[linux-2.6-block.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>
 * Copyright (C) 2007 Patrick McHardy <kaber@trash.net>
 *
 * 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 u_int32_t tcpmss_reverse_mtu(struct net *net,
				    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) {
		struct flowi4 *fl4 = &fl.u.ip4;
		memset(fl4, 0, sizeof(*fl4));
		fl4->daddr = ip_hdr(skb)->saddr;
	} else {
		struct flowi6 *fl6 = &fl.u.ip6;

		memset(fl6, 0, sizeof(*fl6));
		fl6->daddr = ipv6_hdr(skb)->saddr;
	}
	rcu_read_lock();
	ai = nf_get_afinfo(family);
	if (ai != NULL)
		ai->route(net, (struct dst_entry **)&rt, &fl, false);
	rcu_read_unlock();

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

static int
tcpmss_mangle_packet(struct sk_buff *skb,
		     const struct xt_action_param *par,
		     unsigned int family,
		     unsigned int tcphoff,
		     unsigned int minlen)
{
	const struct xt_tcpmss_info *info = par->targinfo;
	struct tcphdr *tcph;
	int len, tcp_hdrlen;
	unsigned int i;
	__be16 oldval;
	u16 newmss;
	u8 *opt;

	/* This is a fragment, no TCP header is available */
	if (par->fragoff != 0)
		return 0;

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

	len = skb->len - tcphoff;
	if (len < (int)sizeof(struct tcphdr))
		return -1;

	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
	tcp_hdrlen = tcph->doff * 4;

	if (len < tcp_hdrlen)
		return -1;

	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
		struct net *net = dev_net(par->in ? par->in : par->out);
		unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);

		if (dst_mtu(skb_dst(skb)) <= minlen) {
			net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
					    dst_mtu(skb_dst(skb)));
			return -1;
		}
		if (in_mtu <= minlen) {
			net_err_ratelimited("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 <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
		if (opt[i] == TCPOPT_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 (len > tcp_hdrlen)
		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);

	/*
	 * IPv4: RFC 1122 states "If an MSS option is not received at
	 * connection setup, TCP MUST assume a default send MSS of 536".
	 * IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
	 * length IPv6 header of 60, ergo the default MSS value is 1220
	 * Since no MSS was provided, we must use the default values
	 */
	if (par->family == NFPROTO_IPV4)
		newmss = min(newmss, (u16)536);
	else
		newmss = min(newmss, (u16)1220);

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

	inet_proto_csum_replace2(&tcph->check, skb,
				 htons(len), htons(len + 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 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,
				   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 IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
static unsigned int
tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
{
	struct ipv6hdr *ipv6h = ipv6_hdr(skb);
	u8 nexthdr;
	__be16 frag_off;
	int tcphoff;
	int ret;

	nexthdr = ipv6h->nexthdr;
	tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
	if (tcphoff < 0)
		return NF_DROP;
	ret = tcpmss_mangle_packet(skb, par,
				   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

/* 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 & TCPHDR_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 IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
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 IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
	{
		.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>
f229f6ce	5	* Copyright (C) 2007 Patrick McHardy <kaber@trash.net>
cdd289a2 PM	6	*
	7	* This program is free software; you can redistribute it and/or modify
	8	* it under the terms of the GNU General Public License version 2 as
	9	* published by the Free Software Foundation.
	10	*/
8bee4bad	11	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
cdd289a2 PM	12	#include <linux/module.h>
	13	#include <linux/skbuff.h>
	14	#include <linux/ip.h>
5a0e3ad6	15	#include <linux/gfp.h>
cdd289a2 PM	16	#include <linux/ipv6.h>
cdd289a2 PM	17	#include <linux/tcp.h>
37c08387 JE	18	#include <net/dst.h>
37c08387 JE	19	#include <net/flow.h>
cdd289a2	20	#include <net/ipv6.h>
37c08387	21	#include <net/route.h>
cdd289a2 PM	22	#include <net/tcp.h>
	23
	24	#include <linux/netfilter_ipv4/ip_tables.h>
	25	#include <linux/netfilter_ipv6/ip6_tables.h>
	26	#include <linux/netfilter/x_tables.h>
	27	#include <linux/netfilter/xt_tcpudp.h>
	28	#include <linux/netfilter/xt_TCPMSS.h>
	29
	30	MODULE_LICENSE("GPL");
	31	MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
2ae15b64	32	MODULE_DESCRIPTION("Xtables: TCP Maximum Segment Size (MSS) adjustment");
cdd289a2 PM	33	MODULE_ALIAS("ipt_TCPMSS");
	34	MODULE_ALIAS("ip6t_TCPMSS");
	35
	36	static inline unsigned int
	37	optlen(const u_int8_t *opt, unsigned int offset)
	38	{
	39	/* Beware zero-length options: make finite progress */
	40	if (opt[offset] <= TCPOPT_NOP \|\| opt[offset+1] == 0)
	41	return 1;
	42	else
	43	return opt[offset+1];
	44	}
	45
7722e0d1 G	46	static u_int32_t tcpmss_reverse_mtu(struct net *net,
7722e0d1 G	47	const struct sk_buff *skb,
de1389b1 G	48	unsigned int family)
	49	{
	50	struct flowi fl;
	51	const struct nf_afinfo *ai;
	52	struct rtable *rt = NULL;
	53	u_int32_t mtu = ~0U;
	54
	55	if (family == PF_INET) {
	56	struct flowi4 *fl4 = &fl.u.ip4;
	57	memset(fl4, 0, sizeof(*fl4));
	58	fl4->daddr = ip_hdr(skb)->saddr;
	59	} else {
	60	struct flowi6 *fl6 = &fl.u.ip6;
	61
	62	memset(fl6, 0, sizeof(*fl6));
	63	fl6->daddr = ipv6_hdr(skb)->saddr;
	64	}
	65	rcu_read_lock();
	66	ai = nf_get_afinfo(family);
	67	if (ai != NULL)
7722e0d1	68	ai->route(net, (struct dst_entry **)&rt, &fl, false);
de1389b1 G	69	rcu_read_unlock();
	70
	71	if (rt != NULL) {
	72	mtu = dst_mtu(&rt->dst);
	73	dst_release(&rt->dst);
	74	}
	75	return mtu;
	76	}
	77
cdd289a2	78	static int
3db05fea	79	tcpmss_mangle_packet(struct sk_buff *skb,
70d19f80	80	const struct xt_action_param *par,
de1389b1	81	unsigned int family,
cdd289a2 PM	82	unsigned int tcphoff,
	83	unsigned int minlen)
	84	{
70d19f80	85	const struct xt_tcpmss_info *info = par->targinfo;
cdd289a2	86	struct tcphdr *tcph;
71ffe9c7 PNA	87	int len, tcp_hdrlen;
71ffe9c7 PNA	88	unsigned int i;
cdd289a2 PM	89	__be16 oldval;
	90	u16 newmss;
	91	u8 *opt;
	92
b396966c PO	93	/* This is a fragment, no TCP header is available */
b396966c PO	94	if (par->fragoff != 0)
1205e1fa	95	return 0;
b396966c	96
3db05fea	97	if (!skb_make_writable(skb, skb->len))
cdd289a2 PM	98	return -1;
cdd289a2 PM	99
71ffe9c7 PNA	100	len = skb->len - tcphoff;
	101	if (len < (int)sizeof(struct tcphdr))
	102	return -1;
	103
3db05fea	104	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
71ffe9c7	105	tcp_hdrlen = tcph->doff * 4;
cdd289a2	106
71ffe9c7	107	if (len < tcp_hdrlen)
cdd289a2	108	return -1;
cdd289a2 PM	109
cdd289a2 PM	110	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
7722e0d1 G	111	struct net *net = dev_net(par->in ? par->in : par->out);
7722e0d1 G	112	unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
de1389b1	113
adf30907	114	if (dst_mtu(skb_dst(skb)) <= minlen) {
e87cc472 JP	115	net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
e87cc472 JP	116	dst_mtu(skb_dst(skb)));
cdd289a2 PM	117	return -1;
cdd289a2 PM	118	}
37c08387	119	if (in_mtu <= minlen) {
e87cc472 JP	120	net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
e87cc472 JP	121	in_mtu);
37c08387 JE	122	return -1;
37c08387 JE	123	}
adf30907	124	newmss = min(dst_mtu(skb_dst(skb)), in_mtu) - minlen;
cdd289a2 PM	125	} else
	126	newmss = info->mss;
	127
	128	opt = (u_int8_t *)tcph;
71ffe9c7 PNA	129	for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
71ffe9c7 PNA	130	if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
cdd289a2 PM	131	u_int16_t oldmss;
	132
	133	oldmss = (opt[i+2] << 8) \| opt[i+3];
	134
17008064 BL	135	/* Never increase MSS, even when setting it, as
	136	* doing so results in problems for hosts that rely
	137	* on MSS being set correctly.
	138	*/
	139	if (oldmss <= newmss)
cdd289a2 PM	140	return 0;
	141
	142	opt[i+2] = (newmss & 0xff00) >> 8;
7c4e36bc	143	opt[i+3] = newmss & 0x00ff;
cdd289a2	144
be0ea7d5 PM	145	inet_proto_csum_replace2(&tcph->check, skb,
	146	htons(oldmss), htons(newmss),
	147	0);
cdd289a2 PM	148	return 0;
	149	}
	150	}
	151
10a19939	152	/* There is data after the header so the option can't be added
71ffe9c7 PNA	153	* without moving it, and doing so may make the SYN packet
	154	* itself too large. Accept the packet unmodified instead.
	155	*/
	156	if (len > tcp_hdrlen)
10a19939 SA	157	return 0;
10a19939 SA	158
cdd289a2 PM	159	/*
	160	* MSS Option not found ?! add it..
	161	*/
3db05fea HX	162	if (skb_tailroom(skb) < TCPOLEN_MSS) {
	163	if (pskb_expand_head(skb, 0,
	164	TCPOLEN_MSS - skb_tailroom(skb),
2ca7b0ac	165	GFP_ATOMIC))
cdd289a2	166	return -1;
3db05fea	167	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
cdd289a2 PM	168	}
cdd289a2 PM	169
3db05fea	170	skb_put(skb, TCPOLEN_MSS);
cdd289a2	171
70d19f80 PO	172	/*
	173	* IPv4: RFC 1122 states "If an MSS option is not received at
	174	* connection setup, TCP MUST assume a default send MSS of 536".
	175	* IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
	176	* length IPv6 header of 60, ergo the default MSS value is 1220
	177	* Since no MSS was provided, we must use the default values
409b545a	178	*/
70d19f80 PO	179	if (par->family == NFPROTO_IPV4)
	180	newmss = min(newmss, (u16)536);
	181	else
	182	newmss = min(newmss, (u16)1220);
409b545a	183
cdd289a2	184	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
71ffe9c7	185	memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
cdd289a2	186
be0ea7d5	187	inet_proto_csum_replace2(&tcph->check, skb,
71ffe9c7	188	htons(len), htons(len + TCPOLEN_MSS), 1);
cdd289a2 PM	189	opt[0] = TCPOPT_MSS;
	190	opt[1] = TCPOLEN_MSS;
	191	opt[2] = (newmss & 0xff00) >> 8;
7c4e36bc	192	opt[3] = newmss & 0x00ff;
cdd289a2	193
be0ea7d5	194	inet_proto_csum_replace4(&tcph->check, skb, 0, ((__be32 )opt), 0);
cdd289a2 PM	195
	196	oldval = ((__be16 *)tcph)[6];
	197	tcph->doff += TCPOLEN_MSS/4;
be0ea7d5 PM	198	inet_proto_csum_replace2(&tcph->check, skb,
be0ea7d5 PM	199	oldval, ((__be16 *)tcph)[6], 0);
cdd289a2 PM	200	return TCPOLEN_MSS;
	201	}
	202
	203	static unsigned int
4b560b44	204	tcpmss_tg4(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	205	{
3db05fea	206	struct iphdr *iph = ip_hdr(skb);
cdd289a2 PM	207	__be16 newlen;
	208	int ret;
	209
70d19f80	210	ret = tcpmss_mangle_packet(skb, par,
de1389b1	211	PF_INET,
37c08387	212	iph->ihl * 4,
cdd289a2 PM	213	sizeof(*iph) + sizeof(struct tcphdr));
	214	if (ret < 0)
	215	return NF_DROP;
	216	if (ret > 0) {
3db05fea	217	iph = ip_hdr(skb);
cdd289a2	218	newlen = htons(ntohs(iph->tot_len) + ret);
be0ea7d5	219	csum_replace2(&iph->check, iph->tot_len, newlen);
cdd289a2 PM	220	iph->tot_len = newlen;
	221	}
	222	return XT_CONTINUE;
	223	}
	224
c0cd1156	225	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	226	static unsigned int
4b560b44	227	tcpmss_tg6(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	228	{
3db05fea	229	struct ipv6hdr *ipv6h = ipv6_hdr(skb);
cdd289a2	230	u8 nexthdr;
75f2811c	231	__be16 frag_off;
cdd289a2 PM	232	int tcphoff;
	233	int ret;
	234
	235	nexthdr = ipv6h->nexthdr;
75f2811c	236	tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
9dc0564e	237	if (tcphoff < 0)
cdd289a2	238	return NF_DROP;
70d19f80	239	ret = tcpmss_mangle_packet(skb, par,
de1389b1	240	PF_INET6,
37c08387	241	tcphoff,
cdd289a2 PM	242	sizeof(*ipv6h) + sizeof(struct tcphdr));
	243	if (ret < 0)
	244	return NF_DROP;
	245	if (ret > 0) {
3db05fea	246	ipv6h = ipv6_hdr(skb);
cdd289a2 PM	247	ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret);
	248	}
	249	return XT_CONTINUE;
	250	}
	251	#endif
	252
cdd289a2	253	/* Must specify -p tcp --syn */
e1931b78	254	static inline bool find_syn_match(const struct xt_entry_match *m)
cdd289a2 PM	255	{
	256	const struct xt_tcp tcpinfo = (const struct xt_tcp )m->data;
	257
	258	if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
a3433f35	259	tcpinfo->flg_cmp & TCPHDR_SYN &&
cdd289a2	260	!(tcpinfo->invflags & XT_TCP_INV_FLAGS))
e1931b78	261	return true;
cdd289a2	262
e1931b78	263	return false;
cdd289a2 PM	264	}
cdd289a2 PM	265
135367b8	266	static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
cdd289a2	267	{
af5d6dc2 JE	268	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	269	const struct ipt_entry *e = par->entryinfo;
dcea992a	270	const struct xt_entry_match *ematch;
cdd289a2 PM	271
cdd289a2 PM	272	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	273	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	274	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	275	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	276	pr_info("path-MTU clamping only supported in "
8bee4bad JE	277	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	278	return -EINVAL;
cdd289a2	279	}
dcea992a JE	280	xt_ematch_foreach(ematch, e)
dcea992a JE	281	if (find_syn_match(ematch))
d6b00a53	282	return 0;
8bee4bad	283	pr_info("Only works on TCP SYN packets\n");
d6b00a53	284	return -EINVAL;
cdd289a2 PM	285	}
cdd289a2 PM	286
c0cd1156	287	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
135367b8	288	static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
cdd289a2	289	{
af5d6dc2 JE	290	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	291	const struct ip6t_entry *e = par->entryinfo;
dcea992a	292	const struct xt_entry_match *ematch;
cdd289a2 PM	293
cdd289a2 PM	294	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	295	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	296	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	297	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	298	pr_info("path-MTU clamping only supported in "
8bee4bad JE	299	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	300	return -EINVAL;
cdd289a2	301	}
dcea992a JE	302	xt_ematch_foreach(ematch, e)
dcea992a JE	303	if (find_syn_match(ematch))
d6b00a53	304	return 0;
8bee4bad	305	pr_info("Only works on TCP SYN packets\n");
d6b00a53	306	return -EINVAL;
cdd289a2 PM	307	}
	308	#endif
	309
d3c5ee6d	310	static struct xt_target tcpmss_tg_reg[] __read_mostly = {
cdd289a2	311	{
ee999d8b	312	.family = NFPROTO_IPV4,
cdd289a2	313	.name = "TCPMSS",
d3c5ee6d JE	314	.checkentry = tcpmss_tg4_check,
d3c5ee6d JE	315	.target = tcpmss_tg4,
cdd289a2 PM	316	.targetsize = sizeof(struct xt_tcpmss_info),
	317	.proto = IPPROTO_TCP,
	318	.me = THIS_MODULE,
	319	},
c0cd1156	320	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	321	{
ee999d8b	322	.family = NFPROTO_IPV6,
cdd289a2	323	.name = "TCPMSS",
d3c5ee6d JE	324	.checkentry = tcpmss_tg6_check,
d3c5ee6d JE	325	.target = tcpmss_tg6,
cdd289a2 PM	326	.targetsize = sizeof(struct xt_tcpmss_info),
	327	.proto = IPPROTO_TCP,
	328	.me = THIS_MODULE,
	329	},
	330	#endif
	331	};
	332
d3c5ee6d	333	static int __init tcpmss_tg_init(void)
cdd289a2	334	{
d3c5ee6d	335	return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	336	}
cdd289a2 PM	337
d3c5ee6d	338	static void __exit tcpmss_tg_exit(void)
cdd289a2	339	{
d3c5ee6d	340	xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	341	}
cdd289a2 PM	342
d3c5ee6d JE	343	module_init(tcpmss_tg_init);
d3c5ee6d JE	344	module_exit(tcpmss_tg_exit);