security/tomoyo/gc.c

   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 }