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