tcpkill.c

/*
 * tcpkill.c
 *
 * Kill TCP connections already in progress.
 *
 * Copyright (c) 2000 Dug Song <dugsong@monkey.org>
 *
 * $Id: tcpkill.c,v 1.17 2001/03/17 08:10:43 dugsong Exp $
 */

#include <sys/types.h>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <err.h>
#include <libnet.h>
#include <pcap.h>

#include "pcaputil.h"
#include "version.h"

#define DEFAULT_SEVERITY	3

int	Opt_severity = DEFAULT_SEVERITY;
int	pcap_off;
pcap_t  *pd;
int     Opt_max_kill = 0;
int     kill_counter = 0;

static void
usage(void)
{
	fprintf(stderr, "Version: " VERSION "\n"
		"Usage: tcpkill [-i interface] [-m max kills] [-1..9] expression\n");
	exit(1);
}

static void
tcp_kill_cb(u_char *user, const struct pcap_pkthdr *pcap, const u_char *pkt)
{
	struct libnet_ipv4_hdr *ip;
	struct libnet_tcp_hdr *tcp;
	char ctext[64];
	u_int32_t seq, win;
	int i, len;
	libnet_t *l;

	l = (libnet_t *)user;
	pkt += pcap_off;
	len = pcap->caplen - pcap_off;

	ip = (struct libnet_ipv4_hdr *)pkt;
	if (ip->ip_p != IPPROTO_TCP)
		return;
	
	tcp = (struct libnet_tcp_hdr *)(pkt + (ip->ip_hl << 2));
	if (tcp->th_flags & (TH_SYN|TH_FIN|TH_RST))
		return;

	seq = ntohl(tcp->th_ack);
	win = ntohs(tcp->th_win);
	
	snprintf(ctext, sizeof(ctext), "%s:%d > %s:%d:",
		 libnet_addr2name4(ip->ip_src.s_addr, LIBNET_DONT_RESOLVE),
		 ntohs(tcp->th_sport),
		 libnet_addr2name4(ip->ip_dst.s_addr, LIBNET_DONT_RESOLVE),
		 ntohs(tcp->th_dport));
	
	for (i = 0; i < Opt_severity; i++) {
		seq += (i * win);
		
		libnet_clear_packet(l);
		
		libnet_build_tcp(ntohs(tcp->th_dport), ntohs(tcp->th_sport),
				 seq, 0, TH_RST, 0, 0, 0, LIBNET_TCP_H, 
				 NULL, 0, l, 0);
		
		libnet_build_ipv4(LIBNET_IPV4_H + LIBNET_TCP_H, 0,
				  libnet_get_prand(LIBNET_PRu16), 0, 64,
				  IPPROTO_TCP, 0, ip->ip_dst.s_addr,
				  ip->ip_src.s_addr, NULL, 0, l, 0);
		
		if (libnet_write(l) < 0)
			warn("write");
		
		fprintf(stderr, "%s R %lu:%lu(0) win 0\n",
                        ctext,
                        (unsigned long) seq,
                        (unsigned long) seq);
	}

        ++kill_counter;
        if (Opt_max_kill && kill_counter >= Opt_max_kill) {
          pcap_breakloop(pd);
        }
}

int
main(int argc, char *argv[])
{
	extern char *optarg;
	extern int optind;
	int c;
	char *p, *intf, *filter, ebuf[PCAP_ERRBUF_SIZE];
	char libnet_ebuf[LIBNET_ERRBUF_SIZE];
	libnet_t *l;
	
	intf = NULL;
	
	while ((c = getopt(argc, argv, "i:m:123456789h?V")) != -1) {
		switch (c) {
		case 'i':
			intf = optarg;
			break;
		case 'm':
			Opt_max_kill = atoi(optarg);
			break;
		case '0': case '1': case '2': case '3': case '4':
		case '5': case '6': case '7': case '8': case '9':
			p = argv[optind - 1];
			if (p[0] == '-' && p[1] == c && p[2] == '\0')
				Opt_severity = atoi(++p);
			else
				Opt_severity = atoi(argv[optind] + 1);
			break;
		default:
			usage();
			break;
		}
	}
	if (intf == NULL && (intf = pcap_lookupdev(ebuf)) == NULL)
		errx(1, "%s", ebuf);

	argc -= optind;
	argv += optind;
	
	if (argc == 0)
		usage();
	
	filter = copy_argv(argv);
	
	if ((pd = pcap_init(intf, filter, 64)) == NULL)
		errx(1, "couldn't initialize sniffing");

	if ((pcap_off = pcap_dloff(pd)) < 0)
		errx(1, "couldn't determine link layer offset");
	
	if ((l = libnet_init(LIBNET_RAW4, intf, libnet_ebuf)) == NULL)
		errx(1, "couldn't initialize sending");
	
	libnet_seed_prand(l);
	
	warnx("listening on %s [%s]", intf, filter);
	
	pcap_loop(pd, -1, tcp_kill_cb, (u_char *)l);
  
	/* NOTREACHED */
	
	exit(0);
}