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abis_rsl: Add rach expiry timeout 

This allows controlling the RACH DoS attack protection without
increasing call drops rate.

Change-Id: Iff7266672dd8bc9ce2b34b0478d98fb70691f425
This commit is contained in:
Matan Perelman 2023-12-31 11:33:54 +02:00
parent f033c82f54
commit 40ecc7d538
4 changed files with 21 additions and 3 deletions
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3
include/osmocom/bsc/bts.h
View File

@ -663,6 +663,9 @@ struct gsm_bts {
/* We will ignore CHAN RQD with access delay greater than rach_max_delay */
uint8_t rach_max_delay;
/* We will ignore CHAN RQD sitting in the queue for period greater than rach_expiry_timeout */
uint8_t rach_expiry_timeout;
/* Is Fast return to LTE allowed during Chan Release in this BTS? */
bool srvcc_fast_return_allowed;

5
src/osmo-bsc/abis_rsl.c
View File

@ -1975,7 +1975,6 @@ static int rsl_rx_pchan_rqd(struct chan_rqd *rqd)
* requests from the queue to prevent the queue from growing indefinetly. */
static void reduce_rach_dos(struct gsm_bts *bts)
{
int rlt = gsm_bts_get_radio_link_timeout(bts);
time_t timestamp_current = time(NULL);
struct chan_rqd *rqd;
struct chan_rqd *rqd_tmp;
@ -1983,9 +1982,9 @@ static void reduce_rach_dos(struct gsm_bts *bts)
/* Drop all expired channel requests in the list */
llist_for_each_entry_safe(rqd, rqd_tmp, &bts->chan_rqd_queue, entry) {
/* If the channel request is older than the radio link timeout we drop it. This also means that the
/* If the channel request is older than the rach expiry timeout we drop it. This also means that the
* queue is under its overflow limit again. */
if (timestamp_current - rqd->timestamp > rlt) {
if (timestamp_current - rqd->timestamp > bts->rach_expiry_timeout) {
LOG_BTS(bts, DRSL, LOGL_INFO, "CHAN RQD: tossing expired channel request"
"(ra=0x%02x, neci=0x%02x, chreq_reason=0x%02x)\n",
rqd->ref.ra, bts->network->neci, rqd->reason);

1
src/osmo-bsc/bts.c
View File

@ -470,6 +470,7 @@ struct gsm_bts *gsm_bts_alloc(struct gsm_network *net, struct gsm_bts_sm *bts_sm
bts->interf_meas_params_cfg = interf_meas_params_def;
bts->rach_max_delay = 63;
bts->rach_expiry_timeout = 32;
/* SRVCC is enabled by default */
bts->srvcc_fast_return_allowed = true;

15
src/osmo-bsc/bts_vty.c
View File

@ -772,6 +772,19 @@ DEFUN_ATTR(cfg_bts_rach_max_delay,
return CMD_SUCCESS;
}
DEFUN_ATTR(cfg_bts_rach_expiry_timeout,
cfg_bts_rach_expiry_timeout_cmd,
"rach expiry-timeout <4-64>",
RACH_STR
"Set the timeout for channel requests expiry\n"
"Maximum timeout before dropping channel requests\n",
CMD_ATTR_IMMEDIATE)
{
struct gsm_bts *bts = vty->index;
bts->rach_expiry_timeout = atoi(argv[0]);
return CMD_SUCCESS;
}
#define REP_ACCH_STR "FACCH/SACCH repetition\n"
DEFUN_USRATTR(cfg_bts_rep_dl_facch,
@ -4516,6 +4529,7 @@ static void config_write_bts_single(struct vty *vty, struct gsm_bts *bts)
rach_max_trans_raw2val(bts->si_common.rach_control.max_trans),
VTY_NEWLINE);
vty_out(vty, " rach max-delay %u%s", bts->rach_max_delay, VTY_NEWLINE);
vty_out(vty, " rach expiry-timeout %u%s", bts->rach_expiry_timeout, VTY_NEWLINE);
vty_out(vty, " channel-description attach %u%s",
bts->si_common.chan_desc.att, VTY_NEWLINE);
@ -4862,6 +4876,7 @@ int bts_vty_init(void)
install_element(BTS_NODE, &cfg_bts_rach_tx_integer_cmd);
install_element(BTS_NODE, &cfg_bts_rach_max_trans_cmd);
install_element(BTS_NODE, &cfg_bts_rach_max_delay_cmd);
install_element(BTS_NODE, &cfg_bts_rach_expiry_timeout_cmd);
install_element(BTS_NODE, &cfg_bts_chan_desc_att_cmd);
install_element(BTS_NODE, &cfg_bts_chan_dscr_att_cmd);
install_element(BTS_NODE, &cfg_bts_chan_desc_bs_pa_mfrms_cmd);