1 /*
2  * ip_conntrack_proto_gre.c - Version 3.0
3  *
4  * Connection tracking protocol helper module for GRE.
5  *
6  * GRE is a generic encapsulation protocol, which is generally not very
7  * suited for NAT, as it has no protocol-specific part as port numbers.
8  *
9  * It has an optional key field, which may help us distinguishing two
10  * connections between the same two hosts.
11  *
12  * GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
13  *
14  * PPTP is built on top of a modified version of GRE, and has a mandatory
15  * field called "CallID", which serves us for the same purpose as the key
16  * field in plain GRE.
17  *
18  * Documentation about PPTP can be found in RFC 2637
19  *
20  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
21  *
22  * Development of this code funded by Astaro AG (http://www.astaro.com/)
23  *
24  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
25  */
26 
27 #include <linux/module.h>
28 #include <linux/types.h>
29 #include <linux/timer.h>
30 #include <linux/list.h>
31 #include <linux/seq_file.h>
32 #include <linux/in.h>
33 #include <linux/netdevice.h>
34 #include <linux/skbuff.h>
35 #include <linux/slab.h>
36 #include <net/dst.h>
37 #include <net/net_namespace.h>
38 #include <net/netns/generic.h>
39 #include <net/netfilter/nf_conntrack_l4proto.h>
40 #include <net/netfilter/nf_conntrack_helper.h>
41 #include <net/netfilter/nf_conntrack_core.h>
42 #include <net/netfilter/nf_conntrack_timeout.h>
43 #include <linux/netfilter/nf_conntrack_proto_gre.h>
44 #include <linux/netfilter/nf_conntrack_pptp.h>
45 
46 enum grep_conntrack {
47 	GRE_CT_UNREPLIED,
48 	GRE_CT_REPLIED,
49 	GRE_CT_MAX
50 };
51 
52 static const unsigned int gre_timeouts[GRE_CT_MAX] = {
53 	[GRE_CT_UNREPLIED]	= 30*HZ,
54 	[GRE_CT_REPLIED]	= 180*HZ,
55 };
56 
57 static unsigned int proto_gre_net_id __read_mostly;
58 struct netns_proto_gre {
59 	struct nf_proto_net	nf;
60 	rwlock_t		keymap_lock;
61 	struct list_head	keymap_list;
62 	unsigned int		gre_timeouts[GRE_CT_MAX];
63 };
64 
65 static inline struct netns_proto_gre *gre_pernet(struct net *net)
66 {
67 	return net_generic(net, proto_gre_net_id);
68 }
69 
70 static void nf_ct_gre_keymap_flush(struct net *net)
71 {
72 	struct netns_proto_gre *net_gre = gre_pernet(net);
73 	struct nf_ct_gre_keymap *km, *tmp;
74 
75 	write_lock_bh(&net_gre->keymap_lock);
76 	list_for_each_entry_safe(km, tmp, &net_gre->keymap_list, list) {
77 		list_del(&km->list);
78 		kfree(km);
79 	}
80 	write_unlock_bh(&net_gre->keymap_lock);
81 }
82 
83 static inline int gre_key_cmpfn(const struct nf_ct_gre_keymap *km,
84 				const struct nf_conntrack_tuple *t)
85 {
86 	return km->tuple.src.l3num == t->src.l3num &&
87 	       !memcmp(&km->tuple.src.u3, &t->src.u3, sizeof(t->src.u3)) &&
88 	       !memcmp(&km->tuple.dst.u3, &t->dst.u3, sizeof(t->dst.u3)) &&
89 	       km->tuple.dst.protonum == t->dst.protonum &&
90 	       km->tuple.dst.u.all == t->dst.u.all;
91 }
92 
93 /* look up the source key for a given tuple */
94 static __be16 gre_keymap_lookup(struct net *net, struct nf_conntrack_tuple *t)
95 {
96 	struct netns_proto_gre *net_gre = gre_pernet(net);
97 	struct nf_ct_gre_keymap *km;
98 	__be16 key = 0;
99 
100 	read_lock_bh(&net_gre->keymap_lock);
101 	list_for_each_entry(km, &net_gre->keymap_list, list) {
102 		if (gre_key_cmpfn(km, t)) {
103 			key = km->tuple.src.u.gre.key;
104 			break;
105 		}
106 	}
107 	read_unlock_bh(&net_gre->keymap_lock);
108 
109 	pr_debug("lookup src key 0x%x for ", key);
110 	nf_ct_dump_tuple(t);
111 
112 	return key;
113 }
114 
115 /* add a single keymap entry, associate with specified master ct */
116 int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir,
117 			 struct nf_conntrack_tuple *t)
118 {
119 	struct net *net = nf_ct_net(ct);
120 	struct netns_proto_gre *net_gre = gre_pernet(net);
121 	struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
122 	struct nf_ct_gre_keymap **kmp, *km;
123 
124 	kmp = &ct_pptp_info->keymap[dir];
125 	if (*kmp) {
126 		/* check whether it's a retransmission */
127 		read_lock_bh(&net_gre->keymap_lock);
128 		list_for_each_entry(km, &net_gre->keymap_list, list) {
129 			if (gre_key_cmpfn(km, t) && km == *kmp) {
130 				read_unlock_bh(&net_gre->keymap_lock);
131 				return 0;
132 			}
133 		}
134 		read_unlock_bh(&net_gre->keymap_lock);
135 		pr_debug("trying to override keymap_%s for ct %p\n",
136 			 dir == IP_CT_DIR_REPLY ? "reply" : "orig", ct);
137 		return -EEXIST;
138 	}
139 
140 	km = kmalloc(sizeof(*km), GFP_ATOMIC);
141 	if (!km)
142 		return -ENOMEM;
143 	memcpy(&km->tuple, t, sizeof(*t));
144 	*kmp = km;
145 
146 	pr_debug("adding new entry %p: ", km);
147 	nf_ct_dump_tuple(&km->tuple);
148 
149 	write_lock_bh(&net_gre->keymap_lock);
150 	list_add_tail(&km->list, &net_gre->keymap_list);
151 	write_unlock_bh(&net_gre->keymap_lock);
152 
153 	return 0;
154 }
155 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_add);
156 
157 /* destroy the keymap entries associated with specified master ct */
158 void nf_ct_gre_keymap_destroy(struct nf_conn *ct)
159 {
160 	struct net *net = nf_ct_net(ct);
161 	struct netns_proto_gre *net_gre = gre_pernet(net);
162 	struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
163 	enum ip_conntrack_dir dir;
164 
165 	pr_debug("entering for ct %p\n", ct);
166 
167 	write_lock_bh(&net_gre->keymap_lock);
168 	for (dir = IP_CT_DIR_ORIGINAL; dir < IP_CT_DIR_MAX; dir++) {
169 		if (ct_pptp_info->keymap[dir]) {
170 			pr_debug("removing %p from list\n",
171 				 ct_pptp_info->keymap[dir]);
172 			list_del(&ct_pptp_info->keymap[dir]->list);
173 			kfree(ct_pptp_info->keymap[dir]);
174 			ct_pptp_info->keymap[dir] = NULL;
175 		}
176 	}
177 	write_unlock_bh(&net_gre->keymap_lock);
178 }
179 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_destroy);
180 
181 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
182 
183 /* gre hdr info to tuple */
184 static bool gre_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
185 			     struct net *net, struct nf_conntrack_tuple *tuple)
186 {
187 	const struct pptp_gre_header *pgrehdr;
188 	struct pptp_gre_header _pgrehdr;
189 	__be16 srckey;
190 	const struct gre_base_hdr *grehdr;
191 	struct gre_base_hdr _grehdr;
192 
193 	/* first only delinearize old RFC1701 GRE header */
194 	grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
195 	if (!grehdr || (grehdr->flags & GRE_VERSION) != GRE_VERSION_1) {
196 		/* try to behave like "nf_conntrack_proto_generic" */
197 		tuple->src.u.all = 0;
198 		tuple->dst.u.all = 0;
199 		return true;
200 	}
201 
202 	/* PPTP header is variable length, only need up to the call_id field */
203 	pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
204 	if (!pgrehdr)
205 		return true;
206 
207 	if (grehdr->protocol != GRE_PROTO_PPP) {
208 		pr_debug("Unsupported GRE proto(0x%x)\n", ntohs(grehdr->protocol));
209 		return false;
210 	}
211 
212 	tuple->dst.u.gre.key = pgrehdr->call_id;
213 	srckey = gre_keymap_lookup(net, tuple);
214 	tuple->src.u.gre.key = srckey;
215 
216 	return true;
217 }
218 
219 #ifdef CONFIG_NF_CONNTRACK_PROCFS
220 /* print private data for conntrack */
221 static void gre_print_conntrack(struct seq_file *s, struct nf_conn *ct)
222 {
223 	seq_printf(s, "timeout=%u, stream_timeout=%u ",
224 		   (ct->proto.gre.timeout / HZ),
225 		   (ct->proto.gre.stream_timeout / HZ));
226 }
227 #endif
228 
229 static unsigned int *gre_get_timeouts(struct net *net)
230 {
231 	return gre_pernet(net)->gre_timeouts;
232 }
233 
234 /* Returns verdict for packet, and may modify conntrack */
235 static int gre_packet(struct nf_conn *ct,
236 		      const struct sk_buff *skb,
237 		      unsigned int dataoff,
238 		      enum ip_conntrack_info ctinfo,
239 		      const struct nf_hook_state *state)
240 {
241 	if (!nf_ct_is_confirmed(ct)) {
242 		unsigned int *timeouts = nf_ct_timeout_lookup(ct);
243 
244 		if (!timeouts)
245 			timeouts = gre_get_timeouts(nf_ct_net(ct));
246 
247 		/* initialize to sane value.  Ideally a conntrack helper
248 		 * (e.g. in case of pptp) is increasing them */
249 		ct->proto.gre.stream_timeout = timeouts[GRE_CT_REPLIED];
250 		ct->proto.gre.timeout = timeouts[GRE_CT_UNREPLIED];
251 	}
252 
253 	/* If we've seen traffic both ways, this is a GRE connection.
254 	 * Extend timeout. */
255 	if (ct->status & IPS_SEEN_REPLY) {
256 		nf_ct_refresh_acct(ct, ctinfo, skb,
257 				   ct->proto.gre.stream_timeout);
258 		/* Also, more likely to be important, and not a probe. */
259 		if (!test_and_set_bit(IPS_ASSURED_BIT, &ct->status))
260 			nf_conntrack_event_cache(IPCT_ASSURED, ct);
261 	} else
262 		nf_ct_refresh_acct(ct, ctinfo, skb,
263 				   ct->proto.gre.timeout);
264 
265 	return NF_ACCEPT;
266 }
267 
268 /* Called when a conntrack entry has already been removed from the hashes
269  * and is about to be deleted from memory */
270 static void gre_destroy(struct nf_conn *ct)
271 {
272 	struct nf_conn *master = ct->master;
273 	pr_debug(" entering\n");
274 
275 	if (!master)
276 		pr_debug("no master !?!\n");
277 	else
278 		nf_ct_gre_keymap_destroy(master);
279 }
280 
281 #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
282 
283 #include <linux/netfilter/nfnetlink.h>
284 #include <linux/netfilter/nfnetlink_cttimeout.h>
285 
286 static int gre_timeout_nlattr_to_obj(struct nlattr *tb[],
287 				     struct net *net, void *data)
288 {
289 	unsigned int *timeouts = data;
290 	struct netns_proto_gre *net_gre = gre_pernet(net);
291 
292 	if (!timeouts)
293 		timeouts = gre_get_timeouts(net);
294 	/* set default timeouts for GRE. */
295 	timeouts[GRE_CT_UNREPLIED] = net_gre->gre_timeouts[GRE_CT_UNREPLIED];
296 	timeouts[GRE_CT_REPLIED] = net_gre->gre_timeouts[GRE_CT_REPLIED];
297 
298 	if (tb[CTA_TIMEOUT_GRE_UNREPLIED]) {
299 		timeouts[GRE_CT_UNREPLIED] =
300 			ntohl(nla_get_be32(tb[CTA_TIMEOUT_GRE_UNREPLIED])) * HZ;
301 	}
302 	if (tb[CTA_TIMEOUT_GRE_REPLIED]) {
303 		timeouts[GRE_CT_REPLIED] =
304 			ntohl(nla_get_be32(tb[CTA_TIMEOUT_GRE_REPLIED])) * HZ;
305 	}
306 	return 0;
307 }
308 
309 static int
310 gre_timeout_obj_to_nlattr(struct sk_buff *skb, const void *data)
311 {
312 	const unsigned int *timeouts = data;
313 
314 	if (nla_put_be32(skb, CTA_TIMEOUT_GRE_UNREPLIED,
315 			 htonl(timeouts[GRE_CT_UNREPLIED] / HZ)) ||
316 	    nla_put_be32(skb, CTA_TIMEOUT_GRE_REPLIED,
317 			 htonl(timeouts[GRE_CT_REPLIED] / HZ)))
318 		goto nla_put_failure;
319 	return 0;
320 
321 nla_put_failure:
322 	return -ENOSPC;
323 }
324 
325 static const struct nla_policy
326 gre_timeout_nla_policy[CTA_TIMEOUT_GRE_MAX+1] = {
327 	[CTA_TIMEOUT_GRE_UNREPLIED]	= { .type = NLA_U32 },
328 	[CTA_TIMEOUT_GRE_REPLIED]	= { .type = NLA_U32 },
329 };
330 #endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
331 
332 static int gre_init_net(struct net *net, u_int16_t proto)
333 {
334 	struct netns_proto_gre *net_gre = gre_pernet(net);
335 	int i;
336 
337 	rwlock_init(&net_gre->keymap_lock);
338 	INIT_LIST_HEAD(&net_gre->keymap_list);
339 	for (i = 0; i < GRE_CT_MAX; i++)
340 		net_gre->gre_timeouts[i] = gre_timeouts[i];
341 
342 	return 0;
343 }
344 
345 /* protocol helper struct */
346 static const struct nf_conntrack_l4proto nf_conntrack_l4proto_gre4 = {
347 	.l3proto	 = AF_INET,
348 	.l4proto	 = IPPROTO_GRE,
349 	.pkt_to_tuple	 = gre_pkt_to_tuple,
350 #ifdef CONFIG_NF_CONNTRACK_PROCFS
351 	.print_conntrack = gre_print_conntrack,
352 #endif
353 	.packet		 = gre_packet,
354 	.destroy	 = gre_destroy,
355 	.me 		 = THIS_MODULE,
356 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
357 	.tuple_to_nlattr = nf_ct_port_tuple_to_nlattr,
358 	.nlattr_tuple_size = nf_ct_port_nlattr_tuple_size,
359 	.nlattr_to_tuple = nf_ct_port_nlattr_to_tuple,
360 	.nla_policy	 = nf_ct_port_nla_policy,
361 #endif
362 #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
363 	.ctnl_timeout    = {
364 		.nlattr_to_obj	= gre_timeout_nlattr_to_obj,
365 		.obj_to_nlattr	= gre_timeout_obj_to_nlattr,
366 		.nlattr_max	= CTA_TIMEOUT_GRE_MAX,
367 		.obj_size	= sizeof(unsigned int) * GRE_CT_MAX,
368 		.nla_policy	= gre_timeout_nla_policy,
369 	},
370 #endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
371 	.net_id		= &proto_gre_net_id,
372 	.init_net	= gre_init_net,
373 };
374 
375 static int proto_gre_net_init(struct net *net)
376 {
377 	int ret = 0;
378 
379 	ret = nf_ct_l4proto_pernet_register_one(net,
380 						&nf_conntrack_l4proto_gre4);
381 	if (ret < 0)
382 		pr_err("nf_conntrack_gre4: pernet registration failed.\n");
383 	return ret;
384 }
385 
386 static void proto_gre_net_exit(struct net *net)
387 {
388 	nf_ct_l4proto_pernet_unregister_one(net, &nf_conntrack_l4proto_gre4);
389 	nf_ct_gre_keymap_flush(net);
390 }
391 
392 static struct pernet_operations proto_gre_net_ops = {
393 	.init = proto_gre_net_init,
394 	.exit = proto_gre_net_exit,
395 	.id   = &proto_gre_net_id,
396 	.size = sizeof(struct netns_proto_gre),
397 };
398 
399 static int __init nf_ct_proto_gre_init(void)
400 {
401 	int ret;
402 
403 	ret = register_pernet_subsys(&proto_gre_net_ops);
404 	if (ret < 0)
405 		goto out_pernet;
406 	ret = nf_ct_l4proto_register_one(&nf_conntrack_l4proto_gre4);
407 	if (ret < 0)
408 		goto out_gre4;
409 
410 	return 0;
411 out_gre4:
412 	unregister_pernet_subsys(&proto_gre_net_ops);
413 out_pernet:
414 	return ret;
415 }
416 
417 static void __exit nf_ct_proto_gre_fini(void)
418 {
419 	nf_ct_l4proto_unregister_one(&nf_conntrack_l4proto_gre4);
420 	unregister_pernet_subsys(&proto_gre_net_ops);
421 }
422 
423 module_init(nf_ct_proto_gre_init);
424 module_exit(nf_ct_proto_gre_fini);
425 
426 MODULE_LICENSE("GPL");
427