53 lines
1.8 KiB
Python
53 lines
1.8 KiB
Python
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# This file is part of Scapy
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# See http://www.secdev.org/projects/scapy for more information
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# Copyright (C) Philippe Biondi <phil@secdev.org>
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# This program is published under a GPLv2 license
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"""
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L2TP (Layer 2 Tunneling Protocol) for VPNs.
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[RFC 2661]
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"""
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import struct
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from scapy.packet import Packet, bind_layers, bind_bottom_up
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from scapy.fields import BitEnumField, ConditionalField, FlagsField, \
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PadField, ShortField
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from scapy.layers.inet import UDP
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from scapy.layers.ppp import PPP
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class L2TP(Packet):
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name = "L2TP"
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fields_desc = [
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FlagsField("hdr", 0, 12, ['res00', 'res01', 'res02', 'res03', 'priority', 'offset', # noqa: E501
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'res06', 'sequence', 'res08', 'res09', 'length', 'control']), # noqa: E501
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BitEnumField("version", 2, 4, {2: 'L2TPv2'}),
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ConditionalField(ShortField("len", 0),
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lambda pkt: pkt.hdr & 'control+length'),
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ShortField("tunnel_id", 0),
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ShortField("session_id", 0),
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ConditionalField(ShortField("ns", 0),
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lambda pkt: pkt.hdr & 'sequence+control'),
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ConditionalField(ShortField("nr", 0),
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lambda pkt: pkt.hdr & 'sequence+control'),
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ConditionalField(
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PadField(ShortField("offset", 0), 4, b"\x00"),
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lambda pkt: not (pkt.hdr & 'control') and pkt.hdr & 'offset'
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)
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]
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def post_build(self, pkt, pay):
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if self.len is None:
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tmp_len = len(pkt) + len(pay)
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pkt = pkt[:2] + struct.pack("!H", tmp_len) + pkt[4:]
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return pkt + pay
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bind_bottom_up(UDP, L2TP, dport=1701)
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bind_bottom_up(UDP, L2TP, sport=1701)
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bind_layers(UDP, L2TP, dport=1701, sport=1701)
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bind_layers(L2TP, PPP,)
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