[mirror_ubuntu-bionic-kernel.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 int
tcpmss_mangle_packet(struct sk_buff *skb,
		     const struct xt_action_param *par,
		     unsigned int in_mtu,
		     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 XT_CONTINUE;

	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) {
		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 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) {
		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(&init_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 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,
				   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 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,
				   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

/* 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
	46	static int
3db05fea	47	tcpmss_mangle_packet(struct sk_buff *skb,
70d19f80	48	const struct xt_action_param *par,
37c08387	49	unsigned int in_mtu,
cdd289a2 PM	50	unsigned int tcphoff,
	51	unsigned int minlen)
	52	{
70d19f80	53	const struct xt_tcpmss_info *info = par->targinfo;
cdd289a2	54	struct tcphdr *tcph;
71ffe9c7 PNA	55	int len, tcp_hdrlen;
71ffe9c7 PNA	56	unsigned int i;
cdd289a2 PM	57	__be16 oldval;
	58	u16 newmss;
	59	u8 *opt;
	60
b396966c PO	61	/* This is a fragment, no TCP header is available */
	62	if (par->fragoff != 0)
	63	return XT_CONTINUE;
	64
3db05fea	65	if (!skb_make_writable(skb, skb->len))
cdd289a2 PM	66	return -1;
cdd289a2 PM	67
71ffe9c7 PNA	68	len = skb->len - tcphoff;
	69	if (len < (int)sizeof(struct tcphdr))
	70	return -1;
	71
3db05fea	72	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
71ffe9c7	73	tcp_hdrlen = tcph->doff * 4;
cdd289a2	74
71ffe9c7	75	if (len < tcp_hdrlen)
cdd289a2	76	return -1;
cdd289a2 PM	77
cdd289a2 PM	78	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
adf30907	79	if (dst_mtu(skb_dst(skb)) <= minlen) {
e87cc472 JP	80	net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
e87cc472 JP	81	dst_mtu(skb_dst(skb)));
cdd289a2 PM	82	return -1;
cdd289a2 PM	83	}
37c08387	84	if (in_mtu <= minlen) {
e87cc472 JP	85	net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
e87cc472 JP	86	in_mtu);
37c08387 JE	87	return -1;
37c08387 JE	88	}
adf30907	89	newmss = min(dst_mtu(skb_dst(skb)), in_mtu) - minlen;
cdd289a2 PM	90	} else
	91	newmss = info->mss;
	92
	93	opt = (u_int8_t *)tcph;
71ffe9c7 PNA	94	for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
71ffe9c7 PNA	95	if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
cdd289a2 PM	96	u_int16_t oldmss;
	97
	98	oldmss = (opt[i+2] << 8) \| opt[i+3];
	99
17008064 BL	100	/* Never increase MSS, even when setting it, as
	101	* doing so results in problems for hosts that rely
	102	* on MSS being set correctly.
	103	*/
	104	if (oldmss <= newmss)
cdd289a2 PM	105	return 0;
	106
	107	opt[i+2] = (newmss & 0xff00) >> 8;
7c4e36bc	108	opt[i+3] = newmss & 0x00ff;
cdd289a2	109
be0ea7d5 PM	110	inet_proto_csum_replace2(&tcph->check, skb,
	111	htons(oldmss), htons(newmss),
	112	0);
cdd289a2 PM	113	return 0;
	114	}
	115	}
	116
10a19939	117	/* There is data after the header so the option can't be added
71ffe9c7 PNA	118	* without moving it, and doing so may make the SYN packet
	119	* itself too large. Accept the packet unmodified instead.
	120	*/
	121	if (len > tcp_hdrlen)
10a19939 SA	122	return 0;
10a19939 SA	123
cdd289a2 PM	124	/*
	125	* MSS Option not found ?! add it..
	126	*/
3db05fea HX	127	if (skb_tailroom(skb) < TCPOLEN_MSS) {
	128	if (pskb_expand_head(skb, 0,
	129	TCPOLEN_MSS - skb_tailroom(skb),
2ca7b0ac	130	GFP_ATOMIC))
cdd289a2	131	return -1;
3db05fea	132	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
cdd289a2 PM	133	}
cdd289a2 PM	134
3db05fea	135	skb_put(skb, TCPOLEN_MSS);
cdd289a2	136
70d19f80 PO	137	/*
	138	* IPv4: RFC 1122 states "If an MSS option is not received at
	139	* connection setup, TCP MUST assume a default send MSS of 536".
	140	* IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
	141	* length IPv6 header of 60, ergo the default MSS value is 1220
	142	* Since no MSS was provided, we must use the default values
409b545a	143	*/
70d19f80 PO	144	if (par->family == NFPROTO_IPV4)
	145	newmss = min(newmss, (u16)536);
	146	else
	147	newmss = min(newmss, (u16)1220);
409b545a	148
cdd289a2	149	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
71ffe9c7	150	memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
cdd289a2	151
be0ea7d5	152	inet_proto_csum_replace2(&tcph->check, skb,
71ffe9c7	153	htons(len), htons(len + TCPOLEN_MSS), 1);
cdd289a2 PM	154	opt[0] = TCPOPT_MSS;
	155	opt[1] = TCPOLEN_MSS;
	156	opt[2] = (newmss & 0xff00) >> 8;
7c4e36bc	157	opt[3] = newmss & 0x00ff;
cdd289a2	158
be0ea7d5	159	inet_proto_csum_replace4(&tcph->check, skb, 0, ((__be32 )opt), 0);
cdd289a2 PM	160
	161	oldval = ((__be16 *)tcph)[6];
	162	tcph->doff += TCPOLEN_MSS/4;
be0ea7d5 PM	163	inet_proto_csum_replace2(&tcph->check, skb,
be0ea7d5 PM	164	oldval, ((__be16 *)tcph)[6], 0);
cdd289a2 PM	165	return TCPOLEN_MSS;
	166	}
	167
db1a75bd JE	168	static u_int32_t tcpmss_reverse_mtu(const struct sk_buff *skb,
db1a75bd JE	169	unsigned int family)
37c08387	170	{
a1bbb0e6	171	struct flowi fl;
37c08387 JE	172	const struct nf_afinfo *ai;
	173	struct rtable *rt = NULL;
	174	u_int32_t mtu = ~0U;
	175
a1bbb0e6 DM	176	if (family == PF_INET) {
	177	struct flowi4 *fl4 = &fl.u.ip4;
	178	memset(fl4, 0, sizeof(*fl4));
	179	fl4->daddr = ip_hdr(skb)->saddr;
	180	} else {
	181	struct flowi6 *fl6 = &fl.u.ip6;
db1a75bd	182
a1bbb0e6	183	memset(fl6, 0, sizeof(*fl6));
4e3fd7a0	184	fl6->daddr = ipv6_hdr(skb)->saddr;
a1bbb0e6	185	}
37c08387	186	rcu_read_lock();
db1a75bd	187	ai = nf_get_afinfo(family);
37c08387	188	if (ai != NULL)
0fae2e77	189	ai->route(&init_net, (struct dst_entry **)&rt, &fl, false);
37c08387 JE	190	rcu_read_unlock();
	191
	192	if (rt != NULL) {
d8d1f30b CG	193	mtu = dst_mtu(&rt->dst);
d8d1f30b CG	194	dst_release(&rt->dst);
37c08387 JE	195	}
	196	return mtu;
	197	}
	198
cdd289a2	199	static unsigned int
4b560b44	200	tcpmss_tg4(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	201	{
3db05fea	202	struct iphdr *iph = ip_hdr(skb);
cdd289a2 PM	203	__be16 newlen;
	204	int ret;
	205
70d19f80	206	ret = tcpmss_mangle_packet(skb, par,
db1a75bd	207	tcpmss_reverse_mtu(skb, PF_INET),
37c08387	208	iph->ihl * 4,
cdd289a2 PM	209	sizeof(*iph) + sizeof(struct tcphdr));
	210	if (ret < 0)
	211	return NF_DROP;
	212	if (ret > 0) {
3db05fea	213	iph = ip_hdr(skb);
cdd289a2	214	newlen = htons(ntohs(iph->tot_len) + ret);
be0ea7d5	215	csum_replace2(&iph->check, iph->tot_len, newlen);
cdd289a2 PM	216	iph->tot_len = newlen;
	217	}
	218	return XT_CONTINUE;
	219	}
	220
c0cd1156	221	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	222	static unsigned int
4b560b44	223	tcpmss_tg6(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	224	{
3db05fea	225	struct ipv6hdr *ipv6h = ipv6_hdr(skb);
cdd289a2	226	u8 nexthdr;
75f2811c	227	__be16 frag_off;
cdd289a2 PM	228	int tcphoff;
	229	int ret;
	230
	231	nexthdr = ipv6h->nexthdr;
75f2811c	232	tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
9dc0564e	233	if (tcphoff < 0)
cdd289a2	234	return NF_DROP;
70d19f80	235	ret = tcpmss_mangle_packet(skb, par,
db1a75bd	236	tcpmss_reverse_mtu(skb, PF_INET6),
37c08387	237	tcphoff,
cdd289a2 PM	238	sizeof(*ipv6h) + sizeof(struct tcphdr));
	239	if (ret < 0)
	240	return NF_DROP;
	241	if (ret > 0) {
3db05fea	242	ipv6h = ipv6_hdr(skb);
cdd289a2 PM	243	ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret);
	244	}
	245	return XT_CONTINUE;
	246	}
	247	#endif
	248
cdd289a2	249	/* Must specify -p tcp --syn */
e1931b78	250	static inline bool find_syn_match(const struct xt_entry_match *m)
cdd289a2 PM	251	{
	252	const struct xt_tcp tcpinfo = (const struct xt_tcp )m->data;
	253
	254	if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
a3433f35	255	tcpinfo->flg_cmp & TCPHDR_SYN &&
cdd289a2	256	!(tcpinfo->invflags & XT_TCP_INV_FLAGS))
e1931b78	257	return true;
cdd289a2	258
e1931b78	259	return false;
cdd289a2 PM	260	}
cdd289a2 PM	261
135367b8	262	static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
cdd289a2	263	{
af5d6dc2 JE	264	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	265	const struct ipt_entry *e = par->entryinfo;
dcea992a	266	const struct xt_entry_match *ematch;
cdd289a2 PM	267
cdd289a2 PM	268	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	269	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	270	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	271	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	272	pr_info("path-MTU clamping only supported in "
8bee4bad JE	273	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	274	return -EINVAL;
cdd289a2	275	}
dcea992a JE	276	xt_ematch_foreach(ematch, e)
dcea992a JE	277	if (find_syn_match(ematch))
d6b00a53	278	return 0;
8bee4bad	279	pr_info("Only works on TCP SYN packets\n");
d6b00a53	280	return -EINVAL;
cdd289a2 PM	281	}
cdd289a2 PM	282
c0cd1156	283	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
135367b8	284	static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
cdd289a2	285	{
af5d6dc2 JE	286	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	287	const struct ip6t_entry *e = par->entryinfo;
dcea992a	288	const struct xt_entry_match *ematch;
cdd289a2 PM	289
cdd289a2 PM	290	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	291	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	292	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	293	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	294	pr_info("path-MTU clamping only supported in "
8bee4bad JE	295	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	296	return -EINVAL;
cdd289a2	297	}
dcea992a JE	298	xt_ematch_foreach(ematch, e)
dcea992a JE	299	if (find_syn_match(ematch))
d6b00a53	300	return 0;
8bee4bad	301	pr_info("Only works on TCP SYN packets\n");
d6b00a53	302	return -EINVAL;
cdd289a2 PM	303	}
	304	#endif
	305
d3c5ee6d	306	static struct xt_target tcpmss_tg_reg[] __read_mostly = {
cdd289a2	307	{
ee999d8b	308	.family = NFPROTO_IPV4,
cdd289a2	309	.name = "TCPMSS",
d3c5ee6d JE	310	.checkentry = tcpmss_tg4_check,
d3c5ee6d JE	311	.target = tcpmss_tg4,
cdd289a2 PM	312	.targetsize = sizeof(struct xt_tcpmss_info),
	313	.proto = IPPROTO_TCP,
	314	.me = THIS_MODULE,
	315	},
c0cd1156	316	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	317	{
ee999d8b	318	.family = NFPROTO_IPV6,
cdd289a2	319	.name = "TCPMSS",
d3c5ee6d JE	320	.checkentry = tcpmss_tg6_check,
d3c5ee6d JE	321	.target = tcpmss_tg6,
cdd289a2 PM	322	.targetsize = sizeof(struct xt_tcpmss_info),
	323	.proto = IPPROTO_TCP,
	324	.me = THIS_MODULE,
	325	},
	326	#endif
	327	};
	328
d3c5ee6d	329	static int __init tcpmss_tg_init(void)
cdd289a2	330	{
d3c5ee6d	331	return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	332	}
cdd289a2 PM	333
d3c5ee6d	334	static void __exit tcpmss_tg_exit(void)
cdd289a2	335	{
d3c5ee6d	336	xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	337	}
cdd289a2 PM	338
d3c5ee6d JE	339	module_init(tcpmss_tg_init);
d3c5ee6d JE	340	module_exit(tcpmss_tg_exit);