fix(security): Tor onions for gated ports forward to the gate, not the app

Tor carries no session cookie, so HiddenServicePort → 127.0.0.1:<port>
reached the app around the gate — the last transport the gate did not
cover. The gate now binds 127.0.0.2 (its own loopback, distinct from the
app's 127.0.0.1, so no app needs a second port), and regenerate_torrc
forwards declared-gated ports there. Undeclared ports keep today's
target: absence of the field is not an instruction.

The 127.0.0.2 claim deliberately does not count toward the unprotected
audit — a port whose only claim is the Tor loopback is still wide open
on the LAN and must keep warning.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/api/rpc/tor/mod.rs

@@ -222,6 +222,18 @@ pub(in crate::api::rpc) async fn regenerate_torrc(config: &ServicesConfig) -> Re
     lines.push("# ControlPort disabled for security".to_string());
     lines.push(String::new());
 
+    // Ports whose manifests declare `auth: gated` forward to the gate's own
+    // loopback (127.0.0.2, where the app-gate listener binds — see
+    // `appgate::listener::GATE_TOR_UPSTREAM`) instead of the app's 127.0.0.1.
+    // Tor carries no session cookie, so an onion pointed at the app is an
+    // unauthenticated bypass of the gate. Declared-gated ports only: an
+    // undeclared port keeps today's target, because absence of the field is
+    // not an instruction (the v1.7.121 incident rule).
+    let gated_ports: std::collections::HashSet<u16> = crate::appgate::identity::build_port_map()
+        .gated_ports()
+        .map(|g| g.port)
+        .collect();
+
     for svc in &config.services {
         if !svc.enabled {
             continue;
@@ -240,7 +252,7 @@ pub(in crate::api::rpc) async fn regenerate_torrc(config: &ServicesConfig) -> Re
                 lines.push("HiddenServicePort 10009 127.0.0.1:10009".to_string());
             }
         } else {
-            lines.push(format!("HiddenServicePort 80 127.0.0.1:{}", svc.local_port));
+            lines.push(app_hidden_service_port_line(svc.local_port, &gated_ports));
         }
 
         lines.push(String::new());
@@ -248,6 +260,24 @@ pub(in crate::api::rpc) async fn regenerate_torrc(config: &ServicesConfig) -> Re
 
     let content = lines.join("\n");
     let staging = "/var/lib/archipelago/tor-config/torrc.staged";
+    write_staged_torrc(&content, staging).await
+}
+
+/// The `HiddenServicePort` line for an HTTP app onion. Gated ports forward to
+/// the gate's Tor upstream; everything else to the app itself.
+fn app_hidden_service_port_line(
+    local_port: u16,
+    gated_ports: &std::collections::HashSet<u16>,
+) -> String {
+    let upstream = if gated_ports.contains(&local_port) {
+        crate::appgate::listener::GATE_TOR_UPSTREAM.to_string()
+    } else {
+        "127.0.0.1".to_string()
+    };
+    format!("HiddenServicePort 80 {}:{}", upstream, local_port)
+}
+
+async fn write_staged_torrc(content: &str, staging: &str) -> Result<()> {
     let config_dir = Path::new(staging)
         .parent()
         .unwrap_or_else(|| Path::new("/var/lib/archipelago/tor-config"));
@@ -256,14 +286,37 @@ pub(in crate::api::rpc) async fn regenerate_torrc(config: &ServicesConfig) -> Re
         .await
         .context("Failed to write staged torrc")?;
 
-    debug!(
-        "Staged torrc with {} enabled services",
-        config.services.iter().filter(|s| s.enabled).count()
-    );
+    debug!("Staged torrc ({} bytes)", content.len());
 
     Ok(())
 }
 
+#[cfg(test)]
+mod torrc_tests {
+    use super::app_hidden_service_port_line;
+    use std::collections::HashSet;
+
+    #[test]
+    fn gated_port_forwards_to_the_gate_not_the_app() {
+        let gated: HashSet<u16> = [8082u16].into_iter().collect();
+        assert_eq!(
+            app_hidden_service_port_line(8082, &gated),
+            "HiddenServicePort 80 127.0.0.2:8082"
+        );
+    }
+
+    #[test]
+    fn undeclared_port_keeps_the_app_loopback_target() {
+        // Absence of `auth: gated` is not an instruction — the onion keeps
+        // pointing at the app, exactly as before this change.
+        let gated: HashSet<u16> = [8082u16].into_iter().collect();
+        assert_eq!(
+            app_hidden_service_port_line(9100, &gated),
+            "HiddenServicePort 80 127.0.0.1:9100"
+        );
+    }
+}
+
 // ─── Hostname Sync ───────────────────────────────────────────────
 
 pub(in crate::api::rpc) async fn sync_single_hostname(name: &str, address: &str) {

core/archipelago/src/appgate/listener.rs

@@ -44,6 +44,15 @@ use tracing::{debug, info, warn};
 /// apps are installed while the daemon runs.
 const SWEEP_INTERVAL: std::time::Duration = std::time::Duration::from_secs(60);
 
+/// The gate's own loopback address, distinct from the app's `127.0.0.1`.
+///
+/// Tor cannot present a session cookie, so `HiddenServicePort → 127.0.0.1`
+/// reaches the app around the gate. Instead torrc forwards gated ports to
+/// this address (`api/rpc/tor`), where the gate — not the app — listens. A
+/// second loopback address rather than a second port number, so no app needs
+/// a port it did not declare.
+pub const GATE_TOR_UPSTREAM: IpAddr = IpAddr::V4(std::net::Ipv4Addr::new(127, 0, 0, 2));
+
 /// A port the gate should own but could not claim, and why.
 #[derive(Debug, Clone, serde::Serialize)]
 pub struct UnprotectedPort {
@@ -192,6 +201,10 @@ async fn sweep(
 
         let mut claimed_any = false;
         let mut blocked = false;
+        // External addresses first, then the gate's Tor upstream. 127.0.0.2
+        // deliberately does NOT count toward `claimed_any`: the warning below
+        // is about external exposure, and a port whose only claim is the Tor
+        // loopback is still wide open on the LAN.
         for &addr in &addresses {
             let key = (app.port, addr);
             if held.contains_key(&key) {
@@ -214,6 +227,23 @@ async fn sweep(
                 Err(_) => blocked = true,
             }
         }
+        let tor_key = (app.port, GATE_TOR_UPSTREAM);
+        if held.contains_key(&tor_key) {
+            claimed.push((app.port, GATE_TOR_UPSTREAM.to_string()));
+        } else {
+            match TcpListener::bind(SocketAddr::new(GATE_TOR_UPSTREAM, app.port)).await {
+                Ok(listener) => {
+                    held.insert(tor_key, ());
+                    claimed.push((app.port, GATE_TOR_UPSTREAM.to_string()));
+                    info!(
+                        port = app.port, app = %app.app_id,
+                        "app gate claimed the Tor upstream (127.0.0.2)"
+                    );
+                    spawn_accept_loop(listener, gate.clone(), app.clone(), shutdown_rx.clone());
+                }
+                Err(_) => blocked = true,
+            }
+        }
 
         if blocked && !claimed_any {
             warn!(