[mirror_ubuntu-jammy-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 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 = xt_net(par);
		unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
		unsigned int min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu);

		if (min_mtu <= minlen) {
			net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
					    min_mtu);
			return -1;
		}
		newmss = min_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),
						 false);
			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 (xt_family(par) == 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), true);
	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), false);

	oldval = ((__be16 *)tcph)[6];
	tcph->doff += TCPOLEN_MSS/4;
	inet_proto_csum_replace2(&tcph->check, skb,
				 oldval, ((__be16 *)tcph)[6], false);
	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, oldlen, newlen;
	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);
		oldlen = ipv6h->payload_len;
		newlen = htons(ntohs(oldlen) + ret);
		if (skb->ip_summed == CHECKSUM_COMPLETE)
			skb->csum = csum_add(csum_sub(skb->csum, oldlen),
					     newlen);
		ipv6h->payload_len = newlen;
	}
	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;
	}
	if (par->nft_compat)
		return 0;

	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;
	}
	if (par->nft_compat)
		return 0;

	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) {
613dbd95	111	struct net *net = xt_net(par);
7722e0d1	112	unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
50f4c7b7	113	unsigned int min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu);
de1389b1	114
50f4c7b7	115	if (min_mtu <= minlen) {
e87cc472	116	net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
50f4c7b7	117	min_mtu);
cdd289a2 PM	118	return -1;
cdd289a2 PM	119	}
50f4c7b7	120	newmss = min_mtu - minlen;
cdd289a2 PM	121	} else
	122	newmss = info->mss;
	123
	124	opt = (u_int8_t *)tcph;
71ffe9c7 PNA	125	for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
71ffe9c7 PNA	126	if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
cdd289a2 PM	127	u_int16_t oldmss;
	128
	129	oldmss = (opt[i+2] << 8) \| opt[i+3];
	130
17008064 BL	131	/* Never increase MSS, even when setting it, as
	132	* doing so results in problems for hosts that rely
	133	* on MSS being set correctly.
	134	*/
	135	if (oldmss <= newmss)
cdd289a2 PM	136	return 0;
	137
	138	opt[i+2] = (newmss & 0xff00) >> 8;
7c4e36bc	139	opt[i+3] = newmss & 0x00ff;
cdd289a2	140
be0ea7d5 PM	141	inet_proto_csum_replace2(&tcph->check, skb,
be0ea7d5 PM	142	htons(oldmss), htons(newmss),
4b048d6d	143	false);
cdd289a2 PM	144	return 0;
	145	}
	146	}
	147
10a19939	148	/* There is data after the header so the option can't be added
71ffe9c7 PNA	149	* without moving it, and doing so may make the SYN packet
	150	* itself too large. Accept the packet unmodified instead.
	151	*/
	152	if (len > tcp_hdrlen)
10a19939 SA	153	return 0;
10a19939 SA	154
cdd289a2 PM	155	/*
	156	* MSS Option not found ?! add it..
	157	*/
3db05fea HX	158	if (skb_tailroom(skb) < TCPOLEN_MSS) {
	159	if (pskb_expand_head(skb, 0,
	160	TCPOLEN_MSS - skb_tailroom(skb),
2ca7b0ac	161	GFP_ATOMIC))
cdd289a2	162	return -1;
3db05fea	163	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
cdd289a2 PM	164	}
cdd289a2 PM	165
3db05fea	166	skb_put(skb, TCPOLEN_MSS);
cdd289a2	167
70d19f80 PO	168	/*
	169	* IPv4: RFC 1122 states "If an MSS option is not received at
	170	* connection setup, TCP MUST assume a default send MSS of 536".
	171	* IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
	172	* length IPv6 header of 60, ergo the default MSS value is 1220
	173	* Since no MSS was provided, we must use the default values
409b545a	174	*/
613dbd95	175	if (xt_family(par) == NFPROTO_IPV4)
70d19f80 PO	176	newmss = min(newmss, (u16)536);
	177	else
	178	newmss = min(newmss, (u16)1220);
409b545a	179
cdd289a2	180	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
71ffe9c7	181	memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
cdd289a2	182
be0ea7d5	183	inet_proto_csum_replace2(&tcph->check, skb,
4b048d6d	184	htons(len), htons(len + TCPOLEN_MSS), true);
cdd289a2 PM	185	opt[0] = TCPOPT_MSS;
	186	opt[1] = TCPOLEN_MSS;
	187	opt[2] = (newmss & 0xff00) >> 8;
7c4e36bc	188	opt[3] = newmss & 0x00ff;
cdd289a2	189
4b048d6d	190	inet_proto_csum_replace4(&tcph->check, skb, 0, ((__be32 )opt), false);
cdd289a2 PM	191
	192	oldval = ((__be16 *)tcph)[6];
	193	tcph->doff += TCPOLEN_MSS/4;
be0ea7d5	194	inet_proto_csum_replace2(&tcph->check, skb,
4b048d6d	195	oldval, ((__be16 *)tcph)[6], false);
cdd289a2 PM	196	return TCPOLEN_MSS;
	197	}
	198
	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,
de1389b1	207	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;
d6b3347b	227	__be16 frag_off, oldlen, newlen;
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,
de1389b1	236	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);
d6b3347b ED	243	oldlen = ipv6h->payload_len;
	244	newlen = htons(ntohs(oldlen) + ret);
	245	if (skb->ip_summed == CHECKSUM_COMPLETE)
	246	skb->csum = csum_add(csum_sub(skb->csum, oldlen),
	247	newlen);
	248	ipv6h->payload_len = newlen;
cdd289a2 PM	249	}
	250	return XT_CONTINUE;
	251	}
	252	#endif
	253
cdd289a2	254	/* Must specify -p tcp --syn */
e1931b78	255	static inline bool find_syn_match(const struct xt_entry_match *m)
cdd289a2 PM	256	{
	257	const struct xt_tcp tcpinfo = (const struct xt_tcp )m->data;
	258
	259	if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
a3433f35	260	tcpinfo->flg_cmp & TCPHDR_SYN &&
cdd289a2	261	!(tcpinfo->invflags & XT_TCP_INV_FLAGS))
e1931b78	262	return true;
cdd289a2	263
e1931b78	264	return false;
cdd289a2 PM	265	}
cdd289a2 PM	266
135367b8	267	static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
cdd289a2	268	{
af5d6dc2 JE	269	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	270	const struct ipt_entry *e = par->entryinfo;
dcea992a	271	const struct xt_entry_match *ematch;
cdd289a2 PM	272
cdd289a2 PM	273	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	274	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	275	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	276	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	277	pr_info("path-MTU clamping only supported in "
8bee4bad JE	278	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	279	return -EINVAL;
cdd289a2	280	}
55917a21 PNA	281	if (par->nft_compat)
	282	return 0;
	283
dcea992a JE	284	xt_ematch_foreach(ematch, e)
dcea992a JE	285	if (find_syn_match(ematch))
d6b00a53	286	return 0;
8bee4bad	287	pr_info("Only works on TCP SYN packets\n");
d6b00a53	288	return -EINVAL;
cdd289a2 PM	289	}
cdd289a2 PM	290
c0cd1156	291	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
135367b8	292	static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
cdd289a2	293	{
af5d6dc2 JE	294	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	295	const struct ip6t_entry *e = par->entryinfo;
dcea992a	296	const struct xt_entry_match *ematch;
cdd289a2 PM	297
cdd289a2 PM	298	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	299	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	300	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	301	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	302	pr_info("path-MTU clamping only supported in "
8bee4bad JE	303	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	304	return -EINVAL;
cdd289a2	305	}
55917a21 PNA	306	if (par->nft_compat)
	307	return 0;
	308
dcea992a JE	309	xt_ematch_foreach(ematch, e)
dcea992a JE	310	if (find_syn_match(ematch))
d6b00a53	311	return 0;
8bee4bad	312	pr_info("Only works on TCP SYN packets\n");
d6b00a53	313	return -EINVAL;
cdd289a2 PM	314	}
	315	#endif
	316
d3c5ee6d	317	static struct xt_target tcpmss_tg_reg[] __read_mostly = {
cdd289a2	318	{
ee999d8b	319	.family = NFPROTO_IPV4,
cdd289a2	320	.name = "TCPMSS",
d3c5ee6d JE	321	.checkentry = tcpmss_tg4_check,
d3c5ee6d JE	322	.target = tcpmss_tg4,
cdd289a2 PM	323	.targetsize = sizeof(struct xt_tcpmss_info),
	324	.proto = IPPROTO_TCP,
	325	.me = THIS_MODULE,
	326	},
c0cd1156	327	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	328	{
ee999d8b	329	.family = NFPROTO_IPV6,
cdd289a2	330	.name = "TCPMSS",
d3c5ee6d JE	331	.checkentry = tcpmss_tg6_check,
d3c5ee6d JE	332	.target = tcpmss_tg6,
cdd289a2 PM	333	.targetsize = sizeof(struct xt_tcpmss_info),
	334	.proto = IPPROTO_TCP,
	335	.me = THIS_MODULE,
	336	},
	337	#endif
	338	};
	339
d3c5ee6d	340	static int __init tcpmss_tg_init(void)
cdd289a2	341	{
d3c5ee6d	342	return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	343	}
cdd289a2 PM	344
d3c5ee6d	345	static void __exit tcpmss_tg_exit(void)
cdd289a2	346	{
d3c5ee6d	347	xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	348	}
cdd289a2 PM	349
d3c5ee6d JE	350	module_init(tcpmss_tg_init);
d3c5ee6d JE	351	module_exit(tcpmss_tg_exit);