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TOMOYO Linux Cross Reference
Linux/net/ipv6/netfilter/ip6t_SYNPROXY.c

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  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 net *net, struct sk_buff *skb,
 24                   const struct in6_addr *saddr,
 25                   const struct in6_addr *daddr)
 26 {
 27         struct ipv6hdr *iph;
 28 
 29         skb_reset_network_header(skb);
 30         iph = skb_put(skb, sizeof(*iph));
 31         ip6_flow_hdr(iph, 0, 0);
 32         iph->hop_limit  = net->ipv6.devconf_all->hop_limit;
 33         iph->nexthdr    = IPPROTO_TCP;
 34         iph->saddr      = *saddr;
 35         iph->daddr      = *daddr;
 36 
 37         return iph;
 38 }
 39 
 40 static void
 41 synproxy_send_tcp(struct net *net,
 42                   const struct sk_buff *skb, struct sk_buff *nskb,
 43                   struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo,
 44                   struct ipv6hdr *niph, struct tcphdr *nth,
 45                   unsigned int tcp_hdr_size)
 46 {
 47         struct dst_entry *dst;
 48         struct flowi6 fl6;
 49 
 50         nth->check = ~tcp_v6_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         memset(&fl6, 0, sizeof(fl6));
 56         fl6.flowi6_proto = IPPROTO_TCP;
 57         fl6.saddr = niph->saddr;
 58         fl6.daddr = niph->daddr;
 59         fl6.fl6_sport = nth->source;
 60         fl6.fl6_dport = nth->dest;
 61         security_skb_classify_flow((struct sk_buff *)skb, flowi6_to_flowi(&fl6));
 62         dst = ip6_route_output(net, NULL, &fl6);
 63         if (dst->error) {
 64                 dst_release(dst);
 65                 goto free_nskb;
 66         }
 67         dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
 68         if (IS_ERR(dst))
 69                 goto free_nskb;
 70 
 71         skb_dst_set(nskb, dst);
 72 
 73         if (nfct) {
 74                 nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo);
 75                 nf_conntrack_get(nfct);
 76         }
 77 
 78         ip6_local_out(net, nskb->sk, nskb);
 79         return;
 80 
 81 free_nskb:
 82         kfree_skb(nskb);
 83 }
 84 
 85 static void
 86 synproxy_send_client_synack(struct net *net,
 87                             const struct sk_buff *skb, const struct tcphdr *th,
 88                             const struct synproxy_options *opts)
 89 {
 90         struct sk_buff *nskb;
 91         struct ipv6hdr *iph, *niph;
 92         struct tcphdr *nth;
 93         unsigned int tcp_hdr_size;
 94         u16 mss = opts->mss;
 95 
 96         iph = ipv6_hdr(skb);
 97 
 98         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
 99         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
100                          GFP_ATOMIC);
101         if (nskb == NULL)
102                 return;
103         skb_reserve(nskb, MAX_TCP_HEADER);
104 
105         niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
106 
107         skb_reset_transport_header(nskb);
108         nth = skb_put(nskb, tcp_hdr_size);
109         nth->source     = th->dest;
110         nth->dest       = th->source;
111         nth->seq        = htonl(__cookie_v6_init_sequence(iph, th, &mss));
112         nth->ack_seq    = htonl(ntohl(th->seq) + 1);
113         tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK;
114         if (opts->options & XT_SYNPROXY_OPT_ECN)
115                 tcp_flag_word(nth) |= TCP_FLAG_ECE;
116         nth->doff       = tcp_hdr_size / 4;
117         nth->window     = 0;
118         nth->check      = 0;
119         nth->urg_ptr    = 0;
120 
121         synproxy_build_options(nth, opts);
122 
123         synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
124                           IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
125 }
126 
127 static void
128 synproxy_send_server_syn(struct net *net,
129                          const struct sk_buff *skb, const struct tcphdr *th,
130                          const struct synproxy_options *opts, u32 recv_seq)
131 {
132         struct synproxy_net *snet = synproxy_pernet(net);
133         struct sk_buff *nskb;
134         struct ipv6hdr *iph, *niph;
135         struct tcphdr *nth;
136         unsigned int tcp_hdr_size;
137 
138         iph = ipv6_hdr(skb);
139 
140         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
141         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
142                          GFP_ATOMIC);
143         if (nskb == NULL)
144                 return;
145         skb_reserve(nskb, MAX_TCP_HEADER);
146 
147         niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
148 
149         skb_reset_transport_header(nskb);
150         nth = skb_put(nskb, tcp_hdr_size);
151         nth->source     = th->source;
152         nth->dest       = th->dest;
153         nth->seq        = htonl(recv_seq - 1);
154         /* ack_seq is used to relay our ISN to the synproxy hook to initialize
155          * sequence number translation once a connection tracking entry exists.
156          */
157         nth->ack_seq    = htonl(ntohl(th->ack_seq) - 1);
158         tcp_flag_word(nth) = TCP_FLAG_SYN;
159         if (opts->options & XT_SYNPROXY_OPT_ECN)
160                 tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR;
161         nth->doff       = tcp_hdr_size / 4;
162         nth->window     = th->window;
163         nth->check      = 0;
164         nth->urg_ptr    = 0;
165 
166         synproxy_build_options(nth, opts);
167 
168         synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
169                           niph, nth, tcp_hdr_size);
170 }
171 
172 static void
173 synproxy_send_server_ack(struct net *net,
174                          const struct ip_ct_tcp *state,
175                          const struct sk_buff *skb, const struct tcphdr *th,
176                          const struct synproxy_options *opts)
177 {
178         struct sk_buff *nskb;
179         struct ipv6hdr *iph, *niph;
180         struct tcphdr *nth;
181         unsigned int tcp_hdr_size;
182 
183         iph = ipv6_hdr(skb);
184 
185         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
186         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
187                          GFP_ATOMIC);
188         if (nskb == NULL)
189                 return;
190         skb_reserve(nskb, MAX_TCP_HEADER);
191 
192         niph = synproxy_build_ip(net, nskb, &iph->daddr, &iph->saddr);
193 
194         skb_reset_transport_header(nskb);
195         nth = skb_put(nskb, tcp_hdr_size);
196         nth->source     = th->dest;
197         nth->dest       = th->source;
198         nth->seq        = htonl(ntohl(th->ack_seq));
199         nth->ack_seq    = htonl(ntohl(th->seq) + 1);
200         tcp_flag_word(nth) = TCP_FLAG_ACK;
201         nth->doff       = tcp_hdr_size / 4;
202         nth->window     = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin);
203         nth->check      = 0;
204         nth->urg_ptr    = 0;
205 
206         synproxy_build_options(nth, opts);
207 
208         synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
209 }
210 
211 static void
212 synproxy_send_client_ack(struct net *net,
213                          const struct sk_buff *skb, const struct tcphdr *th,
214                          const struct synproxy_options *opts)
215 {
216         struct sk_buff *nskb;
217         struct ipv6hdr *iph, *niph;
218         struct tcphdr *nth;
219         unsigned int tcp_hdr_size;
220 
221         iph = ipv6_hdr(skb);
222 
223         tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
224         nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
225                          GFP_ATOMIC);
226         if (nskb == NULL)
227                 return;
228         skb_reserve(nskb, MAX_TCP_HEADER);
229 
230         niph = synproxy_build_ip(net, nskb, &iph->saddr, &iph->daddr);
231 
232         skb_reset_transport_header(nskb);
233         nth = skb_put(nskb, tcp_hdr_size);
234         nth->source     = th->source;
235         nth->dest       = th->dest;
236         nth->seq        = htonl(ntohl(th->seq) + 1);
237         nth->ack_seq    = th->ack_seq;
238         tcp_flag_word(nth) = TCP_FLAG_ACK;
239         nth->doff       = tcp_hdr_size / 4;
240         nth->window     = htons(ntohs(th->window) >> opts->wscale);
241         nth->check      = 0;
242         nth->urg_ptr    = 0;
243 
244         synproxy_build_options(nth, opts);
245 
246         synproxy_send_tcp(net, skb, nskb, skb_nfct(skb),
247                           IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size);
248 }
249 
250 static bool
251 synproxy_recv_client_ack(struct net *net,
252                          const struct sk_buff *skb, const struct tcphdr *th,
253                          struct synproxy_options *opts, u32 recv_seq)
254 {
255         struct synproxy_net *snet = synproxy_pernet(net);
256         int mss;
257 
258         mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
259         if (mss == 0) {
260                 this_cpu_inc(snet->stats->cookie_invalid);
261                 return false;
262         }
263 
264         this_cpu_inc(snet->stats->cookie_valid);
265         opts->mss = mss;
266         opts->options |= XT_SYNPROXY_OPT_MSS;
267 
268         if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
269                 synproxy_check_timestamp_cookie(opts);
270 
271         synproxy_send_server_syn(net, skb, th, opts, recv_seq);
272         return true;
273 }
274 
275 static unsigned int
276 synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
277 {
278         const struct xt_synproxy_info *info = par->targinfo;
279         struct net *net = xt_net(par);
280         struct synproxy_net *snet = synproxy_pernet(net);
281         struct synproxy_options opts = {};
282         struct tcphdr *th, _th;
283 
284         if (nf_ip6_checksum(skb, xt_hooknum(par), par->thoff, IPPROTO_TCP))
285                 return NF_DROP;
286 
287         th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
288         if (th == NULL)
289                 return NF_DROP;
290 
291         if (!synproxy_parse_options(skb, par->thoff, th, &opts))
292                 return NF_DROP;
293 
294         if (th->syn && !(th->ack || th->fin || th->rst)) {
295                 /* Initial SYN from client */
296                 this_cpu_inc(snet->stats->syn_received);
297 
298                 if (th->ece && th->cwr)
299                         opts.options |= XT_SYNPROXY_OPT_ECN;
300 
301                 opts.options &= info->options;
302                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
303                         synproxy_init_timestamp_cookie(info, &opts);
304                 else
305                         opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
306                                           XT_SYNPROXY_OPT_SACK_PERM |
307                                           XT_SYNPROXY_OPT_ECN);
308 
309                 synproxy_send_client_synack(net, skb, th, &opts);
310                 consume_skb(skb);
311                 return NF_STOLEN;
312 
313         } else if (th->ack && !(th->fin || th->rst || th->syn)) {
314                 /* ACK from client */
315                 if (synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq))) {
316                         consume_skb(skb);
317                         return NF_STOLEN;
318                 } else {
319                         return NF_DROP;
320                 }
321         }
322 
323         return XT_CONTINUE;
324 }
325 
326 static unsigned int ipv6_synproxy_hook(void *priv,
327                                        struct sk_buff *skb,
328                                        const struct nf_hook_state *nhs)
329 {
330         struct net *net = nhs->net;
331         struct synproxy_net *snet = synproxy_pernet(net);
332         enum ip_conntrack_info ctinfo;
333         struct nf_conn *ct;
334         struct nf_conn_synproxy *synproxy;
335         struct synproxy_options opts = {};
336         const struct ip_ct_tcp *state;
337         struct tcphdr *th, _th;
338         __be16 frag_off;
339         u8 nexthdr;
340         int thoff;
341 
342         ct = nf_ct_get(skb, &ctinfo);
343         if (ct == NULL)
344                 return NF_ACCEPT;
345 
346         synproxy = nfct_synproxy(ct);
347         if (synproxy == NULL)
348                 return NF_ACCEPT;
349 
350         if (nf_is_loopback_packet(skb))
351                 return NF_ACCEPT;
352 
353         nexthdr = ipv6_hdr(skb)->nexthdr;
354         thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
355                                  &frag_off);
356         if (thoff < 0 || nexthdr != IPPROTO_TCP)
357                 return NF_ACCEPT;
358 
359         th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
360         if (th == NULL)
361                 return NF_DROP;
362 
363         state = &ct->proto.tcp;
364         switch (state->state) {
365         case TCP_CONNTRACK_CLOSE:
366                 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
367                         nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
368                                                       ntohl(th->seq) + 1);
369                         break;
370                 }
371 
372                 if (!th->syn || th->ack ||
373                     CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
374                         break;
375 
376                 /* Reopened connection - reset the sequence number and timestamp
377                  * adjustments, they will get initialized once the connection is
378                  * reestablished.
379                  */
380                 nf_ct_seqadj_init(ct, ctinfo, 0);
381                 synproxy->tsoff = 0;
382                 this_cpu_inc(snet->stats->conn_reopened);
383 
384                 /* fall through */
385         case TCP_CONNTRACK_SYN_SENT:
386                 if (!synproxy_parse_options(skb, thoff, th, &opts))
387                         return NF_DROP;
388 
389                 if (!th->syn && th->ack &&
390                     CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
391                         /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
392                          * therefore we need to add 1 to make the SYN sequence
393                          * number match the one of first SYN.
394                          */
395                         if (synproxy_recv_client_ack(net, skb, th, &opts,
396                                                      ntohl(th->seq) + 1)) {
397                                 this_cpu_inc(snet->stats->cookie_retrans);
398                                 consume_skb(skb);
399                                 return NF_STOLEN;
400                         } else {
401                                 return NF_DROP;
402                         }
403                 }
404 
405                 synproxy->isn = ntohl(th->ack_seq);
406                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
407                         synproxy->its = opts.tsecr;
408                 break;
409         case TCP_CONNTRACK_SYN_RECV:
410                 if (!th->syn || !th->ack)
411                         break;
412 
413                 if (!synproxy_parse_options(skb, thoff, th, &opts))
414                         return NF_DROP;
415 
416                 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
417                         synproxy->tsoff = opts.tsval - synproxy->its;
418 
419                 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
420                                   XT_SYNPROXY_OPT_WSCALE |
421                                   XT_SYNPROXY_OPT_SACK_PERM);
422 
423                 swap(opts.tsval, opts.tsecr);
424                 synproxy_send_server_ack(net, state, skb, th, &opts);
425 
426                 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
427 
428                 swap(opts.tsval, opts.tsecr);
429                 synproxy_send_client_ack(net, skb, th, &opts);
430 
431                 consume_skb(skb);
432                 return NF_STOLEN;
433         default:
434                 break;
435         }
436 
437         synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
438         return NF_ACCEPT;
439 }
440 
441 static const struct nf_hook_ops ipv6_synproxy_ops[] = {
442         {
443                 .hook           = ipv6_synproxy_hook,
444                 .pf             = NFPROTO_IPV6,
445                 .hooknum        = NF_INET_LOCAL_IN,
446                 .priority       = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
447         },
448         {
449                 .hook           = ipv6_synproxy_hook,
450                 .pf             = NFPROTO_IPV6,
451                 .hooknum        = NF_INET_POST_ROUTING,
452                 .priority       = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
453         },
454 };
455 
456 static int synproxy_tg6_check(const struct xt_tgchk_param *par)
457 {
458         struct synproxy_net *snet = synproxy_pernet(par->net);
459         const struct ip6t_entry *e = par->entryinfo;
460         int err;
461 
462         if (!(e->ipv6.flags & IP6T_F_PROTO) ||
463             e->ipv6.proto != IPPROTO_TCP ||
464             e->ipv6.invflags & XT_INV_PROTO)
465                 return -EINVAL;
466 
467         err = nf_ct_netns_get(par->net, par->family);
468         if (err)
469                 return err;
470 
471         if (snet->hook_ref6 == 0) {
472                 err = nf_register_net_hooks(par->net, ipv6_synproxy_ops,
473                                             ARRAY_SIZE(ipv6_synproxy_ops));
474                 if (err) {
475                         nf_ct_netns_put(par->net, par->family);
476                         return err;
477                 }
478         }
479 
480         snet->hook_ref6++;
481         return err;
482 }
483 
484 static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
485 {
486         struct synproxy_net *snet = synproxy_pernet(par->net);
487 
488         snet->hook_ref6--;
489         if (snet->hook_ref6 == 0)
490                 nf_unregister_net_hooks(par->net, ipv6_synproxy_ops,
491                                         ARRAY_SIZE(ipv6_synproxy_ops));
492         nf_ct_netns_put(par->net, par->family);
493 }
494 
495 static struct xt_target synproxy_tg6_reg __read_mostly = {
496         .name           = "SYNPROXY",
497         .family         = NFPROTO_IPV6,
498         .hooks          = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
499         .target         = synproxy_tg6,
500         .targetsize     = sizeof(struct xt_synproxy_info),
501         .checkentry     = synproxy_tg6_check,
502         .destroy        = synproxy_tg6_destroy,
503         .me             = THIS_MODULE,
504 };
505 
506 static int __init synproxy_tg6_init(void)
507 {
508         return xt_register_target(&synproxy_tg6_reg);
509 }
510 
511 static void __exit synproxy_tg6_exit(void)
512 {
513         xt_unregister_target(&synproxy_tg6_reg);
514 }
515 
516 module_init(synproxy_tg6_init);
517 module_exit(synproxy_tg6_exit);
518 
519 MODULE_LICENSE("GPL");
520 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
521 

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