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TOMOYO Linux Cross Reference
Linux/net/ipv4/netfilter/ipt_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/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 *
 21 synproxy_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 
 42 static void
 43 synproxy_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 
 68 free_nskb:
 69         kfree_skb(nskb);
 70 }
 71 
 72 static void
 73 synproxy_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 
114 static void
115 synproxy_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         /* 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 
155         synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
156                           niph, nth, tcp_hdr_size);
157 }
158 
159 static void
160 synproxy_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 
198 static void
199 synproxy_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 
237 static bool
238 synproxy_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 
262 static unsigned int
263 synproxy_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 = xt_net(par);
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, xt_hooknum(par), 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                 /* Initial SYN from client */
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                 /* ACK from client */
301                 synproxy_recv_client_ack(net, skb, th, &opts, ntohl(th->seq));
302                 return NF_DROP;
303         }
304 
305         return XT_CONTINUE;
306 }
307 
308 static 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                 /* Reopened connection - reset the sequence number and timestamp
352                  * adjustments, they will get initialized once the connection is
353                  * reestablished.
354                  */
355                 nf_ct_seqadj_init(ct, ctinfo, 0);
356                 synproxy->tsoff = 0;
357                 this_cpu_inc(snet->stats->conn_reopened);
358 
359                 /* fall through */
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                         /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
367                          * therefore we need to add 1 to make the SYN sequence
368                          * number match the one of first SYN.
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 
413 static 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_netns_get(par->net, par->family);
422 }
423 
424 static void synproxy_tg4_destroy(const struct xt_tgdtor_param *par)
425 {
426         nf_ct_netns_put(par->net, par->family);
427 }
428 
429 static 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 
440 static 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 
455 static 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 
470 err2:
471         nf_unregister_hooks(ipv4_synproxy_ops, ARRAY_SIZE(ipv4_synproxy_ops));
472 err1:
473         return err;
474 }
475 
476 static 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 
482 module_init(synproxy_tg4_init);
483 module_exit(synproxy_tg4_exit);
484 
485 MODULE_LICENSE("GPL");
486 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
487 

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