/* 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");

		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");

		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");

		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");

		parse_tcp_option(optarg, &tcpinfo->option);

		if (invert)

			tcpinfo->invflags |= XT_TCP_INV_OPTION;

		*flags |= TCP_OPTION;

		break;

	}

	return 1;

}

static const char *

port_to_service(int port)

{

	const struct servent *service;

	if ((service = getservbyport(htons(port), "tcp")))

		return service->s_name;

	return NULL;

}

static void

print_port(uint16_t port, int numeric)

{

	const 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 {

			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 ");

		print_tcpf(tcpinfo->flg_mask);

		printf(" ");

		print_tcpf(tcpinfo->flg_cmp);

	}

}

static const struct tcp_flag_names tcp_flag_names_xlate[] = {

	{ "fin", 0x01 },

	{ "syn", 0x02 },

	{ "rst", 0x04 },

	{ "psh", 0x08 },

	{ "ack", 0x10 },

	{ "urg", 0x20 },

};

static void print_tcp_xlate(struct xt_xlate *xl, uint8_t flags)

{

	int have_flag = 0;

	while (flags) {

		unsigned int i;

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

		if (have_flag)

			xt_xlate_add(xl, "|");

		xt_xlate_add(xl, "%s", tcp_flag_names_xlate[i].name);

		have_flag = 1;

		flags &= ~tcp_flag_names_xlate[i].flag;

	}

	if (!have_flag)

		xt_xlate_add(xl, "0x0");

}

static int tcp_xlate(struct xt_xlate *xl,

		     const struct xt_xlate_mt_params *params)

{

	const struct xt_tcp *tcpinfo =

		(const struct xt_tcp *)params->match->data;

	char *space= "";

	if (tcpinfo->spts[0] != 0 || tcpinfo->spts[1] != 0xffff) {

		if (tcpinfo->spts[0] != tcpinfo->spts[1]) {

			xt_xlate_add(xl, "tcp sport %s%u-%u",

				   tcpinfo->invflags & XT_TCP_INV_SRCPT ?

					"!= " : "",

				   tcpinfo->spts[0], tcpinfo->spts[1]);

		} else {

			xt_xlate_add(xl, "tcp sport %s%u",

				   tcpinfo->invflags & XT_TCP_INV_SRCPT ?

					"!= " : "",

				   tcpinfo->spts[0]);

		}

		space = " ";

	}

	if (tcpinfo->dpts[0] != 0 || tcpinfo->dpts[1] != 0xffff) {

		if (tcpinfo->dpts[0] != tcpinfo->dpts[1]) {

			xt_xlate_add(xl, "%stcp dport %s%u-%u", space,

				   tcpinfo->invflags & XT_TCP_INV_DSTPT ?

					"!= " : "",

				   tcpinfo->dpts[0], tcpinfo->dpts[1]);

		} else {

			xt_xlate_add(xl, "%stcp dport %s%u", space,

				   tcpinfo->invflags & XT_TCP_INV_DSTPT ?

					"!= " : "",

				   tcpinfo->dpts[0]);

		}

		space = " ";

	}

	/* XXX not yet implemented */

	if (tcpinfo->option || (tcpinfo->invflags & XT_TCP_INV_OPTION))

		return 0;

	if (tcpinfo->flg_mask || (tcpinfo->invflags & XT_TCP_INV_FLAGS)) {

		xt_xlate_add(xl, "%stcp flags & (", space);

		print_tcp_xlate(xl, tcpinfo->flg_mask);

		xt_xlate_add(xl, ") %s ",

			   tcpinfo->invflags & XT_TCP_INV_FLAGS ? "!=": "==");

		print_tcp_xlate(xl, tcpinfo->flg_cmp);

	}

	return 1;

}

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,

	.xlate		= tcp_xlate,

};

void

_init(void)

{

	xtables_register_match(&tcp_match);

}