nf_conntrack_helper.c revision f229f6ce481ceb33a966311722b8ef0cb6c25de7 
1/* Helper handling for netfilter. */
2
3/* (C) 1999-2001 Paul `Rusty' Russell
4 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
5 * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
6 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License version 2 as
10 * published by the Free Software Foundation.
11 */
12
13#include <linux/types.h>
14#include <linux/netfilter.h>
15#include <linux/module.h>
16#include <linux/skbuff.h>
17#include <linux/vmalloc.h>
18#include <linux/stddef.h>
19#include <linux/random.h>
20#include <linux/err.h>
21#include <linux/kernel.h>
22#include <linux/netdevice.h>
23#include <linux/rculist.h>
24#include <linux/rtnetlink.h>
25
26#include <net/netfilter/nf_conntrack.h>
27#include <net/netfilter/nf_conntrack_l3proto.h>
28#include <net/netfilter/nf_conntrack_l4proto.h>
29#include <net/netfilter/nf_conntrack_helper.h>
30#include <net/netfilter/nf_conntrack_core.h>
31#include <net/netfilter/nf_conntrack_extend.h>
32#include <net/netfilter/nf_log.h>
33
34static DEFINE_MUTEX(nf_ct_helper_mutex);
35struct hlist_head *nf_ct_helper_hash __read_mostly;
36EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
37unsigned int nf_ct_helper_hsize __read_mostly;
38EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
39static unsigned int nf_ct_helper_count __read_mostly;
40
41static bool nf_ct_auto_assign_helper __read_mostly = true;
42module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
43MODULE_PARM_DESC(nf_conntrack_helper,
44		 "Enable automatic conntrack helper assignment (default 1)");
45
46#ifdef CONFIG_SYSCTL
47static struct ctl_table helper_sysctl_table[] = {
48	{
49		.procname	= "nf_conntrack_helper",
50		.data		= &init_net.ct.sysctl_auto_assign_helper,
51		.maxlen		= sizeof(unsigned int),
52		.mode		= 0644,
53		.proc_handler	= proc_dointvec,
54	},
55	{}
56};
57
58static int nf_conntrack_helper_init_sysctl(struct net *net)
59{
60	struct ctl_table *table;
61
62	table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
63			GFP_KERNEL);
64	if (!table)
65		goto out;
66
67	table[0].data = &net->ct.sysctl_auto_assign_helper;
68
69	/* Don't export sysctls to unprivileged users */
70	if (net->user_ns != &init_user_ns)
71		table[0].procname = NULL;
72
73	net->ct.helper_sysctl_header =
74		register_net_sysctl(net, "net/netfilter", table);
75
76	if (!net->ct.helper_sysctl_header) {
77		pr_err("nf_conntrack_helper: can't register to sysctl.\n");
78		goto out_register;
79	}
80	return 0;
81
82out_register:
83	kfree(table);
84out:
85	return -ENOMEM;
86}
87
88static void nf_conntrack_helper_fini_sysctl(struct net *net)
89{
90	struct ctl_table *table;
91
92	table = net->ct.helper_sysctl_header->ctl_table_arg;
93	unregister_net_sysctl_table(net->ct.helper_sysctl_header);
94	kfree(table);
95}
96#else
97static int nf_conntrack_helper_init_sysctl(struct net *net)
98{
99	return 0;
100}
101
102static void nf_conntrack_helper_fini_sysctl(struct net *net)
103{
104}
105#endif /* CONFIG_SYSCTL */
106
107/* Stupid hash, but collision free for the default registrations of the
108 * helpers currently in the kernel. */
109static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
110{
111	return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
112		(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
113}
114
115static struct nf_conntrack_helper *
116__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
117{
118	struct nf_conntrack_helper *helper;
119	struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
120	unsigned int h;
121
122	if (!nf_ct_helper_count)
123		return NULL;
124
125	h = helper_hash(tuple);
126	hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) {
127		if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
128			return helper;
129	}
130	return NULL;
131}
132
133struct nf_conntrack_helper *
134__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
135{
136	struct nf_conntrack_helper *h;
137	unsigned int i;
138
139	for (i = 0; i < nf_ct_helper_hsize; i++) {
140		hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
141			if (!strcmp(h->name, name) &&
142			    h->tuple.src.l3num == l3num &&
143			    h->tuple.dst.protonum == protonum)
144				return h;
145		}
146	}
147	return NULL;
148}
149EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
150
151struct nf_conntrack_helper *
152nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
153{
154	struct nf_conntrack_helper *h;
155
156	h = __nf_conntrack_helper_find(name, l3num, protonum);
157#ifdef CONFIG_MODULES
158	if (h == NULL) {
159		if (request_module("nfct-helper-%s", name) == 0)
160			h = __nf_conntrack_helper_find(name, l3num, protonum);
161	}
162#endif
163	if (h != NULL && !try_module_get(h->me))
164		h = NULL;
165
166	return h;
167}
168EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
169
170struct nf_conn_help *
171nf_ct_helper_ext_add(struct nf_conn *ct,
172		     struct nf_conntrack_helper *helper, gfp_t gfp)
173{
174	struct nf_conn_help *help;
175
176	help = nf_ct_ext_add_length(ct, NF_CT_EXT_HELPER,
177				    helper->data_len, gfp);
178	if (help)
179		INIT_HLIST_HEAD(&help->expectations);
180	else
181		pr_debug("failed to add helper extension area");
182	return help;
183}
184EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
185
186int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
187			      gfp_t flags)
188{
189	struct nf_conntrack_helper *helper = NULL;
190	struct nf_conn_help *help;
191	struct net *net = nf_ct_net(ct);
192	int ret = 0;
193
194	/* We already got a helper explicitly attached. The function
195	 * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
196	 * the helper up again. Since now the user is in full control of
197	 * making consistent helper configurations, skip this automatic
198	 * re-lookup, otherwise we'll lose the helper.
199	 */
200	if (test_bit(IPS_HELPER_BIT, &ct->status))
201		return 0;
202
203	if (tmpl != NULL) {
204		help = nfct_help(tmpl);
205		if (help != NULL) {
206			helper = help->helper;
207			set_bit(IPS_HELPER_BIT, &ct->status);
208		}
209	}
210
211	help = nfct_help(ct);
212	if (net->ct.sysctl_auto_assign_helper && helper == NULL) {
213		helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
214		if (unlikely(!net->ct.auto_assign_helper_warned && helper)) {
215			pr_info("nf_conntrack: automatic helper "
216				"assignment is deprecated and it will "
217				"be removed soon. Use the iptables CT target "
218				"to attach helpers instead.\n");
219			net->ct.auto_assign_helper_warned = true;
220		}
221	}
222
223	if (helper == NULL) {
224		if (help)
225			RCU_INIT_POINTER(help->helper, NULL);
226		goto out;
227	}
228
229	if (help == NULL) {
230		help = nf_ct_helper_ext_add(ct, helper, flags);
231		if (help == NULL) {
232			ret = -ENOMEM;
233			goto out;
234		}
235	} else {
236		/* We only allow helper re-assignment of the same sort since
237		 * we cannot reallocate the helper extension area.
238		 */
239		struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
240
241		if (tmp && tmp->help != helper->help) {
242			RCU_INIT_POINTER(help->helper, NULL);
243			goto out;
244		}
245	}
246
247	rcu_assign_pointer(help->helper, helper);
248out:
249	return ret;
250}
251EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
252
253static inline int unhelp(struct nf_conntrack_tuple_hash *i,
254			 const struct nf_conntrack_helper *me)
255{
256	struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
257	struct nf_conn_help *help = nfct_help(ct);
258
259	if (help && rcu_dereference_protected(
260			help->helper,
261			lockdep_is_held(&nf_conntrack_lock)
262			) == me) {
263		nf_conntrack_event(IPCT_HELPER, ct);
264		RCU_INIT_POINTER(help->helper, NULL);
265	}
266	return 0;
267}
268
269void nf_ct_helper_destroy(struct nf_conn *ct)
270{
271	struct nf_conn_help *help = nfct_help(ct);
272	struct nf_conntrack_helper *helper;
273
274	if (help) {
275		rcu_read_lock();
276		helper = rcu_dereference(help->helper);
277		if (helper && helper->destroy)
278			helper->destroy(ct);
279		rcu_read_unlock();
280	}
281}
282
283static LIST_HEAD(nf_ct_helper_expectfn_list);
284
285void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
286{
287	spin_lock_bh(&nf_conntrack_lock);
288	list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
289	spin_unlock_bh(&nf_conntrack_lock);
290}
291EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
292
293void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
294{
295	spin_lock_bh(&nf_conntrack_lock);
296	list_del_rcu(&n->head);
297	spin_unlock_bh(&nf_conntrack_lock);
298}
299EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
300
301struct nf_ct_helper_expectfn *
302nf_ct_helper_expectfn_find_by_name(const char *name)
303{
304	struct nf_ct_helper_expectfn *cur;
305	bool found = false;
306
307	rcu_read_lock();
308	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
309		if (!strcmp(cur->name, name)) {
310			found = true;
311			break;
312		}
313	}
314	rcu_read_unlock();
315	return found ? cur : NULL;
316}
317EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
318
319struct nf_ct_helper_expectfn *
320nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
321{
322	struct nf_ct_helper_expectfn *cur;
323	bool found = false;
324
325	rcu_read_lock();
326	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
327		if (cur->expectfn == symbol) {
328			found = true;
329			break;
330		}
331	}
332	rcu_read_unlock();
333	return found ? cur : NULL;
334}
335EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
336
337__printf(3, 4)
338void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
339		      const char *fmt, ...)
340{
341	const struct nf_conn_help *help;
342	const struct nf_conntrack_helper *helper;
343	struct va_format vaf;
344	va_list args;
345
346	va_start(args, fmt);
347
348	vaf.fmt = fmt;
349	vaf.va = &args;
350
351	/* Called from the helper function, this call never fails */
352	help = nfct_help(ct);
353
354	/* rcu_read_lock()ed by nf_hook_slow */
355	helper = rcu_dereference(help->helper);
356
357	nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
358		      "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
359
360	va_end(args);
361}
362EXPORT_SYMBOL_GPL(nf_ct_helper_log);
363
364int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
365{
366	int ret = 0;
367	struct nf_conntrack_helper *cur;
368	unsigned int h = helper_hash(&me->tuple);
369
370	BUG_ON(me->expect_policy == NULL);
371	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
372	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
373
374	mutex_lock(&nf_ct_helper_mutex);
375	hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
376		if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 &&
377		    cur->tuple.src.l3num == me->tuple.src.l3num &&
378		    cur->tuple.dst.protonum == me->tuple.dst.protonum) {
379			ret = -EEXIST;
380			goto out;
381		}
382	}
383	hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
384	nf_ct_helper_count++;
385out:
386	mutex_unlock(&nf_ct_helper_mutex);
387	return ret;
388}
389EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
390
391static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
392					     struct net *net)
393{
394	struct nf_conntrack_tuple_hash *h;
395	struct nf_conntrack_expect *exp;
396	const struct hlist_node *next;
397	const struct hlist_nulls_node *nn;
398	unsigned int i;
399
400	/* Get rid of expectations */
401	for (i = 0; i < nf_ct_expect_hsize; i++) {
402		hlist_for_each_entry_safe(exp, next,
403					  &net->ct.expect_hash[i], hnode) {
404			struct nf_conn_help *help = nfct_help(exp->master);
405			if ((rcu_dereference_protected(
406					help->helper,
407					lockdep_is_held(&nf_conntrack_lock)
408					) == me || exp->helper == me) &&
409			    del_timer(&exp->timeout)) {
410				nf_ct_unlink_expect(exp);
411				nf_ct_expect_put(exp);
412			}
413		}
414	}
415
416	/* Get rid of expecteds, set helpers to NULL. */
417	hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
418		unhelp(h, me);
419	for (i = 0; i < net->ct.htable_size; i++) {
420		hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
421			unhelp(h, me);
422	}
423}
424
425void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
426{
427	struct net *net;
428
429	mutex_lock(&nf_ct_helper_mutex);
430	hlist_del_rcu(&me->hnode);
431	nf_ct_helper_count--;
432	mutex_unlock(&nf_ct_helper_mutex);
433
434	/* Make sure every nothing is still using the helper unless its a
435	 * connection in the hash.
436	 */
437	synchronize_rcu();
438
439	rtnl_lock();
440	spin_lock_bh(&nf_conntrack_lock);
441	for_each_net(net)
442		__nf_conntrack_helper_unregister(me, net);
443	spin_unlock_bh(&nf_conntrack_lock);
444	rtnl_unlock();
445}
446EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
447
448static struct nf_ct_ext_type helper_extend __read_mostly = {
449	.len	= sizeof(struct nf_conn_help),
450	.align	= __alignof__(struct nf_conn_help),
451	.id	= NF_CT_EXT_HELPER,
452};
453
454int nf_conntrack_helper_pernet_init(struct net *net)
455{
456	net->ct.auto_assign_helper_warned = false;
457	net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
458	return nf_conntrack_helper_init_sysctl(net);
459}
460
461void nf_conntrack_helper_pernet_fini(struct net *net)
462{
463	nf_conntrack_helper_fini_sysctl(net);
464}
465
466int nf_conntrack_helper_init(void)
467{
468	int ret;
469	nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
470	nf_ct_helper_hash =
471		nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
472	if (!nf_ct_helper_hash)
473		return -ENOMEM;
474
475	ret = nf_ct_extend_register(&helper_extend);
476	if (ret < 0) {
477		pr_err("nf_ct_helper: Unable to register helper extension.\n");
478		goto out_extend;
479	}
480
481	return 0;
482out_extend:
483	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
484	return ret;
485}
486
487void nf_conntrack_helper_fini(void)
488{
489	nf_ct_extend_unregister(&helper_extend);
490	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
491}
492