constrain gsm48_generate_mid() output array bounds
The longest BCd-digit type identity is the IMEISV with 16, so there's
no point in trying to parse up to 255 decimal digits, which will do
nothing but to overflow the caller-provided output buffer.
Let's also clearly define the required minimum size of the output
buffer and add a reltead #define for it.
Change-Id: Ic8488bc7f77dc9182e372741b88f0f06100dddc9
diff --git a/src/gsm/gsm48.c b/src/gsm/gsm48.c
index 795e98b..86d40d4 100644
--- a/src/gsm/gsm48.c
+++ b/src/gsm/gsm48.c
@@ -637,20 +637,23 @@
return 7;
}
-/*! Generate TS 24.008 §10.5.1.4 Mobile ID
- * \param[out] buf Caller-provided output buffer
+/*! Generate TS 24.008 §10.5.1.4 Mobile ID of BCD type from ASCII string
+ * \param[out] buf Caller-provided output buffer of at least GSM48_MID_MAX_SIZE bytes
* \param[in] id Identity to be encoded
- * \param[in] mi_type Type of identity (e.g. GSM_MI_TYPE_TMSI)
+ * \param[in] mi_type Type of identity (e.g. GSM_MI_TYPE_IMSI, IMEI, IMEISV)
* \returns number of bytes used in \a buf */
uint8_t gsm48_generate_mid(uint8_t *buf, const char *id, uint8_t mi_type)
{
- uint8_t length = strnlen(id, 255), i, off = 0, odd = (length & 1) == 1;
+ uint8_t length = strnlen(id, 16), i, off = 0, odd = (length & 1) == 1;
+ /* maximum length == 16 (IMEISV) */
buf[0] = GSM48_IE_MOBILE_ID;
buf[2] = osmo_char2bcd(id[0]) << 4 | (mi_type & GSM_MI_TYPE_MASK) | (odd << 3);
/* if the length is even we will fill half of the last octet */
buf[1] = (length + (odd ? 1 : 2)) >> 1;
+ /* buf[1] maximum = 18/2 = 9 */
+ OSMO_ASSERT(buf[1] <= 9);
for (i = 1; i < buf[1]; ++i) {
uint8_t upper, lower = osmo_char2bcd(id[++off]);
@@ -662,6 +665,7 @@
buf[2 + i] = (upper << 4) | lower;
}
+ /* maximum return value: 2 + 9 = 11 */
return 2 + buf[1];
}