[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 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;
	}
	ai = nf_get_afinfo(family);
	if (ai != NULL)
		ai->route(net, (struct dst_entry **)&rt, &fl, false);

	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 || tcp_hdrlen < sizeof(struct tcphdr))
		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;

	/* tcph->doff has 4 bits, do not wrap it to 0 */
	if (tcp_hdrlen >= 15 * 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 (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	}
de1389b1 G	65	ai = nf_get_afinfo(family);
de1389b1 G	66	if (ai != NULL)
7722e0d1	67	ai->route(net, (struct dst_entry **)&rt, &fl, false);
de1389b1 G	68
	69	if (rt != NULL) {
	70	mtu = dst_mtu(&rt->dst);
	71	dst_release(&rt->dst);
	72	}
	73	return mtu;
	74	}
	75
cdd289a2	76	static int
3db05fea	77	tcpmss_mangle_packet(struct sk_buff *skb,
70d19f80	78	const struct xt_action_param *par,
de1389b1	79	unsigned int family,
cdd289a2 PM	80	unsigned int tcphoff,
	81	unsigned int minlen)
	82	{
70d19f80	83	const struct xt_tcpmss_info *info = par->targinfo;
cdd289a2	84	struct tcphdr *tcph;
71ffe9c7 PNA	85	int len, tcp_hdrlen;
71ffe9c7 PNA	86	unsigned int i;
cdd289a2 PM	87	__be16 oldval;
	88	u16 newmss;
	89	u8 *opt;
	90
b396966c PO	91	/* This is a fragment, no TCP header is available */
b396966c PO	92	if (par->fragoff != 0)
1205e1fa	93	return 0;
b396966c	94
3db05fea	95	if (!skb_make_writable(skb, skb->len))
cdd289a2 PM	96	return -1;
cdd289a2 PM	97
71ffe9c7 PNA	98	len = skb->len - tcphoff;
	99	if (len < (int)sizeof(struct tcphdr))
	100	return -1;
	101
3db05fea	102	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
71ffe9c7	103	tcp_hdrlen = tcph->doff * 4;
cdd289a2	104
2638fd0f	105	if (len < tcp_hdrlen \|\| tcp_hdrlen < sizeof(struct tcphdr))
cdd289a2	106	return -1;
cdd289a2 PM	107
cdd289a2 PM	108	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
613dbd95	109	struct net *net = xt_net(par);
7722e0d1	110	unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
50f4c7b7	111	unsigned int min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu);
de1389b1	112
50f4c7b7	113	if (min_mtu <= minlen) {
e87cc472	114	net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
50f4c7b7	115	min_mtu);
cdd289a2 PM	116	return -1;
cdd289a2 PM	117	}
50f4c7b7	118	newmss = min_mtu - minlen;
cdd289a2 PM	119	} else
	120	newmss = info->mss;
	121
	122	opt = (u_int8_t *)tcph;
71ffe9c7 PNA	123	for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
71ffe9c7 PNA	124	if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
cdd289a2 PM	125	u_int16_t oldmss;
	126
	127	oldmss = (opt[i+2] << 8) \| opt[i+3];
	128
17008064 BL	129	/* Never increase MSS, even when setting it, as
	130	* doing so results in problems for hosts that rely
	131	* on MSS being set correctly.
	132	*/
	133	if (oldmss <= newmss)
cdd289a2 PM	134	return 0;
	135
	136	opt[i+2] = (newmss & 0xff00) >> 8;
7c4e36bc	137	opt[i+3] = newmss & 0x00ff;
cdd289a2	138
be0ea7d5 PM	139	inet_proto_csum_replace2(&tcph->check, skb,
be0ea7d5 PM	140	htons(oldmss), htons(newmss),
4b048d6d	141	false);
cdd289a2 PM	142	return 0;
	143	}
	144	}
	145
10a19939	146	/* There is data after the header so the option can't be added
71ffe9c7 PNA	147	* without moving it, and doing so may make the SYN packet
	148	* itself too large. Accept the packet unmodified instead.
	149	*/
	150	if (len > tcp_hdrlen)
10a19939	151	return 0;
2638fd0f ED	152
	153	/* tcph->doff has 4 bits, do not wrap it to 0 */
	154	if (tcp_hdrlen >= 15 * 4)
	155	return 0;
10a19939	156
cdd289a2 PM	157	/*
	158	* MSS Option not found ?! add it..
	159	*/
3db05fea HX	160	if (skb_tailroom(skb) < TCPOLEN_MSS) {
	161	if (pskb_expand_head(skb, 0,
	162	TCPOLEN_MSS - skb_tailroom(skb),
2ca7b0ac	163	GFP_ATOMIC))
cdd289a2	164	return -1;
3db05fea	165	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
cdd289a2 PM	166	}
cdd289a2 PM	167
3db05fea	168	skb_put(skb, TCPOLEN_MSS);
cdd289a2	169
70d19f80 PO	170	/*
	171	* IPv4: RFC 1122 states "If an MSS option is not received at
	172	* connection setup, TCP MUST assume a default send MSS of 536".
	173	* IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
	174	* length IPv6 header of 60, ergo the default MSS value is 1220
	175	* Since no MSS was provided, we must use the default values
409b545a	176	*/
613dbd95	177	if (xt_family(par) == NFPROTO_IPV4)
70d19f80 PO	178	newmss = min(newmss, (u16)536);
	179	else
	180	newmss = min(newmss, (u16)1220);
409b545a	181
cdd289a2	182	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
71ffe9c7	183	memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
cdd289a2	184
be0ea7d5	185	inet_proto_csum_replace2(&tcph->check, skb,
4b048d6d	186	htons(len), htons(len + TCPOLEN_MSS), true);
cdd289a2 PM	187	opt[0] = TCPOPT_MSS;
	188	opt[1] = TCPOLEN_MSS;
	189	opt[2] = (newmss & 0xff00) >> 8;
7c4e36bc	190	opt[3] = newmss & 0x00ff;
cdd289a2	191
4b048d6d	192	inet_proto_csum_replace4(&tcph->check, skb, 0, ((__be32 )opt), false);
cdd289a2 PM	193
	194	oldval = ((__be16 *)tcph)[6];
	195	tcph->doff += TCPOLEN_MSS/4;
be0ea7d5	196	inet_proto_csum_replace2(&tcph->check, skb,
4b048d6d	197	oldval, ((__be16 *)tcph)[6], false);
cdd289a2 PM	198	return TCPOLEN_MSS;
	199	}
	200
	201	static unsigned int
4b560b44	202	tcpmss_tg4(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	203	{
3db05fea	204	struct iphdr *iph = ip_hdr(skb);
cdd289a2 PM	205	__be16 newlen;
	206	int ret;
	207
70d19f80	208	ret = tcpmss_mangle_packet(skb, par,
de1389b1	209	PF_INET,
37c08387	210	iph->ihl * 4,
cdd289a2 PM	211	sizeof(*iph) + sizeof(struct tcphdr));
	212	if (ret < 0)
	213	return NF_DROP;
	214	if (ret > 0) {
3db05fea	215	iph = ip_hdr(skb);
cdd289a2	216	newlen = htons(ntohs(iph->tot_len) + ret);
be0ea7d5	217	csum_replace2(&iph->check, iph->tot_len, newlen);
cdd289a2 PM	218	iph->tot_len = newlen;
	219	}
	220	return XT_CONTINUE;
	221	}
	222
c0cd1156	223	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	224	static unsigned int
4b560b44	225	tcpmss_tg6(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	226	{
3db05fea	227	struct ipv6hdr *ipv6h = ipv6_hdr(skb);
cdd289a2	228	u8 nexthdr;
d6b3347b	229	__be16 frag_off, oldlen, newlen;
cdd289a2 PM	230	int tcphoff;
	231	int ret;
	232
	233	nexthdr = ipv6h->nexthdr;
75f2811c	234	tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
9dc0564e	235	if (tcphoff < 0)
cdd289a2	236	return NF_DROP;
70d19f80	237	ret = tcpmss_mangle_packet(skb, par,
de1389b1	238	PF_INET6,
37c08387	239	tcphoff,
cdd289a2 PM	240	sizeof(*ipv6h) + sizeof(struct tcphdr));
	241	if (ret < 0)
	242	return NF_DROP;
	243	if (ret > 0) {
3db05fea	244	ipv6h = ipv6_hdr(skb);
d6b3347b ED	245	oldlen = ipv6h->payload_len;
	246	newlen = htons(ntohs(oldlen) + ret);
	247	if (skb->ip_summed == CHECKSUM_COMPLETE)
	248	skb->csum = csum_add(csum_sub(skb->csum, oldlen),
	249	newlen);
	250	ipv6h->payload_len = newlen;
cdd289a2 PM	251	}
	252	return XT_CONTINUE;
	253	}
	254	#endif
	255
cdd289a2	256	/* Must specify -p tcp --syn */
e1931b78	257	static inline bool find_syn_match(const struct xt_entry_match *m)
cdd289a2 PM	258	{
	259	const struct xt_tcp tcpinfo = (const struct xt_tcp )m->data;
	260
	261	if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
a3433f35	262	tcpinfo->flg_cmp & TCPHDR_SYN &&
cdd289a2	263	!(tcpinfo->invflags & XT_TCP_INV_FLAGS))
e1931b78	264	return true;
cdd289a2	265
e1931b78	266	return false;
cdd289a2 PM	267	}
cdd289a2 PM	268
135367b8	269	static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
cdd289a2	270	{
af5d6dc2 JE	271	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	272	const struct ipt_entry *e = par->entryinfo;
dcea992a	273	const struct xt_entry_match *ematch;
cdd289a2 PM	274
cdd289a2 PM	275	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	276	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	277	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	278	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	279	pr_info("path-MTU clamping only supported in "
8bee4bad JE	280	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	281	return -EINVAL;
cdd289a2	282	}
55917a21 PNA	283	if (par->nft_compat)
	284	return 0;
	285
dcea992a JE	286	xt_ematch_foreach(ematch, e)
dcea992a JE	287	if (find_syn_match(ematch))
d6b00a53	288	return 0;
8bee4bad	289	pr_info("Only works on TCP SYN packets\n");
d6b00a53	290	return -EINVAL;
cdd289a2 PM	291	}
cdd289a2 PM	292
c0cd1156	293	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
135367b8	294	static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
cdd289a2	295	{
af5d6dc2 JE	296	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	297	const struct ip6t_entry *e = par->entryinfo;
dcea992a	298	const struct xt_entry_match *ematch;
cdd289a2 PM	299
cdd289a2 PM	300	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	301	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	302	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	303	(1 << NF_INET_POST_ROUTING))) != 0) {
8bee4bad JE	304	pr_info("path-MTU clamping only supported in "
8bee4bad JE	305	"FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	306	return -EINVAL;
cdd289a2	307	}
55917a21 PNA	308	if (par->nft_compat)
	309	return 0;
	310
dcea992a JE	311	xt_ematch_foreach(ematch, e)
dcea992a JE	312	if (find_syn_match(ematch))
d6b00a53	313	return 0;
8bee4bad	314	pr_info("Only works on TCP SYN packets\n");
d6b00a53	315	return -EINVAL;
cdd289a2 PM	316	}
	317	#endif
	318
d3c5ee6d	319	static struct xt_target tcpmss_tg_reg[] __read_mostly = {
cdd289a2	320	{
ee999d8b	321	.family = NFPROTO_IPV4,
cdd289a2	322	.name = "TCPMSS",
d3c5ee6d JE	323	.checkentry = tcpmss_tg4_check,
d3c5ee6d JE	324	.target = tcpmss_tg4,
cdd289a2 PM	325	.targetsize = sizeof(struct xt_tcpmss_info),
	326	.proto = IPPROTO_TCP,
	327	.me = THIS_MODULE,
	328	},
c0cd1156	329	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	330	{
ee999d8b	331	.family = NFPROTO_IPV6,
cdd289a2	332	.name = "TCPMSS",
d3c5ee6d JE	333	.checkentry = tcpmss_tg6_check,
d3c5ee6d JE	334	.target = tcpmss_tg6,
cdd289a2 PM	335	.targetsize = sizeof(struct xt_tcpmss_info),
	336	.proto = IPPROTO_TCP,
	337	.me = THIS_MODULE,
	338	},
	339	#endif
	340	};
	341
d3c5ee6d	342	static int __init tcpmss_tg_init(void)
cdd289a2	343	{
d3c5ee6d	344	return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	345	}
cdd289a2 PM	346
d3c5ee6d	347	static void __exit tcpmss_tg_exit(void)
cdd289a2	348	{
d3c5ee6d	349	xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	350	}
cdd289a2 PM	351
d3c5ee6d JE	352	module_init(tcpmss_tg_init);
d3c5ee6d JE	353	module_exit(tcpmss_tg_exit);