laforge submitted this change.
sgs_iface: clean up code in function decode_mme_name
The function decode_mme_name is a bit hard to read and also has
some minor problems we can optimize.
- Do not call TLVP_LEN each time we need the length of the
TLV IE. Call it once and keep the value in a variable.
- mme_name_enc holds the value part of the TLV IE, we can
use this variable instead of calling TLVP_VAL all all
the time.
- When we have copied the value part of the TLV IE using
memset, let's ensure that the string is terminated.
- Add/fix spec references and improve comments so that it
is more clear how the decoding actually works.
Related: OS#7058
Change-Id: I9aec8300f15264b68ac8e7805e93e621b12cafb2
---
M src/libmsc/sgs_iface.c
1 file changed, 17 insertions(+), 7 deletions(-)
diff --git a/src/libmsc/sgs_iface.c b/src/libmsc/sgs_iface.c
index 4425a93..db9246c 100644
--- a/src/libmsc/sgs_iface.c
+++ b/src/libmsc/sgs_iface.c
@@ -162,27 +162,37 @@
/* Decode and verify MME name */
static int decode_mme_name(char *mme_name, size_t mme_name_len, const struct tlv_parsed *tp)
{
+ /* The MME name is a fixed length FQDN (e.g. mmec00.mmegi0000.mme.epc.mncMNC.mccMCC.3gppnetwork.org,
+ * see also 3GPP TS 23.003, section 19.4.2.1 and 3GPP TS 29.118, section 9.4.13 */
const uint8_t *mme_name_enc = TLVP_VAL_MINLEN(tp, SGSAP_IE_MME_NAME, SGS_MME_NAME_LEN);
+ size_t mme_name_enc_len = TLVP_LEN(tp, SGSAP_IE_MME_NAME);
struct osmo_gummei gummei;
if (!mme_name_enc)
return -EINVAL;
- /* do not accept over-long SGSAP_IE_MME_NAME IEs which would exceed the length
+ /* Do not accept over-long SGSAP_IE_MME_NAME IEs which would exceed the length
* of the output buffer. */
- if (TLVP_LEN(tp, SGSAP_IE_MME_NAME) >= mme_name_len)
+ if (mme_name_enc_len >= mme_name_len)
return -EINVAL;
- /* some implementations use FDQN format violating TS 29.118 9.3.14 */
+ /* We attempt to parse the MME name into a GUMMEI to make sure it has the form
+ * specified by 3GPP TS 29.118, section 9.4.13. In that case, we may copy the
+ * MME name to the output buffer and exit. */
if (!osmo_parse_mme_domain(&gummei, (const char *) mme_name_enc)) {
- memcpy(mme_name, mme_name_enc, TLVP_LEN(tp, SGSAP_IE_MME_NAME));
+ memcpy(mme_name, mme_name_enc, mme_name_enc_len);
+ mme_name[mme_name_enc_len] = '\0';
return 0;
}
- /* decode the MME name from DNS labels to string */
- osmo_apn_to_str(mme_name, TLVP_VAL(tp, SGSAP_IE_MME_NAME), TLVP_LEN(tp, SGSAP_IE_MME_NAME));
+ /* In some cases the MME name may be supplied in the domain name format specified
+ * by RFC-1035, section 3.1, which is a spec violation we want to tolerate. We
+ * may convert the domain name from the LV representtaion into the string string
+ * representation required by 3GPP TS 29.118, section 9.4.13 */
+ osmo_apn_to_str(mme_name, mme_name_enc, mme_name_enc_len);
- /* try to parse the MME name into a GUMMEI as a test for the format */
+ /* To make sure the format conversion has produced a valid MME name, we attempt to
+ * parse the output buffer again. */
if (osmo_parse_mme_domain(&gummei, mme_name) < 0)
return -EINVAL;
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