library/GSM_SystemInformation: add dec_SystemInformationSafe()

Some types of System Information (mostly the Rest Octets) are not
fully implemented, so calling the generic dec_SystemInformation()
may result in a DTE.  Let's add dec_SystemInformationSafeBT() with
"prototype(backtrack)", so it would return a non-zero integer if
decoding fails.  Let's add a wrapper dec_SystemInformationSafe()
that would additionally check the RR Protocol Discriminator.

Change-Id: Id4d73e0f3347e1d4c4c77aec75b767311d662292
Related: OS#4662
changes/12/19212/3
Vadim Yanitskiy 3 years ago committed by laforge
parent f949f465ba
commit cb478ec0ab
  1. 22
      bts/BTS_Tests.ttcn
  2. 25
      library/GSM_SystemInformation.ttcn

@ -3534,7 +3534,6 @@ private function f_TC_imm_ass(integer num_total, float sleep_s, float exp_pass)
repeat;
}
[] L1CTL.receive(tr_L1CTL_DATA_IND(t_RslChanNr_PCH_AGCH(0), ?)) -> value l1_dl {
/* somehow dec_SystemInformation will try to decode even non-RR as SI */
var GsmRrMessage rr := dec_GsmRrMessage(l1_dl.payload.data_ind.payload);
if (not match(rr, tr_IMM_ASS(42, ?, 5, ?, ?))) {
/* FIXME: Why are we seeing paging requests on PCH/AGCH? */
@ -3936,15 +3935,12 @@ return SystemInformationVectorPerTc {
T.start;
alt {
[] pt.receive(tr_L1CTL_DATA_IND(t_RslChanNr_BCCH(0), ?)) -> value l1_dl {
/* somehow dec_SystemInformation will try to decode even non-RR as SI */
if (not (l1_dl.payload.data_ind.payload[1] == '06'O)) {
log("Ignoring non-RR SI ", l1_dl);
var SystemInformationFn sig := { frame_number := l1_dl.dl_info.frame_nr };
if (dec_SystemInformationSafe(l1_dl.payload.data_ind.payload, sig.si) != 0) {
log("Ignoring non-RR or invalid SI ", l1_dl);
repeat;
}
var SystemInformationFn sig := {
frame_number := l1_dl.dl_info.frame_nr,
si := dec_SystemInformation(l1_dl.payload.data_ind.payload)
}
var integer tc := f_gsm_compute_tc(sig.frame_number);
log("SI received at TC=", tc, ": ", sig.si);
/* append to the per-TC bucket */
@ -5227,17 +5223,13 @@ private function f_get_si(L1CTL_PT pt, RrMessageType si_type)
runs on test_CT return SystemInformation {
var L1ctlDlMessage l1_dl;
var SystemInformation si;
var integer rc;
timer T := 5.0;
T.start;
alt {
[] pt.receive(tr_L1CTL_DATA_IND(t_RslChanNr_BCCH(0), ?)) -> value l1_dl {
/* somehow dec_SystemInformation will try to decode even non-RR as SI */
if (not (l1_dl.payload.data_ind.payload[1] == '06'O)) {
log("Ignoring non-RR SI ", l1_dl);
repeat;
}
si := dec_SystemInformation(l1_dl.payload.data_ind.payload)
if (si.header.message_type != si_type) {
rc := dec_SystemInformationSafe(l1_dl.payload.data_ind.payload, si);
if (rc != 0 or si.header.message_type != si_type) {
repeat;
}
}

@ -264,4 +264,29 @@ module GSM_SystemInformation {
}
}
external function dec_SystemInformationSafeBT(in octetstring stream, out SystemInformation si)
return integer /* Decoding result: successful (0) or unsuccessful (1) */
with { extension "prototype(backtrack) decode(RAW)" };
/* Some types of System Information (mostly the Rest Octets) are not fully implemented,
* so calling the generic dec_SystemInformation() may result in a DTE. This function
* additionally checks RR Protocol Discriminator, and should be used in the most cases. */
function dec_SystemInformationSafe(in octetstring stream, out SystemInformation si)
return integer {
/* Try to decode a given octetstring as System Information */
if (dec_SystemInformationSafeBT(stream, si) != 0) {
log("Failed to decode (RR) System Information: ", stream);
return 1;
}
/* Check the protocol discriminator (we expect RR messages) */
if (si.header.rr_protocol_discriminator != bit2int('0110'B)) {
log("Protocol discriminator is not RR (!= '0110'B): ",
si.header.rr_protocol_discriminator);
return 1;
}
return 0;
}
} with { encode "RAW"; variant "FIELDORDER(msb)" }

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