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module_tcp_synackscan.c
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module_tcp_synackscan.c
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/*
* ZMap Copyright 2013 Regents of the University of Michigan
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy
* of the License at http://www.apache.org/licenses/LICENSE-2.0
*/
// probe module for performing TCP SYN scans
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>
#include "../../lib/includes.h"
#include "../fieldset.h"
#include "probe_modules.h"
#include "packet.h"
#include "validate.h"
#include "module_tcp_synscan.h"
#define ZMAP_TCP_SYNACKSCAN_TCP_HEADER_LEN 24
#define ZMAP_TCP_SYNACKSCAN_PACKET_LEN 58
probe_module_t module_tcp_synackscan;
static uint32_t num_ports;
static int synackscan_global_initialize(struct state_conf *state)
{
num_ports = state->source_port_last - state->source_port_first + 1;
return EXIT_SUCCESS;
}
static int synackscan_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw,
UNUSED void *arg_ptr)
{
memset(buf, 0, MAX_PACKET_SIZE);
struct ether_header *eth_header = (struct ether_header *)buf;
make_eth_header(eth_header, src, gw);
struct ip *ip_header = (struct ip *)(ð_header[1]);
uint16_t len =
htons(sizeof(struct ip) + ZMAP_TCP_SYNACKSCAN_TCP_HEADER_LEN);
make_ip_header(ip_header, IPPROTO_TCP, len);
struct tcphdr *tcp_header = (struct tcphdr *)(&ip_header[1]);
make_tcp_header(tcp_header, TH_SYN | TH_ACK);
set_mss_option(tcp_header);
return EXIT_SUCCESS;
}
static int synackscan_make_packet(void *buf, UNUSED size_t *buf_len,
ipaddr_n_t src_ip, ipaddr_n_t dst_ip,
port_n_t dport, uint8_t ttl,
uint32_t *validation, int probe_num,
uint16_t ip_id, UNUSED void *arg)
{
struct ether_header *eth_header = (struct ether_header *)buf;
struct ip *ip_header = (struct ip *)(ð_header[1]);
struct tcphdr *tcp_header = (struct tcphdr *)(&ip_header[1]);
uint32_t tcp_seq = validation[0];
uint32_t tcp_ack =
validation[2]; // get_src_port() below uses validation 1 internally.
ip_header->ip_src.s_addr = src_ip;
ip_header->ip_dst.s_addr = dst_ip;
ip_header->ip_ttl = ttl;
ip_header->ip_id = ip_id;
tcp_header->th_sport =
htons(get_src_port(num_ports, probe_num, validation));
tcp_header->th_dport = dport;
tcp_header->th_seq = tcp_seq;
tcp_header->th_ack = tcp_ack;
tcp_header->th_sum = 0;
tcp_header->th_sum = tcp_checksum(ZMAP_TCP_SYNACKSCAN_TCP_HEADER_LEN,
ip_header->ip_src.s_addr,
ip_header->ip_dst.s_addr, tcp_header);
ip_header->ip_sum = 0;
ip_header->ip_sum = zmap_ip_checksum((unsigned short *)ip_header);
*buf_len = ZMAP_TCP_SYNACKSCAN_PACKET_LEN;
return EXIT_SUCCESS;
}
static int synackscan_validate_packet(const struct ip *ip_hdr, uint32_t len,
UNUSED uint32_t *src_ip,
uint32_t *validation,
const struct port_conf *ports)
{
if (ip_hdr->ip_p == IPPROTO_TCP) {
struct tcphdr *tcp = get_tcp_header(ip_hdr, len);
if (!tcp) {
return PACKET_INVALID;
}
uint16_t sport = ntohs(tcp->th_sport);
uint16_t dport = ntohs(tcp->th_dport);
// validate source port
if (!check_src_port(sport, ports)) {
return PACKET_INVALID;
}
// validate destination port
if (!check_dst_port(dport, num_ports, validation)) {
return PACKET_INVALID;
}
// check whether we'll ever send to this IP during the scan
if (!blocklist_is_allowed(*src_ip)) {
return PACKET_INVALID;
}
// We handle RST packets different than all other packets
if (tcp->th_flags & TH_RST) {
// A RST packet must have either:
// 1) resp(ack) == sent(seq) + 1, or
// 2) resp(seq) == sent(ack), or
// 3) resp(seq) == sent(ack) + 1
// All other cases are a failure.
if (htonl(tcp->th_ack) != htonl(validation[0]) + 1 &&
htonl(tcp->th_seq) != htonl(validation[2]) &&
htonl(tcp->th_seq) != (htonl(validation[2]) + 1)) {
return PACKET_INVALID;
}
} else {
// For non RST packets, we must have resp(ack) == sent(seq) + 1
if (htonl(tcp->th_ack) != htonl(validation[0]) + 1) {
return PACKET_INVALID;
}
}
} else if (ip_hdr->ip_p == IPPROTO_ICMP) {
struct ip *ip_inner;
size_t ip_inner_len;
if (icmp_helper_validate(ip_hdr, len, sizeof(struct udphdr),
&ip_inner,
&ip_inner_len) == PACKET_INVALID) {
return PACKET_INVALID;
}
struct tcphdr *tcp = get_tcp_header(ip_inner, ip_inner_len);
if (!tcp) {
return PACKET_INVALID;
}
// we can always check the destination port because this is the
// original packet and wouldn't have been altered by something
// responding on a different port
uint16_t sport = ntohs(tcp->th_sport);
uint16_t dport = ntohs(tcp->th_dport);
if (!check_src_port(dport, ports)) {
return PACKET_INVALID;
}
validate_gen(ip_hdr->ip_dst.s_addr, ip_inner->ip_dst.s_addr,
tcp->th_dport, (uint8_t *)validation);
if (!check_dst_port(sport, num_ports, validation)) {
return PACKET_INVALID;
}
} else {
return PACKET_INVALID;
}
return PACKET_VALID;
}
static void synackscan_process_packet(const u_char *packet, UNUSED uint32_t len,
fieldset_t *fs,
UNUSED uint32_t *validation,
UNUSED struct timespec ts)
{
struct ip *ip_hdr = get_ip_header(packet, len);
if (ip_hdr->ip_p == IPPROTO_TCP) {
struct tcphdr *tcp = get_tcp_header(ip_hdr, len);
fs_add_uint64(fs, "sport", (uint64_t)ntohs(tcp->th_sport));
fs_add_uint64(fs, "dport", (uint64_t)ntohs(tcp->th_dport));
fs_add_uint64(fs, "seqnum", (uint64_t)ntohl(tcp->th_seq));
fs_add_uint64(fs, "acknum", (uint64_t)ntohl(tcp->th_ack));
fs_add_uint64(fs, "window", (uint64_t)ntohs(tcp->th_win));
if (tcp->th_flags & TH_RST) { // RST packet
fs_add_constchar(fs, "classification", "rst");
} else { // SYNACK packet
fs_add_constchar(fs, "classification", "synack");
}
fs_add_bool(fs, "success", 1);
fs_add_null_icmp(fs);
} else if (ip_hdr->ip_p == IPPROTO_ICMP) {
// tcp
fs_add_null(fs, "sport");
fs_add_null(fs, "dport");
fs_add_null(fs, "seqnum");
fs_add_null(fs, "acknum");
fs_add_null(fs, "window");
// global
fs_add_constchar(fs, "classification", "icmp");
fs_add_bool(fs, "success", 0);
// icmp
fs_populate_icmp_from_iphdr(ip_hdr, len, fs);
}
}
static fielddef_t fields[] = {
{.name = "sport", .type = "int", .desc = "TCP source port"},
{.name = "dport", .type = "int", .desc = "TCP destination port"},
{.name = "seqnum", .type = "int", .desc = "TCP sequence number"},
{.name = "acknum", .type = "int", .desc = "TCP acknowledgement number"},
{.name = "window", .type = "int", .desc = "TCP window"},
CLASSIFICATION_SUCCESS_FIELDSET_FIELDS,
ICMP_FIELDSET_FIELDS,
};
probe_module_t module_tcp_synackscan = {
.name = "tcp_synackscan",
.max_packet_length = ZMAP_TCP_SYNACKSCAN_PACKET_LEN,
.pcap_filter = "(tcp && tcp[13] & 4 != 0 || tcp[13] == 18) || icmp",
.pcap_snaplen = 96,
.port_args = 1,
.global_initialize = &synackscan_global_initialize,
.prepare_packet = &synackscan_prepare_packet,
.make_packet = &synackscan_make_packet,
.print_packet = &synscan_print_packet,
.process_packet = &synackscan_process_packet,
.validate_packet = &synackscan_validate_packet,
.close = NULL,
.helptext = "Probe module that sends a TCP SYNACK packet to a specific "
"port. Possible classifications are: synack and rst. A "
"SYN-ACK packet is considered a failure and a reset packet "
"is considered a success.",
.output_type = OUTPUT_TYPE_STATIC,
.fields = fields,
.numfields = sizeof(fields) / sizeof(fields[0])};