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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
20static struct iphdr *
21synproxy_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 = (struct iphdr *)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
42static void
43synproxy_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 nskb->nfct = nfct;
61 nskb->nfctinfo = ctinfo;
62 nf_conntrack_get(nfct);
63 }
64
65 ip_local_out(net, nskb->sk, nskb);
66 return;
67
68free_nskb:
69 kfree_skb(nskb);
70}
71
72static void
73synproxy_send_client_synack(struct net *net,
74 const struct sk_buff *skb, const struct tcphdr *th,
75 const struct synproxy_options *opts)
76{
77 struct sk_buff *nskb;
78 struct iphdr *iph, *niph;
79 struct tcphdr *nth;
80 unsigned int tcp_hdr_size;
81 u16 mss = opts->mss;
82
83 iph = ip_hdr(skb);
84
85 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
86 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
87 GFP_ATOMIC);
88 if (nskb == NULL)
89 return;
90 skb_reserve(nskb, MAX_TCP_HEADER);
91
92 niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr);
93
94 skb_reset_transport_header(nskb);
95 nth = (struct tcphdr *)skb_put(nskb, tcp_hdr_size);
96 nth->source = th->dest;
97 nth->dest = th->source;
98 nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss));
99 nth->ack_seq = htonl(ntohl(th->seq) + 1);
100 tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
101 if (opts->options & XT_SYNPROXY_OPT_ECN)
102 tcp_flag_word(nth) |= TCP_FLAG_ECE;
103 nth->doff = tcp_hdr_size / 4;
104 nth->window = 0;
105 nth->check = 0;
106 nth->urg_ptr = 0;
107
108 synproxy_build_options(nth, opts);
109
110 synproxy_send_tcp(net, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
111 niph, nth, tcp_hdr_size);
112}
113
114static void
115synproxy_send_server_syn(struct net *net,
116 const struct sk_buff *skb, const struct tcphdr *th,
117 const struct synproxy_options *opts, u32 recv_seq)
118{
119 struct synproxy_net *snet = synproxy_pernet(net);
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(net, 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
142
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
155 synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
156 niph, nth, tcp_hdr_size);
157}
158
159static void
160synproxy_send_server_ack(struct net *net,
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(net, 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
195 synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
196}
197
198static void
199synproxy_send_client_ack(struct net *net,
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(net, 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;
227 nth->window = htons(ntohs(th->window) >> opts->wscale);
228 nth->check = 0;
229 nth->urg_ptr = 0;
230
231 synproxy_build_options(nth, opts);
232
233 synproxy_send_tcp(net, skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
234 niph, nth, tcp_hdr_size);
235}
236
237static bool
238synproxy_recv_client_ack(struct net *net,
239 const struct sk_buff *skb, const struct tcphdr *th,
240 struct synproxy_options *opts, u32 recv_seq)
241{
242 struct synproxy_net *snet = synproxy_pernet(net);
243 int mss;
244
245 mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1);
246 if (mss == 0) {
247 this_cpu_inc(snet->stats->cookie_invalid);
248 return false;
249 }
250
251 this_cpu_inc(snet->stats->cookie_valid);
252 opts->mss = mss;
253 opts->options |= XT_SYNPROXY_OPT_MSS;
254
255 if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
256 synproxy_check_timestamp_cookie(opts);
257
258 synproxy_send_server_syn(net, skb, th, opts, recv_seq);
259 return true;
260}
261
262static unsigned int
263synproxy_tg4(struct sk_buff *skb, const struct xt_action_param *par)
264{
265 const struct xt_synproxy_info *info = par->targinfo;
266 struct net *net = par->net;
267 struct synproxy_net *snet = synproxy_pernet(net);
268 struct synproxy_options opts = {};
269 struct tcphdr *th, _th;
270
271 if (nf_ip_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
272 return NF_DROP;
273
274 th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
275 if (th == NULL)
276 return NF_DROP;
277
278 if (!synproxy_parse_options(skb, par->thoff, th, &opts))
279 return NF_DROP;
280
281 if (th->syn && !(th->ack || th->fin || th->rst)) {
282
283 this_cpu_inc(snet->stats->syn_received);
284
285 if (th->ece && th->cwr)
286 opts.options |= XT_SYNPROXY_OPT_ECN;
287
288 opts.options &= info->options;
289 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
290 synproxy_init_timestamp_cookie(info, &opts);
291 else
292 opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
293 XT_SYNPROXY_OPT_SACK_PERM |
294 XT_SYNPROXY_OPT_ECN);
295
296 synproxy_send_client_synack(net, skb, th, &opts);
297 return NF_DROP;
298
299 } else if (th->ack && !(th->fin || th->rst || th->syn)) {
300
301 synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq));
302 return NF_DROP;
303 }
304
305 return XT_CONTINUE;
306}
307
308static unsigned int ipv4_synproxy_hook(void *priv,
309 struct sk_buff *skb,
310 const struct nf_hook_state *nhs)
311{
312 struct net *net = nhs->net;
313 struct synproxy_net *snet = synproxy_pernet(net);
314 enum ip_conntrack_info ctinfo;
315 struct nf_conn *ct;
316 struct nf_conn_synproxy *synproxy;
317 struct synproxy_options opts = {};
318 const struct ip_ct_tcp *state;
319 struct tcphdr *th, _th;
320 unsigned int thoff;
321
322 ct = nf_ct_get(skb, &ctinfo);
323 if (ct == NULL)
324 return NF_ACCEPT;
325
326 synproxy = nfct_synproxy(ct);
327 if (synproxy == NULL)
328 return NF_ACCEPT;
329
330 if (nf_is_loopback_packet(skb))
331 return NF_ACCEPT;
332
333 thoff = ip_hdrlen(skb);
334 th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
335 if (th == NULL)
336 return NF_DROP;
337
338 state = &ct->proto.tcp;
339 switch (state->state) {
340 case TCP_CONNTRACK_CLOSE:
341 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
342 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
343 ntohl(th->seq) + 1);
344 break;
345 }
346
347 if (!th->syn || th->ack ||
348 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
349 break;
350
351
352
353
354
355 nf_ct_seqadj_init(ct, ctinfo, 0);
356 synproxy->tsoff = 0;
357 this_cpu_inc(snet->stats->conn_reopened);
358
359
360 case TCP_CONNTRACK_SYN_SENT:
361 if (!synproxy_parse_options(skb, thoff, th, &opts))
362 return NF_DROP;
363
364 if (!th->syn && th->ack &&
365 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
366
367
368
369
370 if (synproxy_recv_client_ack(net, skb, th, &opts,
371 ntohl(th->seq) + 1))
372 this_cpu_inc(snet->stats->cookie_retrans);
373
374 return NF_DROP;
375 }
376
377 synproxy->isn = ntohl(th->ack_seq);
378 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
379 synproxy->its = opts.tsecr;
380 break;
381 case TCP_CONNTRACK_SYN_RECV:
382 if (!th->syn || !th->ack)
383 break;
384
385 if (!synproxy_parse_options(skb, thoff, th, &opts))
386 return NF_DROP;
387
388 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
389 synproxy->tsoff = opts.tsval - synproxy->its;
390
391 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
392 XT_SYNPROXY_OPT_WSCALE |
393 XT_SYNPROXY_OPT_SACK_PERM);
394
395 swap(opts.tsval, opts.tsecr);
396 synproxy_send_server_ack(net, state, skb, th, &opts);
397
398 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
399
400 swap(opts.tsval, opts.tsecr);
401 synproxy_send_client_ack(net, skb, th, &opts);
402
403 consume_skb(skb);
404 return NF_STOLEN;
405 default:
406 break;
407 }
408
409 synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
410 return NF_ACCEPT;
411}
412
413static int synproxy_tg4_check(const struct xt_tgchk_param *par)
414{
415 const struct ipt_entry *e = par->entryinfo;
416
417 if (e->ip.proto != IPPROTO_TCP ||
418 e->ip.invflags & XT_INV_PROTO)
419 return -EINVAL;
420
421 return nf_ct_l3proto_try_module_get(par->family);
422}
423
424static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
425{
426 nf_ct_l3proto_module_put(par->family);
427}
428
429static struct xt_target synproxy_tg4_reg __read_mostly = {
430 .name = "SYNPROXY",
431 .family = NFPROTO_IPV4,
432 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
433 .target = synproxy_tg4,
434 .targetsize = sizeof(struct xt_synproxy_info),
435 .checkentry = synproxy_tg4_check,
436 .destroy = synproxy_tg4_destroy,
437 .me = THIS_MODULE,
438};
439
440static struct nf_hook_ops ipv4_synproxy_ops[] __read_mostly = {
441 {
442 .hook = ipv4_synproxy_hook,
443 .pf = NFPROTO_IPV4,
444 .hooknum = NF_INET_LOCAL_IN,
445 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
446 },
447 {
448 .hook = ipv4_synproxy_hook,
449 .pf = NFPROTO_IPV4,
450 .hooknum = NF_INET_POST_ROUTING,
451 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
452 },
453};
454
455static int __init synproxy_tg4_init(void)
456{
457 int err;
458
459 err = nf_register_hooks(ipv4_synproxy_ops,
460 ARRAY_SIZE(ipv4_synproxy_ops));
461 if (err < 0)
462 goto err1;
463
464 err = xt_register_target(&synproxy_tg4_reg);
465 if (err < 0)
466 goto err2;
467
468 return 0;
469
470err2:
471 nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
472err1:
473 return err;
474}
475
476static void __exit synproxy_tg4_exit(void)
477{
478 xt_unregister_target(&synproxy_tg4_reg);
479 nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
480}
481
482module_init(synproxy_tg4_init);
483module_exit(synproxy_tg4_exit);
484
485MODULE_LICENSE("GPL");
486MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
487
