1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
4 */
5
6#include <linux/module.h>
7#include <linux/skbuff.h>
8#include <linux/unaligned.h>
9#include <net/tcp.h>
10#include <net/netns/generic.h>
11#include <linux/proc_fs.h>
12
13#include <linux/netfilter_ipv6.h>
14#include <linux/netfilter/nf_synproxy.h>
15
16#include <net/netfilter/nf_conntrack.h>
17#include <net/netfilter/nf_conntrack_ecache.h>
18#include <net/netfilter/nf_conntrack_extend.h>
19#include <net/netfilter/nf_conntrack_seqadj.h>
20#include <net/netfilter/nf_conntrack_synproxy.h>
21#include <net/netfilter/nf_conntrack_zones.h>
22#include <net/netfilter/nf_synproxy.h>
23
24unsigned int synproxy_net_id;
25EXPORT_SYMBOL_GPL(synproxy_net_id);
26
27bool
28synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
29 const struct tcphdr *th, struct synproxy_options *opts)
30{
31 int length = (th->doff * 4) - sizeof(*th);
32 u8 buf[40], *ptr;
33
34 if (unlikely(length < 0))
35 return false;
36
37 ptr = skb_header_pointer(skb, offset: doff + sizeof(*th), len: length, buffer: buf);
38 if (ptr == NULL)
39 return false;
40
41 opts->options = 0;
42 while (length > 0) {
43 int opcode = *ptr++;
44 int opsize;
45
46 switch (opcode) {
47 case TCPOPT_EOL:
48 return true;
49 case TCPOPT_NOP:
50 length--;
51 continue;
52 default:
53 if (length < 2)
54 return true;
55 opsize = *ptr++;
56 if (opsize < 2)
57 return true;
58 if (opsize > length)
59 return true;
60
61 switch (opcode) {
62 case TCPOPT_MSS:
63 if (opsize == TCPOLEN_MSS) {
64 opts->mss_option = get_unaligned_be16(p: ptr);
65 opts->options |= NF_SYNPROXY_OPT_MSS;
66 }
67 break;
68 case TCPOPT_WINDOW:
69 if (opsize == TCPOLEN_WINDOW) {
70 opts->wscale = *ptr;
71 if (opts->wscale > TCP_MAX_WSCALE)
72 opts->wscale = TCP_MAX_WSCALE;
73 opts->options |= NF_SYNPROXY_OPT_WSCALE;
74 }
75 break;
76 case TCPOPT_TIMESTAMP:
77 if (opsize == TCPOLEN_TIMESTAMP) {
78 opts->tsval = get_unaligned_be32(p: ptr);
79 opts->tsecr = get_unaligned_be32(p: ptr + 4);
80 opts->options |= NF_SYNPROXY_OPT_TIMESTAMP;
81 }
82 break;
83 case TCPOPT_SACK_PERM:
84 if (opsize == TCPOLEN_SACK_PERM)
85 opts->options |= NF_SYNPROXY_OPT_SACK_PERM;
86 break;
87 }
88
89 ptr += opsize - 2;
90 length -= opsize;
91 }
92 }
93 return true;
94}
95EXPORT_SYMBOL_GPL(synproxy_parse_options);
96
97static unsigned int
98synproxy_options_size(const struct synproxy_options *opts)
99{
100 unsigned int size = 0;
101
102 if (opts->options & NF_SYNPROXY_OPT_MSS)
103 size += TCPOLEN_MSS_ALIGNED;
104 if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
105 size += TCPOLEN_TSTAMP_ALIGNED;
106 else if (opts->options & NF_SYNPROXY_OPT_SACK_PERM)
107 size += TCPOLEN_SACKPERM_ALIGNED;
108 if (opts->options & NF_SYNPROXY_OPT_WSCALE)
109 size += TCPOLEN_WSCALE_ALIGNED;
110
111 return size;
112}
113
114static void
115synproxy_build_options(struct tcphdr *th, const struct synproxy_options *opts)
116{
117 __be32 *ptr = (__be32 *)(th + 1);
118 u8 options = opts->options;
119
120 if (options & NF_SYNPROXY_OPT_MSS)
121 *ptr++ = htonl((TCPOPT_MSS << 24) |
122 (TCPOLEN_MSS << 16) |
123 opts->mss_option);
124
125 if (options & NF_SYNPROXY_OPT_TIMESTAMP) {
126 if (options & NF_SYNPROXY_OPT_SACK_PERM)
127 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
128 (TCPOLEN_SACK_PERM << 16) |
129 (TCPOPT_TIMESTAMP << 8) |
130 TCPOLEN_TIMESTAMP);
131 else
132 *ptr++ = htonl((TCPOPT_NOP << 24) |
133 (TCPOPT_NOP << 16) |
134 (TCPOPT_TIMESTAMP << 8) |
135 TCPOLEN_TIMESTAMP);
136
137 *ptr++ = htonl(opts->tsval);
138 *ptr++ = htonl(opts->tsecr);
139 } else if (options & NF_SYNPROXY_OPT_SACK_PERM)
140 *ptr++ = htonl((TCPOPT_NOP << 24) |
141 (TCPOPT_NOP << 16) |
142 (TCPOPT_SACK_PERM << 8) |
143 TCPOLEN_SACK_PERM);
144
145 if (options & NF_SYNPROXY_OPT_WSCALE)
146 *ptr++ = htonl((TCPOPT_NOP << 24) |
147 (TCPOPT_WINDOW << 16) |
148 (TCPOLEN_WINDOW << 8) |
149 opts->wscale);
150}
151
152void synproxy_init_timestamp_cookie(const struct nf_synproxy_info *info,
153 struct synproxy_options *opts)
154{
155 opts->tsecr = opts->tsval;
156 opts->tsval = tcp_clock_ms() & ~0x3f;
157
158 if (opts->options & NF_SYNPROXY_OPT_WSCALE) {
159 opts->tsval |= opts->wscale;
160 opts->wscale = info->wscale;
161 } else
162 opts->tsval |= 0xf;
163
164 if (opts->options & NF_SYNPROXY_OPT_SACK_PERM)
165 opts->tsval |= 1 << 4;
166
167 if (opts->options & NF_SYNPROXY_OPT_ECN)
168 opts->tsval |= 1 << 5;
169}
170EXPORT_SYMBOL_GPL(synproxy_init_timestamp_cookie);
171
172static void
173synproxy_check_timestamp_cookie(struct synproxy_options *opts)
174{
175 opts->wscale = opts->tsecr & 0xf;
176 if (opts->wscale != 0xf)
177 opts->options |= NF_SYNPROXY_OPT_WSCALE;
178
179 opts->options |= opts->tsecr & (1 << 4) ? NF_SYNPROXY_OPT_SACK_PERM : 0;
180
181 opts->options |= opts->tsecr & (1 << 5) ? NF_SYNPROXY_OPT_ECN : 0;
182}
183
184static unsigned int
185synproxy_tstamp_adjust(struct sk_buff *skb, unsigned int protoff,
186 struct tcphdr *th, struct nf_conn *ct,
187 enum ip_conntrack_info ctinfo,
188 const struct nf_conn_synproxy *synproxy)
189{
190 unsigned int optoff, optend;
191 __be32 *ptr, old;
192
193 if (synproxy->tsoff == 0)
194 return 1;
195
196 optoff = protoff + sizeof(struct tcphdr);
197 optend = protoff + th->doff * 4;
198
199 if (skb_ensure_writable(skb, write_len: optend))
200 return 0;
201
202 while (optoff < optend) {
203 unsigned char *op = skb->data + optoff;
204
205 switch (op[0]) {
206 case TCPOPT_EOL:
207 return 1;
208 case TCPOPT_NOP:
209 optoff++;
210 continue;
211 default:
212 if (optoff + 1 == optend ||
213 optoff + op[1] > optend ||
214 op[1] < 2)
215 return 0;
216 if (op[0] == TCPOPT_TIMESTAMP &&
217 op[1] == TCPOLEN_TIMESTAMP) {
218 if (CTINFO2DIR(ctinfo) == IP_CT_DIR_REPLY) {
219 ptr = (__be32 *)&op[2];
220 old = *ptr;
221 *ptr = htonl(ntohl(*ptr) -
222 synproxy->tsoff);
223 } else {
224 ptr = (__be32 *)&op[6];
225 old = *ptr;
226 *ptr = htonl(ntohl(*ptr) +
227 synproxy->tsoff);
228 }
229 inet_proto_csum_replace4(sum: &th->check, skb,
230 from: old, to: *ptr, pseudohdr: false);
231 return 1;
232 }
233 optoff += op[1];
234 }
235 }
236 return 1;
237}
238
239#ifdef CONFIG_PROC_FS
240static void *synproxy_cpu_seq_start(struct seq_file *seq, loff_t *pos)
241{
242 struct synproxy_net *snet = synproxy_pernet(net: seq_file_net(seq));
243 int cpu;
244
245 if (*pos == 0)
246 return SEQ_START_TOKEN;
247
248 for (cpu = *pos - 1; cpu < nr_cpu_ids; cpu++) {
249 if (!cpu_possible(cpu))
250 continue;
251 *pos = cpu + 1;
252 return per_cpu_ptr(snet->stats, cpu);
253 }
254
255 return NULL;
256}
257
258static void *synproxy_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos)
259{
260 struct synproxy_net *snet = synproxy_pernet(net: seq_file_net(seq));
261 int cpu;
262
263 for (cpu = *pos; cpu < nr_cpu_ids; cpu++) {
264 if (!cpu_possible(cpu))
265 continue;
266 *pos = cpu + 1;
267 return per_cpu_ptr(snet->stats, cpu);
268 }
269 (*pos)++;
270 return NULL;
271}
272
273static void synproxy_cpu_seq_stop(struct seq_file *seq, void *v)
274{
275 return;
276}
277
278static int synproxy_cpu_seq_show(struct seq_file *seq, void *v)
279{
280 struct synproxy_stats *stats = v;
281
282 if (v == SEQ_START_TOKEN) {
283 seq_puts(m: seq, s: "entries\t\tsyn_received\t"
284 "cookie_invalid\tcookie_valid\t"
285 "cookie_retrans\tconn_reopened\n");
286 return 0;
287 }
288
289 seq_printf(m: seq, fmt: "%08x\t%08x\t%08x\t%08x\t%08x\t%08x\n", 0,
290 stats->syn_received,
291 stats->cookie_invalid,
292 stats->cookie_valid,
293 stats->cookie_retrans,
294 stats->conn_reopened);
295
296 return 0;
297}
298
299static const struct seq_operations synproxy_cpu_seq_ops = {
300 .start = synproxy_cpu_seq_start,
301 .next = synproxy_cpu_seq_next,
302 .stop = synproxy_cpu_seq_stop,
303 .show = synproxy_cpu_seq_show,
304};
305
306static int __net_init synproxy_proc_init(struct net *net)
307{
308 if (!proc_create_net("synproxy", 0444, net->proc_net_stat,
309 &synproxy_cpu_seq_ops, sizeof(struct seq_net_private)))
310 return -ENOMEM;
311 return 0;
312}
313
314static void __net_exit synproxy_proc_exit(struct net *net)
315{
316 remove_proc_entry("synproxy", net->proc_net_stat);
317}
318#else
319static int __net_init synproxy_proc_init(struct net *net)
320{
321 return 0;
322}
323
324static void __net_exit synproxy_proc_exit(struct net *net)
325{
326 return;
327}
328#endif /* CONFIG_PROC_FS */
329
330static int __net_init synproxy_net_init(struct net *net)
331{
332 struct synproxy_net *snet = synproxy_pernet(net);
333 struct nf_conn *ct;
334 int err = -ENOMEM;
335
336 ct = nf_ct_tmpl_alloc(net, zone: &nf_ct_zone_dflt, GFP_KERNEL);
337 if (!ct)
338 goto err1;
339
340 if (!nfct_seqadj_ext_add(ct))
341 goto err2;
342 if (!nfct_synproxy_ext_add(ct))
343 goto err2;
344
345 __set_bit(IPS_CONFIRMED_BIT, &ct->status);
346 snet->tmpl = ct;
347
348 snet->stats = alloc_percpu(struct synproxy_stats);
349 if (snet->stats == NULL)
350 goto err2;
351
352 err = synproxy_proc_init(net);
353 if (err < 0)
354 goto err3;
355
356 return 0;
357
358err3:
359 free_percpu(pdata: snet->stats);
360err2:
361 nf_ct_tmpl_free(tmpl: ct);
362err1:
363 return err;
364}
365
366static void __net_exit synproxy_net_exit(struct net *net)
367{
368 struct synproxy_net *snet = synproxy_pernet(net);
369
370 nf_ct_put(ct: snet->tmpl);
371 synproxy_proc_exit(net);
372 free_percpu(pdata: snet->stats);
373}
374
375static struct pernet_operations synproxy_net_ops = {
376 .init = synproxy_net_init,
377 .exit = synproxy_net_exit,
378 .id = &synproxy_net_id,
379 .size = sizeof(struct synproxy_net),
380};
381
382static int __init synproxy_core_init(void)
383{
384 return register_pernet_subsys(&synproxy_net_ops);
385}
386
387static void __exit synproxy_core_exit(void)
388{
389 unregister_pernet_subsys(&synproxy_net_ops);
390}
391
392module_init(synproxy_core_init);
393module_exit(synproxy_core_exit);
394
395static struct iphdr *
396synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr,
397 __be32 daddr)
398{
399 struct iphdr *iph;
400
401 skb_reset_network_header(skb);
402 iph = skb_put(skb, len: sizeof(*iph));
403 iph->version = 4;
404 iph->ihl = sizeof(*iph) / 4;
405 iph->tos = 0;
406 iph->id = 0;
407 iph->frag_off = htons(IP_DF);
408 iph->ttl = READ_ONCE(net->ipv4.sysctl_ip_default_ttl);
409 iph->protocol = IPPROTO_TCP;
410 iph->check = 0;
411 iph->saddr = saddr;
412 iph->daddr = daddr;
413
414 return iph;
415}
416
417static void
418synproxy_send_tcp(struct net *net,
419 const struct sk_buff *skb, struct sk_buff *nskb,
420 struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
421 struct iphdr *niph, struct tcphdr *nth,
422 unsigned int tcp_hdr_size)
423{
424 nth->check = ~tcp_v4_check(len: tcp_hdr_size, saddr: niph->saddr, daddr: niph->daddr, base: 0);
425 nskb->ip_summed = CHECKSUM_PARTIAL;
426 nskb->csum_start = (unsigned char *)nth - nskb->head;
427 nskb->csum_offset = offsetof(struct tcphdr, check);
428
429 skb_dst_set_noref(skb: nskb, dst: skb_dst(skb));
430 nskb->protocol = htons(ETH_P_IP);
431 if (ip_route_me_harder(net, sk: nskb->sk, skb: nskb, addr_type: RTN_UNSPEC))
432 goto free_nskb;
433
434 if (nfct) {
435 nf_ct_set(skb: nskb, ct: (struct nf_conn *)nfct, info: ctinfo);
436 nf_conntrack_get(nfct);
437 }
438
439 ip_local_out(net, sk: nskb->sk, skb: nskb);
440 return;
441
442free_nskb:
443 kfree_skb(skb: nskb);
444}
445
446void
447synproxy_send_client_synack(struct net *net,
448 const struct sk_buff *skb, const struct tcphdr *th,
449 const struct synproxy_options *opts)
450{
451 struct sk_buff *nskb;
452 struct iphdr *iph, *niph;
453 struct tcphdr *nth;
454 unsigned int tcp_hdr_size;
455 u16 mss = opts->mss_encode;
456
457 iph = ip_hdr(skb);
458
459 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
460 nskb = alloc_skb(size: sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
461 GFP_ATOMIC);
462 if (!nskb)
463 return;
464 skb_reserve(skb: nskb, MAX_TCP_HEADER);
465
466 niph = synproxy_build_ip(net, skb: nskb, saddr: iph->daddr, daddr: iph->saddr);
467
468 skb_reset_transport_header(skb: nskb);
469 nth = skb_put(skb: nskb, len: tcp_hdr_size);
470 nth->source = th->dest;
471 nth->dest = th->source;
472 nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss));
473 nth->ack_seq = htonl(ntohl(th->seq) + 1);
474 tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
475 if (opts->options & NF_SYNPROXY_OPT_ECN)
476 tcp_flag_word(nth) |= TCP_FLAG_ECE;
477 nth->doff = tcp_hdr_size / 4;
478 nth->window = 0;
479 nth->check = 0;
480 nth->urg_ptr = 0;
481
482 synproxy_build_options(th: nth, opts);
483
484 synproxy_send_tcp(net, skb, nskb, nfct: skb_nfct(skb),
485 ctinfo: IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
486}
487EXPORT_SYMBOL_GPL(synproxy_send_client_synack);
488
489static void
490synproxy_send_server_syn(struct net *net,
491 const struct sk_buff *skb, const struct tcphdr *th,
492 const struct synproxy_options *opts, u32 recv_seq)
493{
494 struct synproxy_net *snet = synproxy_pernet(net);
495 struct sk_buff *nskb;
496 struct iphdr *iph, *niph;
497 struct tcphdr *nth;
498 unsigned int tcp_hdr_size;
499
500 iph = ip_hdr(skb);
501
502 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
503 nskb = alloc_skb(size: sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
504 GFP_ATOMIC);
505 if (!nskb)
506 return;
507 skb_reserve(skb: nskb, MAX_TCP_HEADER);
508
509 niph = synproxy_build_ip(net, skb: nskb, saddr: iph->saddr, daddr: iph->daddr);
510
511 skb_reset_transport_header(skb: nskb);
512 nth = skb_put(skb: nskb, len: tcp_hdr_size);
513 nth->source = th->source;
514 nth->dest = th->dest;
515 nth->seq = htonl(recv_seq - 1);
516 /* ack_seq is used to relay our ISN to the synproxy hook to initialize
517 * sequence number translation once a connection tracking entry exists.
518 */
519 nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
520 tcp_flag_word(nth) = TCP_FLAG_SYN;
521 if (opts->options & NF_SYNPROXY_OPT_ECN)
522 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
523 nth->doff = tcp_hdr_size / 4;
524 nth->window = th->window;
525 nth->check = 0;
526 nth->urg_ptr = 0;
527
528 synproxy_build_options(th: nth, opts);
529
530 synproxy_send_tcp(net, skb, nskb, nfct: &snet->tmpl->ct_general, ctinfo: IP_CT_NEW,
531 niph, nth, tcp_hdr_size);
532}
533
534static void
535synproxy_send_server_ack(struct net *net,
536 const struct ip_ct_tcp *state,
537 const struct sk_buff *skb, const struct tcphdr *th,
538 const struct synproxy_options *opts)
539{
540 struct sk_buff *nskb;
541 struct iphdr *iph, *niph;
542 struct tcphdr *nth;
543 unsigned int tcp_hdr_size;
544
545 iph = ip_hdr(skb);
546
547 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
548 nskb = alloc_skb(size: sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
549 GFP_ATOMIC);
550 if (!nskb)
551 return;
552 skb_reserve(skb: nskb, MAX_TCP_HEADER);
553
554 niph = synproxy_build_ip(net, skb: nskb, saddr: iph->daddr, daddr: iph->saddr);
555
556 skb_reset_transport_header(skb: nskb);
557 nth = skb_put(skb: nskb, len: tcp_hdr_size);
558 nth->source = th->dest;
559 nth->dest = th->source;
560 nth->seq = htonl(ntohl(th->ack_seq));
561 nth->ack_seq = htonl(ntohl(th->seq) + 1);
562 tcp_flag_word(nth) = TCP_FLAG_ACK;
563 nth->doff = tcp_hdr_size / 4;
564 nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
565 nth->check = 0;
566 nth->urg_ptr = 0;
567
568 synproxy_build_options(th: nth, opts);
569
570 synproxy_send_tcp(net, skb, nskb, NULL, ctinfo: 0, niph, nth, tcp_hdr_size);
571}
572
573static void
574synproxy_send_client_ack(struct net *net,
575 const struct sk_buff *skb, const struct tcphdr *th,
576 const struct synproxy_options *opts)
577{
578 struct sk_buff *nskb;
579 struct iphdr *iph, *niph;
580 struct tcphdr *nth;
581 unsigned int tcp_hdr_size;
582
583 iph = ip_hdr(skb);
584
585 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
586 nskb = alloc_skb(size: sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
587 GFP_ATOMIC);
588 if (!nskb)
589 return;
590 skb_reserve(skb: nskb, MAX_TCP_HEADER);
591
592 niph = synproxy_build_ip(net, skb: nskb, saddr: iph->saddr, daddr: iph->daddr);
593
594 skb_reset_transport_header(skb: nskb);
595 nth = skb_put(skb: nskb, len: tcp_hdr_size);
596 nth->source = th->source;
597 nth->dest = th->dest;
598 nth->seq = htonl(ntohl(th->seq) + 1);
599 nth->ack_seq = th->ack_seq;
600 tcp_flag_word(nth) = TCP_FLAG_ACK;
601 nth->doff = tcp_hdr_size / 4;
602 nth->window = htons(ntohs(th->window) >> opts->wscale);
603 nth->check = 0;
604 nth->urg_ptr = 0;
605
606 synproxy_build_options(th: nth, opts);
607
608 synproxy_send_tcp(net, skb, nskb, nfct: skb_nfct(skb),
609 ctinfo: IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
610}
611
612bool
613synproxy_recv_client_ack(struct net *net,
614 const struct sk_buff *skb, const struct tcphdr *th,
615 struct synproxy_options *opts, u32 recv_seq)
616{
617 struct synproxy_net *snet = synproxy_pernet(net);
618 int mss;
619
620 mss = __cookie_v4_check(iph: ip_hdr(skb), th);
621 if (mss == 0) {
622 this_cpu_inc(snet->stats->cookie_invalid);
623 return false;
624 }
625
626 this_cpu_inc(snet->stats->cookie_valid);
627 opts->mss_option = mss;
628 opts->options |= NF_SYNPROXY_OPT_MSS;
629
630 if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
631 synproxy_check_timestamp_cookie(opts);
632
633 synproxy_send_server_syn(net, skb, th, opts, recv_seq);
634 return true;
635}
636EXPORT_SYMBOL_GPL(synproxy_recv_client_ack);
637
638unsigned int
639ipv4_synproxy_hook(void *priv, struct sk_buff *skb,
640 const struct nf_hook_state *nhs)
641{
642 struct net *net = nhs->net;
643 struct synproxy_net *snet = synproxy_pernet(net);
644 enum ip_conntrack_info ctinfo;
645 struct nf_conn *ct;
646 struct nf_conn_synproxy *synproxy;
647 struct synproxy_options opts = {};
648 const struct ip_ct_tcp *state;
649 struct tcphdr *th, _th;
650 unsigned int thoff;
651
652 ct = nf_ct_get(skb, ctinfo: &ctinfo);
653 if (!ct)
654 return NF_ACCEPT;
655
656 synproxy = nfct_synproxy(ct);
657 if (!synproxy)
658 return NF_ACCEPT;
659
660 if (nf_is_loopback_packet(skb) ||
661 ip_hdr(skb)->protocol != IPPROTO_TCP)
662 return NF_ACCEPT;
663
664 thoff = ip_hdrlen(skb);
665 th = skb_header_pointer(skb, offset: thoff, len: sizeof(_th), buffer: &_th);
666 if (!th)
667 return NF_DROP;
668
669 state = &ct->proto.tcp;
670 switch (state->state) {
671 case TCP_CONNTRACK_CLOSE:
672 if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) {
673 nf_ct_seqadj_init(ct, ctinfo, off: synproxy->isn -
674 ntohl(th->seq) + 1);
675 break;
676 }
677
678 if (!th->syn || th->ack ||
679 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
680 break;
681
682 /* Reopened connection - reset the sequence number and timestamp
683 * adjustments, they will get initialized once the connection is
684 * reestablished.
685 */
686 nf_ct_seqadj_init(ct, ctinfo, off: 0);
687 synproxy->tsoff = 0;
688 this_cpu_inc(snet->stats->conn_reopened);
689 fallthrough;
690 case TCP_CONNTRACK_SYN_SENT:
691 if (!synproxy_parse_options(skb, thoff, th, &opts))
692 return NF_DROP;
693
694 if (!th->syn && th->ack &&
695 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
696 /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
697 * therefore we need to add 1 to make the SYN sequence
698 * number match the one of first SYN.
699 */
700 if (synproxy_recv_client_ack(net, skb, th, &opts,
701 ntohl(th->seq) + 1)) {
702 this_cpu_inc(snet->stats->cookie_retrans);
703 consume_skb(skb);
704 return NF_STOLEN;
705 } else {
706 return NF_DROP;
707 }
708 }
709
710 synproxy->isn = ntohl(th->ack_seq);
711 if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP)
712 synproxy->its = opts.tsecr;
713
714 nf_conntrack_event_cache(event: IPCT_SYNPROXY, ct);
715 break;
716 case TCP_CONNTRACK_SYN_RECV:
717 if (!th->syn || !th->ack)
718 break;
719
720 if (!synproxy_parse_options(skb, thoff, th, &opts))
721 return NF_DROP;
722
723 if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP) {
724 synproxy->tsoff = opts.tsval - synproxy->its;
725 nf_conntrack_event_cache(event: IPCT_SYNPROXY, ct);
726 }
727
728 opts.options &= ~(NF_SYNPROXY_OPT_MSS |
729 NF_SYNPROXY_OPT_WSCALE |
730 NF_SYNPROXY_OPT_SACK_PERM);
731
732 swap(opts.tsval, opts.tsecr);
733 synproxy_send_server_ack(net, state, skb, th, opts: &opts);
734
735 nf_ct_seqadj_init(ct, ctinfo, off: synproxy->isn - ntohl(th->seq));
736 nf_conntrack_event_cache(event: IPCT_SEQADJ, ct);
737
738 swap(opts.tsval, opts.tsecr);
739 synproxy_send_client_ack(net, skb, th, opts: &opts);
740
741 consume_skb(skb);
742 return NF_STOLEN;
743 default:
744 break;
745 }
746
747 synproxy_tstamp_adjust(skb, protoff: thoff, th, ct, ctinfo, synproxy);
748 return NF_ACCEPT;
749}
750EXPORT_SYMBOL_GPL(ipv4_synproxy_hook);
751
752static const struct nf_hook_ops ipv4_synproxy_ops[] = {
753 {
754 .hook = ipv4_synproxy_hook,
755 .pf = NFPROTO_IPV4,
756 .hooknum = NF_INET_LOCAL_IN,
757 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
758 },
759 {
760 .hook = ipv4_synproxy_hook,
761 .pf = NFPROTO_IPV4,
762 .hooknum = NF_INET_POST_ROUTING,
763 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
764 },
765};
766
767int nf_synproxy_ipv4_init(struct synproxy_net *snet, struct net *net)
768{
769 int err;
770
771 if (snet->hook_ref4 == 0) {
772 err = nf_register_net_hooks(net, reg: ipv4_synproxy_ops,
773 ARRAY_SIZE(ipv4_synproxy_ops));
774 if (err)
775 return err;
776 }
777
778 snet->hook_ref4++;
779 return 0;
780}
781EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_init);
782
783void nf_synproxy_ipv4_fini(struct synproxy_net *snet, struct net *net)
784{
785 snet->hook_ref4--;
786 if (snet->hook_ref4 == 0)
787 nf_unregister_net_hooks(net, reg: ipv4_synproxy_ops,
788 ARRAY_SIZE(ipv4_synproxy_ops));
789}
790EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_fini);
791
792#if IS_ENABLED(CONFIG_IPV6)
793static struct ipv6hdr *
794synproxy_build_ip_ipv6(struct net *net, struct sk_buff *skb,
795 const struct in6_addr *saddr,
796 const struct in6_addr *daddr)
797{
798 struct ipv6hdr *iph;
799
800 skb_reset_network_header(skb);
801 iph = skb_put(skb, len: sizeof(*iph));
802 ip6_flow_hdr(hdr: iph, tclass: 0, flowlabel: 0);
803 iph->hop_limit = READ_ONCE(net->ipv6.devconf_all->hop_limit);
804 iph->nexthdr = IPPROTO_TCP;
805 iph->saddr = *saddr;
806 iph->daddr = *daddr;
807
808 return iph;
809}
810
811static void
812synproxy_send_tcp_ipv6(struct net *net,
813 const struct sk_buff *skb, struct sk_buff *nskb,
814 struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
815 struct ipv6hdr *niph, struct tcphdr *nth,
816 unsigned int tcp_hdr_size)
817{
818 struct dst_entry *dst;
819 struct flowi6 fl6;
820 int err;
821
822 nth->check = ~tcp_v6_check(len: tcp_hdr_size, saddr: &niph->saddr, daddr: &niph->daddr, base: 0);
823 nskb->ip_summed = CHECKSUM_PARTIAL;
824 nskb->csum_start = (unsigned char *)nth - nskb->head;
825 nskb->csum_offset = offsetof(struct tcphdr, check);
826
827 memset(&fl6, 0, sizeof(fl6));
828 fl6.flowi6_proto = IPPROTO_TCP;
829 fl6.saddr = niph->saddr;
830 fl6.daddr = niph->daddr;
831 fl6.fl6_sport = nth->source;
832 fl6.fl6_dport = nth->dest;
833 security_skb_classify_flow(skb: (struct sk_buff *)skb,
834 flic: flowi6_to_flowi_common(fl6: &fl6));
835 err = nf_ip6_route(net, dst: &dst, fl: flowi6_to_flowi(fl6: &fl6), strict: false);
836 if (err) {
837 goto free_nskb;
838 }
839
840 dst = xfrm_lookup(net, dst_orig: dst, fl: flowi6_to_flowi(fl6: &fl6), NULL, flags: 0);
841 if (IS_ERR(ptr: dst))
842 goto free_nskb;
843
844 skb_dst_set(skb: nskb, dst);
845
846 if (nfct) {
847 nf_ct_set(skb: nskb, ct: (struct nf_conn *)nfct, info: ctinfo);
848 nf_conntrack_get(nfct);
849 }
850
851 ip6_local_out(net, sk: nskb->sk, skb: nskb);
852 return;
853
854free_nskb:
855 kfree_skb(skb: nskb);
856}
857
858void
859synproxy_send_client_synack_ipv6(struct net *net,
860 const struct sk_buff *skb,
861 const struct tcphdr *th,
862 const struct synproxy_options *opts)
863{
864 struct sk_buff *nskb;
865 struct ipv6hdr *iph, *niph;
866 struct tcphdr *nth;
867 unsigned int tcp_hdr_size;
868 u16 mss = opts->mss_encode;
869
870 iph = ipv6_hdr(skb);
871
872 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
873 nskb = alloc_skb(size: sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
874 GFP_ATOMIC);
875 if (!nskb)
876 return;
877 skb_reserve(skb: nskb, MAX_TCP_HEADER);
878
879 niph = synproxy_build_ip_ipv6(net, skb: nskb, saddr: &iph->daddr, daddr: &iph->saddr);
880
881 skb_reset_transport_header(skb: nskb);
882 nth = skb_put(skb: nskb, len: tcp_hdr_size);
883 nth->source = th->dest;
884 nth->dest = th->source;
885 nth->seq = htonl(nf_ipv6_cookie_init_sequence(iph, th, &mss));
886 nth->ack_seq = htonl(ntohl(th->seq) + 1);
887 tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
888 if (opts->options & NF_SYNPROXY_OPT_ECN)
889 tcp_flag_word(nth) |= TCP_FLAG_ECE;
890 nth->doff = tcp_hdr_size / 4;
891 nth->window = 0;
892 nth->check = 0;
893 nth->urg_ptr = 0;
894
895 synproxy_build_options(th: nth, opts);
896
897 synproxy_send_tcp_ipv6(net, skb, nskb, nfct: skb_nfct(skb),
898 ctinfo: IP_CT_ESTABLISHED_REPLY, niph, nth,
899 tcp_hdr_size);
900}
901EXPORT_SYMBOL_GPL(synproxy_send_client_synack_ipv6);
902
903static void
904synproxy_send_server_syn_ipv6(struct net *net, const struct sk_buff *skb,
905 const struct tcphdr *th,
906 const struct synproxy_options *opts, u32 recv_seq)
907{
908 struct synproxy_net *snet = synproxy_pernet(net);
909 struct sk_buff *nskb;
910 struct ipv6hdr *iph, *niph;
911 struct tcphdr *nth;
912 unsigned int tcp_hdr_size;
913
914 iph = ipv6_hdr(skb);
915
916 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
917 nskb = alloc_skb(size: sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
918 GFP_ATOMIC);
919 if (!nskb)
920 return;
921 skb_reserve(skb: nskb, MAX_TCP_HEADER);
922
923 niph = synproxy_build_ip_ipv6(net, skb: nskb, saddr: &iph->saddr, daddr: &iph->daddr);
924
925 skb_reset_transport_header(skb: nskb);
926 nth = skb_put(skb: nskb, len: tcp_hdr_size);
927 nth->source = th->source;
928 nth->dest = th->dest;
929 nth->seq = htonl(recv_seq - 1);
930 /* ack_seq is used to relay our ISN to the synproxy hook to initialize
931 * sequence number translation once a connection tracking entry exists.
932 */
933 nth->ack_seq = htonl(ntohl(th->ack_seq) - 1);
934 tcp_flag_word(nth) = TCP_FLAG_SYN;
935 if (opts->options & NF_SYNPROXY_OPT_ECN)
936 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
937 nth->doff = tcp_hdr_size / 4;
938 nth->window = th->window;
939 nth->check = 0;
940 nth->urg_ptr = 0;
941
942 synproxy_build_options(th: nth, opts);
943
944 synproxy_send_tcp_ipv6(net, skb, nskb, nfct: &snet->tmpl->ct_general,
945 ctinfo: IP_CT_NEW, niph, nth, tcp_hdr_size);
946}
947
948static void
949synproxy_send_server_ack_ipv6(struct net *net, const struct ip_ct_tcp *state,
950 const struct sk_buff *skb,
951 const struct tcphdr *th,
952 const struct synproxy_options *opts)
953{
954 struct sk_buff *nskb;
955 struct ipv6hdr *iph, *niph;
956 struct tcphdr *nth;
957 unsigned int tcp_hdr_size;
958
959 iph = ipv6_hdr(skb);
960
961 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
962 nskb = alloc_skb(size: sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
963 GFP_ATOMIC);
964 if (!nskb)
965 return;
966 skb_reserve(skb: nskb, MAX_TCP_HEADER);
967
968 niph = synproxy_build_ip_ipv6(net, skb: nskb, saddr: &iph->daddr, daddr: &iph->saddr);
969
970 skb_reset_transport_header(skb: nskb);
971 nth = skb_put(skb: nskb, len: tcp_hdr_size);
972 nth->source = th->dest;
973 nth->dest = th->source;
974 nth->seq = htonl(ntohl(th->ack_seq));
975 nth->ack_seq = htonl(ntohl(th->seq) + 1);
976 tcp_flag_word(nth) = TCP_FLAG_ACK;
977 nth->doff = tcp_hdr_size / 4;
978 nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
979 nth->check = 0;
980 nth->urg_ptr = 0;
981
982 synproxy_build_options(th: nth, opts);
983
984 synproxy_send_tcp_ipv6(net, skb, nskb, NULL, ctinfo: 0, niph, nth,
985 tcp_hdr_size);
986}
987
988static void
989synproxy_send_client_ack_ipv6(struct net *net, const struct sk_buff *skb,
990 const struct tcphdr *th,
991 const struct synproxy_options *opts)
992{
993 struct sk_buff *nskb;
994 struct ipv6hdr *iph, *niph;
995 struct tcphdr *nth;
996 unsigned int tcp_hdr_size;
997
998 iph = ipv6_hdr(skb);
999
1000 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
1001 nskb = alloc_skb(size: sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
1002 GFP_ATOMIC);
1003 if (!nskb)
1004 return;
1005 skb_reserve(skb: nskb, MAX_TCP_HEADER);
1006
1007 niph = synproxy_build_ip_ipv6(net, skb: nskb, saddr: &iph->saddr, daddr: &iph->daddr);
1008
1009 skb_reset_transport_header(skb: nskb);
1010 nth = skb_put(skb: nskb, len: tcp_hdr_size);
1011 nth->source = th->source;
1012 nth->dest = th->dest;
1013 nth->seq = htonl(ntohl(th->seq) + 1);
1014 nth->ack_seq = th->ack_seq;
1015 tcp_flag_word(nth) = TCP_FLAG_ACK;
1016 nth->doff = tcp_hdr_size / 4;
1017 nth->window = htons(ntohs(th->window) >> opts->wscale);
1018 nth->check = 0;
1019 nth->urg_ptr = 0;
1020
1021 synproxy_build_options(th: nth, opts);
1022
1023 synproxy_send_tcp_ipv6(net, skb, nskb, nfct: skb_nfct(skb),
1024 ctinfo: IP_CT_ESTABLISHED_REPLY, niph, nth,
1025 tcp_hdr_size);
1026}
1027
1028bool
1029synproxy_recv_client_ack_ipv6(struct net *net,
1030 const struct sk_buff *skb,
1031 const struct tcphdr *th,
1032 struct synproxy_options *opts, u32 recv_seq)
1033{
1034 struct synproxy_net *snet = synproxy_pernet(net);
1035 int mss;
1036
1037 mss = nf_cookie_v6_check(iph: ipv6_hdr(skb), th);
1038 if (mss == 0) {
1039 this_cpu_inc(snet->stats->cookie_invalid);
1040 return false;
1041 }
1042
1043 this_cpu_inc(snet->stats->cookie_valid);
1044 opts->mss_option = mss;
1045 opts->options |= NF_SYNPROXY_OPT_MSS;
1046
1047 if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
1048 synproxy_check_timestamp_cookie(opts);
1049
1050 synproxy_send_server_syn_ipv6(net, skb, th, opts, recv_seq);
1051 return true;
1052}
1053EXPORT_SYMBOL_GPL(synproxy_recv_client_ack_ipv6);
1054
1055unsigned int
1056ipv6_synproxy_hook(void *priv, struct sk_buff *skb,
1057 const struct nf_hook_state *nhs)
1058{
1059 struct net *net = nhs->net;
1060 struct synproxy_net *snet = synproxy_pernet(net);
1061 enum ip_conntrack_info ctinfo;
1062 struct nf_conn *ct;
1063 struct nf_conn_synproxy *synproxy;
1064 struct synproxy_options opts = {};
1065 const struct ip_ct_tcp *state;
1066 struct tcphdr *th, _th;
1067 __be16 frag_off;
1068 u8 nexthdr;
1069 int thoff;
1070
1071 ct = nf_ct_get(skb, ctinfo: &ctinfo);
1072 if (!ct)
1073 return NF_ACCEPT;
1074
1075 synproxy = nfct_synproxy(ct);
1076 if (!synproxy)
1077 return NF_ACCEPT;
1078
1079 if (nf_is_loopback_packet(skb))
1080 return NF_ACCEPT;
1081
1082 nexthdr = ipv6_hdr(skb)->nexthdr;
1083 thoff = ipv6_skip_exthdr(skb, start: sizeof(struct ipv6hdr), nexthdrp: &nexthdr,
1084 frag_offp: &frag_off);
1085 if (thoff < 0 || nexthdr != IPPROTO_TCP)
1086 return NF_ACCEPT;
1087
1088 th = skb_header_pointer(skb, offset: thoff, len: sizeof(_th), buffer: &_th);
1089 if (!th)
1090 return NF_DROP;
1091
1092 state = &ct->proto.tcp;
1093 switch (state->state) {
1094 case TCP_CONNTRACK_CLOSE:
1095 if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) {
1096 nf_ct_seqadj_init(ct, ctinfo, off: synproxy->isn -
1097 ntohl(th->seq) + 1);
1098 break;
1099 }
1100
1101 if (!th->syn || th->ack ||
1102 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
1103 break;
1104
1105 /* Reopened connection - reset the sequence number and timestamp
1106 * adjustments, they will get initialized once the connection is
1107 * reestablished.
1108 */
1109 nf_ct_seqadj_init(ct, ctinfo, off: 0);
1110 synproxy->tsoff = 0;
1111 this_cpu_inc(snet->stats->conn_reopened);
1112 fallthrough;
1113 case TCP_CONNTRACK_SYN_SENT:
1114 if (!synproxy_parse_options(skb, thoff, th, &opts))
1115 return NF_DROP;
1116
1117 if (!th->syn && th->ack &&
1118 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
1119 /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
1120 * therefore we need to add 1 to make the SYN sequence
1121 * number match the one of first SYN.
1122 */
1123 if (synproxy_recv_client_ack_ipv6(net, skb, th, &opts,
1124 ntohl(th->seq) + 1)) {
1125 this_cpu_inc(snet->stats->cookie_retrans);
1126 consume_skb(skb);
1127 return NF_STOLEN;
1128 } else {
1129 return NF_DROP;
1130 }
1131 }
1132
1133 synproxy->isn = ntohl(th->ack_seq);
1134 if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP)
1135 synproxy->its = opts.tsecr;
1136
1137 nf_conntrack_event_cache(event: IPCT_SYNPROXY, ct);
1138 break;
1139 case TCP_CONNTRACK_SYN_RECV:
1140 if (!th->syn || !th->ack)
1141 break;
1142
1143 if (!synproxy_parse_options(skb, thoff, th, &opts))
1144 return NF_DROP;
1145
1146 if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP) {
1147 synproxy->tsoff = opts.tsval - synproxy->its;
1148 nf_conntrack_event_cache(event: IPCT_SYNPROXY, ct);
1149 }
1150
1151 opts.options &= ~(NF_SYNPROXY_OPT_MSS |
1152 NF_SYNPROXY_OPT_WSCALE |
1153 NF_SYNPROXY_OPT_SACK_PERM);
1154
1155 swap(opts.tsval, opts.tsecr);
1156 synproxy_send_server_ack_ipv6(net, state, skb, th, opts: &opts);
1157
1158 nf_ct_seqadj_init(ct, ctinfo, off: synproxy->isn - ntohl(th->seq));
1159 nf_conntrack_event_cache(event: IPCT_SEQADJ, ct);
1160
1161 swap(opts.tsval, opts.tsecr);
1162 synproxy_send_client_ack_ipv6(net, skb, th, opts: &opts);
1163
1164 consume_skb(skb);
1165 return NF_STOLEN;
1166 default:
1167 break;
1168 }
1169
1170 synproxy_tstamp_adjust(skb, protoff: thoff, th, ct, ctinfo, synproxy);
1171 return NF_ACCEPT;
1172}
1173EXPORT_SYMBOL_GPL(ipv6_synproxy_hook);
1174
1175static const struct nf_hook_ops ipv6_synproxy_ops[] = {
1176 {
1177 .hook = ipv6_synproxy_hook,
1178 .pf = NFPROTO_IPV6,
1179 .hooknum = NF_INET_LOCAL_IN,
1180 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
1181 },
1182 {
1183 .hook = ipv6_synproxy_hook,
1184 .pf = NFPROTO_IPV6,
1185 .hooknum = NF_INET_POST_ROUTING,
1186 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
1187 },
1188};
1189
1190int
1191nf_synproxy_ipv6_init(struct synproxy_net *snet, struct net *net)
1192{
1193 int err;
1194
1195 if (snet->hook_ref6 == 0) {
1196 err = nf_register_net_hooks(net, reg: ipv6_synproxy_ops,
1197 ARRAY_SIZE(ipv6_synproxy_ops));
1198 if (err)
1199 return err;
1200 }
1201
1202 snet->hook_ref6++;
1203 return 0;
1204}
1205EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_init);
1206
1207void
1208nf_synproxy_ipv6_fini(struct synproxy_net *snet, struct net *net)
1209{
1210 snet->hook_ref6--;
1211 if (snet->hook_ref6 == 0)
1212 nf_unregister_net_hooks(net, reg: ipv6_synproxy_ops,
1213 ARRAY_SIZE(ipv6_synproxy_ops));
1214}
1215EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_fini);
1216#endif /* CONFIG_IPV6 */
1217
1218MODULE_LICENSE("GPL");
1219MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
1220MODULE_DESCRIPTION("nftables SYNPROXY expression support");
1221

source code of linux/net/netfilter/nf_synproxy_core.c