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 
12 static unsigned int
synproxy_tg6(struct sk_buff * skb,const struct xt_action_param * par)13 synproxy_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 
synproxy_tg6_check(const struct xt_tgchk_param * par)66 static 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 
synproxy_tg6_destroy(const struct xt_tgdtor_param * par)90 static 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 
98 static 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 
synproxy_tg6_init(void)109 static int __init synproxy_tg6_init(void)
110 {
111 	return xt_register_target(&synproxy_tg6_reg);
112 }
113 
synproxy_tg6_exit(void)114 static void __exit synproxy_tg6_exit(void)
115 {
116 	xt_unregister_target(&synproxy_tg6_reg);
117 }
118 
119 module_init(synproxy_tg6_init);
120 module_exit(synproxy_tg6_exit);
121 
122 MODULE_LICENSE("GPL");
123 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
124 MODULE_DESCRIPTION("Intercept IPv6 TCP connections and establish them using syncookies");
125