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 sk_buff *skb, u32 saddr, u32 daddr)
25 skb_reset_network_header(skb);
26 iph = (struct iphdr *)skb_put(skb, sizeof(*iph));
28 iph->ihl = sizeof(*iph) / 4;
31 iph->frag_off = htons(IP_DF);
32 iph->ttl = sysctl_ip_default_ttl;
33 iph->protocol = IPPROTO_TCP;
42 synproxy_send_tcp(const struct sk_buff *skb, struct sk_buff *nskb,
43 struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
44 struct iphdr *niph, struct tcphdr *nth,
45 unsigned int tcp_hdr_size)
47 nth->check = ~tcp_v4_check(tcp_hdr_size, niph->saddr, niph->daddr, 0);
48 nskb->ip_summed = CHECKSUM_PARTIAL;
49 nskb->csum_start = (unsigned char *)nth - nskb->head;
50 nskb->csum_offset = offsetof(struct tcphdr, check);
52 skb_dst_set_noref(nskb, skb_dst(skb));
53 nskb->protocol = htons(ETH_P_IP);
54 if (ip_route_me_harder(nskb, RTN_UNSPEC))
59 nskb->nfctinfo = ctinfo;
60 nf_conntrack_get(nfct);
71 synproxy_send_client_synack(const struct sk_buff *skb, const struct tcphdr *th,
72 const struct synproxy_options *opts)
75 struct iphdr *iph, *niph;
77 unsigned int tcp_hdr_size;
82 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
83 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
87 skb_reserve(nskb, MAX_TCP_HEADER);
89 niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr);
91 skb_reset_transport_header(nskb);
92 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
93 nth->source = th->dest;
94 nth->dest = th->source;
95 nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss));
96 nth->ack_seq = htonl(ntohl(th->seq) + 1);
97 tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
98 if (opts->options & XT_SYNPROXY_OPT_ECN)
99 tcp_flag_word(nth) |= TCP_FLAG_ECE;
100 nth->doff = tcp_hdr_size / 4;
105 synproxy_build_options(nth, opts);
107 synproxy_send_tcp(skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
108 niph, nth, tcp_hdr_size);
112 synproxy_send_server_syn(const struct synproxy_net *snet,
113 const struct sk_buff *skb, const struct tcphdr *th,
114 const struct synproxy_options *opts, u32 recv_seq)
116 struct sk_buff *nskb;
117 struct iphdr *iph, *niph;
119 unsigned int tcp_hdr_size;
123 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
124 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
128 skb_reserve(nskb, MAX_TCP_HEADER);
130 niph = synproxy_build_ip(nskb, iph->saddr, iph->daddr);
132 skb_reset_transport_header(nskb);
133 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
134 nth->source = th->source;
135 nth->dest = th->dest;
136 nth->seq = htonl(recv_seq - 1);
137 /* ack_seq is used to relay our ISN to the synproxy hook to initialize
138 * sequence number translation once a connection tracking entry exists.
140 nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
141 tcp_flag_word(nth) = TCP_FLAG_SYN;
142 if (opts->options & XT_SYNPROXY_OPT_ECN)
143 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
144 nth->doff = tcp_hdr_size / 4;
145 nth->window = th->window;
149 synproxy_build_options(nth, opts);
151 synproxy_send_tcp(skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
152 niph, nth, tcp_hdr_size);
156 synproxy_send_server_ack(const struct synproxy_net *snet,
157 const struct ip_ct_tcp *state,
158 const struct sk_buff *skb, const struct tcphdr *th,
159 const struct synproxy_options *opts)
161 struct sk_buff *nskb;
162 struct iphdr *iph, *niph;
164 unsigned int tcp_hdr_size;
168 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
169 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
173 skb_reserve(nskb, MAX_TCP_HEADER);
175 niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr);
177 skb_reset_transport_header(nskb);
178 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
179 nth->source = th->dest;
180 nth->dest = th->source;
181 nth->seq = htonl(ntohl(th->ack_seq));
182 nth->ack_seq = htonl(ntohl(th->seq) + 1);
183 tcp_flag_word(nth) = TCP_FLAG_ACK;
184 nth->doff = tcp_hdr_size / 4;
185 nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
189 synproxy_build_options(nth, opts);
191 synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
195 synproxy_send_client_ack(const struct synproxy_net *snet,
196 const struct sk_buff *skb, const struct tcphdr *th,
197 const struct synproxy_options *opts)
199 struct sk_buff *nskb;
200 struct iphdr *iph, *niph;
202 unsigned int tcp_hdr_size;
206 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
207 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
211 skb_reserve(nskb, MAX_TCP_HEADER);
213 niph = synproxy_build_ip(nskb, iph->saddr, iph->daddr);
215 skb_reset_transport_header(nskb);
216 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
217 nth->source = th->source;
218 nth->dest = th->dest;
219 nth->seq = htonl(ntohl(th->seq) + 1);
220 nth->ack_seq = th->ack_seq;
221 tcp_flag_word(nth) = TCP_FLAG_ACK;
222 nth->doff = tcp_hdr_size / 4;
223 nth->window = ntohs(htons(th->window) >> opts->wscale);
227 synproxy_build_options(nth, opts);
229 synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
233 synproxy_recv_client_ack(const struct synproxy_net *snet,
234 const struct sk_buff *skb, const struct tcphdr *th,
235 struct synproxy_options *opts, u32 recv_seq)
239 mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1);
241 this_cpu_inc(snet->stats->cookie_invalid);
245 this_cpu_inc(snet->stats->cookie_valid);
248 if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
249 synproxy_check_timestamp_cookie(opts);
251 synproxy_send_server_syn(snet, skb, th, opts, recv_seq);
256 synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
258 const struct xt_synproxy_info *info = par->targinfo;
259 struct synproxy_net *snet = synproxy_pernet(dev_net(par->in));
260 struct synproxy_options opts = {};
261 struct tcphdr *th, _th;
263 if (nf_ip_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
266 th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
270 if (!synproxy_parse_options(skb, par->thoff, th, &opts))
273 if (th->syn && !(th->ack || th->fin || th->rst)) {
274 /* Initial SYN from client */
275 this_cpu_inc(snet->stats->syn_received);
277 if (th->ece && th->cwr)
278 opts.options |= XT_SYNPROXY_OPT_ECN;
280 opts.options &= info->options;
281 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
282 synproxy_init_timestamp_cookie(info, &opts);
284 opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
285 XT_SYNPROXY_OPT_SACK_PERM |
286 XT_SYNPROXY_OPT_ECN);
288 synproxy_send_client_synack(skb, th, &opts);
291 } else if (th->ack && !(th->fin || th->rst || th->syn)) {
292 /* ACK from client */
293 synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
300 static unsigned int ipv4_synproxy_hook(unsigned int hooknum,
302 const struct net_device *in,
303 const struct net_device *out,
304 int (*okfn)(struct sk_buff *))
306 struct synproxy_net *snet = synproxy_pernet(dev_net(in ? : out));
307 enum ip_conntrack_info ctinfo;
309 struct nf_conn_synproxy *synproxy;
310 struct synproxy_options opts = {};
311 const struct ip_ct_tcp *state;
312 struct tcphdr *th, _th;
315 ct = nf_ct_get(skb, &ctinfo);
319 synproxy = nfct_synproxy(ct);
320 if (synproxy == NULL)
323 if (nf_is_loopback_packet(skb))
326 thoff = ip_hdrlen(skb);
327 th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
331 state = &ct->proto.tcp;
332 switch (state->state) {
333 case TCP_CONNTRACK_CLOSE:
334 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
335 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
340 if (!th->syn || th->ack ||
341 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
344 /* Reopened connection - reset the sequence number and timestamp
345 * adjustments, they will get initialized once the connection is
348 nf_ct_seqadj_init(ct, ctinfo, 0);
350 this_cpu_inc(snet->stats->conn_reopened);
353 case TCP_CONNTRACK_SYN_SENT:
354 if (!synproxy_parse_options(skb, thoff, th, &opts))
357 if (!th->syn && th->ack &&
358 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
359 /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
360 * therefore we need to add 1 to make the SYN sequence
361 * number match the one of first SYN.
363 if (synproxy_recv_client_ack(snet, skb, th, &opts,
365 this_cpu_inc(snet->stats->cookie_retrans);
370 synproxy->isn = ntohl(th->ack_seq);
371 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
372 synproxy->its = opts.tsecr;
374 case TCP_CONNTRACK_SYN_RECV:
375 if (!th->syn || !th->ack)
378 if (!synproxy_parse_options(skb, thoff, th, &opts))
381 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
382 synproxy->tsoff = opts.tsval - synproxy->its;
384 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
385 XT_SYNPROXY_OPT_WSCALE |
386 XT_SYNPROXY_OPT_SACK_PERM);
388 swap(opts.tsval, opts.tsecr);
389 synproxy_send_server_ack(snet, state, skb, th, &opts);
391 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
393 swap(opts.tsval, opts.tsecr);
394 synproxy_send_client_ack(snet, skb, th, &opts);
402 synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
406 static int synproxy_tg4_check(const struct xt_tgchk_param *par)
408 const struct ipt_entry *e = par->entryinfo;
410 if (e->ip.proto != IPPROTO_TCP ||
411 e->ip.invflags & XT_INV_PROTO)
414 return nf_ct_l3proto_try_module_get(par->family);
417 static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
419 nf_ct_l3proto_module_put(par->family);
422 static struct xt_target synproxy_tg4_reg __read_mostly = {
424 .family = NFPROTO_IPV4,
425 .target = synproxy_tg4,
426 .targetsize = sizeof(struct xt_synproxy_info),
427 .checkentry = synproxy_tg4_check,
428 .destroy = synproxy_tg4_destroy,
432 static struct nf_hook_ops ipv4_synproxy_ops[] __read_mostly = {
434 .hook = ipv4_synproxy_hook,
435 .owner = THIS_MODULE,
437 .hooknum = NF_INET_LOCAL_IN,
438 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
441 .hook = ipv4_synproxy_hook,
442 .owner = THIS_MODULE,
444 .hooknum = NF_INET_POST_ROUTING,
445 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
449 static int __init synproxy_tg4_init(void)
453 err = nf_register_hooks(ipv4_synproxy_ops,
454 ARRAY_SIZE(ipv4_synproxy_ops));
458 err = xt_register_target(&synproxy_tg4_reg);
465 nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
470 static void __exit synproxy_tg4_exit(void)
472 xt_unregister_target(&synproxy_tg4_reg);
473 nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
476 module_init(synproxy_tg4_init);
477 module_exit(synproxy_tg4_exit);
479 MODULE_LICENSE("GPL");
480 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");