security/keys/keyring.c

   1 /* keyring.c: keyring handling
   2  *
   3  * Copyright (C) 2004 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);
 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 readlock the keyrings as we search down the tree
 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 key_type *type,
 335                                const void *description,
 336                                key_match_func_t match)
 337 {
 338         struct {
 339                 struct keyring_list *keylist;
 340                 int kix;
 341         } stack[KEYRING_SEARCH_MAX_DEPTH];
 342
 343         struct keyring_list *keylist;
 344         struct timespec now;
 345         struct key *key;
 346         long err;
 347         int sp, kix;
 348
 349         key_check(keyring);
 350
 351         rcu_read_lock();
 352
 353         /* top keyring must have search permission to begin the search */
 354         key = ERR_PTR(-EACCES);
 355         if (!key_permission(keyring, KEY_SEARCH))
 356                 goto error;
 357
 358         key = ERR_PTR(-ENOTDIR);
 359         if (keyring->type != &key_type_keyring)
 360                 goto error;
 361
 362         now = current_kernel_time();
 363         err = -EAGAIN;
 364         sp = 0;
 365
 366         /* start processing a new keyring */
 367  descend:
 368         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 369                 goto not_this_keyring;
 370
 371         keylist = rcu_dereference(keyring->payload.subscriptions);
 372         if (!keylist)
 373                 goto not_this_keyring;
 374
 375         /* iterate through the keys in this keyring first */
 376         for (kix = 0; kix < keylist->nkeys; kix++) {
 377                 key = keylist->keys[kix];
 378
 379                 /* ignore keys not of this type */
 380                 if (key->type != type)
 381                         continue;
 382
 383                 /* skip revoked keys and expired keys */
 384                 if (test_bit(KEY_FLAG_REVOKED, &key->flags))
 385                         continue;
 386
 387                 if (key->expiry && now.tv_sec >= key->expiry)
 388                         continue;
 389
 390                 /* keys that don't match */
 391                 if (!match(key, description))
 392                         continue;
 393
 394                 /* key must have search permissions */
 395                 if (!key_permission(key, KEY_SEARCH))
 396                         continue;
 397
 398                 /* we set a different error code if we find a negative key */
 399                 if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
 400                         err = -ENOKEY;
 401                         continue;
 402                 }
 403
 404                 goto found;
 405         }
 406
 407         /* search through the keyrings nested in this one */
 408         kix = 0;
 409  ascend:
 410         for (; kix < keylist->nkeys; kix++) {
 411                 key = keylist->keys[kix];
 412                 if (key->type != &key_type_keyring)
 413                         continue;
 414
 415                 /* recursively search nested keyrings
 416                  * - only search keyrings for which we have search permission
 417                  */
 418                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 419                         continue;
 420
 421                 if (!key_permission(key, KEY_SEARCH))
 422                         continue;
 423
 424                 /* stack the current position */
 425                 stack[sp].keylist = keylist;
 426                 stack[sp].kix = kix;
 427                 sp++;
 428
 429                 /* begin again with the new keyring */
 430                 keyring = key;
 431                 goto descend;
 432         }
 433
 434         /* the keyring we're looking at was disqualified or didn't contain a
 435          * matching key */
 436  not_this_keyring:
 437         if (sp > 0) {
 438                 /* resume the processing of a keyring higher up in the tree */
 439                 sp--;
 440                 keylist = stack[sp].keylist;
 441                 kix = stack[sp].kix + 1;
 442                 goto ascend;
 443         }
 444
 445         key = ERR_PTR(err);
 446         goto error;
 447
 448         /* we found a viable match */
 449  found:
 450         atomic_inc(&key->usage);
 451         key_check(key);
 452  error:
 453         rcu_read_unlock();
 454         return key;
 455
 456 } /* end keyring_search_aux() */
 457
 458 /*****************************************************************************/
 459 /*
 460  * search the supplied keyring tree for a key that matches the criterion
 461  * - perform a breadth-then-depth search up to the prescribed limit
 462  * - we only find keys on which we have search permission
 463  * - we readlock the keyrings as we search down the tree
 464  * - we return -EAGAIN if we didn't find any matching key
 465  * - we return -ENOKEY if we only found negative matching keys
 466  */
 467 struct key *keyring_search(struct key *keyring,
 468                            struct key_type *type,
 469                            const char *description)
 470 {
 471         return keyring_search_aux(keyring, type, description, type->match);
 472
 473 } /* end keyring_search() */
 474
 475 EXPORT_SYMBOL(keyring_search);
 476
 477 /*****************************************************************************/
 478 /*
 479  * search the given keyring only (no recursion)
 480  * - keyring must be locked by caller
 481  */
 482 struct key *__keyring_search_one(struct key *keyring,
 483                                  const struct key_type *ktype,
 484                                  const char *description,
 485                                  key_perm_t perm)
 486 {
 487         struct keyring_list *klist;
 488         struct key *key;
 489         int loop;
 490
 491         rcu_read_lock();
 492
 493         klist = rcu_dereference(keyring->payload.subscriptions);
 494         if (klist) {
 495                 for (loop = 0; loop < klist->nkeys; loop++) {
 496                         key = klist->keys[loop];
 497
 498                         if (key->type == ktype &&
 499                             key->type->match(key, description) &&
 500                             key_permission(key, perm) &&
 501                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
 502                             )
 503                                 goto found;
 504                 }
 505         }
 506
 507         key = ERR_PTR(-ENOKEY);
 508         goto error;
 509
 510  found:
 511         atomic_inc(&key->usage);
 512  error:
 513         rcu_read_unlock();
 514         return key;
 515
 516 } /* end __keyring_search_one() */
 517
 518 /*****************************************************************************/
 519 /*
 520  * find a keyring with the specified name
 521  * - all named keyrings are searched
 522  * - only find keyrings with search permission for the process
 523  * - only find keyrings with a serial number greater than the one specified
 524  */
 525 struct key *find_keyring_by_name(const char *name, key_serial_t bound)
 526 {
 527         struct key *keyring;
 528         int bucket;
 529
 530         keyring = ERR_PTR(-EINVAL);
 531         if (!name)
 532                 goto error;
 533
 534         bucket = keyring_hash(name);
 535
 536         read_lock(&keyring_name_lock);
 537
 538         if (keyring_name_hash[bucket].next) {
 539                 /* search this hash bucket for a keyring with a matching name
 540                  * that's readable and that hasn't been revoked */
 541                 list_for_each_entry(keyring,
 542                                     &keyring_name_hash[bucket],
 543                                     type_data.link
 544                                     ) {
 545                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 546                                 continue;
 547
 548                         if (strcmp(keyring->description, name) != 0)
 549                                 continue;
 550
 551                         if (!key_permission(keyring, KEY_SEARCH))
 552                                 continue;
 553
 554                         /* found a potential candidate, but we still need to
 555                          * check the serial number */
 556                         if (keyring->serial <= bound)
 557                                 continue;
 558
 559                         /* we've got a match */
 560                         atomic_inc(&keyring->usage);
 561                         read_unlock(&keyring_name_lock);
 562                         goto error;
 563                 }
 564         }
 565
 566         read_unlock(&keyring_name_lock);
 567         keyring = ERR_PTR(-ENOKEY);
 568
 569  error:
 570         return keyring;
 571
 572 } /* end find_keyring_by_name() */
 573
 574 /*****************************************************************************/
 575 /*
 576  * see if a cycle will will be created by inserting acyclic tree B in acyclic
 577  * tree A at the topmost level (ie: as a direct child of A)
 578  * - since we are adding B to A at the top level, checking for cycles should
 579  *   just be a matter of seeing if node A is somewhere in tree B
 580  */
 581 static int keyring_detect_cycle(struct key *A, struct key *B)
 582 {
 583         struct {
 584                 struct keyring_list *keylist;
 585                 int kix;
 586         } stack[KEYRING_SEARCH_MAX_DEPTH];
 587
 588         struct keyring_list *keylist;
 589         struct key *subtree, *key;
 590         int sp, kix, ret;
 591
 592         rcu_read_lock();
 593
 594         ret = -EDEADLK;
 595         if (A == B)
 596                 goto cycle_detected;
 597
 598         subtree = B;
 599         sp = 0;
 600
 601         /* start processing a new keyring */
 602  descend:
 603         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
 604                 goto not_this_keyring;
 605
 606         keylist = rcu_dereference(subtree->payload.subscriptions);
 607         if (!keylist)
 608                 goto not_this_keyring;
 609         kix = 0;
 610
 611  ascend:
 612         /* iterate through the remaining keys in this keyring */
 613         for (; kix < keylist->nkeys; kix++) {
 614                 key = keylist->keys[kix];
 615
 616                 if (key == A)
 617                         goto cycle_detected;
 618
 619                 /* recursively check nested keyrings */
 620                 if (key->type == &key_type_keyring) {
 621                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 622                                 goto too_deep;
 623
 624                         /* stack the current position */
 625                         stack[sp].keylist = keylist;
 626                         stack[sp].kix = kix;
 627                         sp++;
 628
 629                         /* begin again with the new keyring */
 630                         subtree = key;
 631                         goto descend;
 632                 }
 633         }
 634
 635         /* the keyring we're looking at was disqualified or didn't contain a
 636          * matching key */
 637  not_this_keyring:
 638         if (sp > 0) {
 639                 /* resume the checking of a keyring higher up in the tree */
 640                 sp--;
 641                 keylist = stack[sp].keylist;
 642                 kix = stack[sp].kix + 1;
 643                 goto ascend;
 644         }
 645
 646         ret = 0; /* no cycles detected */
 647
 648  error:
 649         rcu_read_unlock();
 650         return ret;
 651
 652  too_deep:
 653         ret = -ELOOP;
 654         goto error;
 655
 656  cycle_detected:
 657         ret = -EDEADLK;
 658         goto error;
 659
 660 } /* end keyring_detect_cycle() */
 661
 662 /*****************************************************************************/
 663 /*
 664  * dispose of a keyring list after the RCU grace period
 665  */
 666 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
 667 {
 668         struct keyring_list *klist =
 669                 container_of(rcu, struct keyring_list, rcu);
 670
 671         kfree(klist);
 672
 673 } /* end keyring_link_rcu_disposal() */
 674
 675 /*****************************************************************************/
 676 /*
 677  * link a key into to a keyring
 678  * - must be called with the keyring's semaphore write-locked
 679  */
 680 int __key_link(struct key *keyring, struct key *key)
 681 {
 682         struct keyring_list *klist, *nklist;
 683         unsigned max;
 684         size_t size;
 685         int ret;
 686
 687         ret = -EKEYREVOKED;
 688         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 689                 goto error;
 690
 691         ret = -ENOTDIR;
 692         if (keyring->type != &key_type_keyring)
 693                 goto error;
 694
 695         /* serialise link/link calls to prevent parallel calls causing a
 696          * cycle when applied to two keyring in opposite orders */
 697         down_write(&keyring_serialise_link_sem);
 698
 699         /* check that we aren't going to create a cycle adding one keyring to
 700          * another */
 701         if (key->type == &key_type_keyring) {
 702                 ret = keyring_detect_cycle(keyring, key);
 703                 if (ret < 0)
 704                         goto error2;
 705         }
 706
 707         /* check that we aren't going to overrun the user's quota */
 708         ret = key_payload_reserve(keyring,
 709                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
 710         if (ret < 0)
 711                 goto error2;
 712
 713         klist = keyring->payload.subscriptions;
 714
 715         if (klist && klist->nkeys < klist->maxkeys) {
 716                 /* there's sufficient slack space to add directly */
 717                 atomic_inc(&key->usage);
 718
 719                 klist->keys[klist->nkeys] = key;
 720                 smp_wmb();
 721                 klist->nkeys++;
 722                 smp_wmb();
 723
 724                 ret = 0;
 725         }
 726         else {
 727                 /* grow the key list */
 728                 max = 4;
 729                 if (klist)
 730                         max += klist->maxkeys;
 731
 732                 ret = -ENFILE;
 733                 if (max > 65535)
 734                         goto error3;
 735                 size = sizeof(*klist) + sizeof(*key) * max;
 736                 if (size > PAGE_SIZE)
 737                         goto error3;
 738
 739                 ret = -ENOMEM;
 740                 nklist = kmalloc(size, GFP_KERNEL);
 741                 if (!nklist)
 742                         goto error3;
 743                 nklist->maxkeys = max;
 744                 nklist->nkeys = 0;
 745
 746                 if (klist) {
 747                         nklist->nkeys = klist->nkeys;
 748                         memcpy(nklist->keys,
 749                                klist->keys,
 750                                sizeof(struct key *) * klist->nkeys);
 751                 }
 752
 753                 /* add the key into the new space */
 754                 atomic_inc(&key->usage);
 755                 nklist->keys[nklist->nkeys++] = key;
 756
 757                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 758
 759                 /* dispose of the old keyring list */
 760                 if (klist)
 761                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
 762
 763                 ret = 0;
 764         }
 765
 766  error2:
 767         up_write(&keyring_serialise_link_sem);
 768  error:
 769         return ret;
 770
 771  error3:
 772         /* undo the quota changes */
 773         key_payload_reserve(keyring,
 774                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 775         goto error2;
 776
 777 } /* end __key_link() */
 778
 779 /*****************************************************************************/
 780 /*
 781  * link a key to a keyring
 782  */
 783 int key_link(struct key *keyring, struct key *key)
 784 {
 785         int ret;
 786
 787         key_check(keyring);
 788         key_check(key);
 789
 790         down_write(&keyring->sem);
 791         ret = __key_link(keyring, key);
 792         up_write(&keyring->sem);
 793
 794         return ret;
 795
 796 } /* end key_link() */
 797
 798 EXPORT_SYMBOL(key_link);
 799
 800 /*****************************************************************************/
 801 /*
 802  * dispose of a keyring list after the RCU grace period, freeing the unlinked
 803  * key
 804  */
 805 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
 806 {
 807         struct keyring_list *klist =
 808                 container_of(rcu, struct keyring_list, rcu);
 809
 810         key_put(klist->keys[klist->delkey]);
 811         kfree(klist);
 812
 813 } /* end keyring_unlink_rcu_disposal() */
 814
 815 /*****************************************************************************/
 816 /*
 817  * unlink the first link to a key from a keyring
 818  */
 819 int key_unlink(struct key *keyring, struct key *key)
 820 {
 821         struct keyring_list *klist, *nklist;
 822         int loop, ret;
 823
 824         key_check(keyring);
 825         key_check(key);
 826
 827         ret = -ENOTDIR;
 828         if (keyring->type != &key_type_keyring)
 829                 goto error;
 830
 831         down_write(&keyring->sem);
 832
 833         klist = keyring->payload.subscriptions;
 834         if (klist) {
 835                 /* search the keyring for the key */
 836                 for (loop = 0; loop < klist->nkeys; loop++)
 837                         if (klist->keys[loop] == key)
 838                                 goto key_is_present;
 839         }
 840
 841         up_write(&keyring->sem);
 842         ret = -ENOENT;
 843         goto error;
 844
 845 key_is_present:
 846         /* we need to copy the key list for RCU purposes */
 847         nklist = kmalloc(sizeof(*klist) + sizeof(*key) * klist->maxkeys,
 848                          GFP_KERNEL);
 849         if (!nklist)
 850                 goto nomem;
 851         nklist->maxkeys = klist->maxkeys;
 852         nklist->nkeys = klist->nkeys - 1;
 853
 854         if (loop > 0)
 855                 memcpy(&nklist->keys[0],
 856                        &klist->keys[0],
 857                        loop * sizeof(klist->keys[0]));
 858
 859         if (loop < nklist->nkeys)
 860                 memcpy(&nklist->keys[loop],
 861                        &klist->keys[loop + 1],
 862                        (nklist->nkeys - loop) * sizeof(klist->keys[0]));
 863
 864         /* adjust the user's quota */
 865         key_payload_reserve(keyring,
 866                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 867
 868         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 869
 870         up_write(&keyring->sem);
 871
 872         /* schedule for later cleanup */
 873         klist->delkey = loop;
 874         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
 875
 876         ret = 0;
 877
 878 error:
 879         return ret;
 880 nomem:
 881         ret = -ENOMEM;
 882         up_write(&keyring->sem);
 883         goto error;
 884
 885 } /* end key_unlink() */
 886
 887 EXPORT_SYMBOL(key_unlink);
 888
 889 /*****************************************************************************/
 890 /*
 891  * dispose of a keyring list after the RCU grace period, releasing the keys it
 892  * links to
 893  */
 894 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
 895 {
 896         struct keyring_list *klist;
 897         int loop;
 898
 899         klist = container_of(rcu, struct keyring_list, rcu);
 900
 901         for (loop = klist->nkeys - 1; loop >= 0; loop--)
 902                 key_put(klist->keys[loop]);
 903
 904         kfree(klist);
 905
 906 } /* end keyring_clear_rcu_disposal() */
 907
 908 /*****************************************************************************/
 909 /*
 910  * clear the specified process keyring
 911  * - implements keyctl(KEYCTL_CLEAR)
 912  */
 913 int keyring_clear(struct key *keyring)
 914 {
 915         struct keyring_list *klist;
 916         int ret;
 917
 918         ret = -ENOTDIR;
 919         if (keyring->type == &key_type_keyring) {
 920                 /* detach the pointer block with the locks held */
 921                 down_write(&keyring->sem);
 922
 923                 klist = keyring->payload.subscriptions;
 924                 if (klist) {
 925                         /* adjust the quota */
 926                         key_payload_reserve(keyring,
 927                                             sizeof(struct keyring_list));
 928
 929                         rcu_assign_pointer(keyring->payload.subscriptions,
 930                                            NULL);
 931                 }
 932
 933                 up_write(&keyring->sem);
 934
 935                 /* free the keys after the locks have been dropped */
 936                 if (klist)
 937                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
 938
 939                 ret = 0;
 940         }
 941
 942         return ret;
 943
 944 } /* end keyring_clear() */
 945
 946 EXPORT_SYMBOL(keyring_clear);