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/*
p0f-sendsyn - SYN sender
------------------------
This trivial utility sends 8 SYN packets to open ports on destination hosts,
and lets you capture SYN+ACK signatures. The problem with SYN+ACK
fingerprinting is that on some systems, the response varies depending on the
use of window scaling, timestamps, or selective ACK in the initial SYN - so
this utility is necessary to exercise all the code paths.
Copyright (C) 2012 by Michal Zalewski <lcamtuf@coredump.cx>
Distributed under the terms and conditions of GNU LGPL.
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netdb.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>
#include "../types.h"
#include "../config.h"
#include "../alloc-inl.h"
#include "../debug.h"
#include "../tcp.h"
/* Do a basic IPv4 TCP checksum. */
static void tcp_cksum(u8* src, u8* dst, struct tcp_hdr* t, u8 opt_len) {
u32 sum, i;
u8* p;
if (opt_len % 4) FATAL("Packet size not aligned to 4.");
t->cksum = 0;
sum = PROTO_TCP + sizeof(struct tcp_hdr) + opt_len;
p = (u8*)t;
for (i = 0; i < sizeof(struct tcp_hdr) + opt_len; i += 2, p += 2)
sum += (*p << 8) + p[1];
p = src;
for (i = 0; i < 4; i += 2, p += 2) sum += (*p << 8) + p[1];
p = dst;
for (i = 0; i < 4; i += 2, p += 2) sum += (*p << 8) + p[1];
t->cksum = htons(~(sum + (sum >> 16)));
}
/* Parse IPv4 address into a buffer. */
static void parse_addr(char* str, u8* ret) {
u32 a1, a2, a3, a4;
if (sscanf(str, "%u.%u.%u.%u", &a1, &a2, &a3, &a4) != 4)
FATAL("Malformed IPv4 address.");
if (a1 > 255 || a2 > 255 || a3 > 255 || a4 > 255)
FATAL("Malformed IPv4 address.");
ret[0] = a1;
ret[1] = a2;
ret[2] = a3;
ret[3] = a4;
}
#define W(_x) (_x) >> 8, (_x) & 0xff
#define D(_x) (_x) >> 24, ((_x) >> 16) & 0xff, ((_x) >> 8) & 0xff, (_x) & 0xff
#define EOL TCPOPT_EOL
#define NOP TCPOPT_NOP
#define MSS(_x) TCPOPT_MAXSEG, 4, W(_x)
#define WS(_x) TCPOPT_WSCALE, 3, (_x)
#define SOK TCPOPT_SACKOK, 2
#define TS(_x,_y) TCPOPT_TSTAMP, 10, D(_x), D(_y)
/* There are virtually no OSes that do not send MSS. Support for RFC 1323
and 2018 is not given, so we have to test various combinations here. */
static u8 opt_combos[8][24] = {
{ MSS(SPECIAL_MSS), NOP, EOL }, /* 6 */
{ MSS(SPECIAL_MSS), SOK, NOP, EOL }, /* 8 */
{ MSS(SPECIAL_MSS), WS(5), NOP, EOL }, /* 9 */
{ MSS(SPECIAL_MSS), WS(5), SOK, NOP, EOL }, /* 12 */
{ MSS(SPECIAL_MSS), TS(1337, 0), NOP, EOL }, /* 17 */
{ MSS(SPECIAL_MSS), SOK, TS(1337, 0), NOP, EOL }, /* 19 */
{ MSS(SPECIAL_MSS), WS(5), TS(1337, 0), NOP, EOL }, /* 20 */
{ MSS(SPECIAL_MSS), WS(5), SOK, TS(1337, 0), NOP, EOL } /* 22 */
};
int main(int argc, char** argv) {
static struct sockaddr_in sin;
char one = 1;
s32 sock;
u32 i;
static u8 work_buf[MIN_TCP4 + 24];
struct ipv4_hdr* ip4 = (struct ipv4_hdr*)work_buf;
struct tcp_hdr* tcp = (struct tcp_hdr*)(ip4 + 1);
u8 *opts = work_buf + MIN_TCP4;
if (argc != 4) {
ERRORF("Usage: p0f-sendsyn your_ip dst_ip port\n");
exit(1);
}
parse_addr(argv[1], ip4->src);
parse_addr(argv[2], ip4->dst);
sock = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
if (sock < 0) PFATAL("Can't open raw socket (you need to be root).");
if (setsockopt(sock, IPPROTO_IP, IP_HDRINCL, (char*)&one, sizeof(char)))
PFATAL("setsockopt() on raw socket failed.");
sin.sin_family = PF_INET;
memcpy(&sin.sin_addr.s_addr, ip4->dst, 4);
ip4->ver_hlen = 0x45;
ip4->tot_len = htons(MIN_TCP4 + 24);
ip4->ttl = 192;
ip4->proto = PROTO_TCP;
tcp->dport = htons(atoi(argv[3]));
tcp->seq = htonl(0x12345678);
tcp->doff_rsvd = ((sizeof(struct tcp_hdr) + 24) / 4) << 4;
tcp->flags = TCP_SYN;
tcp->win = htons(SPECIAL_WIN);
for (i = 0; i < 8; i++) {
tcp->sport = htons(65535 - i);
memcpy(opts, opt_combos[i], 24);
tcp_cksum(ip4->src, ip4->dst, tcp, 24);
if (sendto(sock, work_buf, sizeof(work_buf), 0, (struct sockaddr*)&sin,
sizeof(struct sockaddr_in)) < 0) PFATAL("sendto() fails.");
usleep(100000);
}
SAYF("Eight packets sent! Check p0f output to examine responses, if any.\n");
return 0;
}
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