nf_conntrack_helper.c revision 464dc801c76aa0db88e16e8f5f47c6879858b9b2 
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);
33struct hlist_head *nf_ct_helper_hash __read_mostly;
34EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
35unsigned int nf_ct_helper_hsize __read_mostly;
36EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
37static unsigned int nf_ct_helper_count __read_mostly;
38
39static bool nf_ct_auto_assign_helper __read_mostly = true;
40module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
41MODULE_PARM_DESC(nf_conntrack_helper,
42		 "Enable automatic conntrack helper assignment (default 1)");
43
44#ifdef CONFIG_SYSCTL
45static struct ctl_table helper_sysctl_table[] = {
46	{
47		.procname	= "nf_conntrack_helper",
48		.data		= &init_net.ct.sysctl_auto_assign_helper,
49		.maxlen		= sizeof(unsigned int),
50		.mode		= 0644,
51		.proc_handler	= proc_dointvec,
52	},
53	{}
54};
55
56static int nf_conntrack_helper_init_sysctl(struct net *net)
57{
58	struct ctl_table *table;
59
60	table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
61			GFP_KERNEL);
62	if (!table)
63		goto out;
64
65	table[0].data = &net->ct.sysctl_auto_assign_helper;
66
67	/* Don't export sysctls to unprivileged users */
68	if (net->user_ns != &init_user_ns)
69		table[0].procname = NULL;
70
71	net->ct.helper_sysctl_header =
72		register_net_sysctl(net, "net/netfilter", table);
73
74	if (!net->ct.helper_sysctl_header) {
75		pr_err("nf_conntrack_helper: can't register to sysctl.\n");
76		goto out_register;
77	}
78	return 0;
79
80out_register:
81	kfree(table);
82out:
83	return -ENOMEM;
84}
85
86static void nf_conntrack_helper_fini_sysctl(struct net *net)
87{
88	struct ctl_table *table;
89
90	table = net->ct.helper_sysctl_header->ctl_table_arg;
91	unregister_net_sysctl_table(net->ct.helper_sysctl_header);
92	kfree(table);
93}
94#else
95static int nf_conntrack_helper_init_sysctl(struct net *net)
96{
97	return 0;
98}
99
100static void nf_conntrack_helper_fini_sysctl(struct net *net)
101{
102}
103#endif /* CONFIG_SYSCTL */
104
105/* Stupid hash, but collision free for the default registrations of the
106 * helpers currently in the kernel. */
107static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
108{
109	return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
110		(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
111}
112
113static struct nf_conntrack_helper *
114__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
115{
116	struct nf_conntrack_helper *helper;
117	struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
118	struct hlist_node *n;
119	unsigned int h;
120
121	if (!nf_ct_helper_count)
122		return NULL;
123
124	h = helper_hash(tuple);
125	hlist_for_each_entry_rcu(helper, n, &nf_ct_helper_hash[h], hnode) {
126		if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
127			return helper;
128	}
129	return NULL;
130}
131
132struct nf_conntrack_helper *
133__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
134{
135	struct nf_conntrack_helper *h;
136	struct hlist_node *n;
137	unsigned int i;
138
139	for (i = 0; i < nf_ct_helper_hsize; i++) {
140		hlist_for_each_entry_rcu(h, n, &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		if (help->helper != helper) {
240			RCU_INIT_POINTER(help->helper, NULL);
241			goto out;
242		}
243	}
244
245	rcu_assign_pointer(help->helper, helper);
246out:
247	return ret;
248}
249EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
250
251static inline int unhelp(struct nf_conntrack_tuple_hash *i,
252			 const struct nf_conntrack_helper *me)
253{
254	struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
255	struct nf_conn_help *help = nfct_help(ct);
256
257	if (help && rcu_dereference_protected(
258			help->helper,
259			lockdep_is_held(&nf_conntrack_lock)
260			) == me) {
261		nf_conntrack_event(IPCT_HELPER, ct);
262		RCU_INIT_POINTER(help->helper, NULL);
263	}
264	return 0;
265}
266
267void nf_ct_helper_destroy(struct nf_conn *ct)
268{
269	struct nf_conn_help *help = nfct_help(ct);
270	struct nf_conntrack_helper *helper;
271
272	if (help) {
273		rcu_read_lock();
274		helper = rcu_dereference(help->helper);
275		if (helper && helper->destroy)
276			helper->destroy(ct);
277		rcu_read_unlock();
278	}
279}
280
281static LIST_HEAD(nf_ct_helper_expectfn_list);
282
283void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
284{
285	spin_lock_bh(&nf_conntrack_lock);
286	list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
287	spin_unlock_bh(&nf_conntrack_lock);
288}
289EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
290
291void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
292{
293	spin_lock_bh(&nf_conntrack_lock);
294	list_del_rcu(&n->head);
295	spin_unlock_bh(&nf_conntrack_lock);
296}
297EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
298
299struct nf_ct_helper_expectfn *
300nf_ct_helper_expectfn_find_by_name(const char *name)
301{
302	struct nf_ct_helper_expectfn *cur;
303	bool found = false;
304
305	rcu_read_lock();
306	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
307		if (!strcmp(cur->name, name)) {
308			found = true;
309			break;
310		}
311	}
312	rcu_read_unlock();
313	return found ? cur : NULL;
314}
315EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
316
317struct nf_ct_helper_expectfn *
318nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
319{
320	struct nf_ct_helper_expectfn *cur;
321	bool found = false;
322
323	rcu_read_lock();
324	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
325		if (cur->expectfn == symbol) {
326			found = true;
327			break;
328		}
329	}
330	rcu_read_unlock();
331	return found ? cur : NULL;
332}
333EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
334
335int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
336{
337	int ret = 0;
338	struct nf_conntrack_helper *cur;
339	struct hlist_node *n;
340	unsigned int h = helper_hash(&me->tuple);
341
342	BUG_ON(me->expect_policy == NULL);
343	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
344	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
345
346	mutex_lock(&nf_ct_helper_mutex);
347	hlist_for_each_entry(cur, n, &nf_ct_helper_hash[h], hnode) {
348		if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 &&
349		    cur->tuple.src.l3num == me->tuple.src.l3num &&
350		    cur->tuple.dst.protonum == me->tuple.dst.protonum) {
351			ret = -EEXIST;
352			goto out;
353		}
354	}
355	hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
356	nf_ct_helper_count++;
357out:
358	mutex_unlock(&nf_ct_helper_mutex);
359	return ret;
360}
361EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
362
363static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
364					     struct net *net)
365{
366	struct nf_conntrack_tuple_hash *h;
367	struct nf_conntrack_expect *exp;
368	const struct hlist_node *n, *next;
369	const struct hlist_nulls_node *nn;
370	unsigned int i;
371
372	/* Get rid of expectations */
373	for (i = 0; i < nf_ct_expect_hsize; i++) {
374		hlist_for_each_entry_safe(exp, n, next,
375					  &net->ct.expect_hash[i], hnode) {
376			struct nf_conn_help *help = nfct_help(exp->master);
377			if ((rcu_dereference_protected(
378					help->helper,
379					lockdep_is_held(&nf_conntrack_lock)
380					) == me || exp->helper == me) &&
381			    del_timer(&exp->timeout)) {
382				nf_ct_unlink_expect(exp);
383				nf_ct_expect_put(exp);
384			}
385		}
386	}
387
388	/* Get rid of expecteds, set helpers to NULL. */
389	hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
390		unhelp(h, me);
391	for (i = 0; i < net->ct.htable_size; i++) {
392		hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
393			unhelp(h, me);
394	}
395}
396
397void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
398{
399	struct net *net;
400
401	mutex_lock(&nf_ct_helper_mutex);
402	hlist_del_rcu(&me->hnode);
403	nf_ct_helper_count--;
404	mutex_unlock(&nf_ct_helper_mutex);
405
406	/* Make sure every nothing is still using the helper unless its a
407	 * connection in the hash.
408	 */
409	synchronize_rcu();
410
411	rtnl_lock();
412	spin_lock_bh(&nf_conntrack_lock);
413	for_each_net(net)
414		__nf_conntrack_helper_unregister(me, net);
415	spin_unlock_bh(&nf_conntrack_lock);
416	rtnl_unlock();
417}
418EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
419
420static struct nf_ct_ext_type helper_extend __read_mostly = {
421	.len	= sizeof(struct nf_conn_help),
422	.align	= __alignof__(struct nf_conn_help),
423	.id	= NF_CT_EXT_HELPER,
424};
425
426int nf_conntrack_helper_init(struct net *net)
427{
428	int err;
429
430	net->ct.auto_assign_helper_warned = false;
431	net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
432
433	if (net_eq(net, &init_net)) {
434		nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
435		nf_ct_helper_hash =
436			nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
437		if (!nf_ct_helper_hash)
438			return -ENOMEM;
439
440		err = nf_ct_extend_register(&helper_extend);
441		if (err < 0)
442			goto err1;
443	}
444
445	err = nf_conntrack_helper_init_sysctl(net);
446	if (err < 0)
447		goto out_sysctl;
448
449	return 0;
450
451out_sysctl:
452	if (net_eq(net, &init_net))
453		nf_ct_extend_unregister(&helper_extend);
454err1:
455	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
456	return err;
457}
458
459void nf_conntrack_helper_fini(struct net *net)
460{
461	nf_conntrack_helper_fini_sysctl(net);
462	if (net_eq(net, &init_net)) {
463		nf_ct_extend_unregister(&helper_extend);
464		nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
465	}
466}
467