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gtp_v2: allow building IE_Indication, IE_MMContext_EPS, and PCO_S_Nssai without explicit length #5296

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gtp_v2: allow building IE_Indication, IE_MMContext_EPS, and PCO_S_Nssai without explicit length #5296

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18 changes: 11 additions & 7 deletions scapy/contrib/gtp_v2.py
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Original file line number Diff line number Diff line change
Expand Up @@ -573,8 +573,8 @@ class IE_MMContext_EPS(gtp.IE_Base):
ThreeBytesField("Nas_ul_count", 0),
BitField("Kasme", 0, 256),
ConditionalField(StrLenField("fields", "",
length_from=lambda x: x.length - 41),
lambda pkt: pkt.length > 40)]
length_from=lambda x: (x.length - 41) if x.length is not None else 0),
lambda pkt: pkt.length > 40 if pkt.length is not None else False)]


class IE_PDNConnection(gtp.IE_Base):
Expand Down Expand Up @@ -779,7 +779,7 @@ class IE_MSISDN(gtp.IE_Base):
class IE_Indication(gtp.IE_Base):
name = "IE Indication"
fields_desc = [ByteEnumField("ietype", 77, IEType),
ShortField("length", None),
ShortField("length", 3),
BitField("CR_flag", 0, 4),
BitField("instance", 0, 4),
ConditionalField(
Expand Down Expand Up @@ -1151,13 +1151,17 @@ class PCO_S_Nssai(PCO_Protocol):
fields_desc = [ShortEnumField("type", None, PCO_PROTOCOL_TYPES),
ByteField("length", None),
ConditionalField(
ByteField("SST", 0), lambda pkt: pkt.length > 0),
ByteField("SST", 0),
lambda pkt: pkt.length > 0 if pkt.length is not None else True),
ConditionalField(
ShortField("SD", 0), lambda pkt: pkt.length > 1),
ShortField("SD", 0),
lambda pkt: pkt.length > 1 if pkt.length is not None else False),
ConditionalField(
ByteField("Hplmn_Sst", 0), lambda pkt: pkt.length >= 4),
ByteField("Hplmn_Sst", 0),
lambda pkt: pkt.length >= 4 if pkt.length is not None else False),
ConditionalField(
ShortField("Hplmn_Sd", 0), lambda pkt: pkt.length > 4)]
ShortField("Hplmn_Sd", 0),
lambda pkt: pkt.length > 4 if pkt.length is not None else False)]


class PCO_Qos_Rules(PCO_Protocol):
Expand Down
12 changes: 12 additions & 0 deletions test/contrib/gtp_v2.uts
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Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,12 @@ ie.ietype == 77 and ie.PS == 1 and ie.CPRAI == 1
ie = IE_Indication(ietype='Indication', length=8, DTF=1, PPSI=1)
ie.ietype == 77 and ie.DTF == 1 and ie.PPSI == 1

= IE_Indication, build without length
ie = IE_Indication(PS=1)
assert bytes(ie) == b'M\x00\x03\x00\x00\x08\x00'
d = IE_Indication(bytes(ie))
assert d.PS == 1 and d.length == 3

= IE_PCO, dissection
h = "333333333333222222222222810083840800458800a500000000fd1183bb0a2a00010a2a0002084b76a00091cf0b48210085bd574af24c68e300020002001000570009008b000010927f0000025700090187000010927f0000024f000500017f0000037f000100004e00220080000d040a2a0003000d040a2a00038021100300001081060a2a000483060a2a00045d00250049000100660200020010005700090081000010927f0000025700090285000010927f000002dd9f22c6"
gtp = Ether(hex_bytes(h))
Expand Down Expand Up @@ -211,6 +217,12 @@ ie.Sec_Mode == 4 and ie.Nhi == 0 and ie.Drxi == 1 and ie.Ksi == 0 and ie.Num_qui
ie = IE_MMContext_EPS(ietype=107, length=70, CR_flag=0, instance=0, Sec_Mode=4, Nhi=0, Drxi=1, Ksi=0, Num_quint=0, Num_Quad=0, Uambri=0, Osci=0, Sambri=1, Nas_algo=1, Nas_cipher=1, Nas_dl_count=2, Nas_ul_count=2, Kasme=11111111111111111111111111111111111111111111111111111111111111111111111111111)
ie.Sec_Mode == 4 and ie.Nhi == 0 and ie.Drxi == 1 and ie.Ksi == 0 and ie.Num_quint == 0 and ie.Num_Quad == 0 and ie.Uambri == 0 and ie.Osci == 0 and ie.Sambri == 1 and ie.Nas_algo == 1 and ie.Nas_cipher == 1 and ie.Nas_dl_count == 2 and ie.Nas_ul_count == 2 and ie.Kasme == 11111111111111111111111111111111111111111111111111111111111111111111111111111

= IE_MMContext_EPS, build without length
ie = IE_MMContext_EPS()
assert len(bytes(ie)) == 45
d = IE_MMContext_EPS(bytes(ie))
assert d.length == 41

= IE_PDNConnection, IE_FQDN, dissection
h = "d89ef3da40e2fa163e956dce08004500008a0001000040114bbd0a0a0f3d0a0f0b5b084b084b00765a234883006a0000180f76d163006b0046008800910000020000021890aa80be385102083701a2907066f8bd9f2a28b717671c71c71c71c71c71c70100003d090002625a00028040000812345678900000000000000000006d0014008800100004706777310474657374056c6f63616c"
gtp = Ether(hex_bytes(h))
Expand Down