1 /*
2 * Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
3 *
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.
7 */
8
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
22 static struct ipv6hdr *
23 synproxy_build_ip(struct sk_buff *skb, const struct in6_addr *saddr,
24 const struct in6_addr *daddr)
25 {
26 struct ipv6hdr *iph;
27
28 skb_reset_network_header(skb);
29 iph = (struct ipv6hdr *)skb_put(skb, sizeof(*iph));
30 ip6_flow_hdr(iph, 0, 0);
31 iph->hop_limit = 64; //XXX
32 iph->nexthdr = IPPROTO_TCP;
33 iph->saddr = *saddr;
34 iph->daddr = *daddr;
35
36 return iph;
37 }
38
39 static void
40 synproxy_send_tcp(const struct synproxy_net *snet,
41 const struct sk_buff *skb, struct sk_buff *nskb,
42 struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
43 struct ipv6hdr *niph, struct tcphdr *nth,
44 unsigned int tcp_hdr_size)
45 {
46 struct net *net = nf_ct_net(snet->tmpl);
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 == NULL || 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 nskb->nfct = nfct;
75 nskb->nfctinfo = ctinfo;
76 nf_conntrack_get(nfct);
77 }
78
79 ip6_local_out(net, nskb->sk, nskb);
80 return;
81
82 free_nskb:
83 kfree_skb(nskb);
84 }
85
86 static void
87 synproxy_send_client_synack(const struct synproxy_net *snet,
88 const struct sk_buff *skb, const struct tcphdr *th,
89 const struct synproxy_options *opts)
90 {
91 struct sk_buff *nskb;
92 struct ipv6hdr *iph, *niph;
93 struct tcphdr *nth;
94 unsigned int tcp_hdr_size;
95 u16 mss = opts->mss;
96
97 iph = ipv6_hdr(skb);
98
99 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
100 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
101 GFP_ATOMIC);
102 if (nskb == NULL)
103 return;
104 skb_reserve(nskb, MAX_TCP_HEADER);
105
106 niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);
107
108 skb_reset_transport_header(nskb);
109 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
110 nth->source = th->dest;
111 nth->dest = th->source;
112 nth->seq = htonl(__cookie_v6_init_sequence(iph, th, &mss));
113 nth->ack_seq = htonl(ntohl(th->seq) + 1);
114 tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
115 if (opts->options & XT_SYNPROXY_OPT_ECN)
116 tcp_flag_word(nth) |= TCP_FLAG_ECE;
117 nth->doff = tcp_hdr_size / 4;
118 nth->window = 0;
119 nth->check = 0;
120 nth->urg_ptr = 0;
121
122 synproxy_build_options(nth, opts);
123
124 synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
125 niph, nth, tcp_hdr_size);
126 }
127
128 static void
129 synproxy_send_server_syn(const struct synproxy_net *snet,
130 const struct sk_buff *skb, const struct tcphdr *th,
131 const struct synproxy_options *opts, u32 recv_seq)
132 {
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(nskb, &iph->saddr, &iph->daddr);
148
149 skb_reset_transport_header(nskb);
150 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
151 nth->source = th->source;
152 nth->dest = th->dest;
153 nth->seq = htonl(recv_seq - 1);
154 /* ack_seq is used to relay our ISN to the synproxy hook to initialize
155 * sequence number translation once a connection tracking entry exists.
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(snet, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
169 niph, nth, tcp_hdr_size);
170 }
171
172 static void
173 synproxy_send_server_ack(const struct synproxy_net *snet,
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(nskb, &iph->daddr, &iph->saddr);
193
194 skb_reset_transport_header(nskb);
195 nth = (struct tcphdr *)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(snet, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
209 }
210
211 static void
212 synproxy_send_client_ack(const struct synproxy_net *snet,
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(nskb, &iph->saddr, &iph->daddr);
231
232 skb_reset_transport_header(nskb);
233 nth = (struct tcphdr *)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(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
247 niph, nth, tcp_hdr_size);
248 }
249
250 static bool
251 synproxy_recv_client_ack(const struct synproxy_net *snet,
252 const struct sk_buff *skb, const struct tcphdr *th,
253 struct synproxy_options *opts, u32 recv_seq)
254 {
255 int mss;
256
257 mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
258 if (mss == 0) {
259 this_cpu_inc(snet->stats->cookie_invalid);
260 return false;
261 }
262
263 this_cpu_inc(snet->stats->cookie_valid);
264 opts->mss = mss;
265 opts->options |= XT_SYNPROXY_OPT_MSS;
266
267 if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
268 synproxy_check_timestamp_cookie(opts);
269
270 synproxy_send_server_syn(snet, skb, th, opts, recv_seq);
271 return true;
272 }
273
274 static unsigned int
275 synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
276 {
277 const struct xt_synproxy_info *info = par->targinfo;
278 struct synproxy_net *snet = synproxy_pernet(par->net);
279 struct synproxy_options opts = {};
280 struct tcphdr *th, _th;
281
282 if (nf_ip6_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
283 return NF_DROP;
284
285 th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
286 if (th == NULL)
287 return NF_DROP;
288
289 if (!synproxy_parse_options(skb, par->thoff, th, &opts))
290 return NF_DROP;
291
292 if (th->syn && !(th->ack || th->fin || th->rst)) {
293 /* Initial SYN from client */
294 this_cpu_inc(snet->stats->syn_received);
295
296 if (th->ece && th->cwr)
297 opts.options |= XT_SYNPROXY_OPT_ECN;
298
299 opts.options &= info->options;
300 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
301 synproxy_init_timestamp_cookie(info, &opts);
302 else
303 opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
304 XT_SYNPROXY_OPT_SACK_PERM |
305 XT_SYNPROXY_OPT_ECN);
306
307 synproxy_send_client_synack(snet, skb, th, &opts);
308 return NF_DROP;
309
310 } else if (th->ack && !(th->fin || th->rst || th->syn)) {
311 /* ACK from client */
312 synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
313 return NF_DROP;
314 }
315
316 return XT_CONTINUE;
317 }
318
319 static unsigned int ipv6_synproxy_hook(void *priv,
320 struct sk_buff *skb,
321 const struct nf_hook_state *nhs)
322 {
323 struct synproxy_net *snet = synproxy_pernet(nhs->net);
324 enum ip_conntrack_info ctinfo;
325 struct nf_conn *ct;
326 struct nf_conn_synproxy *synproxy;
327 struct synproxy_options opts = {};
328 const struct ip_ct_tcp *state;
329 struct tcphdr *th, _th;
330 __be16 frag_off;
331 u8 nexthdr;
332 int thoff;
333
334 ct = nf_ct_get(skb, &ctinfo);
335 if (ct == NULL)
336 return NF_ACCEPT;
337
338 synproxy = nfct_synproxy(ct);
339 if (synproxy == NULL)
340 return NF_ACCEPT;
341
342 if (nf_is_loopback_packet(skb))
343 return NF_ACCEPT;
344
345 nexthdr = ipv6_hdr(skb)->nexthdr;
346 thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
347 &frag_off);
348 if (thoff < 0)
349 return NF_ACCEPT;
350
351 th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
352 if (th == NULL)
353 return NF_DROP;
354
355 state = &ct->proto.tcp;
356 switch (state->state) {
357 case TCP_CONNTRACK_CLOSE:
358 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
359 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
360 ntohl(th->seq) + 1);
361 break;
362 }
363
364 if (!th->syn || th->ack ||
365 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
366 break;
367
368 /* Reopened connection - reset the sequence number and timestamp
369 * adjustments, they will get initialized once the connection is
370 * reestablished.
371 */
372 nf_ct_seqadj_init(ct, ctinfo, 0);
373 synproxy->tsoff = 0;
374 this_cpu_inc(snet->stats->conn_reopened);
375
376 /* fall through */
377 case TCP_CONNTRACK_SYN_SENT:
378 if (!synproxy_parse_options(skb, thoff, th, &opts))
379 return NF_DROP;
380
381 if (!th->syn && th->ack &&
382 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
383 /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
384 * therefore we need to add 1 to make the SYN sequence
385 * number match the one of first SYN.
386 */
387 if (synproxy_recv_client_ack(snet, skb, th, &opts,
388 ntohl(th->seq) + 1))
389 this_cpu_inc(snet->stats->cookie_retrans);
390
391 return NF_DROP;
392 }
393
394 synproxy->isn = ntohl(th->ack_seq);
395 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
396 synproxy->its = opts.tsecr;
397 break;
398 case TCP_CONNTRACK_SYN_RECV:
399 if (!th->syn || !th->ack)
400 break;
401
402 if (!synproxy_parse_options(skb, thoff, th, &opts))
403 return NF_DROP;
404
405 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
406 synproxy->tsoff = opts.tsval - synproxy->its;
407
408 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
409 XT_SYNPROXY_OPT_WSCALE |
410 XT_SYNPROXY_OPT_SACK_PERM);
411
412 swap(opts.tsval, opts.tsecr);
413 synproxy_send_server_ack(snet, state, skb, th, &opts);
414
415 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
416
417 swap(opts.tsval, opts.tsecr);
418 synproxy_send_client_ack(snet, skb, th, &opts);
419
420 consume_skb(skb);
421 return NF_STOLEN;
422 default:
423 break;
424 }
425
426 synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
427 return NF_ACCEPT;
428 }
429
430 static int synproxy_tg6_check(const struct xt_tgchk_param *par)
431 {
432 const struct ip6t_entry *e = par->entryinfo;
433
434 if (!(e->ipv6.flags & IP6T_F_PROTO) ||
435 e->ipv6.proto != IPPROTO_TCP ||
436 e->ipv6.invflags & XT_INV_PROTO)
437 return -EINVAL;
438
439 return nf_ct_l3proto_try_module_get(par->family);
440 }
441
442 static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
443 {
444 nf_ct_l3proto_module_put(par->family);
445 }
446
447 static struct xt_target synproxy_tg6_reg __read_mostly = {
448 .name = "SYNPROXY",
449 .family = NFPROTO_IPV6,
450 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
451 .target = synproxy_tg6,
452 .targetsize = sizeof(struct xt_synproxy_info),
453 .checkentry = synproxy_tg6_check,
454 .destroy = synproxy_tg6_destroy,
455 .me = THIS_MODULE,
456 };
457
458 static struct nf_hook_ops ipv6_synproxy_ops[] __read_mostly = {
459 {
460 .hook = ipv6_synproxy_hook,
461 .pf = NFPROTO_IPV6,
462 .hooknum = NF_INET_LOCAL_IN,
463 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
464 },
465 {
466 .hook = ipv6_synproxy_hook,
467 .pf = NFPROTO_IPV6,
468 .hooknum = NF_INET_POST_ROUTING,
469 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
470 },
471 };
472
473 static int __init synproxy_tg6_init(void)
474 {
475 int err;
476
477 err = nf_register_hooks(ipv6_synproxy_ops,
478 ARRAY_SIZE(ipv6_synproxy_ops));
479 if (err < 0)
480 goto err1;
481
482 err = xt_register_target(&synproxy_tg6_reg);
483 if (err < 0)
484 goto err2;
485
486 return 0;
487
488 err2:
489 nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
490 err1:
491 return err;
492 }
493
494 static void __exit synproxy_tg6_exit(void)
495 {
496 xt_unregister_target(&synproxy_tg6_reg);
497 nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
498 }
499
500 module_init(synproxy_tg6_init);
501 module_exit(synproxy_tg6_exit);
502
503 MODULE_LICENSE("GPL");
504 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
505
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