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SN_Decode_Header: reject extended-length frame with total_len <= header size #541

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SN_Decode_Header: reject extended-length frame with total_len <= header size #541

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10 changes: 10 additions & 0 deletions src/mqtt_sn_packet.c
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,7 @@ int SN_Decode_Header(byte *rx_buf, int rx_buf_len,
int rc;
SN_MsgType packet_type;
word16 total_len;
byte *rx_buf_orig = rx_buf;

if (rx_buf == NULL || rx_buf_len < MQTT_PACKET_HEADER_MIN_SIZE) {
return MQTT_TRACE_ERROR(MQTT_CODE_ERROR_BAD_ARG);
Expand All @@ -120,6 +121,15 @@ int SN_Decode_Header(byte *rx_buf, int rx_buf_len,
if (total_len > rx_buf_len) {
return MQTT_TRACE_ERROR(MQTT_CODE_ERROR_OUT_OF_BUFFER);
}
/* Reject a declared total_len that does not cover the bytes already
* consumed plus the upcoming message-type read. Without this, a peer
* crafted SN_PACKET_LEN_IND packet whose 2-byte length field decodes
* to a value equal to rx_buf_len (e.g., rx_buf_len == 3 with
* total_len == 3) slips past the > rx_buf_len check above and the
* *rx_buf++ below reads one byte past the caller-supplied buffer. */
if (total_len < (word16)(rx_buf - rx_buf_orig) + 1) {
return MQTT_TRACE_ERROR(MQTT_CODE_ERROR_MALFORMED_DATA);
}

/* Message Type */
packet_type = (SN_MsgType)*rx_buf++;
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