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 <asm/unaligned.h>
12 #include <net/tcp.h>
13 #include <net/netns/generic.h>
14 #include <linux/proc_fs.h>
15 
16 #include <linux/netfilter_ipv4/ip_tables.h>
17 #include <linux/netfilter/x_tables.h>
18 #include <linux/netfilter/xt_tcpudp.h>
19 #include <linux/netfilter/xt_SYNPROXY.h>
20 
21 #include <net/netfilter/nf_conntrack.h>
22 #include <net/netfilter/nf_conntrack_extend.h>
23 #include <net/netfilter/nf_conntrack_seqadj.h>
24 #include <net/netfilter/nf_conntrack_synproxy.h>
25 #include <net/netfilter/nf_conntrack_zones.h>
26 
27 unsigned int synproxy_net_id;
28 EXPORT_SYMBOL_GPL(synproxy_net_id);
29 
30 bool
31 synproxy_parse_options(const struct sk_buff *skb, unsigned int doff,
32 		       const struct tcphdr *th, struct synproxy_options *opts)
33 {
34 	int length = (th->doff * 4) - sizeof(*th);
35 	u8 buf[40], *ptr;
36 
37 	ptr = skb_header_pointer(skb, doff + sizeof(*th), length, 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 			opsize = *ptr++;
54 			if (opsize < 2)
55 				return true;
56 			if (opsize > length)
57 				return true;
58 
59 			switch (opcode) {
60 			case TCPOPT_MSS:
61 				if (opsize == TCPOLEN_MSS) {
62 					opts->mss = get_unaligned_be16(ptr);
63 					opts->options |= XT_SYNPROXY_OPT_MSS;
64 				}
65 				break;
66 			case TCPOPT_WINDOW:
67 				if (opsize == TCPOLEN_WINDOW) {
68 					opts->wscale = *ptr;
69 					if (opts->wscale > TCP_MAX_WSCALE)
70 						opts->wscale = TCP_MAX_WSCALE;
71 					opts->options |= XT_SYNPROXY_OPT_WSCALE;
72 				}
73 				break;
74 			case TCPOPT_TIMESTAMP:
75 				if (opsize == TCPOLEN_TIMESTAMP) {
76 					opts->tsval = get_unaligned_be32(ptr);
77 					opts->tsecr = get_unaligned_be32(ptr + 4);
78 					opts->options |= XT_SYNPROXY_OPT_TIMESTAMP;
79 				}
80 				break;
81 			case TCPOPT_SACK_PERM:
82 				if (opsize == TCPOLEN_SACK_PERM)
83 					opts->options |= XT_SYNPROXY_OPT_SACK_PERM;
84 				break;
85 			}
86 
87 			ptr += opsize - 2;
88 			length -= opsize;
89 		}
90 	}
91 	return true;
92 }
93 EXPORT_SYMBOL_GPL(synproxy_parse_options);
94 
95 unsigned int synproxy_options_size(const struct synproxy_options *opts)
96 {
97 	unsigned int size = 0;
98 
99 	if (opts->options & XT_SYNPROXY_OPT_MSS)
100 		size += TCPOLEN_MSS_ALIGNED;
101 	if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
102 		size += TCPOLEN_TSTAMP_ALIGNED;
103 	else if (opts->options & XT_SYNPROXY_OPT_SACK_PERM)
104 		size += TCPOLEN_SACKPERM_ALIGNED;
105 	if (opts->options & XT_SYNPROXY_OPT_WSCALE)
106 		size += TCPOLEN_WSCALE_ALIGNED;
107 
108 	return size;
109 }
110 EXPORT_SYMBOL_GPL(synproxy_options_size);
111 
112 void
113 synproxy_build_options(struct tcphdr *th, const struct synproxy_options *opts)
114 {
115 	__be32 *ptr = (__be32 *)(th + 1);
116 	u8 options = opts->options;
117 
118 	if (options & XT_SYNPROXY_OPT_MSS)
119 		*ptr++ = htonl((TCPOPT_MSS << 24) |
120 			       (TCPOLEN_MSS << 16) |
121 			       opts->mss);
122 
123 	if (options & XT_SYNPROXY_OPT_TIMESTAMP) {
124 		if (options & XT_SYNPROXY_OPT_SACK_PERM)
125 			*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
126 				       (TCPOLEN_SACK_PERM << 16) |
127 				       (TCPOPT_TIMESTAMP << 8) |
128 				       TCPOLEN_TIMESTAMP);
129 		else
130 			*ptr++ = htonl((TCPOPT_NOP << 24) |
131 				       (TCPOPT_NOP << 16) |
132 				       (TCPOPT_TIMESTAMP << 8) |
133 				       TCPOLEN_TIMESTAMP);
134 
135 		*ptr++ = htonl(opts->tsval);
136 		*ptr++ = htonl(opts->tsecr);
137 	} else if (options & XT_SYNPROXY_OPT_SACK_PERM)
138 		*ptr++ = htonl((TCPOPT_NOP << 24) |
139 			       (TCPOPT_NOP << 16) |
140 			       (TCPOPT_SACK_PERM << 8) |
141 			       TCPOLEN_SACK_PERM);
142 
143 	if (options & XT_SYNPROXY_OPT_WSCALE)
144 		*ptr++ = htonl((TCPOPT_NOP << 24) |
145 			       (TCPOPT_WINDOW << 16) |
146 			       (TCPOLEN_WINDOW << 8) |
147 			       opts->wscale);
148 }
149 EXPORT_SYMBOL_GPL(synproxy_build_options);
150 
151 void synproxy_init_timestamp_cookie(const struct xt_synproxy_info *info,
152 				    struct synproxy_options *opts)
153 {
154 	opts->tsecr = opts->tsval;
155 	opts->tsval = tcp_time_stamp_raw() & ~0x3f;
156 
157 	if (opts->options & XT_SYNPROXY_OPT_WSCALE) {
158 		opts->tsval |= opts->wscale;
159 		opts->wscale = info->wscale;
160 	} else
161 		opts->tsval |= 0xf;
162 
163 	if (opts->options & XT_SYNPROXY_OPT_SACK_PERM)
164 		opts->tsval |= 1 << 4;
165 
166 	if (opts->options & XT_SYNPROXY_OPT_ECN)
167 		opts->tsval |= 1 << 5;
168 }
169 EXPORT_SYMBOL_GPL(synproxy_init_timestamp_cookie);
170 
171 void synproxy_check_timestamp_cookie(struct synproxy_options *opts)
172 {
173 	opts->wscale = opts->tsecr & 0xf;
174 	if (opts->wscale != 0xf)
175 		opts->options |= XT_SYNPROXY_OPT_WSCALE;
176 
177 	opts->options |= opts->tsecr & (1 << 4) ? XT_SYNPROXY_OPT_SACK_PERM : 0;
178 
179 	opts->options |= opts->tsecr & (1 << 5) ? XT_SYNPROXY_OPT_ECN : 0;
180 }
181 EXPORT_SYMBOL_GPL(synproxy_check_timestamp_cookie);
182 
183 unsigned int synproxy_tstamp_adjust(struct sk_buff *skb,
184 				    unsigned int protoff,
185 				    struct tcphdr *th,
186 				    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_make_writable(skb, 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(&th->check, skb,
230 							 old, *ptr, false);
231 				return 1;
232 			}
233 			optoff += op[1];
234 		}
235 	}
236 	return 1;
237 }
238 EXPORT_SYMBOL_GPL(synproxy_tstamp_adjust);
239 
240 static struct nf_ct_ext_type nf_ct_synproxy_extend __read_mostly = {
241 	.len		= sizeof(struct nf_conn_synproxy),
242 	.align		= __alignof__(struct nf_conn_synproxy),
243 	.id		= NF_CT_EXT_SYNPROXY,
244 };
245 
246 #ifdef CONFIG_PROC_FS
247 static void *synproxy_cpu_seq_start(struct seq_file *seq, loff_t *pos)
248 {
249 	struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
250 	int cpu;
251 
252 	if (*pos == 0)
253 		return SEQ_START_TOKEN;
254 
255 	for (cpu = *pos - 1; cpu < nr_cpu_ids; cpu++) {
256 		if (!cpu_possible(cpu))
257 			continue;
258 		*pos = cpu + 1;
259 		return per_cpu_ptr(snet->stats, cpu);
260 	}
261 
262 	return NULL;
263 }
264 
265 static void *synproxy_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos)
266 {
267 	struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq));
268 	int cpu;
269 
270 	for (cpu = *pos; cpu < nr_cpu_ids; cpu++) {
271 		if (!cpu_possible(cpu))
272 			continue;
273 		*pos = cpu + 1;
274 		return per_cpu_ptr(snet->stats, cpu);
275 	}
276 
277 	return NULL;
278 }
279 
280 static void synproxy_cpu_seq_stop(struct seq_file *seq, void *v)
281 {
282 	return;
283 }
284 
285 static int synproxy_cpu_seq_show(struct seq_file *seq, void *v)
286 {
287 	struct synproxy_stats *stats = v;
288 
289 	if (v == SEQ_START_TOKEN) {
290 		seq_puts(seq, "entries\t\tsyn_received\t"
291 			      "cookie_invalid\tcookie_valid\t"
292 			      "cookie_retrans\tconn_reopened\n");
293 		return 0;
294 	}
295 
296 	seq_printf(seq, "%08x\t%08x\t%08x\t%08x\t%08x\t%08x\n", 0,
297 		   stats->syn_received,
298 		   stats->cookie_invalid,
299 		   stats->cookie_valid,
300 		   stats->cookie_retrans,
301 		   stats->conn_reopened);
302 
303 	return 0;
304 }
305 
306 static const struct seq_operations synproxy_cpu_seq_ops = {
307 	.start		= synproxy_cpu_seq_start,
308 	.next		= synproxy_cpu_seq_next,
309 	.stop		= synproxy_cpu_seq_stop,
310 	.show		= synproxy_cpu_seq_show,
311 };
312 
313 static int synproxy_cpu_seq_open(struct inode *inode, struct file *file)
314 {
315 	return seq_open_net(inode, file, &synproxy_cpu_seq_ops,
316 			    sizeof(struct seq_net_private));
317 }
318 
319 static const struct file_operations synproxy_cpu_seq_fops = {
320 	.open		= synproxy_cpu_seq_open,
321 	.read		= seq_read,
322 	.llseek		= seq_lseek,
323 	.release	= seq_release_net,
324 };
325 
326 static int __net_init synproxy_proc_init(struct net *net)
327 {
328 	if (!proc_create("synproxy", S_IRUGO, net->proc_net_stat,
329 			 &synproxy_cpu_seq_fops))
330 		return -ENOMEM;
331 	return 0;
332 }
333 
334 static void __net_exit synproxy_proc_exit(struct net *net)
335 {
336 	remove_proc_entry("synproxy", net->proc_net_stat);
337 }
338 #else
339 static int __net_init synproxy_proc_init(struct net *net)
340 {
341 	return 0;
342 }
343 
344 static void __net_exit synproxy_proc_exit(struct net *net)
345 {
346 	return;
347 }
348 #endif /* CONFIG_PROC_FS */
349 
350 static int __net_init synproxy_net_init(struct net *net)
351 {
352 	struct synproxy_net *snet = synproxy_pernet(net);
353 	struct nf_conn *ct;
354 	int err = -ENOMEM;
355 
356 	ct = nf_ct_tmpl_alloc(net, &nf_ct_zone_dflt, GFP_KERNEL);
357 	if (!ct)
358 		goto err1;
359 
360 	if (!nfct_seqadj_ext_add(ct))
361 		goto err2;
362 	if (!nfct_synproxy_ext_add(ct))
363 		goto err2;
364 
365 	__set_bit(IPS_CONFIRMED_BIT, &ct->status);
366 	nf_conntrack_get(&ct->ct_general);
367 	snet->tmpl = ct;
368 
369 	snet->stats = alloc_percpu(struct synproxy_stats);
370 	if (snet->stats == NULL)
371 		goto err2;
372 
373 	err = synproxy_proc_init(net);
374 	if (err < 0)
375 		goto err3;
376 
377 	return 0;
378 
379 err3:
380 	free_percpu(snet->stats);
381 err2:
382 	nf_ct_tmpl_free(ct);
383 err1:
384 	return err;
385 }
386 
387 static void __net_exit synproxy_net_exit(struct net *net)
388 {
389 	struct synproxy_net *snet = synproxy_pernet(net);
390 
391 	nf_ct_put(snet->tmpl);
392 	synproxy_proc_exit(net);
393 	free_percpu(snet->stats);
394 }
395 
396 static struct pernet_operations synproxy_net_ops = {
397 	.init		= synproxy_net_init,
398 	.exit		= synproxy_net_exit,
399 	.id		= &synproxy_net_id,
400 	.size		= sizeof(struct synproxy_net),
401 };
402 
403 static int __init synproxy_core_init(void)
404 {
405 	int err;
406 
407 	err = nf_ct_extend_register(&nf_ct_synproxy_extend);
408 	if (err < 0)
409 		goto err1;
410 
411 	err = register_pernet_subsys(&synproxy_net_ops);
412 	if (err < 0)
413 		goto err2;
414 
415 	return 0;
416 
417 err2:
418 	nf_ct_extend_unregister(&nf_ct_synproxy_extend);
419 err1:
420 	return err;
421 }
422 
423 static void __exit synproxy_core_exit(void)
424 {
425 	unregister_pernet_subsys(&synproxy_net_ops);
426 	nf_ct_extend_unregister(&nf_ct_synproxy_extend);
427 }
428 
429 module_init(synproxy_core_init);
430 module_exit(synproxy_core_exit);
431 
432 MODULE_LICENSE("GPL");
433 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
434