2 * Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License version 2 as
6 * published by the Free Software Foundation.
9 #include <linux/module.h>
10 #include <linux/skbuff.h>
13 #include <linux/netfilter_ipv4/ip_tables.h>
14 #include <linux/netfilter/x_tables.h>
15 #include <linux/netfilter/xt_SYNPROXY.h>
16 #include <net/netfilter/nf_conntrack.h>
17 #include <net/netfilter/nf_conntrack_seqadj.h>
18 #include <net/netfilter/nf_conntrack_synproxy.h>
21 synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr,
26 skb_reset_network_header(skb);
27 iph = (struct iphdr *)skb_put(skb, sizeof(*iph));
29 iph->ihl = sizeof(*iph) / 4;
32 iph->frag_off = htons(IP_DF);
33 iph->ttl = net->ipv4.sysctl_ip_default_ttl;
34 iph->protocol = IPPROTO_TCP;
43 synproxy_send_tcp(struct net *net,
44 const struct sk_buff *skb, struct sk_buff *nskb,
45 struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
46 struct iphdr *niph, struct tcphdr *nth,
47 unsigned int tcp_hdr_size)
49 nth->check = ~tcp_v4_check(tcp_hdr_size, niph->saddr, niph->daddr, 0);
50 nskb->ip_summed = CHECKSUM_PARTIAL;
51 nskb->csum_start = (unsigned char *)nth - nskb->head;
52 nskb->csum_offset = offsetof(struct tcphdr, check);
54 skb_dst_set_noref(nskb, skb_dst(skb));
55 nskb->protocol = htons(ETH_P_IP);
56 if (ip_route_me_harder(net, nskb, RTN_UNSPEC))
61 nskb->nfctinfo = ctinfo;
62 nf_conntrack_get(nfct);
65 ip_local_out(net, nskb->sk, nskb);
73 synproxy_send_client_synack(struct net *net,
74 const struct sk_buff *skb, const struct tcphdr *th,
75 const struct synproxy_options *opts)
78 struct iphdr *iph, *niph;
80 unsigned int tcp_hdr_size;
85 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
86 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
90 skb_reserve(nskb, MAX_TCP_HEADER);
92 niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
94 skb_reset_transport_header(nskb);
95 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
96 nth->source = th->dest;
97 nth->dest = th->source;
98 nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss));
99 nth->ack_seq = htonl(ntohl(th->seq) + 1);
100 tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
101 if (opts->options & XT_SYNPROXY_OPT_ECN)
102 tcp_flag_word(nth) |= TCP_FLAG_ECE;
103 nth->doff = tcp_hdr_size / 4;
108 synproxy_build_options(nth, opts);
110 synproxy_send_tcp(net, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
111 niph, nth, tcp_hdr_size);
115 synproxy_send_server_syn(struct net *net,
116 const struct sk_buff *skb, const struct tcphdr *th,
117 const struct synproxy_options *opts, u32 recv_seq)
119 struct synproxy_net *snet = synproxy_pernet(net);
120 struct sk_buff *nskb;
121 struct iphdr *iph, *niph;
123 unsigned int tcp_hdr_size;
127 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
128 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
132 skb_reserve(nskb, MAX_TCP_HEADER);
134 niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
136 skb_reset_transport_header(nskb);
137 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
138 nth->source = th->source;
139 nth->dest = th->dest;
140 nth->seq = htonl(recv_seq - 1);
141 /* ack_seq is used to relay our ISN to the synproxy hook to initialize
142 * sequence number translation once a connection tracking entry exists.
144 nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
145 tcp_flag_word(nth) = TCP_FLAG_SYN;
146 if (opts->options & XT_SYNPROXY_OPT_ECN)
147 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
148 nth->doff = tcp_hdr_size / 4;
149 nth->window = th->window;
153 synproxy_build_options(nth, opts);
155 synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
156 niph, nth, tcp_hdr_size);
160 synproxy_send_server_ack(struct net *net,
161 const struct ip_ct_tcp *state,
162 const struct sk_buff *skb, const struct tcphdr *th,
163 const struct synproxy_options *opts)
165 struct sk_buff *nskb;
166 struct iphdr *iph, *niph;
168 unsigned int tcp_hdr_size;
172 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
173 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
177 skb_reserve(nskb, MAX_TCP_HEADER);
179 niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
181 skb_reset_transport_header(nskb);
182 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
183 nth->source = th->dest;
184 nth->dest = th->source;
185 nth->seq = htonl(ntohl(th->ack_seq));
186 nth->ack_seq = htonl(ntohl(th->seq) + 1);
187 tcp_flag_word(nth) = TCP_FLAG_ACK;
188 nth->doff = tcp_hdr_size / 4;
189 nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
193 synproxy_build_options(nth, opts);
195 synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
199 synproxy_send_client_ack(struct net *net,
200 const struct sk_buff *skb, const struct tcphdr *th,
201 const struct synproxy_options *opts)
203 struct sk_buff *nskb;
204 struct iphdr *iph, *niph;
206 unsigned int tcp_hdr_size;
210 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
211 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
215 skb_reserve(nskb, MAX_TCP_HEADER);
217 niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
219 skb_reset_transport_header(nskb);
220 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
221 nth->source = th->source;
222 nth->dest = th->dest;
223 nth->seq = htonl(ntohl(th->seq) + 1);
224 nth->ack_seq = th->ack_seq;
225 tcp_flag_word(nth) = TCP_FLAG_ACK;
226 nth->doff = tcp_hdr_size / 4;
227 nth->window = htons(ntohs(th->window) >> opts->wscale);
231 synproxy_build_options(nth, opts);
233 synproxy_send_tcp(net, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
234 niph, nth, tcp_hdr_size);
238 synproxy_recv_client_ack(struct net *net,
239 const struct sk_buff *skb, const struct tcphdr *th,
240 struct synproxy_options *opts, u32 recv_seq)
242 struct synproxy_net *snet = synproxy_pernet(net);
245 mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1);
247 this_cpu_inc(snet->stats->cookie_invalid);
251 this_cpu_inc(snet->stats->cookie_valid);
253 opts->options |= XT_SYNPROXY_OPT_MSS;
255 if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
256 synproxy_check_timestamp_cookie(opts);
258 synproxy_send_server_syn(net, skb, th, opts, recv_seq);
263 synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
265 const struct xt_synproxy_info *info = par->targinfo;
266 struct net *net = par->net;
267 struct synproxy_net *snet = synproxy_pernet(net);
268 struct synproxy_options opts = {};
269 struct tcphdr *th, _th;
271 if (nf_ip_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
274 th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
278 if (!synproxy_parse_options(skb, par->thoff, th, &opts))
281 if (th->syn && !(th->ack || th->fin || th->rst)) {
282 /* Initial SYN from client */
283 this_cpu_inc(snet->stats->syn_received);
285 if (th->ece && th->cwr)
286 opts.options |= XT_SYNPROXY_OPT_ECN;
288 opts.options &= info->options;
289 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
290 synproxy_init_timestamp_cookie(info, &opts);
292 opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
293 XT_SYNPROXY_OPT_SACK_PERM |
294 XT_SYNPROXY_OPT_ECN);
296 synproxy_send_client_synack(net, skb, th, &opts);
299 } else if (th->ack && !(th->fin || th->rst || th->syn)) {
300 /* ACK from client */
301 synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq));
308 static unsigned int ipv4_synproxy_hook(void *priv,
310 const struct nf_hook_state *nhs)
312 struct net *net = nhs->net;
313 struct synproxy_net *snet = synproxy_pernet(net);
314 enum ip_conntrack_info ctinfo;
316 struct nf_conn_synproxy *synproxy;
317 struct synproxy_options opts = {};
318 const struct ip_ct_tcp *state;
319 struct tcphdr *th, _th;
322 ct = nf_ct_get(skb, &ctinfo);
326 synproxy = nfct_synproxy(ct);
327 if (synproxy == NULL)
330 if (nf_is_loopback_packet(skb))
333 thoff = ip_hdrlen(skb);
334 th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
338 state = &ct->proto.tcp;
339 switch (state->state) {
340 case TCP_CONNTRACK_CLOSE:
341 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
342 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
347 if (!th->syn || th->ack ||
348 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
351 /* Reopened connection - reset the sequence number and timestamp
352 * adjustments, they will get initialized once the connection is
355 nf_ct_seqadj_init(ct, ctinfo, 0);
357 this_cpu_inc(snet->stats->conn_reopened);
360 case TCP_CONNTRACK_SYN_SENT:
361 if (!synproxy_parse_options(skb, thoff, th, &opts))
364 if (!th->syn && th->ack &&
365 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
366 /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
367 * therefore we need to add 1 to make the SYN sequence
368 * number match the one of first SYN.
370 if (synproxy_recv_client_ack(net, skb, th, &opts,
372 this_cpu_inc(snet->stats->cookie_retrans);
377 synproxy->isn = ntohl(th->ack_seq);
378 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
379 synproxy->its = opts.tsecr;
381 case TCP_CONNTRACK_SYN_RECV:
382 if (!th->syn || !th->ack)
385 if (!synproxy_parse_options(skb, thoff, th, &opts))
388 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
389 synproxy->tsoff = opts.tsval - synproxy->its;
391 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
392 XT_SYNPROXY_OPT_WSCALE |
393 XT_SYNPROXY_OPT_SACK_PERM);
395 swap(opts.tsval, opts.tsecr);
396 synproxy_send_server_ack(net, state, skb, th, &opts);
398 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
400 swap(opts.tsval, opts.tsecr);
401 synproxy_send_client_ack(net, skb, th, &opts);
409 synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
413 static int synproxy_tg4_check(const struct xt_tgchk_param *par)
415 const struct ipt_entry *e = par->entryinfo;
417 if (e->ip.proto != IPPROTO_TCP ||
418 e->ip.invflags & XT_INV_PROTO)
421 return nf_ct_l3proto_try_module_get(par->family);
424 static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
426 nf_ct_l3proto_module_put(par->family);
429 static struct xt_target synproxy_tg4_reg __read_mostly = {
431 .family = NFPROTO_IPV4,
432 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
433 .target = synproxy_tg4,
434 .targetsize = sizeof(struct xt_synproxy_info),
435 .checkentry = synproxy_tg4_check,
436 .destroy = synproxy_tg4_destroy,
440 static struct nf_hook_ops ipv4_synproxy_ops[] __read_mostly = {
442 .hook = ipv4_synproxy_hook,
444 .hooknum = NF_INET_LOCAL_IN,
445 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
448 .hook = ipv4_synproxy_hook,
450 .hooknum = NF_INET_POST_ROUTING,
451 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
455 static int __init synproxy_tg4_init(void)
459 err = nf_register_hooks(ipv4_synproxy_ops,
460 ARRAY_SIZE(ipv4_synproxy_ops));
464 err = xt_register_target(&synproxy_tg4_reg);
471 nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
476 static void __exit synproxy_tg4_exit(void)
478 xt_unregister_target(&synproxy_tg4_reg);
479 nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
482 module_init(synproxy_tg4_init);
483 module_exit(synproxy_tg4_exit);
485 MODULE_LICENSE("GPL");
486 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");