feat(vpnserver): add nftables-backed destination policy enforcement for TUN mode

ts/smartvpn.classes.vpnserver.ts

@@ -12,6 +12,7 @@ import type {
   IWgPeerInfo,
   IClientEntry,
   IClientConfigBundle,
+  IDestinationPolicy,
   TVpnServerCommands,
 } from './smartvpn.interfaces.js';
 
@@ -21,6 +22,10 @@ import type {
 export class VpnServer extends plugins.events.EventEmitter {
   private bridge: VpnBridge<TVpnServerCommands>;
   private options: IVpnServerOptions;
+  private nft?: plugins.smartnftables.SmartNftables;
+  private nftHealthInterval?: ReturnType<typeof setInterval>;
+  private nftSubnet?: string;
+  private nftPolicy?: IDestinationPolicy;
 
   constructor(options: IVpnServerOptions) {
     super();
@@ -50,6 +55,11 @@ export class VpnServer extends plugins.events.EventEmitter {
     const cfg = config || this.options.config;
     if (cfg) {
       await this.bridge.sendCommand('start', { config: cfg });
+
+      // For TUN mode with a destination policy, set up nftables rules
+      if (cfg.forwardingMode === 'tun' && cfg.destinationPolicy) {
+        await this.setupTunDestinationPolicy(cfg.subnet, cfg.destinationPolicy);
+      }
     }
   }
 
@@ -229,10 +239,110 @@ export class VpnServer extends plugins.events.EventEmitter {
     return this.bridge.sendCommand('generateClientKeypair', {} as Record<string, never>);
   }
 
+  // ── TUN Destination Policy via nftables ──────────────────────────────
+
+  /**
+   * Set up nftables rules for TUN mode destination policy.
+   * Also starts a 60-second health check interval to re-apply if rules are removed externally.
+   */
+  private async setupTunDestinationPolicy(subnet: string, policy: IDestinationPolicy): Promise<void> {
+    this.nftSubnet = subnet;
+    this.nftPolicy = policy;
+    this.nft = new plugins.smartnftables.SmartNftables({
+      tableName: 'smartvpn_tun',
+      dryRun: process.getuid?.() !== 0,
+    });
+
+    await this.nft.initialize();
+    await this.applyDestinationPolicyRules();
+
+    // Health check: re-apply rules if they disappear
+    this.nftHealthInterval = setInterval(async () => {
+      if (!this.nft) return;
+      try {
+        const exists = await this.nft.tableExists();
+        if (!exists) {
+          console.warn('[smartvpn] nftables rules missing, re-applying destination policy');
+          this.nft = new plugins.smartnftables.SmartNftables({
+            tableName: 'smartvpn_tun',
+          });
+          await this.nft.initialize();
+          await this.applyDestinationPolicyRules();
+        }
+      } catch (err) {
+        console.warn(`[smartvpn] nftables health check failed: ${err}`);
+      }
+    }, 60_000);
+  }
+
+  /**
+   * Apply destination policy as nftables rules.
+   * Order: blockList (drop) → allowList (accept) → default action.
+   */
+  private async applyDestinationPolicyRules(): Promise<void> {
+    if (!this.nft || !this.nftSubnet || !this.nftPolicy) return;
+
+    const subnet = this.nftSubnet;
+    const policy = this.nftPolicy;
+    const family = 'ip';
+    const table = 'smartvpn_tun';
+    const commands: string[] = [];
+
+    // 1. Block list (deny wins — evaluated first)
+    if (policy.blockList) {
+      for (const dest of policy.blockList) {
+        commands.push(
+          `nft add rule ${family} ${table} prerouting ip saddr ${subnet} ip daddr ${dest} drop`
+        );
+      }
+    }
+
+    // 2. Allow list (pass through directly — skip DNAT)
+    if (policy.allowList) {
+      for (const dest of policy.allowList) {
+        commands.push(
+          `nft add rule ${family} ${table} prerouting ip saddr ${subnet} ip daddr ${dest} accept`
+        );
+      }
+    }
+
+    // 3. Default action
+    switch (policy.default) {
+      case 'forceTarget': {
+        const target = policy.target || '127.0.0.1';
+        commands.push(
+          `nft add rule ${family} ${table} prerouting ip saddr ${subnet} dnat to ${target}`
+        );
+        break;
+      }
+      case 'block':
+        commands.push(
+          `nft add rule ${family} ${table} prerouting ip saddr ${subnet} drop`
+        );
+        break;
+      case 'allow':
+        // No rule needed — kernel default allows
+        break;
+    }
+
+    if (commands.length > 0) {
+      await this.nft.applyRuleGroup('vpn-destination-policy', commands);
+    }
+  }
+
   /**
    * Stop the daemon bridge.
    */
   public stop(): void {
+    // Clean up nftables rules
+    if (this.nftHealthInterval) {
+      clearInterval(this.nftHealthInterval);
+      this.nftHealthInterval = undefined;
+    }
+    if (this.nft) {
+      this.nft.cleanup().catch(() => {}); // best-effort cleanup
+      this.nft = undefined;
+    }
     this.bridge.stop();
   }