ipt_SYNPROXY.c

  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");