nf_conntrack_helper.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/* Helper handling for netfilter. */
  3
  4/* (C) 1999-2001 Paul `Rusty' Russell
  5 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
  6 * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
  7 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
  8 */
  9
 10#include <linux/types.h>
 11#include <linux/netfilter.h>
 12#include <linux/module.h>
 13#include <linux/skbuff.h>
 14#include <linux/vmalloc.h>
 15#include <linux/stddef.h>
 16#include <linux/random.h>
 17#include <linux/err.h>
 18#include <linux/kernel.h>
 19#include <linux/netdevice.h>
 20#include <linux/rculist.h>
 21#include <linux/rtnetlink.h>
 22
 23#include <net/netfilter/nf_conntrack.h>
 24#include <net/netfilter/nf_conntrack_core.h>
 25#include <net/netfilter/nf_conntrack_ecache.h>
 26#include <net/netfilter/nf_conntrack_extend.h>
 27#include <net/netfilter/nf_conntrack_helper.h>
 28#include <net/netfilter/nf_conntrack_l4proto.h>
 29#include <net/netfilter/nf_conntrack_seqadj.h>
 30#include <net/netfilter/nf_log.h>
 31#include <net/ip.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 DEFINE_MUTEX(nf_ct_nat_helpers_mutex);
 41static struct list_head nf_ct_nat_helpers __read_mostly;
 42
 43/* Stupid hash, but collision free for the default registrations of the
 44 * helpers currently in the kernel. */
 45static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
 46{
 47	return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
 48		(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
 49}
 50
 51struct nf_conntrack_helper *
 52__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
 53{
 54	struct nf_conntrack_helper *h;
 55	unsigned int i;
 56
 57	for (i = 0; i < nf_ct_helper_hsize; i++) {
 58		hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
 59			if (strcmp(h->name, name))
 60				continue;
 61
 62			if (h->tuple.src.l3num != NFPROTO_UNSPEC &&
 63			    h->tuple.src.l3num != l3num)
 64				continue;
 65
 66			if (h->tuple.dst.protonum == protonum)
 67				return h;
 68		}
 69	}
 70	return NULL;
 71}
 72EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
 73
 74struct nf_conntrack_helper *
 75nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 76{
 77	struct nf_conntrack_helper *h;
 78
 79	rcu_read_lock();
 80
 81	h = __nf_conntrack_helper_find(name, l3num, protonum);
 82#ifdef CONFIG_MODULES
 83	if (h == NULL) {
 84		rcu_read_unlock();
 85		if (request_module("nfct-helper-%s", name) == 0) {
 86			rcu_read_lock();
 87			h = __nf_conntrack_helper_find(name, l3num, protonum);
 88		} else {
 89			return h;
 90		}
 91	}
 92#endif
 93	if (h != NULL && !try_module_get(h->me))
 94		h = NULL;
 95	if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) {
 96		module_put(h->me);
 97		h = NULL;
 98	}
 99
100	rcu_read_unlock();
101
102	return h;
103}
104EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
105
106void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
107{
108	refcount_dec(&helper->refcnt);
109	module_put(helper->me);
110}
111EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);
112
113static struct nf_conntrack_nat_helper *
114nf_conntrack_nat_helper_find(const char *mod_name)
115{
116	struct nf_conntrack_nat_helper *cur;
117	bool found = false;
118
119	list_for_each_entry_rcu(cur, &nf_ct_nat_helpers, list) {
120		if (!strcmp(cur->mod_name, mod_name)) {
121			found = true;
122			break;
123		}
124	}
125	return found ? cur : NULL;
126}
127
128int
129nf_nat_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
130{
131	struct nf_conntrack_helper *h;
132	struct nf_conntrack_nat_helper *nat;
133	char mod_name[NF_CT_HELPER_NAME_LEN];
134	int ret = 0;
135
136	rcu_read_lock();
137	h = __nf_conntrack_helper_find(name, l3num, protonum);
138	if (!h) {
139		rcu_read_unlock();
140		return -ENOENT;
141	}
142
143	nat = nf_conntrack_nat_helper_find(h->nat_mod_name);
144	if (!nat) {
145		snprintf(mod_name, sizeof(mod_name), "%s", h->nat_mod_name);
146		rcu_read_unlock();
147		request_module("%s", mod_name);
148
149		rcu_read_lock();
150		nat = nf_conntrack_nat_helper_find(mod_name);
151		if (!nat) {
152			rcu_read_unlock();
153			return -ENOENT;
154		}
155	}
156
157	if (!try_module_get(nat->module))
158		ret = -ENOENT;
159
160	rcu_read_unlock();
161	return ret;
162}
163EXPORT_SYMBOL_GPL(nf_nat_helper_try_module_get);
164
165void nf_nat_helper_put(struct nf_conntrack_helper *helper)
166{
167	struct nf_conntrack_nat_helper *nat;
168
169	nat = nf_conntrack_nat_helper_find(helper->nat_mod_name);
170	if (WARN_ON_ONCE(!nat))
171		return;
172
173	module_put(nat->module);
174}
175EXPORT_SYMBOL_GPL(nf_nat_helper_put);
176
177struct nf_conn_help *
178nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
179{
180	struct nf_conn_help *help;
181
182	help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
183	if (help)
184		INIT_HLIST_HEAD(&help->expectations);
185	else
186		pr_debug("failed to add helper extension area");
187	return help;
188}
189EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
190
191int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
192			      gfp_t flags)
193{
194	struct nf_conntrack_helper *helper = NULL;
195	struct nf_conn_help *help;
196
197	/* We already got a helper explicitly attached (e.g. nft_ct) */
198	if (test_bit(IPS_HELPER_BIT, &ct->status))
199		return 0;
200
201	if (WARN_ON_ONCE(!tmpl))
202		return 0;
203
204	help = nfct_help(tmpl);
205	if (help != NULL) {
206		helper = rcu_dereference(help->helper);
207		set_bit(IPS_HELPER_BIT, &ct->status);
208	}
209
210	help = nfct_help(ct);
211
212	if (helper == NULL) {
213		if (help)
214			RCU_INIT_POINTER(help->helper, NULL);
215		return 0;
216	}
217
218	if (help == NULL) {
219		help = nf_ct_helper_ext_add(ct, flags);
220		if (help == NULL)
221			return -ENOMEM;
222	} else {
223		/* We only allow helper re-assignment of the same sort since
224		 * we cannot reallocate the helper extension area.
225		 */
226		struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
227
228		if (tmp && tmp->help != helper->help) {
229			RCU_INIT_POINTER(help->helper, NULL);
230			return 0;
231		}
232	}
233
234	rcu_assign_pointer(help->helper, helper);
235
236	return 0;
237}
238EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
239
240/* appropriate ct lock protecting must be taken by caller */
241static int unhelp(struct nf_conn *ct, void *me)
242{
243	struct nf_conn_help *help = nfct_help(ct);
244
245	if (help && rcu_dereference_raw(help->helper) == me) {
246		nf_conntrack_event(IPCT_HELPER, ct);
247		RCU_INIT_POINTER(help->helper, NULL);
248	}
249
250	/* We are not intended to delete this conntrack. */
251	return 0;
252}
253
254void nf_ct_helper_destroy(struct nf_conn *ct)
255{
256	struct nf_conn_help *help = nfct_help(ct);
257	struct nf_conntrack_helper *helper;
258
259	if (help) {
260		rcu_read_lock();
261		helper = rcu_dereference(help->helper);
262		if (helper && helper->destroy)
263			helper->destroy(ct);
264		rcu_read_unlock();
265	}
266}
267
268static LIST_HEAD(nf_ct_helper_expectfn_list);
269
270void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
271{
272	spin_lock_bh(&nf_conntrack_expect_lock);
273	list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
274	spin_unlock_bh(&nf_conntrack_expect_lock);
275}
276EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
277
278void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
279{
280	spin_lock_bh(&nf_conntrack_expect_lock);
281	list_del_rcu(&n->head);
282	spin_unlock_bh(&nf_conntrack_expect_lock);
283}
284EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
285
286/* Caller should hold the rcu lock */
287struct nf_ct_helper_expectfn *
288nf_ct_helper_expectfn_find_by_name(const char *name)
289{
290	struct nf_ct_helper_expectfn *cur;
291	bool found = false;
292
293	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
294		if (!strcmp(cur->name, name)) {
295			found = true;
296			break;
297		}
298	}
299	return found ? cur : NULL;
300}
301EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
302
303/* Caller should hold the rcu lock */
304struct nf_ct_helper_expectfn *
305nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
306{
307	struct nf_ct_helper_expectfn *cur;
308	bool found = false;
309
310	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
311		if (cur->expectfn == symbol) {
312			found = true;
313			break;
314		}
315	}
316	return found ? cur : NULL;
317}
318EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
319
320__printf(3, 4)
321void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
322		      const char *fmt, ...)
323{
324	const struct nf_conn_help *help;
325	const struct nf_conntrack_helper *helper;
326	struct va_format vaf;
327	va_list args;
328
329	va_start(args, fmt);
330
331	vaf.fmt = fmt;
332	vaf.va = &args;
333
334	/* Called from the helper function, this call never fails */
335	help = nfct_help(ct);
336
337	/* rcu_read_lock()ed by nf_hook_thresh */
338	helper = rcu_dereference(help->helper);
339
340	nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
341		      "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
342
343	va_end(args);
344}
345EXPORT_SYMBOL_GPL(nf_ct_helper_log);
346
347int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
348{
349	struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
350	unsigned int h = helper_hash(&me->tuple);
351	struct nf_conntrack_helper *cur;
352	int ret = 0, i;
353
354	BUG_ON(me->expect_policy == NULL);
355	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
356	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
357
358	if (!nf_ct_helper_hash)
359		return -ENOENT;
360
361	if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
362		return -EINVAL;
363
364	mutex_lock(&nf_ct_helper_mutex);
365	for (i = 0; i < nf_ct_helper_hsize; i++) {
366		hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
367			if (!strcmp(cur->name, me->name) &&
368			    (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
369			     cur->tuple.src.l3num == me->tuple.src.l3num) &&
370			    cur->tuple.dst.protonum == me->tuple.dst.protonum) {
371				ret = -EBUSY;
372				goto out;
373			}
374		}
375	}
376
377	/* avoid unpredictable behaviour for auto_assign_helper */
378	if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
379		hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
380			if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
381						     &mask)) {
382				ret = -EBUSY;
383				goto out;
384			}
385		}
386	}
387	refcount_set(&me->refcnt, 1);
388	hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
389	nf_ct_helper_count++;
390out:
391	mutex_unlock(&nf_ct_helper_mutex);
392	return ret;
393}
394EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
395
396static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
397{
398	const struct nf_conntrack_helper *me = data;
399	const struct nf_conntrack_helper *this;
400
401	this = rcu_dereference_protected(exp->helper,
402					 lockdep_is_held(&nf_conntrack_expect_lock));
403	return this == me;
404}
405
406void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
407{
408	mutex_lock(&nf_ct_helper_mutex);
409	hlist_del_rcu(&me->hnode);
410	nf_ct_helper_count--;
411	mutex_unlock(&nf_ct_helper_mutex);
412
413	/* Make sure every nothing is still using the helper unless its a
414	 * connection in the hash.
415	 */
416	synchronize_rcu();
417
418	nf_ct_expect_iterate_destroy(expect_iter_me, me);
419	nf_ct_iterate_destroy(unhelp, me);
420
421	/* nf_ct_iterate_destroy() does an unconditional synchronize_rcu() as
422	 * last step, this ensures rcu readers of exp->helper are done.
423	 * No need for another synchronize_rcu() here.
424	 */
425}
426EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
427
428void nf_ct_helper_init(struct nf_conntrack_helper *helper,
429		       u16 l3num, u16 protonum, const char *name,
430		       u16 default_port, u16 spec_port, u32 id,
431		       const struct nf_conntrack_expect_policy *exp_pol,
432		       u32 expect_class_max,
433		       int (*help)(struct sk_buff *skb, unsigned int protoff,
434				   struct nf_conn *ct,
435				   enum ip_conntrack_info ctinfo),
436		       int (*from_nlattr)(struct nlattr *attr,
437					  struct nf_conn *ct),
438		       struct module *module)
439{
440	helper->tuple.src.l3num = l3num;
441	helper->tuple.dst.protonum = protonum;
442	helper->tuple.src.u.all = htons(spec_port);
443	helper->expect_policy = exp_pol;
444	helper->expect_class_max = expect_class_max;
445	helper->help = help;
446	helper->from_nlattr = from_nlattr;
447	helper->me = module;
448	snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
449		 NF_NAT_HELPER_PREFIX "%s", name);
450
451	if (spec_port == default_port)
452		snprintf(helper->name, sizeof(helper->name), "%s", name);
453	else
454		snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
455}
456EXPORT_SYMBOL_GPL(nf_ct_helper_init);
457
458int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
459				  unsigned int n)
460{
461	unsigned int i;
462	int err = 0;
463
464	for (i = 0; i < n; i++) {
465		err = nf_conntrack_helper_register(&helper[i]);
466		if (err < 0)
467			goto err;
468	}
469
470	return err;
471err:
472	if (i > 0)
473		nf_conntrack_helpers_unregister(helper, i);
474	return err;
475}
476EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
477
478void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
479				unsigned int n)
480{
481	while (n-- > 0)
482		nf_conntrack_helper_unregister(&helper[n]);
483}
484EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
485
486void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
487{
488	mutex_lock(&nf_ct_nat_helpers_mutex);
489	list_add_rcu(&nat->list, &nf_ct_nat_helpers);
490	mutex_unlock(&nf_ct_nat_helpers_mutex);
491}
492EXPORT_SYMBOL_GPL(nf_nat_helper_register);
493
494void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
495{
496	mutex_lock(&nf_ct_nat_helpers_mutex);
497	list_del_rcu(&nat->list);
498	mutex_unlock(&nf_ct_nat_helpers_mutex);
499}
500EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
501
502int nf_conntrack_helper_init(void)
503{
504	nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
505	nf_ct_helper_hash =
506		nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
507	if (!nf_ct_helper_hash)
508		return -ENOMEM;
509
510	INIT_LIST_HEAD(&nf_ct_nat_helpers);
511	return 0;
512}
513
514void nf_conntrack_helper_fini(void)
515{
516	kvfree(nf_ct_helper_hash);
517	nf_ct_helper_hash = NULL;
518}