security/keys/keyring.c

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