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nsh: dissect MD-Type 2 variable length context headers #5096

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nsh: dissect MD-Type 2 variable length context headers #5096

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22 changes: 14 additions & 8 deletions scapy/contrib/nsh.py
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@
from scapy.all import bind_layers
from scapy.fields import BitField, ByteField, ByteEnumField, BitEnumField, \
ShortField, X3BytesField, XIntField, XStrFixedLenField, \
ConditionalField, PacketListField, BitFieldLenField
ConditionalField, FieldListField, PacketListField, BitFieldLenField
from scapy.layers.inet import Ether, IP
from scapy.layers.inet6 import IPv6
from scapy.layers.vxlan import VXLAN
Expand All @@ -30,10 +30,15 @@ class NSHTLV(Packet):
ShortField('class_', 0),
BitField('type', 0, 8),
BitField('reserved', 0, 1),
BitField('length', 0, 7),
PacketListField('metadata', None, XIntField, count_from='length')
BitFieldLenField('length', None, 7, count_of='metadata',
adjust=lambda pkt, x: x * 4),
FieldListField('metadata', [], XIntField('', 0),
length_from=lambda pkt: (pkt.length + 3) // 4 * 4)
]

def extract_padding(self, s):
return b'', s


class NSH(Packet):
"""Network Service Header.
Expand All @@ -46,9 +51,9 @@ class NSH(Packet):
BitField('unused1', 0, 1),
BitField('ttl', 63, 6),
BitFieldLenField('length', None, 6,
count_of='vlch',
length_of='vlch',
adjust=lambda pkt, x: 6 if pkt.mdtype == 1
else x + 2),
else x // 4 + 2),
BitField('unused2', 0, 4),
BitEnumField('mdtype', 1, 4, {0: 'Reserved MDType',
1: 'Fixed Length',
Expand All @@ -65,9 +70,10 @@ class NSH(Packet):
ByteField('si', 0xFF),
ConditionalField(XStrFixedLenField("context_header", "", 16),
lambda pkt: pkt.mdtype == 1),
ConditionalField(PacketListField("vlch", None, NSHTLV,
count_from="length"),
lambda pkt: pkt.mdtype == 2)
ConditionalField(PacketListField(
"vlch", None, NSHTLV,
length_from=lambda pkt: (pkt.length - 2) * 4),
lambda pkt: pkt.mdtype == 2)
]

def mysummary(self):
Expand Down
27 changes: 27 additions & 0 deletions test/contrib/nsh.uts
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Original file line number Diff line number Diff line change
Expand Up @@ -18,3 +18,30 @@ raw(NSH(mdtype=2, spi=0xF0F0F0, si=0xFF)) == b'\x0f\xc2\x02\x03\xf0\xf0\xf0\xff
= Build a NSH over VXLAN packet and verify bindings
raw(Ether(dst='0c:42:a1:5f:fb:e0', src='b8:59:9f:cd:de:3e')/IPv6(src='::1', dst='::2')/UDP(sport=10, dport=8472)/VXLAN(NextProtocol=4, vni=4660)/NSH()/NSH()/Ether(dst='0c:42:a1:5f:fb:e4', src='b8:59:9f:cd:de:33')/IP(src='10.200.100.10', dst='2.2.2.3')/TCP(sport=123, dport=333)) == b'\x0cB\xa1_\xfb\xe0\xb8Y\x9f\xcd\xde>\x86\xdd`\x00\x00\x00\x00v\x11@\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\n!\x18\x00v\x05F\x0c\x00\x00\x04\x00\x124\x00\x0f\xc6\x01\x04\x00\x00\x00\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0f\xc6\x01\x03\x00\x00\x00\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0cB\xa1_\xfb\xe4\xb8Y\x9f\xcd\xde3\x08\x00E\x00\x00(\x00\x01\x00\x00@\x06\x07\xf9\n\xc8d\n\x02\x02\x02\x03\x00{\x01M\x00\x00\x00\x00\x00\x00\x00\x00P\x02 \x00\x1bD\x00\x00'


+ MD-Type 2 variable length context headers

= Dissect a NSH MD-Type 2 packet carrying one context header
p = NSH(hex_bytes('0fc40203000001ff00010204deadbeef'))
assert p.mdtype == 2
assert p.length == 4
assert len(p.vlch) == 1
assert p.vlch[0].class_ == 1
assert p.vlch[0].type == 2
assert p.vlch[0].length == 4
assert p.vlch[0].metadata == [0xdeadbeef]
assert raw(p) == hex_bytes('0fc40203000001ff00010204deadbeef')

= Dissect a NSH MD-Type 2 packet carrying two context headers
p = NSH(hex_bytes('0fc60203000001ff00010204deadbeef00020104cafebabe'))
assert p.length == 6
assert len(p.vlch) == 2
assert p.vlch[0].metadata == [0xdeadbeef]
assert p.vlch[1].class_ == 2
assert p.vlch[1].metadata == [0xcafebabe]
assert raw(p) == hex_bytes('0fc60203000001ff00010204deadbeef00020104cafebabe')

= Build a NSH MD-Type 2 packet and check the computed length
p = NSH(mdtype=2, nextproto=3, spi=1, si=255, vlch=[NSHTLV(class_=1, type=2, metadata=[0xdeadbeef])])
assert raw(p) == hex_bytes('0fc40203000001ff00010204deadbeef')
assert NSH(raw(p)).length == 4
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