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/*
* tftp.c
*
* Copyright (C) 2009-11 - ipoque GmbH
* Copyright (C) 2011-22 - ntop.org
*
* This file is part of nDPI, an open source deep packet inspection
* library based on the OpenDPI and PACE technology by ipoque GmbH
*
* nDPI is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* nDPI is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with nDPI. If not, see <http://www.gnu.org/licenses/>.
*
*/
#include "ndpi_protocol_ids.h"
#define NDPI_CURRENT_PROTO NDPI_PROTOCOL_TFTP
#include "ndpi_api.h"
/* see: https://datatracker.ietf.org/doc/html/rfc1350 */
static void ndpi_int_tftp_add_connection(struct ndpi_detection_module_struct
*ndpi_struct, struct ndpi_flow_struct *flow)
{
ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_TFTP, NDPI_PROTOCOL_UNKNOWN, NDPI_CONFIDENCE_DPI);
}
static void ndpi_search_tftp(struct ndpi_detection_module_struct *ndpi_struct,
struct ndpi_flow_struct *flow)
{
struct ndpi_packet_struct *packet = &ndpi_struct->packet;
u_int16_t block_num;
u_int16_t prev_num;
NDPI_LOG_DBG(ndpi_struct, "search TFTP\n");
if (packet->payload_packet_len < 4 /* min. header size */ ||
get_u_int8_t(packet->payload, 0) != 0x00)
{
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
/* parse TFTP opcode */
switch (get_u_int8_t(packet->payload, 1))
{
case 0x01:
/* Read request (RRQ) */
case 0x02:
/* Write request (WWQ) */
if (packet->payload[packet->payload_packet_len - 1] != 0x00 /* last pdu element is a nul terminated string */)
{
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
{
uint8_t mode_found = 0;
size_t mode_len;
int i;
size_t filename_len = 0;
const char *string;
size_t len = 0;
bool first = true;
/* Skip 2 byte opcode. */
for (i = 2; i < packet->payload_packet_len; i++)
{
/* Search through the payload until we find a NULL terminated string. */
if (packet->payload[i] != '\0')
{
len++;
continue;
}
string = (const char *)&packet->payload[i - len];
/* Filename should be immediately after opcode followed by the mode. */
if (first)
{
filename_len = len;
len = 0;
first = false;
continue;
}
char const * const possible_modes[] = { "netascii", "octet", "mail" };
uint8_t mode_idx;
/* Check the string in the payload against the possible TFTP modes. */
for(mode_idx = 0; mode_idx < NDPI_ARRAY_LENGTH(possible_modes); ++mode_idx)
{
mode_len = strlen(possible_modes[mode_idx]);
/* Both are now null terminated */
if (len != mode_len)
{
continue;
}
if (strncasecmp(string, possible_modes[mode_idx], mode_len) == 0)
{
mode_found = 1;
break;
}
}
/* Second string searched must've been the mode, break out before any following options. */
break;
}
/* Exclude the flow as TFPT if there was no filename and mode in the first two strings. */
if (filename_len == 0 || ndpi_is_printable_buffer(&packet->payload[2], filename_len) == 0 ||
mode_found == 0)
{
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
/* Dissect RRQ/WWQ filename. */
filename_len = ndpi_min(filename_len, sizeof(flow->protos.tftp.filename) - 1);
memcpy(flow->protos.tftp.filename, &packet->payload[2], filename_len);
flow->protos.tftp.filename[filename_len] = '\0';
/* We have seen enough and do not need any more TFTP packets. */
NDPI_LOG_INFO(ndpi_struct, "found tftp (RRQ/WWQ)\n");
ndpi_int_tftp_add_connection(ndpi_struct, flow);
}
return;
case 0x03:
/* Data (DATA) */
if (packet->payload_packet_len <= 4 /* min DATA header size */)
{
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
/* First 2 bytes were opcode so next 16 bits are the block number.
* This should increment every packet but give some leeway for midstream and packet loss. */
block_num = ntohs(get_u_int16_t(packet->payload, 2));
prev_num = flow->l4.udp.tftp_data_num;
flow->l4.udp.tftp_data_num = block_num;
if (!(block_num == prev_num + 1 || (prev_num != 0 && block_num == prev_num)))
{
return;
}
break;
case 0x04:
/* Acknowledgment (ACK) */
if (packet->payload_packet_len != 4 /* ACK has a fixed packet size */)
{
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
/* First 2 bytes were opcode so next 16 bits are the block number.
* This should increment every packet but give some leeway for midstream and packet loss. */
block_num = ntohs(get_u_int16_t(packet->payload, 2));
prev_num = flow->l4.udp.tftp_ack_num;
flow->l4.udp.tftp_ack_num = block_num;
if (!(block_num == prev_num + 1 || (block_num == prev_num)))
{
return;
}
break;
case 0x05:
/* Error (ERROR) */
if (packet->payload_packet_len < 5 ||
packet->payload[packet->payload_packet_len - 1] != 0x00 ||
packet->payload[2] != 0x00 || packet->payload[3] > 0x07)
{
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
break;
case 0x06:
/* Option Acknowledgment (OACK) */
/* No fixed lengths as it can include the options from the request. */
break;
default:
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
if (flow->l4.udp.tftp_stage < 3)
{
NDPI_LOG_DBG2(ndpi_struct, "maybe tftp. need next packet\n");
flow->l4.udp.tftp_stage++;
return;
}
NDPI_LOG_INFO(ndpi_struct, "found tftp\n");
ndpi_int_tftp_add_connection(ndpi_struct, flow);
}
void init_tftp_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id)
{
ndpi_set_bitmask_protocol_detection("TFTP", ndpi_struct, *id,
NDPI_PROTOCOL_TFTP,
ndpi_search_tftp,
NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_UDP_WITH_PAYLOAD,
SAVE_DETECTION_BITMASK_AS_UNKNOWN,
ADD_TO_DETECTION_BITMASK);
*id += 1;
}
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