[net-next-2.6.git] / net / netfilter / xt_TCPMSS.c

/*
 * This is a module which is used for setting the MSS option in TCP packets.
 *
 * Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/gfp.h>
#include <linux/ipv6.h>
#include <linux/tcp.h>
#include <net/dst.h>
#include <net/flow.h>
#include <net/ipv6.h>
#include <net/route.h>
#include <net/tcp.h>

#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_tcpudp.h>
#include <linux/netfilter/xt_TCPMSS.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
MODULE_DESCRIPTION("Xtables: TCP Maximum Segment Size (MSS) adjustment");
MODULE_ALIAS("ipt_TCPMSS");
MODULE_ALIAS("ip6t_TCPMSS");

static inline unsigned int
optlen(const u_int8_t *opt, unsigned int offset)
{
	/* Beware zero-length options: make finite progress */
	if (opt[offset] <= TCPOPT_NOP || opt[offset+1] == 0)
		return 1;
	else
		return opt[offset+1];
}

static int
tcpmss_mangle_packet(struct sk_buff *skb,
		     const struct xt_tcpmss_info *info,
		     unsigned int in_mtu,
		     unsigned int tcphoff,
		     unsigned int minlen)
{
	struct tcphdr *tcph;
	unsigned int tcplen, i;
	__be16 oldval;
	u16 newmss;
	u8 *opt;

	if (!skb_make_writable(skb, skb->len))
		return -1;

	tcplen = skb->len - tcphoff;
	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);

	/* Header cannot be larger than the packet */
	if (tcplen < tcph->doff*4)
		return -1;

	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
		if (dst_mtu(skb_dst(skb)) <= minlen) {
			if (net_ratelimit())
				pr_err("unknown or invalid path-MTU (%u)\n",
				       dst_mtu(skb_dst(skb)));
			return -1;
		}
		if (in_mtu <= minlen) {
			if (net_ratelimit())
				pr_err("unknown or invalid path-MTU (%u)\n",
				       in_mtu);
			return -1;
		}
		newmss = min(dst_mtu(skb_dst(skb)), in_mtu) - minlen;
	} else
		newmss = info->mss;

	opt = (u_int8_t *)tcph;
	for (i = sizeof(struct tcphdr); i < tcph->doff*4; i += optlen(opt, i)) {
		if (opt[i] == TCPOPT_MSS && tcph->doff*4 - i >= TCPOLEN_MSS &&
		    opt[i+1] == TCPOLEN_MSS) {
			u_int16_t oldmss;

			oldmss = (opt[i+2] << 8) | opt[i+3];

			/* Never increase MSS, even when setting it, as
			 * doing so results in problems for hosts that rely
			 * on MSS being set correctly.
			 */
			if (oldmss <= newmss)
				return 0;

			opt[i+2] = (newmss & 0xff00) >> 8;
			opt[i+3] = newmss & 0x00ff;

			inet_proto_csum_replace2(&tcph->check, skb,
						 htons(oldmss), htons(newmss),
						 0);
			return 0;
		}
	}

	/* There is data after the header so the option can't be added
	   without moving it, and doing so may make the SYN packet
	   itself too large. Accept the packet unmodified instead. */
	if (tcplen > tcph->doff*4)
		return 0;

	/*
	 * MSS Option not found ?! add it..
	 */
	if (skb_tailroom(skb) < TCPOLEN_MSS) {
		if (pskb_expand_head(skb, 0,
				     TCPOLEN_MSS - skb_tailroom(skb),
				     GFP_ATOMIC))
			return -1;
		tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
	}

	skb_put(skb, TCPOLEN_MSS);

	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
	memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));

	inet_proto_csum_replace2(&tcph->check, skb,
				 htons(tcplen), htons(tcplen + TCPOLEN_MSS), 1);
	opt[0] = TCPOPT_MSS;
	opt[1] = TCPOLEN_MSS;
	opt[2] = (newmss & 0xff00) >> 8;
	opt[3] = newmss & 0x00ff;

	inet_proto_csum_replace4(&tcph->check, skb, 0, *((__be32 *)opt), 0);

	oldval = ((__be16 *)tcph)[6];
	tcph->doff += TCPOLEN_MSS/4;
	inet_proto_csum_replace2(&tcph->check, skb,
				 oldval, ((__be16 *)tcph)[6], 0);
	return TCPOLEN_MSS;
}

static u_int32_t tcpmss_reverse_mtu(const struct sk_buff *skb,
				    unsigned int family)
{
	struct flowi fl = {};
	const struct nf_afinfo *ai;
	struct rtable *rt = NULL;
	u_int32_t mtu     = ~0U;

	if (family == PF_INET)
		fl.fl4_dst = ip_hdr(skb)->saddr;
	else
		fl.fl6_dst = ipv6_hdr(skb)->saddr;

	rcu_read_lock();
	ai = nf_get_afinfo(family);
	if (ai != NULL)
		ai->route((struct dst_entry **)&rt, &fl);
	rcu_read_unlock();

	if (rt != NULL) {
		mtu = dst_mtu(&rt->dst);
		dst_release(&rt->dst);
	}
	return mtu;
}

static unsigned int
tcpmss_tg4(struct sk_buff *skb, const struct xt_action_param *par)
{
	struct iphdr *iph = ip_hdr(skb);
	__be16 newlen;
	int ret;

	ret = tcpmss_mangle_packet(skb, par->targinfo,
				   tcpmss_reverse_mtu(skb, PF_INET),
				   iph->ihl * 4,
				   sizeof(*iph) + sizeof(struct tcphdr));
	if (ret < 0)
		return NF_DROP;
	if (ret > 0) {
		iph = ip_hdr(skb);
		newlen = htons(ntohs(iph->tot_len) + ret);
		csum_replace2(&iph->check, iph->tot_len, newlen);
		iph->tot_len = newlen;
	}
	return XT_CONTINUE;
}

#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
static unsigned int
tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
{
	struct ipv6hdr *ipv6h = ipv6_hdr(skb);
	u8 nexthdr;
	int tcphoff;
	int ret;

	nexthdr = ipv6h->nexthdr;
	tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr);
	if (tcphoff < 0)
		return NF_DROP;
	ret = tcpmss_mangle_packet(skb, par->targinfo,
				   tcpmss_reverse_mtu(skb, PF_INET6),
				   tcphoff,
				   sizeof(*ipv6h) + sizeof(struct tcphdr));
	if (ret < 0)
		return NF_DROP;
	if (ret > 0) {
		ipv6h = ipv6_hdr(skb);
		ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret);
	}
	return XT_CONTINUE;
}
#endif

#define TH_SYN 0x02

/* Must specify -p tcp --syn */
static inline bool find_syn_match(const struct xt_entry_match *m)
{
	const struct xt_tcp *tcpinfo = (const struct xt_tcp *)m->data;

	if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
	    tcpinfo->flg_cmp & TH_SYN &&
	    !(tcpinfo->invflags & XT_TCP_INV_FLAGS))
		return true;

	return false;
}

static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
{
	const struct xt_tcpmss_info *info = par->targinfo;
	const struct ipt_entry *e = par->entryinfo;
	const struct xt_entry_match *ematch;

	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
	    (par->hook_mask & ~((1 << NF_INET_FORWARD) |
			   (1 << NF_INET_LOCAL_OUT) |
			   (1 << NF_INET_POST_ROUTING))) != 0) {
		pr_info("path-MTU clamping only supported in "
			"FORWARD, OUTPUT and POSTROUTING hooks\n");
		return -EINVAL;
	}
	xt_ematch_foreach(ematch, e)
		if (find_syn_match(ematch))
			return 0;
	pr_info("Only works on TCP SYN packets\n");
	return -EINVAL;
}

#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
{
	const struct xt_tcpmss_info *info = par->targinfo;
	const struct ip6t_entry *e = par->entryinfo;
	const struct xt_entry_match *ematch;

	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
	    (par->hook_mask & ~((1 << NF_INET_FORWARD) |
			   (1 << NF_INET_LOCAL_OUT) |
			   (1 << NF_INET_POST_ROUTING))) != 0) {
		pr_info("path-MTU clamping only supported in "
			"FORWARD, OUTPUT and POSTROUTING hooks\n");
		return -EINVAL;
	}
	xt_ematch_foreach(ematch, e)
		if (find_syn_match(ematch))
			return 0;
	pr_info("Only works on TCP SYN packets\n");
	return -EINVAL;
}
#endif

static struct xt_target tcpmss_tg_reg[] __read_mostly = {
	{
		.family		= NFPROTO_IPV4,
		.name		= "TCPMSS",
		.checkentry	= tcpmss_tg4_check,
		.target		= tcpmss_tg4,
		.targetsize	= sizeof(struct xt_tcpmss_info),
		.proto		= IPPROTO_TCP,
		.me		= THIS_MODULE,
	},
#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
	{
		.family		= NFPROTO_IPV6,
		.name		= "TCPMSS",
		.checkentry	= tcpmss_tg6_check,
		.target		= tcpmss_tg6,
		.targetsize	= sizeof(struct xt_tcpmss_info),
		.proto		= IPPROTO_TCP,
		.me		= THIS_MODULE,
	},
#endif
};

static int __init tcpmss_tg_init(void)
{
	return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
}

static void __exit tcpmss_tg_exit(void)
{
	xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
}

module_init(tcpmss_tg_init);
module_exit(tcpmss_tg_exit);
Commit	Line	Data
cdd289a2 PM	1	/*
	2	* This is a module which is used for setting the MSS option in TCP packets.
	3	*
	4	* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
	5	*
	6	* This program is free software; you can redistribute it and/or modify
	7	* it under the terms of the GNU General Public License version 2 as
	8	* published by the Free Software Foundation.
	9	*/
8bee4bad	10	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
cdd289a2 PM	11	#include <linux/module.h>
	12	#include <linux/skbuff.h>
	13	#include <linux/ip.h>
5a0e3ad6	14	#include <linux/gfp.h>
cdd289a2 PM	15	#include <linux/ipv6.h>
cdd289a2 PM	16	#include <linux/tcp.h>
37c08387 JE	17	#include <net/dst.h>
37c08387 JE	18	#include <net/flow.h>
cdd289a2	19	#include <net/ipv6.h>
37c08387	20	#include <net/route.h>
cdd289a2 PM	21	#include <net/tcp.h>
	22
	23	#include <linux/netfilter_ipv4/ip_tables.h>
	24	#include <linux/netfilter_ipv6/ip6_tables.h>
	25	#include <linux/netfilter/x_tables.h>
	26	#include <linux/netfilter/xt_tcpudp.h>
	27	#include <linux/netfilter/xt_TCPMSS.h>
	28
	29	MODULE_LICENSE("GPL");
	30	MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
2ae15b64	31	MODULE_DESCRIPTION("Xtables: TCP Maximum Segment Size (MSS) adjustment");
cdd289a2 PM	32	MODULE_ALIAS("ipt_TCPMSS");
	33	MODULE_ALIAS("ip6t_TCPMSS");
	34
	35	static inline unsigned int
	36	optlen(const u_int8_t *opt, unsigned int offset)
	37	{
	38	/* Beware zero-length options: make finite progress */
	39	if (opt[offset] <= TCPOPT_NOP \|\| opt[offset+1] == 0)
	40	return 1;
	41	else
	42	return opt[offset+1];
	43	}
	44
	45	static int
3db05fea	46	tcpmss_mangle_packet(struct sk_buff *skb,
cdd289a2	47	const struct xt_tcpmss_info *info,
37c08387	48	unsigned int in_mtu,
cdd289a2 PM	49	unsigned int tcphoff,
	50	unsigned int minlen)
	51	{
	52	struct tcphdr *tcph;
	53	unsigned int tcplen, i;
	54	__be16 oldval;
	55	u16 newmss;
	56	u8 *opt;
	57
3db05fea	58	if (!skb_make_writable(skb, skb->len))
cdd289a2 PM	59	return -1;
cdd289a2 PM	60
3db05fea HX	61	tcplen = skb->len - tcphoff;
3db05fea HX	62	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
cdd289a2	63
10a19939 SA	64	/* Header cannot be larger than the packet */
10a19939 SA	65	if (tcplen < tcph->doff*4)
cdd289a2	66	return -1;
cdd289a2 PM	67
cdd289a2 PM	68	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
adf30907	69	if (dst_mtu(skb_dst(skb)) <= minlen) {
cdd289a2	70	if (net_ratelimit())
ff67e4e4	71	pr_err("unknown or invalid path-MTU (%u)\n",
adf30907	72	dst_mtu(skb_dst(skb)));
cdd289a2 PM	73	return -1;
cdd289a2 PM	74	}
37c08387 JE	75	if (in_mtu <= minlen) {
37c08387 JE	76	if (net_ratelimit())
ff67e4e4 JE	77	pr_err("unknown or invalid path-MTU (%u)\n",
ff67e4e4 JE	78	in_mtu);
37c08387 JE	79	return -1;
37c08387 JE	80	}
adf30907	81	newmss = min(dst_mtu(skb_dst(skb)), in_mtu) - minlen;
cdd289a2 PM	82	} else
	83	newmss = info->mss;
	84
	85	opt = (u_int8_t *)tcph;
	86	for (i = sizeof(struct tcphdr); i < tcph->doff*4; i += optlen(opt, i)) {
	87	if (opt[i] == TCPOPT_MSS && tcph->doff*4 - i >= TCPOLEN_MSS &&
	88	opt[i+1] == TCPOLEN_MSS) {
	89	u_int16_t oldmss;
	90
	91	oldmss = (opt[i+2] << 8) \| opt[i+3];
	92
17008064 BL	93	/* Never increase MSS, even when setting it, as
	94	* doing so results in problems for hosts that rely
	95	* on MSS being set correctly.
	96	*/
	97	if (oldmss <= newmss)
cdd289a2 PM	98	return 0;
	99
	100	opt[i+2] = (newmss & 0xff00) >> 8;
7c4e36bc	101	opt[i+3] = newmss & 0x00ff;
cdd289a2	102
be0ea7d5 PM	103	inet_proto_csum_replace2(&tcph->check, skb,
	104	htons(oldmss), htons(newmss),
	105	0);
cdd289a2 PM	106	return 0;
	107	}
	108	}
	109
10a19939 SA	110	/* There is data after the header so the option can't be added
	111	without moving it, and doing so may make the SYN packet
	112	itself too large. Accept the packet unmodified instead. */
	113	if (tcplen > tcph->doff*4)
	114	return 0;
	115
cdd289a2 PM	116	/*
	117	* MSS Option not found ?! add it..
	118	*/
3db05fea HX	119	if (skb_tailroom(skb) < TCPOLEN_MSS) {
	120	if (pskb_expand_head(skb, 0,
	121	TCPOLEN_MSS - skb_tailroom(skb),
2ca7b0ac	122	GFP_ATOMIC))
cdd289a2	123	return -1;
3db05fea	124	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
cdd289a2 PM	125	}
cdd289a2 PM	126
3db05fea	127	skb_put(skb, TCPOLEN_MSS);
cdd289a2 PM	128
	129	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
	130	memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));
	131
be0ea7d5 PM	132	inet_proto_csum_replace2(&tcph->check, skb,
be0ea7d5 PM	133	htons(tcplen), htons(tcplen + TCPOLEN_MSS), 1);
cdd289a2 PM	134	opt[0] = TCPOPT_MSS;
	135	opt[1] = TCPOLEN_MSS;
	136	opt[2] = (newmss & 0xff00) >> 8;
7c4e36bc	137	opt[3] = newmss & 0x00ff;
cdd289a2	138
be0ea7d5	139	inet_proto_csum_replace4(&tcph->check, skb, 0, ((__be32 )opt), 0);
cdd289a2 PM	140
	141	oldval = ((__be16 *)tcph)[6];
	142	tcph->doff += TCPOLEN_MSS/4;
be0ea7d5 PM	143	inet_proto_csum_replace2(&tcph->check, skb,
be0ea7d5 PM	144	oldval, ((__be16 *)tcph)[6], 0);
cdd289a2 PM	145	return TCPOLEN_MSS;
	146	}
	147
db1a75bd JE	148	static u_int32_t tcpmss_reverse_mtu(const struct sk_buff *skb,
db1a75bd JE	149	unsigned int family)
37c08387	150	{
db1a75bd	151	struct flowi fl = {};
37c08387 JE	152	const struct nf_afinfo *ai;
	153	struct rtable *rt = NULL;
	154	u_int32_t mtu = ~0U;
	155
db1a75bd JE	156	if (family == PF_INET)
	157	fl.fl4_dst = ip_hdr(skb)->saddr;
	158	else
	159	fl.fl6_dst = ipv6_hdr(skb)->saddr;
	160
37c08387	161	rcu_read_lock();
db1a75bd	162	ai = nf_get_afinfo(family);
37c08387 JE	163	if (ai != NULL)
	164	ai->route((struct dst_entry **)&rt, &fl);
	165	rcu_read_unlock();
	166
	167	if (rt != NULL) {
d8d1f30b CG	168	mtu = dst_mtu(&rt->dst);
d8d1f30b CG	169	dst_release(&rt->dst);
37c08387 JE	170	}
	171	return mtu;
	172	}
	173
cdd289a2	174	static unsigned int
4b560b44	175	tcpmss_tg4(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	176	{
3db05fea	177	struct iphdr *iph = ip_hdr(skb);
cdd289a2 PM	178	__be16 newlen;
	179	int ret;
	180
7eb35586	181	ret = tcpmss_mangle_packet(skb, par->targinfo,
db1a75bd	182	tcpmss_reverse_mtu(skb, PF_INET),
37c08387	183	iph->ihl * 4,
cdd289a2 PM	184	sizeof(*iph) + sizeof(struct tcphdr));
	185	if (ret < 0)
	186	return NF_DROP;
	187	if (ret > 0) {
3db05fea	188	iph = ip_hdr(skb);
cdd289a2	189	newlen = htons(ntohs(iph->tot_len) + ret);
be0ea7d5	190	csum_replace2(&iph->check, iph->tot_len, newlen);
cdd289a2 PM	191	iph->tot_len = newlen;
	192	}
	193	return XT_CONTINUE;
	194	}
	195
	196	#if defined(CONFIG_IP6_NF_IPTABLES) \|\| defined(CONFIG_IP6_NF_IPTABLES_MODULE)
	197	static unsigned int
4b560b44	198	tcpmss_tg6(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	199	{
3db05fea	200	struct ipv6hdr *ipv6h = ipv6_hdr(skb);
cdd289a2 PM	201	u8 nexthdr;
	202	int tcphoff;
	203	int ret;
	204
	205	nexthdr = ipv6h->nexthdr;
3db05fea	206	tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr);
9dc0564e	207	if (tcphoff < 0)
cdd289a2	208	return NF_DROP;
7eb35586	209	ret = tcpmss_mangle_packet(skb, par->targinfo,
db1a75bd	210	tcpmss_reverse_mtu(skb, PF_INET6),
37c08387	211	tcphoff,
cdd289a2 PM	212	sizeof(*ipv6h) + sizeof(struct tcphdr));
	213	if (ret < 0)
	214	return NF_DROP;
	215	if (ret > 0) {
3db05fea	216	ipv6h = ipv6_hdr(skb);
cdd289a2 PM	217	ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret);
	218	}
	219	return XT_CONTINUE;
	220	}
	221	#endif
	222
	223	#define TH_SYN 0x02
	224
	225	/* Must specify -p tcp --syn */
e1931b78	226	static inline bool find_syn_match(const struct xt_entry_match *m)
cdd289a2 PM	227	{
	228	const struct xt_tcp tcpinfo = (const struct xt_tcp )m->data;
	229
	230	if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
	231	tcpinfo->flg_cmp & TH_SYN &&
	232	!(tcpinfo->invflags & XT_TCP_INV_FLAGS))
e1931b78	233	return true;
cdd289a2	234
e1931b78	235	return false;
cdd289a2 PM	236	}
cdd289a2 PM	237
135367b8	238	static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
cdd289a2	239	{
af5d6dc2 JE	240	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	241	const struct ipt_entry *e = par->entryinfo;
dcea992a	242	const struct xt_entry_match *ematch;
cdd289a2 PM	243
cdd289a2 PM	244	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	245	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	246	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	247	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	248	pr_info("path-MTU clamping only supported in "
8bee4bad JE	249	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	250	return -EINVAL;
cdd289a2	251	}
dcea992a JE	252	xt_ematch_foreach(ematch, e)
dcea992a JE	253	if (find_syn_match(ematch))
d6b00a53	254	return 0;
8bee4bad	255	pr_info("Only works on TCP SYN packets\n");
d6b00a53	256	return -EINVAL;
cdd289a2 PM	257	}
	258
	259	#if defined(CONFIG_IP6_NF_IPTABLES) \|\| defined(CONFIG_IP6_NF_IPTABLES_MODULE)
135367b8	260	static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
cdd289a2	261	{
af5d6dc2 JE	262	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	263	const struct ip6t_entry *e = par->entryinfo;
dcea992a	264	const struct xt_entry_match *ematch;
cdd289a2 PM	265
cdd289a2 PM	266	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	267	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	268	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	269	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	270	pr_info("path-MTU clamping only supported in "
8bee4bad JE	271	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	272	return -EINVAL;
cdd289a2	273	}
dcea992a JE	274	xt_ematch_foreach(ematch, e)
dcea992a JE	275	if (find_syn_match(ematch))
d6b00a53	276	return 0;
8bee4bad	277	pr_info("Only works on TCP SYN packets\n");
d6b00a53	278	return -EINVAL;
cdd289a2 PM	279	}
	280	#endif
	281
d3c5ee6d	282	static struct xt_target tcpmss_tg_reg[] __read_mostly = {
cdd289a2	283	{
ee999d8b	284	.family = NFPROTO_IPV4,
cdd289a2	285	.name = "TCPMSS",
d3c5ee6d JE	286	.checkentry = tcpmss_tg4_check,
d3c5ee6d JE	287	.target = tcpmss_tg4,
cdd289a2 PM	288	.targetsize = sizeof(struct xt_tcpmss_info),
	289	.proto = IPPROTO_TCP,
	290	.me = THIS_MODULE,
	291	},
	292	#if defined(CONFIG_IP6_NF_IPTABLES) \|\| defined(CONFIG_IP6_NF_IPTABLES_MODULE)
	293	{
ee999d8b	294	.family = NFPROTO_IPV6,
cdd289a2	295	.name = "TCPMSS",
d3c5ee6d JE	296	.checkentry = tcpmss_tg6_check,
d3c5ee6d JE	297	.target = tcpmss_tg6,
cdd289a2 PM	298	.targetsize = sizeof(struct xt_tcpmss_info),
	299	.proto = IPPROTO_TCP,
	300	.me = THIS_MODULE,
	301	},
	302	#endif
	303	};
	304
d3c5ee6d	305	static int __init tcpmss_tg_init(void)
cdd289a2	306	{
d3c5ee6d	307	return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	308	}
cdd289a2 PM	309
d3c5ee6d	310	static void __exit tcpmss_tg_exit(void)
cdd289a2	311	{
d3c5ee6d	312	xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	313	}
cdd289a2 PM	314
d3c5ee6d JE	315	module_init(tcpmss_tg_init);
d3c5ee6d JE	316	module_exit(tcpmss_tg_exit);