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TOMOYO Linux Cross Reference
Linux/net/netfilter/nf_conntrack_helper.c

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  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  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
  7  *
  8  * This program is free software; you can redistribute it and/or modify
  9  * it under the terms of the GNU General Public License version 2 as
 10  * published by the Free Software Foundation.
 11  */
 12 
 13 #include <linux/types.h>
 14 #include <linux/netfilter.h>
 15 #include <linux/module.h>
 16 #include <linux/skbuff.h>
 17 #include <linux/vmalloc.h>
 18 #include <linux/stddef.h>
 19 #include <linux/random.h>
 20 #include <linux/err.h>
 21 #include <linux/kernel.h>
 22 #include <linux/netdevice.h>
 23 #include <linux/rculist.h>
 24 #include <linux/rtnetlink.h>
 25 
 26 #include <net/netfilter/nf_conntrack.h>
 27 #include <net/netfilter/nf_conntrack_l3proto.h>
 28 #include <net/netfilter/nf_conntrack_l4proto.h>
 29 #include <net/netfilter/nf_conntrack_helper.h>
 30 #include <net/netfilter/nf_conntrack_core.h>
 31 #include <net/netfilter/nf_conntrack_extend.h>
 32 #include <net/netfilter/nf_log.h>
 33 
 34 static DEFINE_MUTEX(nf_ct_helper_mutex);
 35 struct hlist_head *nf_ct_helper_hash __read_mostly;
 36 EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
 37 unsigned int nf_ct_helper_hsize __read_mostly;
 38 EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
 39 static unsigned int nf_ct_helper_count __read_mostly;
 40 
 41 static bool nf_ct_auto_assign_helper __read_mostly = true;
 42 module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
 43 MODULE_PARM_DESC(nf_conntrack_helper,
 44                  "Enable automatic conntrack helper assignment (default 1)");
 45 
 46 #ifdef CONFIG_SYSCTL
 47 static struct ctl_table helper_sysctl_table[] = {
 48         {
 49                 .procname       = "nf_conntrack_helper",
 50                 .data           = &init_net.ct.sysctl_auto_assign_helper,
 51                 .maxlen         = sizeof(unsigned int),
 52                 .mode           = 0644,
 53                 .proc_handler   = proc_dointvec,
 54         },
 55         {}
 56 };
 57 
 58 static int nf_conntrack_helper_init_sysctl(struct net *net)
 59 {
 60         struct ctl_table *table;
 61 
 62         table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
 63                         GFP_KERNEL);
 64         if (!table)
 65                 goto out;
 66 
 67         table[0].data = &net->ct.sysctl_auto_assign_helper;
 68 
 69         /* Don't export sysctls to unprivileged users */
 70         if (net->user_ns != &init_user_ns)
 71                 table[0].procname = NULL;
 72 
 73         net->ct.helper_sysctl_header =
 74                 register_net_sysctl(net, "net/netfilter", table);
 75 
 76         if (!net->ct.helper_sysctl_header) {
 77                 pr_err("nf_conntrack_helper: can't register to sysctl.\n");
 78                 goto out_register;
 79         }
 80         return 0;
 81 
 82 out_register:
 83         kfree(table);
 84 out:
 85         return -ENOMEM;
 86 }
 87 
 88 static void nf_conntrack_helper_fini_sysctl(struct net *net)
 89 {
 90         struct ctl_table *table;
 91 
 92         table = net->ct.helper_sysctl_header->ctl_table_arg;
 93         unregister_net_sysctl_table(net->ct.helper_sysctl_header);
 94         kfree(table);
 95 }
 96 #else
 97 static int nf_conntrack_helper_init_sysctl(struct net *net)
 98 {
 99         return 0;
100 }
101 
102 static void nf_conntrack_helper_fini_sysctl(struct net *net)
103 {
104 }
105 #endif /* CONFIG_SYSCTL */
106 
107 /* Stupid hash, but collision free for the default registrations of the
108  * helpers currently in the kernel. */
109 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
110 {
111         return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
112                 (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
113 }
114 
115 static struct nf_conntrack_helper *
116 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
117 {
118         struct nf_conntrack_helper *helper;
119         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
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, &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 
133 struct nf_conntrack_helper *
134 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
135 {
136         struct nf_conntrack_helper *h;
137         unsigned int i;
138 
139         for (i = 0; i < nf_ct_helper_hsize; i++) {
140                 hlist_for_each_entry_rcu(h, &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 }
149 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
150 
151 struct nf_conntrack_helper *
152 nf_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 }
168 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
169 
170 struct nf_conn_help *
171 nf_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 }
184 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
185 
186 int __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                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
240 
241                 if (tmp && tmp->help != helper->help) {
242                         RCU_INIT_POINTER(help->helper, NULL);
243                         goto out;
244                 }
245         }
246 
247         rcu_assign_pointer(help->helper, helper);
248 out:
249         return ret;
250 }
251 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
252 
253 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
254                          const struct nf_conntrack_helper *me)
255 {
256         struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
257         struct nf_conn_help *help = nfct_help(ct);
258 
259         if (help && rcu_dereference_protected(
260                         help->helper,
261                         lockdep_is_held(&nf_conntrack_lock)
262                         ) == me) {
263                 nf_conntrack_event(IPCT_HELPER, ct);
264                 RCU_INIT_POINTER(help->helper, NULL);
265         }
266         return 0;
267 }
268 
269 void nf_ct_helper_destroy(struct nf_conn *ct)
270 {
271         struct nf_conn_help *help = nfct_help(ct);
272         struct nf_conntrack_helper *helper;
273 
274         if (help) {
275                 rcu_read_lock();
276                 helper = rcu_dereference(help->helper);
277                 if (helper && helper->destroy)
278                         helper->destroy(ct);
279                 rcu_read_unlock();
280         }
281 }
282 
283 static LIST_HEAD(nf_ct_helper_expectfn_list);
284 
285 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
286 {
287         spin_lock_bh(&nf_conntrack_lock);
288         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
289         spin_unlock_bh(&nf_conntrack_lock);
290 }
291 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
292 
293 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
294 {
295         spin_lock_bh(&nf_conntrack_lock);
296         list_del_rcu(&n->head);
297         spin_unlock_bh(&nf_conntrack_lock);
298 }
299 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
300 
301 struct nf_ct_helper_expectfn *
302 nf_ct_helper_expectfn_find_by_name(const char *name)
303 {
304         struct nf_ct_helper_expectfn *cur;
305         bool found = false;
306 
307         rcu_read_lock();
308         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
309                 if (!strcmp(cur->name, name)) {
310                         found = true;
311                         break;
312                 }
313         }
314         rcu_read_unlock();
315         return found ? cur : NULL;
316 }
317 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
318 
319 struct nf_ct_helper_expectfn *
320 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
321 {
322         struct nf_ct_helper_expectfn *cur;
323         bool found = false;
324 
325         rcu_read_lock();
326         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
327                 if (cur->expectfn == symbol) {
328                         found = true;
329                         break;
330                 }
331         }
332         rcu_read_unlock();
333         return found ? cur : NULL;
334 }
335 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
336 
337 __printf(3, 4)
338 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
339                       const char *fmt, ...)
340 {
341         const struct nf_conn_help *help;
342         const struct nf_conntrack_helper *helper;
343         struct va_format vaf;
344         va_list args;
345 
346         va_start(args, fmt);
347 
348         vaf.fmt = fmt;
349         vaf.va = &args;
350 
351         /* Called from the helper function, this call never fails */
352         help = nfct_help(ct);
353 
354         /* rcu_read_lock()ed by nf_hook_slow */
355         helper = rcu_dereference(help->helper);
356 
357         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
358                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
359 
360         va_end(args);
361 }
362 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
363 
364 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
365 {
366         int ret = 0;
367         struct nf_conntrack_helper *cur;
368         unsigned int h = helper_hash(&me->tuple);
369 
370         BUG_ON(me->expect_policy == NULL);
371         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
372         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
373 
374         mutex_lock(&nf_ct_helper_mutex);
375         hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
376                 if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 &&
377                     cur->tuple.src.l3num == me->tuple.src.l3num &&
378                     cur->tuple.dst.protonum == me->tuple.dst.protonum) {
379                         ret = -EEXIST;
380                         goto out;
381                 }
382         }
383         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
384         nf_ct_helper_count++;
385 out:
386         mutex_unlock(&nf_ct_helper_mutex);
387         return ret;
388 }
389 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
390 
391 static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
392                                              struct net *net)
393 {
394         struct nf_conntrack_tuple_hash *h;
395         struct nf_conntrack_expect *exp;
396         const struct hlist_node *next;
397         const struct hlist_nulls_node *nn;
398         unsigned int i;
399 
400         /* Get rid of expectations */
401         for (i = 0; i < nf_ct_expect_hsize; i++) {
402                 hlist_for_each_entry_safe(exp, next,
403                                           &net->ct.expect_hash[i], hnode) {
404                         struct nf_conn_help *help = nfct_help(exp->master);
405                         if ((rcu_dereference_protected(
406                                         help->helper,
407                                         lockdep_is_held(&nf_conntrack_lock)
408                                         ) == me || exp->helper == me) &&
409                             del_timer(&exp->timeout)) {
410                                 nf_ct_unlink_expect(exp);
411                                 nf_ct_expect_put(exp);
412                         }
413                 }
414         }
415 
416         /* Get rid of expecteds, set helpers to NULL. */
417         hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
418                 unhelp(h, me);
419         for (i = 0; i < net->ct.htable_size; i++) {
420                 hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
421                         unhelp(h, me);
422         }
423 }
424 
425 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
426 {
427         struct net *net;
428 
429         mutex_lock(&nf_ct_helper_mutex);
430         hlist_del_rcu(&me->hnode);
431         nf_ct_helper_count--;
432         mutex_unlock(&nf_ct_helper_mutex);
433 
434         /* Make sure every nothing is still using the helper unless its a
435          * connection in the hash.
436          */
437         synchronize_rcu();
438 
439         rtnl_lock();
440         spin_lock_bh(&nf_conntrack_lock);
441         for_each_net(net)
442                 __nf_conntrack_helper_unregister(me, net);
443         spin_unlock_bh(&nf_conntrack_lock);
444         rtnl_unlock();
445 }
446 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
447 
448 static struct nf_ct_ext_type helper_extend __read_mostly = {
449         .len    = sizeof(struct nf_conn_help),
450         .align  = __alignof__(struct nf_conn_help),
451         .id     = NF_CT_EXT_HELPER,
452 };
453 
454 int nf_conntrack_helper_pernet_init(struct net *net)
455 {
456         net->ct.auto_assign_helper_warned = false;
457         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
458         return nf_conntrack_helper_init_sysctl(net);
459 }
460 
461 void nf_conntrack_helper_pernet_fini(struct net *net)
462 {
463         nf_conntrack_helper_fini_sysctl(net);
464 }
465 
466 int nf_conntrack_helper_init(void)
467 {
468         int ret;
469         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
470         nf_ct_helper_hash =
471                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
472         if (!nf_ct_helper_hash)
473                 return -ENOMEM;
474 
475         ret = nf_ct_extend_register(&helper_extend);
476         if (ret < 0) {
477                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
478                 goto out_extend;
479         }
480 
481         return 0;
482 out_extend:
483         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
484         return ret;
485 }
486 
487 void nf_conntrack_helper_fini(void)
488 {
489         nf_ct_extend_unregister(&helper_extend);
490         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
491 }
492 

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