rules6, "REJECT rule not found in ip6tables"
+
+    # Wait for the dummy interface to be created
+    machine.wait_for_unit("setup-wg0-interface.service")
+    machine.wait_for_unit("nginx.service")
+    machine.wait_for_open_port(8081, "10.100.0.2")
+
+    # Check that wg0 interface exists
+    machine.succeed("ip link show wg0")
+    machine.succeed("ip addr show wg0")
+
+    # The key test: users should be able to connect via wg0 interface
+    # For alice (exempt user) - should work
+    machine.succeed("runuser -u alice -- curl -s --interface wg0 http://10.100.0.2:8081/")
+    machine.succeed("runuser -u alice -- curl -s --interface wg0 http://[fd00::2]:8081/")  # IPv6 test
+
+    # For bob (restricted user) - should also work because wg* is in default allowedInterfaces
+    machine.succeed("runuser -u bob -- curl -s --interface wg0 http://10.100.0.2:8081/")
+    machine.succeed("runuser -u bob -- curl -s --interface wg0 http://[fd00::2]:8081/")  # IPv6 test
+
+    # Verify that wg* interfaces are allowed in the firewall rules
+    machine.succeed("iptables -L user-firewall-output -n -v | grep -E 'wg0|wg\\+' >&2")
+  '';
+}

checks/user-firewall/nftables.nix

@@ -0,0 +1,77 @@
+{
+  name = "user-firewall-nftables";
+
+  nodes = {
+    router = {
+      imports = [ ./router.nix ];
+    };
+
+    machine = {
+      imports = [ ./common.nix ];
+
+      # Force nftables backend
+      networking.nftables.enable = true;
+    };
+  };
+
+  testScript = ''
+    start_all()
+    router.wait_for_unit("multi-user.target")
+    router.wait_for_unit("nginx.service")
+    machine.wait_for_unit("multi-user.target")
+    machine.wait_for_unit("nginx.service")
+
+    # Get router IPs (both IPv4 and IPv6)
+    router_ip = router.succeed("ip -4 addr show eth1 | grep -oP '(?<=inet\\s)\\d+(\\.\\d+){3}'").strip()
+    router_ip6 = router.succeed("ip -6 addr show eth1 | grep -oP '(?<=inet6\\s)[0-9a-f:]+' | grep -v '^fe80' | head -1").strip()
+    print(f"Router IPv4: {router_ip}")
+    print(f"Router IPv6: {router_ip6}")
+
+    # Test nftables restart
+    machine.succeed("systemctl restart nftables")
+    machine.wait_for_unit("nftables.service")
+
+    # Verify rules are loaded
+    machine.succeed("nft list table inet user-firewall >&2")
+
+    # Test alice (exempt user) - should succeed both locally and to router
+    machine.wait_until_succeeds("runuser -u alice -- curl -s http://127.0.0.1:8080")
+    machine.succeed(f"runuser -u alice -- curl -s http://{router_ip}")
+    machine.succeed(f"runuser -u alice -- curl -s http://[{router_ip6}]")
+
+    # Test bob (restricted user) - localhost should work, external should fail
+    machine.succeed("runuser -u bob -- curl -s http://127.0.0.1:8080")
+    # This should be blocked by firewall - IPv4
+    result = machine.succeed(f"runuser -u bob -- curl -s --connect-timeout 2 http://{router_ip} 2>&1 || echo 'EXIT_CODE='$?")
+    assert "EXIT_CODE=7" in result, f"Bob should be blocked from external IPv4 access (expected EXIT_CODE=7) but got: {result}"
+    # This should be blocked by firewall - IPv6
+    result6 = machine.succeed(f"runuser -u bob -- curl -s --connect-timeout 2 http://[{router_ip6}] 2>&1 || echo 'EXIT_CODE='$?")
+    assert "EXIT_CODE=7" in result6, f"Bob should be blocked from external IPv6 access (expected EXIT_CODE=7) but got: {result6}"
+
+    # Verify the rules are actually present
+    rules = machine.succeed("nft list table inet user-firewall")
+    assert 'meta skuid 1002' in rules and 'reject' in rules, f"Reject rule for bob (uid 1002) not found in nftables. Actual rules:\n{rules}"
+    assert "oifname" in rules, f"Interface rules not found in nftables. Actual rules:\n{rules}"
+
+    # Wait for the dummy interface to be created
+    machine.wait_for_unit("setup-wg0-interface.service")
+    machine.wait_for_unit("nginx.service")
+    machine.wait_for_open_port(8081, "10.100.0.2")
+
+    # Check that wg0 interface exists
+    machine.succeed("ip link show wg0")
+    machine.succeed("ip addr show wg0")
+
+    # The key test: users should be able to connect via wg0 interface
+    # For alice (exempt user) - should work
+    machine.succeed("runuser -u alice -- curl -s --interface wg0 http://10.100.0.2:8081/")
+    machine.succeed("runuser -u alice -- curl -s --interface wg0 http://[fd00::2]:8081/")  # IPv6 test
+
+    # For bob (restricted user) - should also work because wg* is in default allowedInterfaces
+    machine.succeed("runuser -u bob -- curl -s --interface wg0 http://10.100.0.2:8081/")
+    machine.succeed("runuser -u bob -- curl -s --interface wg0 http://[fd00::2]:8081/")  # IPv6 test
+
+    # Verify that wg* interfaces are allowed in the nftables rules
+    rules_with_wg = machine.succeed("nft list table inet user-firewall | grep -E 'oifname.*wg' >&2")
+  '';
+}

checks/user-firewall/router.nix

@@ -0,0 +1,32 @@
+# Shared router configuration for user firewall tests
+{ ... }:
+{
+  networking.firewall.enable = false;
+  networking.useNetworkd = true;
+
+  # Simple web server to test connectivity
+  services.nginx = {
+    enable = true;
+    virtualHosts."router" = {
+      listen = [
+        {
+          addr = "0.0.0.0";
+          port = 80;
+        }
+        {
+          addr = "[::]";
+          port = 80;
+        }
+        {
+          addr = "10.100.0.1";
+          port = 80;
+        }
+      ];
+      locations."/" = {
+        return = "200 'router response'";
+        extraConfig = "add_header Content-Type text/plain;";
+      };
+    };
+  };
+
+}

nixosModules/flake-module.nix

@@ -26,6 +26,7 @@ in
 {
   flake.nixosModules.hidden-ssh-announce = ./hidden-ssh-announce.nix;
   flake.nixosModules.bcachefs = ./bcachefs.nix;
+  flake.nixosModules.user-firewall = ./user-firewall;
   flake.nixosModules.installer.imports = [
     ./installer
     self.nixosModules.hidden-ssh-announce

nixosModules/user-firewall/README.md

@@ -0,0 +1,179 @@
+# User Firewall Module
+
+This NixOS module provides network access restrictions for non-privileged users, ensuring they can only access local services and VPN interfaces while blocking direct internet access.
+
+## Overview
+
+The `user-firewall` module implements firewall rules that:
+- Block all outbound network traffic for normal (non-system) users by default
+- Allow specific users to bypass restrictions (exemptUsers)
+- Permit traffic on specific interfaces (like VPNs and localhost)
+- Support both iptables and nftables backends
+- Handle both IPv4 and IPv6 traffic
+
+## Installation
+
+Add the module to your NixOS configuration:
+
+```nix
+{
+  imports = [
+    self.inputs.clan-core.nixosModules.user-firewall
+  ];
+}
+```
+
+The module is automatically enabled once imported. It will immediately start restricting network access for all normal users except those listed in `exemptUsers`.
+
+## Configuration
+
+### Basic Usage
+
+```nix
+{
+  networking.user-firewall = {
+    exemptUsers = [ "alice" ];  # Users who can access the internet
+  };
+}
+```
+
+### Full Configuration Example
+
+```nix
+{
+  networking.user-firewall = {
+    # Users who are exempt from network restrictions
+    exemptUsers = [
+      "alice"
+      "admin"
+    ];
+
+    # Network interfaces that all users can use
+    # Default includes common VPN interfaces
+    allowedInterfaces = [
+      "lo"          # localhost (required for local services)
+      "tun*"        # OpenVPN, OpenConnect
+      "wg*"         # WireGuard (wg0, wg-home, etc.)
+      "tailscale*"  # Tailscale
+      # Add custom interfaces as needed
+    ];
+  };
+}
+```
+
+## How It Works
+
+1. **User Classification**: The module automatically identifies all normal users (non-system users) and applies restrictions to those not in the `exemptUsers` list.
+
+2. **Firewall Rules**:
+   - For iptables: Creates a custom chain `user-firewall-output` in the OUTPUT table
+   - For nftables: Creates a table `inet user-firewall` with an output chain
+   - Rules check outgoing packets and reject those from restricted users
+
+3. **Interface Patterns**: Supports wildcards in interface names:
+   - `*` matches any characters (e.g., `wg*` matches `wg0`, `wg-home`)
+
+## Default Allowed Interfaces
+
+The module comes with sensible defaults for common VPN and overlay network interfaces:
+
+- `lo` - Loopback (localhost access)
+- `tun*` - OpenVPN, OpenConnect
+- `tap*` - OpenVPN (bridged mode)
+- `wg*` - WireGuard
+- `tailscale*` - Tailscale
+- `zt*` - ZeroTier
+- `hyprspace` - Hyprpspace
+- `vpn*` - Generic VPN interfaces
+- `nebula*` - Nebula mesh network
+- `tinc*` - Tinc VPN
+- `edge*` - n2n
+- `ham0` - Hamachi
+- `easytier` - EasyTier
+- `mycelium` - Mycelium
+
+## Use Cases
+
+### 1. Public Kiosk Systems
+Restrict users to only access local services:
+```nix
+{
+  networking.user-firewall = {
+    allowedInterfaces = [ "lo" ];  # Only localhost
+    exemptUsers = [ ];  # No exempt users
+  };
+}
+```
+
+### 2. Corporate Workstations
+Force all traffic through corporate VPN:
+```nix
+{
+  networking.user-firewall = {
+    allowedInterfaces = [ "lo" "wg-corp" ];
+    exemptUsers = [ "sysadmin" ];
+  };
+}
+```
+
+## Testing
+
+The module includes comprehensive tests for both iptables and nftables backends:
+
+```bash
+# Run iptables backend test
+nix build .#checks.x86_64-linux.user-firewall-iptables
+
+# Run nftables backend test
+nix build .#checks.x86_64-linux.user-firewall-nftables
+```
+
+## Troubleshooting
+
+### Check Active Rules
+
+The output includes package counters for each firewall rule, that can help to debug connectivity issues.
+
+For iptables:
+```bash
+sudo iptables -L user-firewall-output -n -v
+sudo ip6tables -L user-firewall-output -n -v
+```
+
+For nftables:
+```bash
+sudo nft list table inet user-firewall
+
+# Watch counters in real-time
+sudo watch -n1 'nft list table inet user-firewall'
+```
+
+Check which rule your VPN traffic is hitting. If packets are being rejected, verify:
+1. Your VPN interface name matches the patterns in `allowedInterfaces`
+2. Your user is listed in `exemptUsers` if needed
+
+To see your current network interfaces:
+```bash
+ip link show | grep -E '^[0-9]+:'
+```
+
+### Common Issues
+
+1. **Service Connection Failures**: If local services fail to connect, ensure `lo` is in `allowedInterfaces`.
+
+2. **VPN Not Working**: Check that your VPN interface name matches the patterns in `allowedInterfaces`. You can find your interface name with `ip link show`.
+
+3. **User Still Has Access**: Verify the user is a normal user (not a system user) and not in `exemptUsers`.
+
+## Security Considerations
+
+- This module provides defense in depth but should not be the only security measure
+- System users (like `nginx`, `systemd-*`) are not restricted
+- Root user always has full network access
+- Restrictions apply at the packet filter level, not application level
+
+## Limitations
+
+- Requires `networking.firewall.enable = true`
+- Cannot restrict system users or root
+- Interface patterns are evaluated at rule creation time, not dynamically

nixosModules/user-firewall/default.nix

@@ -0,0 +1,147 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  cfg = config.networking.user-firewall;
+
+  # Get all normal users (excluding system users)
+  normalUsers = lib.filterAttrs (_name: user: user.isNormalUser) config.users.users;
+
+  # Get usernames for normal users who aren't exempt
+  restrictedUsers = lib.attrNames (
+    lib.filterAttrs (name: _user: !(lib.elem name cfg.exemptUsers)) normalUsers
+  );
+
+  # Convert interface patterns for iptables
+  # iptables uses + for one-or-more, but we use * in our interface
+  toIptablesPattern =
+    pattern:
+    if lib.hasSuffix "*" pattern && pattern != "*" then
+      # Convert "wg*" to "wg+" for iptables
+      lib.removeSuffix "*" pattern + "+"
+    else
+      pattern;
+
+  # Build interface patterns for iptables with proper escaping
+  interfaceRules = lib.concatMapStringsSep "\n    " (
+    iface:
+    "ip46tables -A user-firewall-output -o ${lib.escapeShellArg (toIptablesPattern iface)} -j RETURN"
+  ) cfg.allowedInterfaces;
+
+in
+{
+  options.networking.user-firewall = {
+    allowedInterfaces = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [
+        "lo" # loopback (allows Tor on localhost)
+        "tun*" # OpenVPN, OpenConnect
+        "tap*" # OpenVPN (bridged mode)
+        "wg*" # WireGuard (wg0, wg-home, etc.)
+        "tailscale*" # Tailscale
+        "zt*" # ZeroTier
+        "vpn*" # Generic VPN interfaces
+        "ipsec*" # IPSec
+        "nebula*" # Nebula
+        "tinc*" # Tinc
+        "edge*" # n2n
+        "hyprspace" # Hyprspace
+        "ham0" # Hamachi
+        "easytier" # EasyTier
+        "mycelium" # Mycelium
+      ];
+      description = ''
+        Network interfaces that normal users can use.
+        Supports wildcards: * (zero or more characters).
+      '';
+    };
+
+    exemptUsers = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      description = ''
+        Users exempt from network restrictions.
+      '';
+    };
+
+  };
+
+  config = {
+    assertions = [
+      {
+        assertion = config.networking.firewall.enable;
+        message = "networking.user-firewall requires networking.firewall.enable to be true";
+      }
+    ];
+
+    # For nftables: create fake passwd file for build-time validation
+    networking.nftables.checkRulesetRedirects = lib.mkIf config.networking.nftables.enable (
+      lib.mkOptionDefault {
+        "/etc/passwd" = pkgs.writeText "passwd" (
+          let
+            userList = lib.attrNames config.users.users;
+            indexedUsers = lib.imap0 (
+              i: name: "${name}:x:${toString (1000 + i)}:100::/home/${name}:/bin/sh"
+            ) userList;
+          in
+          lib.concatStringsSep "\n" indexedUsers
+        );
+      }
+    );
+
+    # For iptables backend
+    networking.firewall.extraCommands = lib.mkIf (!config.networking.nftables.enable) ''
+      # Create custom chain for user firewall output
+      ip46tables -N user-firewall-output 2>/dev/null || true
+      ip46tables -F user-firewall-output
+
+      # Allow traffic on permitted interfaces
+      ${interfaceRules}
+
+
+      # Reject traffic from restricted users (TCP RST for TCP, ICMP for UDP)
+      ${lib.concatMapStringsSep "\n      " (
+        user: "ip46tables -A user-firewall-output -m owner --uid-owner ${lib.escapeShellArg user} -j REJECT"
+      ) restrictedUsers}
+
+      # Allow all other traffic
+      ip46tables -A user-firewall-output -j RETURN
+
+      # Insert our chain at the beginning of OUTPUT
+      ip46tables -D OUTPUT -j user-firewall-output 2>/dev/null || true
+      ip46tables -I OUTPUT -j user-firewall-output
+    '';
+
+    networking.firewall.extraStopCommands = lib.mkIf (!config.networking.nftables.enable) ''
+      # Remove our custom chain
+      ip46tables -D OUTPUT -j user-firewall-output 2>/dev/null || true
+      ip46tables -F user-firewall-output 2>/dev/null || true
+      ip46tables -X user-firewall-output 2>/dev/null || true
+    '';
+
+    # For nftables backend
+    networking.nftables.tables = lib.mkIf config.networking.nftables.enable {
+      user-firewall = {
+        family = "inet";
+        content = ''
+          chain output {
+            type filter hook output priority 0; policy accept;
+
+            # Allow traffic on permitted interfaces
+            ${lib.concatMapStringsSep "\n            " (
+              iface: ''oifname "${iface}" counter accept comment "allow ${iface}"''
+            ) cfg.allowedInterfaces}
+
+            # Reject traffic from restricted users (TCP RST for TCP, ICMP for UDP)
+            ${lib.concatMapStringsSep "\n            " (
+              user: ''meta skuid "${user}" counter reject comment "blocked user ${user}"''
+            ) restrictedUsers}
+          }
+        '';
+      };
+    };
+  };
+}