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48b1de4c PM |
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 * | |
ba6d0564 | 21 | synproxy_build_ip(struct sk_buff *skb, __be32 saddr, __be32 daddr) |
48b1de4c PM |
22 | { |
23 | struct iphdr *iph; | |
24 | ||
25 | skb_reset_network_header(skb); | |
26 | iph = (struct iphdr *)skb_put(skb, sizeof(*iph)); | |
27 | iph->version = 4; | |
28 | iph->ihl = sizeof(*iph) / 4; | |
29 | iph->tos = 0; | |
30 | iph->id = 0; | |
31 | iph->frag_off = htons(IP_DF); | |
32 | iph->ttl = sysctl_ip_default_ttl; | |
33 | iph->protocol = IPPROTO_TCP; | |
34 | iph->check = 0; | |
35 | iph->saddr = saddr; | |
36 | iph->daddr = daddr; | |
37 | ||
38 | return iph; | |
39 | } | |
40 | ||
41 | static void | |
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) | |
46 | { | |
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); | |
51 | ||
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)) | |
55 | goto free_nskb; | |
56 | ||
57 | if (nfct) { | |
58 | nskb->nfct = nfct; | |
59 | nskb->nfctinfo = ctinfo; | |
60 | nf_conntrack_get(nfct); | |
61 | } | |
62 | ||
63 | ip_local_out(nskb); | |
64 | return; | |
65 | ||
66 | free_nskb: | |
67 | kfree_skb(nskb); | |
68 | } | |
69 | ||
70 | static void | |
71 | synproxy_send_client_synack(const struct sk_buff *skb, const struct tcphdr *th, | |
72 | const struct synproxy_options *opts) | |
73 | { | |
74 | struct sk_buff *nskb; | |
75 | struct iphdr *iph, *niph; | |
76 | struct tcphdr *nth; | |
77 | unsigned int tcp_hdr_size; | |
78 | u16 mss = opts->mss; | |
79 | ||
80 | iph = ip_hdr(skb); | |
81 | ||
82 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
83 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
84 | GFP_ATOMIC); | |
85 | if (nskb == NULL) | |
86 | return; | |
87 | skb_reserve(nskb, MAX_TCP_HEADER); | |
88 | ||
89 | niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr); | |
90 | ||
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; | |
101 | nth->window = 0; | |
102 | nth->check = 0; | |
103 | nth->urg_ptr = 0; | |
104 | ||
105 | synproxy_build_options(nth, opts); | |
106 | ||
107 | synproxy_send_tcp(skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY, | |
108 | niph, nth, tcp_hdr_size); | |
109 | } | |
110 | ||
111 | static void | |
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) | |
115 | { | |
116 | struct sk_buff *nskb; | |
117 | struct iphdr *iph, *niph; | |
118 | struct tcphdr *nth; | |
119 | unsigned int tcp_hdr_size; | |
120 | ||
121 | iph = ip_hdr(skb); | |
122 | ||
123 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
124 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
125 | GFP_ATOMIC); | |
126 | if (nskb == NULL) | |
127 | return; | |
128 | skb_reserve(nskb, MAX_TCP_HEADER); | |
129 | ||
130 | niph = synproxy_build_ip(nskb, iph->saddr, iph->daddr); | |
131 | ||
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. | |
139 | */ | |
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; | |
146 | nth->check = 0; | |
147 | nth->urg_ptr = 0; | |
148 | ||
149 | synproxy_build_options(nth, opts); | |
150 | ||
151 | synproxy_send_tcp(skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW, | |
152 | niph, nth, tcp_hdr_size); | |
153 | } | |
154 | ||
155 | static void | |
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) | |
160 | { | |
161 | struct sk_buff *nskb; | |
162 | struct iphdr *iph, *niph; | |
163 | struct tcphdr *nth; | |
164 | unsigned int tcp_hdr_size; | |
165 | ||
166 | iph = ip_hdr(skb); | |
167 | ||
168 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
169 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
170 | GFP_ATOMIC); | |
171 | if (nskb == NULL) | |
172 | return; | |
173 | skb_reserve(nskb, MAX_TCP_HEADER); | |
174 | ||
175 | niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr); | |
176 | ||
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); | |
186 | nth->check = 0; | |
187 | nth->urg_ptr = 0; | |
188 | ||
189 | synproxy_build_options(nth, opts); | |
190 | ||
191 | synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size); | |
192 | } | |
193 | ||
194 | static void | |
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) | |
198 | { | |
199 | struct sk_buff *nskb; | |
200 | struct iphdr *iph, *niph; | |
201 | struct tcphdr *nth; | |
202 | unsigned int tcp_hdr_size; | |
203 | ||
204 | iph = ip_hdr(skb); | |
205 | ||
206 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
207 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
208 | GFP_ATOMIC); | |
209 | if (nskb == NULL) | |
210 | return; | |
211 | skb_reserve(nskb, MAX_TCP_HEADER); | |
212 | ||
213 | niph = synproxy_build_ip(nskb, iph->saddr, iph->daddr); | |
214 | ||
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; | |
ba6d0564 | 223 | nth->window = htons(ntohs(th->window) >> opts->wscale); |
48b1de4c PM |
224 | nth->check = 0; |
225 | nth->urg_ptr = 0; | |
226 | ||
227 | synproxy_build_options(nth, opts); | |
228 | ||
3c16241c PS |
229 | synproxy_send_tcp(skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY, |
230 | niph, nth, tcp_hdr_size); | |
48b1de4c PM |
231 | } |
232 | ||
233 | static bool | |
234 | synproxy_recv_client_ack(const struct synproxy_net *snet, | |
235 | const struct sk_buff *skb, const struct tcphdr *th, | |
236 | struct synproxy_options *opts, u32 recv_seq) | |
237 | { | |
238 | int mss; | |
239 | ||
240 | mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1); | |
241 | if (mss == 0) { | |
242 | this_cpu_inc(snet->stats->cookie_invalid); | |
243 | return false; | |
244 | } | |
245 | ||
246 | this_cpu_inc(snet->stats->cookie_valid); | |
247 | opts->mss = mss; | |
a6441b7a | 248 | opts->options |= XT_SYNPROXY_OPT_MSS; |
48b1de4c PM |
249 | |
250 | if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP) | |
251 | synproxy_check_timestamp_cookie(opts); | |
252 | ||
253 | synproxy_send_server_syn(snet, skb, th, opts, recv_seq); | |
254 | return true; | |
255 | } | |
256 | ||
257 | static unsigned int | |
258 | synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par) | |
259 | { | |
260 | const struct xt_synproxy_info *info = par->targinfo; | |
261 | struct synproxy_net *snet = synproxy_pernet(dev_net(par->in)); | |
262 | struct synproxy_options opts = {}; | |
263 | struct tcphdr *th, _th; | |
264 | ||
265 | if (nf_ip_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP)) | |
266 | return NF_DROP; | |
267 | ||
268 | th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th); | |
269 | if (th == NULL) | |
270 | return NF_DROP; | |
271 | ||
f4a87e7b PM |
272 | if (!synproxy_parse_options(skb, par->thoff, th, &opts)) |
273 | return NF_DROP; | |
48b1de4c | 274 | |
775ada6d | 275 | if (th->syn && !(th->ack || th->fin || th->rst)) { |
48b1de4c PM |
276 | /* Initial SYN from client */ |
277 | this_cpu_inc(snet->stats->syn_received); | |
278 | ||
279 | if (th->ece && th->cwr) | |
280 | opts.options |= XT_SYNPROXY_OPT_ECN; | |
281 | ||
282 | opts.options &= info->options; | |
283 | if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) | |
284 | synproxy_init_timestamp_cookie(info, &opts); | |
285 | else | |
286 | opts.options &= ~(XT_SYNPROXY_OPT_WSCALE | | |
287 | XT_SYNPROXY_OPT_SACK_PERM | | |
288 | XT_SYNPROXY_OPT_ECN); | |
289 | ||
290 | synproxy_send_client_synack(skb, th, &opts); | |
7cc9eb6e JDB |
291 | return NF_DROP; |
292 | ||
293 | } else if (th->ack && !(th->fin || th->rst || th->syn)) { | |
48b1de4c PM |
294 | /* ACK from client */ |
295 | synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq)); | |
7cc9eb6e JDB |
296 | return NF_DROP; |
297 | } | |
48b1de4c | 298 | |
7cc9eb6e | 299 | return XT_CONTINUE; |
48b1de4c PM |
300 | } |
301 | ||
795aa6ef | 302 | static unsigned int ipv4_synproxy_hook(const struct nf_hook_ops *ops, |
48b1de4c | 303 | struct sk_buff *skb, |
238e54c9 | 304 | const struct nf_hook_state *nhs) |
48b1de4c | 305 | { |
238e54c9 | 306 | struct synproxy_net *snet = synproxy_pernet(dev_net(nhs->in ? : nhs->out)); |
48b1de4c PM |
307 | enum ip_conntrack_info ctinfo; |
308 | struct nf_conn *ct; | |
309 | struct nf_conn_synproxy *synproxy; | |
310 | struct synproxy_options opts = {}; | |
311 | const struct ip_ct_tcp *state; | |
312 | struct tcphdr *th, _th; | |
313 | unsigned int thoff; | |
314 | ||
315 | ct = nf_ct_get(skb, &ctinfo); | |
316 | if (ct == NULL) | |
317 | return NF_ACCEPT; | |
318 | ||
319 | synproxy = nfct_synproxy(ct); | |
320 | if (synproxy == NULL) | |
321 | return NF_ACCEPT; | |
322 | ||
323 | if (nf_is_loopback_packet(skb)) | |
324 | return NF_ACCEPT; | |
325 | ||
326 | thoff = ip_hdrlen(skb); | |
327 | th = skb_header_pointer(skb, thoff, sizeof(_th), &_th); | |
328 | if (th == NULL) | |
329 | return NF_DROP; | |
330 | ||
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 - | |
336 | ntohl(th->seq) + 1); | |
337 | break; | |
338 | } | |
339 | ||
340 | if (!th->syn || th->ack || | |
341 | CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) | |
342 | break; | |
343 | ||
344 | /* Reopened connection - reset the sequence number and timestamp | |
345 | * adjustments, they will get initialized once the connection is | |
346 | * reestablished. | |
347 | */ | |
348 | nf_ct_seqadj_init(ct, ctinfo, 0); | |
349 | synproxy->tsoff = 0; | |
350 | this_cpu_inc(snet->stats->conn_reopened); | |
351 | ||
352 | /* fall through */ | |
353 | case TCP_CONNTRACK_SYN_SENT: | |
f4a87e7b PM |
354 | if (!synproxy_parse_options(skb, thoff, th, &opts)) |
355 | return NF_DROP; | |
48b1de4c PM |
356 | |
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. | |
362 | */ | |
363 | if (synproxy_recv_client_ack(snet, skb, th, &opts, | |
364 | ntohl(th->seq) + 1)) | |
365 | this_cpu_inc(snet->stats->cookie_retrans); | |
366 | ||
367 | return NF_DROP; | |
368 | } | |
369 | ||
370 | synproxy->isn = ntohl(th->ack_seq); | |
371 | if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) | |
372 | synproxy->its = opts.tsecr; | |
373 | break; | |
374 | case TCP_CONNTRACK_SYN_RECV: | |
375 | if (!th->syn || !th->ack) | |
376 | break; | |
377 | ||
f4a87e7b PM |
378 | if (!synproxy_parse_options(skb, thoff, th, &opts)) |
379 | return NF_DROP; | |
380 | ||
48b1de4c PM |
381 | if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) |
382 | synproxy->tsoff = opts.tsval - synproxy->its; | |
383 | ||
384 | opts.options &= ~(XT_SYNPROXY_OPT_MSS | | |
385 | XT_SYNPROXY_OPT_WSCALE | | |
386 | XT_SYNPROXY_OPT_SACK_PERM); | |
387 | ||
388 | swap(opts.tsval, opts.tsecr); | |
389 | synproxy_send_server_ack(snet, state, skb, th, &opts); | |
390 | ||
391 | nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq)); | |
392 | ||
393 | swap(opts.tsval, opts.tsecr); | |
394 | synproxy_send_client_ack(snet, skb, th, &opts); | |
395 | ||
396 | consume_skb(skb); | |
397 | return NF_STOLEN; | |
398 | default: | |
399 | break; | |
400 | } | |
401 | ||
402 | synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy); | |
403 | return NF_ACCEPT; | |
404 | } | |
405 | ||
406 | static int synproxy_tg4_check(const struct xt_tgchk_param *par) | |
407 | { | |
408 | const struct ipt_entry *e = par->entryinfo; | |
409 | ||
410 | if (e->ip.proto != IPPROTO_TCP || | |
411 | e->ip.invflags & XT_INV_PROTO) | |
412 | return -EINVAL; | |
413 | ||
414 | return nf_ct_l3proto_try_module_get(par->family); | |
415 | } | |
416 | ||
417 | static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par) | |
418 | { | |
419 | nf_ct_l3proto_module_put(par->family); | |
420 | } | |
421 | ||
422 | static struct xt_target synproxy_tg4_reg __read_mostly = { | |
423 | .name = "SYNPROXY", | |
424 | .family = NFPROTO_IPV4, | |
f01b3926 | 425 | .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD), |
48b1de4c PM |
426 | .target = synproxy_tg4, |
427 | .targetsize = sizeof(struct xt_synproxy_info), | |
428 | .checkentry = synproxy_tg4_check, | |
429 | .destroy = synproxy_tg4_destroy, | |
430 | .me = THIS_MODULE, | |
431 | }; | |
432 | ||
433 | static struct nf_hook_ops ipv4_synproxy_ops[] __read_mostly = { | |
434 | { | |
435 | .hook = ipv4_synproxy_hook, | |
436 | .owner = THIS_MODULE, | |
437 | .pf = NFPROTO_IPV4, | |
438 | .hooknum = NF_INET_LOCAL_IN, | |
439 | .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, | |
440 | }, | |
441 | { | |
442 | .hook = ipv4_synproxy_hook, | |
443 | .owner = THIS_MODULE, | |
444 | .pf = NFPROTO_IPV4, | |
445 | .hooknum = NF_INET_POST_ROUTING, | |
446 | .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, | |
447 | }, | |
448 | }; | |
449 | ||
450 | static int __init synproxy_tg4_init(void) | |
451 | { | |
452 | int err; | |
453 | ||
454 | err = nf_register_hooks(ipv4_synproxy_ops, | |
455 | ARRAY_SIZE(ipv4_synproxy_ops)); | |
456 | if (err < 0) | |
457 | goto err1; | |
458 | ||
459 | err = xt_register_target(&synproxy_tg4_reg); | |
460 | if (err < 0) | |
461 | goto err2; | |
462 | ||
463 | return 0; | |
464 | ||
465 | err2: | |
466 | nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops)); | |
467 | err1: | |
468 | return err; | |
469 | } | |
470 | ||
471 | static void __exit synproxy_tg4_exit(void) | |
472 | { | |
473 | xt_unregister_target(&synproxy_tg4_reg); | |
474 | nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops)); | |
475 | } | |
476 | ||
477 | module_init(synproxy_tg4_init); | |
478 | module_exit(synproxy_tg4_exit); | |
479 | ||
480 | MODULE_LICENSE("GPL"); | |
481 | MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>"); |