#!/usr/bin/env python3 """ net_alerter.py — Net alerter persistent daemon. Monitors device presence via DHCP sniffing + Netlink neighbor events. Zero active probing. No traffic generated. Three concurrent threads: 1. DHCP sniffer — AF_PACKET raw socket, captures DHCP traffic passively 2. RTM_NEWNEIGH watcher — Netlink socket, kernel pushes new ARP neighbor events 3. RTM_DELNEIGH watcher — Netlink socket, kernel pushes deleted ARP neighbor events """ import json import logging import os import socket import struct import sys import threading import time import urllib.parse import urllib.request import sqlite3 from pathlib import Path # --- Config (from .env or env vars) --- MATRIX_HOMESERVER = "" MATRIX_ACCESS_TOKEN = "" MATRIX_ROOM_ID = "" LOG_FILE = "/opt/net_alerter/net_alerter.log" OUI_DB_PATH = "/opt/net_alerter/oui.db" known_devices = {} # {mac: {ip, hostname, vendor, first_seen, last_seen, infrastructure (opt)}} known_lock = threading.Lock() infrastructure_ips = set() # IPs that should never trigger alerts (gateway, broadcast, self) departure_timers = {} # {mac: threading.Timer} for 15-min departure debounce departure_lock = threading.Lock() # Protects departure_timers and last_departed_time last_departed_time = {} # {mac: timestamp} when device was actually alerted as departed # Top 200 common device OUI prefixes (MAC first 3 octets) OUI_DICT = { "88A29E": "Apple", "001A7D": "Apple", "185F3F": "Apple", "A4C3F0": "Apple", "0899D8": "Apple", "004096": "Apple", "00219B": "Apple", "0021E9": "Apple", "005973": "Apple", "006377": "Apple", "0064B9": "Apple", "0084F3": "Apple", "00A04D": "Apple", "00D04B": "Apple", "28879F": "Google", "2887BA": "Google", "5427EB": "Google", "542758": "Google", "341513": "Amazon", "0C47C2": "Amazon", "B827EB": "Raspberry Pi", "2C56DC": "Raspberry Pi", "E45F01": "Raspberry Pi", "000D82": "Intel", "001025": "Intel", "001ABA": "Intel", "001F3B": "Intel", "001F3C": "Intel", "001BA9": "Intel", "001BFB": "Intel", "001D7A": "Intel", "001DB8": "Intel", "001E67": "Intel", "001F29": "Intel", "F44DA2": "Intel", "B03C1C": "Intel", "00166B": "Qualcomm", "001BF3": "Qualcomm", "001C47": "Qualcomm", "002000": "Qualcomm", "0026F2": "Qualcomm", "0026F3": "Qualcomm", "0026F4": "Qualcomm", "002618": "Qualcomm", "FFFFFF": "Espressif", "687DA8": "Espressif", "A01D48": "Espressif", "30AEA4": "Espressif", "B4E63B": "Espressif", "80E386": "TP-Link", "8CBF26": "TP-Link", "90843F": "TP-Link", "A838B4": "TP-Link", "C81F66": "TP-Link", "DCFEEE": "TP-Link", "F81A67": "TP-Link", "689B5A": "Netgear", "6C46CB": "Netgear", "78A21B": "Netgear", "94B3D5": "Netgear", "B0EE7B": "Netgear", "B4FBE4": "Netgear", "C8D7B4": "Netgear", "D8BB85": "Netgear", "F8AB05": "Netgear", "001D2F": "Cisco", "001930": "Cisco", "001A2F": "Cisco", "001C0E": "Cisco", "001CED": "Cisco", "001EBD": "Cisco", "001F6C": "Cisco", "0021A0": "Cisco", "002678": "Cisco", "0026CB": "Cisco", "00266E": "Cisco", "00269F": "Cisco", "0026A6": "Cisco", "002700": "Cisco", "0026FA": "Cisco", "00267B": "Cisco", "0C1234": "Cisco", "001BD7": "Dell", "001BDB": "Dell", "001A6B": "Dell", "003067": "Dell", "00188B": "Dell", "001B21": "Dell", "001E67": "Dell", "0026F7": "Dell", "00242A": "Dell", "001C23": "HP", "001E0B": "HP", "001EBB": "HP", "001F2F": "HP", "001BFC": "HP", "002219": "HP", "0022A6": "HP", "002264": "HP", "0024A9": "HP", "0026B9": "HP", "0026DF": "HP", "001A6C": "Lenovo", "001DFB": "Lenovo", "001F3A": "Lenovo", "001A73": "Lenovo", "00238B": "Lenovo", "002264": "Lenovo", "00B0D0": "Lenovo", "9C2EBF": "Lenovo", "F0DE8D": "Lenovo", "00E04C": "Huawei", "001097": "Huawei", "001093": "Huawei", "001A2B": "Huawei", "001D3C": "Huawei", "001E37": "Huawei", "001F3E": "Huawei", "001ECE": "Huawei", "002074": "Huawei", "00207B": "Huawei", "0020E2": "Huawei", "0020F1": "Huawei", "0020F5": "Huawei", "002268": "Huawei", "002269": "Huawei", "00226A": "Huawei", "0022AA": "Xiaomi", "002255": "Xiaomi", "003677": "Xiaomi", "3418C2": "Xiaomi", "50EB71": "Xiaomi", "5CF4D4": "Xiaomi", "78111D": "Xiaomi", "78E1D3": "Xiaomi", "A4ABDA": "Xiaomi", "E4F47A": "Xiaomi", "F45EAB": "Xiaomi", "A4D18D": "OnePlus", "50F5DA": "OnePlus", "8C03BE": "OnePlus", "002261": "LG", "002265": "LG", "0022D2": "LG", "0022D3": "LG", "000426": "LG", "001854": "LG", "001E8F": "LG", "001F5B": "LG", "002038": "LG", "0020A6": "LG", "0020F8": "LG", "002220": "LG", "00222D": "LG", "0027E4": "LG", "00242C": "LG", "002531": "LG", "001054": "Sony", "001458": "Sony", "0014EA": "Sony", "001525": "Sony", "00188A": "Sony", "001B44": "Sony", "00215E": "Sony", "002178": "Sony", "0021C5": "Sony", "002333": "Sony", "002481": "Sony", "0026FF": "Sony", "002702": "Nintendo", "0008FE": "Nintendo", "0013F7": "Nintendo", "001BDB": "Nintendo", "001EEE": "Nintendo", "001FEE": "Nintendo", "0020F8": "Nintendo", "002095": "Nintendo", "0020FA": "Nintendo", "00227B": "Nintendo", } def setup_logging(): """Setup logging to file + stdout.""" formatter = logging.Formatter( fmt='%(asctime)s [%(levelname)s] %(message)s', datefmt='%Y-%m-%dT%H:%M:%S' ) # File handler Path(LOG_FILE).parent.mkdir(parents=True, exist_ok=True) file_handler = logging.FileHandler(LOG_FILE) file_handler.setFormatter(formatter) # Stdout handler stdout_handler = logging.StreamHandler(sys.stdout) stdout_handler.setFormatter(formatter) logger = logging.getLogger() logger.setLevel(logging.DEBUG) logger.addHandler(file_handler) logger.addHandler(stdout_handler) return logger def load_env(): """Parse .env file manually (key=value), no dependency required.""" global MATRIX_HOMESERVER, MATRIX_ACCESS_TOKEN, MATRIX_ROOM_ID env_path = Path(os.getenv("NET_ALERTER_ENV", "/opt/net_alerter/.env")) if not env_path.exists(): logging.warning(f".env not found at {env_path}, using env vars only") MATRIX_HOMESERVER = os.getenv("MATRIX_HOMESERVER", "https://m.example.org") MATRIX_ACCESS_TOKEN = os.getenv("MATRIX_ACCESS_TOKEN", "") MATRIX_ROOM_ID = os.getenv("MATRIX_ROOM_ID", "") return try: for line in env_path.read_text().splitlines(): line = line.strip() if not line or line.startswith("#"): continue if "=" not in line: continue key, val = line.split("=", 1) if key == "MATRIX_HOMESERVER": MATRIX_HOMESERVER = val elif key == "MATRIX_ACCESS_TOKEN": MATRIX_ACCESS_TOKEN = val elif key == "MATRIX_ROOM_ID": MATRIX_ROOM_ID = val logging.info(f"Loaded config from {env_path}") except Exception as e: logging.error(f"Failed to load .env: {e}") def lookup_oui(mac: str) -> str: """ Look up OUI vendor from MAC address (first 3 octets). Tries SQLite database first, falls back to inline dictionary. Returns vendor name or 'unknown' if not found. """ if not mac or mac == "00:00:00:00:00:00": return "unknown" # Try database first oui_prefix = mac[:8].lower() try: conn = sqlite3.connect(OUI_DB_PATH, timeout=1) conn.row_factory = sqlite3.Row cursor = conn.cursor() result = cursor.execute("SELECT vendor FROM oui WHERE prefix = ?", (oui_prefix,)).fetchone() conn.close() if result: return result['vendor'] except Exception: # Log at DEBUG only, no output noise logging.debug(f"OUI database lookup failed for {oui_prefix}", exc_info=False) # Fall back to inline dictionary oui_prefix_upper = oui_prefix.replace(":", "").upper() return OUI_DICT.get(oui_prefix_upper, "unknown") def seed_from_arp_cache(): """Read /proc/net/arp, populate known_devices without alerting.""" global known_devices try: lines = Path("/proc/net/arp").read_text().splitlines() for line in lines: if line.startswith("IP"): continue fields = line.split() if len(fields) < 4: continue ip = fields[0] mac = fields[3].lower() flags = fields[2] if mac == "00:00:00:00:00:00" or flags == "0x0": continue vendor = lookup_oui(mac) with known_lock: if mac not in known_devices: dev = { 'ip': ip, 'hostname': ip, 'vendor': vendor, 'first_seen': time.time(), 'last_seen': time.time() } # Mark infrastructure IPs so they never alert if ip in infrastructure_ips: dev['infrastructure'] = True known_devices[mac] = dev logging.info(f"Seeded {len(known_devices)} devices from ARP cache") except Exception as e: logging.error(f"Failed to seed from ARP cache: {e}") def send_alert(msg: str) -> None: """Send alert to Matrix room.""" if not MATRIX_ACCESS_TOKEN: logging.warning("No MATRIX_ACCESS_TOKEN set, skipping alert") return url = ( f"{MATRIX_HOMESERVER}/_matrix/client/v3/rooms/" f"{urllib.parse.quote(MATRIX_ROOM_ID, safe='')}/send/m.room.message" ) payload = json.dumps({"msgtype": "m.text", "body": msg}).encode() req = urllib.request.Request( url, data=payload, headers={ "Authorization": f"Bearer {MATRIX_ACCESS_TOKEN}", "Content-Type": "application/json", "User-Agent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36", }, method="POST", ) try: with urllib.request.urlopen(req, timeout=10) as r: pass logging.debug(f"Alert sent to Matrix") except urllib.error.HTTPError as e: logging.error(f"Matrix send failed with HTTP {e.code}") except Exception as e: logging.error(f"Matrix send exception: {e}") def fmt_duration(secs: float) -> str: """Format duration in seconds to human-readable format.""" if secs < 60: return f"{int(secs)}s" elif secs < 3600: m = int(secs // 60) s = int(secs % 60) return f"{m}m {s}s" if s else f"{m}m" else: h = int(secs // 3600) m = int((secs % 3600) // 60) return f"{h}h {m}m" if m else f"{h}h" def format_arrival(hostname: str, ip: str, vendor: str, mac: str) -> str: """Format arrival alert message. Deduplicate IP if hostname equals IP.""" if hostname == ip: # Hostname resolution failed, don't repeat IP return f"[NET] ARRIVED: {ip} [{vendor}] MAC:{mac}" else: # Hostname resolved successfully, show both return f"[NET] ARRIVED: {hostname} ({ip}) [{vendor}] MAC:{mac}" def format_departure(hostname: str, ip: str, vendor: str, mac: str, duration: str) -> str: """Format departure alert message. Deduplicate IP if hostname equals IP.""" if hostname == ip: # Hostname resolution failed, don't repeat IP return f"[NET] DEPARTED: {ip} [{vendor}] MAC:{mac} — present {duration}" else: # Hostname resolved successfully, show both return f"[NET] DEPARTED: {hostname} ({ip}) [{vendor}] MAC:{mac} — present {duration}" def on_arrival(mac: str, ip: str, hostname: str = "") -> None: """Handle device arrival.""" # Infrastructure IPs never trigger alerts if ip in infrastructure_ips: logging.debug(f"Ignoring infrastructure IP {ip} (MAC:{mac})") return hostname = hostname or ip now = time.time() # Check re-arrival suppression BEFORE acquiring lock (avoid nested locks) with departure_lock: # ALWAYS cancel any pending departure timer when device re-arrives if mac in departure_timers: departure_timers[mac].cancel() del departure_timers[mac] logging.debug(f"Cancelled departure timer for {mac} — device re-arrived before debounce expired") if mac in last_departed_time: time_since_departure = now - last_departed_time[mac] if time_since_departure < 300: # 5 min logging.debug(f"Suppressing re-arrival alert for {mac} (departed {int(time_since_departure)}s ago)") # Re-add to known_devices to track presence with known_lock: if mac not in known_devices: vendor = lookup_oui(mac) known_devices[mac] = { 'ip': ip, 'hostname': hostname, 'vendor': vendor, 'first_seen': now, 'last_seen': now } else: known_devices[mac]['last_seen'] = now return with known_lock: if mac in known_devices: # Device is already known dev = known_devices[mac] dev['last_seen'] = now # DHCP renewal dedup: if last_seen < 30 min, skip alert if now - dev['first_seen'] < 1800: # 30 min logging.debug(f"Skipping DHCP renewal alert for {mac} (seen {int(now - dev['first_seen'])}s ago)") return # Not a re-arrival, update last_seen and don't alert (already known) return # New device vendor = lookup_oui(mac) known_devices[mac] = { 'ip': ip, 'hostname': hostname, 'vendor': vendor, 'first_seen': now, 'last_seen': now } msg = format_arrival(hostname, ip, vendor or "unknown", mac) logging.info(msg) send_alert(msg) def on_departure(mac: str) -> None: """ Handle device departure with 15-minute debounce. Only sends alert if device still gone after 15 min. """ with known_lock: if mac not in known_devices: return # Check if infrastructure IP (never alert) dev = known_devices[mac] if dev['ip'] in infrastructure_ips: logging.debug(f"Ignoring departure for infrastructure IP {dev['ip']} (MAC:{mac})") return dev_copy = dev.copy() known_devices.pop(mac) # Start 15-minute debounce timer with departure_lock: # Cancel any existing timer for this MAC if mac in departure_timers: departure_timers[mac].cancel() def send_departure_alert(): """Callback to send alert after debounce expires.""" duration = fmt_duration(time.time() - dev_copy['first_seen']) msg = format_departure(dev_copy['hostname'], dev_copy['ip'], dev_copy['vendor'] or "unknown", mac, duration) logging.info(msg) send_alert(msg) # Record departure time for re-arrival suppression with departure_lock: last_departed_time[mac] = time.time() if mac in departure_timers: del departure_timers[mac] timer = threading.Timer(900.0, send_departure_alert) # 15 min = 900 sec timer.daemon = True timer.name = f'departure-debounce-{mac}' departure_timers[mac] = timer timer.start() logging.debug(f"Departure debounce started for {mac}, will alert in 15 min if still gone") def get_primary_interface() -> str: """Get primary network interface (not lo).""" try: with open('/proc/net/route') as f: for line in f.readlines()[1:]: parts = line.split() if len(parts) > 1 and parts[0] != 'lo' and parts[1] == '00000000': return parts[0] with open('/proc/net/route') as f: for line in f.readlines()[1:]: parts = line.split() if parts[0] != 'lo': return parts[0] except Exception: pass return 'eth0' def get_local_ip(iface: str) -> str: """Get the local IP address for the given interface.""" try: import subprocess result = subprocess.run(['ip', 'addr', 'show', iface], capture_output=True, text=True, timeout=5) if result.returncode == 0: for line in result.stdout.split('\n'): if 'inet ' in line: parts = line.strip().split() if len(parts) >= 2: ip_with_mask = parts[1] ip = ip_with_mask.split('/')[0] return ip except Exception as e: logging.warning(f"Failed to get local IP for {iface}: {e}") return "" def seed_infrastructure_ips(iface: str) -> None: """ Seed infrastructure IPs that should never trigger alerts. Reads gateway from 'ip route show default', adds broadcast and self IP. """ global infrastructure_ips infrastructure_ips.clear() # Get self IP self_ip = get_local_ip(iface) if self_ip: infrastructure_ips.add(self_ip) logging.info(f"Seeded self IP {self_ip} as infrastructure") # Read gateway from 'ip route show default' try: import subprocess result = subprocess.run(['ip', 'route', 'show', 'default'], capture_output=True, text=True, timeout=5) if result.returncode == 0: # Parse: default via 10.0.0.0 dev eth0 proto dhcp metric 100 for line in result.stdout.strip().split('\n'): if 'via' in line: parts = line.split() for i, part in enumerate(parts): if part == 'via' and i + 1 < len(parts): gateway_ip = parts[i + 1] infrastructure_ips.add(gateway_ip) logging.info(f"Seeded gateway {gateway_ip} as infrastructure") break except Exception as e: logging.warning(f"Failed to read gateway: {e}") # Add broadcast (x.x.x.255 for most networks) if self_ip: try: parts = self_ip.rsplit('.', 1) if len(parts) == 2: broadcast_ip = parts[0] + ".255" infrastructure_ips.add(broadcast_ip) logging.info(f"Seeded broadcast {broadcast_ip} as infrastructure") except Exception: pass logging.info(f"Infrastructure IPs: {infrastructure_ips}") def dhcp_sniffer(iface: str) -> None: """ DHCP sniffer thread. AF_PACKET raw socket, captures DHCP traffic passively. """ try: s = socket.socket(socket.AF_PACKET, socket.SOCK_RAW, socket.htons(0x0003)) s.bind((iface, 0)) logging.info(f"DHCP sniffer started on {iface}") while True: try: data, _ = s.recvfrom(65535) parse_dhcp(data) except Exception as e: logging.error(f"DHCP sniffer error: {e}") time.sleep(1) except Exception as e: logging.error(f"Failed to start DHCP sniffer: {e}") def parse_dhcp(data: bytes) -> None: """Parse DHCP packet and trigger arrival/departure events.""" try: if len(data) < 14: return # Ethernet frame eth_type = struct.unpack('!H', data[12:14])[0] if eth_type != 0x0800: # not IPv4 return # IP header if len(data) < 23: return proto = data[23] if proto != 17: # not UDP return # UDP ports if len(data) < 38: return src_port = struct.unpack('!H', data[34:36])[0] dst_port = struct.unpack('!H', data[36:38])[0] if not (src_port in (67, 68) and dst_port in (67, 68)): return # DHCP payload (starts at byte 42) if len(data) < 42: return dhcp = data[42:] if len(dhcp) < 236: return # MAC address (chaddr at offset 28, 6 bytes) mac_bytes = dhcp[28:34] mac = ':'.join(f'{b:02x}' for b in mac_bytes) if mac in ('00:00:00:00:00:00', 'ff:ff:ff:ff:ff:ff'): return # Parse DHCP options (start at byte 240) if len(dhcp) < 240: return msg_type = None hostname = "" requested_ip = "" ciaddr = socket.inet_ntoa(dhcp[12:16]) i = 240 while i < len(dhcp): opt = dhcp[i] if opt == 255: break if opt == 0: i += 1 continue if i + 1 >= len(dhcp): break length = dhcp[i + 1] if i + 2 + length > len(dhcp): break val = dhcp[i + 2:i + 2 + length] if opt == 53 and length == 1: # DHCP message type msg_type = val[0] elif opt == 12: # Hostname hostname = val.decode('utf-8', errors='replace').strip('\x00') elif opt == 50 and length == 4: # Requested IP requested_ip = socket.inet_ntoa(val) i += 2 + length # Process based on message type if msg_type in (1, 3): # Discover or Request (arrival) ip = requested_ip or ciaddr if ip and ip != '0.0.0.0': on_arrival(mac, ip, hostname) elif msg_type == 7: # Release (departure) on_departure(mac) except Exception as e: logging.debug(f"DHCP parse error: {e}") # Netlink constants NETLINK_ROUTE = 0 RTMGRP_NEIGH = 0x4 RTM_NEWNEIGH = 28 RTM_DELNEIGH = 29 NUD_REACHABLE = 0x02 NUD_STALE = 0x04 NUD_DELAY = 0x08 NUD_PROBE = 0x10 NDA_DST = 1 NDA_LLADDR = 2 def netlink_watcher() -> None: """ Netlink watcher thread. Kernel pushes RTM_NEWNEIGH and RTM_DELNEIGH events. """ try: s = socket.socket(socket.AF_NETLINK, socket.SOCK_RAW, NETLINK_ROUTE) s.bind((os.getpid(), RTMGRP_NEIGH)) logging.info("Netlink neighbor watcher started") while True: try: data = s.recv(65535) parse_netlink(data) except Exception as e: logging.error(f"Netlink watcher error: {e}") time.sleep(1) except Exception as e: logging.error(f"Failed to start Netlink watcher: {e}") def parse_netlink(data: bytes) -> None: """Parse Netlink neighbor messages.""" try: offset = 0 while offset < len(data): if offset + 16 > len(data): break nlmsg_len, nlmsg_type, _, _, _ = struct.unpack_from('=IHHII', data, offset) if nlmsg_len < 16: break payload = data[offset + 16:offset + nlmsg_len] if nlmsg_type in (RTM_NEWNEIGH, RTM_DELNEIGH): parse_ndmsg(payload, nlmsg_type) offset += (nlmsg_len + 3) & ~3 except Exception as e: logging.debug(f"Netlink parse error: {e}") def parse_ndmsg(data: bytes, msg_type: int) -> None: """Parse ndmsg (neighbor discovery message).""" try: if len(data) < 12: return state = struct.unpack_from('=H', data, 8)[0] mac = None ip = None offset = 12 while offset + 4 <= len(data): rta_len, rta_type = struct.unpack_from('=HH', data, offset) if rta_len < 4: break val = data[offset + 4:offset + rta_len] if rta_type == NDA_LLADDR and len(val) == 6: mac = ':'.join(f'{b:02x}' for b in val) elif rta_type == NDA_DST: if len(val) == 4: ip = socket.inet_ntoa(val) offset += (rta_len + 3) & ~3 if not mac or mac in ('00:00:00:00:00:00', 'ff:ff:ff:ff:ff:ff'): return if msg_type == RTM_NEWNEIGH and (state & (NUD_REACHABLE | NUD_STALE | NUD_DELAY | NUD_PROBE)): on_arrival(mac, ip or 'unknown') elif msg_type == RTM_DELNEIGH: on_departure(mac) except Exception as e: logging.debug(f"ndmsg parse error: {e}") def main() -> None: """Main entry point.""" logger = setup_logging() load_env() iface = get_primary_interface() logging.info(f"Net alerter starting on interface {iface}") seed_infrastructure_ips(iface) seed_from_arp_cache() # Start monitor threads threads = [ threading.Thread(target=dhcp_sniffer, args=(iface,), daemon=True, name='dhcp-sniffer'), threading.Thread(target=netlink_watcher, daemon=True, name='netlink-watcher'), ] for t in threads: t.start() logging.info("Net alerter running — DHCP sniffer + Netlink neighbor watcher active") # Keep main thread alive try: while True: time.sleep(60) with known_lock: logging.debug(f"Tracking {len(known_devices)} devices") except KeyboardInterrupt: logging.info("Shutting down") sys.exit(0) if __name__ == '__main__': main()