security/keys/keyring.c

   1 /* keyring.c: keyring handling
   2  *
   3  * Copyright (C) 2004-5 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/init.h>
  14 #include <linux/sched.h>
  15 #include <linux/slab.h>
  16 #include <linux/seq_file.h>
  17 #include <linux/err.h>
  18 #include <asm/uaccess.h>
  19 #include "internal.h"
  20
  21 /*
  22  * when plumbing the depths of the key tree, this sets a hard limit set on how
  23  * deep we're willing to go
  24  */
  25 #define KEYRING_SEARCH_MAX_DEPTH 6
  26
  27 /*
  28  * we keep all named keyrings in a hash to speed looking them up
  29  */
  30 #define KEYRING_NAME_HASH_SIZE  (1 << 5)
  31
  32 static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
  33 static DEFINE_RWLOCK(keyring_name_lock);
  34
  35 static inline unsigned keyring_hash(const char *desc)
  36 {
  37         unsigned bucket = 0;
  38
  39         for (; *desc; desc++)
  40                 bucket += (unsigned char) *desc;
  41
  42         return bucket & (KEYRING_NAME_HASH_SIZE - 1);
  43 }
  44
  45 /*
  46  * the keyring type definition
  47  */
  48 static int keyring_instantiate(struct key *keyring,
  49                                const void *data, size_t datalen);
  50 static int keyring_duplicate(struct key *keyring, const struct key *source);
  51 static int keyring_match(const struct key *keyring, const void *criterion);
  52 static void keyring_destroy(struct key *keyring);
  53 static void keyring_describe(const struct key *keyring, struct seq_file *m);
  54 static long keyring_read(const struct key *keyring,
  55                          char __user *buffer, size_t buflen);
  56
  57 struct key_type key_type_keyring = {
  58         .name           = "keyring",
  59         .def_datalen    = sizeof(struct keyring_list),
  60         .instantiate    = keyring_instantiate,
  61         .duplicate      = keyring_duplicate,
  62         .match          = keyring_match,
  63         .destroy        = keyring_destroy,
  64         .describe       = keyring_describe,
  65         .read           = keyring_read,
  66 };
  67
  68 /*
  69  * semaphore to serialise link/link calls to prevent two link calls in parallel
  70  * introducing a cycle
  71  */
  72 DECLARE_RWSEM(keyring_serialise_link_sem);
  73
  74 /*****************************************************************************/
  75 /*
  76  * publish the name of a keyring so that it can be found by name (if it has
  77  * one)
  78  */
  79 void keyring_publish_name(struct key *keyring)
  80 {
  81         int bucket;
  82
  83         if (keyring->description) {
  84                 bucket = keyring_hash(keyring->description);
  85
  86                 write_lock(&keyring_name_lock);
  87
  88                 if (!keyring_name_hash[bucket].next)
  89                         INIT_LIST_HEAD(&keyring_name_hash[bucket]);
  90
  91                 list_add_tail(&keyring->type_data.link,
  92                               &keyring_name_hash[bucket]);
  93
  94                 write_unlock(&keyring_name_lock);
  95         }
  96
  97 } /* end keyring_publish_name() */
  98
  99 /*****************************************************************************/
 100 /*
 101  * initialise a keyring
 102  * - we object if we were given any data
 103  */
 104 static int keyring_instantiate(struct key *keyring,
 105                                const void *data, size_t datalen)
 106 {
 107         int ret;
 108
 109         ret = -EINVAL;
 110         if (datalen == 0) {
 111                 /* make the keyring available by name if it has one */
 112                 keyring_publish_name(keyring);
 113                 ret = 0;
 114         }
 115
 116         return ret;
 117
 118 } /* end keyring_instantiate() */
 119
 120 /*****************************************************************************/
 121 /*
 122  * duplicate the list of subscribed keys from a source keyring into this one
 123  */
 124 static int keyring_duplicate(struct key *keyring, const struct key *source)
 125 {
 126         struct keyring_list *sklist, *klist;
 127         unsigned max;
 128         size_t size;
 129         int loop, ret;
 130
 131         const unsigned limit =
 132                 (PAGE_SIZE - sizeof(*klist)) / sizeof(struct key *);
 133
 134         ret = 0;
 135
 136         /* find out how many keys are currently linked */
 137         rcu_read_lock();
 138         sklist = rcu_dereference(source->payload.subscriptions);
 139         max = 0;
 140         if (sklist)
 141                 max = sklist->nkeys;
 142         rcu_read_unlock();
 143
 144         /* allocate a new payload and stuff load with key links */
 145         if (max > 0) {
 146                 BUG_ON(max > limit);
 147
 148                 max = (max + 3) & ~3;
 149                 if (max > limit)
 150                         max = limit;
 151
 152                 ret = -ENOMEM;
 153                 size = sizeof(*klist) + sizeof(struct key *) * max;
 154                 klist = kmalloc(size, GFP_KERNEL);
 155                 if (!klist)
 156                         goto error;
 157
 158                 /* set links */
 159                 rcu_read_lock();
 160                 sklist = rcu_dereference(source->payload.subscriptions);
 161
 162                 klist->maxkeys = max;
 163                 klist->nkeys = sklist->nkeys;
 164                 memcpy(klist->keys,
 165                        sklist->keys,
 166                        sklist->nkeys * sizeof(struct key *));
 167
 168                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
 169                         atomic_inc(&klist->keys[loop]->usage);
 170
 171                 rcu_read_unlock();
 172
 173                 rcu_assign_pointer(keyring->payload.subscriptions, klist);
 174                 ret = 0;
 175         }
 176
 177  error:
 178         return ret;
 179
 180 } /* end keyring_duplicate() */
 181
 182 /*****************************************************************************/
 183 /*
 184  * match keyrings on their name
 185  */
 186 static int keyring_match(const struct key *keyring, const void *description)
 187 {
 188         return keyring->description &&
 189                 strcmp(keyring->description, description) == 0;
 190
 191 } /* end keyring_match() */
 192
 193 /*****************************************************************************/
 194 /*
 195  * dispose of the data dangling from the corpse of a keyring
 196  */
 197 static void keyring_destroy(struct key *keyring)
 198 {
 199         struct keyring_list *klist;
 200         int loop;
 201
 202         if (keyring->description) {
 203                 write_lock(&keyring_name_lock);
 204
 205                 if (keyring->type_data.link.next != NULL &&
 206                     !list_empty(&keyring->type_data.link))
 207                         list_del(&keyring->type_data.link);
 208
 209                 write_unlock(&keyring_name_lock);
 210         }
 211
 212         klist = rcu_dereference(keyring->payload.subscriptions);
 213         if (klist) {
 214                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
 215                         key_put(klist->keys[loop]);
 216                 kfree(klist);
 217         }
 218
 219 } /* end keyring_destroy() */
 220
 221 /*****************************************************************************/
 222 /*
 223  * describe the keyring
 224  */
 225 static void keyring_describe(const struct key *keyring, struct seq_file *m)
 226 {
 227         struct keyring_list *klist;
 228
 229         if (keyring->description) {
 230                 seq_puts(m, keyring->description);
 231         }
 232         else {
 233                 seq_puts(m, "[anon]");
 234         }
 235
 236         rcu_read_lock();
 237         klist = rcu_dereference(keyring->payload.subscriptions);
 238         if (klist)
 239                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
 240         else
 241                 seq_puts(m, ": empty");
 242         rcu_read_unlock();
 243
 244 } /* end keyring_describe() */
 245
 246 /*****************************************************************************/
 247 /*
 248  * read a list of key IDs from the keyring's contents
 249  * - the keyring's semaphore is read-locked
 250  */
 251 static long keyring_read(const struct key *keyring,
 252                          char __user *buffer, size_t buflen)
 253 {
 254         struct keyring_list *klist;
 255         struct key *key;
 256         size_t qty, tmp;
 257         int loop, ret;
 258
 259         ret = 0;
 260         klist = rcu_dereference(keyring->payload.subscriptions);
 261
 262         if (klist) {
 263                 /* calculate how much data we could return */
 264                 qty = klist->nkeys * sizeof(key_serial_t);
 265
 266                 if (buffer && buflen > 0) {
 267                         if (buflen > qty)
 268                                 buflen = qty;
 269
 270                         /* copy the IDs of the subscribed keys into the
 271                          * buffer */
 272                         ret = -EFAULT;
 273
 274                         for (loop = 0; loop < klist->nkeys; loop++) {
 275                                 key = klist->keys[loop];
 276
 277                                 tmp = sizeof(key_serial_t);
 278                                 if (tmp > buflen)
 279                                         tmp = buflen;
 280
 281                                 if (copy_to_user(buffer,
 282                                                  &key->serial,
 283                                                  tmp) != 0)
 284                                         goto error;
 285
 286                                 buflen -= tmp;
 287                                 if (buflen == 0)
 288                                         break;
 289                                 buffer += tmp;
 290                         }
 291                 }
 292
 293                 ret = qty;
 294         }
 295
 296  error:
 297         return ret;
 298
 299 } /* end keyring_read() */
 300
 301 /*****************************************************************************/
 302 /*
 303  * allocate a keyring and link into the destination keyring
 304  */
 305 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
 306                           int not_in_quota, struct key *dest)
 307 {
 308         struct key *keyring;
 309         int ret;
 310
 311         keyring = key_alloc(&key_type_keyring, description,
 312                             uid, gid, KEY_POS_ALL | KEY_USR_ALL, not_in_quota);
 313
 314         if (!IS_ERR(keyring)) {
 315                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
 316                 if (ret < 0) {
 317                         key_put(keyring);
 318                         keyring = ERR_PTR(ret);
 319                 }
 320         }
 321
 322         return keyring;
 323
 324 } /* end keyring_alloc() */
 325
 326 /*****************************************************************************/
 327 /*
 328  * search the supplied keyring tree for a key that matches the criterion
 329  * - perform a breadth-then-depth search up to the prescribed limit
 330  * - we only find keys on which we have search permission
 331  * - we use the supplied match function to see if the description (or other
 332  *   feature of interest) matches
 333  * - we rely on RCU to prevent the keyring lists from disappearing on us
 334  * - we return -EAGAIN if we didn't find any matching key
 335  * - we return -ENOKEY if we only found negative matching keys
 336  * - we propagate the possession attribute from the keyring ref to the key ref
 337  */
 338 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
 339                              struct task_struct *context,
 340                              struct key_type *type,
 341                              const void *description,
 342                              key_match_func_t match)
 343 {
 344         struct {
 345                 struct keyring_list *keylist;
 346                 int kix;
 347         } stack[KEYRING_SEARCH_MAX_DEPTH];
 348
 349         struct keyring_list *keylist;
 350         struct timespec now;
 351         unsigned long possessed;
 352         struct key *keyring, *key;
 353         key_ref_t key_ref;
 354         long err;
 355         int sp, kix;
 356
 357         keyring = key_ref_to_ptr(keyring_ref);
 358         possessed = is_key_possessed(keyring_ref);
 359         key_check(keyring);
 360
 361         /* top keyring must have search permission to begin the search */
 362         key_ref = ERR_PTR(-EACCES);
 363         if (!key_task_permission(keyring_ref, context, KEY_SEARCH))
 364                 goto error;
 365
 366         key_ref = ERR_PTR(-ENOTDIR);
 367         if (keyring->type != &key_type_keyring)
 368                 goto error;
 369
 370         rcu_read_lock();
 371
 372         now = current_kernel_time();
 373         err = -EAGAIN;
 374         sp = 0;
 375
 376         /* start processing a new keyring */
 377 descend:
 378         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 379                 goto not_this_keyring;
 380
 381         keylist = rcu_dereference(keyring->payload.subscriptions);
 382         if (!keylist)
 383                 goto not_this_keyring;
 384
 385         /* iterate through the keys in this keyring first */
 386         for (kix = 0; kix < keylist->nkeys; kix++) {
 387                 key = keylist->keys[kix];
 388
 389                 /* ignore keys not of this type */
 390                 if (key->type != type)
 391                         continue;
 392
 393                 /* skip revoked keys and expired keys */
 394                 if (test_bit(KEY_FLAG_REVOKED, &key->flags))
 395                         continue;
 396
 397                 if (key->expiry && now.tv_sec >= key->expiry)
 398                         continue;
 399
 400                 /* keys that don't match */
 401                 if (!match(key, description))
 402                         continue;
 403
 404                 /* key must have search permissions */
 405                 if (!key_task_permission(make_key_ref(key, possessed),
 406                                          context, KEY_SEARCH))
 407                         continue;
 408
 409                 /* we set a different error code if we find a negative key */
 410                 if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
 411                         err = -ENOKEY;
 412                         continue;
 413                 }
 414
 415                 goto found;
 416         }
 417
 418         /* search through the keyrings nested in this one */
 419         kix = 0;
 420 ascend:
 421         for (; kix < keylist->nkeys; kix++) {
 422                 key = keylist->keys[kix];
 423                 if (key->type != &key_type_keyring)
 424                         continue;
 425
 426                 /* recursively search nested keyrings
 427                  * - only search keyrings for which we have search permission
 428                  */
 429                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 430                         continue;
 431
 432                 if (!key_task_permission(make_key_ref(key, possessed),
 433                                          context, KEY_SEARCH))
 434                         continue;
 435
 436                 /* stack the current position */
 437                 stack[sp].keylist = keylist;
 438                 stack[sp].kix = kix;
 439                 sp++;
 440
 441                 /* begin again with the new keyring */
 442                 keyring = key;
 443                 goto descend;
 444         }
 445
 446         /* the keyring we're looking at was disqualified or didn't contain a
 447          * matching key */
 448 not_this_keyring:
 449         if (sp > 0) {
 450                 /* resume the processing of a keyring higher up in the tree */
 451                 sp--;
 452                 keylist = stack[sp].keylist;
 453                 kix = stack[sp].kix + 1;
 454                 goto ascend;
 455         }
 456
 457         key_ref = ERR_PTR(err);
 458         goto error_2;
 459
 460         /* we found a viable match */
 461 found:
 462         atomic_inc(&key->usage);
 463         key_check(key);
 464         key_ref = make_key_ref(key, possessed);
 465 error_2:
 466         rcu_read_unlock();
 467 error:
 468         return key_ref;
 469
 470 } /* end keyring_search_aux() */
 471
 472 /*****************************************************************************/
 473 /*
 474  * search the supplied keyring tree for a key that matches the criterion
 475  * - perform a breadth-then-depth search up to the prescribed limit
 476  * - we only find keys on which we have search permission
 477  * - we readlock the keyrings as we search down the tree
 478  * - we return -EAGAIN if we didn't find any matching key
 479  * - we return -ENOKEY if we only found negative matching keys
 480  */
 481 key_ref_t keyring_search(key_ref_t keyring,
 482                          struct key_type *type,
 483                          const char *description)
 484 {
 485         if (!type->match)
 486                 return ERR_PTR(-ENOKEY);
 487
 488         return keyring_search_aux(keyring, current,
 489                                   type, description, type->match);
 490
 491 } /* end keyring_search() */
 492
 493 EXPORT_SYMBOL(keyring_search);
 494
 495 /*****************************************************************************/
 496 /*
 497  * search the given keyring only (no recursion)
 498  * - keyring must be locked by caller
 499  */
 500 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
 501                                const struct key_type *ktype,
 502                                const char *description,
 503                                key_perm_t perm)
 504 {
 505         struct keyring_list *klist;
 506         unsigned long possessed;
 507         struct key *keyring, *key;
 508         int loop;
 509
 510         keyring = key_ref_to_ptr(keyring_ref);
 511         possessed = is_key_possessed(keyring_ref);
 512
 513         rcu_read_lock();
 514
 515         klist = rcu_dereference(keyring->payload.subscriptions);
 516         if (klist) {
 517                 for (loop = 0; loop < klist->nkeys; loop++) {
 518                         key = klist->keys[loop];
 519
 520                         if (key->type == ktype &&
 521                             (!key->type->match ||
 522                              key->type->match(key, description)) &&
 523                             key_permission(make_key_ref(key, possessed),
 524                                            perm) &&
 525                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
 526                             )
 527                                 goto found;
 528                 }
 529         }
 530
 531         rcu_read_unlock();
 532         return ERR_PTR(-ENOKEY);
 533
 534  found:
 535         atomic_inc(&key->usage);
 536         rcu_read_unlock();
 537         return make_key_ref(key, possessed);
 538
 539 } /* end __keyring_search_one() */
 540
 541 /*****************************************************************************/
 542 /*
 543  * search for an instantiation authorisation key matching a target key
 544  * - the RCU read lock must be held by the caller
 545  * - a target_id of zero specifies any valid token
 546  */
 547 struct key *keyring_search_instkey(struct key *keyring,
 548                                    key_serial_t target_id)
 549 {
 550         struct request_key_auth *rka;
 551         struct keyring_list *klist;
 552         struct key *instkey;
 553         int loop;
 554
 555         klist = rcu_dereference(keyring->payload.subscriptions);
 556         if (klist) {
 557                 for (loop = 0; loop < klist->nkeys; loop++) {
 558                         instkey = klist->keys[loop];
 559
 560                         if (instkey->type != &key_type_request_key_auth)
 561                                 continue;
 562
 563                         rka = instkey->payload.data;
 564                         if (target_id && rka->target_key->serial != target_id)
 565                                 continue;
 566
 567                         /* the auth key is revoked during instantiation */
 568                         if (!test_bit(KEY_FLAG_REVOKED, &instkey->flags))
 569                                 goto found;
 570
 571                         instkey = ERR_PTR(-EKEYREVOKED);
 572                         goto error;
 573                 }
 574         }
 575
 576         instkey = ERR_PTR(-EACCES);
 577         goto error;
 578
 579 found:
 580         atomic_inc(&instkey->usage);
 581 error:
 582         return instkey;
 583
 584 } /* end keyring_search_instkey() */
 585
 586 /*****************************************************************************/
 587 /*
 588  * find a keyring with the specified name
 589  * - all named keyrings are searched
 590  * - only find keyrings with search permission for the process
 591  * - only find keyrings with a serial number greater than the one specified
 592  */
 593 struct key *find_keyring_by_name(const char *name, key_serial_t bound)
 594 {
 595         struct key *keyring;
 596         int bucket;
 597
 598         keyring = ERR_PTR(-EINVAL);
 599         if (!name)
 600                 goto error;
 601
 602         bucket = keyring_hash(name);
 603
 604         read_lock(&keyring_name_lock);
 605
 606         if (keyring_name_hash[bucket].next) {
 607                 /* search this hash bucket for a keyring with a matching name
 608                  * that's readable and that hasn't been revoked */
 609                 list_for_each_entry(keyring,
 610                                     &keyring_name_hash[bucket],
 611                                     type_data.link
 612                                     ) {
 613                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 614                                 continue;
 615
 616                         if (strcmp(keyring->description, name) != 0)
 617                                 continue;
 618
 619                         if (!key_permission(make_key_ref(keyring, 0),
 620                                             KEY_SEARCH))
 621                                 continue;
 622
 623                         /* found a potential candidate, but we still need to
 624                          * check the serial number */
 625                         if (keyring->serial <= bound)
 626                                 continue;
 627
 628                         /* we've got a match */
 629                         atomic_inc(&keyring->usage);
 630                         read_unlock(&keyring_name_lock);
 631                         goto error;
 632                 }
 633         }
 634
 635         read_unlock(&keyring_name_lock);
 636         keyring = ERR_PTR(-ENOKEY);
 637
 638  error:
 639         return keyring;
 640
 641 } /* end find_keyring_by_name() */
 642
 643 /*****************************************************************************/
 644 /*
 645  * see if a cycle will will be created by inserting acyclic tree B in acyclic
 646  * tree A at the topmost level (ie: as a direct child of A)
 647  * - since we are adding B to A at the top level, checking for cycles should
 648  *   just be a matter of seeing if node A is somewhere in tree B
 649  */
 650 static int keyring_detect_cycle(struct key *A, struct key *B)
 651 {
 652         struct {
 653                 struct keyring_list *keylist;
 654                 int kix;
 655         } stack[KEYRING_SEARCH_MAX_DEPTH];
 656
 657         struct keyring_list *keylist;
 658         struct key *subtree, *key;
 659         int sp, kix, ret;
 660
 661         rcu_read_lock();
 662
 663         ret = -EDEADLK;
 664         if (A == B)
 665                 goto cycle_detected;
 666
 667         subtree = B;
 668         sp = 0;
 669
 670         /* start processing a new keyring */
 671  descend:
 672         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
 673                 goto not_this_keyring;
 674
 675         keylist = rcu_dereference(subtree->payload.subscriptions);
 676         if (!keylist)
 677                 goto not_this_keyring;
 678         kix = 0;
 679
 680  ascend:
 681         /* iterate through the remaining keys in this keyring */
 682         for (; kix < keylist->nkeys; kix++) {
 683                 key = keylist->keys[kix];
 684
 685                 if (key == A)
 686                         goto cycle_detected;
 687
 688                 /* recursively check nested keyrings */
 689                 if (key->type == &key_type_keyring) {
 690                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 691                                 goto too_deep;
 692
 693                         /* stack the current position */
 694                         stack[sp].keylist = keylist;
 695                         stack[sp].kix = kix;
 696                         sp++;
 697
 698                         /* begin again with the new keyring */
 699                         subtree = key;
 700                         goto descend;
 701                 }
 702         }
 703
 704         /* the keyring we're looking at was disqualified or didn't contain a
 705          * matching key */
 706  not_this_keyring:
 707         if (sp > 0) {
 708                 /* resume the checking of a keyring higher up in the tree */
 709                 sp--;
 710                 keylist = stack[sp].keylist;
 711                 kix = stack[sp].kix + 1;
 712                 goto ascend;
 713         }
 714
 715         ret = 0; /* no cycles detected */
 716
 717  error:
 718         rcu_read_unlock();
 719         return ret;
 720
 721  too_deep:
 722         ret = -ELOOP;
 723         goto error;
 724
 725  cycle_detected:
 726         ret = -EDEADLK;
 727         goto error;
 728
 729 } /* end keyring_detect_cycle() */
 730
 731 /*****************************************************************************/
 732 /*
 733  * dispose of a keyring list after the RCU grace period
 734  */
 735 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
 736 {
 737         struct keyring_list *klist =
 738                 container_of(rcu, struct keyring_list, rcu);
 739
 740         kfree(klist);
 741
 742 } /* end keyring_link_rcu_disposal() */
 743
 744 /*****************************************************************************/
 745 /*
 746  * link a key into to a keyring
 747  * - must be called with the keyring's semaphore write-locked
 748  */
 749 int __key_link(struct key *keyring, struct key *key)
 750 {
 751         struct keyring_list *klist, *nklist;
 752         unsigned max;
 753         size_t size;
 754         int ret;
 755
 756         ret = -EKEYREVOKED;
 757         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 758                 goto error;
 759
 760         ret = -ENOTDIR;
 761         if (keyring->type != &key_type_keyring)
 762                 goto error;
 763
 764         /* serialise link/link calls to prevent parallel calls causing a
 765          * cycle when applied to two keyring in opposite orders */
 766         down_write(&keyring_serialise_link_sem);
 767
 768         /* check that we aren't going to create a cycle adding one keyring to
 769          * another */
 770         if (key->type == &key_type_keyring) {
 771                 ret = keyring_detect_cycle(keyring, key);
 772                 if (ret < 0)
 773                         goto error2;
 774         }
 775
 776         /* check that we aren't going to overrun the user's quota */
 777         ret = key_payload_reserve(keyring,
 778                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
 779         if (ret < 0)
 780                 goto error2;
 781
 782         klist = keyring->payload.subscriptions;
 783
 784         if (klist && klist->nkeys < klist->maxkeys) {
 785                 /* there's sufficient slack space to add directly */
 786                 atomic_inc(&key->usage);
 787
 788                 klist->keys[klist->nkeys] = key;
 789                 smp_wmb();
 790                 klist->nkeys++;
 791                 smp_wmb();
 792
 793                 ret = 0;
 794         }
 795         else {
 796                 /* grow the key list */
 797                 max = 4;
 798                 if (klist)
 799                         max += klist->maxkeys;
 800
 801                 ret = -ENFILE;
 802                 if (max > 65535)
 803                         goto error3;
 804                 size = sizeof(*klist) + sizeof(struct key *) * max;
 805                 if (size > PAGE_SIZE)
 806                         goto error3;
 807
 808                 ret = -ENOMEM;
 809                 nklist = kmalloc(size, GFP_KERNEL);
 810                 if (!nklist)
 811                         goto error3;
 812                 nklist->maxkeys = max;
 813                 nklist->nkeys = 0;
 814
 815                 if (klist) {
 816                         nklist->nkeys = klist->nkeys;
 817                         memcpy(nklist->keys,
 818                                klist->keys,
 819                                sizeof(struct key *) * klist->nkeys);
 820                 }
 821
 822                 /* add the key into the new space */
 823                 atomic_inc(&key->usage);
 824                 nklist->keys[nklist->nkeys++] = key;
 825
 826                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 827
 828                 /* dispose of the old keyring list */
 829                 if (klist)
 830                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
 831
 832                 ret = 0;
 833         }
 834
 835  error2:
 836         up_write(&keyring_serialise_link_sem);
 837  error:
 838         return ret;
 839
 840  error3:
 841         /* undo the quota changes */
 842         key_payload_reserve(keyring,
 843                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 844         goto error2;
 845
 846 } /* end __key_link() */
 847
 848 /*****************************************************************************/
 849 /*
 850  * link a key to a keyring
 851  */
 852 int key_link(struct key *keyring, struct key *key)
 853 {
 854         int ret;
 855
 856         key_check(keyring);
 857         key_check(key);
 858
 859         down_write(&keyring->sem);
 860         ret = __key_link(keyring, key);
 861         up_write(&keyring->sem);
 862
 863         return ret;
 864
 865 } /* end key_link() */
 866
 867 EXPORT_SYMBOL(key_link);
 868
 869 /*****************************************************************************/
 870 /*
 871  * dispose of a keyring list after the RCU grace period, freeing the unlinked
 872  * key
 873  */
 874 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
 875 {
 876         struct keyring_list *klist =
 877                 container_of(rcu, struct keyring_list, rcu);
 878
 879         key_put(klist->keys[klist->delkey]);
 880         kfree(klist);
 881
 882 } /* end keyring_unlink_rcu_disposal() */
 883
 884 /*****************************************************************************/
 885 /*
 886  * unlink the first link to a key from a keyring
 887  */
 888 int key_unlink(struct key *keyring, struct key *key)
 889 {
 890         struct keyring_list *klist, *nklist;
 891         int loop, ret;
 892
 893         key_check(keyring);
 894         key_check(key);
 895
 896         ret = -ENOTDIR;
 897         if (keyring->type != &key_type_keyring)
 898                 goto error;
 899
 900         down_write(&keyring->sem);
 901
 902         klist = keyring->payload.subscriptions;
 903         if (klist) {
 904                 /* search the keyring for the key */
 905                 for (loop = 0; loop < klist->nkeys; loop++)
 906                         if (klist->keys[loop] == key)
 907                                 goto key_is_present;
 908         }
 909
 910         up_write(&keyring->sem);
 911         ret = -ENOENT;
 912         goto error;
 913
 914 key_is_present:
 915         /* we need to copy the key list for RCU purposes */
 916         nklist = kmalloc(sizeof(*klist) +
 917                          sizeof(struct key *) * klist->maxkeys,
 918                          GFP_KERNEL);
 919         if (!nklist)
 920                 goto nomem;
 921         nklist->maxkeys = klist->maxkeys;
 922         nklist->nkeys = klist->nkeys - 1;
 923
 924         if (loop > 0)
 925                 memcpy(&nklist->keys[0],
 926                        &klist->keys[0],
 927                        loop * sizeof(struct key *));
 928
 929         if (loop < nklist->nkeys)
 930                 memcpy(&nklist->keys[loop],
 931                        &klist->keys[loop + 1],
 932                        (nklist->nkeys - loop) * sizeof(struct key *));
 933
 934         /* adjust the user's quota */
 935         key_payload_reserve(keyring,
 936                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 937
 938         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 939
 940         up_write(&keyring->sem);
 941
 942         /* schedule for later cleanup */
 943         klist->delkey = loop;
 944         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
 945
 946         ret = 0;
 947
 948 error:
 949         return ret;
 950 nomem:
 951         ret = -ENOMEM;
 952         up_write(&keyring->sem);
 953         goto error;
 954
 955 } /* end key_unlink() */
 956
 957 EXPORT_SYMBOL(key_unlink);
 958
 959 /*****************************************************************************/
 960 /*
 961  * dispose of a keyring list after the RCU grace period, releasing the keys it
 962  * links to
 963  */
 964 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
 965 {
 966         struct keyring_list *klist;
 967         int loop;
 968
 969         klist = container_of(rcu, struct keyring_list, rcu);
 970
 971         for (loop = klist->nkeys - 1; loop >= 0; loop--)
 972                 key_put(klist->keys[loop]);
 973
 974         kfree(klist);
 975
 976 } /* end keyring_clear_rcu_disposal() */
 977
 978 /*****************************************************************************/
 979 /*
 980  * clear the specified process keyring
 981  * - implements keyctl(KEYCTL_CLEAR)
 982  */
 983 int keyring_clear(struct key *keyring)
 984 {
 985         struct keyring_list *klist;
 986         int ret;
 987
 988         ret = -ENOTDIR;
 989         if (keyring->type == &key_type_keyring) {
 990                 /* detach the pointer block with the locks held */
 991                 down_write(&keyring->sem);
 992
 993                 klist = keyring->payload.subscriptions;
 994                 if (klist) {
 995                         /* adjust the quota */
 996                         key_payload_reserve(keyring,
 997                                             sizeof(struct keyring_list));
 998
 999                         rcu_assign_pointer(keyring->payload.subscriptions,
1000                                            NULL);
1001                 }
1002
1003                 up_write(&keyring->sem);
1004
1005                 /* free the keys after the locks have been dropped */
1006                 if (klist)
1007                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1008
1009                 ret = 0;
1010         }
1011
1012         return ret;
1013
1014 } /* end keyring_clear() */
1015
1016 EXPORT_SYMBOL(keyring_clear);