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_log.h>
30 
31 static DEFINE_MUTEX(nf_ct_helper_mutex);
32 struct hlist_head *nf_ct_helper_hash __read_mostly;
33 EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
34 unsigned int nf_ct_helper_hsize __read_mostly;
35 EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
36 static unsigned int nf_ct_helper_count __read_mostly;
37 
38 static DEFINE_MUTEX(nf_ct_nat_helpers_mutex);
39 static struct list_head nf_ct_nat_helpers __read_mostly;
40 
41 /* Stupid hash, but collision free for the default registrations of the
42  * helpers currently in the kernel. */
helper_hash(const struct nf_conntrack_tuple * tuple)43 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
44 {
45 	return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
46 		(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
47 }
48 
49 struct nf_conntrack_helper *
__nf_conntrack_helper_find(const char * name,u16 l3num,u8 protonum)50 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
51 {
52 	struct nf_conntrack_helper *h;
53 	unsigned int i;
54 
55 	for (i = 0; i < nf_ct_helper_hsize; i++) {
56 		hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
57 			if (strcmp(h->name, name))
58 				continue;
59 
60 			if (h->tuple.src.l3num != NFPROTO_UNSPEC &&
61 			    h->tuple.src.l3num != l3num)
62 				continue;
63 
64 			if (h->tuple.dst.protonum == protonum)
65 				return h;
66 		}
67 	}
68 	return NULL;
69 }
70 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
71 
72 struct nf_conntrack_helper *
nf_conntrack_helper_try_module_get(const char * name,u16 l3num,u8 protonum)73 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
74 {
75 	struct nf_conntrack_helper *h;
76 
77 	rcu_read_lock();
78 
79 	h = __nf_conntrack_helper_find(name, l3num, protonum);
80 #ifdef CONFIG_MODULES
81 	if (h == NULL) {
82 		rcu_read_unlock();
83 		if (request_module("nfct-helper-%s", name) == 0) {
84 			rcu_read_lock();
85 			h = __nf_conntrack_helper_find(name, l3num, protonum);
86 		} else {
87 			return h;
88 		}
89 	}
90 #endif
91 	if (h != NULL && !try_module_get(h->me))
92 		h = NULL;
93 	if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) {
94 		module_put(h->me);
95 		h = NULL;
96 	}
97 
98 	rcu_read_unlock();
99 
100 	return h;
101 }
102 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
103 
nf_conntrack_helper_put(struct nf_conntrack_helper * helper)104 void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
105 {
106 	refcount_dec(&helper->refcnt);
107 	module_put(helper->me);
108 }
109 EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);
110 
111 static struct nf_conntrack_nat_helper *
nf_conntrack_nat_helper_find(const char * mod_name)112 nf_conntrack_nat_helper_find(const char *mod_name)
113 {
114 	struct nf_conntrack_nat_helper *cur;
115 	bool found = false;
116 
117 	list_for_each_entry_rcu(cur, &nf_ct_nat_helpers, list) {
118 		if (!strcmp(cur->mod_name, mod_name)) {
119 			found = true;
120 			break;
121 		}
122 	}
123 	return found ? cur : NULL;
124 }
125 
126 int
nf_nat_helper_try_module_get(const char * name,u16 l3num,u8 protonum)127 nf_nat_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
128 {
129 	struct nf_conntrack_helper *h;
130 	struct nf_conntrack_nat_helper *nat;
131 	char mod_name[NF_CT_HELPER_NAME_LEN];
132 	int ret = 0;
133 
134 	rcu_read_lock();
135 	h = __nf_conntrack_helper_find(name, l3num, protonum);
136 	if (!h) {
137 		rcu_read_unlock();
138 		return -ENOENT;
139 	}
140 
141 	nat = nf_conntrack_nat_helper_find(h->nat_mod_name);
142 	if (!nat) {
143 		snprintf(mod_name, sizeof(mod_name), "%s", h->nat_mod_name);
144 		rcu_read_unlock();
145 		request_module("%s", mod_name);
146 
147 		rcu_read_lock();
148 		nat = nf_conntrack_nat_helper_find(mod_name);
149 		if (!nat) {
150 			rcu_read_unlock();
151 			return -ENOENT;
152 		}
153 	}
154 
155 	if (!try_module_get(nat->module))
156 		ret = -ENOENT;
157 
158 	rcu_read_unlock();
159 	return ret;
160 }
161 EXPORT_SYMBOL_GPL(nf_nat_helper_try_module_get);
162 
nf_nat_helper_put(struct nf_conntrack_helper * helper)163 void nf_nat_helper_put(struct nf_conntrack_helper *helper)
164 {
165 	struct nf_conntrack_nat_helper *nat;
166 
167 	nat = nf_conntrack_nat_helper_find(helper->nat_mod_name);
168 	if (WARN_ON_ONCE(!nat))
169 		return;
170 
171 	module_put(nat->module);
172 }
173 EXPORT_SYMBOL_GPL(nf_nat_helper_put);
174 
175 struct nf_conn_help *
nf_ct_helper_ext_add(struct nf_conn * ct,gfp_t gfp)176 nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
177 {
178 	struct nf_conn_help *help;
179 
180 	help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
181 	if (help)
182 		INIT_HLIST_HEAD(&help->expectations);
183 	else
184 		pr_debug("failed to add helper extension area");
185 	return help;
186 }
187 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
188 
__nf_ct_try_assign_helper(struct nf_conn * ct,struct nf_conn * tmpl,gfp_t flags)189 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
190 			      gfp_t flags)
191 {
192 	struct nf_conntrack_helper *helper = NULL;
193 	struct nf_conn_help *help;
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 (WARN_ON_ONCE(!tmpl))
205 		return 0;
206 
207 	help = nfct_help(tmpl);
208 	if (help != NULL) {
209 		helper = rcu_dereference(help->helper);
210 		set_bit(IPS_HELPER_BIT, &ct->status);
211 	}
212 
213 	help = nfct_help(ct);
214 
215 	if (helper == NULL) {
216 		if (help)
217 			RCU_INIT_POINTER(help->helper, NULL);
218 		return 0;
219 	}
220 
221 	if (help == NULL) {
222 		help = nf_ct_helper_ext_add(ct, flags);
223 		if (help == NULL)
224 			return -ENOMEM;
225 	} else {
226 		/* We only allow helper re-assignment of the same sort since
227 		 * we cannot reallocate the helper extension area.
228 		 */
229 		struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
230 
231 		if (tmp && tmp->help != helper->help) {
232 			RCU_INIT_POINTER(help->helper, NULL);
233 			return 0;
234 		}
235 	}
236 
237 	rcu_assign_pointer(help->helper, helper);
238 
239 	return 0;
240 }
241 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
242 
243 /* appropriate ct lock protecting must be taken by caller */
unhelp(struct nf_conn * ct,void * me)244 static int unhelp(struct nf_conn *ct, void *me)
245 {
246 	struct nf_conn_help *help = nfct_help(ct);
247 
248 	if (help && rcu_dereference_raw(help->helper) == me) {
249 		nf_conntrack_event(IPCT_HELPER, ct);
250 		RCU_INIT_POINTER(help->helper, NULL);
251 	}
252 
253 	/* We are not intended to delete this conntrack. */
254 	return 0;
255 }
256 
nf_ct_helper_destroy(struct nf_conn * ct)257 void nf_ct_helper_destroy(struct nf_conn *ct)
258 {
259 	struct nf_conn_help *help = nfct_help(ct);
260 	struct nf_conntrack_helper *helper;
261 
262 	if (help) {
263 		rcu_read_lock();
264 		helper = rcu_dereference(help->helper);
265 		if (helper && helper->destroy)
266 			helper->destroy(ct);
267 		rcu_read_unlock();
268 	}
269 }
270 
271 static LIST_HEAD(nf_ct_helper_expectfn_list);
272 
nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn * n)273 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
274 {
275 	spin_lock_bh(&nf_conntrack_expect_lock);
276 	list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
277 	spin_unlock_bh(&nf_conntrack_expect_lock);
278 }
279 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
280 
nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn * n)281 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
282 {
283 	spin_lock_bh(&nf_conntrack_expect_lock);
284 	list_del_rcu(&n->head);
285 	spin_unlock_bh(&nf_conntrack_expect_lock);
286 }
287 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
288 
289 /* Caller should hold the rcu lock */
290 struct nf_ct_helper_expectfn *
nf_ct_helper_expectfn_find_by_name(const char * name)291 nf_ct_helper_expectfn_find_by_name(const char *name)
292 {
293 	struct nf_ct_helper_expectfn *cur;
294 	bool found = false;
295 
296 	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
297 		if (!strcmp(cur->name, name)) {
298 			found = true;
299 			break;
300 		}
301 	}
302 	return found ? cur : NULL;
303 }
304 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
305 
306 /* Caller should hold the rcu lock */
307 struct nf_ct_helper_expectfn *
nf_ct_helper_expectfn_find_by_symbol(const void * symbol)308 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
309 {
310 	struct nf_ct_helper_expectfn *cur;
311 	bool found = false;
312 
313 	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
314 		if (cur->expectfn == symbol) {
315 			found = true;
316 			break;
317 		}
318 	}
319 	return found ? cur : NULL;
320 }
321 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
322 
323 __printf(3, 4)
nf_ct_helper_log(struct sk_buff * skb,const struct nf_conn * ct,const char * fmt,...)324 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
325 		      const char *fmt, ...)
326 {
327 	const struct nf_conn_help *help;
328 	const struct nf_conntrack_helper *helper;
329 	struct va_format vaf;
330 	va_list args;
331 
332 	va_start(args, fmt);
333 
334 	vaf.fmt = fmt;
335 	vaf.va = &args;
336 
337 	/* Called from the helper function, this call never fails */
338 	help = nfct_help(ct);
339 
340 	/* rcu_read_lock()ed by nf_hook_thresh */
341 	helper = rcu_dereference(help->helper);
342 
343 	nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
344 		      "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
345 
346 	va_end(args);
347 }
348 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
349 
nf_conntrack_helper_register(struct nf_conntrack_helper * me)350 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
351 {
352 	struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
353 	unsigned int h = helper_hash(&me->tuple);
354 	struct nf_conntrack_helper *cur;
355 	int ret = 0, i;
356 
357 	BUG_ON(me->expect_policy == NULL);
358 	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
359 	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
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 = -EEXIST;
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 = -EEXIST;
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++;
390 out:
391 	mutex_unlock(&nf_ct_helper_mutex);
392 	return ret;
393 }
394 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
395 
expect_iter_me(struct nf_conntrack_expect * exp,void * data)396 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
397 {
398 	struct nf_conn_help *help = nfct_help(exp->master);
399 	const struct nf_conntrack_helper *me = data;
400 	const struct nf_conntrack_helper *this;
401 
402 	if (exp->helper == me)
403 		return true;
404 
405 	this = rcu_dereference_protected(help->helper,
406 					 lockdep_is_held(&nf_conntrack_expect_lock));
407 	return this == me;
408 }
409 
nf_conntrack_helper_unregister(struct nf_conntrack_helper * me)410 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
411 {
412 	mutex_lock(&nf_ct_helper_mutex);
413 	hlist_del_rcu(&me->hnode);
414 	nf_ct_helper_count--;
415 	mutex_unlock(&nf_ct_helper_mutex);
416 
417 	/* Make sure every nothing is still using the helper unless its a
418 	 * connection in the hash.
419 	 */
420 	synchronize_rcu();
421 
422 	nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
423 	nf_ct_iterate_destroy(unhelp, me);
424 }
425 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
426 
nf_ct_helper_init(struct nf_conntrack_helper * helper,u16 l3num,u16 protonum,const char * name,u16 default_port,u16 spec_port,u32 id,const struct nf_conntrack_expect_policy * exp_pol,u32 expect_class_max,int (* help)(struct sk_buff * skb,unsigned int protoff,struct nf_conn * ct,enum ip_conntrack_info ctinfo),int (* from_nlattr)(struct nlattr * attr,struct nf_conn * ct),struct module * module)427 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
428 		       u16 l3num, u16 protonum, const char *name,
429 		       u16 default_port, u16 spec_port, u32 id,
430 		       const struct nf_conntrack_expect_policy *exp_pol,
431 		       u32 expect_class_max,
432 		       int (*help)(struct sk_buff *skb, unsigned int protoff,
433 				   struct nf_conn *ct,
434 				   enum ip_conntrack_info ctinfo),
435 		       int (*from_nlattr)(struct nlattr *attr,
436 					  struct nf_conn *ct),
437 		       struct module *module)
438 {
439 	helper->tuple.src.l3num = l3num;
440 	helper->tuple.dst.protonum = protonum;
441 	helper->tuple.src.u.all = htons(spec_port);
442 	helper->expect_policy = exp_pol;
443 	helper->expect_class_max = expect_class_max;
444 	helper->help = help;
445 	helper->from_nlattr = from_nlattr;
446 	helper->me = module;
447 	snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
448 		 NF_NAT_HELPER_PREFIX "%s", name);
449 
450 	if (spec_port == default_port)
451 		snprintf(helper->name, sizeof(helper->name), "%s", name);
452 	else
453 		snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
454 }
455 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
456 
nf_conntrack_helpers_register(struct nf_conntrack_helper * helper,unsigned int n)457 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
458 				  unsigned int n)
459 {
460 	unsigned int i;
461 	int err = 0;
462 
463 	for (i = 0; i < n; i++) {
464 		err = nf_conntrack_helper_register(&helper[i]);
465 		if (err < 0)
466 			goto err;
467 	}
468 
469 	return err;
470 err:
471 	if (i > 0)
472 		nf_conntrack_helpers_unregister(helper, i);
473 	return err;
474 }
475 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
476 
nf_conntrack_helpers_unregister(struct nf_conntrack_helper * helper,unsigned int n)477 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
478 				unsigned int n)
479 {
480 	while (n-- > 0)
481 		nf_conntrack_helper_unregister(&helper[n]);
482 }
483 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
484 
nf_nat_helper_register(struct nf_conntrack_nat_helper * nat)485 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
486 {
487 	mutex_lock(&nf_ct_nat_helpers_mutex);
488 	list_add_rcu(&nat->list, &nf_ct_nat_helpers);
489 	mutex_unlock(&nf_ct_nat_helpers_mutex);
490 }
491 EXPORT_SYMBOL_GPL(nf_nat_helper_register);
492 
nf_nat_helper_unregister(struct nf_conntrack_nat_helper * nat)493 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
494 {
495 	mutex_lock(&nf_ct_nat_helpers_mutex);
496 	list_del_rcu(&nat->list);
497 	mutex_unlock(&nf_ct_nat_helpers_mutex);
498 }
499 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
500 
nf_conntrack_helper_init(void)501 int nf_conntrack_helper_init(void)
502 {
503 	nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
504 	nf_ct_helper_hash =
505 		nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
506 	if (!nf_ct_helper_hash)
507 		return -ENOMEM;
508 
509 	INIT_LIST_HEAD(&nf_ct_nat_helpers);
510 	return 0;
511 }
512 
nf_conntrack_helper_fini(void)513 void nf_conntrack_helper_fini(void)
514 {
515 	kvfree(nf_ct_helper_hash);
516 }
517