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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 | |
6a1d689d EB |
42 | synproxy_send_tcp(const struct synproxy_net *snet, |
43 | const struct sk_buff *skb, struct sk_buff *nskb, | |
48b1de4c PM |
44 | struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo, |
45 | struct iphdr *niph, struct tcphdr *nth, | |
46 | unsigned int tcp_hdr_size) | |
47 | { | |
e45f5066 EB |
48 | struct net *net = nf_ct_net(snet->tmpl); |
49 | ||
48b1de4c PM |
50 | nth->check = ~tcp_v4_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 | skb_dst_set_noref(nskb, skb_dst(skb)); | |
56 | nskb->protocol = htons(ETH_P_IP); | |
e45f5066 | 57 | if (ip_route_me_harder(net, nskb, RTN_UNSPEC)) |
48b1de4c PM |
58 | goto free_nskb; |
59 | ||
60 | if (nfct) { | |
61 | nskb->nfct = nfct; | |
62 | nskb->nfctinfo = ctinfo; | |
63 | nf_conntrack_get(nfct); | |
64 | } | |
65 | ||
33224b16 | 66 | ip_local_out(net, nskb->sk, nskb); |
48b1de4c PM |
67 | return; |
68 | ||
69 | free_nskb: | |
70 | kfree_skb(nskb); | |
71 | } | |
72 | ||
73 | static void | |
6a1d689d EB |
74 | synproxy_send_client_synack(const struct synproxy_net *snet, |
75 | const struct sk_buff *skb, const struct tcphdr *th, | |
48b1de4c PM |
76 | const struct synproxy_options *opts) |
77 | { | |
78 | struct sk_buff *nskb; | |
79 | struct iphdr *iph, *niph; | |
80 | struct tcphdr *nth; | |
81 | unsigned int tcp_hdr_size; | |
82 | u16 mss = opts->mss; | |
83 | ||
84 | iph = ip_hdr(skb); | |
85 | ||
86 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
87 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
88 | GFP_ATOMIC); | |
89 | if (nskb == NULL) | |
90 | return; | |
91 | skb_reserve(nskb, MAX_TCP_HEADER); | |
92 | ||
93 | niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr); | |
94 | ||
95 | skb_reset_transport_header(nskb); | |
96 | nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size); | |
97 | nth->source = th->dest; | |
98 | nth->dest = th->source; | |
99 | nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss)); | |
100 | nth->ack_seq = htonl(ntohl(th->seq) + 1); | |
101 | tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK; | |
102 | if (opts->options & XT_SYNPROXY_OPT_ECN) | |
103 | tcp_flag_word(nth) |= TCP_FLAG_ECE; | |
104 | nth->doff = tcp_hdr_size / 4; | |
105 | nth->window = 0; | |
106 | nth->check = 0; | |
107 | nth->urg_ptr = 0; | |
108 | ||
109 | synproxy_build_options(nth, opts); | |
110 | ||
6a1d689d | 111 | synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY, |
48b1de4c PM |
112 | niph, nth, tcp_hdr_size); |
113 | } | |
114 | ||
115 | static void | |
116 | synproxy_send_server_syn(const struct synproxy_net *snet, | |
117 | const struct sk_buff *skb, const struct tcphdr *th, | |
118 | const struct synproxy_options *opts, u32 recv_seq) | |
119 | { | |
120 | struct sk_buff *nskb; | |
121 | struct iphdr *iph, *niph; | |
122 | struct tcphdr *nth; | |
123 | unsigned int tcp_hdr_size; | |
124 | ||
125 | iph = ip_hdr(skb); | |
126 | ||
127 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
128 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
129 | GFP_ATOMIC); | |
130 | if (nskb == NULL) | |
131 | return; | |
132 | skb_reserve(nskb, MAX_TCP_HEADER); | |
133 | ||
134 | niph = synproxy_build_ip(nskb, iph->saddr, iph->daddr); | |
135 | ||
136 | skb_reset_transport_header(nskb); | |
137 | nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size); | |
138 | nth->source = th->source; | |
139 | nth->dest = th->dest; | |
140 | nth->seq = htonl(recv_seq - 1); | |
141 | /* ack_seq is used to relay our ISN to the synproxy hook to initialize | |
142 | * sequence number translation once a connection tracking entry exists. | |
143 | */ | |
144 | nth->ack_seq = htonl(ntohl(th->ack_seq) - 1); | |
145 | tcp_flag_word(nth) = TCP_FLAG_SYN; | |
146 | if (opts->options & XT_SYNPROXY_OPT_ECN) | |
147 | tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR; | |
148 | nth->doff = tcp_hdr_size / 4; | |
149 | nth->window = th->window; | |
150 | nth->check = 0; | |
151 | nth->urg_ptr = 0; | |
152 | ||
153 | synproxy_build_options(nth, opts); | |
154 | ||
6a1d689d | 155 | synproxy_send_tcp(snet, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW, |
48b1de4c PM |
156 | niph, nth, tcp_hdr_size); |
157 | } | |
158 | ||
159 | static void | |
160 | synproxy_send_server_ack(const struct synproxy_net *snet, | |
161 | const struct ip_ct_tcp *state, | |
162 | const struct sk_buff *skb, const struct tcphdr *th, | |
163 | const struct synproxy_options *opts) | |
164 | { | |
165 | struct sk_buff *nskb; | |
166 | struct iphdr *iph, *niph; | |
167 | struct tcphdr *nth; | |
168 | unsigned int tcp_hdr_size; | |
169 | ||
170 | iph = ip_hdr(skb); | |
171 | ||
172 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
173 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
174 | GFP_ATOMIC); | |
175 | if (nskb == NULL) | |
176 | return; | |
177 | skb_reserve(nskb, MAX_TCP_HEADER); | |
178 | ||
179 | niph = synproxy_build_ip(nskb, iph->daddr, iph->saddr); | |
180 | ||
181 | skb_reset_transport_header(nskb); | |
182 | nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size); | |
183 | nth->source = th->dest; | |
184 | nth->dest = th->source; | |
185 | nth->seq = htonl(ntohl(th->ack_seq)); | |
186 | nth->ack_seq = htonl(ntohl(th->seq) + 1); | |
187 | tcp_flag_word(nth) = TCP_FLAG_ACK; | |
188 | nth->doff = tcp_hdr_size / 4; | |
189 | nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin); | |
190 | nth->check = 0; | |
191 | nth->urg_ptr = 0; | |
192 | ||
193 | synproxy_build_options(nth, opts); | |
194 | ||
6a1d689d | 195 | synproxy_send_tcp(snet, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size); |
48b1de4c PM |
196 | } |
197 | ||
198 | static void | |
199 | synproxy_send_client_ack(const struct synproxy_net *snet, | |
200 | const struct sk_buff *skb, const struct tcphdr *th, | |
201 | const struct synproxy_options *opts) | |
202 | { | |
203 | struct sk_buff *nskb; | |
204 | struct iphdr *iph, *niph; | |
205 | struct tcphdr *nth; | |
206 | unsigned int tcp_hdr_size; | |
207 | ||
208 | iph = ip_hdr(skb); | |
209 | ||
210 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
211 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
212 | GFP_ATOMIC); | |
213 | if (nskb == NULL) | |
214 | return; | |
215 | skb_reserve(nskb, MAX_TCP_HEADER); | |
216 | ||
217 | niph = synproxy_build_ip(nskb, iph->saddr, iph->daddr); | |
218 | ||
219 | skb_reset_transport_header(nskb); | |
220 | nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size); | |
221 | nth->source = th->source; | |
222 | nth->dest = th->dest; | |
223 | nth->seq = htonl(ntohl(th->seq) + 1); | |
224 | nth->ack_seq = th->ack_seq; | |
225 | tcp_flag_word(nth) = TCP_FLAG_ACK; | |
226 | nth->doff = tcp_hdr_size / 4; | |
ba6d0564 | 227 | nth->window = htons(ntohs(th->window) >> opts->wscale); |
48b1de4c PM |
228 | nth->check = 0; |
229 | nth->urg_ptr = 0; | |
230 | ||
231 | synproxy_build_options(nth, opts); | |
232 | ||
6a1d689d | 233 | synproxy_send_tcp(snet, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY, |
3c16241c | 234 | niph, nth, tcp_hdr_size); |
48b1de4c PM |
235 | } |
236 | ||
237 | static bool | |
238 | synproxy_recv_client_ack(const struct synproxy_net *snet, | |
239 | const struct sk_buff *skb, const struct tcphdr *th, | |
240 | struct synproxy_options *opts, u32 recv_seq) | |
241 | { | |
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; | |
a6441b7a | 252 | opts->options |= XT_SYNPROXY_OPT_MSS; |
48b1de4c PM |
253 | |
254 | if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP) | |
255 | synproxy_check_timestamp_cookie(opts); | |
256 | ||
257 | synproxy_send_server_syn(snet, 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; | |
686c9b50 | 265 | struct synproxy_net *snet = synproxy_pernet(par->net); |
48b1de4c PM |
266 | struct synproxy_options opts = {}; |
267 | struct tcphdr *th, _th; | |
268 | ||
269 | if (nf_ip_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP)) | |
270 | return NF_DROP; | |
271 | ||
272 | th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th); | |
273 | if (th == NULL) | |
274 | return NF_DROP; | |
275 | ||
f4a87e7b PM |
276 | if (!synproxy_parse_options(skb, par->thoff, th, &opts)) |
277 | return NF_DROP; | |
48b1de4c | 278 | |
775ada6d | 279 | if (th->syn && !(th->ack || th->fin || th->rst)) { |
48b1de4c PM |
280 | /* Initial SYN from client */ |
281 | this_cpu_inc(snet->stats->syn_received); | |
282 | ||
283 | if (th->ece && th->cwr) | |
284 | opts.options |= XT_SYNPROXY_OPT_ECN; | |
285 | ||
286 | opts.options &= info->options; | |
287 | if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) | |
288 | synproxy_init_timestamp_cookie(info, &opts); | |
289 | else | |
290 | opts.options &= ~(XT_SYNPROXY_OPT_WSCALE | | |
291 | XT_SYNPROXY_OPT_SACK_PERM | | |
292 | XT_SYNPROXY_OPT_ECN); | |
293 | ||
6a1d689d | 294 | synproxy_send_client_synack(snet, skb, th, &opts); |
7cc9eb6e JDB |
295 | return NF_DROP; |
296 | ||
297 | } else if (th->ack && !(th->fin || th->rst || th->syn)) { | |
48b1de4c PM |
298 | /* ACK from client */ |
299 | synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq)); | |
7cc9eb6e JDB |
300 | return NF_DROP; |
301 | } | |
48b1de4c | 302 | |
7cc9eb6e | 303 | return XT_CONTINUE; |
48b1de4c PM |
304 | } |
305 | ||
06198b34 | 306 | static unsigned int ipv4_synproxy_hook(void *priv, |
48b1de4c | 307 | struct sk_buff *skb, |
238e54c9 | 308 | const struct nf_hook_state *nhs) |
48b1de4c | 309 | { |
9dff2c96 | 310 | struct synproxy_net *snet = synproxy_pernet(nhs->net); |
48b1de4c PM |
311 | enum ip_conntrack_info ctinfo; |
312 | struct nf_conn *ct; | |
313 | struct nf_conn_synproxy *synproxy; | |
314 | struct synproxy_options opts = {}; | |
315 | const struct ip_ct_tcp *state; | |
316 | struct tcphdr *th, _th; | |
317 | unsigned int thoff; | |
318 | ||
319 | ct = nf_ct_get(skb, &ctinfo); | |
320 | if (ct == NULL) | |
321 | return NF_ACCEPT; | |
322 | ||
323 | synproxy = nfct_synproxy(ct); | |
324 | if (synproxy == NULL) | |
325 | return NF_ACCEPT; | |
326 | ||
327 | if (nf_is_loopback_packet(skb)) | |
328 | return NF_ACCEPT; | |
329 | ||
330 | thoff = ip_hdrlen(skb); | |
331 | th = skb_header_pointer(skb, thoff, sizeof(_th), &_th); | |
332 | if (th == NULL) | |
333 | return NF_DROP; | |
334 | ||
335 | state = &ct->proto.tcp; | |
336 | switch (state->state) { | |
337 | case TCP_CONNTRACK_CLOSE: | |
338 | if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) { | |
339 | nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - | |
340 | ntohl(th->seq) + 1); | |
341 | break; | |
342 | } | |
343 | ||
344 | if (!th->syn || th->ack || | |
345 | CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) | |
346 | break; | |
347 | ||
348 | /* Reopened connection - reset the sequence number and timestamp | |
349 | * adjustments, they will get initialized once the connection is | |
350 | * reestablished. | |
351 | */ | |
352 | nf_ct_seqadj_init(ct, ctinfo, 0); | |
353 | synproxy->tsoff = 0; | |
354 | this_cpu_inc(snet->stats->conn_reopened); | |
355 | ||
356 | /* fall through */ | |
357 | case TCP_CONNTRACK_SYN_SENT: | |
f4a87e7b PM |
358 | if (!synproxy_parse_options(skb, thoff, th, &opts)) |
359 | return NF_DROP; | |
48b1de4c PM |
360 | |
361 | if (!th->syn && th->ack && | |
362 | CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) { | |
363 | /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1, | |
364 | * therefore we need to add 1 to make the SYN sequence | |
365 | * number match the one of first SYN. | |
366 | */ | |
367 | if (synproxy_recv_client_ack(snet, skb, th, &opts, | |
368 | ntohl(th->seq) + 1)) | |
369 | this_cpu_inc(snet->stats->cookie_retrans); | |
370 | ||
371 | return NF_DROP; | |
372 | } | |
373 | ||
374 | synproxy->isn = ntohl(th->ack_seq); | |
375 | if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) | |
376 | synproxy->its = opts.tsecr; | |
377 | break; | |
378 | case TCP_CONNTRACK_SYN_RECV: | |
379 | if (!th->syn || !th->ack) | |
380 | break; | |
381 | ||
f4a87e7b PM |
382 | if (!synproxy_parse_options(skb, thoff, th, &opts)) |
383 | return NF_DROP; | |
384 | ||
48b1de4c PM |
385 | if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) |
386 | synproxy->tsoff = opts.tsval - synproxy->its; | |
387 | ||
388 | opts.options &= ~(XT_SYNPROXY_OPT_MSS | | |
389 | XT_SYNPROXY_OPT_WSCALE | | |
390 | XT_SYNPROXY_OPT_SACK_PERM); | |
391 | ||
392 | swap(opts.tsval, opts.tsecr); | |
393 | synproxy_send_server_ack(snet, state, skb, th, &opts); | |
394 | ||
395 | nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq)); | |
396 | ||
397 | swap(opts.tsval, opts.tsecr); | |
398 | synproxy_send_client_ack(snet, skb, th, &opts); | |
399 | ||
400 | consume_skb(skb); | |
401 | return NF_STOLEN; | |
402 | default: | |
403 | break; | |
404 | } | |
405 | ||
406 | synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy); | |
407 | return NF_ACCEPT; | |
408 | } | |
409 | ||
410 | static int synproxy_tg4_check(const struct xt_tgchk_param *par) | |
411 | { | |
412 | const struct ipt_entry *e = par->entryinfo; | |
413 | ||
414 | if (e->ip.proto != IPPROTO_TCP || | |
415 | e->ip.invflags & XT_INV_PROTO) | |
416 | return -EINVAL; | |
417 | ||
418 | return nf_ct_l3proto_try_module_get(par->family); | |
419 | } | |
420 | ||
421 | static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par) | |
422 | { | |
423 | nf_ct_l3proto_module_put(par->family); | |
424 | } | |
425 | ||
426 | static struct xt_target synproxy_tg4_reg __read_mostly = { | |
427 | .name = "SYNPROXY", | |
428 | .family = NFPROTO_IPV4, | |
f01b3926 | 429 | .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD), |
48b1de4c PM |
430 | .target = synproxy_tg4, |
431 | .targetsize = sizeof(struct xt_synproxy_info), | |
432 | .checkentry = synproxy_tg4_check, | |
433 | .destroy = synproxy_tg4_destroy, | |
434 | .me = THIS_MODULE, | |
435 | }; | |
436 | ||
437 | static struct nf_hook_ops ipv4_synproxy_ops[] __read_mostly = { | |
438 | { | |
439 | .hook = ipv4_synproxy_hook, | |
440 | .owner = THIS_MODULE, | |
441 | .pf = NFPROTO_IPV4, | |
442 | .hooknum = NF_INET_LOCAL_IN, | |
443 | .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, | |
444 | }, | |
445 | { | |
446 | .hook = ipv4_synproxy_hook, | |
447 | .owner = THIS_MODULE, | |
448 | .pf = NFPROTO_IPV4, | |
449 | .hooknum = NF_INET_POST_ROUTING, | |
450 | .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, | |
451 | }, | |
452 | }; | |
453 | ||
454 | static int __init synproxy_tg4_init(void) | |
455 | { | |
456 | int err; | |
457 | ||
458 | err = nf_register_hooks(ipv4_synproxy_ops, | |
459 | ARRAY_SIZE(ipv4_synproxy_ops)); | |
460 | if (err < 0) | |
461 | goto err1; | |
462 | ||
463 | err = xt_register_target(&synproxy_tg4_reg); | |
464 | if (err < 0) | |
465 | goto err2; | |
466 | ||
467 | return 0; | |
468 | ||
469 | err2: | |
470 | nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops)); | |
471 | err1: | |
472 | return err; | |
473 | } | |
474 | ||
475 | static void __exit synproxy_tg4_exit(void) | |
476 | { | |
477 | xt_unregister_target(&synproxy_tg4_reg); | |
478 | nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops)); | |
479 | } | |
480 | ||
481 | module_init(synproxy_tg4_init); | |
482 | module_exit(synproxy_tg4_exit); | |
483 | ||
484 | MODULE_LICENSE("GPL"); | |
485 | MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>"); |