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gsm0480: fix USSD OCTET STRING length confusion 

According to the GSM 04.80 (version 5.0.0) specification Annex A
"Expanded ASN.1 Module "SS-Protocol", the maximum size of a USSD
OCTET STRING is 160 bytes.

Thus according to ETSI TS 123 038 (version 10.0.0) specification
6.1.2.3 "USSD packing of 7 bit characters", in 160 octets, it's
possible to pack (160 * 8) / 7 = 182.8, that is 182 characters.
The remaining 6 bits are set to zero.

This change defines both mentioned values:

  - GSM0480_USSD_OCTET_STRING_LEN  160
  - GSM0480_USSD_7BIT_STRING_LEN   182

keeping the old MAX_LEN_USSD_STRING 'as is' due to compatibility
reasons. Now the new value is used for ss_request structure, while
old one is still used for deprecated ussd_request structure.

Change-Id: I6dead74f9ecea079752ff2400cdaf7c30187784e
This commit is contained in:
Vadim Yanitskiy 2017-08-09 17:38:39 +06:00 committed by Harald Welte
parent 04ee9c04f4
commit fa6c2b9b53
2 changed files with 24 additions and 4 deletions
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24
include/osmocom/gsm/gsm0480.h
View File

@ -7,7 +7,27 @@
#include <osmocom/gsm/protocol/gsm_04_08.h>
#include <osmocom/gsm/protocol/gsm_04_80.h>
#define MAX_LEN_USSD_STRING 31
/**
* According to the GSM 04.80 (version 5.0.0) specification Annex A
* "Expanded ASN.1 Module "SS-Protocol", the maximum size of a USSD
* OCTET STRING field is 160 bytes.
*/
#define GSM0480_USSD_OCTET_STRING_LEN 160
/**
* Thus according to ETSI TS 123 038 (version 10.0.0) specification
* 6.1.2.3 "USSD packing of 7 bit characters", in 160 octets, it's
* possible to pack (160 * 8) / 7 = 182.8, that is 182 characters.
* The remaining 6 bits are set to zero.
*/
#define GSM0480_USSD_7BIT_STRING_LEN 182
/**
* DEPRECATED: this definition doesn't follow any specification,
* so we only keep it for compatibility reasons. It's strongly
* recommended to use correct definitions above.
*/
#define MAX_LEN_USSD_STRING 31
/* deprecated */
struct ussd_request {
@ -23,7 +43,7 @@ int gsm0480_decode_ussd_request(const struct gsm48_hdr *hdr, uint16_t len,
struct ss_request {
uint8_t opcode;
uint8_t ss_code;
uint8_t ussd_text[MAX_LEN_USSD_STRING + 1];
uint8_t ussd_text[GSM0480_USSD_OCTET_STRING_LEN];
uint8_t transaction_id;
uint8_t invoke_id;
};

4
src/gsm/gsm0480.c
View File

@ -456,8 +456,8 @@ static int parse_process_uss_req(const uint8_t *uss_req_data, uint16_t length,
(uss_req_data[5] == ASN1_OCTET_STRING_TAG)) {
num_chars = (uss_req_data[6] * 8) / 7;
/* Prevent a mobile-originated buffer-overrun! */
if (num_chars > MAX_LEN_USSD_STRING)
num_chars = MAX_LEN_USSD_STRING;
if (num_chars > GSM0480_USSD_7BIT_STRING_LEN)
num_chars = GSM0480_USSD_7BIT_STRING_LEN;
gsm_7bit_decode_n_ussd((char *)req->ussd_text,
sizeof(req->ussd_text),
&(uss_req_data[7]), num_chars);