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Added additional checks that HDLC frames arriving at the T.38 gateway engine 

begin with the correct 2 bytes.
This commit is contained in:
Steve Underwood 2014-07-08 20:48:15 +08:00
parent ebe4238a7e
commit 40214821cb
1 changed files with 15 additions and 0 deletions
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15
libs/spandsp/src/t38_gateway.c
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@ -1934,6 +1934,21 @@ static void t38_hdlc_rx_put_bit(hdlc_rx_state_t *t, int new_bit)
s = (t38_gateway_state_t *) t->frame_user_data;
u = &s->core.to_t38;
t->buffer[t->len] = (uint8_t) t->byte_in_progress;
if (t->len == 1)
{
/* All valid HDLC frames in FAX communication begin 0xFF 0x03 or 0xFF 0x13.
Anything else is bogus, */
if (t->buffer[0] != 0xFF || (t->buffer[1] & 0xEF) != 0x03)
{
/* Abandon the frame, and wait for the next flag octet. */
span_log(&s->logging, SPAN_LOG_FLOW, "Bad HDLC frame header. Abandoning frame.\n");
t->flags_seen = t->framing_ok_threshold - 1;
t->len = 0;
return;
}
/*endif*/
}
/*endif*/
/* Calculate the CRC progressively, before we start altering the frame */
u->crc = crc_itu16_calc(&t->buffer[t->len], 1, u->crc);
/* Make the transmission lag by two octets, so we do not send the CRC, and