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