add gsm48_decode_bcd_number2() from osmo-msc

gsm48_decode_bcd_number() is unable to provide proper bounds validation of
input and output data, hence osmo-msc's vlr.c introduced a static
decode_bcd_number_safe() a long time ago. Move to libosmocore.

I need to use the same function to decode an MSISDN during inter-MSC Handover,
instead of making it public in osmo-msc, rather deprecate the unsafe function
and provide a safer version for all callers. Mark the old one deprecated.

Change-Id: Idb6ae6e2f3bea11ad420dae14d021ac36d99e921

include/osmocom/gsm/gsm48_ie.h

@@ -13,7 +13,11 @@
 
 /* decode a 'called/calling/connect party BCD number' as in 10.5.4.7 */
 int gsm48_decode_bcd_number(char *output, int output_len,
-			    const uint8_t *bcd_lv, int h_len);
+			    const uint8_t *bcd_lv, int h_len)
+	OSMO_DEPRECATED("Use gsm48_decode_bcd_number2() for improved bounds checking");
+int gsm48_decode_bcd_number2(char *output, size_t output_len,
+			     const uint8_t *bcd_lv, size_t input_len,
+			     size_t h_len);
 
 /* convert a ASCII phone number to 'called/calling/connect party BCD number' */
 int gsm48_encode_bcd_number(uint8_t *bcd_lv, uint8_t max_len,

src/gsm/gsm48_ie.c

@@ -46,7 +46,7 @@ static const char bcd_num_digits[] = {
 	'8', '9', '*', '#', 'a', 'b', 'c', '\0'
 };
 
-/*! decode a 'called/calling/connect party BCD number' as in 10.5.4.7
+/*! Like gsm48_decode_bcd_number2() but with less airtight bounds checking.
  *  \param[out] Caller-provided output buffer
  *  \param[in] bcd_lv Length-Value portion of to-be-decoded IE
  *  \param[in] h_len Length of an optional heder between L and V portion
@@ -76,6 +76,32 @@ int gsm48_decode_bcd_number(char *output, int output_len,
 	return 0;
 }
 
+/*! Decode a 'called/calling/connect party BCD number' as in 10.5.4.7.
+ * \param[out] output  Caller-provided output buffer.
+ * \param[in] output_len  sizeof(output).
+ * \param[in] bcd_lv  Length-Value part of to-be-decoded IE.
+ * \param[in] input_len  Size of the buffer to read the IE from.
+ * \param[in] h_len  Length of an optional header between L and V parts.
+ * \return 0 in case of success, negative on error. Errors checked: no or too little input data, no or too little
+ * output buffer size, IE length exceeds input data size, decoded number exceeds size of the output buffer. The output
+ * is guaranteed to be nul terminated iff output_len > 0.
+ */
+int gsm48_decode_bcd_number2(char *output, size_t output_len,
+			     const uint8_t *bcd_lv, size_t input_len,
+			     size_t h_len)
+{
+	uint8_t len;
+	if (output_len < 1)
+		return -ENOSPC;
+	*output = '\0';
+	if (input_len < 1)
+		return -EIO;
+	len = bcd_lv[0];
+	if (input_len < len)
+		return -EIO;
+	return gsm48_decode_bcd_number(output, output_len, bcd_lv, h_len);
+}
+
 /*! convert a single ASCII character to call-control BCD */
 static int asc_to_bcd(const char asc)
 {

src/gsm/libosmogsm.map

@@ -312,6 +312,7 @@ gsm48_construct_ra;
 gsm48_encode_ra;
 gsm48_hdr_gmm_cipherable;
 gsm48_decode_bcd_number;
+gsm48_decode_bcd_number2;
 gsm48_decode_bearer_cap;
 gsm48_decode_called;
 gsm48_decode_callerid;