security/keys/keyring.c

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