#include <stdio.h>

#include <netdb.h>

#include <string.h>

#include <stdlib.h>

#include <getopt.h>

#include <xtables.h>

#include <limits.h> /* INT_MAX in ip_tables.h */

#include <linux/netfilter_ipv4/ip_tables.h>

#include <linux/netfilter/nf_nat.h>

enum {

	O_TO_PORTS = 0,

	O_RANDOM,

	O_RANDOM_FULLY,

};

static void MASQUERADE_help(void)

{

	printf(

"MASQUERADE target options:\n"

" --to-ports <port>[-<port>]\n"

"				Port (range) to map to.\n"

" --random\n"

"				Randomize source port.\n"

" --random-fully\n"

"				Fully randomize source port.\n");

}

static const struct xt_option_entry MASQUERADE_opts[] = {

	{.name = "to-ports", .id = O_TO_PORTS, .type = XTTYPE_STRING},

	{.name = "random", .id = O_RANDOM, .type = XTTYPE_NONE},

	{.name = "random-fully", .id = O_RANDOM_FULLY, .type = XTTYPE_NONE},

	XTOPT_TABLEEND,

};

static void MASQUERADE_init(struct xt_entry_target *t)

{

	struct nf_nat_ipv4_multi_range_compat *mr = (struct nf_nat_ipv4_multi_range_compat *)t->data;

	/* Actually, it's 0, but it's ignored at the moment. */

	mr->rangesize = 1;

}

/* Parses ports */

static void

parse_ports(const char *arg, struct nf_nat_ipv4_multi_range_compat *mr)

{

	char *end;

	unsigned int port, maxport;

	mr->range[0].flags |= NF_NAT_RANGE_PROTO_SPECIFIED;

	if (!xtables_strtoui(arg, &end, &port, 0, UINT16_MAX))

		xtables_param_act(XTF_BAD_VALUE, "MASQUERADE", "--to-ports", arg);

	switch (*end) {

	case '\0':

		mr->range[0].min.tcp.port

			= mr->range[0].max.tcp.port

			= htons(port);

		return;

	case '-':

		if (!xtables_strtoui(end + 1, NULL, &maxport, 0, UINT16_MAX))

			break;

		if (maxport < port)

			break;

		mr->range[0].min.tcp.port = htons(port);

		mr->range[0].max.tcp.port = htons(maxport);

		return;

	default:

		break;

	}

	xtables_param_act(XTF_BAD_VALUE, "MASQUERADE", "--to-ports", arg);

}

static void MASQUERADE_parse(struct xt_option_call *cb)

{

	const struct ipt_entry *entry = cb->xt_entry;

	int portok;

	struct nf_nat_ipv4_multi_range_compat *mr = cb->data;

	if (entry->ip.proto == IPPROTO_TCP

	    || entry->ip.proto == IPPROTO_UDP

	    || entry->ip.proto == IPPROTO_SCTP

	    || entry->ip.proto == IPPROTO_DCCP

	    || entry->ip.proto == IPPROTO_ICMP)

		portok = 1;

	else

		portok = 0;

	xtables_option_parse(cb);

	switch (cb->entry->id) {

	case O_TO_PORTS:

		if (!portok)

			xtables_error(PARAMETER_PROBLEM,

				   "Need TCP, UDP, SCTP or DCCP with port specification");

		parse_ports(cb->arg, mr);

		break;

	case O_RANDOM:

		mr->range[0].flags |=  NF_NAT_RANGE_PROTO_RANDOM;

		break;

	case O_RANDOM_FULLY:

		mr->range[0].flags |=  NF_NAT_RANGE_PROTO_RANDOM_FULLY;

		break;

	}

}

static void

MASQUERADE_print(const void *ip, const struct xt_entry_target *target,

                 int numeric)

{

	const struct nf_nat_ipv4_multi_range_compat *mr = (const void *)target->data;

	const struct nf_nat_ipv4_range *r = &mr->range[0];

	if (r->flags & NF_NAT_RANGE_PROTO_SPECIFIED) {

		printf(" masq ports: ");

		printf("%hu", ntohs(r->min.tcp.port));

		if (r->max.tcp.port != r->min.tcp.port)

			printf("-%hu", ntohs(r->max.tcp.port));

	}

	if (r->flags & NF_NAT_RANGE_PROTO_RANDOM)

		printf(" random");

	if (r->flags & NF_NAT_RANGE_PROTO_RANDOM_FULLY)

		printf(" random-fully");

}

static void

MASQUERADE_save(const void *ip, const struct xt_entry_target *target)

{

	const struct nf_nat_ipv4_multi_range_compat *mr = (const void *)target->data;

	const struct nf_nat_ipv4_range *r = &mr->range[0];

	if (r->flags & NF_NAT_RANGE_PROTO_SPECIFIED) {

		printf(" --to-ports %hu", ntohs(r->min.tcp.port));

		if (r->max.tcp.port != r->min.tcp.port)

			printf("-%hu", ntohs(r->max.tcp.port));

	}

	if (r->flags & NF_NAT_RANGE_PROTO_RANDOM)

		printf(" --random");

	if (r->flags & NF_NAT_RANGE_PROTO_RANDOM_FULLY)

		printf(" --random-fully");

}

static int MASQUERADE_xlate(struct xt_xlate *xl,

			    const struct xt_xlate_tg_params *params)

{

	const struct nf_nat_ipv4_multi_range_compat *mr =

		(const void *)params->target->data;

	const struct nf_nat_ipv4_range *r = &mr->range[0];

	xt_xlate_add(xl, "masquerade");

	if (r->flags & NF_NAT_RANGE_PROTO_SPECIFIED) {

		xt_xlate_add(xl, " to :%hu", ntohs(r->min.tcp.port));

		if (r->max.tcp.port != r->min.tcp.port)

			xt_xlate_add(xl, "-%hu", ntohs(r->max.tcp.port));

        }

	xt_xlate_add(xl, " ");

	if (r->flags & NF_NAT_RANGE_PROTO_RANDOM)

		xt_xlate_add(xl, "random ");

	return 1;

}

static struct xtables_target masquerade_tg_reg = {

	.name		= "MASQUERADE",

	.version	= XTABLES_VERSION,

	.family		= NFPROTO_IPV4,

	.size		= XT_ALIGN(sizeof(struct nf_nat_ipv4_multi_range_compat)),

	.userspacesize	= XT_ALIGN(sizeof(struct nf_nat_ipv4_multi_range_compat)),

	.help		= MASQUERADE_help,

	.init		= MASQUERADE_init,

	.x6_parse	= MASQUERADE_parse,

	.print		= MASQUERADE_print,

	.save		= MASQUERADE_save,

	.x6_options	= MASQUERADE_opts,

	.xlate		= MASQUERADE_xlate,

};

void _init(void)

{

	xtables_register_target(&masquerade_tg_reg);

}