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TOMOYO Linux Cross Reference
Linux/security/tomoyo/gc.c

Version: ~ [ linux-5.3-rc5 ] ~ [ linux-5.2.9 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.67 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.139 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.189 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.189 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.72 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
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  1 /*
  2  * security/tomoyo/gc.c
  3  *
  4  * Copyright (C) 2005-2011  NTT DATA CORPORATION
  5  */
  6 
  7 #include "common.h"
  8 #include <linux/kthread.h>
  9 #include <linux/slab.h>
 10 
 11 /**
 12  * tomoyo_memory_free - Free memory for elements.
 13  *
 14  * @ptr:  Pointer to allocated memory.
 15  *
 16  * Returns nothing.
 17  *
 18  * Caller holds tomoyo_policy_lock mutex.
 19  */
 20 static inline void tomoyo_memory_free(void *ptr)
 21 {
 22         tomoyo_memory_used[TOMOYO_MEMORY_POLICY] -= ksize(ptr);
 23         kfree(ptr);
 24 }
 25 
 26 /* The list for "struct tomoyo_io_buffer". */
 27 static LIST_HEAD(tomoyo_io_buffer_list);
 28 /* Lock for protecting tomoyo_io_buffer_list. */
 29 static DEFINE_SPINLOCK(tomoyo_io_buffer_list_lock);
 30 
 31 /**
 32  * tomoyo_struct_used_by_io_buffer - Check whether the list element is used by /sys/kernel/security/tomoyo/ users or not.
 33  *
 34  * @element: Pointer to "struct list_head".
 35  *
 36  * Returns true if @element is used by /sys/kernel/security/tomoyo/ users,
 37  * false otherwise.
 38  */
 39 static bool tomoyo_struct_used_by_io_buffer(const struct list_head *element)
 40 {
 41         struct tomoyo_io_buffer *head;
 42         bool in_use = false;
 43 
 44         spin_lock(&tomoyo_io_buffer_list_lock);
 45         list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
 46                 head->users++;
 47                 spin_unlock(&tomoyo_io_buffer_list_lock);
 48                 mutex_lock(&head->io_sem);
 49                 if (head->r.domain == element || head->r.group == element ||
 50                     head->r.acl == element || &head->w.domain->list == element)
 51                         in_use = true;
 52                 mutex_unlock(&head->io_sem);
 53                 spin_lock(&tomoyo_io_buffer_list_lock);
 54                 head->users--;
 55                 if (in_use)
 56                         break;
 57         }
 58         spin_unlock(&tomoyo_io_buffer_list_lock);
 59         return in_use;
 60 }
 61 
 62 /**
 63  * tomoyo_name_used_by_io_buffer - Check whether the string is used by /sys/kernel/security/tomoyo/ users or not.
 64  *
 65  * @string: String to check.
 66  *
 67  * Returns true if @string is used by /sys/kernel/security/tomoyo/ users,
 68  * false otherwise.
 69  */
 70 static bool tomoyo_name_used_by_io_buffer(const char *string)
 71 {
 72         struct tomoyo_io_buffer *head;
 73         const size_t size = strlen(string) + 1;
 74         bool in_use = false;
 75 
 76         spin_lock(&tomoyo_io_buffer_list_lock);
 77         list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
 78                 int i;
 79                 head->users++;
 80                 spin_unlock(&tomoyo_io_buffer_list_lock);
 81                 mutex_lock(&head->io_sem);
 82                 for (i = 0; i < TOMOYO_MAX_IO_READ_QUEUE; i++) {
 83                         const char *w = head->r.w[i];
 84                         if (w < string || w > string + size)
 85                                 continue;
 86                         in_use = true;
 87                         break;
 88                 }
 89                 mutex_unlock(&head->io_sem);
 90                 spin_lock(&tomoyo_io_buffer_list_lock);
 91                 head->users--;
 92                 if (in_use)
 93                         break;
 94         }
 95         spin_unlock(&tomoyo_io_buffer_list_lock);
 96         return in_use;
 97 }
 98 
 99 /**
100  * tomoyo_del_transition_control - Delete members in "struct tomoyo_transition_control".
101  *
102  * @element: Pointer to "struct list_head".
103  *
104  * Returns nothing.
105  */
106 static inline void tomoyo_del_transition_control(struct list_head *element)
107 {
108         struct tomoyo_transition_control *ptr =
109                 container_of(element, typeof(*ptr), head.list);
110         tomoyo_put_name(ptr->domainname);
111         tomoyo_put_name(ptr->program);
112 }
113 
114 /**
115  * tomoyo_del_aggregator - Delete members in "struct tomoyo_aggregator".
116  *
117  * @element: Pointer to "struct list_head".
118  *
119  * Returns nothing.
120  */
121 static inline void tomoyo_del_aggregator(struct list_head *element)
122 {
123         struct tomoyo_aggregator *ptr =
124                 container_of(element, typeof(*ptr), head.list);
125         tomoyo_put_name(ptr->original_name);
126         tomoyo_put_name(ptr->aggregated_name);
127 }
128 
129 /**
130  * tomoyo_del_manager - Delete members in "struct tomoyo_manager".
131  *
132  * @element: Pointer to "struct list_head".
133  *
134  * Returns nothing.
135  */
136 static inline void tomoyo_del_manager(struct list_head *element)
137 {
138         struct tomoyo_manager *ptr =
139                 container_of(element, typeof(*ptr), head.list);
140         tomoyo_put_name(ptr->manager);
141 }
142 
143 /**
144  * tomoyo_del_acl - Delete members in "struct tomoyo_acl_info".
145  *
146  * @element: Pointer to "struct list_head".
147  *
148  * Returns nothing.
149  */
150 static void tomoyo_del_acl(struct list_head *element)
151 {
152         struct tomoyo_acl_info *acl =
153                 container_of(element, typeof(*acl), list);
154         tomoyo_put_condition(acl->cond);
155         switch (acl->type) {
156         case TOMOYO_TYPE_PATH_ACL:
157                 {
158                         struct tomoyo_path_acl *entry
159                                 = container_of(acl, typeof(*entry), head);
160                         tomoyo_put_name_union(&entry->name);
161                 }
162                 break;
163         case TOMOYO_TYPE_PATH2_ACL:
164                 {
165                         struct tomoyo_path2_acl *entry
166                                 = container_of(acl, typeof(*entry), head);
167                         tomoyo_put_name_union(&entry->name1);
168                         tomoyo_put_name_union(&entry->name2);
169                 }
170                 break;
171         case TOMOYO_TYPE_PATH_NUMBER_ACL:
172                 {
173                         struct tomoyo_path_number_acl *entry
174                                 = container_of(acl, typeof(*entry), head);
175                         tomoyo_put_name_union(&entry->name);
176                         tomoyo_put_number_union(&entry->number);
177                 }
178                 break;
179         case TOMOYO_TYPE_MKDEV_ACL:
180                 {
181                         struct tomoyo_mkdev_acl *entry
182                                 = container_of(acl, typeof(*entry), head);
183                         tomoyo_put_name_union(&entry->name);
184                         tomoyo_put_number_union(&entry->mode);
185                         tomoyo_put_number_union(&entry->major);
186                         tomoyo_put_number_union(&entry->minor);
187                 }
188                 break;
189         case TOMOYO_TYPE_MOUNT_ACL:
190                 {
191                         struct tomoyo_mount_acl *entry
192                                 = container_of(acl, typeof(*entry), head);
193                         tomoyo_put_name_union(&entry->dev_name);
194                         tomoyo_put_name_union(&entry->dir_name);
195                         tomoyo_put_name_union(&entry->fs_type);
196                         tomoyo_put_number_union(&entry->flags);
197                 }
198                 break;
199         case TOMOYO_TYPE_ENV_ACL:
200                 {
201                         struct tomoyo_env_acl *entry =
202                                 container_of(acl, typeof(*entry), head);
203 
204                         tomoyo_put_name(entry->env);
205                 }
206                 break;
207         case TOMOYO_TYPE_INET_ACL:
208                 {
209                         struct tomoyo_inet_acl *entry =
210                                 container_of(acl, typeof(*entry), head);
211 
212                         tomoyo_put_group(entry->address.group);
213                         tomoyo_put_number_union(&entry->port);
214                 }
215                 break;
216         case TOMOYO_TYPE_UNIX_ACL:
217                 {
218                         struct tomoyo_unix_acl *entry =
219                                 container_of(acl, typeof(*entry), head);
220 
221                         tomoyo_put_name_union(&entry->name);
222                 }
223                 break;
224         case TOMOYO_TYPE_MANUAL_TASK_ACL:
225                 {
226                         struct tomoyo_task_acl *entry =
227                                 container_of(acl, typeof(*entry), head);
228                         tomoyo_put_name(entry->domainname);
229                 }
230                 break;
231         }
232 }
233 
234 /**
235  * tomoyo_del_domain - Delete members in "struct tomoyo_domain_info".
236  *
237  * @element: Pointer to "struct list_head".
238  *
239  * Returns nothing.
240  *
241  * Caller holds tomoyo_policy_lock mutex.
242  */
243 static inline void tomoyo_del_domain(struct list_head *element)
244 {
245         struct tomoyo_domain_info *domain =
246                 container_of(element, typeof(*domain), list);
247         struct tomoyo_acl_info *acl;
248         struct tomoyo_acl_info *tmp;
249         /*
250          * Since this domain is referenced from neither
251          * "struct tomoyo_io_buffer" nor "struct cred"->security, we can delete
252          * elements without checking for is_deleted flag.
253          */
254         list_for_each_entry_safe(acl, tmp, &domain->acl_info_list, list) {
255                 tomoyo_del_acl(&acl->list);
256                 tomoyo_memory_free(acl);
257         }
258         tomoyo_put_name(domain->domainname);
259 }
260 
261 /**
262  * tomoyo_del_condition - Delete members in "struct tomoyo_condition".
263  *
264  * @element: Pointer to "struct list_head".
265  *
266  * Returns nothing.
267  */
268 void tomoyo_del_condition(struct list_head *element)
269 {
270         struct tomoyo_condition *cond = container_of(element, typeof(*cond),
271                                                      head.list);
272         const u16 condc = cond->condc;
273         const u16 numbers_count = cond->numbers_count;
274         const u16 names_count = cond->names_count;
275         const u16 argc = cond->argc;
276         const u16 envc = cond->envc;
277         unsigned int i;
278         const struct tomoyo_condition_element *condp
279                 = (const struct tomoyo_condition_element *) (cond + 1);
280         struct tomoyo_number_union *numbers_p
281                 = (struct tomoyo_number_union *) (condp + condc);
282         struct tomoyo_name_union *names_p
283                 = (struct tomoyo_name_union *) (numbers_p + numbers_count);
284         const struct tomoyo_argv *argv
285                 = (const struct tomoyo_argv *) (names_p + names_count);
286         const struct tomoyo_envp *envp
287                 = (const struct tomoyo_envp *) (argv + argc);
288         for (i = 0; i < numbers_count; i++)
289                 tomoyo_put_number_union(numbers_p++);
290         for (i = 0; i < names_count; i++)
291                 tomoyo_put_name_union(names_p++);
292         for (i = 0; i < argc; argv++, i++)
293                 tomoyo_put_name(argv->value);
294         for (i = 0; i < envc; envp++, i++) {
295                 tomoyo_put_name(envp->name);
296                 tomoyo_put_name(envp->value);
297         }
298 }
299 
300 /**
301  * tomoyo_del_name - Delete members in "struct tomoyo_name".
302  *
303  * @element: Pointer to "struct list_head".
304  *
305  * Returns nothing.
306  */
307 static inline void tomoyo_del_name(struct list_head *element)
308 {
309         /* Nothing to do. */
310 }
311 
312 /**
313  * tomoyo_del_path_group - Delete members in "struct tomoyo_path_group".
314  *
315  * @element: Pointer to "struct list_head".
316  *
317  * Returns nothing.
318  */
319 static inline void tomoyo_del_path_group(struct list_head *element)
320 {
321         struct tomoyo_path_group *member =
322                 container_of(element, typeof(*member), head.list);
323         tomoyo_put_name(member->member_name);
324 }
325 
326 /**
327  * tomoyo_del_group - Delete "struct tomoyo_group".
328  *
329  * @element: Pointer to "struct list_head".
330  *
331  * Returns nothing.
332  */
333 static inline void tomoyo_del_group(struct list_head *element)
334 {
335         struct tomoyo_group *group =
336                 container_of(element, typeof(*group), head.list);
337         tomoyo_put_name(group->group_name);
338 }
339 
340 /**
341  * tomoyo_del_address_group - Delete members in "struct tomoyo_address_group".
342  *
343  * @element: Pointer to "struct list_head".
344  *
345  * Returns nothing.
346  */
347 static inline void tomoyo_del_address_group(struct list_head *element)
348 {
349         /* Nothing to do. */
350 }
351 
352 /**
353  * tomoyo_del_number_group - Delete members in "struct tomoyo_number_group".
354  *
355  * @element: Pointer to "struct list_head".
356  *
357  * Returns nothing.
358  */
359 static inline void tomoyo_del_number_group(struct list_head *element)
360 {
361         /* Nothing to do. */
362 }
363 
364 /**
365  * tomoyo_try_to_gc - Try to kfree() an entry.
366  *
367  * @type:    One of values in "enum tomoyo_policy_id".
368  * @element: Pointer to "struct list_head".
369  *
370  * Returns nothing.
371  *
372  * Caller holds tomoyo_policy_lock mutex.
373  */
374 static void tomoyo_try_to_gc(const enum tomoyo_policy_id type,
375                              struct list_head *element)
376 {
377         /*
378          * __list_del_entry() guarantees that the list element became no longer
379          * reachable from the list which the element was originally on (e.g.
380          * tomoyo_domain_list). Also, synchronize_srcu() guarantees that the
381          * list element became no longer referenced by syscall users.
382          */
383         __list_del_entry(element);
384         mutex_unlock(&tomoyo_policy_lock);
385         synchronize_srcu(&tomoyo_ss);
386         /*
387          * However, there are two users which may still be using the list
388          * element. We need to defer until both users forget this element.
389          *
390          * Don't kfree() until "struct tomoyo_io_buffer"->r.{domain,group,acl}
391          * and "struct tomoyo_io_buffer"->w.domain forget this element.
392          */
393         if (tomoyo_struct_used_by_io_buffer(element))
394                 goto reinject;
395         switch (type) {
396         case TOMOYO_ID_TRANSITION_CONTROL:
397                 tomoyo_del_transition_control(element);
398                 break;
399         case TOMOYO_ID_MANAGER:
400                 tomoyo_del_manager(element);
401                 break;
402         case TOMOYO_ID_AGGREGATOR:
403                 tomoyo_del_aggregator(element);
404                 break;
405         case TOMOYO_ID_GROUP:
406                 tomoyo_del_group(element);
407                 break;
408         case TOMOYO_ID_PATH_GROUP:
409                 tomoyo_del_path_group(element);
410                 break;
411         case TOMOYO_ID_ADDRESS_GROUP:
412                 tomoyo_del_address_group(element);
413                 break;
414         case TOMOYO_ID_NUMBER_GROUP:
415                 tomoyo_del_number_group(element);
416                 break;
417         case TOMOYO_ID_CONDITION:
418                 tomoyo_del_condition(element);
419                 break;
420         case TOMOYO_ID_NAME:
421                 /*
422                  * Don't kfree() until all "struct tomoyo_io_buffer"->r.w[]
423                  * forget this element.
424                  */
425                 if (tomoyo_name_used_by_io_buffer
426                     (container_of(element, typeof(struct tomoyo_name),
427                                   head.list)->entry.name))
428                         goto reinject;
429                 tomoyo_del_name(element);
430                 break;
431         case TOMOYO_ID_ACL:
432                 tomoyo_del_acl(element);
433                 break;
434         case TOMOYO_ID_DOMAIN:
435                 /*
436                  * Don't kfree() until all "struct cred"->security forget this
437                  * element.
438                  */
439                 if (atomic_read(&container_of
440                                 (element, typeof(struct tomoyo_domain_info),
441                                  list)->users))
442                         goto reinject;
443                 break;
444         case TOMOYO_MAX_POLICY:
445                 break;
446         }
447         mutex_lock(&tomoyo_policy_lock);
448         if (type == TOMOYO_ID_DOMAIN)
449                 tomoyo_del_domain(element);
450         tomoyo_memory_free(element);
451         return;
452 reinject:
453         /*
454          * We can safely reinject this element here bacause
455          * (1) Appending list elements and removing list elements are protected
456          *     by tomoyo_policy_lock mutex.
457          * (2) Only this function removes list elements and this function is
458          *     exclusively executed by tomoyo_gc_mutex mutex.
459          * are true.
460          */
461         mutex_lock(&tomoyo_policy_lock);
462         list_add_rcu(element, element->prev);
463 }
464 
465 /**
466  * tomoyo_collect_member - Delete elements with "struct tomoyo_acl_head".
467  *
468  * @id:          One of values in "enum tomoyo_policy_id".
469  * @member_list: Pointer to "struct list_head".
470  *
471  * Returns nothing.
472  */
473 static void tomoyo_collect_member(const enum tomoyo_policy_id id,
474                                   struct list_head *member_list)
475 {
476         struct tomoyo_acl_head *member;
477         struct tomoyo_acl_head *tmp;
478         list_for_each_entry_safe(member, tmp, member_list, list) {
479                 if (!member->is_deleted)
480                         continue;
481                 member->is_deleted = TOMOYO_GC_IN_PROGRESS;
482                 tomoyo_try_to_gc(id, &member->list);
483         }
484 }
485 
486 /**
487  * tomoyo_collect_acl - Delete elements in "struct tomoyo_domain_info".
488  *
489  * @list: Pointer to "struct list_head".
490  *
491  * Returns nothing.
492  */
493 static void tomoyo_collect_acl(struct list_head *list)
494 {
495         struct tomoyo_acl_info *acl;
496         struct tomoyo_acl_info *tmp;
497         list_for_each_entry_safe(acl, tmp, list, list) {
498                 if (!acl->is_deleted)
499                         continue;
500                 acl->is_deleted = TOMOYO_GC_IN_PROGRESS;
501                 tomoyo_try_to_gc(TOMOYO_ID_ACL, &acl->list);
502         }
503 }
504 
505 /**
506  * tomoyo_collect_entry - Try to kfree() deleted elements.
507  *
508  * Returns nothing.
509  */
510 static void tomoyo_collect_entry(void)
511 {
512         int i;
513         enum tomoyo_policy_id id;
514         struct tomoyo_policy_namespace *ns;
515         mutex_lock(&tomoyo_policy_lock);
516         {
517                 struct tomoyo_domain_info *domain;
518                 struct tomoyo_domain_info *tmp;
519                 list_for_each_entry_safe(domain, tmp, &tomoyo_domain_list,
520                                          list) {
521                         tomoyo_collect_acl(&domain->acl_info_list);
522                         if (!domain->is_deleted || atomic_read(&domain->users))
523                                 continue;
524                         tomoyo_try_to_gc(TOMOYO_ID_DOMAIN, &domain->list);
525                 }
526         }
527         list_for_each_entry(ns, &tomoyo_namespace_list, namespace_list) {
528                 for (id = 0; id < TOMOYO_MAX_POLICY; id++)
529                         tomoyo_collect_member(id, &ns->policy_list[id]);
530                 for (i = 0; i < TOMOYO_MAX_ACL_GROUPS; i++)
531                         tomoyo_collect_acl(&ns->acl_group[i]);
532         }
533         {
534                 struct tomoyo_shared_acl_head *ptr;
535                 struct tomoyo_shared_acl_head *tmp;
536                 list_for_each_entry_safe(ptr, tmp, &tomoyo_condition_list,
537                                          list) {
538                         if (atomic_read(&ptr->users) > 0)
539                                 continue;
540                         atomic_set(&ptr->users, TOMOYO_GC_IN_PROGRESS);
541                         tomoyo_try_to_gc(TOMOYO_ID_CONDITION, &ptr->list);
542                 }
543         }
544         list_for_each_entry(ns, &tomoyo_namespace_list, namespace_list) {
545                 for (i = 0; i < TOMOYO_MAX_GROUP; i++) {
546                         struct list_head *list = &ns->group_list[i];
547                         struct tomoyo_group *group;
548                         struct tomoyo_group *tmp;
549                         switch (i) {
550                         case 0:
551                                 id = TOMOYO_ID_PATH_GROUP;
552                                 break;
553                         case 1:
554                                 id = TOMOYO_ID_NUMBER_GROUP;
555                                 break;
556                         default:
557                                 id = TOMOYO_ID_ADDRESS_GROUP;
558                                 break;
559                         }
560                         list_for_each_entry_safe(group, tmp, list, head.list) {
561                                 tomoyo_collect_member(id, &group->member_list);
562                                 if (!list_empty(&group->member_list) ||
563                                     atomic_read(&group->head.users) > 0)
564                                         continue;
565                                 atomic_set(&group->head.users,
566                                            TOMOYO_GC_IN_PROGRESS);
567                                 tomoyo_try_to_gc(TOMOYO_ID_GROUP,
568                                                  &group->head.list);
569                         }
570                 }
571         }
572         for (i = 0; i < TOMOYO_MAX_HASH; i++) {
573                 struct list_head *list = &tomoyo_name_list[i];
574                 struct tomoyo_shared_acl_head *ptr;
575                 struct tomoyo_shared_acl_head *tmp;
576                 list_for_each_entry_safe(ptr, tmp, list, list) {
577                         if (atomic_read(&ptr->users) > 0)
578                                 continue;
579                         atomic_set(&ptr->users, TOMOYO_GC_IN_PROGRESS);
580                         tomoyo_try_to_gc(TOMOYO_ID_NAME, &ptr->list);
581                 }
582         }
583         mutex_unlock(&tomoyo_policy_lock);
584 }
585 
586 /**
587  * tomoyo_gc_thread - Garbage collector thread function.
588  *
589  * @unused: Unused.
590  *
591  * Returns 0.
592  */
593 static int tomoyo_gc_thread(void *unused)
594 {
595         /* Garbage collector thread is exclusive. */
596         static DEFINE_MUTEX(tomoyo_gc_mutex);
597         if (!mutex_trylock(&tomoyo_gc_mutex))
598                 goto out;
599         tomoyo_collect_entry();
600         {
601                 struct tomoyo_io_buffer *head;
602                 struct tomoyo_io_buffer *tmp;
603 
604                 spin_lock(&tomoyo_io_buffer_list_lock);
605                 list_for_each_entry_safe(head, tmp, &tomoyo_io_buffer_list,
606                                          list) {
607                         if (head->users)
608                                 continue;
609                         list_del(&head->list);
610                         kfree(head->read_buf);
611                         kfree(head->write_buf);
612                         kfree(head);
613                 }
614                 spin_unlock(&tomoyo_io_buffer_list_lock);
615         }
616         mutex_unlock(&tomoyo_gc_mutex);
617 out:
618         /* This acts as do_exit(0). */
619         return 0;
620 }
621 
622 /**
623  * tomoyo_notify_gc - Register/unregister /sys/kernel/security/tomoyo/ users.
624  *
625  * @head:        Pointer to "struct tomoyo_io_buffer".
626  * @is_register: True if register, false if unregister.
627  *
628  * Returns nothing.
629  */
630 void tomoyo_notify_gc(struct tomoyo_io_buffer *head, const bool is_register)
631 {
632         bool is_write = false;
633 
634         spin_lock(&tomoyo_io_buffer_list_lock);
635         if (is_register) {
636                 head->users = 1;
637                 list_add(&head->list, &tomoyo_io_buffer_list);
638         } else {
639                 is_write = head->write_buf != NULL;
640                 if (!--head->users) {
641                         list_del(&head->list);
642                         kfree(head->read_buf);
643                         kfree(head->write_buf);
644                         kfree(head);
645                 }
646         }
647         spin_unlock(&tomoyo_io_buffer_list_lock);
648         if (is_write) {
649                 struct task_struct *task = kthread_create(tomoyo_gc_thread,
650                                                           NULL,
651                                                           "GC for TOMOYO");
652                 if (!IS_ERR(task))
653                         wake_up_process(task);
654         }
655 }
656 

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