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author | Neels Hofmeyr <neels@hofmeyr.de> | 2020-05-26 02:45:23 +0200 |
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committer | Neels Hofmeyr <neels@hofmeyr.de> | 2020-06-16 15:17:48 +0200 |
commit | 83025bf1a6a97d2b3931ea3f0bebf63afd8ccd11 (patch) | |
tree | 94c03ffb53088ff9f388c98a44d9c832fa4138eb /src/gsm/libosmogsm.map | |
parent | a13fb750305cad14df5ecc98ee3006965b418cbc (diff) |
add osmo_mobile_identity API
Implement better API around 3GPP TS 24.008 Mobile Identity coding.
struct osmo_mobile_identity is a decoded representation of the raw Mobile
Identity, with a string representation as well as dedicated raw uint32_t TMSI.
The aim is to remove all uncertainty about decoded buffer sizes / data types.
I have patches ready for current osmo CNI programs, replacing the Mobile
Identity coding with this new API. Deprecate the old MI API.
osmo-bsc: I71c3b4c65dbfdfa51409e09d4868aea83225338a
osmo-msc: Ic3f969e739654c1e8c387aedeeba5cce07fe2307
osmo-sgsn: I4cacb10bac419633ca0c14f244f9903f7f517b49
Note that some GPRS and SGs related coding is done here in libosmocore and
hence currently remains using the old implementation (see previous version of
this patch: Ic3f969e739654c1e8c387aedeeba5cce07fe2307).
New API functions provide properly size-checking implementations of:
- decoding a raw MI from a bunch of MI octets;
- locating and decoding MI from a full 3GPP TS 24.008 Complete Layer 3 msgb;
- encoding to a buffer;
- encoding to the end of a msgb.
Other than the old gsm48_generate_mid(), omit a TLV tag and length from
encoding. Many callers manually stripped the tag and value after calling
gsm48_generate_mid(). The aim is to leave writing a TL to the caller entirely,
especially since some callers need to use a TvL, i.e. support a variable-size
length of 8 or 16 bit.
New validity checks so far not implemented anywhere else:
- stricter validation of number of digits of IMSI, IMEI, IMEI-SV MI.
- stricter on filler nibbles to be 0xf.
As a result, applications using osmo_mobile_identity will be stricter in
rejecting coding mistakes (some of which we currently have in our test suites,
and which we'll need to fix).
Rationale:
While implementing osmo-bsc's MSC pooling feature in osmo-bsc, this API will be
used to reduce the number of times a Mobile Identity is extracted from a raw
RSL message.
Extracting the Mobile Identity from messages has numerous duplicate
implementations across our code with various levels of specialization.
https://xkcd.com/927/
To name a few:
- libosmocore: gsm48_mi_to_string(), osmo_mi_name_buf()
- osmo-bsc: extract_sub()
- osmo-msc: mm_rx_loc_upd_req(), cm_serv_reuse_conn(), gsm48_rx_mm_serv_req(),
vlr_proc_acc_req()
We have existing functions to produce a human readable string from a Mobile
Identity, more or less awkward:
- gsm48_mi_to_string() decodes a TMSI as a decimal number. These days we use
hexadecimal TMSI everywhere.
- osmo_mi_name_buf() decodes the BCD digits from a raw MI every time, so we'd
need to pass around the raw message bytes. Also, osmo_mi_name_buf() has the
wrong signature, it should return a length like snprintf().
- osmo-bsc's extract_sub() first uses gsm48_mi_to_string() which encodes the
raw uint32_t TMSI to a string, and then calls strtoul() via
tmsi_from_string() to code those back to a raw uint32_t.
Each of the above implementations employ their own size overflow checks, each
invoke osmo_bcd2str() and implement their own TMSI osmo_load32be() handling.
Too much code dup, let's hope that each and every one is correct.
In osmo-bsc, I am now implementing MSC pooling, and need to extract NRI bits
from a TMSI Mobile Identity. Since none of the above functions are general
enough to be re-used, I found myself again copy-pasting Mobile Identity code:
locating the MI in a 24.008 message with proper size checks, decoding MI
octets.
This time I would like it to become a generally re-usable API.
This patch was first merged as Ic3f969e739654c1e8c387aedeeba5cce07fe2307 and
caused test fallout, because it re-implemented old API with the new stricter
decoding. In this patch version, old API remains 1:1 unchanged to avoid such
fallout. Applications will soon switch to the new osmo_mobile_identity API and
become stricter on MI coding when that happens, not implicitly by a new
libosmocore version.
Change-Id: If4f7be606e54cfa1c59084cf169785b1cbda5cf5
Diffstat (limited to 'src/gsm/libosmogsm.map')
-rw-r--r-- | src/gsm/libosmogsm.map | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map index ac9aeb21..742cec38 100644 --- a/src/gsm/libosmogsm.map +++ b/src/gsm/libosmogsm.map @@ -363,6 +363,14 @@ gsm48_generate_mid; gsm48_generate_mid_from_imsi; gsm48_generate_mid_from_tmsi; gsm48_mi_to_string; +osmo_mobile_identity_to_str_buf; +osmo_mobile_identity_to_str_c; +osmo_mobile_identity_cmp; +osmo_mobile_identity_decode; +osmo_mobile_identity_decode_from_l3; +osmo_mobile_identity_encoded_len; +osmo_mobile_identity_encode_buf; +osmo_mobile_identity_encode_msgb; gsm48_mm_att_tlvdef; gsm48_number_of_paging_subchannels; gsm48_parse_ra; |