1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
4 */
5
6#include <linux/netfilter_ipv4/ip_tables.h>
7#include <linux/netfilter/x_tables.h>
8#include <linux/netfilter/xt_SYNPROXY.h>
9
10#include <net/netfilter/nf_synproxy.h>
11
12static unsigned int
13synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
14{
15	const struct xt_synproxy_info *info = par->targinfo;
16	struct net *net = xt_net(par);
17	struct synproxy_net *snet = synproxy_pernet(net);
18	struct synproxy_options opts = {};
19	struct tcphdr *th, _th;
20
21	if (nf_ip_checksum(skb, xt_hooknum(par), par->thoff, IPPROTO_TCP))
22		return NF_DROP;
23
24	th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
25	if (th == NULL)
26		return NF_DROP;
27
28	if (!synproxy_parse_options(skb, par->thoff, th, &opts))
29		return NF_DROP;
30
31	if (th->syn && !(th->ack || th->fin || th->rst)) {
32		/* Initial SYN from client */
33		this_cpu_inc(snet->stats->syn_received);
34
35		if (th->ece && th->cwr)
36			opts.options |= XT_SYNPROXY_OPT_ECN;
37
38		opts.options &= info->options;
39		opts.mss_encode = opts.mss_option;
40		opts.mss_option = info->mss;
41		if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
42			synproxy_init_timestamp_cookie(info, &opts);
43		else
44			opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
45					  XT_SYNPROXY_OPT_SACK_PERM |
46					  XT_SYNPROXY_OPT_ECN);
47
48		synproxy_send_client_synack(net, skb, th, &opts);
49		consume_skb(skb);
50		return NF_STOLEN;
51	} else if (th->ack && !(th->fin || th->rst || th->syn)) {
52		/* ACK from client */
53		if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) {
54			consume_skb(skb);
55			return NF_STOLEN;
56		} else {
57			return NF_DROP;
58		}
59	}
60
61	return XT_CONTINUE;
62}
63
64static int synproxy_tg4_check(const struct xt_tgchk_param *par)
65{
66	struct synproxy_net *snet = synproxy_pernet(par->net);
67	const struct ipt_entry *e = par->entryinfo;
68	int err;
69
70	if (e->ip.proto != IPPROTO_TCP ||
71	    e->ip.invflags & XT_INV_PROTO)
72		return -EINVAL;
73
74	err = nf_ct_netns_get(par->net, par->family);
75	if (err)
76		return err;
77
78	err = nf_synproxy_ipv4_init(snet, par->net);
79	if (err) {
80		nf_ct_netns_put(par->net, par->family);
81		return err;
82	}
83
84	return err;
85}
86
87static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
88{
89	struct synproxy_net *snet = synproxy_pernet(par->net);
90
91	nf_synproxy_ipv4_fini(snet, par->net);
92	nf_ct_netns_put(par->net, par->family);
93}
94
95static struct xt_target synproxy_tg4_reg __read_mostly = {
96	.name		= "SYNPROXY",
97	.family		= NFPROTO_IPV4,
98	.hooks		= (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
99	.target		= synproxy_tg4,
100	.targetsize	= sizeof(struct xt_synproxy_info),
101	.checkentry	= synproxy_tg4_check,
102	.destroy	= synproxy_tg4_destroy,
103	.me		= THIS_MODULE,
104};
105
106static int __init synproxy_tg4_init(void)
107{
108	return xt_register_target(&synproxy_tg4_reg);
109}
110
111static void __exit synproxy_tg4_exit(void)
112{
113	xt_unregister_target(&synproxy_tg4_reg);
114}
115
116module_init(synproxy_tg4_init);
117module_exit(synproxy_tg4_exit);
118
119MODULE_LICENSE("GPL");
120MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
121MODULE_DESCRIPTION("Intercept TCP connections and establish them using syncookies");
122