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4ad36228 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/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 sk_buff *skb, struct sk_buff *nskb, | |
41 | struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo, | |
42 | struct ipv6hdr *niph, struct tcphdr *nth, | |
43 | unsigned int tcp_hdr_size) | |
44 | { | |
45 | struct net *net = nf_ct_net((struct nf_conn *)nfct); | |
46 | struct dst_entry *dst; | |
47 | struct flowi6 fl6; | |
48 | ||
49 | nth->check = ~tcp_v6_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 | memset(&fl6, 0, sizeof(fl6)); | |
55 | fl6.flowi6_proto = IPPROTO_TCP; | |
56 | fl6.saddr = niph->saddr; | |
57 | fl6.daddr = niph->daddr; | |
58 | fl6.fl6_sport = nth->source; | |
59 | fl6.fl6_dport = nth->dest; | |
60 | security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6)); | |
61 | dst = ip6_route_output(net, NULL, &fl6); | |
62 | if (dst == NULL || dst->error) { | |
63 | dst_release(dst); | |
64 | goto free_nskb; | |
65 | } | |
66 | dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0); | |
67 | if (IS_ERR(dst)) | |
68 | goto free_nskb; | |
69 | ||
70 | skb_dst_set(nskb, dst); | |
71 | ||
72 | if (nfct) { | |
73 | nskb->nfct = nfct; | |
74 | nskb->nfctinfo = ctinfo; | |
75 | nf_conntrack_get(nfct); | |
76 | } | |
77 | ||
78 | ip6_local_out(nskb); | |
79 | return; | |
80 | ||
81 | free_nskb: | |
82 | kfree_skb(nskb); | |
83 | } | |
84 | ||
85 | static void | |
86 | synproxy_send_client_synack(const struct sk_buff *skb, const struct tcphdr *th, | |
87 | const struct synproxy_options *opts) | |
88 | { | |
89 | struct sk_buff *nskb; | |
90 | struct ipv6hdr *iph, *niph; | |
91 | struct tcphdr *nth; | |
92 | unsigned int tcp_hdr_size; | |
93 | u16 mss = opts->mss; | |
94 | ||
95 | iph = ipv6_hdr(skb); | |
96 | ||
97 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
98 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
99 | GFP_ATOMIC); | |
100 | if (nskb == NULL) | |
101 | return; | |
102 | skb_reserve(nskb, MAX_TCP_HEADER); | |
103 | ||
104 | niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr); | |
105 | ||
106 | skb_reset_transport_header(nskb); | |
107 | nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size); | |
108 | nth->source = th->dest; | |
109 | nth->dest = th->source; | |
110 | nth->seq = htonl(__cookie_v6_init_sequence(iph, th, &mss)); | |
111 | nth->ack_seq = htonl(ntohl(th->seq) + 1); | |
112 | tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK; | |
113 | if (opts->options & XT_SYNPROXY_OPT_ECN) | |
114 | tcp_flag_word(nth) |= TCP_FLAG_ECE; | |
115 | nth->doff = tcp_hdr_size / 4; | |
116 | nth->window = 0; | |
117 | nth->check = 0; | |
118 | nth->urg_ptr = 0; | |
119 | ||
120 | synproxy_build_options(nth, opts); | |
121 | ||
122 | synproxy_send_tcp(skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY, | |
123 | niph, nth, tcp_hdr_size); | |
124 | } | |
125 | ||
126 | static void | |
127 | synproxy_send_server_syn(const struct synproxy_net *snet, | |
128 | const struct sk_buff *skb, const struct tcphdr *th, | |
129 | const struct synproxy_options *opts, u32 recv_seq) | |
130 | { | |
131 | struct sk_buff *nskb; | |
132 | struct ipv6hdr *iph, *niph; | |
133 | struct tcphdr *nth; | |
134 | unsigned int tcp_hdr_size; | |
135 | ||
136 | iph = ipv6_hdr(skb); | |
137 | ||
138 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
139 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
140 | GFP_ATOMIC); | |
141 | if (nskb == NULL) | |
142 | return; | |
143 | skb_reserve(nskb, MAX_TCP_HEADER); | |
144 | ||
145 | niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr); | |
146 | ||
147 | skb_reset_transport_header(nskb); | |
148 | nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size); | |
149 | nth->source = th->source; | |
150 | nth->dest = th->dest; | |
151 | nth->seq = htonl(recv_seq - 1); | |
152 | /* ack_seq is used to relay our ISN to the synproxy hook to initialize | |
153 | * sequence number translation once a connection tracking entry exists. | |
154 | */ | |
155 | nth->ack_seq = htonl(ntohl(th->ack_seq) - 1); | |
156 | tcp_flag_word(nth) = TCP_FLAG_SYN; | |
157 | if (opts->options & XT_SYNPROXY_OPT_ECN) | |
158 | tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR; | |
159 | nth->doff = tcp_hdr_size / 4; | |
160 | nth->window = th->window; | |
161 | nth->check = 0; | |
162 | nth->urg_ptr = 0; | |
163 | ||
164 | synproxy_build_options(nth, opts); | |
165 | ||
166 | synproxy_send_tcp(skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW, | |
167 | niph, nth, tcp_hdr_size); | |
168 | } | |
169 | ||
170 | static void | |
171 | synproxy_send_server_ack(const struct synproxy_net *snet, | |
172 | const struct ip_ct_tcp *state, | |
173 | const struct sk_buff *skb, const struct tcphdr *th, | |
174 | const struct synproxy_options *opts) | |
175 | { | |
176 | struct sk_buff *nskb; | |
177 | struct ipv6hdr *iph, *niph; | |
178 | struct tcphdr *nth; | |
179 | unsigned int tcp_hdr_size; | |
180 | ||
181 | iph = ipv6_hdr(skb); | |
182 | ||
183 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
184 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
185 | GFP_ATOMIC); | |
186 | if (nskb == NULL) | |
187 | return; | |
188 | skb_reserve(nskb, MAX_TCP_HEADER); | |
189 | ||
190 | niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr); | |
191 | ||
192 | skb_reset_transport_header(nskb); | |
193 | nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size); | |
194 | nth->source = th->dest; | |
195 | nth->dest = th->source; | |
196 | nth->seq = htonl(ntohl(th->ack_seq)); | |
197 | nth->ack_seq = htonl(ntohl(th->seq) + 1); | |
198 | tcp_flag_word(nth) = TCP_FLAG_ACK; | |
199 | nth->doff = tcp_hdr_size / 4; | |
200 | nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin); | |
201 | nth->check = 0; | |
202 | nth->urg_ptr = 0; | |
203 | ||
204 | synproxy_build_options(nth, opts); | |
205 | ||
206 | synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size); | |
207 | } | |
208 | ||
209 | static void | |
210 | synproxy_send_client_ack(const struct synproxy_net *snet, | |
211 | const struct sk_buff *skb, const struct tcphdr *th, | |
212 | const struct synproxy_options *opts) | |
213 | { | |
214 | struct sk_buff *nskb; | |
215 | struct ipv6hdr *iph, *niph; | |
216 | struct tcphdr *nth; | |
217 | unsigned int tcp_hdr_size; | |
218 | ||
219 | iph = ipv6_hdr(skb); | |
220 | ||
221 | tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); | |
222 | nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, | |
223 | GFP_ATOMIC); | |
224 | if (nskb == NULL) | |
225 | return; | |
226 | skb_reserve(nskb, MAX_TCP_HEADER); | |
227 | ||
228 | niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr); | |
229 | ||
230 | skb_reset_transport_header(nskb); | |
231 | nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size); | |
232 | nth->source = th->source; | |
233 | nth->dest = th->dest; | |
234 | nth->seq = htonl(ntohl(th->seq) + 1); | |
235 | nth->ack_seq = th->ack_seq; | |
236 | tcp_flag_word(nth) = TCP_FLAG_ACK; | |
237 | nth->doff = tcp_hdr_size / 4; | |
238 | nth->window = ntohs(htons(th->window) >> opts->wscale); | |
239 | nth->check = 0; | |
240 | nth->urg_ptr = 0; | |
241 | ||
242 | synproxy_build_options(nth, opts); | |
243 | ||
244 | synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size); | |
245 | } | |
246 | ||
247 | static bool | |
248 | synproxy_recv_client_ack(const struct synproxy_net *snet, | |
249 | const struct sk_buff *skb, const struct tcphdr *th, | |
250 | struct synproxy_options *opts, u32 recv_seq) | |
251 | { | |
252 | int mss; | |
253 | ||
254 | mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1); | |
255 | if (mss == 0) { | |
256 | this_cpu_inc(snet->stats->cookie_invalid); | |
257 | return false; | |
258 | } | |
259 | ||
260 | this_cpu_inc(snet->stats->cookie_valid); | |
261 | opts->mss = mss; | |
a6441b7a | 262 | opts->options |= XT_SYNPROXY_OPT_MSS; |
4ad36228 PM |
263 | |
264 | if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP) | |
265 | synproxy_check_timestamp_cookie(opts); | |
266 | ||
267 | synproxy_send_server_syn(snet, skb, th, opts, recv_seq); | |
268 | return true; | |
269 | } | |
270 | ||
271 | static unsigned int | |
272 | synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par) | |
273 | { | |
274 | const struct xt_synproxy_info *info = par->targinfo; | |
275 | struct synproxy_net *snet = synproxy_pernet(dev_net(par->in)); | |
276 | struct synproxy_options opts = {}; | |
277 | struct tcphdr *th, _th; | |
278 | ||
279 | if (nf_ip6_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP)) | |
280 | return NF_DROP; | |
281 | ||
282 | th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th); | |
283 | if (th == NULL) | |
284 | return NF_DROP; | |
285 | ||
f4a87e7b PM |
286 | if (!synproxy_parse_options(skb, par->thoff, th, &opts)) |
287 | return NF_DROP; | |
4ad36228 | 288 | |
775ada6d | 289 | if (th->syn && !(th->ack || th->fin || th->rst)) { |
4ad36228 PM |
290 | /* Initial SYN from client */ |
291 | this_cpu_inc(snet->stats->syn_received); | |
292 | ||
293 | if (th->ece && th->cwr) | |
294 | opts.options |= XT_SYNPROXY_OPT_ECN; | |
295 | ||
296 | opts.options &= info->options; | |
297 | if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) | |
298 | synproxy_init_timestamp_cookie(info, &opts); | |
299 | else | |
300 | opts.options &= ~(XT_SYNPROXY_OPT_WSCALE | | |
301 | XT_SYNPROXY_OPT_SACK_PERM | | |
302 | XT_SYNPROXY_OPT_ECN); | |
303 | ||
304 | synproxy_send_client_synack(skb, th, &opts); | |
7cc9eb6e JDB |
305 | return NF_DROP; |
306 | ||
307 | } else if (th->ack && !(th->fin || th->rst || th->syn)) { | |
4ad36228 PM |
308 | /* ACK from client */ |
309 | synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq)); | |
7cc9eb6e JDB |
310 | return NF_DROP; |
311 | } | |
4ad36228 | 312 | |
7cc9eb6e | 313 | return XT_CONTINUE; |
4ad36228 PM |
314 | } |
315 | ||
795aa6ef | 316 | static unsigned int ipv6_synproxy_hook(const struct nf_hook_ops *ops, |
4ad36228 PM |
317 | struct sk_buff *skb, |
318 | const struct net_device *in, | |
319 | const struct net_device *out, | |
320 | int (*okfn)(struct sk_buff *)) | |
321 | { | |
322 | struct synproxy_net *snet = synproxy_pernet(dev_net(in ? : out)); | |
323 | enum ip_conntrack_info ctinfo; | |
324 | struct nf_conn *ct; | |
325 | struct nf_conn_synproxy *synproxy; | |
326 | struct synproxy_options opts = {}; | |
327 | const struct ip_ct_tcp *state; | |
328 | struct tcphdr *th, _th; | |
329 | __be16 frag_off; | |
330 | u8 nexthdr; | |
331 | int thoff; | |
332 | ||
333 | ct = nf_ct_get(skb, &ctinfo); | |
334 | if (ct == NULL) | |
335 | return NF_ACCEPT; | |
336 | ||
337 | synproxy = nfct_synproxy(ct); | |
338 | if (synproxy == NULL) | |
339 | return NF_ACCEPT; | |
340 | ||
341 | if (nf_is_loopback_packet(skb)) | |
342 | return NF_ACCEPT; | |
343 | ||
344 | nexthdr = ipv6_hdr(skb)->nexthdr; | |
345 | thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr, | |
346 | &frag_off); | |
347 | if (thoff < 0) | |
348 | return NF_ACCEPT; | |
349 | ||
350 | th = skb_header_pointer(skb, thoff, sizeof(_th), &_th); | |
351 | if (th == NULL) | |
352 | return NF_DROP; | |
353 | ||
354 | state = &ct->proto.tcp; | |
355 | switch (state->state) { | |
356 | case TCP_CONNTRACK_CLOSE: | |
357 | if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) { | |
358 | nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - | |
359 | ntohl(th->seq) + 1); | |
360 | break; | |
361 | } | |
362 | ||
363 | if (!th->syn || th->ack || | |
364 | CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) | |
365 | break; | |
366 | ||
367 | /* Reopened connection - reset the sequence number and timestamp | |
368 | * adjustments, they will get initialized once the connection is | |
369 | * reestablished. | |
370 | */ | |
371 | nf_ct_seqadj_init(ct, ctinfo, 0); | |
372 | synproxy->tsoff = 0; | |
373 | this_cpu_inc(snet->stats->conn_reopened); | |
374 | ||
375 | /* fall through */ | |
376 | case TCP_CONNTRACK_SYN_SENT: | |
f4a87e7b PM |
377 | if (!synproxy_parse_options(skb, thoff, th, &opts)) |
378 | return NF_DROP; | |
4ad36228 PM |
379 | |
380 | if (!th->syn && th->ack && | |
381 | CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) { | |
382 | /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1, | |
383 | * therefore we need to add 1 to make the SYN sequence | |
384 | * number match the one of first SYN. | |
385 | */ | |
386 | if (synproxy_recv_client_ack(snet, skb, th, &opts, | |
387 | ntohl(th->seq) + 1)) | |
388 | this_cpu_inc(snet->stats->cookie_retrans); | |
389 | ||
390 | return NF_DROP; | |
391 | } | |
392 | ||
393 | synproxy->isn = ntohl(th->ack_seq); | |
394 | if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) | |
395 | synproxy->its = opts.tsecr; | |
396 | break; | |
397 | case TCP_CONNTRACK_SYN_RECV: | |
398 | if (!th->syn || !th->ack) | |
399 | break; | |
400 | ||
f4a87e7b PM |
401 | if (!synproxy_parse_options(skb, thoff, th, &opts)) |
402 | return NF_DROP; | |
403 | ||
4ad36228 PM |
404 | if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP) |
405 | synproxy->tsoff = opts.tsval - synproxy->its; | |
406 | ||
407 | opts.options &= ~(XT_SYNPROXY_OPT_MSS | | |
408 | XT_SYNPROXY_OPT_WSCALE | | |
409 | XT_SYNPROXY_OPT_SACK_PERM); | |
410 | ||
411 | swap(opts.tsval, opts.tsecr); | |
412 | synproxy_send_server_ack(snet, state, skb, th, &opts); | |
413 | ||
414 | nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq)); | |
415 | ||
416 | swap(opts.tsval, opts.tsecr); | |
417 | synproxy_send_client_ack(snet, skb, th, &opts); | |
418 | ||
419 | consume_skb(skb); | |
420 | return NF_STOLEN; | |
421 | default: | |
422 | break; | |
423 | } | |
424 | ||
425 | synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy); | |
426 | return NF_ACCEPT; | |
427 | } | |
428 | ||
429 | static int synproxy_tg6_check(const struct xt_tgchk_param *par) | |
430 | { | |
431 | const struct ip6t_entry *e = par->entryinfo; | |
432 | ||
433 | if (!(e->ipv6.flags & IP6T_F_PROTO) || | |
434 | e->ipv6.proto != IPPROTO_TCP || | |
435 | e->ipv6.invflags & XT_INV_PROTO) | |
436 | return -EINVAL; | |
437 | ||
438 | return nf_ct_l3proto_try_module_get(par->family); | |
439 | } | |
440 | ||
441 | static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par) | |
442 | { | |
443 | nf_ct_l3proto_module_put(par->family); | |
444 | } | |
445 | ||
446 | static struct xt_target synproxy_tg6_reg __read_mostly = { | |
447 | .name = "SYNPROXY", | |
448 | .family = NFPROTO_IPV6, | |
f01b3926 | 449 | .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD), |
4ad36228 PM |
450 | .target = synproxy_tg6, |
451 | .targetsize = sizeof(struct xt_synproxy_info), | |
452 | .checkentry = synproxy_tg6_check, | |
453 | .destroy = synproxy_tg6_destroy, | |
454 | .me = THIS_MODULE, | |
455 | }; | |
456 | ||
457 | static struct nf_hook_ops ipv6_synproxy_ops[] __read_mostly = { | |
458 | { | |
459 | .hook = ipv6_synproxy_hook, | |
460 | .owner = THIS_MODULE, | |
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 | .owner = THIS_MODULE, | |
468 | .pf = NFPROTO_IPV6, | |
469 | .hooknum = NF_INET_POST_ROUTING, | |
470 | .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, | |
471 | }, | |
472 | }; | |
473 | ||
474 | static int __init synproxy_tg6_init(void) | |
475 | { | |
476 | int err; | |
477 | ||
478 | err = nf_register_hooks(ipv6_synproxy_ops, | |
479 | ARRAY_SIZE(ipv6_synproxy_ops)); | |
480 | if (err < 0) | |
481 | goto err1; | |
482 | ||
483 | err = xt_register_target(&synproxy_tg6_reg); | |
484 | if (err < 0) | |
485 | goto err2; | |
486 | ||
487 | return 0; | |
488 | ||
489 | err2: | |
490 | nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops)); | |
491 | err1: | |
492 | return err; | |
493 | } | |
494 | ||
495 | static void __exit synproxy_tg6_exit(void) | |
496 | { | |
497 | xt_unregister_target(&synproxy_tg6_reg); | |
498 | nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops)); | |
499 | } | |
500 | ||
501 | module_init(synproxy_tg6_init); | |
502 | module_exit(synproxy_tg6_exit); | |
503 | ||
504 | MODULE_LICENSE("GPL"); | |
505 | MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>"); |