nf_conntrack_helper.c revision 6714cf5465d2803a21c6a46c1ea747795a8889fa 
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
32static DEFINE_MUTEX(nf_ct_helper_mutex);
33static struct hlist_head *nf_ct_helper_hash __read_mostly;
34static unsigned int nf_ct_helper_hsize __read_mostly;
35static unsigned int nf_ct_helper_count __read_mostly;
36
37static bool nf_ct_auto_assign_helper __read_mostly = true;
38module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
39MODULE_PARM_DESC(nf_conntrack_helper,
40		 "Enable automatic conntrack helper assignment (default 1)");
41
42#ifdef CONFIG_SYSCTL
43static struct ctl_table helper_sysctl_table[] = {
44	{
45		.procname	= "nf_conntrack_helper",
46		.data		= &init_net.ct.sysctl_auto_assign_helper,
47		.maxlen		= sizeof(unsigned int),
48		.mode		= 0644,
49		.proc_handler	= proc_dointvec,
50	},
51	{}
52};
53
54static int nf_conntrack_helper_init_sysctl(struct net *net)
55{
56	struct ctl_table *table;
57
58	table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
59			GFP_KERNEL);
60	if (!table)
61		goto out;
62
63	table[0].data = &net->ct.sysctl_auto_assign_helper;
64
65	net->ct.helper_sysctl_header =
66		register_net_sysctl(net, "net/netfilter", table);
67
68	if (!net->ct.helper_sysctl_header) {
69		pr_err("nf_conntrack_helper: can't register to sysctl.\n");
70		goto out_register;
71	}
72	return 0;
73
74out_register:
75	kfree(table);
76out:
77	return -ENOMEM;
78}
79
80static void nf_conntrack_helper_fini_sysctl(struct net *net)
81{
82	struct ctl_table *table;
83
84	table = net->ct.helper_sysctl_header->ctl_table_arg;
85	unregister_net_sysctl_table(net->ct.helper_sysctl_header);
86	kfree(table);
87}
88#else
89static int nf_conntrack_helper_init_sysctl(struct net *net)
90{
91	return 0;
92}
93
94static void nf_conntrack_helper_fini_sysctl(struct net *net)
95{
96}
97#endif /* CONFIG_SYSCTL */
98
99/* Stupid hash, but collision free for the default registrations of the
100 * helpers currently in the kernel. */
101static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
102{
103	return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
104		(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
105}
106
107static struct nf_conntrack_helper *
108__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
109{
110	struct nf_conntrack_helper *helper;
111	struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
112	struct hlist_node *n;
113	unsigned int h;
114
115	if (!nf_ct_helper_count)
116		return NULL;
117
118	h = helper_hash(tuple);
119	hlist_for_each_entry_rcu(helper, n, &nf_ct_helper_hash[h], hnode) {
120		if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
121			return helper;
122	}
123	return NULL;
124}
125
126struct nf_conntrack_helper *
127__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
128{
129	struct nf_conntrack_helper *h;
130	struct hlist_node *n;
131	unsigned int i;
132
133	for (i = 0; i < nf_ct_helper_hsize; i++) {
134		hlist_for_each_entry_rcu(h, n, &nf_ct_helper_hash[i], hnode) {
135			if (!strcmp(h->name, name) &&
136			    h->tuple.src.l3num == l3num &&
137			    h->tuple.dst.protonum == protonum)
138				return h;
139		}
140	}
141	return NULL;
142}
143EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
144
145struct nf_conntrack_helper *
146nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
147{
148	struct nf_conntrack_helper *h;
149
150	h = __nf_conntrack_helper_find(name, l3num, protonum);
151#ifdef CONFIG_MODULES
152	if (h == NULL) {
153		if (request_module("nfct-helper-%s", name) == 0)
154			h = __nf_conntrack_helper_find(name, l3num, protonum);
155	}
156#endif
157	if (h != NULL && !try_module_get(h->me))
158		h = NULL;
159
160	return h;
161}
162EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
163
164struct nf_conn_help *nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
165{
166	struct nf_conn_help *help;
167
168	help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
169	if (help)
170		INIT_HLIST_HEAD(&help->expectations);
171	else
172		pr_debug("failed to add helper extension area");
173	return help;
174}
175EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
176
177int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
178			      gfp_t flags)
179{
180	struct nf_conntrack_helper *helper = NULL;
181	struct nf_conn_help *help;
182	struct net *net = nf_ct_net(ct);
183	int ret = 0;
184
185	/* We already got a helper explicitly attached. The function
186	 * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
187	 * the helper up again. Since now the user is in full control of
188	 * making consistent helper configurations, skip this automatic
189	 * re-lookup, otherwise we'll lose the helper.
190	 */
191	if (test_bit(IPS_HELPER_BIT, &ct->status))
192		return 0;
193
194	if (tmpl != NULL) {
195		help = nfct_help(tmpl);
196		if (help != NULL) {
197			helper = help->helper;
198			set_bit(IPS_HELPER_BIT, &ct->status);
199		}
200	}
201
202	help = nfct_help(ct);
203	if (net->ct.sysctl_auto_assign_helper && helper == NULL) {
204		helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
205		if (unlikely(!net->ct.auto_assign_helper_warned && helper)) {
206			pr_info("nf_conntrack: automatic helper "
207				"assignment is deprecated and it will "
208				"be removed soon. Use the iptables CT target "
209				"to attach helpers instead.\n");
210			net->ct.auto_assign_helper_warned = true;
211		}
212	}
213
214	if (helper == NULL) {
215		if (help)
216			RCU_INIT_POINTER(help->helper, NULL);
217		goto out;
218	}
219
220	if (help == NULL) {
221		help = nf_ct_helper_ext_add(ct, flags);
222		if (help == NULL) {
223			ret = -ENOMEM;
224			goto out;
225		}
226	} else {
227		memset(&help->help, 0, sizeof(help->help));
228	}
229
230	rcu_assign_pointer(help->helper, helper);
231out:
232	return ret;
233}
234EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
235
236static inline int unhelp(struct nf_conntrack_tuple_hash *i,
237			 const struct nf_conntrack_helper *me)
238{
239	struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
240	struct nf_conn_help *help = nfct_help(ct);
241
242	if (help && rcu_dereference_protected(
243			help->helper,
244			lockdep_is_held(&nf_conntrack_lock)
245			) == me) {
246		nf_conntrack_event(IPCT_HELPER, ct);
247		RCU_INIT_POINTER(help->helper, NULL);
248	}
249	return 0;
250}
251
252void nf_ct_helper_destroy(struct nf_conn *ct)
253{
254	struct nf_conn_help *help = nfct_help(ct);
255	struct nf_conntrack_helper *helper;
256
257	if (help) {
258		rcu_read_lock();
259		helper = rcu_dereference(help->helper);
260		if (helper && helper->destroy)
261			helper->destroy(ct);
262		rcu_read_unlock();
263	}
264}
265
266static LIST_HEAD(nf_ct_helper_expectfn_list);
267
268void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
269{
270	spin_lock_bh(&nf_conntrack_lock);
271	list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
272	spin_unlock_bh(&nf_conntrack_lock);
273}
274EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
275
276void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
277{
278	spin_lock_bh(&nf_conntrack_lock);
279	list_del_rcu(&n->head);
280	spin_unlock_bh(&nf_conntrack_lock);
281}
282EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
283
284struct nf_ct_helper_expectfn *
285nf_ct_helper_expectfn_find_by_name(const char *name)
286{
287	struct nf_ct_helper_expectfn *cur;
288	bool found = false;
289
290	rcu_read_lock();
291	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
292		if (!strcmp(cur->name, name)) {
293			found = true;
294			break;
295		}
296	}
297	rcu_read_unlock();
298	return found ? cur : NULL;
299}
300EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
301
302struct nf_ct_helper_expectfn *
303nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
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 (cur->expectfn == symbol) {
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_symbol);
319
320int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
321{
322	unsigned int h = helper_hash(&me->tuple);
323
324	BUG_ON(me->expect_policy == NULL);
325	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
326	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
327
328	mutex_lock(&nf_ct_helper_mutex);
329	hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
330	nf_ct_helper_count++;
331	mutex_unlock(&nf_ct_helper_mutex);
332
333	return 0;
334}
335EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
336
337static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
338					     struct net *net)
339{
340	struct nf_conntrack_tuple_hash *h;
341	struct nf_conntrack_expect *exp;
342	const struct hlist_node *n, *next;
343	const struct hlist_nulls_node *nn;
344	unsigned int i;
345
346	/* Get rid of expectations */
347	for (i = 0; i < nf_ct_expect_hsize; i++) {
348		hlist_for_each_entry_safe(exp, n, next,
349					  &net->ct.expect_hash[i], hnode) {
350			struct nf_conn_help *help = nfct_help(exp->master);
351			if ((rcu_dereference_protected(
352					help->helper,
353					lockdep_is_held(&nf_conntrack_lock)
354					) == me || exp->helper == me) &&
355			    del_timer(&exp->timeout)) {
356				nf_ct_unlink_expect(exp);
357				nf_ct_expect_put(exp);
358			}
359		}
360	}
361
362	/* Get rid of expecteds, set helpers to NULL. */
363	hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
364		unhelp(h, me);
365	for (i = 0; i < net->ct.htable_size; i++) {
366		hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
367			unhelp(h, me);
368	}
369}
370
371void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
372{
373	struct net *net;
374
375	mutex_lock(&nf_ct_helper_mutex);
376	hlist_del_rcu(&me->hnode);
377	nf_ct_helper_count--;
378	mutex_unlock(&nf_ct_helper_mutex);
379
380	/* Make sure every nothing is still using the helper unless its a
381	 * connection in the hash.
382	 */
383	synchronize_rcu();
384
385	rtnl_lock();
386	spin_lock_bh(&nf_conntrack_lock);
387	for_each_net(net)
388		__nf_conntrack_helper_unregister(me, net);
389	spin_unlock_bh(&nf_conntrack_lock);
390	rtnl_unlock();
391}
392EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
393
394static struct nf_ct_ext_type helper_extend __read_mostly = {
395	.len	= sizeof(struct nf_conn_help),
396	.align	= __alignof__(struct nf_conn_help),
397	.id	= NF_CT_EXT_HELPER,
398};
399
400int nf_conntrack_helper_init(struct net *net)
401{
402	int err;
403
404	net->ct.auto_assign_helper_warned = false;
405	net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
406
407	if (net_eq(net, &init_net)) {
408		nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
409		nf_ct_helper_hash =
410			nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
411		if (!nf_ct_helper_hash)
412			return -ENOMEM;
413
414		err = nf_ct_extend_register(&helper_extend);
415		if (err < 0)
416			goto err1;
417	}
418
419	err = nf_conntrack_helper_init_sysctl(net);
420	if (err < 0)
421		goto out_sysctl;
422
423	return 0;
424
425out_sysctl:
426	if (net_eq(net, &init_net))
427		nf_ct_extend_unregister(&helper_extend);
428err1:
429	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
430	return err;
431}
432
433void nf_conntrack_helper_fini(struct net *net)
434{
435	nf_conntrack_helper_fini_sysctl(net);
436	if (net_eq(net, &init_net)) {
437		nf_ct_extend_unregister(&helper_extend);
438		nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
439	}
440}
441