[mirror_ubuntu-kernels.git] / net / ipv4 / netfilter / ipt_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/tcp.h>

#include <linux/netfilter_ipv4/ip_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 iphdr *
synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr,
		  __be32 daddr)
{
	struct iphdr *iph;

	skb_reset_network_header(skb);
	iph = (struct iphdr *)skb_put(skb, sizeof(*iph));
	iph->version	= 4;
	iph->ihl	= sizeof(*iph) / 4;
	iph->tos	= 0;
	iph->id		= 0;
	iph->frag_off	= htons(IP_DF);
	iph->ttl	= net->ipv4.sysctl_ip_default_ttl;
	iph->protocol	= IPPROTO_TCP;
	iph->check	= 0;
	iph->saddr	= saddr;
	iph->daddr	= daddr;

	return iph;
}

static void
synproxy_send_tcp(struct net *net,
		  const struct sk_buff *skb, struct sk_buff *nskb,
		  struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
		  struct iphdr *niph, struct tcphdr *nth,
		  unsigned int tcp_hdr_size)
{
	nth->check = ~tcp_v4_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);

	skb_dst_set_noref(nskb, skb_dst(skb));
	nskb->protocol = htons(ETH_P_IP);
	if (ip_route_me_harder(net, nskb, RTN_UNSPEC))
		goto free_nskb;

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

	ip_local_out(net, nskb->sk, nskb);
	return;

free_nskb:
	kfree_skb(nskb);
}

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

	iph = ip_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(net, 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_v4_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(net, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
			  niph, nth, tcp_hdr_size);
}

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

	iph = ip_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(net, 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(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
			  niph, nth, tcp_hdr_size);
}

static void
synproxy_send_server_ack(struct net *net,
			 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 iphdr *iph, *niph;
	struct tcphdr *nth;
	unsigned int tcp_hdr_size;

	iph = ip_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(net, 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(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
}

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

	iph = ip_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(net, 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	= htons(ntohs(th->window) >> opts->wscale);
	nth->check	= 0;
	nth->urg_ptr	= 0;

	synproxy_build_options(nth, opts);

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

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

	mss = __cookie_v4_check(ip_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(net, skb, th, opts, recv_seq);
	return true;
}

static unsigned int
synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
{
	const struct xt_synproxy_info *info = par->targinfo;
	struct net *net = par->net;
	struct synproxy_net *snet = synproxy_pernet(net);
	struct synproxy_options opts = {};
	struct tcphdr *th, _th;

	if (nf_ip_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(net, skb, th, &opts);
		return NF_DROP;

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

	return XT_CONTINUE;
}

static unsigned int ipv4_synproxy_hook(void *priv,
				       struct sk_buff *skb,
				       const struct nf_hook_state *nhs)
{
	struct net *net = nhs->net;
	struct synproxy_net *snet = synproxy_pernet(net);
	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;
	unsigned 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;

	thoff = ip_hdrlen(skb);
	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(net, 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(net, state, skb, th, &opts);

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

		swap(opts.tsval, opts.tsecr);
		synproxy_send_client_ack(net, 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_tg4_check(const struct xt_tgchk_param *par)
{
	const struct ipt_entry *e = par->entryinfo;

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

	return nf_ct_l3proto_try_module_get(par->family);
}

static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
{
	nf_ct_l3proto_module_put(par->family);
}

static struct xt_target synproxy_tg4_reg __read_mostly = {
	.name		= "SYNPROXY",
	.family		= NFPROTO_IPV4,
	.hooks		= (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
	.target		= synproxy_tg4,
	.targetsize	= sizeof(struct xt_synproxy_info),
	.checkentry	= synproxy_tg4_check,
	.destroy	= synproxy_tg4_destroy,
	.me		= THIS_MODULE,
};

static struct nf_hook_ops ipv4_synproxy_ops[] __read_mostly = {
	{
		.hook		= ipv4_synproxy_hook,
		.pf		= NFPROTO_IPV4,
		.hooknum	= NF_INET_LOCAL_IN,
		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
	},
	{
		.hook		= ipv4_synproxy_hook,
		.pf		= NFPROTO_IPV4,
		.hooknum	= NF_INET_POST_ROUTING,
		.priority	= NF_IP_PRI_CONNTRACK_CONFIRM - 1,
	},
};

static int __init synproxy_tg4_init(void)
{
	int err;

	err = nf_register_hooks(ipv4_synproxy_ops,
				ARRAY_SIZE(ipv4_synproxy_ops));
	if (err < 0)
		goto err1;

	err = xt_register_target(&synproxy_tg4_reg);
	if (err < 0)
		goto err2;

	return 0;

err2:
	nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
err1:
	return err;
}

static void __exit synproxy_tg4_exit(void)
{
	xt_unregister_target(&synproxy_tg4_reg);
	nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
}

module_init(synproxy_tg4_init);
module_exit(synproxy_tg4_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
Commit	Line	Data
48b1de4c 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/tcp.h>
	12
	13	#include <linux/netfilter_ipv4/ip_tables.h>
	14	#include <linux/netfilter/x_tables.h>
	15	#include <linux/netfilter/xt_SYNPROXY.h>
	16	#include <net/netfilter/nf_conntrack.h>
	17	#include <net/netfilter/nf_conntrack_seqadj.h>
	18	#include <net/netfilter/nf_conntrack_synproxy.h>
	19
	20	static struct iphdr *
29421198 LZ	21	synproxy_build_ip(struct net net, struct sk_buff skb, __be32 saddr,
29421198 LZ	22	__be32 daddr)
48b1de4c PM	23	{
	24	struct iphdr *iph;
	25
	26	skb_reset_network_header(skb);
	27	iph = (struct iphdr )skb_put(skb, sizeof(iph));
	28	iph->version = 4;
	29	iph->ihl = sizeof(*iph) / 4;
	30	iph->tos = 0;
	31	iph->id = 0;
	32	iph->frag_off = htons(IP_DF);
fa50d974	33	iph->ttl = net->ipv4.sysctl_ip_default_ttl;
48b1de4c PM	34	iph->protocol = IPPROTO_TCP;
	35	iph->check = 0;
	36	iph->saddr = saddr;
	37	iph->daddr = daddr;
	38
	39	return iph;
	40	}
	41
	42	static void
29421198	43	synproxy_send_tcp(struct net *net,
6a1d689d	44	const struct sk_buff skb, struct sk_buff nskb,
48b1de4c PM	45	struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
	46	struct iphdr niph, struct tcphdr nth,
	47	unsigned int tcp_hdr_size)
	48	{
	49	nth->check = ~tcp_v4_check(tcp_hdr_size, niph->saddr, niph->daddr, 0);
	50	nskb->ip_summed = CHECKSUM_PARTIAL;
	51	nskb->csum_start = (unsigned char *)nth - nskb->head;
	52	nskb->csum_offset = offsetof(struct tcphdr, check);
	53
	54	skb_dst_set_noref(nskb, skb_dst(skb));
	55	nskb->protocol = htons(ETH_P_IP);
e45f5066	56	if (ip_route_me_harder(net, nskb, RTN_UNSPEC))
48b1de4c PM	57	goto free_nskb;
	58
	59	if (nfct) {
	60	nskb->nfct = nfct;
	61	nskb->nfctinfo = ctinfo;
	62	nf_conntrack_get(nfct);
	63	}
	64
33224b16	65	ip_local_out(net, nskb->sk, nskb);
48b1de4c PM	66	return;
	67
	68	free_nskb:
	69	kfree_skb(nskb);
	70	}
	71
	72	static void
29421198	73	synproxy_send_client_synack(struct net *net,
6a1d689d	74	const struct sk_buff skb, const struct tcphdr th,
48b1de4c PM	75	const struct synproxy_options *opts)
	76	{
	77	struct sk_buff *nskb;
	78	struct iphdr iph, niph;
	79	struct tcphdr *nth;
	80	unsigned int tcp_hdr_size;
	81	u16 mss = opts->mss;
	82
	83	iph = ip_hdr(skb);
	84
	85	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	86	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
	87	GFP_ATOMIC);
	88	if (nskb == NULL)
	89	return;
	90	skb_reserve(nskb, MAX_TCP_HEADER);
	91
29421198	92	niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
48b1de4c PM	93
	94	skb_reset_transport_header(nskb);
	95	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	96	nth->source = th->dest;
	97	nth->dest = th->source;
	98	nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss));
	99	nth->ack_seq = htonl(ntohl(th->seq) + 1);
	100	tcp_flag_word(nth) = TCP_FLAG_SYN \| TCP_FLAG_ACK;
	101	if (opts->options & XT_SYNPROXY_OPT_ECN)
	102	tcp_flag_word(nth) \|= TCP_FLAG_ECE;
	103	nth->doff = tcp_hdr_size / 4;
	104	nth->window = 0;
	105	nth->check = 0;
	106	nth->urg_ptr = 0;
	107
	108	synproxy_build_options(nth, opts);
	109
29421198	110	synproxy_send_tcp(net, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
48b1de4c PM	111	niph, nth, tcp_hdr_size);
	112	}
	113
	114	static void
29421198	115	synproxy_send_server_syn(struct net *net,
48b1de4c PM	116	const struct sk_buff skb, const struct tcphdr th,
	117	const struct synproxy_options *opts, u32 recv_seq)
	118	{
29421198	119	struct synproxy_net *snet = synproxy_pernet(net);
48b1de4c PM	120	struct sk_buff *nskb;
	121	struct iphdr iph, niph;
	122	struct tcphdr *nth;
	123	unsigned int tcp_hdr_size;
	124
	125	iph = ip_hdr(skb);
	126
	127	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	128	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
	129	GFP_ATOMIC);
	130	if (nskb == NULL)
	131	return;
	132	skb_reserve(nskb, MAX_TCP_HEADER);
	133
29421198	134	niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
48b1de4c PM	135
	136	skb_reset_transport_header(nskb);
	137	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	138	nth->source = th->source;
	139	nth->dest = th->dest;
	140	nth->seq = htonl(recv_seq - 1);
	141	/* ack_seq is used to relay our ISN to the synproxy hook to initialize
	142	* sequence number translation once a connection tracking entry exists.
	143	*/
	144	nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
	145	tcp_flag_word(nth) = TCP_FLAG_SYN;
	146	if (opts->options & XT_SYNPROXY_OPT_ECN)
	147	tcp_flag_word(nth) \|= TCP_FLAG_ECE \| TCP_FLAG_CWR;
	148	nth->doff = tcp_hdr_size / 4;
	149	nth->window = th->window;
	150	nth->check = 0;
	151	nth->urg_ptr = 0;
	152
	153	synproxy_build_options(nth, opts);
	154
29421198	155	synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
48b1de4c PM	156	niph, nth, tcp_hdr_size);
	157	}
	158
	159	static void
29421198	160	synproxy_send_server_ack(struct net *net,
48b1de4c PM	161	const struct ip_ct_tcp *state,
	162	const struct sk_buff skb, const struct tcphdr th,
	163	const struct synproxy_options *opts)
	164	{
	165	struct sk_buff *nskb;
	166	struct iphdr iph, niph;
	167	struct tcphdr *nth;
	168	unsigned int tcp_hdr_size;
	169
	170	iph = ip_hdr(skb);
	171
	172	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	173	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
	174	GFP_ATOMIC);
	175	if (nskb == NULL)
	176	return;
	177	skb_reserve(nskb, MAX_TCP_HEADER);
	178
29421198	179	niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
48b1de4c PM	180
	181	skb_reset_transport_header(nskb);
	182	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	183	nth->source = th->dest;
	184	nth->dest = th->source;
	185	nth->seq = htonl(ntohl(th->ack_seq));
	186	nth->ack_seq = htonl(ntohl(th->seq) + 1);
	187	tcp_flag_word(nth) = TCP_FLAG_ACK;
	188	nth->doff = tcp_hdr_size / 4;
	189	nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
	190	nth->check = 0;
	191	nth->urg_ptr = 0;
	192
	193	synproxy_build_options(nth, opts);
	194
29421198	195	synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
48b1de4c PM	196	}
	197
	198	static void
29421198	199	synproxy_send_client_ack(struct net *net,
48b1de4c PM	200	const struct sk_buff skb, const struct tcphdr th,
	201	const struct synproxy_options *opts)
	202	{
	203	struct sk_buff *nskb;
	204	struct iphdr iph, niph;
	205	struct tcphdr *nth;
	206	unsigned int tcp_hdr_size;
	207
	208	iph = ip_hdr(skb);
	209
	210	tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
	211	nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
	212	GFP_ATOMIC);
	213	if (nskb == NULL)
	214	return;
	215	skb_reserve(nskb, MAX_TCP_HEADER);
	216
29421198	217	niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
48b1de4c PM	218
	219	skb_reset_transport_header(nskb);
	220	nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
	221	nth->source = th->source;
	222	nth->dest = th->dest;
	223	nth->seq = htonl(ntohl(th->seq) + 1);
	224	nth->ack_seq = th->ack_seq;
	225	tcp_flag_word(nth) = TCP_FLAG_ACK;
	226	nth->doff = tcp_hdr_size / 4;
ba6d0564	227	nth->window = htons(ntohs(th->window) >> opts->wscale);
48b1de4c PM	228	nth->check = 0;
	229	nth->urg_ptr = 0;
	230
	231	synproxy_build_options(nth, opts);
	232
29421198	233	synproxy_send_tcp(net, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
24cebe3f	234	niph, nth, tcp_hdr_size);
48b1de4c PM	235	}
	236
	237	static bool
29421198	238	synproxy_recv_client_ack(struct net *net,
48b1de4c PM	239	const struct sk_buff skb, const struct tcphdr th,
	240	struct synproxy_options *opts, u32 recv_seq)
	241	{
29421198	242	struct synproxy_net *snet = synproxy_pernet(net);
48b1de4c PM	243	int mss;
	244
	245	mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1);
	246	if (mss == 0) {
	247	this_cpu_inc(snet->stats->cookie_invalid);
	248	return false;
	249	}
	250
	251	this_cpu_inc(snet->stats->cookie_valid);
	252	opts->mss = mss;
a6441b7a	253	opts->options \|= XT_SYNPROXY_OPT_MSS;
48b1de4c PM	254
	255	if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
	256	synproxy_check_timestamp_cookie(opts);
	257
29421198	258	synproxy_send_server_syn(net, skb, th, opts, recv_seq);
48b1de4c PM	259	return true;
	260	}
	261
	262	static unsigned int
	263	synproxy_tg4(struct sk_buff skb, const struct xt_action_param par)
	264	{
	265	const struct xt_synproxy_info *info = par->targinfo;
29421198 LZ	266	struct net *net = par->net;
29421198 LZ	267	struct synproxy_net *snet = synproxy_pernet(net);
48b1de4c PM	268	struct synproxy_options opts = {};
	269	struct tcphdr *th, _th;
	270
	271	if (nf_ip_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
	272	return NF_DROP;
	273
	274	th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
	275	if (th == NULL)
	276	return NF_DROP;
	277
f4a87e7b PM	278	if (!synproxy_parse_options(skb, par->thoff, th, &opts))
f4a87e7b PM	279	return NF_DROP;
48b1de4c	280
775ada6d	281	if (th->syn && !(th->ack \|\| th->fin \|\| th->rst)) {
48b1de4c PM	282	/* Initial SYN from client */
	283	this_cpu_inc(snet->stats->syn_received);
	284
	285	if (th->ece && th->cwr)
	286	opts.options \|= XT_SYNPROXY_OPT_ECN;
	287
	288	opts.options &= info->options;
	289	if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
	290	synproxy_init_timestamp_cookie(info, &opts);
	291	else
	292	opts.options &= ~(XT_SYNPROXY_OPT_WSCALE \|
	293	XT_SYNPROXY_OPT_SACK_PERM \|
	294	XT_SYNPROXY_OPT_ECN);
	295
29421198	296	synproxy_send_client_synack(net, skb, th, &opts);
7cc9eb6e JDB	297	return NF_DROP;
	298
	299	} else if (th->ack && !(th->fin \|\| th->rst \|\| th->syn)) {
48b1de4c	300	/* ACK from client */
29421198	301	synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq));
7cc9eb6e JDB	302	return NF_DROP;
7cc9eb6e JDB	303	}
48b1de4c	304
7cc9eb6e	305	return XT_CONTINUE;
48b1de4c PM	306	}
48b1de4c PM	307
06198b34	308	static unsigned int ipv4_synproxy_hook(void *priv,
48b1de4c	309	struct sk_buff *skb,
238e54c9	310	const struct nf_hook_state *nhs)
48b1de4c	311	{
29421198 LZ	312	struct net *net = nhs->net;
29421198 LZ	313	struct synproxy_net *snet = synproxy_pernet(net);
48b1de4c PM	314	enum ip_conntrack_info ctinfo;
	315	struct nf_conn *ct;
	316	struct nf_conn_synproxy *synproxy;
	317	struct synproxy_options opts = {};
	318	const struct ip_ct_tcp *state;
	319	struct tcphdr *th, _th;
	320	unsigned int thoff;
	321
	322	ct = nf_ct_get(skb, &ctinfo);
	323	if (ct == NULL)
	324	return NF_ACCEPT;
	325
	326	synproxy = nfct_synproxy(ct);
	327	if (synproxy == NULL)
	328	return NF_ACCEPT;
	329
	330	if (nf_is_loopback_packet(skb))
	331	return NF_ACCEPT;
	332
	333	thoff = ip_hdrlen(skb);
	334	th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
	335	if (th == NULL)
	336	return NF_DROP;
	337
	338	state = &ct->proto.tcp;
	339	switch (state->state) {
	340	case TCP_CONNTRACK_CLOSE:
	341	if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
	342	nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
	343	ntohl(th->seq) + 1);
	344	break;
	345	}
	346
	347	if (!th->syn \|\| th->ack \|\|
	348	CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
	349	break;
	350
	351	/* Reopened connection - reset the sequence number and timestamp
	352	* adjustments, they will get initialized once the connection is
	353	* reestablished.
	354	*/
	355	nf_ct_seqadj_init(ct, ctinfo, 0);
	356	synproxy->tsoff = 0;
	357	this_cpu_inc(snet->stats->conn_reopened);
	358
	359	/* fall through */
	360	case TCP_CONNTRACK_SYN_SENT:
f4a87e7b PM	361	if (!synproxy_parse_options(skb, thoff, th, &opts))
f4a87e7b PM	362	return NF_DROP;
48b1de4c PM	363
	364	if (!th->syn && th->ack &&
	365	CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
	366	/* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
	367	* therefore we need to add 1 to make the SYN sequence
	368	* number match the one of first SYN.
	369	*/
29421198	370	if (synproxy_recv_client_ack(net, skb, th, &opts,
48b1de4c PM	371	ntohl(th->seq) + 1))
	372	this_cpu_inc(snet->stats->cookie_retrans);
	373
	374	return NF_DROP;
	375	}
	376
	377	synproxy->isn = ntohl(th->ack_seq);
	378	if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
	379	synproxy->its = opts.tsecr;
	380	break;
	381	case TCP_CONNTRACK_SYN_RECV:
	382	if (!th->syn \|\| !th->ack)
	383	break;
	384
f4a87e7b PM	385	if (!synproxy_parse_options(skb, thoff, th, &opts))
	386	return NF_DROP;
	387
48b1de4c PM	388	if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
	389	synproxy->tsoff = opts.tsval - synproxy->its;
	390
	391	opts.options &= ~(XT_SYNPROXY_OPT_MSS \|
	392	XT_SYNPROXY_OPT_WSCALE \|
	393	XT_SYNPROXY_OPT_SACK_PERM);
	394
	395	swap(opts.tsval, opts.tsecr);
29421198	396	synproxy_send_server_ack(net, state, skb, th, &opts);
48b1de4c PM	397
	398	nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
	399
	400	swap(opts.tsval, opts.tsecr);
29421198	401	synproxy_send_client_ack(net, skb, th, &opts);
48b1de4c PM	402
	403	consume_skb(skb);
	404	return NF_STOLEN;
	405	default:
	406	break;
	407	}
	408
	409	synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
	410	return NF_ACCEPT;
	411	}
	412
	413	static int synproxy_tg4_check(const struct xt_tgchk_param *par)
	414	{
	415	const struct ipt_entry *e = par->entryinfo;
	416
	417	if (e->ip.proto != IPPROTO_TCP \|\|
	418	e->ip.invflags & XT_INV_PROTO)
	419	return -EINVAL;
	420
	421	return nf_ct_l3proto_try_module_get(par->family);
	422	}
	423
	424	static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
	425	{
	426	nf_ct_l3proto_module_put(par->family);
	427	}
	428
	429	static struct xt_target synproxy_tg4_reg __read_mostly = {
	430	.name = "SYNPROXY",
	431	.family = NFPROTO_IPV4,
f01b3926	432	.hooks = (1 << NF_INET_LOCAL_IN) \| (1 << NF_INET_FORWARD),
48b1de4c PM	433	.target = synproxy_tg4,
	434	.targetsize = sizeof(struct xt_synproxy_info),
	435	.checkentry = synproxy_tg4_check,
	436	.destroy = synproxy_tg4_destroy,
	437	.me = THIS_MODULE,
	438	};
	439
	440	static struct nf_hook_ops ipv4_synproxy_ops[] __read_mostly = {
	441	{
	442	.hook = ipv4_synproxy_hook,
48b1de4c PM	443	.pf = NFPROTO_IPV4,
	444	.hooknum = NF_INET_LOCAL_IN,
	445	.priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
	446	},
	447	{
	448	.hook = ipv4_synproxy_hook,
48b1de4c PM	449	.pf = NFPROTO_IPV4,
	450	.hooknum = NF_INET_POST_ROUTING,
	451	.priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
	452	},
	453	};
	454
	455	static int __init synproxy_tg4_init(void)
	456	{
	457	int err;
	458
	459	err = nf_register_hooks(ipv4_synproxy_ops,
	460	ARRAY_SIZE(ipv4_synproxy_ops));
	461	if (err < 0)
	462	goto err1;
	463
	464	err = xt_register_target(&synproxy_tg4_reg);
	465	if (err < 0)
	466	goto err2;
	467
	468	return 0;
	469
	470	err2:
	471	nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
	472	err1:
	473	return err;
	474	}
	475
	476	static void __exit synproxy_tg4_exit(void)
	477	{
	478	xt_unregister_target(&synproxy_tg4_reg);
	479	nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
	480	}
	481
	482	module_init(synproxy_tg4_init);
	483	module_exit(synproxy_tg4_exit);
	484
	485	MODULE_LICENSE("GPL");
	486	MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");