[GitHub/mt8127/android_kernel_alcatel_ttab.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;
	unsigned int tcplen, 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;

	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) {
			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 < 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);

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