pespin has submitted this change. (
https://gerrit.osmocom.org/c/libosmo-gprs/+/34025 )
Change subject: llc: Silently discard UI Dummy commands
......................................................................
llc: Silently discard UI Dummy commands
Change-Id: I807e140b96de7140d8f6922417f3eaf0eadeed84
---
M src/llc/llc.c
1 file changed, 23 insertions(+), 0 deletions(-)
Approvals:
Jenkins Builder: Verified
pespin: Looks good to me, approved
diff --git a/src/llc/llc.c b/src/llc/llc.c
index be1ebec..dc1a7b6 100644
--- a/src/llc/llc.c
+++ b/src/llc/llc.c
@@ -53,6 +53,11 @@
{ 0, NULL }
};
+/* 3GPP TS 44.064 6.4.2.2 */
+static const uint8_t gprs_llc_ui_dummy_command[] = {
+ 0x43, 0xc0, 0x01, 0x2b, 0x2b, 0x2b
+};
+
/* Section 8.9.9 LLC layer parameter default values */
static const struct gprs_llc_params llc_default_params[NUM_SAPIS] = {
[1] = {
@@ -844,6 +849,15 @@
if (~pdu_dec->flags & OSMO_GPRS_LLC_PDU_F_PROT_MODE)
crc_length = OSMO_MIN(crc_length, UI_HDR_LEN + N202);
if (pdu_dec->fcs != gprs_llc_fcs(ll_pdu, crc_length)) {
+ if (ll_pdu_len >= sizeof(gprs_llc_ui_dummy_command) ||
+ memcmp(ll_pdu, gprs_llc_ui_dummy_command,
sizeof(gprs_llc_ui_dummy_command)) == 0) {
+ /* 6.4.2.2: "If the LLC entity at the MS receives a UI
Dummy command, it shall discard
+ * it without any further actions" [...]
+ * "The format specified for the UI Dummy command
ensures that a receiving LLC entity
+ * will always discard it, since the FCS field check
always fails" "*/
+ LOGLLE(lle, LOGL_DEBUG, "Dropping UI Dummy command
len=%zu\n", ll_pdu_len);
+ return 0;
+ }
LOGLLE(lle, LOGL_NOTICE, "Dropping frame with invalid FCS
0x%06x vs exp 0x%06x: %s\n",
pdu_dec->fcs, gprs_llc_fcs(ll_pdu, crc_length),
osmo_hexdump(ll_pdu, ll_pdu_len));
--
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Gerrit-Project: libosmo-gprs
Gerrit-Branch: master
Gerrit-Change-Id: I807e140b96de7140d8f6922417f3eaf0eadeed84
Gerrit-Change-Number: 34025
Gerrit-PatchSet: 2
Gerrit-Owner: pespin <[email protected]>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: fixeria <[email protected]>
Gerrit-Reviewer: osmith <[email protected]>
Gerrit-Reviewer: pespin <[email protected]>
Gerrit-MessageType: merged
