feat(cloak): wire cloak into the deploy path for windows* deckies

Base containers whose nmap_os has a mangle profile now build the cloak image
(FROM the per-decky distro), ship the light decnet subtree, and run
'python -m decnet.cloak' alongside holding the MACVLAN IP — netns-safe (cloak
backgrounded behind 'exec sleep infinity' so a cloak crash never tears down the
base/netns). composer injects build/command/NET_RAW/env (DECNET_NMAP_OS,
DECNET_OPEN_PORTS, DECKY_IP); deployer._sync_cloak_sources syncs the subtree;
non-windows deckies are unchanged. Mangler signal-guarded for thread use;
entry runs mangler in main thread, responder as daemon.

Verified live: real path makes nmap -O read 'Microsoft Windows Server 2012/2016'
with handshakes intact.

decnet/cloak/__main__.py

@@ -35,17 +35,15 @@ def main() -> int:
         log.info("cloak: no mangle profile for %r — exiting", nmap_os)
         return 0
 
-    threads = [
-        threading.Thread(target=mangler.run, args=(nmap_os,),
-                         name="cloak-mangler", daemon=True),
-        threading.Thread(target=responder.run, args=(nmap_os, _open_ports()),
-                         name="cloak-responder", daemon=True),
-    ]
-    for t in threads:
-        t.start()
+    # Responder runs in a daemon thread; the mangler runs in the MAIN thread so
+    # its SIGTERM/SIGINT iptables-teardown handlers can be installed (signal only
+    # works in the main thread).
+    threading.Thread(
+        target=responder.run, args=(nmap_os, _open_ports()),
+        name="cloak-responder", daemon=True,
+    ).start()
     log.info("cloak: started for nmap_os=%r", nmap_os)
-    for t in threads:
-        t.join()
+    mangler.run(nmap_os)
     return 0
 
 

decnet/cloak/mangler.py

@@ -18,6 +18,7 @@ import os
 import signal
 import subprocess  # nosec B404 — fixed-arg iptables, no shell
 import sys
+import threading
 from typing import Any
 
 from decnet.logging import get_logger
@@ -120,8 +121,12 @@ def run(nmap_os: str) -> int:
         finally:
             sys.exit(0)
 
-    signal.signal(signal.SIGTERM, _cleanup)
-    signal.signal(signal.SIGINT, _cleanup)
+    # signal.signal() only works in the main thread; the `finally` below still
+    # removes the rule on a normal exit, and on container stop the netns (and
+    # its iptables rules) are torn down regardless.
+    if threading.current_thread() is threading.main_thread():
+        signal.signal(signal.SIGTERM, _cleanup)
+        signal.signal(signal.SIGINT, _cleanup)
     log.info("cloak.mangler: rewriting SYN-ACK -> %s (window=%#x ipid=%s)",
              nmap_os, profile.window, profile.ipid)
     try:

decnet/composer.py

@@ -21,7 +21,7 @@ import yaml
 
 from decnet.config import DecnetConfig
 from decnet.network import MACVLAN_NETWORK_NAME
-from decnet.os_fingerprint import get_os_sysctls
+from decnet.os_fingerprint import get_os_mangle, get_os_sysctls
 from decnet.services.registry import get_service
 
 _DOCKER_LOGGING = {
@@ -32,6 +32,26 @@ _DOCKER_LOGGING = {
     },
 }
 
+# Build context for the cloak base image (decnet subtree synced in by
+# deployer._sync_cloak_sources before build).
+_CLOAK_CONTEXT = Path(__file__).parent / "templates" / "_shared" / "cloak"
+
+# Netns-safe: run the cloak best-effort in the background, but keep `sleep
+# infinity` as PID 1 in the foreground so a cloak crash never tears down the
+# base container (and with it the netns every service container shares).
+_CLOAK_COMMAND = ["sh", "-c", "python3 -m decnet.cloak & exec sleep infinity"]
+
+
+def _decky_open_tcp_ports(services: list[str]) -> list[int]:
+    """Sorted, de-duped TCP ports a decky's services listen on (for the cloak
+    responder's T2/T3 classification — DECNET_OPEN_PORTS)."""
+    ports: set[int] = set()
+    for svc_name in services:
+        svc = get_service(svc_name)
+        if svc is not None:
+            ports.update(svc.ports)
+    return sorted(ports)
+
 
 def generate_compose(config: DecnetConfig) -> dict:
     """Build and return the full docker-compose data structure."""
@@ -60,6 +80,25 @@ def generate_compose(config: DecnetConfig) -> dict:
         base["sysctls"] = get_os_sysctls(decky.nmap_os)
         base["cap_add"] = ["NET_ADMIN"]
 
+        # sysctls reach only global packet fields. nmap_os families with an
+        # egress mangle profile (windows*) additionally run the cloak in the
+        # base container to rewrite SYN-ACK shape + synthesize T2/T3 replies, so
+        # they read as the claimed OS under active fingerprinting (nmap -O).
+        if get_os_mangle(decky.nmap_os) is not None:
+            base.pop("image", None)
+            base["build"] = {
+                "context": str(_CLOAK_CONTEXT),
+                "args": {"BASE_IMAGE": decky.build_base},
+            }
+            base["command"] = _CLOAK_COMMAND
+            base["cap_add"] = ["NET_ADMIN", "NET_RAW"]  # NET_RAW: responder send/sniff
+            ports = _decky_open_tcp_ports(decky.services)
+            base["environment"] = {
+                "DECNET_NMAP_OS": decky.nmap_os,
+                "DECNET_OPEN_PORTS": ",".join(str(p) for p in ports),
+                "DECKY_IP": decky.ip,
+            }
+
         services[base_key] = base
 
         # --- Service containers: share base network namespace ---

decnet/engine/deployer.py

@@ -65,6 +65,20 @@ _CANONICAL_NTLMSSP = Path(__file__).parent.parent / "templates" / "_shared" / "n
 _NTLMSSP_SERVICES = {"smb", "rdp"}
 _CANONICAL_CADDY_MODULES_DIR = Path(__file__).parent.parent / "templates" / "_caddy_modules"
 _CADDY_SERVICES = {"http", "https"}
+# Cloak base image: the decnet package root + the 8 light files shipped into the
+# cloak build context so `python -m decnet.cloak` runs in the base container.
+_DECNET_SRC = Path(__file__).parent.parent
+_CANONICAL_CLOAK_DIR = _DECNET_SRC / "templates" / "_shared" / "cloak"
+_CLOAK_SHIP_FILES = (
+    "__init__.py",
+    "config_ini.py",
+    "logging/__init__.py",
+    "os_fingerprint.py",
+    "cloak/__init__.py",
+    "cloak/__main__.py",
+    "cloak/mangler.py",
+    "cloak/responder.py",
+)
 
 
 def _sync_logging_helper(config: DecnetConfig) -> None:
@@ -87,6 +101,26 @@ def _sync_logging_helper(config: DecnetConfig) -> None:
                     shutil.copy2(src, dest)
 
 
+def _sync_cloak_sources(config: DecnetConfig) -> None:
+    """Ship the light decnet subtree into the cloak base-image build context.
+
+    Only when at least one decky has an egress mangle profile (windows*). Copies
+    the 8 files in _CLOAK_SHIP_FILES into <cloak ctx>/decnet/ preserving package
+    structure so the image's `python -m decnet.cloak` resolves. The dest tree is
+    gitignored. Mirrors the _sync_*_sources copy-if-changed idiom.
+    """
+    from decnet.os_fingerprint import get_os_mangle
+    if not any(get_os_mangle(d.nmap_os) is not None for d in config.deckies):
+        return
+    dest_root = _CANONICAL_CLOAK_DIR / "decnet"
+    for rel in _CLOAK_SHIP_FILES:
+        src = _DECNET_SRC / rel
+        dest = dest_root / rel
+        dest.parent.mkdir(parents=True, exist_ok=True)
+        if not dest.exists() or dest.read_bytes() != src.read_bytes():
+            shutil.copy2(src, dest)
+
+
 def _sync_auth_helper_sources(config: DecnetConfig) -> None:
     """Copy auth-helper.c into SSH/Telnet build contexts as auth-helper/.
 
@@ -679,6 +713,7 @@ def deploy(config: DecnetConfig, dry_run: bool = False, no_cache: bool = False,
     _sync_auth_helper_sources(config)
     _sync_ntlmssp_sources(config)
     _sync_caddy_modules(config)
+    _sync_cloak_sources(config)
 
     compose_path = write_compose(config, COMPOSE_FILE)
     console.print(f"[bold cyan]Compose file written[/] → {compose_path}")

decnet/templates/_shared/cloak/Dockerfile

@@ -0,0 +1,32 @@
+# Cloak base image — the IP-holder/netns container for deckies whose nmap_os has
+# an egress mangle profile (windows, windows_server). Runs `python -m decnet.cloak`
+# (SYN-ACK mangler + T2/T3 responder) alongside holding the MACVLAN IP.
+#
+# FROM the per-decky distro so the base still varies by distro (BASE_IMAGE arg,
+# set by the composer from decky.build_base — same pattern as service images).
+# The decnet/ subtree is synced into this context by deployer._sync_cloak_sources
+# before build (8 light, stdlib-only files; scapy/netfilterqueue are pip'd here).
+ARG BASE_IMAGE=debian:bookworm-slim
+FROM ${BASE_IMAGE}
+
+# Runtime: iptables (NFQUEUE rules), python3, libpcap (scapy BPF sniff in the
+# responder). Build-only: gcc + headers for the netfilterqueue C extension,
+# purged after the wheel is built to keep the image lean.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        python3 python3-pip iptables libpcap0.8 \
+        libnetfilter-queue1 libnfnetlink0 \
+        gcc python3-dev libnetfilter-queue-dev libnfnetlink-dev \
+    && pip3 install --no-cache-dir --break-system-packages \
+        "scapy>=2.6.1" "netfilterqueue>=1.1.0" \
+    && apt-get purge -y gcc python3-dev libnetfilter-queue-dev libnfnetlink-dev \
+    && apt-get autoremove -y \
+    && rm -rf /var/lib/apt/lists/*
+
+# Synced 8-file decnet subtree (decnet/__init__, config_ini, logging/, os_fingerprint,
+# cloak/). PYTHONPATH=/opt makes `python3 -m decnet.cloak` importable.
+COPY decnet/ /opt/decnet/
+ENV PYTHONPATH=/opt
+
+# The compose `command` drives runtime (netns-safe supervisor: cloak in background,
+# sleep infinity in foreground so a cloak crash never tears down the netns holder).
+CMD ["sleep", "infinity"]