security/keys/keyring.c

   1 /* Keyring handling
   2  *
   3  * Copyright (C) 2004-2005, 2008 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 <keys/keyring-type.h>
  20 #include <asm/uaccess.h>
  21 #include "internal.h"
  22
  23 /*
  24  * when plumbing the depths of the key tree, this sets a hard limit set on how
  25  * deep we're willing to go
  26  */
  27 #define KEYRING_SEARCH_MAX_DEPTH 6
  28
  29 /*
  30  * we keep all named keyrings in a hash to speed looking them up
  31  */
  32 #define KEYRING_NAME_HASH_SIZE  (1 << 5)
  33
  34 static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
  35 static DEFINE_RWLOCK(keyring_name_lock);
  36
  37 static inline unsigned keyring_hash(const char *desc)
  38 {
  39         unsigned bucket = 0;
  40
  41         for (; *desc; desc++)
  42                 bucket += (unsigned char) *desc;
  43
  44         return bucket & (KEYRING_NAME_HASH_SIZE - 1);
  45 }
  46
  47 /*
  48  * the keyring type definition
  49  */
  50 static int keyring_instantiate(struct key *keyring,
  51                                const void *data, size_t datalen);
  52 static int keyring_match(const struct key *keyring, const void *criterion);
  53 static void keyring_revoke(struct key *keyring);
  54 static void keyring_destroy(struct key *keyring);
  55 static void keyring_describe(const struct key *keyring, struct seq_file *m);
  56 static long keyring_read(const struct key *keyring,
  57                          char __user *buffer, size_t buflen);
  58
  59 struct key_type key_type_keyring = {
  60         .name           = "keyring",
  61         .def_datalen    = sizeof(struct keyring_list),
  62         .instantiate    = keyring_instantiate,
  63         .match          = keyring_match,
  64         .revoke         = keyring_revoke,
  65         .destroy        = keyring_destroy,
  66         .describe       = keyring_describe,
  67         .read           = keyring_read,
  68 };
  69
  70 EXPORT_SYMBOL(key_type_keyring);
  71
  72 /*
  73  * semaphore to serialise link/link calls to prevent two link calls in parallel
  74  * introducing a cycle
  75  */
  76 static DECLARE_RWSEM(keyring_serialise_link_sem);
  77
  78 /*****************************************************************************/
  79 /*
  80  * publish the name of a keyring so that it can be found by name (if it has
  81  * one)
  82  */
  83 static void keyring_publish_name(struct key *keyring)
  84 {
  85         int bucket;
  86
  87         if (keyring->description) {
  88                 bucket = keyring_hash(keyring->description);
  89
  90                 write_lock(&keyring_name_lock);
  91
  92                 if (!keyring_name_hash[bucket].next)
  93                         INIT_LIST_HEAD(&keyring_name_hash[bucket]);
  94
  95                 list_add_tail(&keyring->type_data.link,
  96                               &keyring_name_hash[bucket]);
  97
  98                 write_unlock(&keyring_name_lock);
  99         }
 100
 101 } /* end keyring_publish_name() */
 102
 103 /*****************************************************************************/
 104 /*
 105  * initialise a keyring
 106  * - we object if we were given any data
 107  */
 108 static int keyring_instantiate(struct key *keyring,
 109                                const void *data, size_t datalen)
 110 {
 111         int ret;
 112
 113         ret = -EINVAL;
 114         if (datalen == 0) {
 115                 /* make the keyring available by name if it has one */
 116                 keyring_publish_name(keyring);
 117                 ret = 0;
 118         }
 119
 120         return ret;
 121
 122 } /* end keyring_instantiate() */
 123
 124 /*****************************************************************************/
 125 /*
 126  * match keyrings on their name
 127  */
 128 static int keyring_match(const struct key *keyring, const void *description)
 129 {
 130         return keyring->description &&
 131                 strcmp(keyring->description, description) == 0;
 132
 133 } /* end keyring_match() */
 134
 135 /*****************************************************************************/
 136 /*
 137  * dispose of the data dangling from the corpse of a keyring
 138  */
 139 static void keyring_destroy(struct key *keyring)
 140 {
 141         struct keyring_list *klist;
 142         int loop;
 143
 144         if (keyring->description) {
 145                 write_lock(&keyring_name_lock);
 146
 147                 if (keyring->type_data.link.next != NULL &&
 148                     !list_empty(&keyring->type_data.link))
 149                         list_del(&keyring->type_data.link);
 150
 151                 write_unlock(&keyring_name_lock);
 152         }
 153
 154         klist = rcu_dereference(keyring->payload.subscriptions);
 155         if (klist) {
 156                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
 157                         key_put(klist->keys[loop]);
 158                 kfree(klist);
 159         }
 160
 161 } /* end keyring_destroy() */
 162
 163 /*****************************************************************************/
 164 /*
 165  * describe the keyring
 166  */
 167 static void keyring_describe(const struct key *keyring, struct seq_file *m)
 168 {
 169         struct keyring_list *klist;
 170
 171         if (keyring->description) {
 172                 seq_puts(m, keyring->description);
 173         }
 174         else {
 175                 seq_puts(m, "[anon]");
 176         }
 177
 178         rcu_read_lock();
 179         klist = rcu_dereference(keyring->payload.subscriptions);
 180         if (klist)
 181                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
 182         else
 183                 seq_puts(m, ": empty");
 184         rcu_read_unlock();
 185
 186 } /* end keyring_describe() */
 187
 188 /*****************************************************************************/
 189 /*
 190  * read a list of key IDs from the keyring's contents
 191  * - the keyring's semaphore is read-locked
 192  */
 193 static long keyring_read(const struct key *keyring,
 194                          char __user *buffer, size_t buflen)
 195 {
 196         struct keyring_list *klist;
 197         struct key *key;
 198         size_t qty, tmp;
 199         int loop, ret;
 200
 201         ret = 0;
 202         klist = rcu_dereference(keyring->payload.subscriptions);
 203
 204         if (klist) {
 205                 /* calculate how much data we could return */
 206                 qty = klist->nkeys * sizeof(key_serial_t);
 207
 208                 if (buffer && buflen > 0) {
 209                         if (buflen > qty)
 210                                 buflen = qty;
 211
 212                         /* copy the IDs of the subscribed keys into the
 213                          * buffer */
 214                         ret = -EFAULT;
 215
 216                         for (loop = 0; loop < klist->nkeys; loop++) {
 217                                 key = klist->keys[loop];
 218
 219                                 tmp = sizeof(key_serial_t);
 220                                 if (tmp > buflen)
 221                                         tmp = buflen;
 222
 223                                 if (copy_to_user(buffer,
 224                                                  &key->serial,
 225                                                  tmp) != 0)
 226                                         goto error;
 227
 228                                 buflen -= tmp;
 229                                 if (buflen == 0)
 230                                         break;
 231                                 buffer += tmp;
 232                         }
 233                 }
 234
 235                 ret = qty;
 236         }
 237
 238  error:
 239         return ret;
 240
 241 } /* end keyring_read() */
 242
 243 /*****************************************************************************/
 244 /*
 245  * allocate a keyring and link into the destination keyring
 246  */
 247 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
 248                           const struct cred *cred, unsigned long flags,
 249                           struct key *dest)
 250 {
 251         struct key *keyring;
 252         int ret;
 253
 254         keyring = key_alloc(&key_type_keyring, description,
 255                             uid, gid, cred,
 256                             (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
 257                             flags);
 258
 259         if (!IS_ERR(keyring)) {
 260                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
 261                 if (ret < 0) {
 262                         key_put(keyring);
 263                         keyring = ERR_PTR(ret);
 264                 }
 265         }
 266
 267         return keyring;
 268
 269 } /* end keyring_alloc() */
 270
 271 /*****************************************************************************/
 272 /*
 273  * search the supplied keyring tree for a key that matches the criterion
 274  * - perform a breadth-then-depth search up to the prescribed limit
 275  * - we only find keys on which we have search permission
 276  * - we use the supplied match function to see if the description (or other
 277  *   feature of interest) matches
 278  * - we rely on RCU to prevent the keyring lists from disappearing on us
 279  * - we return -EAGAIN if we didn't find any matching key
 280  * - we return -ENOKEY if we only found negative matching keys
 281  * - we propagate the possession attribute from the keyring ref to the key ref
 282  */
 283 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
 284                              const struct cred *cred,
 285                              struct key_type *type,
 286                              const void *description,
 287                              key_match_func_t match)
 288 {
 289         struct {
 290                 struct keyring_list *keylist;
 291                 int kix;
 292         } stack[KEYRING_SEARCH_MAX_DEPTH];
 293
 294         struct keyring_list *keylist;
 295         struct timespec now;
 296         unsigned long possessed, kflags;
 297         struct key *keyring, *key;
 298         key_ref_t key_ref;
 299         long err;
 300         int sp, kix;
 301
 302         keyring = key_ref_to_ptr(keyring_ref);
 303         possessed = is_key_possessed(keyring_ref);
 304         key_check(keyring);
 305
 306         /* top keyring must have search permission to begin the search */
 307         err = key_task_permission(keyring_ref, cred, KEY_SEARCH);
 308         if (err < 0) {
 309                 key_ref = ERR_PTR(err);
 310                 goto error;
 311         }
 312
 313         key_ref = ERR_PTR(-ENOTDIR);
 314         if (keyring->type != &key_type_keyring)
 315                 goto error;
 316
 317         rcu_read_lock();
 318
 319         now = current_kernel_time();
 320         err = -EAGAIN;
 321         sp = 0;
 322
 323         /* firstly we should check to see if this top-level keyring is what we
 324          * are looking for */
 325         key_ref = ERR_PTR(-EAGAIN);
 326         kflags = keyring->flags;
 327         if (keyring->type == type && match(keyring, description)) {
 328                 key = keyring;
 329
 330                 /* check it isn't negative and hasn't expired or been
 331                  * revoked */
 332                 if (kflags & (1 << KEY_FLAG_REVOKED))
 333                         goto error_2;
 334                 if (key->expiry && now.tv_sec >= key->expiry)
 335                         goto error_2;
 336                 key_ref = ERR_PTR(-ENOKEY);
 337                 if (kflags & (1 << KEY_FLAG_NEGATIVE))
 338                         goto error_2;
 339                 goto found;
 340         }
 341
 342         /* otherwise, the top keyring must not be revoked, expired, or
 343          * negatively instantiated if we are to search it */
 344         key_ref = ERR_PTR(-EAGAIN);
 345         if (kflags & ((1 << KEY_FLAG_REVOKED) | (1 << KEY_FLAG_NEGATIVE)) ||
 346             (keyring->expiry && now.tv_sec >= keyring->expiry))
 347                 goto error_2;
 348
 349         /* start processing a new keyring */
 350 descend:
 351         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 352                 goto not_this_keyring;
 353
 354         keylist = rcu_dereference(keyring->payload.subscriptions);
 355         if (!keylist)
 356                 goto not_this_keyring;
 357
 358         /* iterate through the keys in this keyring first */
 359         for (kix = 0; kix < keylist->nkeys; kix++) {
 360                 key = keylist->keys[kix];
 361                 kflags = key->flags;
 362
 363                 /* ignore keys not of this type */
 364                 if (key->type != type)
 365                         continue;
 366
 367                 /* skip revoked keys and expired keys */
 368                 if (kflags & (1 << KEY_FLAG_REVOKED))
 369                         continue;
 370
 371                 if (key->expiry && now.tv_sec >= key->expiry)
 372                         continue;
 373
 374                 /* keys that don't match */
 375                 if (!match(key, description))
 376                         continue;
 377
 378                 /* key must have search permissions */
 379                 if (key_task_permission(make_key_ref(key, possessed),
 380                                         cred, KEY_SEARCH) < 0)
 381                         continue;
 382
 383                 /* we set a different error code if we pass a negative key */
 384                 if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
 385                         err = -ENOKEY;
 386                         continue;
 387                 }
 388
 389                 goto found;
 390         }
 391
 392         /* search through the keyrings nested in this one */
 393         kix = 0;
 394 ascend:
 395         for (; kix < keylist->nkeys; kix++) {
 396                 key = keylist->keys[kix];
 397                 if (key->type != &key_type_keyring)
 398                         continue;
 399
 400                 /* recursively search nested keyrings
 401                  * - only search keyrings for which we have search permission
 402                  */
 403                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 404                         continue;
 405
 406                 if (key_task_permission(make_key_ref(key, possessed),
 407                                         cred, KEY_SEARCH) < 0)
 408                         continue;
 409
 410                 /* stack the current position */
 411                 stack[sp].keylist = keylist;
 412                 stack[sp].kix = kix;
 413                 sp++;
 414
 415                 /* begin again with the new keyring */
 416                 keyring = key;
 417                 goto descend;
 418         }
 419
 420         /* the keyring we're looking at was disqualified or didn't contain a
 421          * matching key */
 422 not_this_keyring:
 423         if (sp > 0) {
 424                 /* resume the processing of a keyring higher up in the tree */
 425                 sp--;
 426                 keylist = stack[sp].keylist;
 427                 kix = stack[sp].kix + 1;
 428                 goto ascend;
 429         }
 430
 431         key_ref = ERR_PTR(err);
 432         goto error_2;
 433
 434         /* we found a viable match */
 435 found:
 436         atomic_inc(&key->usage);
 437         key_check(key);
 438         key_ref = make_key_ref(key, possessed);
 439 error_2:
 440         rcu_read_unlock();
 441 error:
 442         return key_ref;
 443
 444 } /* end keyring_search_aux() */
 445
 446 /*****************************************************************************/
 447 /*
 448  * search the supplied keyring tree for a key that matches the criterion
 449  * - perform a breadth-then-depth search up to the prescribed limit
 450  * - we only find keys on which we have search permission
 451  * - we readlock the keyrings as we search down the tree
 452  * - we return -EAGAIN if we didn't find any matching key
 453  * - we return -ENOKEY if we only found negative matching keys
 454  */
 455 key_ref_t keyring_search(key_ref_t keyring,
 456                          struct key_type *type,
 457                          const char *description)
 458 {
 459         if (!type->match)
 460                 return ERR_PTR(-ENOKEY);
 461
 462         return keyring_search_aux(keyring, current->cred,
 463                                   type, description, type->match);
 464
 465 } /* end keyring_search() */
 466
 467 EXPORT_SYMBOL(keyring_search);
 468
 469 /*****************************************************************************/
 470 /*
 471  * search the given keyring only (no recursion)
 472  * - keyring must be locked by caller
 473  * - caller must guarantee that the keyring is a keyring
 474  */
 475 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
 476                                const struct key_type *ktype,
 477                                const char *description,
 478                                key_perm_t perm)
 479 {
 480         struct keyring_list *klist;
 481         unsigned long possessed;
 482         struct key *keyring, *key;
 483         int loop;
 484
 485         keyring = key_ref_to_ptr(keyring_ref);
 486         possessed = is_key_possessed(keyring_ref);
 487
 488         rcu_read_lock();
 489
 490         klist = rcu_dereference(keyring->payload.subscriptions);
 491         if (klist) {
 492                 for (loop = 0; loop < klist->nkeys; loop++) {
 493                         key = klist->keys[loop];
 494
 495                         if (key->type == ktype &&
 496                             (!key->type->match ||
 497                              key->type->match(key, description)) &&
 498                             key_permission(make_key_ref(key, possessed),
 499                                            perm) == 0 &&
 500                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
 501                             )
 502                                 goto found;
 503                 }
 504         }
 505
 506         rcu_read_unlock();
 507         return ERR_PTR(-ENOKEY);
 508
 509  found:
 510         atomic_inc(&key->usage);
 511         rcu_read_unlock();
 512         return make_key_ref(key, possessed);
 513
 514 } /* end __keyring_search_one() */
 515
 516 /*****************************************************************************/
 517 /*
 518  * find a keyring with the specified name
 519  * - all named keyrings are searched
 520  * - normally only finds keyrings with search permission for the current process
 521  */
 522 struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
 523 {
 524         struct key *keyring;
 525         int bucket;
 526
 527         keyring = ERR_PTR(-EINVAL);
 528         if (!name)
 529                 goto error;
 530
 531         bucket = keyring_hash(name);
 532
 533         read_lock(&keyring_name_lock);
 534
 535         if (keyring_name_hash[bucket].next) {
 536                 /* search this hash bucket for a keyring with a matching name
 537                  * that's readable and that hasn't been revoked */
 538                 list_for_each_entry(keyring,
 539                                     &keyring_name_hash[bucket],
 540                                     type_data.link
 541                                     ) {
 542                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 543                                 continue;
 544
 545                         if (strcmp(keyring->description, name) != 0)
 546                                 continue;
 547
 548                         if (!skip_perm_check &&
 549                             key_permission(make_key_ref(keyring, 0),
 550                                            KEY_SEARCH) < 0)
 551                                 continue;
 552
 553                         /* we've got a match */
 554                         atomic_inc(&keyring->usage);
 555                         read_unlock(&keyring_name_lock);
 556                         goto error;
 557                 }
 558         }
 559
 560         read_unlock(&keyring_name_lock);
 561         keyring = ERR_PTR(-ENOKEY);
 562
 563  error:
 564         return keyring;
 565
 566 } /* end find_keyring_by_name() */
 567
 568 /*****************************************************************************/
 569 /*
 570  * see if a cycle will will be created by inserting acyclic tree B in acyclic
 571  * tree A at the topmost level (ie: as a direct child of A)
 572  * - since we are adding B to A at the top level, checking for cycles should
 573  *   just be a matter of seeing if node A is somewhere in tree B
 574  */
 575 static int keyring_detect_cycle(struct key *A, struct key *B)
 576 {
 577         struct {
 578                 struct keyring_list *keylist;
 579                 int kix;
 580         } stack[KEYRING_SEARCH_MAX_DEPTH];
 581
 582         struct keyring_list *keylist;
 583         struct key *subtree, *key;
 584         int sp, kix, ret;
 585
 586         rcu_read_lock();
 587
 588         ret = -EDEADLK;
 589         if (A == B)
 590                 goto cycle_detected;
 591
 592         subtree = B;
 593         sp = 0;
 594
 595         /* start processing a new keyring */
 596  descend:
 597         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
 598                 goto not_this_keyring;
 599
 600         keylist = rcu_dereference(subtree->payload.subscriptions);
 601         if (!keylist)
 602                 goto not_this_keyring;
 603         kix = 0;
 604
 605  ascend:
 606         /* iterate through the remaining keys in this keyring */
 607         for (; kix < keylist->nkeys; kix++) {
 608                 key = keylist->keys[kix];
 609
 610                 if (key == A)
 611                         goto cycle_detected;
 612
 613                 /* recursively check nested keyrings */
 614                 if (key->type == &key_type_keyring) {
 615                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 616                                 goto too_deep;
 617
 618                         /* stack the current position */
 619                         stack[sp].keylist = keylist;
 620                         stack[sp].kix = kix;
 621                         sp++;
 622
 623                         /* begin again with the new keyring */
 624                         subtree = key;
 625                         goto descend;
 626                 }
 627         }
 628
 629         /* the keyring we're looking at was disqualified or didn't contain a
 630          * matching key */
 631  not_this_keyring:
 632         if (sp > 0) {
 633                 /* resume the checking of a keyring higher up in the tree */
 634                 sp--;
 635                 keylist = stack[sp].keylist;
 636                 kix = stack[sp].kix + 1;
 637                 goto ascend;
 638         }
 639
 640         ret = 0; /* no cycles detected */
 641
 642  error:
 643         rcu_read_unlock();
 644         return ret;
 645
 646  too_deep:
 647         ret = -ELOOP;
 648         goto error;
 649
 650  cycle_detected:
 651         ret = -EDEADLK;
 652         goto error;
 653
 654 } /* end keyring_detect_cycle() */
 655
 656 /*****************************************************************************/
 657 /*
 658  * dispose of a keyring list after the RCU grace period
 659  */
 660 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
 661 {
 662         struct keyring_list *klist =
 663                 container_of(rcu, struct keyring_list, rcu);
 664
 665         kfree(klist);
 666
 667 } /* end keyring_link_rcu_disposal() */
 668
 669 /*****************************************************************************/
 670 /*
 671  * dispose of a keyring list after the RCU grace period, freeing the unlinked
 672  * key
 673  */
 674 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
 675 {
 676         struct keyring_list *klist =
 677                 container_of(rcu, struct keyring_list, rcu);
 678
 679         key_put(klist->keys[klist->delkey]);
 680         kfree(klist);
 681
 682 } /* end keyring_unlink_rcu_disposal() */
 683
 684 /*****************************************************************************/
 685 /*
 686  * link a key into to a keyring
 687  * - must be called with the keyring's semaphore write-locked
 688  * - discard already extant link to matching key if there is one
 689  */
 690 int __key_link(struct key *keyring, struct key *key)
 691 {
 692         struct keyring_list *klist, *nklist;
 693         unsigned max;
 694         size_t size;
 695         int loop, ret;
 696
 697         ret = -EKEYREVOKED;
 698         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 699                 goto error;
 700
 701         ret = -ENOTDIR;
 702         if (keyring->type != &key_type_keyring)
 703                 goto error;
 704
 705         /* serialise link/link calls to prevent parallel calls causing a
 706          * cycle when applied to two keyring in opposite orders */
 707         down_write(&keyring_serialise_link_sem);
 708
 709         /* check that we aren't going to create a cycle adding one keyring to
 710          * another */
 711         if (key->type == &key_type_keyring) {
 712                 ret = keyring_detect_cycle(keyring, key);
 713                 if (ret < 0)
 714                         goto error2;
 715         }
 716
 717         /* see if there's a matching key we can displace */
 718         klist = keyring->payload.subscriptions;
 719
 720         if (klist && klist->nkeys > 0) {
 721                 struct key_type *type = key->type;
 722
 723                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
 724                         if (klist->keys[loop]->type == type &&
 725                             strcmp(klist->keys[loop]->description,
 726                                    key->description) == 0
 727                             ) {
 728                                 /* found a match - replace with new key */
 729                                 size = sizeof(struct key *) * klist->maxkeys;
 730                                 size += sizeof(*klist);
 731                                 BUG_ON(size > PAGE_SIZE);
 732
 733                                 ret = -ENOMEM;
 734                                 nklist = kmemdup(klist, size, GFP_KERNEL);
 735                                 if (!nklist)
 736                                         goto error2;
 737
 738                                 /* replace matched key */
 739                                 atomic_inc(&key->usage);
 740                                 nklist->keys[loop] = key;
 741
 742                                 rcu_assign_pointer(
 743                                         keyring->payload.subscriptions,
 744                                         nklist);
 745
 746                                 /* dispose of the old keyring list and the
 747                                  * displaced key */
 748                                 klist->delkey = loop;
 749                                 call_rcu(&klist->rcu,
 750                                          keyring_unlink_rcu_disposal);
 751
 752                                 goto done;
 753                         }
 754                 }
 755         }
 756
 757         /* check that we aren't going to overrun the user's quota */
 758         ret = key_payload_reserve(keyring,
 759                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
 760         if (ret < 0)
 761                 goto error2;
 762
 763         klist = keyring->payload.subscriptions;
 764
 765         if (klist && klist->nkeys < klist->maxkeys) {
 766                 /* there's sufficient slack space to add directly */
 767                 atomic_inc(&key->usage);
 768
 769                 klist->keys[klist->nkeys] = key;
 770                 smp_wmb();
 771                 klist->nkeys++;
 772                 smp_wmb();
 773         }
 774         else {
 775                 /* grow the key list */
 776                 max = 4;
 777                 if (klist)
 778                         max += klist->maxkeys;
 779
 780                 ret = -ENFILE;
 781                 if (max > 65535)
 782                         goto error3;
 783                 size = sizeof(*klist) + sizeof(struct key *) * max;
 784                 if (size > PAGE_SIZE)
 785                         goto error3;
 786
 787                 ret = -ENOMEM;
 788                 nklist = kmalloc(size, GFP_KERNEL);
 789                 if (!nklist)
 790                         goto error3;
 791                 nklist->maxkeys = max;
 792                 nklist->nkeys = 0;
 793
 794                 if (klist) {
 795                         nklist->nkeys = klist->nkeys;
 796                         memcpy(nklist->keys,
 797                                klist->keys,
 798                                sizeof(struct key *) * klist->nkeys);
 799                 }
 800
 801                 /* add the key into the new space */
 802                 atomic_inc(&key->usage);
 803                 nklist->keys[nklist->nkeys++] = key;
 804
 805                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 806
 807                 /* dispose of the old keyring list */
 808                 if (klist)
 809                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
 810         }
 811
 812 done:
 813         ret = 0;
 814 error2:
 815         up_write(&keyring_serialise_link_sem);
 816 error:
 817         return ret;
 818
 819 error3:
 820         /* undo the quota changes */
 821         key_payload_reserve(keyring,
 822                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 823         goto error2;
 824
 825 } /* end __key_link() */
 826
 827 /*****************************************************************************/
 828 /*
 829  * link a key to a keyring
 830  */
 831 int key_link(struct key *keyring, struct key *key)
 832 {
 833         int ret;
 834
 835         key_check(keyring);
 836         key_check(key);
 837
 838         down_write(&keyring->sem);
 839         ret = __key_link(keyring, key);
 840         up_write(&keyring->sem);
 841
 842         return ret;
 843
 844 } /* end key_link() */
 845
 846 EXPORT_SYMBOL(key_link);
 847
 848 /*****************************************************************************/
 849 /*
 850  * unlink the first link to a key from a keyring
 851  */
 852 int key_unlink(struct key *keyring, struct key *key)
 853 {
 854         struct keyring_list *klist, *nklist;
 855         int loop, ret;
 856
 857         key_check(keyring);
 858         key_check(key);
 859
 860         ret = -ENOTDIR;
 861         if (keyring->type != &key_type_keyring)
 862                 goto error;
 863
 864         down_write(&keyring->sem);
 865
 866         klist = keyring->payload.subscriptions;
 867         if (klist) {
 868                 /* search the keyring for the key */
 869                 for (loop = 0; loop < klist->nkeys; loop++)
 870                         if (klist->keys[loop] == key)
 871                                 goto key_is_present;
 872         }
 873
 874         up_write(&keyring->sem);
 875         ret = -ENOENT;
 876         goto error;
 877
 878 key_is_present:
 879         /* we need to copy the key list for RCU purposes */
 880         nklist = kmalloc(sizeof(*klist) +
 881                          sizeof(struct key *) * klist->maxkeys,
 882                          GFP_KERNEL);
 883         if (!nklist)
 884                 goto nomem;
 885         nklist->maxkeys = klist->maxkeys;
 886         nklist->nkeys = klist->nkeys - 1;
 887
 888         if (loop > 0)
 889                 memcpy(&nklist->keys[0],
 890                        &klist->keys[0],
 891                        loop * sizeof(struct key *));
 892
 893         if (loop < nklist->nkeys)
 894                 memcpy(&nklist->keys[loop],
 895                        &klist->keys[loop + 1],
 896                        (nklist->nkeys - loop) * sizeof(struct key *));
 897
 898         /* adjust the user's quota */
 899         key_payload_reserve(keyring,
 900                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 901
 902         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 903
 904         up_write(&keyring->sem);
 905
 906         /* schedule for later cleanup */
 907         klist->delkey = loop;
 908         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
 909
 910         ret = 0;
 911
 912 error:
 913         return ret;
 914 nomem:
 915         ret = -ENOMEM;
 916         up_write(&keyring->sem);
 917         goto error;
 918
 919 } /* end key_unlink() */
 920
 921 EXPORT_SYMBOL(key_unlink);
 922
 923 /*****************************************************************************/
 924 /*
 925  * dispose of a keyring list after the RCU grace period, releasing the keys it
 926  * links to
 927  */
 928 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
 929 {
 930         struct keyring_list *klist;
 931         int loop;
 932
 933         klist = container_of(rcu, struct keyring_list, rcu);
 934
 935         for (loop = klist->nkeys - 1; loop >= 0; loop--)
 936                 key_put(klist->keys[loop]);
 937
 938         kfree(klist);
 939
 940 } /* end keyring_clear_rcu_disposal() */
 941
 942 /*****************************************************************************/
 943 /*
 944  * clear the specified process keyring
 945  * - implements keyctl(KEYCTL_CLEAR)
 946  */
 947 int keyring_clear(struct key *keyring)
 948 {
 949         struct keyring_list *klist;
 950         int ret;
 951
 952         ret = -ENOTDIR;
 953         if (keyring->type == &key_type_keyring) {
 954                 /* detach the pointer block with the locks held */
 955                 down_write(&keyring->sem);
 956
 957                 klist = keyring->payload.subscriptions;
 958                 if (klist) {
 959                         /* adjust the quota */
 960                         key_payload_reserve(keyring,
 961                                             sizeof(struct keyring_list));
 962
 963                         rcu_assign_pointer(keyring->payload.subscriptions,
 964                                            NULL);
 965                 }
 966
 967                 up_write(&keyring->sem);
 968
 969                 /* free the keys after the locks have been dropped */
 970                 if (klist)
 971                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
 972
 973                 ret = 0;
 974         }
 975
 976         return ret;
 977
 978 } /* end keyring_clear() */
 979
 980 EXPORT_SYMBOL(keyring_clear);
 981
 982 /*****************************************************************************/
 983 /*
 984  * dispose of the links from a revoked keyring
 985  * - called with the key sem write-locked
 986  */
 987 static void keyring_revoke(struct key *keyring)
 988 {
 989         struct keyring_list *klist = keyring->payload.subscriptions;
 990
 991         /* adjust the quota */
 992         key_payload_reserve(keyring, 0);
 993
 994         if (klist) {
 995                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
 996                 call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
 997         }
 998
 999 } /* end keyring_revoke() */