[linux-2.6-block.git] / net / netfilter / xt_TCPMSS.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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>
 */
#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_ensure_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
d2912cb1	1	// SPDX-License-Identifier: GPL-2.0-only
cdd289a2 PM	2	/*
	3	* This is a module which is used for setting the MSS option in TCP packets.
	4	*
	5	* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
f229f6ce	6	* Copyright (C) 2007 Patrick McHardy <kaber@trash.net>
cdd289a2	7	*/
8bee4bad	8	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
cdd289a2 PM	9	#include <linux/module.h>
	10	#include <linux/skbuff.h>
	11	#include <linux/ip.h>
5a0e3ad6	12	#include <linux/gfp.h>
cdd289a2 PM	13	#include <linux/ipv6.h>
cdd289a2 PM	14	#include <linux/tcp.h>
37c08387 JE	15	#include <net/dst.h>
37c08387 JE	16	#include <net/flow.h>
cdd289a2	17	#include <net/ipv6.h>
37c08387	18	#include <net/route.h>
cdd289a2 PM	19	#include <net/tcp.h>
	20
	21	#include <linux/netfilter_ipv4/ip_tables.h>
	22	#include <linux/netfilter_ipv6/ip6_tables.h>
	23	#include <linux/netfilter/x_tables.h>
	24	#include <linux/netfilter/xt_tcpudp.h>
	25	#include <linux/netfilter/xt_TCPMSS.h>
	26
	27	MODULE_LICENSE("GPL");
	28	MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
2ae15b64	29	MODULE_DESCRIPTION("Xtables: TCP Maximum Segment Size (MSS) adjustment");
cdd289a2 PM	30	MODULE_ALIAS("ipt_TCPMSS");
	31	MODULE_ALIAS("ip6t_TCPMSS");
	32
	33	static inline unsigned int
	34	optlen(const u_int8_t *opt, unsigned int offset)
	35	{
	36	/* Beware zero-length options: make finite progress */
	37	if (opt[offset] <= TCPOPT_NOP \|\| opt[offset+1] == 0)
	38	return 1;
	39	else
	40	return opt[offset+1];
	41	}
	42
7722e0d1 G	43	static u_int32_t tcpmss_reverse_mtu(struct net *net,
7722e0d1 G	44	const struct sk_buff *skb,
de1389b1 G	45	unsigned int family)
	46	{
	47	struct flowi fl;
de1389b1 G	48	struct rtable *rt = NULL;
	49	u_int32_t mtu = ~0U;
	50
	51	if (family == PF_INET) {
	52	struct flowi4 *fl4 = &fl.u.ip4;
	53	memset(fl4, 0, sizeof(*fl4));
	54	fl4->daddr = ip_hdr(skb)->saddr;
	55	} else {
	56	struct flowi6 *fl6 = &fl.u.ip6;
	57
	58	memset(fl6, 0, sizeof(*fl6));
	59	fl6->daddr = ipv6_hdr(skb)->saddr;
	60	}
de1389b1	61
3f87c08c	62	nf_route(net, (struct dst_entry **)&rt, &fl, false, family);
de1389b1 G	63	if (rt != NULL) {
	64	mtu = dst_mtu(&rt->dst);
	65	dst_release(&rt->dst);
	66	}
	67	return mtu;
	68	}
	69
cdd289a2	70	static int
3db05fea	71	tcpmss_mangle_packet(struct sk_buff *skb,
70d19f80	72	const struct xt_action_param *par,
de1389b1	73	unsigned int family,
cdd289a2 PM	74	unsigned int tcphoff,
	75	unsigned int minlen)
	76	{
70d19f80	77	const struct xt_tcpmss_info *info = par->targinfo;
cdd289a2	78	struct tcphdr *tcph;
71ffe9c7 PNA	79	int len, tcp_hdrlen;
71ffe9c7 PNA	80	unsigned int i;
cdd289a2 PM	81	__be16 oldval;
	82	u16 newmss;
	83	u8 *opt;
	84
b396966c PO	85	/* This is a fragment, no TCP header is available */
b396966c PO	86	if (par->fragoff != 0)
1205e1fa	87	return 0;
b396966c	88
fb2eb1c1	89	if (skb_ensure_writable(skb, skb->len))
cdd289a2 PM	90	return -1;
cdd289a2 PM	91
71ffe9c7 PNA	92	len = skb->len - tcphoff;
	93	if (len < (int)sizeof(struct tcphdr))
	94	return -1;
	95
3db05fea	96	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
71ffe9c7	97	tcp_hdrlen = tcph->doff * 4;
cdd289a2	98
2638fd0f	99	if (len < tcp_hdrlen \|\| tcp_hdrlen < sizeof(struct tcphdr))
cdd289a2	100	return -1;
cdd289a2 PM	101
cdd289a2 PM	102	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
613dbd95	103	struct net *net = xt_net(par);
7722e0d1	104	unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
50f4c7b7	105	unsigned int min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu);
de1389b1	106
50f4c7b7	107	if (min_mtu <= minlen) {
e87cc472	108	net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
50f4c7b7	109	min_mtu);
cdd289a2 PM	110	return -1;
cdd289a2 PM	111	}
50f4c7b7	112	newmss = min_mtu - minlen;
cdd289a2 PM	113	} else
	114	newmss = info->mss;
	115
	116	opt = (u_int8_t *)tcph;
71ffe9c7 PNA	117	for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
71ffe9c7 PNA	118	if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
cdd289a2 PM	119	u_int16_t oldmss;
	120
	121	oldmss = (opt[i+2] << 8) \| opt[i+3];
	122
17008064 BL	123	/* Never increase MSS, even when setting it, as
	124	* doing so results in problems for hosts that rely
	125	* on MSS being set correctly.
	126	*/
	127	if (oldmss <= newmss)
cdd289a2 PM	128	return 0;
	129
	130	opt[i+2] = (newmss & 0xff00) >> 8;
7c4e36bc	131	opt[i+3] = newmss & 0x00ff;
cdd289a2	132
be0ea7d5 PM	133	inet_proto_csum_replace2(&tcph->check, skb,
be0ea7d5 PM	134	htons(oldmss), htons(newmss),
4b048d6d	135	false);
cdd289a2 PM	136	return 0;
	137	}
	138	}
	139
10a19939	140	/* There is data after the header so the option can't be added
71ffe9c7 PNA	141	* without moving it, and doing so may make the SYN packet
	142	* itself too large. Accept the packet unmodified instead.
	143	*/
	144	if (len > tcp_hdrlen)
10a19939	145	return 0;
2638fd0f ED	146
	147	/* tcph->doff has 4 bits, do not wrap it to 0 */
	148	if (tcp_hdrlen >= 15 * 4)
	149	return 0;
10a19939	150
cdd289a2 PM	151	/*
	152	* MSS Option not found ?! add it..
	153	*/
3db05fea HX	154	if (skb_tailroom(skb) < TCPOLEN_MSS) {
	155	if (pskb_expand_head(skb, 0,
	156	TCPOLEN_MSS - skb_tailroom(skb),
2ca7b0ac	157	GFP_ATOMIC))
cdd289a2	158	return -1;
3db05fea	159	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
cdd289a2 PM	160	}
cdd289a2 PM	161
3db05fea	162	skb_put(skb, TCPOLEN_MSS);
cdd289a2	163
70d19f80 PO	164	/*
	165	* IPv4: RFC 1122 states "If an MSS option is not received at
	166	* connection setup, TCP MUST assume a default send MSS of 536".
	167	* IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
	168	* length IPv6 header of 60, ergo the default MSS value is 1220
	169	* Since no MSS was provided, we must use the default values
409b545a	170	*/
613dbd95	171	if (xt_family(par) == NFPROTO_IPV4)
70d19f80 PO	172	newmss = min(newmss, (u16)536);
	173	else
	174	newmss = min(newmss, (u16)1220);
409b545a	175
cdd289a2	176	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
71ffe9c7	177	memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
cdd289a2	178
be0ea7d5	179	inet_proto_csum_replace2(&tcph->check, skb,
4b048d6d	180	htons(len), htons(len + TCPOLEN_MSS), true);
cdd289a2 PM	181	opt[0] = TCPOPT_MSS;
	182	opt[1] = TCPOLEN_MSS;
	183	opt[2] = (newmss & 0xff00) >> 8;
7c4e36bc	184	opt[3] = newmss & 0x00ff;
cdd289a2	185
4b048d6d	186	inet_proto_csum_replace4(&tcph->check, skb, 0, ((__be32 )opt), false);
cdd289a2 PM	187
	188	oldval = ((__be16 *)tcph)[6];
	189	tcph->doff += TCPOLEN_MSS/4;
be0ea7d5	190	inet_proto_csum_replace2(&tcph->check, skb,
4b048d6d	191	oldval, ((__be16 *)tcph)[6], false);
cdd289a2 PM	192	return TCPOLEN_MSS;
	193	}
	194
	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,
de1389b1	203	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;
d6b3347b	223	__be16 frag_off, oldlen, newlen;
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,
de1389b1	232	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);
d6b3347b ED	239	oldlen = ipv6h->payload_len;
	240	newlen = htons(ntohs(oldlen) + ret);
	241	if (skb->ip_summed == CHECKSUM_COMPLETE)
	242	skb->csum = csum_add(csum_sub(skb->csum, oldlen),
	243	newlen);
	244	ipv6h->payload_len = newlen;
cdd289a2 PM	245	}
	246	return XT_CONTINUE;
	247	}
	248	#endif
	249
cdd289a2	250	/* Must specify -p tcp --syn */
e1931b78	251	static inline bool find_syn_match(const struct xt_entry_match *m)
cdd289a2 PM	252	{
	253	const struct xt_tcp tcpinfo = (const struct xt_tcp )m->data;
	254
	255	if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
a3433f35	256	tcpinfo->flg_cmp & TCPHDR_SYN &&
cdd289a2	257	!(tcpinfo->invflags & XT_TCP_INV_FLAGS))
e1931b78	258	return true;
cdd289a2	259
e1931b78	260	return false;
cdd289a2 PM	261	}
cdd289a2 PM	262
135367b8	263	static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
cdd289a2	264	{
af5d6dc2 JE	265	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	266	const struct ipt_entry *e = par->entryinfo;
dcea992a	267	const struct xt_entry_match *ematch;
cdd289a2 PM	268
cdd289a2 PM	269	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	270	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	271	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	272	(1 << NF_INET_POST_ROUTING))) != 0) {
b2606644	273	pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	274	return -EINVAL;
cdd289a2	275	}
55917a21 PNA	276	if (par->nft_compat)
	277	return 0;
	278
dcea992a JE	279	xt_ematch_foreach(ematch, e)
dcea992a JE	280	if (find_syn_match(ematch))
d6b00a53	281	return 0;
b2606644	282	pr_info_ratelimited("Only works on TCP SYN packets\n");
d6b00a53	283	return -EINVAL;
cdd289a2 PM	284	}
cdd289a2 PM	285
c0cd1156	286	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
135367b8	287	static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
cdd289a2	288	{
af5d6dc2 JE	289	const struct xt_tcpmss_info *info = par->targinfo;
af5d6dc2 JE	290	const struct ip6t_entry *e = par->entryinfo;
dcea992a	291	const struct xt_entry_match *ematch;
cdd289a2 PM	292
cdd289a2 PM	293	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
af5d6dc2	294	(par->hook_mask & ~((1 << NF_INET_FORWARD) \|
6e23ae2a PM	295	(1 << NF_INET_LOCAL_OUT) \|
6e23ae2a PM	296	(1 << NF_INET_POST_ROUTING))) != 0) {
b2606644	297	pr_info_ratelimited("path-MTU clamping only supported in FORWARD, OUTPUT and POSTROUTING hooks\n");
d6b00a53	298	return -EINVAL;
cdd289a2	299	}
55917a21 PNA	300	if (par->nft_compat)
	301	return 0;
	302
dcea992a JE	303	xt_ematch_foreach(ematch, e)
dcea992a JE	304	if (find_syn_match(ematch))
d6b00a53	305	return 0;
b2606644	306	pr_info_ratelimited("Only works on TCP SYN packets\n");
d6b00a53	307	return -EINVAL;
cdd289a2 PM	308	}
	309	#endif
	310
d3c5ee6d	311	static struct xt_target tcpmss_tg_reg[] __read_mostly = {
cdd289a2	312	{
ee999d8b	313	.family = NFPROTO_IPV4,
cdd289a2	314	.name = "TCPMSS",
d3c5ee6d JE	315	.checkentry = tcpmss_tg4_check,
d3c5ee6d JE	316	.target = tcpmss_tg4,
cdd289a2 PM	317	.targetsize = sizeof(struct xt_tcpmss_info),
	318	.proto = IPPROTO_TCP,
	319	.me = THIS_MODULE,
	320	},
c0cd1156	321	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
cdd289a2	322	{
ee999d8b	323	.family = NFPROTO_IPV6,
cdd289a2	324	.name = "TCPMSS",
d3c5ee6d JE	325	.checkentry = tcpmss_tg6_check,
d3c5ee6d JE	326	.target = tcpmss_tg6,
cdd289a2 PM	327	.targetsize = sizeof(struct xt_tcpmss_info),
	328	.proto = IPPROTO_TCP,
	329	.me = THIS_MODULE,
	330	},
	331	#endif
	332	};
	333
d3c5ee6d	334	static int __init tcpmss_tg_init(void)
cdd289a2	335	{
d3c5ee6d	336	return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	337	}
cdd289a2 PM	338
d3c5ee6d	339	static void __exit tcpmss_tg_exit(void)
cdd289a2	340	{
d3c5ee6d	341	xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
cdd289a2 PM	342	}
cdd289a2 PM	343
d3c5ee6d JE	344	module_init(tcpmss_tg_init);
d3c5ee6d JE	345	module_exit(tcpmss_tg_exit);