nf_conntrack_helper.c revision f9caed59f801f77a2844ab04d2dea8df33ac862b 
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 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10 */
11
12#include <linux/types.h>
13#include <linux/netfilter.h>
14#include <linux/module.h>
15#include <linux/skbuff.h>
16#include <linux/vmalloc.h>
17#include <linux/stddef.h>
18#include <linux/random.h>
19#include <linux/err.h>
20#include <linux/kernel.h>
21#include <linux/netdevice.h>
22#include <linux/rculist.h>
23#include <linux/rtnetlink.h>
24
25#include <net/netfilter/nf_conntrack.h>
26#include <net/netfilter/nf_conntrack_l3proto.h>
27#include <net/netfilter/nf_conntrack_l4proto.h>
28#include <net/netfilter/nf_conntrack_helper.h>
29#include <net/netfilter/nf_conntrack_core.h>
30#include <net/netfilter/nf_conntrack_extend.h>
31#include <net/netfilter/nf_log.h>
32
33static DEFINE_MUTEX(nf_ct_helper_mutex);
34struct hlist_head *nf_ct_helper_hash __read_mostly;
35EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
36unsigned int nf_ct_helper_hsize __read_mostly;
37EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
38static unsigned int nf_ct_helper_count __read_mostly;
39
40static bool nf_ct_auto_assign_helper __read_mostly = true;
41module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
42MODULE_PARM_DESC(nf_conntrack_helper,
43		 "Enable automatic conntrack helper assignment (default 1)");
44
45#ifdef CONFIG_SYSCTL
46static struct ctl_table helper_sysctl_table[] = {
47	{
48		.procname	= "nf_conntrack_helper",
49		.data		= &init_net.ct.sysctl_auto_assign_helper,
50		.maxlen		= sizeof(unsigned int),
51		.mode		= 0644,
52		.proc_handler	= proc_dointvec,
53	},
54	{}
55};
56
57static int nf_conntrack_helper_init_sysctl(struct net *net)
58{
59	struct ctl_table *table;
60
61	table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
62			GFP_KERNEL);
63	if (!table)
64		goto out;
65
66	table[0].data = &net->ct.sysctl_auto_assign_helper;
67
68	/* Don't export sysctls to unprivileged users */
69	if (net->user_ns != &init_user_ns)
70		table[0].procname = NULL;
71
72	net->ct.helper_sysctl_header =
73		register_net_sysctl(net, "net/netfilter", table);
74
75	if (!net->ct.helper_sysctl_header) {
76		pr_err("nf_conntrack_helper: can't register to sysctl.\n");
77		goto out_register;
78	}
79	return 0;
80
81out_register:
82	kfree(table);
83out:
84	return -ENOMEM;
85}
86
87static void nf_conntrack_helper_fini_sysctl(struct net *net)
88{
89	struct ctl_table *table;
90
91	table = net->ct.helper_sysctl_header->ctl_table_arg;
92	unregister_net_sysctl_table(net->ct.helper_sysctl_header);
93	kfree(table);
94}
95#else
96static int nf_conntrack_helper_init_sysctl(struct net *net)
97{
98	return 0;
99}
100
101static void nf_conntrack_helper_fini_sysctl(struct net *net)
102{
103}
104#endif /* CONFIG_SYSCTL */
105
106/* Stupid hash, but collision free for the default registrations of the
107 * helpers currently in the kernel. */
108static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
109{
110	return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
111		(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
112}
113
114static struct nf_conntrack_helper *
115__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
116{
117	struct nf_conntrack_helper *helper;
118	struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
119	struct hlist_node *n;
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, n, &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	struct hlist_node *n;
138	unsigned int i;
139
140	for (i = 0; i < nf_ct_helper_hsize; i++) {
141		hlist_for_each_entry_rcu(h, n, &nf_ct_helper_hash[i], hnode) {
142			if (!strcmp(h->name, name) &&
143			    h->tuple.src.l3num == l3num &&
144			    h->tuple.dst.protonum == protonum)
145				return h;
146		}
147	}
148	return NULL;
149}
150EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
151
152struct nf_conntrack_helper *
153nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
154{
155	struct nf_conntrack_helper *h;
156
157	h = __nf_conntrack_helper_find(name, l3num, protonum);
158#ifdef CONFIG_MODULES
159	if (h == NULL) {
160		if (request_module("nfct-helper-%s", name) == 0)
161			h = __nf_conntrack_helper_find(name, l3num, protonum);
162	}
163#endif
164	if (h != NULL && !try_module_get(h->me))
165		h = NULL;
166
167	return h;
168}
169EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
170
171struct nf_conn_help *
172nf_ct_helper_ext_add(struct nf_conn *ct,
173		     struct nf_conntrack_helper *helper, gfp_t gfp)
174{
175	struct nf_conn_help *help;
176
177	help = nf_ct_ext_add_length(ct, NF_CT_EXT_HELPER,
178				    helper->data_len, gfp);
179	if (help)
180		INIT_HLIST_HEAD(&help->expectations);
181	else
182		pr_debug("failed to add helper extension area");
183	return help;
184}
185EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
186
187int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
188			      gfp_t flags)
189{
190	struct nf_conntrack_helper *helper = NULL;
191	struct nf_conn_help *help;
192	struct net *net = nf_ct_net(ct);
193	int ret = 0;
194
195	/* We already got a helper explicitly attached. The function
196	 * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
197	 * the helper up again. Since now the user is in full control of
198	 * making consistent helper configurations, skip this automatic
199	 * re-lookup, otherwise we'll lose the helper.
200	 */
201	if (test_bit(IPS_HELPER_BIT, &ct->status))
202		return 0;
203
204	if (tmpl != NULL) {
205		help = nfct_help(tmpl);
206		if (help != NULL) {
207			helper = help->helper;
208			set_bit(IPS_HELPER_BIT, &ct->status);
209		}
210	}
211
212	help = nfct_help(ct);
213	if (net->ct.sysctl_auto_assign_helper && helper == NULL) {
214		helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
215		if (unlikely(!net->ct.auto_assign_helper_warned && helper)) {
216			pr_info("nf_conntrack: automatic helper "
217				"assignment is deprecated and it will "
218				"be removed soon. Use the iptables CT target "
219				"to attach helpers instead.\n");
220			net->ct.auto_assign_helper_warned = true;
221		}
222	}
223
224	if (helper == NULL) {
225		if (help)
226			RCU_INIT_POINTER(help->helper, NULL);
227		goto out;
228	}
229
230	if (help == NULL) {
231		help = nf_ct_helper_ext_add(ct, helper, flags);
232		if (help == NULL) {
233			ret = -ENOMEM;
234			goto out;
235		}
236	} else {
237		/* We only allow helper re-assignment of the same sort since
238		 * we cannot reallocate the helper extension area.
239		 */
240		struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
241
242		if (tmp && tmp->help != helper->help) {
243			RCU_INIT_POINTER(help->helper, NULL);
244			goto out;
245		}
246	}
247
248	rcu_assign_pointer(help->helper, helper);
249out:
250	return ret;
251}
252EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
253
254static inline int unhelp(struct nf_conntrack_tuple_hash *i,
255			 const struct nf_conntrack_helper *me)
256{
257	struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
258	struct nf_conn_help *help = nfct_help(ct);
259
260	if (help && rcu_dereference_protected(
261			help->helper,
262			lockdep_is_held(&nf_conntrack_lock)
263			) == me) {
264		nf_conntrack_event(IPCT_HELPER, ct);
265		RCU_INIT_POINTER(help->helper, NULL);
266	}
267	return 0;
268}
269
270void nf_ct_helper_destroy(struct nf_conn *ct)
271{
272	struct nf_conn_help *help = nfct_help(ct);
273	struct nf_conntrack_helper *helper;
274
275	if (help) {
276		rcu_read_lock();
277		helper = rcu_dereference(help->helper);
278		if (helper && helper->destroy)
279			helper->destroy(ct);
280		rcu_read_unlock();
281	}
282}
283
284static LIST_HEAD(nf_ct_helper_expectfn_list);
285
286void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
287{
288	spin_lock_bh(&nf_conntrack_lock);
289	list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
290	spin_unlock_bh(&nf_conntrack_lock);
291}
292EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
293
294void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
295{
296	spin_lock_bh(&nf_conntrack_lock);
297	list_del_rcu(&n->head);
298	spin_unlock_bh(&nf_conntrack_lock);
299}
300EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
301
302struct nf_ct_helper_expectfn *
303nf_ct_helper_expectfn_find_by_name(const char *name)
304{
305	struct nf_ct_helper_expectfn *cur;
306	bool found = false;
307
308	rcu_read_lock();
309	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
310		if (!strcmp(cur->name, name)) {
311			found = true;
312			break;
313		}
314	}
315	rcu_read_unlock();
316	return found ? cur : NULL;
317}
318EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
319
320struct nf_ct_helper_expectfn *
321nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
322{
323	struct nf_ct_helper_expectfn *cur;
324	bool found = false;
325
326	rcu_read_lock();
327	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
328		if (cur->expectfn == symbol) {
329			found = true;
330			break;
331		}
332	}
333	rcu_read_unlock();
334	return found ? cur : NULL;
335}
336EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
337
338__printf(3, 4)
339void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
340		      const char *fmt, ...)
341{
342	const struct nf_conn_help *help;
343	const struct nf_conntrack_helper *helper;
344	struct va_format vaf;
345	va_list args;
346
347	va_start(args, fmt);
348
349	vaf.fmt = fmt;
350	vaf.va = &args;
351
352	/* Called from the helper function, this call never fails */
353	help = nfct_help(ct);
354
355	/* rcu_read_lock()ed by nf_hook_slow */
356	helper = rcu_dereference(help->helper);
357
358	nf_log_packet(nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
359		      "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
360
361	va_end(args);
362}
363EXPORT_SYMBOL_GPL(nf_ct_helper_log);
364
365int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
366{
367	int ret = 0;
368	struct nf_conntrack_helper *cur;
369	struct hlist_node *n;
370	unsigned int h = helper_hash(&me->tuple);
371
372	BUG_ON(me->expect_policy == NULL);
373	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
374	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
375
376	mutex_lock(&nf_ct_helper_mutex);
377	hlist_for_each_entry(cur, n, &nf_ct_helper_hash[h], hnode) {
378		if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 &&
379		    cur->tuple.src.l3num == me->tuple.src.l3num &&
380		    cur->tuple.dst.protonum == me->tuple.dst.protonum) {
381			ret = -EEXIST;
382			goto out;
383		}
384	}
385	hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
386	nf_ct_helper_count++;
387out:
388	mutex_unlock(&nf_ct_helper_mutex);
389	return ret;
390}
391EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
392
393static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
394					     struct net *net)
395{
396	struct nf_conntrack_tuple_hash *h;
397	struct nf_conntrack_expect *exp;
398	const struct hlist_node *n, *next;
399	const struct hlist_nulls_node *nn;
400	unsigned int i;
401
402	/* Get rid of expectations */
403	for (i = 0; i < nf_ct_expect_hsize; i++) {
404		hlist_for_each_entry_safe(exp, n, next,
405					  &net->ct.expect_hash[i], hnode) {
406			struct nf_conn_help *help = nfct_help(exp->master);
407			if ((rcu_dereference_protected(
408					help->helper,
409					lockdep_is_held(&nf_conntrack_lock)
410					) == me || exp->helper == me) &&
411			    del_timer(&exp->timeout)) {
412				nf_ct_unlink_expect(exp);
413				nf_ct_expect_put(exp);
414			}
415		}
416	}
417
418	/* Get rid of expecteds, set helpers to NULL. */
419	hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
420		unhelp(h, me);
421	for (i = 0; i < net->ct.htable_size; i++) {
422		hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
423			unhelp(h, me);
424	}
425}
426
427void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
428{
429	struct net *net;
430
431	mutex_lock(&nf_ct_helper_mutex);
432	hlist_del_rcu(&me->hnode);
433	nf_ct_helper_count--;
434	mutex_unlock(&nf_ct_helper_mutex);
435
436	/* Make sure every nothing is still using the helper unless its a
437	 * connection in the hash.
438	 */
439	synchronize_rcu();
440
441	rtnl_lock();
442	spin_lock_bh(&nf_conntrack_lock);
443	for_each_net(net)
444		__nf_conntrack_helper_unregister(me, net);
445	spin_unlock_bh(&nf_conntrack_lock);
446	rtnl_unlock();
447}
448EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
449
450static struct nf_ct_ext_type helper_extend __read_mostly = {
451	.len	= sizeof(struct nf_conn_help),
452	.align	= __alignof__(struct nf_conn_help),
453	.id	= NF_CT_EXT_HELPER,
454};
455
456int nf_conntrack_helper_pernet_init(struct net *net)
457{
458	net->ct.auto_assign_helper_warned = false;
459	net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
460	return nf_conntrack_helper_init_sysctl(net);
461}
462
463void nf_conntrack_helper_pernet_fini(struct net *net)
464{
465	nf_conntrack_helper_fini_sysctl(net);
466}
467
468int nf_conntrack_helper_init(void)
469{
470	int ret;
471	nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
472	nf_ct_helper_hash =
473		nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
474	if (!nf_ct_helper_hash)
475		return -ENOMEM;
476
477	ret = nf_ct_extend_register(&helper_extend);
478	if (ret < 0) {
479		pr_err("nf_ct_helper: Unable to register helper extension.\n");
480		goto out_extend;
481	}
482
483	return 0;
484out_extend:
485	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
486	return ret;
487}
488
489void nf_conntrack_helper_fini(void)
490{
491	nf_ct_extend_unregister(&helper_extend);
492	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
493}
494