Add runtime Tor-egress self-check (fail-closed) for Nostr relays

Runtime-verified whether Apple's URLSession honors connectionProxyDictionary SOCKS settings for Nostr relay traffic (plain HTTPS + URLSessionWebSocketTask), since the app routes all Nostr traffic through Arti's local SOCKS5 proxy solely via those keys and Apple does not officially support SOCKS for URLSession on iOS. Verification harness (scripts/tor-egress-verification/): a minimal SOCKS5 CONNECT proxy that logs arriving connections, plus a Swift probe that runs an HTTPS GET and a WebSocket ping through a URLSession configured with the proxy dict. Result: on macOS (kCFNetworkProxiesSOCKS* constants) and the iOS simulator (raw "SOCKSProxy"/"SOCKSPort" string keys, the exact app path) BOTH HTTP and WebSocket are proxied, do remote DNS through the proxy, and the proxied session is fail-closed (every request errors when the SOCKS proxy is down). The feared direct-egress leak did not reproduce on the tested platforms. Defense-in-depth for the platform Apple does not guarantee (physical iOS): add TorEgressVerifier, which performs a canary request through the proxied session and asserts the exit is a Tor node (check.torproject.org IsTor==true), positively detecting a direct egress even if the OS silently ignored the proxy. Policy: verifiedTor allows (cached for a TTL); notTor refuses (leak detected, never open relays); unreachable allows-with-warning (session stays fail-closed by construction). Wired into TorManager.awaitEgressReady() and required by both NostrRelayManager and GeoRelayDirectory before opening connections. Cache is invalidated on Tor restart/dormant/shutdown. Never falls back to a direct connection. Probe is injected so the policy/caching is unit-tested offline; the live-network harness lives under scripts/ and is not run by CI. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-07-25 10:45:20 +00:00 · 2026-07-01 23:34:10 +02:00
parent f688e529f6
commit c7ee2a4cb4
9 changed files with 675 additions and 2 deletions
@@ -0,0 +1,90 @@
+// Standalone harness: does Apple's URLSession honor connectionProxyDictionary
+// SOCKS settings for a plain HTTPS GET and for URLSessionWebSocketTask?
+//
+// Build:  swiftc -O proxy_probe.swift -o proxy_probe
+// Usage:  proxy_probe <http|ws> <cf|raw> <proxyPort> [targetURL]
+//
+// Prints a single RESULT line: RESULT <mode> <keyStyle> <outcome> <detail>
+// The caller correlates this with the SOCKS proxy's connection log to decide
+// whether the request was proxied.
+#if canImport(CFNetwork)
+import CFNetwork
+#endif
+import Foundation
+
+let args = CommandLine.arguments
+guard args.count >= 4 else {
+    FileHandle.standardError.write(Data("usage: proxy_probe <http|ws> <cf|raw> <proxyPort> [targetURL]\n".utf8))
+    exit(2)
+}
+let mode = args[1]
+let keyStyle = args[2]
+let proxyPort = Int(args[3]) ?? 19999
+let host = "127.0.0.1"
+
+func makeProxyDict() -> [AnyHashable: Any] {
+    switch keyStyle {
+#if os(macOS)
+    case "cf":
+        // The exact constants the app uses on macOS.
+        return [
+            kCFNetworkProxiesSOCKSEnable as String: 1,
+            kCFNetworkProxiesSOCKSProxy as String: host,
+            kCFNetworkProxiesSOCKSPort as String: proxyPort
+        ]
+#endif
+    default:
+        // The exact raw string keys the app uses on iOS.
+        return [
+            "SOCKSEnable": 1,
+            "SOCKSProxy": host,
+            "SOCKSPort": proxyPort
+        ]
+    }
+}
+
+let cfg = URLSessionConfiguration.ephemeral
+cfg.waitsForConnectivity = false
+cfg.timeoutIntervalForRequest = 20
+cfg.connectionProxyDictionary = makeProxyDict()
+let session = URLSession(configuration: cfg)
+
+func emit(_ outcome: String, _ detail: String) {
+    print("RESULT \(mode) \(keyStyle) \(outcome) \(detail)")
+    exit(outcome == "ERROR" ? 1 : 0)
+}
+
+let sem = DispatchSemaphore(value: 0)
+
+if mode == "http" {
+    let target = URL(string: args.count >= 5 ? args[4] : "https://raw.githubusercontent.com/permissionlesstech/georelays/refs/heads/main/nostr_relays.csv")!
+    let task = session.dataTask(with: target) { data, resp, err in
+        if let err = err {
+            emit("ERROR", "\(err.localizedDescription)")
+        } else if let http = resp as? HTTPURLResponse {
+            emit("OK", "status=\(http.statusCode) bytes=\(data?.count ?? 0)")
+        } else {
+            emit("OK", "bytes=\(data?.count ?? 0)")
+        }
+    }
+    task.resume()
+} else {
+    // WebSocket
+    let target = URL(string: args.count >= 5 ? args[4] : "wss://relay.damus.io")!
+    let ws = session.webSocketTask(with: target)
+    ws.resume()
+    // A successful ping proves the TLS+WS handshake completed end-to-end.
+    ws.sendPing { err in
+        if let err = err {
+            emit("ERROR", "\(err.localizedDescription)")
+        } else {
+            emit("OK", "ws-ping-ok")
+        }
+    }
+}
+
+// Global watchdog so we never hang.
+DispatchQueue.global().asyncAfter(deadline: .now() + 25) {
+    emit("ERROR", "timeout")
+}
+sem.wait()
@@ -0,0 +1,73 @@
+#!/usr/bin/env bash
+# Orchestrates the Tor-egress proxy-honoring verification on macOS.
+#
+# For each (request-type x key-style) it runs two experiments:
+#   A) proxy UP   — did a connection arrive at the SOCKS proxy? (log grows)
+#   B) proxy DOWN — pointed at a dead port; does the request still SUCCEED?
+#      If it succeeds with no proxy, egress went DIRECT (proxy ignored).
+#      If it fails, the proxy setting is being enforced (fail-closed).
+#
+# Discriminator: PROXIED  = connection observed at proxy AND fails when proxy down
+#                DIRECT   = no connection at proxy OR succeeds when proxy down
+set -u
+DIR="$(cd "$(dirname "$0")" && pwd)"
+PORT=19999
+DEADPORT=19998   # nothing listens here
+LOG="$(mktemp -t sockslog)"
+BIN="$(mktemp -t proxyprobe)"
+
+echo "== building swift probe =="
+swiftc -O "$DIR/proxy_probe.swift" -o "$BIN" || { echo "swiftc failed"; exit 1; }
+
+echo "== starting SOCKS proxy on $PORT =="
+: > "$LOG"
+python3 "$DIR/socks5_probe_proxy.py" "$PORT" "$LOG" >/tmp/socksproxy.out 2>&1 &
+PROXY_PID=$!
+trap 'kill $PROXY_PID 2>/dev/null' EXIT
+# wait for READY
+for _ in $(seq 1 50); do
+  grep -q READY /tmp/socksproxy.out 2>/dev/null && break
+  sleep 0.1
+done
+
+run_case() {
+  local mode="$1" key="$2"
+  # Experiment A: proxy up, watch log
+  local before after target
+  before=$(wc -l < "$LOG" | tr -d ' ')
+  local outA
+  outA=$("$BIN" "$mode" "$key" "$PORT" 2>/dev/null | grep '^RESULT' || echo "RESULT $mode $key ERROR no-output")
+  sleep 0.3
+  after=$(wc -l < "$LOG" | tr -d ' ')
+  local proxied="NO"
+  if [ "$after" -gt "$before" ]; then proxied="YES"; fi
+  local newlines
+  newlines=$(tail -n +"$((before+1))" "$LOG" | tr '\t' ' ' | tr '\n' '|')
+
+  # Experiment B: proxy down (dead port), same request
+  local outB
+  outB=$("$BIN" "$mode" "$key" "$DEADPORT" 2>/dev/null | grep '^RESULT' || echo "RESULT $mode $key ERROR no-output")
+
+  echo "----------------------------------------"
+  echo "CASE mode=$mode key=$key"
+  echo "  A(proxy up):   $outA   | connection_at_proxy=$proxied  [$newlines]"
+  echo "  B(proxy down): $outB"
+  # verdict
+  local a_ok b_ok
+  a_ok=$(echo "$outA" | awk '{print $4}')
+  b_ok=$(echo "$outB" | awk '{print $4}')
+  local verdict="UNKNOWN"
+  if [ "$proxied" = "YES" ] && [ "$b_ok" = "ERROR" ]; then verdict="PROXIED (enforced)"; fi
+  if [ "$proxied" = "NO" ] && [ "$b_ok" = "OK" ]; then verdict="DIRECT (proxy ignored)"; fi
+  if [ "$proxied" = "YES" ] && [ "$b_ok" = "OK" ]; then verdict="AMBIGUOUS (uses proxy if up, but egresses direct if down)"; fi
+  if [ "$proxied" = "NO" ] && [ "$b_ok" = "ERROR" ]; then verdict="BLOCKED both (network/target issue?)"; fi
+  echo "  VERDICT: $verdict"
+}
+
+for mode in http ws; do
+  for key in cf raw; do
+    run_case "$mode" "$key"
+  done
+done
+echo "========================================"
+echo "raw proxy log:"; cat "$LOG" | tr '\t' ' '
@@ -0,0 +1,166 @@
+#!/usr/bin/env python3
+"""
+Minimal threaded SOCKS5 CONNECT proxy used to verify whether Apple's
+URLSession actually honors `connectionProxyDictionary` SOCKS settings for
+different request types (plain HTTPS vs URLSessionWebSocketTask).
+
+Behavior:
+  - Speaks enough SOCKS5 (no-auth) to complete a CONNECT and then relays
+    bytes bidirectionally to the real destination.
+  - Every accepted CONNECT is appended to a log file as one line:
+        <iso8601>\tCONNECT\t<host>:<port>
+  - Any raw connection that is NOT valid SOCKS5 is logged as:
+        <iso8601>\tNON_SOCKS\t<first-bytes-hex>
+    (this catches the feared case where URLSession sends a raw TLS/HTTP
+     ClientHello straight at the proxy port instead of a SOCKS greeting).
+
+If a request egresses DIRECTLY (proxy ignored), nothing is logged at all.
+
+Usage: socks5_probe_proxy.py <listen_port> <log_file>
+"""
+import selectors
+import socket
+import sys
+import threading
+from datetime import datetime, timezone
+
+LOG_LOCK = threading.Lock()
+
+
+def log(logfile, kind, detail):
+    line = f"{datetime.now(timezone.utc).isoformat()}\t{kind}\t{detail}\n"
+    with LOG_LOCK:
+        with open(logfile, "a") as f:
+            f.write(line)
+    sys.stderr.write("[proxy] " + line)
+    sys.stderr.flush()
+
+
+def recv_exact(sock, n):
+    buf = b""
+    while len(buf) < n:
+        chunk = sock.recv(n - len(buf))
+        if not chunk:
+            return None
+        buf += chunk
+    return buf
+
+
+def handle(client, logfile):
+    client.settimeout(15)
+    try:
+        # SOCKS5 greeting: VER=0x05, NMETHODS, METHODS...
+        head = recv_exact(client, 2)
+        if not head:
+            return
+        if head[0] != 0x05:
+            # Not SOCKS5 at all — this is the smoking gun for a direct egress
+            # that mistakenly hit the proxy port. Log the first bytes.
+            rest = b""
+            try:
+                client.setblocking(False)
+                rest = client.recv(64)
+            except Exception:
+                pass
+            log(logfile, "NON_SOCKS", (head + rest).hex())
+            return
+        nmethods = head[1]
+        if nmethods:
+            recv_exact(client, nmethods)
+        # Reply: no authentication required
+        client.sendall(b"\x05\x00")
+
+        # Request: VER, CMD, RSV, ATYP, ADDR, PORT
+        req = recv_exact(client, 4)
+        if not req or req[1] != 0x01:  # only CONNECT
+            client.sendall(b"\x05\x07\x00\x01\x00\x00\x00\x00\x00\x00")
+            return
+        atyp = req[3]
+        if atyp == 0x01:  # IPv4
+            addr = socket.inet_ntoa(recv_exact(client, 4))
+        elif atyp == 0x03:  # domain
+            ln = recv_exact(client, 1)[0]
+            addr = recv_exact(client, ln).decode("ascii", errors="replace")
+        elif atyp == 0x04:  # IPv6
+            addr = socket.inet_ntop(socket.AF_INET6, recv_exact(client, 16))
+        else:
+            client.sendall(b"\x05\x08\x00\x01\x00\x00\x00\x00\x00\x00")
+            return
+        port = int.from_bytes(recv_exact(client, 2), "big")
+
+        log(logfile, "CONNECT", f"{addr}:{port}")
+
+        # Connect to the real destination and reply success.
+        try:
+            remote = socket.create_connection((addr, port), timeout=15)
+        except Exception as e:
+            log(logfile, "CONNECT_FAIL", f"{addr}:{port} {e}")
+            client.sendall(b"\x05\x01\x00\x01\x00\x00\x00\x00\x00\x00")
+            return
+        client.sendall(b"\x05\x00\x00\x01\x00\x00\x00\x00\x00\x00")
+
+        relay(client, remote)
+    except Exception:
+        pass
+    finally:
+        try:
+            client.close()
+        except Exception:
+            pass
+
+
+def relay(a, b):
+    a.setblocking(False)
+    b.setblocking(False)
+    sel = selectors.DefaultSelector()
+    sel.register(a, selectors.EVENT_READ, b)
+    sel.register(b, selectors.EVENT_READ, a)
+    try:
+        while True:
+            events = sel.select(timeout=30)
+            if not events:
+                break
+            for key, _ in events:
+                src = key.fileobj
+                dst = key.data
+                try:
+                    data = src.recv(65536)
+                except (BlockingIOError, InterruptedError):
+                    continue
+                except Exception:
+                    return
+                if not data:
+                    return
+                try:
+                    dst.sendall(data)
+                except Exception:
+                    return
+    finally:
+        sel.close()
+        for s in (a, b):
+            try:
+                s.close()
+            except Exception:
+                pass
+
+
+def main():
+    if len(sys.argv) != 3:
+        print("usage: socks5_probe_proxy.py <port> <logfile>", file=sys.stderr)
+        sys.exit(2)
+    port = int(sys.argv[1])
+    logfile = sys.argv[2]
+    srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    srv.bind(("127.0.0.1", port))
+    srv.listen(64)
+    sys.stderr.write(f"[proxy] listening on 127.0.0.1:{port}, log={logfile}\n")
+    sys.stderr.flush()
+    print("READY", flush=True)
+    while True:
+        client, _ = srv.accept()
+        threading.Thread(target=handle, args=(client, logfile), daemon=True).start()
+
+
+if __name__ == "__main__":
+    main()