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9#include <linux/module.h>
10#include <linux/skbuff.h>
11#include <net/ip6_checksum.h>
12#include <net/ip6_route.h>
13#include <net/tcp.h>
14
15#include <linux/netfilter_ipv6/ip6_tables.h>
16#include <linux/netfilter/x_tables.h>
17#include <linux/netfilter/xt_SYNPROXY.h>
18#include <net/netfilter/nf_conntrack.h>
19#include <net/netfilter/nf_conntrack_seqadj.h>
20#include <net/netfilter/nf_conntrack_synproxy.h>
21
22static struct ipv6hdr *
23synproxy_build_ip(struct net *net, struct sk_buff *skb,
24 const struct in6_addr *saddr,
25 const struct in6_addr *daddr)
26{
27 struct ipv6hdr *iph;
28
29 skb_reset_network_header(skb);
30 iph = skb_put(skb, sizeof(*iph));
31 ip6_flow_hdr(iph, 0, 0);
32 iph->hop_limit = net->ipv6.devconf_all->hop_limit;
33 iph->nexthdr = IPPROTO_TCP;
34 iph->saddr = *saddr;
35 iph->daddr = *daddr;
36
37 return iph;
38}
39
40static void
41synproxy_send_tcp(struct net *net,
42 const struct sk_buff *skb, struct sk_buff *nskb,
43 struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
44 struct ipv6hdr *niph, struct tcphdr *nth,
45 unsigned int tcp_hdr_size)
46{
47 struct dst_entry *dst;
48 struct flowi6 fl6;
49
50 nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0);
51 nskb->ip_summed = CHECKSUM_PARTIAL;
52 nskb->csum_start = (unsigned char *)nth - nskb->head;
53 nskb->csum_offset = offsetof(struct tcphdr, check);
54
55 memset(&fl6, 0, sizeof(fl6));
56 fl6.flowi6_proto = IPPROTO_TCP;
57 fl6.saddr = niph->saddr;
58 fl6.daddr = niph->daddr;
59 fl6.fl6_sport = nth->source;
60 fl6.fl6_dport = nth->dest;
61 security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
62 dst = ip6_route_output(net, NULL, &fl6);
63 if (dst->error) {
64 dst_release(dst);
65 goto free_nskb;
66 }
67 dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
68 if (IS_ERR(dst))
69 goto free_nskb;
70
71 skb_dst_set(nskb, dst);
72
73 if (nfct) {
74 nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
75 nf_conntrack_get(nfct);
76 }
77
78 ip6_local_out(net, nskb->sk, nskb);
79 return;
80
81free_nskb:
82 kfree_skb(nskb);
83}
84
85static void
86synproxy_send_client_synack(struct net *net,
87 const struct sk_buff *skb, const struct tcphdr *th,
88 const struct synproxy_options *opts)
89{
90 struct sk_buff *nskb;
91 struct ipv6hdr *iph, *niph;
92 struct tcphdr *nth;
93 unsigned int tcp_hdr_size;
94 u16 mss = opts->mss;
95
96 iph = ipv6_hdr(skb);
97
98 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
99 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
100 GFP_ATOMIC);
101 if (nskb == NULL)
102 return;
103 skb_reserve(nskb, MAX_TCP_HEADER);
104
105 niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
106
107 skb_reset_transport_header(nskb);
108 nth = skb_put(nskb, tcp_hdr_size);
109 nth->source = th->dest;
110 nth->dest = th->source;
111 nth->seq = htonl(__cookie_v6_init_sequence(iph, th, &mss));
112 nth->ack_seq = htonl(ntohl(th->seq) + 1);
113 tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
114 if (opts->options & XT_SYNPROXY_OPT_ECN)
115 tcp_flag_word(nth) |= TCP_FLAG_ECE;
116 nth->doff = tcp_hdr_size / 4;
117 nth->window = 0;
118 nth->check = 0;
119 nth->urg_ptr = 0;
120
121 synproxy_build_options(nth, opts);
122
123 synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
124 IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
125}
126
127static void
128synproxy_send_server_syn(struct net *net,
129 const struct sk_buff *skb, const struct tcphdr *th,
130 const struct synproxy_options *opts, u32 recv_seq)
131{
132 struct synproxy_net *snet = synproxy_pernet(net);
133 struct sk_buff *nskb;
134 struct ipv6hdr *iph, *niph;
135 struct tcphdr *nth;
136 unsigned int tcp_hdr_size;
137
138 iph = ipv6_hdr(skb);
139
140 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
141 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
142 GFP_ATOMIC);
143 if (nskb == NULL)
144 return;
145 skb_reserve(nskb, MAX_TCP_HEADER);
146
147 niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
148
149 skb_reset_transport_header(nskb);
150 nth = skb_put(nskb, tcp_hdr_size);
151 nth->source = th->source;
152 nth->dest = th->dest;
153 nth->seq = htonl(recv_seq - 1);
154
155
156
157 nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
158 tcp_flag_word(nth) = TCP_FLAG_SYN;
159 if (opts->options & XT_SYNPROXY_OPT_ECN)
160 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
161 nth->doff = tcp_hdr_size / 4;
162 nth->window = th->window;
163 nth->check = 0;
164 nth->urg_ptr = 0;
165
166 synproxy_build_options(nth, opts);
167
168 synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
169 niph, nth, tcp_hdr_size);
170}
171
172static void
173synproxy_send_server_ack(struct net *net,
174 const struct ip_ct_tcp *state,
175 const struct sk_buff *skb, const struct tcphdr *th,
176 const struct synproxy_options *opts)
177{
178 struct sk_buff *nskb;
179 struct ipv6hdr *iph, *niph;
180 struct tcphdr *nth;
181 unsigned int tcp_hdr_size;
182
183 iph = ipv6_hdr(skb);
184
185 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
186 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
187 GFP_ATOMIC);
188 if (nskb == NULL)
189 return;
190 skb_reserve(nskb, MAX_TCP_HEADER);
191
192 niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
193
194 skb_reset_transport_header(nskb);
195 nth = skb_put(nskb, tcp_hdr_size);
196 nth->source = th->dest;
197 nth->dest = th->source;
198 nth->seq = htonl(ntohl(th->ack_seq));
199 nth->ack_seq = htonl(ntohl(th->seq) + 1);
200 tcp_flag_word(nth) = TCP_FLAG_ACK;
201 nth->doff = tcp_hdr_size / 4;
202 nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
203 nth->check = 0;
204 nth->urg_ptr = 0;
205
206 synproxy_build_options(nth, opts);
207
208 synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
209}
210
211static void
212synproxy_send_client_ack(struct net *net,
213 const struct sk_buff *skb, const struct tcphdr *th,
214 const struct synproxy_options *opts)
215{
216 struct sk_buff *nskb;
217 struct ipv6hdr *iph, *niph;
218 struct tcphdr *nth;
219 unsigned int tcp_hdr_size;
220
221 iph = ipv6_hdr(skb);
222
223 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
224 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
225 GFP_ATOMIC);
226 if (nskb == NULL)
227 return;
228 skb_reserve(nskb, MAX_TCP_HEADER);
229
230 niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
231
232 skb_reset_transport_header(nskb);
233 nth = skb_put(nskb, tcp_hdr_size);
234 nth->source = th->source;
235 nth->dest = th->dest;
236 nth->seq = htonl(ntohl(th->seq) + 1);
237 nth->ack_seq = th->ack_seq;
238 tcp_flag_word(nth) = TCP_FLAG_ACK;
239 nth->doff = tcp_hdr_size / 4;
240 nth->window = htons(ntohs(th->window) >> opts->wscale);
241 nth->check = 0;
242 nth->urg_ptr = 0;
243
244 synproxy_build_options(nth, opts);
245
246 synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
247 IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
248}
249
250static bool
251synproxy_recv_client_ack(struct net *net,
252 const struct sk_buff *skb, const struct tcphdr *th,
253 struct synproxy_options *opts, u32 recv_seq)
254{
255 struct synproxy_net *snet = synproxy_pernet(net);
256 int mss;
257
258 mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
259 if (mss == 0) {
260 this_cpu_inc(snet->stats->cookie_invalid);
261 return false;
262 }
263
264 this_cpu_inc(snet->stats->cookie_valid);
265 opts->mss = mss;
266 opts->options |= XT_SYNPROXY_OPT_MSS;
267
268 if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
269 synproxy_check_timestamp_cookie(opts);
270
271 synproxy_send_server_syn(net, skb, th, opts, recv_seq);
272 return true;
273}
274
275static unsigned int
276synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
277{
278 const struct xt_synproxy_info *info = par->targinfo;
279 struct net *net = xt_net(par);
280 struct synproxy_net *snet = synproxy_pernet(net);
281 struct synproxy_options opts = {};
282 struct tcphdr *th, _th;
283
284 if (nf_ip6_checksum(skb, xt_hooknum(par), par->thoff, IPPROTO_TCP))
285 return NF_DROP;
286
287 th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
288 if (th == NULL)
289 return NF_DROP;
290
291 if (!synproxy_parse_options(skb, par->thoff, th, &opts))
292 return NF_DROP;
293
294 if (th->syn && !(th->ack || th->fin || th->rst)) {
295
296 this_cpu_inc(snet->stats->syn_received);
297
298 if (th->ece && th->cwr)
299 opts.options |= XT_SYNPROXY_OPT_ECN;
300
301 opts.options &= info->options;
302 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
303 synproxy_init_timestamp_cookie(info, &opts);
304 else
305 opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
306 XT_SYNPROXY_OPT_SACK_PERM |
307 XT_SYNPROXY_OPT_ECN);
308
309 synproxy_send_client_synack(net, skb, th, &opts);
310 consume_skb(skb);
311 return NF_STOLEN;
312
313 } else if (th->ack && !(th->fin || th->rst || th->syn)) {
314
315 if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) {
316 consume_skb(skb);
317 return NF_STOLEN;
318 } else {
319 return NF_DROP;
320 }
321 }
322
323 return XT_CONTINUE;
324}
325
326static unsigned int ipv6_synproxy_hook(void *priv,
327 struct sk_buff *skb,
328 const struct nf_hook_state *nhs)
329{
330 struct net *net = nhs->net;
331 struct synproxy_net *snet = synproxy_pernet(net);
332 enum ip_conntrack_info ctinfo;
333 struct nf_conn *ct;
334 struct nf_conn_synproxy *synproxy;
335 struct synproxy_options opts = {};
336 const struct ip_ct_tcp *state;
337 struct tcphdr *th, _th;
338 __be16 frag_off;
339 u8 nexthdr;
340 int thoff;
341
342 ct = nf_ct_get(skb, &ctinfo);
343 if (ct == NULL)
344 return NF_ACCEPT;
345
346 synproxy = nfct_synproxy(ct);
347 if (synproxy == NULL)
348 return NF_ACCEPT;
349
350 if (nf_is_loopback_packet(skb))
351 return NF_ACCEPT;
352
353 nexthdr = ipv6_hdr(skb)->nexthdr;
354 thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
355 &frag_off);
356 if (thoff < 0 || nexthdr != IPPROTO_TCP)
357 return NF_ACCEPT;
358
359 th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
360 if (th == NULL)
361 return NF_DROP;
362
363 state = &ct->proto.tcp;
364 switch (state->state) {
365 case TCP_CONNTRACK_CLOSE:
366 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
367 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
368 ntohl(th->seq) + 1);
369 break;
370 }
371
372 if (!th->syn || th->ack ||
373 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
374 break;
375
376
377
378
379
380 nf_ct_seqadj_init(ct, ctinfo, 0);
381 synproxy->tsoff = 0;
382 this_cpu_inc(snet->stats->conn_reopened);
383
384
385 case TCP_CONNTRACK_SYN_SENT:
386 if (!synproxy_parse_options(skb, thoff, th, &opts))
387 return NF_DROP;
388
389 if (!th->syn && th->ack &&
390 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
391
392
393
394
395 if (synproxy_recv_client_ack(net, skb, th, &opts,
396 ntohl(th->seq) + 1)) {
397 this_cpu_inc(snet->stats->cookie_retrans);
398 consume_skb(skb);
399 return NF_STOLEN;
400 } else {
401 return NF_DROP;
402 }
403 }
404
405 synproxy->isn = ntohl(th->ack_seq);
406 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
407 synproxy->its = opts.tsecr;
408 break;
409 case TCP_CONNTRACK_SYN_RECV:
410 if (!th->syn || !th->ack)
411 break;
412
413 if (!synproxy_parse_options(skb, thoff, th, &opts))
414 return NF_DROP;
415
416 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
417 synproxy->tsoff = opts.tsval - synproxy->its;
418
419 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
420 XT_SYNPROXY_OPT_WSCALE |
421 XT_SYNPROXY_OPT_SACK_PERM);
422
423 swap(opts.tsval, opts.tsecr);
424 synproxy_send_server_ack(net, state, skb, th, &opts);
425
426 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
427
428 swap(opts.tsval, opts.tsecr);
429 synproxy_send_client_ack(net, skb, th, &opts);
430
431 consume_skb(skb);
432 return NF_STOLEN;
433 default:
434 break;
435 }
436
437 synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
438 return NF_ACCEPT;
439}
440
441static const struct nf_hook_ops ipv6_synproxy_ops[] = {
442 {
443 .hook = ipv6_synproxy_hook,
444 .pf = NFPROTO_IPV6,
445 .hooknum = NF_INET_LOCAL_IN,
446 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
447 },
448 {
449 .hook = ipv6_synproxy_hook,
450 .pf = NFPROTO_IPV6,
451 .hooknum = NF_INET_POST_ROUTING,
452 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
453 },
454};
455
456static int synproxy_tg6_check(const struct xt_tgchk_param *par)
457{
458 struct synproxy_net *snet = synproxy_pernet(par->net);
459 const struct ip6t_entry *e = par->entryinfo;
460 int err;
461
462 if (!(e->ipv6.flags & IP6T_F_PROTO) ||
463 e->ipv6.proto != IPPROTO_TCP ||
464 e->ipv6.invflags & XT_INV_PROTO)
465 return -EINVAL;
466
467 err = nf_ct_netns_get(par->net, par->family);
468 if (err)
469 return err;
470
471 if (snet->hook_ref6 == 0) {
472 err = nf_register_net_hooks(par->net, ipv6_synproxy_ops,
473 ARRAY_SIZE(ipv6_synproxy_ops));
474 if (err) {
475 nf_ct_netns_put(par->net, par->family);
476 return err;
477 }
478 }
479
480 snet->hook_ref6++;
481 return err;
482}
483
484static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
485{
486 struct synproxy_net *snet = synproxy_pernet(par->net);
487
488 snet->hook_ref6--;
489 if (snet->hook_ref6 == 0)
490 nf_unregister_net_hooks(par->net, ipv6_synproxy_ops,
491 ARRAY_SIZE(ipv6_synproxy_ops));
492 nf_ct_netns_put(par->net, par->family);
493}
494
495static struct xt_target synproxy_tg6_reg __read_mostly = {
496 .name = "SYNPROXY",
497 .family = NFPROTO_IPV6,
498 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
499 .target = synproxy_tg6,
500 .targetsize = sizeof(struct xt_synproxy_info),
501 .checkentry = synproxy_tg6_check,
502 .destroy = synproxy_tg6_destroy,
503 .me = THIS_MODULE,
504};
505
506static int __init synproxy_tg6_init(void)
507{
508 return xt_register_target(&synproxy_tg6_reg);
509}
510
511static void __exit synproxy_tg6_exit(void)
512{
513 xt_unregister_target(&synproxy_tg6_reg);
514}
515
516module_init(synproxy_tg6_init);
517module_exit(synproxy_tg6_exit);
518
519MODULE_LICENSE("GPL");
520MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
521
