[linux-2.6-block.git] / net / ipv6 / netfilter / ip6t_SYNPROXY.c

/*
 * Copyright (c) 2013 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.
 */

#include <linux/module.h>
#include <linux/skbuff.h>
#include <net/ip6_checksum.h>
#include <net/ip6_route.h>
#include <net/tcp.h>

#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_SYNPROXY.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_seqadj.h>
#include <net/netfilter/nf_conntrack_synproxy.h>

static struct ipv6hdr *
synproxy_build_ip(struct sk_buff *skb, const struct in6_addr *saddr,
				       const struct in6_addr *daddr)
{
	struct ipv6hdr *iph;

	skb_reset_network_header(skb);
	iph = (struct ipv6hdr *)skb_put(skb, sizeof(*iph));
	ip6_flow_hdr(iph, 0, 0);
	iph->hop_limit	= 64;	//XXX
	iph->nexthdr	= IPPROTO_TCP;
	iph->saddr	= *saddr;
	iph->daddr	= *daddr;

	return iph;
}

static void
synproxy_send_tcp(const struct synproxy_net *snet,
		  const struct sk_buff *skb, struct sk_buff *nskb,
		  struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
		  struct ipv6hdr *niph, struct tcphdr *nth,
		  unsigned int tcp_hdr_size)
{
	struct net *net = nf_ct_net(snet->tmpl);
	struct dst_entry *dst;
	struct flowi6 fl6;

	nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
	nskb->ip_summed   = CHECKSUM_PARTIAL;
	nskb->csum_start  = (unsigned char *)nth - nskb->head;
	nskb->csum_offset = offsetof(struct tcphdr, check);

	memset(&fl6, 0, sizeof(fl6));
	fl6.flowi6_proto = IPPROTO_TCP;
	fl6.saddr = niph->saddr;
	fl6.daddr = niph->daddr;
	fl6.fl6_sport = nth->source;
	fl6.fl6_dport = nth->dest;
	security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
	dst = ip6_route_output(net, NULL, &fl6);
	if (dst == NULL || dst->error) {
		dst_release(dst);
		goto free_nskb;
	}
	dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
	if (IS_ERR(dst))
		goto free_nskb;

	skb_dst_set(nskb, dst);

	if (nfct) {
		nskb->nfct = nfct;
		nskb->nfctinfo = ctinfo;
		nf_conntrack_get(nfct);
	}

	ip6_local_out(nskb);
	return;

free_nskb:
	kfree_skb(nskb);
}

static void
synproxy_send_client_synack(const struct synproxy_net *snet,
			    const struct sk_buff *skb, const struct tcphdr *th,
			    const struct synproxy_options *opts)
{
	struct sk_buff *nskb;
	struct ipv6hdr *iph, *niph;
	struct tcphdr *nth;
	unsigned int tcp_hdr_size;
	u16 mss = opts->mss;

	iph = ipv6_hdr(skb);

	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
			 GFP_ATOMIC);
	if (nskb == NULL)
		return;
	skb_reserve(nskb, MAX_TCP_HEADER);

	niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);

	skb_reset_transport_header(nskb);
	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	nth->source	= th->dest;
	nth->dest	= th->source;
	nth->seq	= htonl(__cookie_v6_init_sequence(iph, th, &mss));
	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
	tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
	if (opts->options & XT_SYNPROXY_OPT_ECN)
		tcp_flag_word(nth) |= TCP_FLAG_ECE;
	nth->doff	= tcp_hdr_size / 4;
	nth->window	= 0;
	nth->check	= 0;
	nth->urg_ptr	= 0;

	synproxy_build_options(nth, opts);

	synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
			  niph, nth, tcp_hdr_size);
}

static void
synproxy_send_server_syn(const struct synproxy_net *snet,
			 const struct sk_buff *skb, const struct tcphdr *th,
			 const struct synproxy_options *opts, u32 recv_seq)
{
	struct sk_buff *nskb;
	struct ipv6hdr *iph, *niph;
	struct tcphdr *nth;
	unsigned int tcp_hdr_size;

	iph = ipv6_hdr(skb);

	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
			 GFP_ATOMIC);
	if (nskb == NULL)
		return;
	skb_reserve(nskb, MAX_TCP_HEADER);

	niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);

	skb_reset_transport_header(nskb);
	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	nth->source	= th->source;
	nth->dest	= th->dest;
	nth->seq	= htonl(recv_seq - 1);
	/* ack_seq is used to relay our ISN to the synproxy hook to initialize
	 * sequence number translation once a connection tracking entry exists.
	 */
	nth->ack_seq	= htonl(ntohl(th->ack_seq) - 1);
	tcp_flag_word(nth) = TCP_FLAG_SYN;
	if (opts->options & XT_SYNPROXY_OPT_ECN)
		tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
	nth->doff	= tcp_hdr_size / 4;
	nth->window	= th->window;
	nth->check	= 0;
	nth->urg_ptr	= 0;

	synproxy_build_options(nth, opts);

	synproxy_send_tcp(snet, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
			  niph, nth, tcp_hdr_size);
}

static void
synproxy_send_server_ack(const struct synproxy_net *snet,
			 const struct ip_ct_tcp *state,
			 const struct sk_buff *skb, const struct tcphdr *th,
			 const struct synproxy_options *opts)
{
	struct sk_buff *nskb;
	struct ipv6hdr *iph, *niph;
	struct tcphdr *nth;
	unsigned int tcp_hdr_size;

	iph = ipv6_hdr(skb);

	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
			 GFP_ATOMIC);
	if (nskb == NULL)
		return;
	skb_reserve(nskb, MAX_TCP_HEADER);

	niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);

	skb_reset_transport_header(nskb);
	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	nth->source	= th->dest;
	nth->dest	= th->source;
	nth->seq	= htonl(ntohl(th->ack_seq));
	nth->ack_seq	= htonl(ntohl(th->seq) + 1);
	tcp_flag_word(nth) = TCP_FLAG_ACK;
	nth->doff	= tcp_hdr_size / 4;
	nth->window	= htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
	nth->check	= 0;
	nth->urg_ptr	= 0;

	synproxy_build_options(nth, opts);

	synproxy_send_tcp(snet, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
}

static void
synproxy_send_client_ack(const struct synproxy_net *snet,
			 const struct sk_buff *skb, const struct tcphdr *th,
			 const struct synproxy_options *opts)
{
	struct sk_buff *nskb;
	struct ipv6hdr *iph, *niph;
	struct tcphdr *nth;
	unsigned int tcp_hdr_size;

	iph = ipv6_hdr(skb);

	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
			 GFP_ATOMIC);
	if (nskb == NULL)
		return;
	skb_reserve(nskb, MAX_TCP_HEADER);

	niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);

	skb_reset_transport_header(nskb);
	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	nth->source	= th->source;
	nth->dest	= th->dest;
	nth->seq	= htonl(ntohl(th->seq) + 1);
	nth->ack_seq	= th->ack_seq;
	tcp_flag_word(nth) = TCP_FLAG_ACK;
	nth->doff	= tcp_hdr_size / 4;
	nth->window	= ntohs(htons(th->window) >> opts->wscale);
	nth->check	= 0;
	nth->urg_ptr	= 0;

	synproxy_build_options(nth, opts);

	synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
	                  niph, nth, tcp_hdr_size);
}

static bool
synproxy_recv_client_ack(const struct synproxy_net *snet,
			 const struct sk_buff *skb, const struct tcphdr *th,
			 struct synproxy_options *opts, u32 recv_seq)
{
	int mss;

	mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
	if (mss == 0) {
		this_cpu_inc(snet->stats->cookie_invalid);
		return false;
	}

	this_cpu_inc(snet->stats->cookie_valid);
	opts->mss = mss;
	opts->options |= XT_SYNPROXY_OPT_MSS;

	if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
		synproxy_check_timestamp_cookie(opts);

	synproxy_send_server_syn(snet, skb, th, opts, recv_seq);
	return true;
}

static unsigned int
synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
{
	const struct xt_synproxy_info *info = par->targinfo;
	struct synproxy_net *snet = synproxy_pernet(dev_net(par->in));
	struct synproxy_options opts = {};
	struct tcphdr *th, _th;

	if (nf_ip6_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
		return NF_DROP;

	th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
	if (th == NULL)
		return NF_DROP;

	if (!synproxy_parse_options(skb, par->thoff, th, &opts))
		return NF_DROP;

	if (th->syn && !(th->ack || th->fin || th->rst)) {
		/* Initial SYN from client */
		this_cpu_inc(snet->stats->syn_received);

		if (th->ece && th->cwr)
			opts.options |= XT_SYNPROXY_OPT_ECN;

		opts.options &= info->options;
		if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
			synproxy_init_timestamp_cookie(info, &opts);
		else
			opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
					  XT_SYNPROXY_OPT_SACK_PERM |
					  XT_SYNPROXY_OPT_ECN);

		synproxy_send_client_synack(snet, skb, th, &opts);
		return NF_DROP;

	} else if (th->ack && !(th->fin || th->rst || th->syn)) {
		/* ACK from client */
		synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
		return NF_DROP;
	}

	return XT_CONTINUE;
}

static unsigned int ipv6_synproxy_hook(const struct nf_hook_ops *ops,
				       struct sk_buff *skb,
				       const struct nf_hook_state *nhs)
{
	struct synproxy_net *snet = synproxy_pernet(dev_net(nhs->in ? : nhs->out));
	enum ip_conntrack_info ctinfo;
	struct nf_conn *ct;
	struct nf_conn_synproxy *synproxy;
	struct synproxy_options opts = {};
	const struct ip_ct_tcp *state;
	struct tcphdr *th, _th;
	__be16 frag_off;
	u8 nexthdr;
	int thoff;

	ct = nf_ct_get(skb, &ctinfo);
	if (ct == NULL)
		return NF_ACCEPT;

	synproxy = nfct_synproxy(ct);
	if (synproxy == NULL)
		return NF_ACCEPT;

	if (nf_is_loopback_packet(skb))
		return NF_ACCEPT;

	nexthdr = ipv6_hdr(skb)->nexthdr;
	thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
				 &frag_off);
	if (thoff < 0)
		return NF_ACCEPT;

	th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
	if (th == NULL)
		return NF_DROP;

	state = &ct->proto.tcp;
	switch (state->state) {
	case TCP_CONNTRACK_CLOSE:
		if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
			nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
						      ntohl(th->seq) + 1);
			break;
		}

		if (!th->syn || th->ack ||
		    CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
			break;

		/* Reopened connection - reset the sequence number and timestamp
		 * adjustments, they will get initialized once the connection is
		 * reestablished.
		 */
		nf_ct_seqadj_init(ct, ctinfo, 0);
		synproxy->tsoff = 0;
		this_cpu_inc(snet->stats->conn_reopened);

		/* fall through */
	case TCP_CONNTRACK_SYN_SENT:
		if (!synproxy_parse_options(skb, thoff, th, &opts))
			return NF_DROP;

		if (!th->syn && th->ack &&
		    CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
			/* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
			 * therefore we need to add 1 to make the SYN sequence
			 * number match the one of first SYN.
			 */
			if (synproxy_recv_client_ack(snet, skb, th, &opts,
						     ntohl(th->seq) + 1))
				this_cpu_inc(snet->stats->cookie_retrans);

			return NF_DROP;
		}

		synproxy->isn = ntohl(th->ack_seq);
		if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
			synproxy->its = opts.tsecr;
		break;
	case TCP_CONNTRACK_SYN_RECV:
		if (!th->syn || !th->ack)
			break;

		if (!synproxy_parse_options(skb, thoff, th, &opts))
			return NF_DROP;

		if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
			synproxy->tsoff = opts.tsval - synproxy->its;

		opts.options &= ~(XT_SYNPROXY_OPT_MSS |
				  XT_SYNPROXY_OPT_WSCALE |
				  XT_SYNPROXY_OPT_SACK_PERM);

		swap(opts.tsval, opts.tsecr);
		synproxy_send_server_ack(snet, state, skb, th, &opts);

		nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));

		swap(opts.tsval, opts.tsecr);
		synproxy_send_client_ack(snet, skb, th, &opts);

		consume_skb(skb);
		return NF_STOLEN;
	default:
		break;
	}

	synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
	return NF_ACCEPT;
}

static int synproxy_tg6_check(const struct xt_tgchk_param *par)
{
	const struct ip6t_entry *e = par->entryinfo;

	if (!(e->ipv6.flags & IP6T_F_PROTO) ||
	    e->ipv6.proto != IPPROTO_TCP ||
	    e->ipv6.invflags & XT_INV_PROTO)
		return -EINVAL;

	return nf_ct_l3proto_try_module_get(par->family);
}

static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
{
	nf_ct_l3proto_module_put(par->family);
}

static struct xt_target synproxy_tg6_reg __read_mostly = {
	.name		= "SYNPROXY",
	.family		= NFPROTO_IPV6,
	.hooks		= (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
	.target		= synproxy_tg6,
	.targetsize	= sizeof(struct xt_synproxy_info),
	.checkentry	= synproxy_tg6_check,
	.destroy	= synproxy_tg6_destroy,
	.me		= THIS_MODULE,
};

static struct nf_hook_ops ipv6_synproxy_ops[] __read_mostly = {
	{
		.hook		= ipv6_synproxy_hook,
		.owner		= THIS_MODULE,
		.pf		= NFPROTO_IPV6,
		.hooknum	= NF_INET_LOCAL_IN,
		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
	},
	{
		.hook		= ipv6_synproxy_hook,
		.owner		= THIS_MODULE,
		.pf		= NFPROTO_IPV6,
		.hooknum	= NF_INET_POST_ROUTING,
		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
	},
};

static int __init synproxy_tg6_init(void)
{
	int err;

	err = nf_register_hooks(ipv6_synproxy_ops,
				ARRAY_SIZE(ipv6_synproxy_ops));
	if (err < 0)
		goto err1;

	err = xt_register_target(&synproxy_tg6_reg);
	if (err < 0)
		goto err2;

	return 0;

err2:
	nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
err1:
	return err;
}

static void __exit synproxy_tg6_exit(void)
{
	xt_unregister_target(&synproxy_tg6_reg);
	nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
}

module_init(synproxy_tg6_init);
module_exit(synproxy_tg6_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
Commit	Line	Data
4ad36228 PM	1	/*
	2	* Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
	3	*
	4	* This program is free software; you can redistribute it and/or modify
	5	* it under the terms of the GNU General Public License version 2 as
	6	* published by the Free Software Foundation.
	7	*/
	8
	9	#include <linux/module.h>
	10	#include <linux/skbuff.h>
	11	#include <net/ip6_checksum.h>
	12	#include <net/ip6_route.h>
	13	#include <net/tcp.h>
	14
	15	#include <linux/netfilter_ipv6/ip6_tables.h>
	16	#include <linux/netfilter/x_tables.h>
	17	#include <linux/netfilter/xt_SYNPROXY.h>
	18	#include <net/netfilter/nf_conntrack.h>
	19	#include <net/netfilter/nf_conntrack_seqadj.h>
	20	#include <net/netfilter/nf_conntrack_synproxy.h>
	21
	22	static struct ipv6hdr *
	23	synproxy_build_ip(struct sk_buff skb, const struct in6_addr saddr,
	24	const struct in6_addr *daddr)
	25	{
	26	struct ipv6hdr *iph;
	27
	28	skb_reset_network_header(skb);
	29	iph = (struct ipv6hdr )skb_put(skb, sizeof(iph));
	30	ip6_flow_hdr(iph, 0, 0);
	31	iph->hop_limit = 64; //XXX
	32	iph->nexthdr = IPPROTO_TCP;
	33	iph->saddr = *saddr;
	34	iph->daddr = *daddr;
	35
	36	return iph;
	37	}
	38
	39	static void
96fffb4f PS	40	synproxy_send_tcp(const struct synproxy_net *snet,
96fffb4f PS	41	const struct sk_buff skb, struct sk_buff nskb,
4ad36228 PM	42	struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
	43	struct ipv6hdr niph, struct tcphdr nth,
	44	unsigned int tcp_hdr_size)
	45	{
96fffb4f	46	struct net *net = nf_ct_net(snet->tmpl);
4ad36228 PM	47	struct dst_entry *dst;
	48	struct flowi6 fl6;
	49
	50	nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
	51	nskb->ip_summed = CHECKSUM_PARTIAL;
	52	nskb->csum_start = (unsigned char *)nth - nskb->head;
	53	nskb->csum_offset = offsetof(struct tcphdr, check);
	54
	55	memset(&fl6, 0, sizeof(fl6));
	56	fl6.flowi6_proto = IPPROTO_TCP;
	57	fl6.saddr = niph->saddr;
	58	fl6.daddr = niph->daddr;
	59	fl6.fl6_sport = nth->source;
	60	fl6.fl6_dport = nth->dest;
	61	security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
	62	dst = ip6_route_output(net, NULL, &fl6);
	63	if (dst == NULL \|\| dst->error) {
	64	dst_release(dst);
	65	goto free_nskb;
	66	}
	67	dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
	68	if (IS_ERR(dst))
	69	goto free_nskb;
	70
	71	skb_dst_set(nskb, dst);
	72
	73	if (nfct) {
	74	nskb->nfct = nfct;
	75	nskb->nfctinfo = ctinfo;
	76	nf_conntrack_get(nfct);
	77	}
	78
	79	ip6_local_out(nskb);
	80	return;
	81
	82	free_nskb:
	83	kfree_skb(nskb);
	84	}
	85
	86	static void
96fffb4f PS	87	synproxy_send_client_synack(const struct synproxy_net *snet,
96fffb4f PS	88	const struct sk_buff skb, const struct tcphdr th,
4ad36228 PM	89	const struct synproxy_options *opts)
	90	{
	91	struct sk_buff *nskb;
	92	struct ipv6hdr iph, niph;
	93	struct tcphdr *nth;
	94	unsigned int tcp_hdr_size;
	95	u16 mss = opts->mss;
	96
	97	iph = ipv6_hdr(skb);
	98
	99	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	100	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
	101	GFP_ATOMIC);
	102	if (nskb == NULL)
	103	return;
	104	skb_reserve(nskb, MAX_TCP_HEADER);
	105
	106	niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);
	107
	108	skb_reset_transport_header(nskb);
	109	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	110	nth->source = th->dest;
	111	nth->dest = th->source;
	112	nth->seq = htonl(__cookie_v6_init_sequence(iph, th, &mss));
	113	nth->ack_seq = htonl(ntohl(th->seq) + 1);
	114	tcp_flag_word(nth) = TCP_FLAG_SYN \| TCP_FLAG_ACK;
	115	if (opts->options & XT_SYNPROXY_OPT_ECN)
	116	tcp_flag_word(nth) \|= TCP_FLAG_ECE;
	117	nth->doff = tcp_hdr_size / 4;
	118	nth->window = 0;
	119	nth->check = 0;
	120	nth->urg_ptr = 0;
	121
	122	synproxy_build_options(nth, opts);
	123
96fffb4f	124	synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
4ad36228 PM	125	niph, nth, tcp_hdr_size);
	126	}
	127
	128	static void
	129	synproxy_send_server_syn(const struct synproxy_net *snet,
	130	const struct sk_buff skb, const struct tcphdr th,
	131	const struct synproxy_options *opts, u32 recv_seq)
	132	{
	133	struct sk_buff *nskb;
	134	struct ipv6hdr iph, niph;
	135	struct tcphdr *nth;
	136	unsigned int tcp_hdr_size;
	137
	138	iph = ipv6_hdr(skb);
	139
	140	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	141	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
	142	GFP_ATOMIC);
	143	if (nskb == NULL)
	144	return;
	145	skb_reserve(nskb, MAX_TCP_HEADER);
	146
	147	niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);
	148
	149	skb_reset_transport_header(nskb);
	150	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	151	nth->source = th->source;
	152	nth->dest = th->dest;
	153	nth->seq = htonl(recv_seq - 1);
	154	/* ack_seq is used to relay our ISN to the synproxy hook to initialize
	155	* sequence number translation once a connection tracking entry exists.
	156	*/
	157	nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
	158	tcp_flag_word(nth) = TCP_FLAG_SYN;
	159	if (opts->options & XT_SYNPROXY_OPT_ECN)
	160	tcp_flag_word(nth) \|= TCP_FLAG_ECE \| TCP_FLAG_CWR;
	161	nth->doff = tcp_hdr_size / 4;
	162	nth->window = th->window;
	163	nth->check = 0;
	164	nth->urg_ptr = 0;
	165
	166	synproxy_build_options(nth, opts);
	167
96fffb4f	168	synproxy_send_tcp(snet, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
4ad36228 PM	169	niph, nth, tcp_hdr_size);
	170	}
	171
	172	static void
	173	synproxy_send_server_ack(const struct synproxy_net *snet,
	174	const struct ip_ct_tcp *state,
	175	const struct sk_buff skb, const struct tcphdr th,
	176	const struct synproxy_options *opts)
	177	{
	178	struct sk_buff *nskb;
	179	struct ipv6hdr iph, niph;
	180	struct tcphdr *nth;
	181	unsigned int tcp_hdr_size;
	182
	183	iph = ipv6_hdr(skb);
	184
	185	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	186	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
	187	GFP_ATOMIC);
	188	if (nskb == NULL)
	189	return;
	190	skb_reserve(nskb, MAX_TCP_HEADER);
	191
	192	niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);
	193
	194	skb_reset_transport_header(nskb);
	195	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	196	nth->source = th->dest;
	197	nth->dest = th->source;
	198	nth->seq = htonl(ntohl(th->ack_seq));
	199	nth->ack_seq = htonl(ntohl(th->seq) + 1);
	200	tcp_flag_word(nth) = TCP_FLAG_ACK;
	201	nth->doff = tcp_hdr_size / 4;
	202	nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
	203	nth->check = 0;
	204	nth->urg_ptr = 0;
	205
	206	synproxy_build_options(nth, opts);
	207
96fffb4f	208	synproxy_send_tcp(snet, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
4ad36228 PM	209	}
	210
	211	static void
	212	synproxy_send_client_ack(const struct synproxy_net *snet,
	213	const struct sk_buff skb, const struct tcphdr th,
	214	const struct synproxy_options *opts)
	215	{
	216	struct sk_buff *nskb;
	217	struct ipv6hdr iph, niph;
	218	struct tcphdr *nth;
	219	unsigned int tcp_hdr_size;
	220
	221	iph = ipv6_hdr(skb);
	222
	223	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	224	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
	225	GFP_ATOMIC);
	226	if (nskb == NULL)
	227	return;
	228	skb_reserve(nskb, MAX_TCP_HEADER);
	229
	230	niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);
	231
	232	skb_reset_transport_header(nskb);
	233	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	234	nth->source = th->source;
	235	nth->dest = th->dest;
	236	nth->seq = htonl(ntohl(th->seq) + 1);
	237	nth->ack_seq = th->ack_seq;
	238	tcp_flag_word(nth) = TCP_FLAG_ACK;
	239	nth->doff = tcp_hdr_size / 4;
	240	nth->window = ntohs(htons(th->window) >> opts->wscale);
	241	nth->check = 0;
	242	nth->urg_ptr = 0;
	243
	244	synproxy_build_options(nth, opts);
	245
3c16241c PS	246	synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
3c16241c PS	247	niph, nth, tcp_hdr_size);
4ad36228 PM	248	}
	249
	250	static bool
	251	synproxy_recv_client_ack(const struct synproxy_net *snet,
	252	const struct sk_buff skb, const struct tcphdr th,
	253	struct synproxy_options *opts, u32 recv_seq)
	254	{
	255	int mss;
	256
	257	mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
	258	if (mss == 0) {
	259	this_cpu_inc(snet->stats->cookie_invalid);
	260	return false;
	261	}
	262
	263	this_cpu_inc(snet->stats->cookie_valid);
	264	opts->mss = mss;
a6441b7a	265	opts->options \|= XT_SYNPROXY_OPT_MSS;
4ad36228 PM	266
	267	if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
	268	synproxy_check_timestamp_cookie(opts);
	269
	270	synproxy_send_server_syn(snet, skb, th, opts, recv_seq);
	271	return true;
	272	}
	273
	274	static unsigned int
	275	synproxy_tg6(struct sk_buff skb, const struct xt_action_param par)
	276	{
	277	const struct xt_synproxy_info *info = par->targinfo;
	278	struct synproxy_net *snet = synproxy_pernet(dev_net(par->in));
	279	struct synproxy_options opts = {};
	280	struct tcphdr *th, _th;
	281
	282	if (nf_ip6_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
	283	return NF_DROP;
	284
	285	th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
	286	if (th == NULL)
	287	return NF_DROP;
	288
f4a87e7b PM	289	if (!synproxy_parse_options(skb, par->thoff, th, &opts))
f4a87e7b PM	290	return NF_DROP;
4ad36228	291
775ada6d	292	if (th->syn && !(th->ack \|\| th->fin \|\| th->rst)) {
4ad36228 PM	293	/* Initial SYN from client */
	294	this_cpu_inc(snet->stats->syn_received);
	295
	296	if (th->ece && th->cwr)
	297	opts.options \|= XT_SYNPROXY_OPT_ECN;
	298
	299	opts.options &= info->options;
	300	if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
	301	synproxy_init_timestamp_cookie(info, &opts);
	302	else
	303	opts.options &= ~(XT_SYNPROXY_OPT_WSCALE \|
	304	XT_SYNPROXY_OPT_SACK_PERM \|
	305	XT_SYNPROXY_OPT_ECN);
	306
96fffb4f	307	synproxy_send_client_synack(snet, skb, th, &opts);
7cc9eb6e JDB	308	return NF_DROP;
	309
	310	} else if (th->ack && !(th->fin \|\| th->rst \|\| th->syn)) {
4ad36228 PM	311	/* ACK from client */
4ad36228 PM	312	synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
7cc9eb6e JDB	313	return NF_DROP;
7cc9eb6e JDB	314	}
4ad36228	315
7cc9eb6e	316	return XT_CONTINUE;
4ad36228 PM	317	}
4ad36228 PM	318
795aa6ef	319	static unsigned int ipv6_synproxy_hook(const struct nf_hook_ops *ops,
4ad36228	320	struct sk_buff *skb,
238e54c9	321	const struct nf_hook_state *nhs)
4ad36228	322	{
238e54c9	323	struct synproxy_net *snet = synproxy_pernet(dev_net(nhs->in ? : nhs->out));
4ad36228 PM	324	enum ip_conntrack_info ctinfo;
	325	struct nf_conn *ct;
	326	struct nf_conn_synproxy *synproxy;
	327	struct synproxy_options opts = {};
	328	const struct ip_ct_tcp *state;
	329	struct tcphdr *th, _th;
	330	__be16 frag_off;
	331	u8 nexthdr;
	332	int thoff;
	333
	334	ct = nf_ct_get(skb, &ctinfo);
	335	if (ct == NULL)
	336	return NF_ACCEPT;
	337
	338	synproxy = nfct_synproxy(ct);
	339	if (synproxy == NULL)
	340	return NF_ACCEPT;
	341
	342	if (nf_is_loopback_packet(skb))
	343	return NF_ACCEPT;
	344
	345	nexthdr = ipv6_hdr(skb)->nexthdr;
	346	thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
	347	&frag_off);
	348	if (thoff < 0)
	349	return NF_ACCEPT;
	350
	351	th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
	352	if (th == NULL)
	353	return NF_DROP;
	354
	355	state = &ct->proto.tcp;
	356	switch (state->state) {
	357	case TCP_CONNTRACK_CLOSE:
	358	if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
	359	nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
	360	ntohl(th->seq) + 1);
	361	break;
	362	}
	363
	364	if (!th->syn \|\| th->ack \|\|
	365	CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
	366	break;
	367
	368	/* Reopened connection - reset the sequence number and timestamp
	369	* adjustments, they will get initialized once the connection is
	370	* reestablished.
	371	*/
	372	nf_ct_seqadj_init(ct, ctinfo, 0);
	373	synproxy->tsoff = 0;
	374	this_cpu_inc(snet->stats->conn_reopened);
	375
	376	/* fall through */
	377	case TCP_CONNTRACK_SYN_SENT:
f4a87e7b PM	378	if (!synproxy_parse_options(skb, thoff, th, &opts))
f4a87e7b PM	379	return NF_DROP;
4ad36228 PM	380
	381	if (!th->syn && th->ack &&
	382	CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
	383	/* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
	384	* therefore we need to add 1 to make the SYN sequence
	385	* number match the one of first SYN.
	386	*/
	387	if (synproxy_recv_client_ack(snet, skb, th, &opts,
	388	ntohl(th->seq) + 1))
	389	this_cpu_inc(snet->stats->cookie_retrans);
	390
	391	return NF_DROP;
	392	}
	393
	394	synproxy->isn = ntohl(th->ack_seq);
	395	if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
	396	synproxy->its = opts.tsecr;
	397	break;
	398	case TCP_CONNTRACK_SYN_RECV:
	399	if (!th->syn \|\| !th->ack)
	400	break;
	401
f4a87e7b PM	402	if (!synproxy_parse_options(skb, thoff, th, &opts))
	403	return NF_DROP;
	404
4ad36228 PM	405	if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
	406	synproxy->tsoff = opts.tsval - synproxy->its;
	407
	408	opts.options &= ~(XT_SYNPROXY_OPT_MSS \|
	409	XT_SYNPROXY_OPT_WSCALE \|
	410	XT_SYNPROXY_OPT_SACK_PERM);
	411
	412	swap(opts.tsval, opts.tsecr);
	413	synproxy_send_server_ack(snet, state, skb, th, &opts);
	414
	415	nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
	416
	417	swap(opts.tsval, opts.tsecr);
	418	synproxy_send_client_ack(snet, skb, th, &opts);
	419
	420	consume_skb(skb);
	421	return NF_STOLEN;
	422	default:
	423	break;
	424	}
	425
	426	synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
	427	return NF_ACCEPT;
	428	}
	429
	430	static int synproxy_tg6_check(const struct xt_tgchk_param *par)
	431	{
	432	const struct ip6t_entry *e = par->entryinfo;
	433
	434	if (!(e->ipv6.flags & IP6T_F_PROTO) \|\|
	435	e->ipv6.proto != IPPROTO_TCP \|\|
	436	e->ipv6.invflags & XT_INV_PROTO)
	437	return -EINVAL;
	438
	439	return nf_ct_l3proto_try_module_get(par->family);
	440	}
	441
	442	static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
	443	{
	444	nf_ct_l3proto_module_put(par->family);
	445	}
	446
	447	static struct xt_target synproxy_tg6_reg __read_mostly = {
	448	.name = "SYNPROXY",
	449	.family = NFPROTO_IPV6,
f01b3926	450	.hooks = (1 << NF_INET_LOCAL_IN) \| (1 << NF_INET_FORWARD),
4ad36228 PM	451	.target = synproxy_tg6,
	452	.targetsize = sizeof(struct xt_synproxy_info),
	453	.checkentry = synproxy_tg6_check,
	454	.destroy = synproxy_tg6_destroy,
	455	.me = THIS_MODULE,
	456	};
	457
	458	static struct nf_hook_ops ipv6_synproxy_ops[] __read_mostly = {
	459	{
	460	.hook = ipv6_synproxy_hook,
	461	.owner = THIS_MODULE,
	462	.pf = NFPROTO_IPV6,
	463	.hooknum = NF_INET_LOCAL_IN,
	464	.priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
	465	},
	466	{
	467	.hook = ipv6_synproxy_hook,
	468	.owner = THIS_MODULE,
	469	.pf = NFPROTO_IPV6,
	470	.hooknum = NF_INET_POST_ROUTING,
	471	.priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
	472	},
	473	};
	474
	475	static int __init synproxy_tg6_init(void)
	476	{
	477	int err;
	478
	479	err = nf_register_hooks(ipv6_synproxy_ops,
	480	ARRAY_SIZE(ipv6_synproxy_ops));
	481	if (err < 0)
	482	goto err1;
	483
	484	err = xt_register_target(&synproxy_tg6_reg);
	485	if (err < 0)
	486	goto err2;
	487
	488	return 0;
	489
	490	err2:
	491	nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
	492	err1:
	493	return err;
	494	}
	495
	496	static void __exit synproxy_tg6_exit(void)
	497	{
	498	xt_unregister_target(&synproxy_tg6_reg);
	499	nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
	500	}
	501
	502	module_init(synproxy_tg6_init);
	503	module_exit(synproxy_tg6_exit);
	504
	505	MODULE_LICENSE("GPL");
	506	MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");