ussd: Make sure that we at least have 8 bytes when decoding the string

The actual gsm_7bit_decode can still cause a buffer overrun
but at least we are safe until this point.

diff --git a/src/gsm0480.c b/src/gsm0480.c
index 73be8ac..4b1471f 100644 (file)
--- a/src/gsm0480.c
+++ b/src/gsm0480.c
@@ -386,6 +386,12 @@ static int parse_process_uss_req(const uint8_t *uss_req_data, uint16_t length,
        int num_chars;
        uint8_t dcs;
 
+
+       /* we need at least that much */
+       if (length < 8)
+               return 0;
+
+
        if (uss_req_data[0] == GSM_0480_SEQUENCE_TAG) {
                if (uss_req_data[2] == ASN1_OCTET_STRING_TAG) {
                        dcs = uss_req_data[4];