[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;
	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;
	}

	nf_route(net, (struct dst_entry **)&rt, &fl, false, family);
	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_ratelimited("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_ratelimited("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_ratelimited("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_ratelimited("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;
de1389b1 G	51	struct rtable *rt = NULL;
	52	u_int32_t mtu = ~0U;
	53
	54	if (family == PF_INET) {
	55	struct flowi4 *fl4 = &fl.u.ip4;
	56	memset(fl4, 0, sizeof(*fl4));
	57	fl4->daddr = ip_hdr(skb)->saddr;
	58	} else {
	59	struct flowi6 *fl6 = &fl.u.ip6;
	60
	61	memset(fl6, 0, sizeof(*fl6));
	62	fl6->daddr = ipv6_hdr(skb)->saddr;
	63	}
de1389b1	64
3f87c08c	65	nf_route(net, (struct dst_entry **)&rt, &fl, false, family);
de1389b1 G	66	if (rt != NULL) {
	67	mtu = dst_mtu(&rt->dst);
	68	dst_release(&rt->dst);
	69	}
	70	return mtu;
	71	}
	72
cdd289a2	73	static int
3db05fea	74	tcpmss_mangle_packet(struct sk_buff *skb,
70d19f80	75	const struct xt_action_param *par,
de1389b1	76	unsigned int family,
cdd289a2 PM	77	unsigned int tcphoff,
	78	unsigned int minlen)
	79	{
70d19f80	80	const struct xt_tcpmss_info *info = par->targinfo;
cdd289a2	81	struct tcphdr *tcph;
71ffe9c7 PNA	82	int len, tcp_hdrlen;
71ffe9c7 PNA	83	unsigned int i;
cdd289a2 PM	84	__be16 oldval;
	85	u16 newmss;
	86	u8 *opt;
	87
b396966c PO	88	/* This is a fragment, no TCP header is available */
b396966c PO	89	if (par->fragoff != 0)
1205e1fa	90	return 0;
b396966c	91
3db05fea	92	if (!skb_make_writable(skb, skb->len))
cdd289a2 PM	93	return -1;
cdd289a2 PM	94
71ffe9c7 PNA	95	len = skb->len - tcphoff;
	96	if (len < (int)sizeof(struct tcphdr))
	97	return -1;
	98
3db05fea	99	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
71ffe9c7	100	tcp_hdrlen = tcph->doff * 4;
cdd289a2	101
2638fd0f	102	if (len < tcp_hdrlen \|\| tcp_hdrlen < sizeof(struct tcphdr))
cdd289a2	103	return -1;
cdd289a2 PM	104
cdd289a2 PM	105	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
613dbd95	106	struct net *net = xt_net(par);
7722e0d1	107	unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
50f4c7b7	108	unsigned int min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu);
de1389b1	109
50f4c7b7	110	if (min_mtu <= minlen) {
e87cc472	111	net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
50f4c7b7	112	min_mtu);
cdd289a2 PM	113	return -1;
cdd289a2 PM	114	}
50f4c7b7	115	newmss = min_mtu - minlen;
cdd289a2 PM	116	} else
	117	newmss = info->mss;
	118
	119	opt = (u_int8_t *)tcph;
71ffe9c7 PNA	120	for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
71ffe9c7 PNA	121	if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
cdd289a2 PM	122	u_int16_t oldmss;
	123
	124	oldmss = (opt[i+2] << 8) \| opt[i+3];
	125
17008064 BL	126	/* Never increase MSS, even when setting it, as
	127	* doing so results in problems for hosts that rely
	128	* on MSS being set correctly.
	129	*/
	130	if (oldmss <= newmss)
cdd289a2 PM	131	return 0;
	132
	133	opt[i+2] = (newmss & 0xff00) >> 8;
7c4e36bc	134	opt[i+3] = newmss & 0x00ff;
cdd289a2	135
be0ea7d5 PM	136	inet_proto_csum_replace2(&tcph->check, skb,
be0ea7d5 PM	137	htons(oldmss), htons(newmss),
4b048d6d	138	false);
cdd289a2 PM	139	return 0;
	140	}
	141	}
	142
10a19939	143	/* There is data after the header so the option can't be added
71ffe9c7 PNA	144	* without moving it, and doing so may make the SYN packet
	145	* itself too large. Accept the packet unmodified instead.
	146	*/
	147	if (len > tcp_hdrlen)
10a19939	148	return 0;
2638fd0f ED	149
	150	/* tcph->doff has 4 bits, do not wrap it to 0 */
	151	if (tcp_hdrlen >= 15 * 4)
	152	return 0;
10a19939	153
cdd289a2 PM	154	/*
	155	* MSS Option not found ?! add it..
	156	*/
3db05fea HX	157	if (skb_tailroom(skb) < TCPOLEN_MSS) {
	158	if (pskb_expand_head(skb, 0,
	159	TCPOLEN_MSS - skb_tailroom(skb),
2ca7b0ac	160	GFP_ATOMIC))
cdd289a2	161	return -1;
3db05fea	162	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
cdd289a2 PM	163	}
cdd289a2 PM	164
3db05fea	165	skb_put(skb, TCPOLEN_MSS);
cdd289a2	166
70d19f80 PO	167	/*
	168	* IPv4: RFC 1122 states "If an MSS option is not received at
	169	* connection setup, TCP MUST assume a default send MSS of 536".
	170	* IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
	171	* length IPv6 header of 60, ergo the default MSS value is 1220
	172	* Since no MSS was provided, we must use the default values
409b545a	173	*/
613dbd95	174	if (xt_family(par) == NFPROTO_IPV4)
70d19f80 PO	175	newmss = min(newmss, (u16)536);
	176	else
	177	newmss = min(newmss, (u16)1220);
409b545a	178
cdd289a2	179	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
71ffe9c7	180	memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
cdd289a2	181
be0ea7d5	182	inet_proto_csum_replace2(&tcph->check, skb,
4b048d6d	183	htons(len), htons(len + TCPOLEN_MSS), true);
cdd289a2 PM	184	opt[0] = TCPOPT_MSS;
	185	opt[1] = TCPOLEN_MSS;
	186	opt[2] = (newmss & 0xff00) >> 8;
7c4e36bc	187	opt[3] = newmss & 0x00ff;
cdd289a2	188
4b048d6d	189	inet_proto_csum_replace4(&tcph->check, skb, 0, ((__be32 )opt), false);
cdd289a2 PM	190
	191	oldval = ((__be16 *)tcph)[6];
	192	tcph->doff += TCPOLEN_MSS/4;
be0ea7d5	193	inet_proto_csum_replace2(&tcph->check, skb,
4b048d6d	194	oldval, ((__be16 *)tcph)[6], false);
cdd289a2 PM	195	return TCPOLEN_MSS;
	196	}
	197
	198	static unsigned int
4b560b44	199	tcpmss_tg4(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	200	{
3db05fea	201	struct iphdr *iph = ip_hdr(skb);
cdd289a2 PM	202	__be16 newlen;
	203	int ret;
	204
70d19f80	205	ret = tcpmss_mangle_packet(skb, par,
de1389b1	206	PF_INET,
37c08387	207	iph->ihl * 4,
cdd289a2 PM	208	sizeof(*iph) + sizeof(struct tcphdr));
	209	if (ret < 0)
	210	return NF_DROP;
	211	if (ret > 0) {
3db05fea	212	iph = ip_hdr(skb);
cdd289a2	213	newlen = htons(ntohs(iph->tot_len) + ret);
be0ea7d5	214	csum_replace2(&iph->check, iph->tot_len, newlen);
cdd289a2 PM	215	iph->tot_len = newlen;
	216	}
	217	return XT_CONTINUE;
	218	}
	219
c0cd1156	220	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	221	static unsigned int
4b560b44	222	tcpmss_tg6(struct sk_buff skb, const struct xt_action_param par)
cdd289a2	223	{
3db05fea	224	struct ipv6hdr *ipv6h = ipv6_hdr(skb);
cdd289a2	225	u8 nexthdr;
d6b3347b	226	__be16 frag_off, oldlen, newlen;
cdd289a2 PM	227	int tcphoff;
	228	int ret;
	229
	230	nexthdr = ipv6h->nexthdr;
75f2811c	231	tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
9dc0564e	232	if (tcphoff < 0)
cdd289a2	233	return NF_DROP;
70d19f80	234	ret = tcpmss_mangle_packet(skb, par,
de1389b1	235	PF_INET6,
37c08387	236	tcphoff,
cdd289a2 PM	237	sizeof(*ipv6h) + sizeof(struct tcphdr));
	238	if (ret < 0)
	239	return NF_DROP;
	240	if (ret > 0) {
3db05fea	241	ipv6h = ipv6_hdr(skb);
d6b3347b ED	242	oldlen = ipv6h->payload_len;
	243	newlen = htons(ntohs(oldlen) + ret);
	244	if (skb->ip_summed == CHECKSUM_COMPLETE)
	245	skb->csum = csum_add(csum_sub(skb->csum, oldlen),
	246	newlen);
	247	ipv6h->payload_len = newlen;
cdd289a2 PM	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) {
b2606644	276	pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	277	return -EINVAL;
cdd289a2	278	}
55917a21 PNA	279	if (par->nft_compat)
	280	return 0;
	281
dcea992a JE	282	xt_ematch_foreach(ematch, e)
dcea992a JE	283	if (find_syn_match(ematch))
d6b00a53	284	return 0;
b2606644	285	pr_info_ratelimited("Only works on TCP SYN packets\n");
d6b00a53	286	return -EINVAL;
cdd289a2 PM	287	}
cdd289a2 PM	288
c0cd1156	289	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
135367b8	290	static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
cdd289a2	291	{
af5d6dc2 JE	292	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	293	const struct ip6t_entry *e = par->entryinfo;
dcea992a	294	const struct xt_entry_match *ematch;
cdd289a2 PM	295
cdd289a2 PM	296	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	297	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	298	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	299	(1 << NF_INET_POST_ROUTING))) != 0) {
b2606644	300	pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	301	return -EINVAL;
cdd289a2	302	}
55917a21 PNA	303	if (par->nft_compat)
	304	return 0;
	305
dcea992a JE	306	xt_ematch_foreach(ematch, e)
dcea992a JE	307	if (find_syn_match(ematch))
d6b00a53	308	return 0;
b2606644	309	pr_info_ratelimited("Only works on TCP SYN packets\n");
d6b00a53	310	return -EINVAL;
cdd289a2 PM	311	}
	312	#endif
	313
d3c5ee6d	314	static struct xt_target tcpmss_tg_reg[] __read_mostly = {
cdd289a2	315	{
ee999d8b	316	.family = NFPROTO_IPV4,
cdd289a2	317	.name = "TCPMSS",
d3c5ee6d JE	318	.checkentry = tcpmss_tg4_check,
d3c5ee6d JE	319	.target = tcpmss_tg4,
cdd289a2 PM	320	.targetsize = sizeof(struct xt_tcpmss_info),
	321	.proto = IPPROTO_TCP,
	322	.me = THIS_MODULE,
	323	},
c0cd1156	324	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	325	{
ee999d8b	326	.family = NFPROTO_IPV6,
cdd289a2	327	.name = "TCPMSS",
d3c5ee6d JE	328	.checkentry = tcpmss_tg6_check,
d3c5ee6d JE	329	.target = tcpmss_tg6,
cdd289a2 PM	330	.targetsize = sizeof(struct xt_tcpmss_info),
	331	.proto = IPPROTO_TCP,
	332	.me = THIS_MODULE,
	333	},
	334	#endif
	335	};
	336
d3c5ee6d	337	static int __init tcpmss_tg_init(void)
cdd289a2	338	{
d3c5ee6d	339	return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	340	}
cdd289a2 PM	341
d3c5ee6d	342	static void __exit tcpmss_tg_exit(void)
cdd289a2	343	{
d3c5ee6d	344	xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	345	}
cdd289a2 PM	346
d3c5ee6d JE	347	module_init(tcpmss_tg_init);
d3c5ee6d JE	348	module_exit(tcpmss_tg_exit);