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MqttDecode_FixedHeader: bound VBI by rx_buf_len - 1 #544

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MqttDecode_FixedHeader: bound VBI by rx_buf_len - 1 #544

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12 changes: 11 additions & 1 deletion src/mqtt_packet.c
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Original file line number Diff line number Diff line change
Expand Up @@ -369,8 +369,18 @@ static int MqttDecode_FixedHeader(byte *rx_buf, int rx_buf_len, int *remain_len,
int header_len;
MqttPacket* header = (MqttPacket*)rx_buf;

/* header->len starts one byte into rx_buf (after type_flags), so the
* Remaining-Length VBI has at most rx_buf_len - 1 bytes available.
* Without this guard MqttDecode_Vbi was passed rx_buf_len and could
* read one byte past the caller-supplied buffer when the only length
* byte present has the continuation bit set. */
if (rx_buf_len < MQTT_PACKET_HEADER_MIN_SIZE) {
return MQTT_TRACE_ERROR(MQTT_CODE_ERROR_OUT_OF_BUFFER);
}

/* Decode the length remaining */
header_len = MqttDecode_Vbi(header->len, (word32*)remain_len, rx_buf_len);
header_len = MqttDecode_Vbi(header->len, (word32*)remain_len,
(word32)(rx_buf_len - sizeof(header->type_flags)));
if (header_len < 0) {
return header_len;
}
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