bug in wireshark decoder of osmo-pcu

hi, i get wrong decoding of RLCMAC control block. the decoder of osmo-pcu is decoding following sequence: 0x40,0x16,0x76,0x67,0x74,0x02,0x26,0x64,0xe8,0x65,0x64,0x69,0x00,0x3e,0x4c,0x00,0x2b,0x2b,0x2b,0x2b,0x2b,0x2b,0x2 this is the result: PayloadType = 1 | spare = 0 | R = 0 | MESSAGE_TYPE = 5 | Exist_ACCESS_TYPE = 1 | ACCESS_TYPE = 0 | : ID | Choice PacketResourceRequestID = 1 | u.TLLI = 0xd99dd008 | : End ID | Exist_MS_Radio_Access_capability = 1 | : MS_Radio_Access_capability | MS_RA_capability_value[0] { | Choice MS_RA_capability_value_Choice = 3 | u.Content length = 25 ... at this point, the length of the content is 25 bits: | RF_Power_Capability = 1 | Exist_A5_bits = 1 | A5_bits = 80 | ES_IND = 1 | PS = 1 | VGCS = 0 | VBS = 0 | Exist_Multislot_capability = 1 | : Multislot_capability | Exist_HSCSD_multislot_class = 0 | Exist_GPRS_multislot_class = 1 | GPRS_multislot_class = 12 | GPRS_Extended_Dynamic_Allocation_Capability = 1 | Exist_SM = 0 ... at this point all 25 bits are decoded, so the decoder must abort decoding of content of Multislot_capability_t (see gsm_rlcmac.cpp). instead, it continues with the data found after these 25 bits: (all crap from now on) | Exist_ECSD_multislot_class = 0 | Exist_EGPRS_multislot_class = 0 | Exist_DTM_GPRS_multislot_class = 1 | DTM_GPRS_multislot_class = 2 | Single_Slot_DTM = 1 | : DTM_EGPRS_Params | Exist_DTM_EGPRS_multislot_class = 0 | : End DTM_EGPRS_Params | : End Multislot_capability | Exist_Eight_PSK_Power_Capability = 0 | COMPACT_Interference_Measurement_Capability = 1 | Revision_Level_Indicator = 0 | UMTS_FDD_Radio_Access_Technology_Capability = 0 | UMTS_384_TDD_Radio_Access_Technology_Capability = 0 | CDMA2000_Radio_Access_Technology_Capability = 0 | UMTS_128_TDD_Radio_Access_Technology_Capability = 0 | GERAN_Feature_Package_1 = 0 | Exist_Extended_DTM_multislot_class = 0 | Modulation_based_multislot_class_support = 0 | Exist_HighMultislotCapability = 0 | Exist_GERAN_lu_ModeCapability = 0 | GMSK_MultislotPowerProfile = 3 | EightPSK_MultislotProfile = 3 | MultipleTBF_Capability = 1 | DownlinkAdvancedReceiverPerformance = 0 | ExtendedRLC_MAC_ControlMessageSegmentionsCapability = 1 | DTM_EnhancementsCapability = 0 | Exist_DTM_GPRS_HighMultislotClass = 0 | PS_HandoverCapability = 1 | MS_RA_capability_value[0] } | MS_RA_capability_value[0] { | Choice MS_RA_capability_value_Choice = 0 | u.Content length = 0 | RF_Power_Capability = 2 | Exist_A5_bits = 1 | A5_bits = 50 | ES_IND = 1 | PS = 0 | VGCS = 1 | VBS = 1 | Exist_Multislot_capability = 0 | Exist_Eight_PSK_Power_Capability = 0 | COMPACT_Interference_Measurement_Capability = 1 | Revision_Level_Indicator = 0 | UMTS_FDD_Radio_Access_Technology_Capability = 1 | UMTS_384_TDD_Radio_Access_Technology_Capability = 0 | CDMA2000_Radio_Access_Technology_Capability = 1 | UMTS_128_TDD_Radio_Access_Technology_Capability = 1 | GERAN_Feature_Package_1 = 0 | Exist_Extended_DTM_multislot_class = 0 | Modulation_based_multislot_class_support = 1 | Exist_HighMultislotCapability = 0 | Exist_GERAN_lu_ModeCapability = 1 | GERAN_lu_ModeCapability = 6 | GMSK_MultislotPowerProfile = 1 | EightPSK_MultislotProfile = 1 | MultipleTBF_Capability = 0 | DownlinkAdvancedReceiverPerformance = 3 | ExtendedRLC_MAC_ControlMessageSegmentionsCapability = 0 | DTM_EnhancementsCapability = 0 | Exist_DTM_GPRS_HighMultislotClass = 1 | DTM_GPRS_HighMultislotClass = 2 | : DTM_EGPRS_HighMultislotClass | Exist_DTM_EGPRS_HighMultislotClass = 1 | : End DTM_EGPRS_HighMultislotClass | : End MS_Radio_Access_capability | there are two problems with the decoder: - it does not check if the length has been exceeded while decoding Multislot_capability_t content. if the length is lower than all elements in Multislot_capabilit_t, the decoder must abort decoding the content. this is no bug. (the definition used at that point should be M_NEXT_EXIST_OR_NULL instead of M_NEXT_EXIST, see gsm_rlcmac.cpp) - even if the correct definition is used, the csn1 decoder will not use the length given at "u.Content length" to abort. instead it checks for reaching total length of coded data. i played a bit with the code, but could not fix it without breaking other things. but decoding with wireshark works. would it be possible to port latest wireshark code? regards, andreas