extensions/libxt_tcp.c - platform/external/iptables - Git at Google

 /* Shared library add-on to iptables to add TCP support. */
 #include <stdbool.h>
 #include <stdio.h>
 #include <netdb.h>
 #include <string.h>
 #include <stdlib.h>
 #include <getopt.h>
 #include <netinet/in.h>
 #include <xtables.h>
 #include <linux/netfilter/xt_tcpudp.h>

 static void tcp_help(void)
 {
 	printf(
 "tcp match options:\n"
 "[!] --tcp-flags mask comp	match when TCP flags & mask == comp\n"
 "				(Flags: SYN ACK FIN RST URG PSH ALL NONE)\n"
 "[!] --syn			match when only SYN flag set\n"
 "				(equivalent to --tcp-flags SYN,RST,ACK,FIN SYN)\n"
 "[!] --source-port port[:port]\n"
 " --sport ...\n"
 "				match source port(s)\n"
 "[!] --destination-port port[:port]\n"
 " --dport ...\n"
 "				match destination port(s)\n"
 "[!] --tcp-option number        match if TCP option set\n");
 }

 static const struct option tcp_opts[] = {
 	{.name = "source-port",      .has_arg = true,  .val = '1'},
 	{.name = "sport",            .has_arg = true,  .val = '1'}, /* synonym */
 	{.name = "destination-port", .has_arg = true,  .val = '2'},
 	{.name = "dport",            .has_arg = true,  .val = '2'}, /* synonym */
 	{.name = "syn",              .has_arg = false, .val = '3'},
 	{.name = "tcp-flags",        .has_arg = true,  .val = '4'},
 	{.name = "tcp-option",       .has_arg = true,  .val = '5'},
 	XT_GETOPT_TABLEEND,
 };

 static void
 parse_tcp_ports(const char *portstring, uint16_t *ports)
 {
 	char *buffer;
 	char *cp;

 	buffer = strdup(portstring);
 	if ((cp = strchr(buffer, ':')) == NULL)
 		ports[0] = ports[1] = xtables_parse_port(buffer, "tcp");
 	else {
 		*cp = '\0';
 		cp++;

 		ports[0] = buffer[0] ? xtables_parse_port(buffer, "tcp") : 0;
 		ports[1] = cp[0] ? xtables_parse_port(cp, "tcp") : 0xFFFF;

 		if (ports[0] > ports[1])
 			xtables_error(PARAMETER_PROBLEM,
 				   "invalid portrange (min > max)");
 	}
 	free(buffer);
 }

 struct tcp_flag_names {
 	const char *name;
 	unsigned int flag;
 };

 static const struct tcp_flag_names tcp_flag_names[]
 = { { "FIN", 0x01 },
     { "SYN", 0x02 },
     { "RST", 0x04 },
     { "PSH", 0x08 },
     { "ACK", 0x10 },
     { "URG", 0x20 },
     { "ALL", 0x3F },
     { "NONE", 0 },
 };

 static unsigned int
 parse_tcp_flag(const char *flags)
 {
 	unsigned int ret = 0;
 	char *ptr;
 	char *buffer;

 	buffer = strdup(flags);

 	for (ptr = strtok(buffer, ","); ptr; ptr = strtok(NULL, ",")) {
 		unsigned int i;
 		for (i = 0; i < ARRAY_SIZE(tcp_flag_names); ++i)
 			if (strcasecmp(tcp_flag_names[i].name, ptr) == 0) {
 				ret |= tcp_flag_names[i].flag;
 				break;
 			}
 		if (i == ARRAY_SIZE(tcp_flag_names))
 			xtables_error(PARAMETER_PROBLEM,
 				   "Unknown TCP flag `%s'", ptr);
 	}

 	free(buffer);
 	return ret;
 }

 static void
 parse_tcp_flags(struct xt_tcp *tcpinfo,
 		const char *mask,
 		const char *cmp,
 		int invert)
 {
 	tcpinfo->flg_mask = parse_tcp_flag(mask);
 	tcpinfo->flg_cmp = parse_tcp_flag(cmp);

 	if (invert)
 		tcpinfo->invflags |= XT_TCP_INV_FLAGS;
 }

 static void
 parse_tcp_option(const char *option, uint8_t *result)
 {
 	unsigned int ret;

 	if (!xtables_strtoui(option, NULL, &ret, 1, UINT8_MAX))
 		xtables_error(PARAMETER_PROBLEM, "Bad TCP option \"%s\"", option);

 	*result = ret;
 }

 static void tcp_init(struct xt_entry_match *m)
 {
 	struct xt_tcp *tcpinfo = (struct xt_tcp *)m->data;

 	tcpinfo->spts[1] = tcpinfo->dpts[1] = 0xFFFF;
 }

 #define TCP_SRC_PORTS 0x01
 #define TCP_DST_PORTS 0x02
 #define TCP_FLAGS 0x04
 #define TCP_OPTION	0x08

 static int
 tcp_parse(int c, char **argv, int invert, unsigned int *flags,
           const void *entry, struct xt_entry_match **match)
 {
 	struct xt_tcp *tcpinfo = (struct xt_tcp *)(*match)->data;

 	switch (c) {
 	case '1':
 		if (*flags & TCP_SRC_PORTS)
 			xtables_error(PARAMETER_PROBLEM,
 				   "Only one `--source-port' allowed");
 		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
 		parse_tcp_ports(optarg, tcpinfo->spts);
 		if (invert)
 			tcpinfo->invflags |= XT_TCP_INV_SRCPT;
 		*flags |= TCP_SRC_PORTS;
 		break;

 	case '2':
 		if (*flags & TCP_DST_PORTS)
 			xtables_error(PARAMETER_PROBLEM,
 				   "Only one `--destination-port' allowed");
 		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
 		parse_tcp_ports(optarg, tcpinfo->dpts);
 		if (invert)
 			tcpinfo->invflags |= XT_TCP_INV_DSTPT;
 		*flags |= TCP_DST_PORTS;
 		break;

 	case '3':
 		if (*flags & TCP_FLAGS)
 			xtables_error(PARAMETER_PROBLEM,
 				   "Only one of `--syn' or `--tcp-flags' "
 				   " allowed");
 		parse_tcp_flags(tcpinfo, "SYN,RST,ACK,FIN", "SYN", invert);
 		*flags |= TCP_FLAGS;
 		break;

 	case '4':
 		if (*flags & TCP_FLAGS)
 			xtables_error(PARAMETER_PROBLEM,
 				   "Only one of `--syn' or `--tcp-flags' "
 				   " allowed");
 		xtables_check_inverse(optarg, &invert, &optind, 0, argv);

 		if (!argv[optind]
 		    || argv[optind][0] == '-' || argv[optind][0] == '!')
 			xtables_error(PARAMETER_PROBLEM,
 				   "--tcp-flags requires two args.");

 		parse_tcp_flags(tcpinfo, optarg, argv[optind],
 				invert);
 		optind++;
 		*flags |= TCP_FLAGS;
 		break;

 	case '5':
 		if (*flags & TCP_OPTION)
 			xtables_error(PARAMETER_PROBLEM,
 				   "Only one `--tcp-option' allowed");
 		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
 		parse_tcp_option(optarg, &tcpinfo->option);
 		if (invert)
 			tcpinfo->invflags |= XT_TCP_INV_OPTION;
 		*flags |= TCP_OPTION;
 		break;
 	}

 	return 1;
 }

 static char *
 port_to_service(int port)
 {
 	struct servent *service;

 	if ((service = getservbyport(htons(port), "tcp")))
 		return service->s_name;

 	return NULL;
 }

 static void
 print_port(uint16_t port, int numeric)
 {
 	char *service;

 	if (numeric || (service = port_to_service(port)) == NULL)
 		printf("%u", port);
 	else
 		printf("%s", service);
 }

 static void
 print_ports(const char *name, uint16_t min, uint16_t max,
 	    int invert, int numeric)
 {
 	const char *inv = invert ? "!" : "";

 	if (min != 0 || max != 0xFFFF || invert) {
 		printf(" %s", name);
 		if (min == max) {
 			printf(":%s", inv);
 			print_port(min, numeric);
 		} else {
 			printf("s:%s", inv);
 			print_port(min, numeric);
 			printf(":");
 			print_port(max, numeric);
 		}
 	}
 }

 static void
 print_option(uint8_t option, int invert, int numeric)
 {
 	if (option || invert)
 		printf(" option=%s%u", invert ? "!" : "", option);
 }

 static void
 print_tcpf(uint8_t flags)
 {
 	int have_flag = 0;

 	while (flags) {
 		unsigned int i;

 		for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);

 		if (have_flag)
 			printf(",");
 		printf("%s", tcp_flag_names[i].name);
 		have_flag = 1;

 		flags &= ~tcp_flag_names[i].flag;
 	}

 	if (!have_flag)
 		printf("NONE");
 }

 static void
 print_flags(uint8_t mask, uint8_t cmp, int invert, int numeric)
 {
 	if (mask || invert) {
 		printf("flags:%s", invert ? "!" : "");
 		if (numeric)
 			printf(" 0x%02X/0x%02X", mask, cmp);
 		else {
 			printf(" ");
 			print_tcpf(mask);
 			printf("/");
 			print_tcpf(cmp);
 		}
 	}
 }

 static void
 tcp_print(const void *ip, const struct xt_entry_match *match, int numeric)
 {
 	const struct xt_tcp *tcp = (struct xt_tcp *)match->data;

 	printf(" tcp");
 	print_ports("spt", tcp->spts[0], tcp->spts[1],
 		    tcp->invflags & XT_TCP_INV_SRCPT,
 		    numeric);
 	print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
 		    tcp->invflags & XT_TCP_INV_DSTPT,
 		    numeric);
 	print_option(tcp->option,
 		     tcp->invflags & XT_TCP_INV_OPTION,
 		     numeric);
 	print_flags(tcp->flg_mask, tcp->flg_cmp,
 		    tcp->invflags & XT_TCP_INV_FLAGS,
 		    numeric);
 	if (tcp->invflags & ~XT_TCP_INV_MASK)
 		printf(" Unknown invflags: 0x%X",
 		       tcp->invflags & ~XT_TCP_INV_MASK);
 }

 static void tcp_save(const void *ip, const struct xt_entry_match *match)
 {
 	const struct xt_tcp *tcpinfo = (struct xt_tcp *)match->data;

 	if (tcpinfo->spts[0] != 0
 	    || tcpinfo->spts[1] != 0xFFFF) {
 		if (tcpinfo->invflags & XT_TCP_INV_SRCPT)
 			printf(" !");
 		if (tcpinfo->spts[0]
 		    != tcpinfo->spts[1])
 			printf(" --sport %u:%u",
 			       tcpinfo->spts[0],
 			       tcpinfo->spts[1]);
 		else
 			printf(" --sport %u",
 			       tcpinfo->spts[0]);
 	}

 	if (tcpinfo->dpts[0] != 0
 	    || tcpinfo->dpts[1] != 0xFFFF) {
 		if (tcpinfo->invflags & XT_TCP_INV_DSTPT)
 			printf(" !");
 		if (tcpinfo->dpts[0]
 		    != tcpinfo->dpts[1])
 			printf(" --dport %u:%u",
 			       tcpinfo->dpts[0],
 			       tcpinfo->dpts[1]);
 		else
 			printf(" --dport %u",
 			       tcpinfo->dpts[0]);
 	}

 	if (tcpinfo->option
 	    || (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
 		if (tcpinfo->invflags & XT_TCP_INV_OPTION)
 			printf(" !");
 		printf(" --tcp-option %u", tcpinfo->option);
 	}

 	if (tcpinfo->flg_mask
 	    || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
 		if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
 			printf(" !");
 		printf(" --tcp-flags ");
 		if (tcpinfo->flg_mask != 0xFF) {
 			print_tcpf(tcpinfo->flg_mask);
 		}
 		printf(" ");
 		print_tcpf(tcpinfo->flg_cmp);
 	}
 }

 static struct xtables_match tcp_match = {
 	.family		= NFPROTO_UNSPEC,
 	.name		= "tcp",
 	.version	= XTABLES_VERSION,
 	.size		= XT_ALIGN(sizeof(struct xt_tcp)),
 	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcp)),
 	.help		= tcp_help,
 	.init		= tcp_init,
 	.parse		= tcp_parse,
 	.print		= tcp_print,
 	.save		= tcp_save,
 	.extra_opts	= tcp_opts,
 };

 void
 _init(void)
 {
 	xtables_register_match(&tcp_match);
 }
	/* Shared library add-on to iptables to add TCP support. */
	#include <stdbool.h>
	#include <stdio.h>
	#include <netdb.h>
	#include <string.h>
	#include <stdlib.h>
	#include <getopt.h>
	#include <netinet/in.h>
	#include <xtables.h>
	#include <linux/netfilter/xt_tcpudp.h>

	static void tcp_help(void)
	{
	printf(
	"tcp match options:\n"
	"[!] --tcp-flags mask comp match when TCP flags & mask == comp\n"
	" (Flags: SYN ACK FIN RST URG PSH ALL NONE)\n"
	"[!] --syn match when only SYN flag set\n"
	" (equivalent to --tcp-flags SYN,RST,ACK,FIN SYN)\n"
	"[!] --source-port port[:port]\n"
	" --sport ...\n"
	" match source port(s)\n"
	"[!] --destination-port port[:port]\n"
	" --dport ...\n"
	" match destination port(s)\n"
	"[!] --tcp-option number match if TCP option set\n");
	}

	static const struct option tcp_opts[] = {
	{.name = "source-port", .has_arg = true, .val = '1'},
	{.name = "sport", .has_arg = true, .val = '1'}, /* synonym */
	{.name = "destination-port", .has_arg = true, .val = '2'},
	{.name = "dport", .has_arg = true, .val = '2'}, /* synonym */
	{.name = "syn", .has_arg = false, .val = '3'},
	{.name = "tcp-flags", .has_arg = true, .val = '4'},
	{.name = "tcp-option", .has_arg = true, .val = '5'},
	XT_GETOPT_TABLEEND,
	};

	static void
	parse_tcp_ports(const char portstring, uint16_t ports)
	{
	char *buffer;
	char *cp;

	buffer = strdup(portstring);
	if ((cp = strchr(buffer, ':')) == NULL)
	ports[0] = ports[1] = xtables_parse_port(buffer, "tcp");
	else {
	*cp = '\0';
	cp++;

	ports[0] = buffer[0] ? xtables_parse_port(buffer, "tcp") : 0;
	ports[1] = cp[0] ? xtables_parse_port(cp, "tcp") : 0xFFFF;

	if (ports[0] > ports[1])
	xtables_error(PARAMETER_PROBLEM,
	"invalid portrange (min > max)");
	}
	free(buffer);
	}

	struct tcp_flag_names {
	const char *name;
	unsigned int flag;
	};

	static const struct tcp_flag_names tcp_flag_names[]
	= { { "FIN", 0x01 },
	{ "SYN", 0x02 },
	{ "RST", 0x04 },
	{ "PSH", 0x08 },
	{ "ACK", 0x10 },
	{ "URG", 0x20 },
	{ "ALL", 0x3F },
	{ "NONE", 0 },
	};

	static unsigned int
	parse_tcp_flag(const char *flags)
	{
	unsigned int ret = 0;
	char *ptr;
	char *buffer;

	buffer = strdup(flags);

	for (ptr = strtok(buffer, ","); ptr; ptr = strtok(NULL, ",")) {
	unsigned int i;
	for (i = 0; i < ARRAY_SIZE(tcp_flag_names); ++i)
	if (strcasecmp(tcp_flag_names[i].name, ptr) == 0) {
	ret \|= tcp_flag_names[i].flag;
	break;
	}
	if (i == ARRAY_SIZE(tcp_flag_names))
	xtables_error(PARAMETER_PROBLEM,
	"Unknown TCP flag `%s'", ptr);
	}

	free(buffer);
	return ret;
	}

	static void
	parse_tcp_flags(struct xt_tcp *tcpinfo,
	const char *mask,
	const char *cmp,
	int invert)
	{
	tcpinfo->flg_mask = parse_tcp_flag(mask);
	tcpinfo->flg_cmp = parse_tcp_flag(cmp);

	if (invert)
	tcpinfo->invflags \|= XT_TCP_INV_FLAGS;
	}

	static void
	parse_tcp_option(const char option, uint8_t result)
	{
	unsigned int ret;

	if (!xtables_strtoui(option, NULL, &ret, 1, UINT8_MAX))
	xtables_error(PARAMETER_PROBLEM, "Bad TCP option \"%s\"", option);

	*result = ret;
	}

	static void tcp_init(struct xt_entry_match *m)
	{
	struct xt_tcp tcpinfo = (struct xt_tcp )m->data;

	tcpinfo->spts[1] = tcpinfo->dpts[1] = 0xFFFF;
	}

	#define TCP_SRC_PORTS 0x01
	#define TCP_DST_PORTS 0x02
	#define TCP_FLAGS 0x04
	#define TCP_OPTION 0x08

	static int
	tcp_parse(int c, char *argv, int invert, unsigned int flags,
	const void entry, struct xt_entry_match *match)
	{
	struct xt_tcp tcpinfo = (struct xt_tcp )(*match)->data;

	switch (c) {
	case '1':
	if (*flags & TCP_SRC_PORTS)
	xtables_error(PARAMETER_PROBLEM,
	"Only one `--source-port' allowed");
	xtables_check_inverse(optarg, &invert, &optind, 0, argv);
	parse_tcp_ports(optarg, tcpinfo->spts);
	if (invert)
	tcpinfo->invflags \|= XT_TCP_INV_SRCPT;
	*flags \|= TCP_SRC_PORTS;
	break;

	case '2':
	if (*flags & TCP_DST_PORTS)
	xtables_error(PARAMETER_PROBLEM,
	"Only one `--destination-port' allowed");
	xtables_check_inverse(optarg, &invert, &optind, 0, argv);
	parse_tcp_ports(optarg, tcpinfo->dpts);
	if (invert)
	tcpinfo->invflags \|= XT_TCP_INV_DSTPT;
	*flags \|= TCP_DST_PORTS;
	break;

	case '3':
	if (*flags & TCP_FLAGS)
	xtables_error(PARAMETER_PROBLEM,
	"Only one of `--syn' or `--tcp-flags' "
	" allowed");
	parse_tcp_flags(tcpinfo, "SYN,RST,ACK,FIN", "SYN", invert);
	*flags \|= TCP_FLAGS;
	break;

	case '4':
	if (*flags & TCP_FLAGS)
	xtables_error(PARAMETER_PROBLEM,
	"Only one of `--syn' or `--tcp-flags' "
	" allowed");
	xtables_check_inverse(optarg, &invert, &optind, 0, argv);

	if (!argv[optind]
	\|\| argv[optind][0] == '-' \|\| argv[optind][0] == '!')
	xtables_error(PARAMETER_PROBLEM,
	"--tcp-flags requires two args.");

	parse_tcp_flags(tcpinfo, optarg, argv[optind],
	invert);
	optind++;
	*flags \|= TCP_FLAGS;
	break;

	case '5':
	if (*flags & TCP_OPTION)
	xtables_error(PARAMETER_PROBLEM,
	"Only one `--tcp-option' allowed");
	xtables_check_inverse(optarg, &invert, &optind, 0, argv);
	parse_tcp_option(optarg, &tcpinfo->option);
	if (invert)
	tcpinfo->invflags \|= XT_TCP_INV_OPTION;
	*flags \|= TCP_OPTION;
	break;
	}

	return 1;
	}

	static char *
	port_to_service(int port)
	{
	struct servent *service;

	if ((service = getservbyport(htons(port), "tcp")))
	return service->s_name;

	return NULL;
	}

	static void
	print_port(uint16_t port, int numeric)
	{
	char *service;

	if (numeric \|\| (service = port_to_service(port)) == NULL)
	printf("%u", port);
	else
	printf("%s", service);
	}

	static void
	print_ports(const char *name, uint16_t min, uint16_t max,
	int invert, int numeric)
	{
	const char *inv = invert ? "!" : "";

	if (min != 0 \|\| max != 0xFFFF \|\| invert) {
	printf(" %s", name);
	if (min == max) {
	printf(":%s", inv);
	print_port(min, numeric);
	} else {
	printf("s:%s", inv);
	print_port(min, numeric);
	printf(":");
	print_port(max, numeric);
	}
	}
	}

	static void
	print_option(uint8_t option, int invert, int numeric)
	{
	if (option \|\| invert)
	printf(" option=%s%u", invert ? "!" : "", option);
	}

	static void
	print_tcpf(uint8_t flags)
	{
	int have_flag = 0;

	while (flags) {
	unsigned int i;

	for (i = 0; (flags & tcp_flag_names[i].flag) == 0; i++);

	if (have_flag)
	printf(",");
	printf("%s", tcp_flag_names[i].name);
	have_flag = 1;

	flags &= ~tcp_flag_names[i].flag;
	}

	if (!have_flag)
	printf("NONE");
	}

	static void
	print_flags(uint8_t mask, uint8_t cmp, int invert, int numeric)
	{
	if (mask \|\| invert) {
	printf("flags:%s", invert ? "!" : "");
	if (numeric)
	printf(" 0x%02X/0x%02X", mask, cmp);
	else {
	printf(" ");
	print_tcpf(mask);
	printf("/");
	print_tcpf(cmp);
	}
	}
	}

	static void
	tcp_print(const void ip, const struct xt_entry_match match, int numeric)
	{
	const struct xt_tcp tcp = (struct xt_tcp )match->data;

	printf(" tcp");
	print_ports("spt", tcp->spts[0], tcp->spts[1],
	tcp->invflags & XT_TCP_INV_SRCPT,
	numeric);
	print_ports("dpt", tcp->dpts[0], tcp->dpts[1],
	tcp->invflags & XT_TCP_INV_DSTPT,
	numeric);
	print_option(tcp->option,
	tcp->invflags & XT_TCP_INV_OPTION,
	numeric);
	print_flags(tcp->flg_mask, tcp->flg_cmp,
	tcp->invflags & XT_TCP_INV_FLAGS,
	numeric);
	if (tcp->invflags & ~XT_TCP_INV_MASK)
	printf(" Unknown invflags: 0x%X",
	tcp->invflags & ~XT_TCP_INV_MASK);
	}

	static void tcp_save(const void ip, const struct xt_entry_match match)
	{
	const struct xt_tcp tcpinfo = (struct xt_tcp )match->data;

	if (tcpinfo->spts[0] != 0
	\|\| tcpinfo->spts[1] != 0xFFFF) {
	if (tcpinfo->invflags & XT_TCP_INV_SRCPT)
	printf(" !");
	if (tcpinfo->spts[0]
	!= tcpinfo->spts[1])
	printf(" --sport %u:%u",
	tcpinfo->spts[0],
	tcpinfo->spts[1]);
	else
	printf(" --sport %u",
	tcpinfo->spts[0]);
	}

	if (tcpinfo->dpts[0] != 0
	\|\| tcpinfo->dpts[1] != 0xFFFF) {
	if (tcpinfo->invflags & XT_TCP_INV_DSTPT)
	printf(" !");
	if (tcpinfo->dpts[0]
	!= tcpinfo->dpts[1])
	printf(" --dport %u:%u",
	tcpinfo->dpts[0],
	tcpinfo->dpts[1]);
	else
	printf(" --dport %u",
	tcpinfo->dpts[0]);
	}

	if (tcpinfo->option
	\|\| (tcpinfo->invflags & XT_TCP_INV_OPTION)) {
	if (tcpinfo->invflags & XT_TCP_INV_OPTION)
	printf(" !");
	printf(" --tcp-option %u", tcpinfo->option);
	}

	if (tcpinfo->flg_mask
	\|\| (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {
	if (tcpinfo->invflags & XT_TCP_INV_FLAGS)
	printf(" !");
	printf(" --tcp-flags ");
	if (tcpinfo->flg_mask != 0xFF) {
	print_tcpf(tcpinfo->flg_mask);
	}
	printf(" ");
	print_tcpf(tcpinfo->flg_cmp);
	}
	}

	static struct xtables_match tcp_match = {
	.family = NFPROTO_UNSPEC,
	.name = "tcp",
	.version = XTABLES_VERSION,
	.size = XT_ALIGN(sizeof(struct xt_tcp)),
	.userspacesize = XT_ALIGN(sizeof(struct xt_tcp)),
	.help = tcp_help,
	.init = tcp_init,
	.parse = tcp_parse,
	.print = tcp_print,
	.save = tcp_save,
	.extra_opts = tcp_opts,
	};

	void
	_init(void)
	{
	xtables_register_match(&tcp_match);
	}