2 * Copyright (c) 2013 Patrick McHardy <kaber@trash.net>
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.
9 #include <linux/module.h>
10 #include <linux/skbuff.h>
11 #include <net/ip6_checksum.h>
12 #include <net/ip6_route.h>
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>
22 static struct ipv6hdr *
23 synproxy_build_ip(struct sk_buff *skb, const struct in6_addr *saddr,
24 const struct in6_addr *daddr)
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;
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)
45 struct net *net = nf_ct_net((struct nf_conn *)nfct);
46 struct dst_entry *dst;
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);
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) {
66 dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
70 skb_dst_set(nskb, dst);
74 nskb->nfctinfo = ctinfo;
75 nf_conntrack_get(nfct);
86 synproxy_send_client_synack(const struct sk_buff *skb, const struct tcphdr *th,
87 const struct synproxy_options *opts)
90 struct ipv6hdr *iph, *niph;
92 unsigned int tcp_hdr_size;
97 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
98 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
102 skb_reserve(nskb, MAX_TCP_HEADER);
104 niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);
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;
120 synproxy_build_options(nth, opts);
122 synproxy_send_tcp(skb, nskb, skb->nfct, IP_CT_ESTABLISHED_REPLY,
123 niph, nth, tcp_hdr_size);
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)
131 struct sk_buff *nskb;
132 struct ipv6hdr *iph, *niph;
134 unsigned int tcp_hdr_size;
138 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
139 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
143 skb_reserve(nskb, MAX_TCP_HEADER);
145 niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);
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.
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;
164 synproxy_build_options(nth, opts);
166 synproxy_send_tcp(skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW,
167 niph, nth, tcp_hdr_size);
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)
176 struct sk_buff *nskb;
177 struct ipv6hdr *iph, *niph;
179 unsigned int tcp_hdr_size;
183 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
184 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
188 skb_reserve(nskb, MAX_TCP_HEADER);
190 niph = synproxy_build_ip(nskb, &iph->daddr, &iph->saddr);
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);
204 synproxy_build_options(nth, opts);
206 synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
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)
214 struct sk_buff *nskb;
215 struct ipv6hdr *iph, *niph;
217 unsigned int tcp_hdr_size;
221 tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts);
222 nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER,
226 skb_reserve(nskb, MAX_TCP_HEADER);
228 niph = synproxy_build_ip(nskb, &iph->saddr, &iph->daddr);
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);
242 synproxy_build_options(nth, opts);
244 synproxy_send_tcp(skb, nskb, NULL, 0, niph, nth, tcp_hdr_size);
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)
254 mss = __cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1);
256 this_cpu_inc(snet->stats->cookie_invalid);
260 this_cpu_inc(snet->stats->cookie_valid);
262 opts->options |= XT_SYNPROXY_OPT_MSS;
264 if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
265 synproxy_check_timestamp_cookie(opts);
267 synproxy_send_server_syn(snet, skb, th, opts, recv_seq);
272 synproxy_tg6(struct sk_buff *skb, const struct xt_action_param *par)
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;
279 if (nf_ip6_checksum(skb, par->hooknum, par->thoff, IPPROTO_TCP))
282 th = skb_header_pointer(skb, par->thoff, sizeof(_th), &_th);
286 if (!synproxy_parse_options(skb, par->thoff, th, &opts))
289 if (th->syn && !(th->ack || th->fin || th->rst)) {
290 /* Initial SYN from client */
291 this_cpu_inc(snet->stats->syn_received);
293 if (th->ece && th->cwr)
294 opts.options |= XT_SYNPROXY_OPT_ECN;
296 opts.options &= info->options;
297 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
298 synproxy_init_timestamp_cookie(info, &opts);
300 opts.options &= ~(XT_SYNPROXY_OPT_WSCALE |
301 XT_SYNPROXY_OPT_SACK_PERM |
302 XT_SYNPROXY_OPT_ECN);
304 synproxy_send_client_synack(skb, th, &opts);
307 } else if (th->ack && !(th->fin || th->rst || th->syn)) {
308 /* ACK from client */
309 synproxy_recv_client_ack(snet, skb, th, &opts, ntohl(th->seq));
316 static unsigned int ipv6_synproxy_hook(const struct nf_hook_ops *ops,
318 const struct nf_hook_state *nhs)
320 struct synproxy_net *snet = synproxy_pernet(dev_net(nhs->in ? : nhs->out));
321 enum ip_conntrack_info ctinfo;
323 struct nf_conn_synproxy *synproxy;
324 struct synproxy_options opts = {};
325 const struct ip_ct_tcp *state;
326 struct tcphdr *th, _th;
331 ct = nf_ct_get(skb, &ctinfo);
335 synproxy = nfct_synproxy(ct);
336 if (synproxy == NULL)
339 if (nf_is_loopback_packet(skb))
342 nexthdr = ipv6_hdr(skb)->nexthdr;
343 thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
348 th = skb_header_pointer(skb, thoff, sizeof(_th), &_th);
352 state = &ct->proto.tcp;
353 switch (state->state) {
354 case TCP_CONNTRACK_CLOSE:
355 if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) {
356 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn -
361 if (!th->syn || th->ack ||
362 CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
365 /* Reopened connection - reset the sequence number and timestamp
366 * adjustments, they will get initialized once the connection is
369 nf_ct_seqadj_init(ct, ctinfo, 0);
371 this_cpu_inc(snet->stats->conn_reopened);
374 case TCP_CONNTRACK_SYN_SENT:
375 if (!synproxy_parse_options(skb, thoff, th, &opts))
378 if (!th->syn && th->ack &&
379 CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
380 /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1,
381 * therefore we need to add 1 to make the SYN sequence
382 * number match the one of first SYN.
384 if (synproxy_recv_client_ack(snet, skb, th, &opts,
386 this_cpu_inc(snet->stats->cookie_retrans);
391 synproxy->isn = ntohl(th->ack_seq);
392 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
393 synproxy->its = opts.tsecr;
395 case TCP_CONNTRACK_SYN_RECV:
396 if (!th->syn || !th->ack)
399 if (!synproxy_parse_options(skb, thoff, th, &opts))
402 if (opts.options & XT_SYNPROXY_OPT_TIMESTAMP)
403 synproxy->tsoff = opts.tsval - synproxy->its;
405 opts.options &= ~(XT_SYNPROXY_OPT_MSS |
406 XT_SYNPROXY_OPT_WSCALE |
407 XT_SYNPROXY_OPT_SACK_PERM);
409 swap(opts.tsval, opts.tsecr);
410 synproxy_send_server_ack(snet, state, skb, th, &opts);
412 nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq));
414 swap(opts.tsval, opts.tsecr);
415 synproxy_send_client_ack(snet, skb, th, &opts);
423 synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy);
427 static int synproxy_tg6_check(const struct xt_tgchk_param *par)
429 const struct ip6t_entry *e = par->entryinfo;
431 if (!(e->ipv6.flags & IP6T_F_PROTO) ||
432 e->ipv6.proto != IPPROTO_TCP ||
433 e->ipv6.invflags & XT_INV_PROTO)
436 return nf_ct_l3proto_try_module_get(par->family);
439 static void synproxy_tg6_destroy(const struct xt_tgdtor_param *par)
441 nf_ct_l3proto_module_put(par->family);
444 static struct xt_target synproxy_tg6_reg __read_mostly = {
446 .family = NFPROTO_IPV6,
447 .hooks = (1 << NF_INET_LOCAL_IN) | (1 << NF_INET_FORWARD),
448 .target = synproxy_tg6,
449 .targetsize = sizeof(struct xt_synproxy_info),
450 .checkentry = synproxy_tg6_check,
451 .destroy = synproxy_tg6_destroy,
455 static struct nf_hook_ops ipv6_synproxy_ops[] __read_mostly = {
457 .hook = ipv6_synproxy_hook,
458 .owner = THIS_MODULE,
460 .hooknum = NF_INET_LOCAL_IN,
461 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
464 .hook = ipv6_synproxy_hook,
465 .owner = THIS_MODULE,
467 .hooknum = NF_INET_POST_ROUTING,
468 .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1,
472 static int __init synproxy_tg6_init(void)
476 err = nf_register_hooks(ipv6_synproxy_ops,
477 ARRAY_SIZE(ipv6_synproxy_ops));
481 err = xt_register_target(&synproxy_tg6_reg);
488 nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
493 static void __exit synproxy_tg6_exit(void)
495 xt_unregister_target(&synproxy_tg6_reg);
496 nf_unregister_hooks(ipv6_synproxy_ops, ARRAY_SIZE(ipv6_synproxy_ops));
499 module_init(synproxy_tg6_init);
500 module_exit(synproxy_tg6_exit);
502 MODULE_LICENSE("GPL");
503 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");