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netfilter: SYNPROXY: skip non-tcp packet in {ipv4, ipv6}_synproxy_hook
[linux-2.6/btrfs-unstable.git] / net / ipv4 / netfilter / ipt_SYNPROXY.c
blobf75fc6b531152a4d1f4fb96052ad47f3e76c9a21
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/tcp.h>
12
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>
19
20 static struct iphdr *
21 synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr,
22 __be32 daddr)
23 {
24 struct iphdr *iph;
25
26 skb_reset_network_header(skb);
27 iph = skb_put(skb, sizeof(*iph));
28 iph->version = 4;
29 iph->ihl = sizeof(*iph) / 4;
30 iph->tos = 0;
31 iph->id = 0;
32 iph->frag_off = htons(IP_DF);
33 iph->ttl = net->ipv4.sysctl_ip_default_ttl;
34 iph->protocol = IPPROTO_TCP;
35 iph->check = 0;
36 iph->saddr = saddr;
37 iph->daddr = daddr;
38
39 return iph;
40 }
41
42 static void
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)
48 {
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);
53
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))
57 goto free_nskb;
58
59 if (nfct) {
60 nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
61 nf_conntrack_get(nfct);
62 }
63
64 ip_local_out(net, nskb->sk, nskb);
65 return;
66
67 free_nskb:
68 kfree_skb(nskb);
69 }
70
71 static void
72 synproxy_send_client_synack(struct net *net,
73 const struct sk_buff *skb, const struct tcphdr *th,
74 const struct synproxy_options *opts)
75 {
76 struct sk_buff *nskb;
77 struct iphdr *iph, *niph;
78 struct tcphdr *nth;
79 unsigned int tcp_hdr_size;
80 u16 mss = opts->mss;
81
82 iph = ip_hdr(skb);
83
84 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
85 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
86 GFP_ATOMIC);
87 if (nskb == NULL)
88 return;
89 skb_reserve(nskb, MAX_TCP_HEADER);
90
91 niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
92
93 skb_reset_transport_header(nskb);
94 nth = skb_put(nskb, tcp_hdr_size);
95 nth->source = th->dest;
96 nth->dest = th->source;
97 nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss));
98 nth->ack_seq = htonl(ntohl(th->seq) + 1);
99 tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
100 if (opts->options & XT_SYNPROXY_OPT_ECN)
101 tcp_flag_word(nth) |= TCP_FLAG_ECE;
102 nth->doff = tcp_hdr_size / 4;
103 nth->window = 0;
104 nth->check = 0;
105 nth->urg_ptr = 0;
106
107 synproxy_build_options(nth, opts);
108
109 synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
110 IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
111 }
112
113 static void
114 synproxy_send_server_syn(struct net *net,
115 const struct sk_buff *skb, const struct tcphdr *th,
116 const struct synproxy_options *opts, u32 recv_seq)
117 {
118 struct synproxy_net *snet = synproxy_pernet(net);
119 struct sk_buff *nskb;
120 struct iphdr *iph, *niph;
121 struct tcphdr *nth;
122 unsigned int tcp_hdr_size;
123
124 iph = ip_hdr(skb);
125
126 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
127 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
128 GFP_ATOMIC);
129 if (nskb == NULL)
130 return;
131 skb_reserve(nskb, MAX_TCP_HEADER);
132
133 niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
134
135 skb_reset_transport_header(nskb);
136 nth = skb_put(nskb, tcp_hdr_size);
137 nth->source = th->source;
138 nth->dest = th->dest;
139 nth->seq = htonl(recv_seq - 1);
140 /* ack_seq is used to relay our ISN to the synproxy hook to initialize
141 * sequence number translation once a connection tracking entry exists.
142 */
143 nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
144 tcp_flag_word(nth) = TCP_FLAG_SYN;
145 if (opts->options & XT_SYNPROXY_OPT_ECN)
146 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
147 nth->doff = tcp_hdr_size / 4;
148 nth->window = th->window;
149 nth->check = 0;
150 nth->urg_ptr = 0;
151
152 synproxy_build_options(nth, opts);
153
154 synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
155 niph, nth, tcp_hdr_size);
156 }
157
158 static void
159 synproxy_send_server_ack(struct net *net,
160 const struct ip_ct_tcp *state,
161 const struct sk_buff *skb, const struct tcphdr *th,
162 const struct synproxy_options *opts)
163 {
164 struct sk_buff *nskb;
165 struct iphdr *iph, *niph;
166 struct tcphdr *nth;
167 unsigned int tcp_hdr_size;
168
169 iph = ip_hdr(skb);
170
171 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
172 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
173 GFP_ATOMIC);
174 if (nskb == NULL)
175 return;
176 skb_reserve(nskb, MAX_TCP_HEADER);
177
178 niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
179
180 skb_reset_transport_header(nskb);
181 nth = skb_put(nskb, tcp_hdr_size);
182 nth->source = th->dest;
183 nth->dest = th->source;
184 nth->seq = htonl(ntohl(th->ack_seq));
185 nth->ack_seq = htonl(ntohl(th->seq) + 1);
186 tcp_flag_word(nth) = TCP_FLAG_ACK;
187 nth->doff = tcp_hdr_size / 4;
188 nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
189 nth->check = 0;
190 nth->urg_ptr = 0;
191
192 synproxy_build_options(nth, opts);
193
194 synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
195 }
196
197 static void
198 synproxy_send_client_ack(struct net *net,
199 const struct sk_buff *skb, const struct tcphdr *th,
200 const struct synproxy_options *opts)
201 {
202 struct sk_buff *nskb;
203 struct iphdr *iph, *niph;
204 struct tcphdr *nth;
205 unsigned int tcp_hdr_size;
206
207 iph = ip_hdr(skb);
208
209 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
210 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
211 GFP_ATOMIC);
212 if (nskb == NULL)
213 return;
214 skb_reserve(nskb, MAX_TCP_HEADER);
215
216 niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr);
217
218 skb_reset_transport_header(nskb);
219 nth = skb_put(nskb, tcp_hdr_size);
220 nth->source = th->source;
221 nth->dest = th->dest;
222 nth->seq = htonl(ntohl(th->seq) + 1);
223 nth->ack_seq = th->ack_seq;
224 tcp_flag_word(nth) = TCP_FLAG_ACK;
225 nth->doff = tcp_hdr_size / 4;
226 nth->window = htons(ntohs(th->window) >> opts->wscale);
227 nth->check = 0;
228 nth->urg_ptr = 0;
229
230 synproxy_build_options(nth, opts);
231
232 synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
233 IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
234 }
235
236 static bool
237 synproxy_recv_client_ack(struct net *net,
238 const struct sk_buff *skb, const struct tcphdr *th,
239 struct synproxy_options *opts, u32 recv_seq)
240 {
241 struct synproxy_net *snet = synproxy_pernet(net);
242 int mss;
243
244 mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1);
245 if (mss == 0) {
246 this_cpu_inc(snet->stats->cookie_invalid);
247 return false;
248 }
249
250 this_cpu_inc(snet->stats->cookie_valid);
251 opts->mss = mss;
252 opts->options |= XT_SYNPROXY_OPT_MSS;
253
254 if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
255 synproxy_check_timestamp_cookie(opts);
256
257 synproxy_send_server_syn(net, skb, th, opts, recv_seq);
258 return true;
259 }
260
261 static unsigned int
262 synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
263 {
264 const struct xt_synproxy_info *info = par->targinfo;
265 struct net *net = xt_net(par);
266 struct synproxy_net *snet = synproxy_pernet(net);
267 struct synproxy_options opts = {};
268 struct tcphdr *th, _th;
269
270 if (nf_ip_checksum(skb, xt_hooknum(par), par->thoff, IPPROTO_TCP))
271 return NF_DROP;
272
273 th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
274 if (th == NULL)
275 return NF_DROP;
276
277 if (!synproxy_parse_options(skb, par->thoff, th, &opts))
278 return NF_DROP;
279
280 if (th->syn && !(th->ack || th->fin || th->rst)) {
281 /* Initial SYN from client */
282 this_cpu_inc(snet->stats->syn_received);
283
284 if (th->ece && th->cwr)
285 opts.options |= XT_SYNPROXY_OPT_ECN;
286
287 opts.options &= info->options;
288 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
289 synproxy_init_timestamp_cookie(info, &opts);
290 else
291 opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
292 XT_SYNPROXY_OPT_SACK_PERM |
293 XT_SYNPROXY_OPT_ECN);
294
295 synproxy_send_client_synack(net, skb, th, &opts);
296 consume_skb(skb);
297 return NF_STOLEN;
298 } else if (th->ack && !(th->fin || th->rst || th->syn)) {
299 /* ACK from client */
300 if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) {
301 consume_skb(skb);
302 return NF_STOLEN;
303 } else {
304 return NF_DROP;
305 }
306 }
307
308 return XT_CONTINUE;
309 }
310
311 static unsigned int ipv4_synproxy_hook(void *priv,
312 struct sk_buff *skb,
313 const struct nf_hook_state *nhs)
314 {
315 struct net *net = nhs->net;
316 struct synproxy_net *snet = synproxy_pernet(net);
317 enum ip_conntrack_info ctinfo;
318 struct nf_conn *ct;
319 struct nf_conn_synproxy *synproxy;
320 struct synproxy_options opts = {};
321 const struct ip_ct_tcp *state;
322 struct tcphdr *th, _th;
323 unsigned int thoff;
324
325 ct = nf_ct_get(skb, &ctinfo);
326 if (ct == NULL)
327 return NF_ACCEPT;
328
329 synproxy = nfct_synproxy(ct);
330 if (synproxy == NULL)
331 return NF_ACCEPT;
332
333 if (nf_is_loopback_packet(skb) ||
334 ip_hdr(skb)->protocol != IPPROTO_TCP)
335 return NF_ACCEPT;
336
337 thoff = ip_hdrlen(skb);
338 th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
339 if (th == NULL)
340 return NF_DROP;
341
342 state = &ct->proto.tcp;
343 switch (state->state) {
344 case TCP_CONNTRACK_CLOSE:
345 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
346 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
347 ntohl(th->seq) + 1);
348 break;
349 }
350
351 if (!th->syn || th->ack ||
352 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
353 break;
354
355 /* Reopened connection - reset the sequence number and timestamp
356 * adjustments, they will get initialized once the connection is
357 * reestablished.
358 */
359 nf_ct_seqadj_init(ct, ctinfo, 0);
360 synproxy->tsoff = 0;
361 this_cpu_inc(snet->stats->conn_reopened);
362
363 /* fall through */
364 case TCP_CONNTRACK_SYN_SENT:
365 if (!synproxy_parse_options(skb, thoff, th, &opts))
366 return NF_DROP;
367
368 if (!th->syn && th->ack &&
369 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
370 /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
371 * therefore we need to add 1 to make the SYN sequence
372 * number match the one of first SYN.
373 */
374 if (synproxy_recv_client_ack(net, skb, th, &opts,
375 ntohl(th->seq) + 1)) {
376 this_cpu_inc(snet->stats->cookie_retrans);
377 consume_skb(skb);
378 return NF_STOLEN;
379 } else {
380 return NF_DROP;
381 }
382 }
383
384 synproxy->isn = ntohl(th->ack_seq);
385 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
386 synproxy->its = opts.tsecr;
387 break;
388 case TCP_CONNTRACK_SYN_RECV:
389 if (!th->syn || !th->ack)
390 break;
391
392 if (!synproxy_parse_options(skb, thoff, th, &opts))
393 return NF_DROP;
394
395 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
396 synproxy->tsoff = opts.tsval - synproxy->its;
397
398 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
399 XT_SYNPROXY_OPT_WSCALE |
400 XT_SYNPROXY_OPT_SACK_PERM);
401
402 swap(opts.tsval, opts.tsecr);
403 synproxy_send_server_ack(net, state, skb, th, &opts);
404
405 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
406
407 swap(opts.tsval, opts.tsecr);
408 synproxy_send_client_ack(net, skb, th, &opts);
409
410 consume_skb(skb);
411 return NF_STOLEN;
412 default:
413 break;
414 }
415
416 synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
417 return NF_ACCEPT;
418 }
419
420 static const struct nf_hook_ops ipv4_synproxy_ops[] = {
421 {
422 .hook = ipv4_synproxy_hook,
423 .pf = NFPROTO_IPV4,
424 .hooknum = NF_INET_LOCAL_IN,
425 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
426 },
427 {
428 .hook = ipv4_synproxy_hook,
429 .pf = NFPROTO_IPV4,
430 .hooknum = NF_INET_POST_ROUTING,
431 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
432 },
433 };
434
435 static int synproxy_tg4_check(const struct xt_tgchk_param *par)
436 {
437 struct synproxy_net *snet = synproxy_pernet(par->net);
438 const struct ipt_entry *e = par->entryinfo;
439 int err;
440
441 if (e->ip.proto != IPPROTO_TCP ||
442 e->ip.invflags & XT_INV_PROTO)
443 return -EINVAL;
444
445 err = nf_ct_netns_get(par->net, par->family);
446 if (err)
447 return err;
448
449 if (snet->hook_ref4 == 0) {
450 err = nf_register_net_hooks(par->net, ipv4_synproxy_ops,
451 ARRAY_SIZE(ipv4_synproxy_ops));
452 if (err) {
453 nf_ct_netns_put(par->net, par->family);
454 return err;
455 }
456 }
457
458 snet->hook_ref4++;
459 return err;
460 }
461
462 static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
463 {
464 struct synproxy_net *snet = synproxy_pernet(par->net);
465
466 snet->hook_ref4--;
467 if (snet->hook_ref4 == 0)
468 nf_unregister_net_hooks(par->net, ipv4_synproxy_ops,
469 ARRAY_SIZE(ipv4_synproxy_ops));
470 nf_ct_netns_put(par->net, par->family);
471 }
472
473 static struct xt_target synproxy_tg4_reg __read_mostly = {
474 .name = "SYNPROXY",
475 .family = NFPROTO_IPV4,
476 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
477 .target = synproxy_tg4,
478 .targetsize = sizeof(struct xt_synproxy_info),
479 .checkentry = synproxy_tg4_check,
480 .destroy = synproxy_tg4_destroy,
481 .me = THIS_MODULE,
482 };
483
484 static int __init synproxy_tg4_init(void)
485 {
486 return xt_register_target(&synproxy_tg4_reg);
487 }
488
489 static void __exit synproxy_tg4_exit(void)
490 {
491 xt_unregister_target(&synproxy_tg4_reg);
492 }
493
494 module_init(synproxy_tg4_init);
495 module_exit(synproxy_tg4_exit);
496
497 MODULE_LICENSE("GPL");
498 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
(deprecated) Btrfs devel tree