1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
4 */
5
6#include <linux/netfilter_ipv6/ip6_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_tg6(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_ip6_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_ipv6(net, skb, th, &opts);
49		consume_skb(skb);
50		return NF_STOLEN;
51
52	} else if (th->ack && !(th->fin || th->rst || th->syn)) {
53		/* ACK from client */
54		if (synproxy_recv_client_ack_ipv6(net, skb, th, &opts,
55						  ntohl(th->seq))) {
56			consume_skb(skb);
57			return NF_STOLEN;
58		} else {
59			return NF_DROP;
60		}
61	}
62
63	return XT_CONTINUE;
64}
65
66static int synproxy_tg6_check(const struct xt_tgchk_param *par)
67{
68	struct synproxy_net *snet = synproxy_pernet(par->net);
69	const struct ip6t_entry *e = par->entryinfo;
70	int err;
71
72	if (!(e->ipv6.flags & IP6T_F_PROTO) ||
73	    e->ipv6.proto != IPPROTO_TCP ||
74	    e->ipv6.invflags & XT_INV_PROTO)
75		return -EINVAL;
76
77	err = nf_ct_netns_get(par->net, par->family);
78	if (err)
79		return err;
80
81	err = nf_synproxy_ipv6_init(snet, par->net);
82	if (err) {
83		nf_ct_netns_put(par->net, par->family);
84		return err;
85	}
86
87	return err;
88}
89
90static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
91{
92	struct synproxy_net *snet = synproxy_pernet(par->net);
93
94	nf_synproxy_ipv6_fini(snet, par->net);
95	nf_ct_netns_put(par->net, par->family);
96}
97
98static struct xt_target synproxy_tg6_reg __read_mostly = {
99	.name		= "SYNPROXY",
100	.family		= NFPROTO_IPV6,
101	.hooks		= (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
102	.target		= synproxy_tg6,
103	.targetsize	= sizeof(struct xt_synproxy_info),
104	.checkentry	= synproxy_tg6_check,
105	.destroy	= synproxy_tg6_destroy,
106	.me		= THIS_MODULE,
107};
108
109static int __init synproxy_tg6_init(void)
110{
111	return xt_register_target(&synproxy_tg6_reg);
112}
113
114static void __exit synproxy_tg6_exit(void)
115{
116	xt_unregister_target(&synproxy_tg6_reg);
117}
118
119module_init(synproxy_tg6_init);
120module_exit(synproxy_tg6_exit);
121
122MODULE_LICENSE("GPL");
123MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
124MODULE_DESCRIPTION("Intercept IPv6 TCP connections and establish them using syncookies");
125