/* Shared library add-on to iptables to add TCPMSS target support.
 *
 * Copyright (c) 2000 Marc Boucher
*/
#include <stdio.h>
#include <xtables.h>
#include <netinet/ip.h>
#include <netinet/ip6.h>
#include <linux/netfilter/xt_TCPMSS.h>

enum {
	O_SET_MSS = 0,
	O_CLAMP_MSS,
};

struct mssinfo {
	struct xt_entry_target t;
	struct xt_tcpmss_info mss;
};

static void __TCPMSS_help(int hdrsize)
{
	printf(
"TCPMSS target mutually-exclusive options:\n"
"  --set-mss value               explicitly set MSS option to specified value\n"
"  --clamp-mss-to-pmtu           automatically clamp MSS value to (path_MTU - %d)\n",
hdrsize);
}

static void TCPMSS_help(void)
{
	__TCPMSS_help(sizeof(struct iphdr));
}

static void TCPMSS_help6(void)
{
	__TCPMSS_help(sizeof(struct ip6_hdr));
}

static const struct xt_option_entry TCPMSS4_opts[] = {
	{.name = "set-mss", .id = O_SET_MSS, .type = XTTYPE_UINT16,
	 .min = 0, .max = UINT16_MAX - sizeof(struct iphdr),
	 .flags = XTOPT_PUT, XTOPT_POINTER(struct xt_tcpmss_info, mss)},
	{.name = "clamp-mss-to-pmtu", .id = O_CLAMP_MSS, .type = XTTYPE_NONE},
	XTOPT_TABLEEND,
};

static const struct xt_option_entry TCPMSS6_opts[] = {
	{.name = "set-mss", .id = O_SET_MSS, .type = XTTYPE_UINT16,
	 .min = 0, .max = UINT16_MAX - sizeof(struct ip6_hdr),
	 .flags = XTOPT_PUT, XTOPT_POINTER(struct xt_tcpmss_info, mss)},
	{.name = "clamp-mss-to-pmtu", .id = O_CLAMP_MSS, .type = XTTYPE_NONE},
	XTOPT_TABLEEND,
};

static void TCPMSS_parse(struct xt_option_call *cb)
{
	struct xt_tcpmss_info *mssinfo = cb->data;

	xtables_option_parse(cb);
	if (cb->entry->id == O_CLAMP_MSS)
		mssinfo->mss = XT_TCPMSS_CLAMP_PMTU;
}

static void TCPMSS_check(struct xt_fcheck_call *cb)
{
	if (cb->xflags == 0)
		xtables_error(PARAMETER_PROBLEM,
		           "TCPMSS target: At least one parameter is required");
}

static void TCPMSS_print(const void *ip, const struct xt_entry_target *target,
                         int numeric)
{
	const struct xt_tcpmss_info *mssinfo =
		(const struct xt_tcpmss_info *)target->data;
	if(mssinfo->mss == XT_TCPMSS_CLAMP_PMTU)
		printf(" TCPMSS clamp to PMTU");
	else
		printf(" TCPMSS set %u", mssinfo->mss);
}

static void TCPMSS_save(const void *ip, const struct xt_entry_target *target)
{
	const struct xt_tcpmss_info *mssinfo =
		(const struct xt_tcpmss_info *)target->data;

	if(mssinfo->mss == XT_TCPMSS_CLAMP_PMTU)
		printf(" --clamp-mss-to-pmtu");
	else
		printf(" --set-mss %u", mssinfo->mss);
}

static struct xtables_target tcpmss_target = {
	.family		= NFPROTO_IPV4,
	.name		= "TCPMSS",
	.version	= XTABLES_VERSION,
	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
	.help		= TCPMSS_help,
	.print		= TCPMSS_print,
	.save		= TCPMSS_save,
	.x6_parse	= TCPMSS_parse,
	.x6_fcheck	= TCPMSS_check,
	.x6_options	= TCPMSS4_opts,
};

static struct xtables_target tcpmss_target6 = {
	.family		= NFPROTO_IPV6,
	.name		= "TCPMSS",
	.version	= XTABLES_VERSION,
	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
	.help		= TCPMSS_help6,
	.print		= TCPMSS_print,
	.save		= TCPMSS_save,
	.x6_parse	= TCPMSS_parse,
	.x6_fcheck	= TCPMSS_check,
	.x6_options	= TCPMSS6_opts,
};

void _init(void)
{
	xtables_register_target(&tcpmss_target);
	xtables_register_target(&tcpmss_target6);
}