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
12 static unsigned int
synproxy_tg4(struct sk_buff * skb,const struct xt_action_param * par)13 synproxy_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
synproxy_tg4_check(const struct xt_tgchk_param * par)64 static 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
synproxy_tg4_destroy(const struct xt_tgdtor_param * par)87 static 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
95 static 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
synproxy_tg4_init(void)106 static int __init synproxy_tg4_init(void)
107 {
108 return xt_register_target(&synproxy_tg4_reg);
109 }
110
synproxy_tg4_exit(void)111 static void __exit synproxy_tg4_exit(void)
112 {
113 xt_unregister_target(&synproxy_tg4_reg);
114 }
115
116 module_init(synproxy_tg4_init);
117 module_exit(synproxy_tg4_exit);
118
119 MODULE_LICENSE("GPL");
120 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
121 MODULE_DESCRIPTION("Intercept TCP connections and establish them using syncookies");
122