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- // SPDX-License-Identifier: GPL-2.0-only
- /*
- * Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
- */
- #include <linux/netfilter_ipv4/ip_tables.h>
- #include <linux/netfilter/x_tables.h>
- #include <linux/netfilter/xt_SYNPROXY.h>
- #include <net/netfilter/nf_synproxy.h>
- static unsigned int
- synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
- {
- const struct xt_synproxy_info *info = par->targinfo;
- struct net *net = xt_net(par);
- struct synproxy_net *snet = synproxy_pernet(net);
- struct synproxy_options opts = {};
- struct tcphdr *th, _th;
- if (nf_ip_checksum(skb, xt_hooknum(par), par->thoff, IPPROTO_TCP))
- return NF_DROP;
- th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
- if (th == NULL)
- return NF_DROP;
- if (!synproxy_parse_options(skb, par->thoff, th, &opts))
- return NF_DROP;
- if (th->syn && !(th->ack || th->fin || th->rst)) {
- /* Initial SYN from client */
- this_cpu_inc(snet->stats->syn_received);
- if (th->ece && th->cwr)
- opts.options |= XT_SYNPROXY_OPT_ECN;
- opts.options &= info->options;
- opts.mss_encode = opts.mss_option;
- opts.mss_option = info->mss;
- if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
- synproxy_init_timestamp_cookie(info, &opts);
- else
- opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
- XT_SYNPROXY_OPT_SACK_PERM |
- XT_SYNPROXY_OPT_ECN);
- synproxy_send_client_synack(net, skb, th, &opts);
- consume_skb(skb);
- return NF_STOLEN;
- } else if (th->ack && !(th->fin || th->rst || th->syn)) {
- /* ACK from client */
- if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) {
- consume_skb(skb);
- return NF_STOLEN;
- } else {
- return NF_DROP;
- }
- }
- return XT_CONTINUE;
- }
- static int synproxy_tg4_check(const struct xt_tgchk_param *par)
- {
- struct synproxy_net *snet = synproxy_pernet(par->net);
- const struct ipt_entry *e = par->entryinfo;
- int err;
- if (e->ip.proto != IPPROTO_TCP ||
- e->ip.invflags & XT_INV_PROTO)
- return -EINVAL;
- err = nf_ct_netns_get(par->net, par->family);
- if (err)
- return err;
- err = nf_synproxy_ipv4_init(snet, par->net);
- if (err) {
- nf_ct_netns_put(par->net, par->family);
- return err;
- }
- return err;
- }
- static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
- {
- struct synproxy_net *snet = synproxy_pernet(par->net);
- nf_synproxy_ipv4_fini(snet, par->net);
- nf_ct_netns_put(par->net, par->family);
- }
- static struct xt_target synproxy_tg4_reg __read_mostly = {
- .name = "SYNPROXY",
- .family = NFPROTO_IPV4,
- .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
- .target = synproxy_tg4,
- .targetsize = sizeof(struct xt_synproxy_info),
- .checkentry = synproxy_tg4_check,
- .destroy = synproxy_tg4_destroy,
- .me = THIS_MODULE,
- };
- static int __init synproxy_tg4_init(void)
- {
- return xt_register_target(&synproxy_tg4_reg);
- }
- static void __exit synproxy_tg4_exit(void)
- {
- xt_unregister_target(&synproxy_tg4_reg);
- }
- module_init(synproxy_tg4_init);
- module_exit(synproxy_tg4_exit);
- MODULE_LICENSE("GPL");
- MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
- MODULE_DESCRIPTION("Intercept TCP connections and establish them using syncookies");
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