# SPDX-License-Identifier: GPL-2.0-only
# This file is part of Scapy
# See https://scapy.net/ for more information
# Copyright (C) Philippe Biondi <phil@secdev.org>

"""
Clone of p0f v2 passive OS fingerprinting
"""

import time
import struct
import os
import socket
import random

from scapy.data import KnowledgeBase, select_path
from scapy.config import conf
from scapy.compat import raw
from scapy.layers.inet import IP, TCP, TCPOptions
from scapy.packet import NoPayload, Packet
from scapy.error import warning, Scapy_Exception, log_runtime
from scapy.volatile import RandInt, RandByte, RandNum, RandShort, RandString
from scapy.sendrecv import sniff
if conf.route is None:
    # unused import, only to initialize conf.route
    import scapy.route  # noqa: F401

_p0fpaths = ["/etc/p0f", "/usr/share/p0f", "/opt/local"]

conf.p0f_base = select_path(_p0fpaths, "p0f.fp")
conf.p0fa_base = select_path(_p0fpaths, "p0fa.fp")
conf.p0fr_base = select_path(_p0fpaths, "p0fr.fp")
conf.p0fo_base = select_path(_p0fpaths, "p0fo.fp")


###############
#  p0f stuff  #
###############

# File format (according to p0f.fp) :
#
# wwww:ttt:D:ss:OOO...:QQ:OS:Details
#
# wwww    - window size
# ttt     - initial TTL
# D       - don't fragment bit  (0=unset, 1=set)
# ss      - overall SYN packet size
# OOO     - option value and order specification
# QQ      - quirks list
# OS      - OS genre
# details - OS description

class p0fKnowledgeBase(KnowledgeBase):
    def __init__(self, filename):
        KnowledgeBase.__init__(self, filename)
        # self.ttl_range=[255]

    def lazy_init(self):
        try:
            f = open(self.filename)
        except IOError:
            warning("Can't open base %s", self.filename)
            return
        try:
            self.base = []
            for line in f:
                if line[0] in ["#", "\n"]:
                    continue
                line = tuple(line.split(":"))
                if len(line) < 8:
                    continue

                def a2i(x):
                    if x.isdigit():
                        return int(x)
                    return x
                li = [a2i(e) for e in line[1:4]]
                # if li[0] not in self.ttl_range:
                #    self.ttl_range.append(li[0])
                #    self.ttl_range.sort()
                self.base.append((line[0], li[0], li[1], li[2], line[4],
                                  line[5], line[6], line[7][:-1]))
        except Exception:
            warning("Can't parse p0f database (new p0f version ?)")
            self.base = None
        f.close()


p0f_kdb, p0fa_kdb, p0fr_kdb, p0fo_kdb = None, None, None, None


def p0f_load_knowledgebases():
    global p0f_kdb, p0fa_kdb, p0fr_kdb, p0fo_kdb
    p0f_kdb = p0fKnowledgeBase(conf.p0f_base)
    p0fa_kdb = p0fKnowledgeBase(conf.p0fa_base)
    p0fr_kdb = p0fKnowledgeBase(conf.p0fr_base)
    p0fo_kdb = p0fKnowledgeBase(conf.p0fo_base)


p0f_load_knowledgebases()


def p0f_selectdb(flags):
    # tested flags: S, R, A
    if flags & 0x16 == 0x2:
        # SYN
        return p0f_kdb
    elif flags & 0x16 == 0x12:
        # SYN/ACK
        return p0fa_kdb
    elif flags & 0x16 in [0x4, 0x14]:
        # RST RST/ACK
        return p0fr_kdb
    elif flags & 0x16 == 0x10:
        # ACK
        return p0fo_kdb
    else:
        return None


def packet2p0f(pkt):
    pkt = pkt.copy()
    pkt = pkt.__class__(raw(pkt))
    while pkt.haslayer(IP) and pkt.haslayer(TCP):
        pkt = pkt.getlayer(IP)
        if isinstance(pkt.payload, TCP):
            break
        pkt = pkt.payload

    if not isinstance(pkt, IP) or not isinstance(pkt.payload, TCP):
        raise TypeError("Not a TCP/IP packet")
    # if pkt.payload.flags & 0x7 != 0x02: #S,!F,!R
    #    raise TypeError("Not a SYN or SYN/ACK packet")

    db = p0f_selectdb(pkt.payload.flags)

    # t = p0f_kdb.ttl_range[:]
    # t += [pkt.ttl]
    # t.sort()
    # ttl=t[t.index(pkt.ttl)+1]
    ttl = pkt.ttl

    ss = len(pkt)
    # from p0f/config.h : PACKET_BIG = 100
    if ss > 100:
        if db == p0fr_kdb:
            # p0fr.fp: "Packet size may be wildcarded. The meaning of
            #           wildcard is, however, hardcoded as 'size >
            #           PACKET_BIG'"
            ss = '*'
        else:
            ss = 0
    if db == p0fo_kdb:
        # p0fo.fp: "Packet size MUST be wildcarded."
        ss = '*'

    ooo = ""
    mss = -1
    qqT = False
    qqP = False
    # qqBroken = False
    ilen = (pkt.payload.dataofs << 2) - 20  # from p0f.c
    for option in pkt.payload.options:
        ilen -= 1
        if option[0] == "MSS":
            ooo += "M" + str(option[1]) + ","
            mss = option[1]
            # FIXME: qqBroken
            ilen -= 3
        elif option[0] == "WScale":
            ooo += "W" + str(option[1]) + ","
            # FIXME: qqBroken
            ilen -= 2
        elif option[0] == "Timestamp":
            if option[1][0] == 0:
                ooo += "T0,"
            else:
                ooo += "T,"
            if option[1][1] != 0:
                qqT = True
            ilen -= 9
        elif option[0] == "SAckOK":
            ooo += "S,"
            ilen -= 1
        elif option[0] == "NOP":
            ooo += "N,"
        elif option[0] == "EOL":
            ooo += "E,"
            if ilen > 0:
                qqP = True
        else:
            if isinstance(option[0], str):
                ooo += "?%i," % TCPOptions[1][option[0]]
            else:
                ooo += "?%i," % option[0]
            # FIXME: ilen
    ooo = ooo[:-1]
    if ooo == "":
        ooo = "."

    win = pkt.payload.window
    if mss != -1:
        if mss != 0 and win % mss == 0:
            win = "S" + str(win / mss)
        elif win % (mss + 40) == 0:
            win = "T" + str(win / (mss + 40))
    win = str(win)

    qq = ""

    if db == p0fr_kdb:
        if pkt.payload.flags & 0x10 == 0x10:
            # p0fr.fp: "A new quirk, 'K', is introduced to denote
            #           RST+ACK packets"
            qq += "K"
    # The two next cases should also be only for p0f*r*, but although
    # it's not documented (or I have not noticed), p0f seems to
    # support the '0' and 'Q' quirks on any databases (or at the least
    # "classical" p0f.fp).
    if pkt.payload.seq == pkt.payload.ack:
        # p0fr.fp: "A new quirk, 'Q', is used to denote SEQ number
        #           equal to ACK number."
        qq += "Q"
    if pkt.payload.seq == 0:
        # p0fr.fp: "A new quirk, '0', is used to denote packets
        #           with SEQ number set to 0."
        qq += "0"
    if qqP:
        qq += "P"
    if pkt.id == 0:
        qq += "Z"
    if pkt.options != []:
        qq += "I"
    if pkt.payload.urgptr != 0:
        qq += "U"
    if pkt.payload.reserved != 0:
        qq += "X"
    if pkt.payload.ack != 0:
        qq += "A"
    if qqT:
        qq += "T"
    if db == p0fo_kdb:
        if pkt.payload.flags & 0x20 != 0:
            # U
            # p0fo.fp: "PUSH flag is excluded from 'F' quirk checks"
            qq += "F"
    else:
        if pkt.payload.flags & 0x28 != 0:
            # U or P
            qq += "F"
    if db != p0fo_kdb and not isinstance(pkt.payload.payload, NoPayload):
        # p0fo.fp: "'D' quirk is not checked for."
        qq += "D"
    # FIXME : "!" - broken options segment: not handled yet

    if qq == "":
        qq = "."

    return (db, (win, ttl, pkt.flags.DF, ss, ooo, qq))


def p0f_correl(x, y):
    d = 0
    # wwww can be "*" or "%nn". "Tnn" and "Snn" should work fine with
    # the x[0] == y[0] test.
    d += (x[0] == y[0] or y[0] == "*" or (y[0][0] == "%" and x[0].isdigit() and (int(x[0]) % int(y[0][1:])) == 0))  # noqa: E501
    # ttl
    d += (y[1] >= x[1] and y[1] - x[1] < 32)
    for i in [2, 5]:
        d += (x[i] == y[i] or y[i] == '*')
    # '*' has a special meaning for ss
    d += x[3] == y[3]
    xopt = x[4].split(",")
    yopt = y[4].split(",")
    if len(xopt) == len(yopt):
        same = True
        for i in range(len(xopt)):
            if not (xopt[i] == yopt[i] or
                    (len(yopt[i]) == 2 and len(xopt[i]) > 1 and
                     yopt[i][1] == "*" and xopt[i][0] == yopt[i][0]) or
                    (len(yopt[i]) > 2 and len(xopt[i]) > 1 and
                     yopt[i][1] == "%" and xopt[i][0] == yopt[i][0] and
                     int(xopt[i][1:]) % int(yopt[i][2:]) == 0)):
                same = False
                break
        if same:
            d += len(xopt)
    return d


@conf.commands.register
def p0f(pkt):
    """Passive OS fingerprinting: which OS emitted this TCP packet ?
p0f(packet) -> accuracy, [list of guesses]
"""
    db, sig = packet2p0f(pkt)
    if db:
        pb = db.get_base()
    else:
        pb = []
    if not pb:
        warning("p0f base empty.")
        return []
    # s = len(pb[0][0])
    r = []
    max = len(sig[4].split(",")) + 5
    for b in pb:
        d = p0f_correl(sig, b)
        if d == max:
            r.append((b[6], b[7], b[1] - pkt[IP].ttl))
    return r


def prnp0f(pkt):
    """Calls p0f and returns a user-friendly output"""
    # we should print which DB we use
    try:
        r = p0f(pkt)
    except Exception:
        return
    if r == []:
        r = ("UNKNOWN", "[" + ":".join(map(str, packet2p0f(pkt)[1])) + ":?:?]", None)  # noqa: E501
    else:
        r = r[0]
    uptime = None
    try:
        uptime = pkt2uptime(pkt)
    except Exception:
        pass
    if uptime == 0:
        uptime = None
    res = pkt.sprintf("%IP.src%:%TCP.sport% - " + r[0] + " " + r[1])
    if uptime is not None:
        res += pkt.sprintf(" (up: " + str(uptime / 3600) + " hrs)\n  -> %IP.dst%:%TCP.dport% (%TCP.flags%)")  # noqa: E501
    else:
        res += pkt.sprintf("\n  -> %IP.dst%:%TCP.dport% (%TCP.flags%)")
    if r[2] is not None:
        res += " (distance " + str(r[2]) + ")"
    print(res)


@conf.commands.register
def pkt2uptime(pkt, HZ=100):
    """Calculate the date the machine which emitted the packet booted using TCP timestamp  # noqa: E501
pkt2uptime(pkt, [HZ=100])"""
    if not isinstance(pkt, Packet):
        raise TypeError("Not a TCP packet")
    if isinstance(pkt, NoPayload):
        raise TypeError("Not a TCP packet")
    if not isinstance(pkt, TCP):
        return pkt2uptime(pkt.payload)
    for opt in pkt.options:
        if opt[0] == "Timestamp":
            # t = pkt.time - opt[1][0] * 1.0/HZ
            # return time.ctime(t)
            t = opt[1][0] / HZ
            return t
    raise TypeError("No timestamp option")


def p0f_impersonate(pkt, osgenre=None, osdetails=None, signature=None,
                    extrahops=0, mtu=1500, uptime=None):
    """Modifies pkt so that p0f will think it has been sent by a
specific OS.  If osdetails is None, then we randomly pick up a
personality matching osgenre. If osgenre and signature are also None,
we use a local signature (using p0f_getlocalsigs). If signature is
specified (as a tuple), we use the signature.

For now, only TCP Syn packets are supported.
Some specifications of the p0f.fp file are not (yet) implemented."""
    pkt = pkt.copy()
    # pkt = pkt.__class__(raw(pkt))
    while pkt.haslayer(IP) and pkt.haslayer(TCP):
        pkt = pkt.getlayer(IP)
        if isinstance(pkt.payload, TCP):
            break
        pkt = pkt.payload

    if not isinstance(pkt, IP) or not isinstance(pkt.payload, TCP):
        raise TypeError("Not a TCP/IP packet")

    db = p0f_selectdb(pkt.payload.flags)
    if osgenre:
        pb = db.get_base()
        if pb is None:
            pb = []
        pb = [x for x in pb if x[6] == osgenre]
        if osdetails:
            pb = [x for x in pb if x[7] == osdetails]
    elif signature:
        pb = [signature]
    else:
        pb = p0f_getlocalsigs()[db]
    if db == p0fr_kdb:
        # 'K' quirk <=> RST+ACK
        if pkt.payload.flags & 0x4 == 0x4:
            pb = [x for x in pb if 'K' in x[5]]
        else:
            pb = [x for x in pb if 'K' not in x[5]]
    if not pb:
        raise Scapy_Exception("No match in the p0f database")
    pers = pb[random.randint(0, len(pb) - 1)]

    # options (we start with options because of MSS)
    # Take the options already set as "hints" to use in the new packet if we
    # can. MSS, WScale and Timestamp can all be wildcarded in a signature, so
    # we'll use the already-set values if they're valid integers.
    orig_opts = dict(pkt.payload.options)
    int_only = lambda val: val if isinstance(val, int) else None
    mss_hint = int_only(orig_opts.get('MSS'))
    wscale_hint = int_only(orig_opts.get('WScale'))
    ts_hint = [int_only(o) for o in orig_opts.get('Timestamp', (None, None))]

    options = []
    if pers[4] != '.':
        for opt in pers[4].split(','):
            if opt[0] == 'M':
                # MSS might have a maximum size because of window size
                # specification
                if pers[0][0] == 'S':
                    maxmss = (2**16 - 1) // int(pers[0][1:])
                else:
                    maxmss = (2**16 - 1)
                # disregard hint if out of range
                if mss_hint and not 0 <= mss_hint <= maxmss:
                    mss_hint = None
                # If we have to randomly pick up a value, we cannot use
                # scapy RandXXX() functions, because the value has to be
                # set in case we need it for the window size value. That's
                # why we use random.randint()
                if opt[1:] == '*':
                    if mss_hint is not None:
                        options.append(('MSS', mss_hint))
                    else:
                        options.append(('MSS', random.randint(1, maxmss)))
                elif opt[1] == '%':
                    coef = int(opt[2:])
                    if mss_hint is not None and mss_hint % coef == 0:
                        options.append(('MSS', mss_hint))
                    else:
                        options.append((
                            'MSS', coef * random.randint(1, maxmss // coef)))
                else:
                    options.append(('MSS', int(opt[1:])))
            elif opt[0] == 'W':
                if wscale_hint and not 0 <= wscale_hint < 2**8:
                    wscale_hint = None
                if opt[1:] == '*':
                    if wscale_hint is not None:
                        options.append(('WScale', wscale_hint))
                    else:
                        options.append(('WScale', RandByte()))
                elif opt[1] == '%':
                    coef = int(opt[2:])
                    if wscale_hint is not None and wscale_hint % coef == 0:
                        options.append(('WScale', wscale_hint))
                    else:
                        options.append((
                            'WScale', coef * RandNum(min=1, max=(2**8 - 1) // coef)))  # noqa: E501
                else:
                    options.append(('WScale', int(opt[1:])))
            elif opt == 'T0':
                options.append(('Timestamp', (0, 0)))
            elif opt == 'T':
                # Determine first timestamp.
                if uptime is not None:
                    ts_a = uptime
                elif ts_hint[0] and 0 < ts_hint[0] < 2**32:
                    # Note: if first ts is 0, p0f registers it as "T0" not "T",
                    # hence we don't want to use the hint if it was 0.
                    ts_a = ts_hint[0]
                else:
                    ts_a = random.randint(120, 100 * 60 * 60 * 24 * 365)
                # Determine second timestamp.
                if 'T' not in pers[5]:
                    ts_b = 0
                elif ts_hint[1] and 0 < ts_hint[1] < 2**32:
                    ts_b = ts_hint[1]
                else:
                    # FIXME: RandInt() here does not work (bug (?) in
                    # TCPOptionsField.m2i often raises "OverflowError:
                    # long int too large to convert to int" in:
                    #    oval = struct.pack(ofmt, *oval)"
                    # Actually, this is enough to often raise the error:
                    #    struct.pack('I', RandInt())
                    ts_b = random.randint(1, 2**32 - 1)
                options.append(('Timestamp', (ts_a, ts_b)))
            elif opt == 'S':
                options.append(('SAckOK', ''))
            elif opt == 'N':
                options.append(('NOP', None))
            elif opt == 'E':
                options.append(('EOL', None))
            elif opt[0] == '?':
                if int(opt[1:]) in TCPOptions[0]:
                    optname = TCPOptions[0][int(opt[1:])][0]
                    optstruct = TCPOptions[0][int(opt[1:])][1]
                    options.append((optname,
                                    struct.unpack(optstruct,
                                                  RandString(struct.calcsize(optstruct))._fix())))  # noqa: E501
                else:
                    options.append((int(opt[1:]), ''))
            # FIXME: qqP not handled
            else:
                warning("unhandled TCP option %s", opt)
            pkt.payload.options = options

    # window size
    if pers[0] == '*':
        pkt.payload.window = RandShort()
    elif pers[0].isdigit():
        pkt.payload.window = int(pers[0])
    elif pers[0][0] == '%':
        coef = int(pers[0][1:])
        pkt.payload.window = coef * RandNum(min=1, max=(2**16 - 1) // coef)
    elif pers[0][0] == 'T':
        pkt.payload.window = mtu * int(pers[0][1:])
    elif pers[0][0] == 'S':
        # needs MSS set
        mss = [x for x in options if x[0] == 'MSS']
        if not mss:
            raise Scapy_Exception("TCP window value requires MSS, and MSS option not set")  # noqa: E501
        pkt.payload.window = mss[0][1] * int(pers[0][1:])
    else:
        raise Scapy_Exception('Unhandled window size specification')

    # ttl
    pkt.ttl = pers[1] - extrahops
    # DF flag
    pkt.flags |= (2 * pers[2])
    # FIXME: ss (packet size) not handled (how ? may be with D quirk
    # if present)
    # Quirks
    if pers[5] != '.':
        for qq in pers[5]:
            # FIXME: not handled: P, I, X, !
            # T handled with the Timestamp option
            if qq == 'Z':
                pkt.id = 0
            elif qq == 'U':
                pkt.payload.urgptr = RandShort()
            elif qq == 'A':
                pkt.payload.ack = RandInt()
            elif qq == 'F':
                if db == p0fo_kdb:
                    pkt.payload.flags |= 0x20  # U
                else:
                    pkt.payload.flags |= random.choice([8, 32, 40])  # P/U/PU
            elif qq == 'D' and db != p0fo_kdb:
                pkt /= conf.raw_layer(load=RandString(random.randint(1, 10)))  # XXX p0fo.fp  # noqa: E501
            elif qq == 'Q':
                pkt.payload.seq = pkt.payload.ack
            # elif qq == '0': pkt.payload.seq = 0
        # if db == p0fr_kdb:
        # '0' quirk is actually not only for p0fr.fp (see
        # packet2p0f())
    if '0' in pers[5]:
        pkt.payload.seq = 0
    elif pkt.payload.seq == 0:
        pkt.payload.seq = RandInt()

    while pkt.underlayer:
        pkt = pkt.underlayer
    return pkt


def p0f_getlocalsigs():
    """This function returns a dictionary of signatures indexed by p0f
db (e.g., p0f_kdb, p0fa_kdb, ...) for the local TCP/IP stack.

You need to have your firewall at least accepting the TCP packets
from/to a high port (30000 <= x <= 40000) on your loopback interface.

Please note that the generated signatures come from the loopback
interface and may (are likely to) be different than those generated on
"normal" interfaces."""
    pid = os.fork()
    port = random.randint(30000, 40000)
    if pid > 0:
        # parent: sniff
        result = {}

        def addresult(res):
            # TODO: wildcard window size in some cases? and maybe some
            # other values?
            if res[0] not in result:
                result[res[0]] = [res[1]]
            else:
                if res[1] not in result[res[0]]:
                    result[res[0]].append(res[1])
        # XXX could we try with a "normal" interface using other hosts
        iface = conf.route.route('127.0.0.1')[0]
        # each packet is seen twice: S + RA, S + SA + A + FA + A
        # XXX are the packets also seen twice on non Linux systems ?
        count = 14
        pl = sniff(iface=iface, filter='tcp and port ' + str(port), count=count, timeout=3)  # noqa: E501
        for pkt in pl:
            for elt in packet2p0f(pkt):
                addresult(elt)
        os.waitpid(pid, 0)
    elif pid < 0:
        log_runtime.error("fork error")
    else:
        # child: send
        # XXX erk
        time.sleep(1)
        s1 = socket.socket(socket.AF_INET, type=socket.SOCK_STREAM)
        # S & RA
        try:
            s1.connect(('127.0.0.1', port))
        except socket.error:
            pass
        # S, SA, A, FA, A
        s1.bind(('127.0.0.1', port))
        s1.connect(('127.0.0.1', port))
        # howto: get an RST w/o ACK packet
        s1.close()
        os._exit(0)
    return result
