security/keys/keyring.c

   1 /* keyring.c: keyring handling
   2  *
   3  * Copyright (C) 2004-5 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/init.h>
  14 #include <linux/sched.h>
  15 #include <linux/slab.h>
  16 #include <linux/security.h>
  17 #include <linux/seq_file.h>
  18 #include <linux/err.h>
  19 #include <asm/uaccess.h>
  20 #include "internal.h"
  21
  22 /*
  23  * when plumbing the depths of the key tree, this sets a hard limit set on how
  24  * deep we're willing to go
  25  */
  26 #define KEYRING_SEARCH_MAX_DEPTH 6
  27
  28 /*
  29  * we keep all named keyrings in a hash to speed looking them up
  30  */
  31 #define KEYRING_NAME_HASH_SIZE  (1 << 5)
  32
  33 static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
  34 static DEFINE_RWLOCK(keyring_name_lock);
  35
  36 static inline unsigned keyring_hash(const char *desc)
  37 {
  38         unsigned bucket = 0;
  39
  40         for (; *desc; desc++)
  41                 bucket += (unsigned char) *desc;
  42
  43         return bucket & (KEYRING_NAME_HASH_SIZE - 1);
  44 }
  45
  46 /*
  47  * the keyring type definition
  48  */
  49 static int keyring_instantiate(struct key *keyring,
  50                                const void *data, size_t datalen);
  51 static int keyring_match(const struct key *keyring, const void *criterion);
  52 static void keyring_revoke(struct key *keyring);
  53 static void keyring_destroy(struct key *keyring);
  54 static void keyring_describe(const struct key *keyring, struct seq_file *m);
  55 static long keyring_read(const struct key *keyring,
  56                          char __user *buffer, size_t buflen);
  57
  58 struct key_type key_type_keyring = {
  59         .name           = "keyring",
  60         .def_datalen    = sizeof(struct keyring_list),
  61         .instantiate    = keyring_instantiate,
  62         .match          = keyring_match,
  63         .revoke         = keyring_revoke,
  64         .destroy        = keyring_destroy,
  65         .describe       = keyring_describe,
  66         .read           = keyring_read,
  67 };
  68
  69 EXPORT_SYMBOL(key_type_keyring);
  70
  71 /*
  72  * semaphore to serialise link/link calls to prevent two link calls in parallel
  73  * introducing a cycle
  74  */
  75 static DECLARE_RWSEM(keyring_serialise_link_sem);
  76
  77 /*****************************************************************************/
  78 /*
  79  * publish the name of a keyring so that it can be found by name (if it has
  80  * one)
  81  */
  82 void keyring_publish_name(struct key *keyring)
  83 {
  84         int bucket;
  85
  86         if (keyring->description) {
  87                 bucket = keyring_hash(keyring->description);
  88
  89                 write_lock(&keyring_name_lock);
  90
  91                 if (!keyring_name_hash[bucket].next)
  92                         INIT_LIST_HEAD(&keyring_name_hash[bucket]);
  93
  94                 list_add_tail(&keyring->type_data.link,
  95                               &keyring_name_hash[bucket]);
  96
  97                 write_unlock(&keyring_name_lock);
  98         }
  99
 100 } /* end keyring_publish_name() */
 101
 102 /*****************************************************************************/
 103 /*
 104  * initialise a keyring
 105  * - we object if we were given any data
 106  */
 107 static int keyring_instantiate(struct key *keyring,
 108                                const void *data, size_t datalen)
 109 {
 110         int ret;
 111
 112         ret = -EINVAL;
 113         if (datalen == 0) {
 114                 /* make the keyring available by name if it has one */
 115                 keyring_publish_name(keyring);
 116                 ret = 0;
 117         }
 118
 119         return ret;
 120
 121 } /* end keyring_instantiate() */
 122
 123 /*****************************************************************************/
 124 /*
 125  * match keyrings on their name
 126  */
 127 static int keyring_match(const struct key *keyring, const void *description)
 128 {
 129         return keyring->description &&
 130                 strcmp(keyring->description, description) == 0;
 131
 132 } /* end keyring_match() */
 133
 134 /*****************************************************************************/
 135 /*
 136  * dispose of the data dangling from the corpse of a keyring
 137  */
 138 static void keyring_destroy(struct key *keyring)
 139 {
 140         struct keyring_list *klist;
 141         int loop;
 142
 143         if (keyring->description) {
 144                 write_lock(&keyring_name_lock);
 145
 146                 if (keyring->type_data.link.next != NULL &&
 147                     !list_empty(&keyring->type_data.link))
 148                         list_del(&keyring->type_data.link);
 149
 150                 write_unlock(&keyring_name_lock);
 151         }
 152
 153         klist = rcu_dereference(keyring->payload.subscriptions);
 154         if (klist) {
 155                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
 156                         key_put(klist->keys[loop]);
 157                 kfree(klist);
 158         }
 159
 160 } /* end keyring_destroy() */
 161
 162 /*****************************************************************************/
 163 /*
 164  * describe the keyring
 165  */
 166 static void keyring_describe(const struct key *keyring, struct seq_file *m)
 167 {
 168         struct keyring_list *klist;
 169
 170         if (keyring->description) {
 171                 seq_puts(m, keyring->description);
 172         }
 173         else {
 174                 seq_puts(m, "[anon]");
 175         }
 176
 177         rcu_read_lock();
 178         klist = rcu_dereference(keyring->payload.subscriptions);
 179         if (klist)
 180                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
 181         else
 182                 seq_puts(m, ": empty");
 183         rcu_read_unlock();
 184
 185 } /* end keyring_describe() */
 186
 187 /*****************************************************************************/
 188 /*
 189  * read a list of key IDs from the keyring's contents
 190  * - the keyring's semaphore is read-locked
 191  */
 192 static long keyring_read(const struct key *keyring,
 193                          char __user *buffer, size_t buflen)
 194 {
 195         struct keyring_list *klist;
 196         struct key *key;
 197         size_t qty, tmp;
 198         int loop, ret;
 199
 200         ret = 0;
 201         klist = rcu_dereference(keyring->payload.subscriptions);
 202
 203         if (klist) {
 204                 /* calculate how much data we could return */
 205                 qty = klist->nkeys * sizeof(key_serial_t);
 206
 207                 if (buffer && buflen > 0) {
 208                         if (buflen > qty)
 209                                 buflen = qty;
 210
 211                         /* copy the IDs of the subscribed keys into the
 212                          * buffer */
 213                         ret = -EFAULT;
 214
 215                         for (loop = 0; loop < klist->nkeys; loop++) {
 216                                 key = klist->keys[loop];
 217
 218                                 tmp = sizeof(key_serial_t);
 219                                 if (tmp > buflen)
 220                                         tmp = buflen;
 221
 222                                 if (copy_to_user(buffer,
 223                                                  &key->serial,
 224                                                  tmp) != 0)
 225                                         goto error;
 226
 227                                 buflen -= tmp;
 228                                 if (buflen == 0)
 229                                         break;
 230                                 buffer += tmp;
 231                         }
 232                 }
 233
 234                 ret = qty;
 235         }
 236
 237  error:
 238         return ret;
 239
 240 } /* end keyring_read() */
 241
 242 /*****************************************************************************/
 243 /*
 244  * allocate a keyring and link into the destination keyring
 245  */
 246 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
 247                           struct task_struct *ctx, unsigned long flags,
 248                           struct key *dest)
 249 {
 250         struct key *keyring;
 251         int ret;
 252
 253         keyring = key_alloc(&key_type_keyring, description,
 254                             uid, gid, ctx,
 255                             (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
 256                             flags);
 257
 258         if (!IS_ERR(keyring)) {
 259                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
 260                 if (ret < 0) {
 261                         key_put(keyring);
 262                         keyring = ERR_PTR(ret);
 263                 }
 264         }
 265
 266         return keyring;
 267
 268 } /* end keyring_alloc() */
 269
 270 /*****************************************************************************/
 271 /*
 272  * search the supplied keyring tree for a key that matches the criterion
 273  * - perform a breadth-then-depth search up to the prescribed limit
 274  * - we only find keys on which we have search permission
 275  * - we use the supplied match function to see if the description (or other
 276  *   feature of interest) matches
 277  * - we rely on RCU to prevent the keyring lists from disappearing on us
 278  * - we return -EAGAIN if we didn't find any matching key
 279  * - we return -ENOKEY if we only found negative matching keys
 280  * - we propagate the possession attribute from the keyring ref to the key ref
 281  */
 282 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
 283                              struct task_struct *context,
 284                              struct key_type *type,
 285                              const void *description,
 286                              key_match_func_t match)
 287 {
 288         struct {
 289                 struct keyring_list *keylist;
 290                 int kix;
 291         } stack[KEYRING_SEARCH_MAX_DEPTH];
 292
 293         struct keyring_list *keylist;
 294         struct timespec now;
 295         unsigned long possessed, kflags;
 296         struct key *keyring, *key;
 297         key_ref_t key_ref;
 298         long err;
 299         int sp, kix;
 300
 301         keyring = key_ref_to_ptr(keyring_ref);
 302         possessed = is_key_possessed(keyring_ref);
 303         key_check(keyring);
 304
 305         /* top keyring must have search permission to begin the search */
 306         err = key_task_permission(keyring_ref, context, KEY_SEARCH);
 307         if (err < 0) {
 308                 key_ref = ERR_PTR(err);
 309                 goto error;
 310         }
 311
 312         key_ref = ERR_PTR(-ENOTDIR);
 313         if (keyring->type != &key_type_keyring)
 314                 goto error;
 315
 316         rcu_read_lock();
 317
 318         now = current_kernel_time();
 319         err = -EAGAIN;
 320         sp = 0;
 321
 322         /* firstly we should check to see if this top-level keyring is what we
 323          * are looking for */
 324         key_ref = ERR_PTR(-EAGAIN);
 325         kflags = keyring->flags;
 326         if (keyring->type == type && match(keyring, description)) {
 327                 key = keyring;
 328
 329                 /* check it isn't negative and hasn't expired or been
 330                  * revoked */
 331                 if (kflags & (1 << KEY_FLAG_REVOKED))
 332                         goto error_2;
 333                 if (key->expiry && now.tv_sec >= key->expiry)
 334                         goto error_2;
 335                 key_ref = ERR_PTR(-ENOKEY);
 336                 if (kflags & (1 << KEY_FLAG_NEGATIVE))
 337                         goto error_2;
 338                 goto found;
 339         }
 340
 341         /* otherwise, the top keyring must not be revoked, expired, or
 342          * negatively instantiated if we are to search it */
 343         key_ref = ERR_PTR(-EAGAIN);
 344         if (kflags & ((1 << KEY_FLAG_REVOKED) | (1 << KEY_FLAG_NEGATIVE)) ||
 345             (keyring->expiry && now.tv_sec >= keyring->expiry))
 346                 goto error_2;
 347
 348         /* start processing a new keyring */
 349 descend:
 350         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 351                 goto not_this_keyring;
 352
 353         keylist = rcu_dereference(keyring->payload.subscriptions);
 354         if (!keylist)
 355                 goto not_this_keyring;
 356
 357         /* iterate through the keys in this keyring first */
 358         for (kix = 0; kix < keylist->nkeys; kix++) {
 359                 key = keylist->keys[kix];
 360                 kflags = key->flags;
 361
 362                 /* ignore keys not of this type */
 363                 if (key->type != type)
 364                         continue;
 365
 366                 /* skip revoked keys and expired keys */
 367                 if (kflags & (1 << KEY_FLAG_REVOKED))
 368                         continue;
 369
 370                 if (key->expiry && now.tv_sec >= key->expiry)
 371                         continue;
 372
 373                 /* keys that don't match */
 374                 if (!match(key, description))
 375                         continue;
 376
 377                 /* key must have search permissions */
 378                 if (key_task_permission(make_key_ref(key, possessed),
 379                                         context, KEY_SEARCH) < 0)
 380                         continue;
 381
 382                 /* we set a different error code if we pass a negative key */
 383                 if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
 384                         err = -ENOKEY;
 385                         continue;
 386                 }
 387
 388                 goto found;
 389         }
 390
 391         /* search through the keyrings nested in this one */
 392         kix = 0;
 393 ascend:
 394         for (; kix < keylist->nkeys; kix++) {
 395                 key = keylist->keys[kix];
 396                 if (key->type != &key_type_keyring)
 397                         continue;
 398
 399                 /* recursively search nested keyrings
 400                  * - only search keyrings for which we have search permission
 401                  */
 402                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 403                         continue;
 404
 405                 if (key_task_permission(make_key_ref(key, possessed),
 406                                         context, KEY_SEARCH) < 0)
 407                         continue;
 408
 409                 /* stack the current position */
 410                 stack[sp].keylist = keylist;
 411                 stack[sp].kix = kix;
 412                 sp++;
 413
 414                 /* begin again with the new keyring */
 415                 keyring = key;
 416                 goto descend;
 417         }
 418
 419         /* the keyring we're looking at was disqualified or didn't contain a
 420          * matching key */
 421 not_this_keyring:
 422         if (sp > 0) {
 423                 /* resume the processing of a keyring higher up in the tree */
 424                 sp--;
 425                 keylist = stack[sp].keylist;
 426                 kix = stack[sp].kix + 1;
 427                 goto ascend;
 428         }
 429
 430         key_ref = ERR_PTR(err);
 431         goto error_2;
 432
 433         /* we found a viable match */
 434 found:
 435         atomic_inc(&key->usage);
 436         key_check(key);
 437         key_ref = make_key_ref(key, possessed);
 438 error_2:
 439         rcu_read_unlock();
 440 error:
 441         return key_ref;
 442
 443 } /* end keyring_search_aux() */
 444
 445 /*****************************************************************************/
 446 /*
 447  * search the supplied keyring tree for a key that matches the criterion
 448  * - perform a breadth-then-depth search up to the prescribed limit
 449  * - we only find keys on which we have search permission
 450  * - we readlock the keyrings as we search down the tree
 451  * - we return -EAGAIN if we didn't find any matching key
 452  * - we return -ENOKEY if we only found negative matching keys
 453  */
 454 key_ref_t keyring_search(key_ref_t keyring,
 455                          struct key_type *type,
 456                          const char *description)
 457 {
 458         if (!type->match)
 459                 return ERR_PTR(-ENOKEY);
 460
 461         return keyring_search_aux(keyring, current,
 462                                   type, description, type->match);
 463
 464 } /* end keyring_search() */
 465
 466 EXPORT_SYMBOL(keyring_search);
 467
 468 /*****************************************************************************/
 469 /*
 470  * search the given keyring only (no recursion)
 471  * - keyring must be locked by caller
 472  * - caller must guarantee that the keyring is a keyring
 473  */
 474 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
 475                                const struct key_type *ktype,
 476                                const char *description,
 477                                key_perm_t perm)
 478 {
 479         struct keyring_list *klist;
 480         unsigned long possessed;
 481         struct key *keyring, *key;
 482         int loop;
 483
 484         keyring = key_ref_to_ptr(keyring_ref);
 485         possessed = is_key_possessed(keyring_ref);
 486
 487         rcu_read_lock();
 488
 489         klist = rcu_dereference(keyring->payload.subscriptions);
 490         if (klist) {
 491                 for (loop = 0; loop < klist->nkeys; loop++) {
 492                         key = klist->keys[loop];
 493
 494                         if (key->type == ktype &&
 495                             (!key->type->match ||
 496                              key->type->match(key, description)) &&
 497                             key_permission(make_key_ref(key, possessed),
 498                                            perm) == 0 &&
 499                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
 500                             )
 501                                 goto found;
 502                 }
 503         }
 504
 505         rcu_read_unlock();
 506         return ERR_PTR(-ENOKEY);
 507
 508  found:
 509         atomic_inc(&key->usage);
 510         rcu_read_unlock();
 511         return make_key_ref(key, possessed);
 512
 513 } /* end __keyring_search_one() */
 514
 515 /*****************************************************************************/
 516 /*
 517  * find a keyring with the specified name
 518  * - all named keyrings are searched
 519  * - only find keyrings with search permission for the process
 520  * - only find keyrings with a serial number greater than the one specified
 521  */
 522 struct key *find_keyring_by_name(const char *name, key_serial_t bound)
 523 {
 524         struct key *keyring;
 525         int bucket;
 526
 527         keyring = ERR_PTR(-EINVAL);
 528         if (!name)
 529                 goto error;
 530
 531         bucket = keyring_hash(name);
 532
 533         read_lock(&keyring_name_lock);
 534
 535         if (keyring_name_hash[bucket].next) {
 536                 /* search this hash bucket for a keyring with a matching name
 537                  * that's readable and that hasn't been revoked */
 538                 list_for_each_entry(keyring,
 539                                     &keyring_name_hash[bucket],
 540                                     type_data.link
 541                                     ) {
 542                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 543                                 continue;
 544
 545                         if (strcmp(keyring->description, name) != 0)
 546                                 continue;
 547
 548                         if (key_permission(make_key_ref(keyring, 0),
 549                                            KEY_SEARCH) < 0)
 550                                 continue;
 551
 552                         /* found a potential candidate, but we still need to
 553                          * check the serial number */
 554                         if (keyring->serial <= bound)
 555                                 continue;
 556
 557                         /* we've got a match */
 558                         atomic_inc(&keyring->usage);
 559                         read_unlock(&keyring_name_lock);
 560                         goto error;
 561                 }
 562         }
 563
 564         read_unlock(&keyring_name_lock);
 565         keyring = ERR_PTR(-ENOKEY);
 566
 567  error:
 568         return keyring;
 569
 570 } /* end find_keyring_by_name() */
 571
 572 /*****************************************************************************/
 573 /*
 574  * see if a cycle will will be created by inserting acyclic tree B in acyclic
 575  * tree A at the topmost level (ie: as a direct child of A)
 576  * - since we are adding B to A at the top level, checking for cycles should
 577  *   just be a matter of seeing if node A is somewhere in tree B
 578  */
 579 static int keyring_detect_cycle(struct key *A, struct key *B)
 580 {
 581         struct {
 582                 struct keyring_list *keylist;
 583                 int kix;
 584         } stack[KEYRING_SEARCH_MAX_DEPTH];
 585
 586         struct keyring_list *keylist;
 587         struct key *subtree, *key;
 588         int sp, kix, ret;
 589
 590         rcu_read_lock();
 591
 592         ret = -EDEADLK;
 593         if (A == B)
 594                 goto cycle_detected;
 595
 596         subtree = B;
 597         sp = 0;
 598
 599         /* start processing a new keyring */
 600  descend:
 601         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
 602                 goto not_this_keyring;
 603
 604         keylist = rcu_dereference(subtree->payload.subscriptions);
 605         if (!keylist)
 606                 goto not_this_keyring;
 607         kix = 0;
 608
 609  ascend:
 610         /* iterate through the remaining keys in this keyring */
 611         for (; kix < keylist->nkeys; kix++) {
 612                 key = keylist->keys[kix];
 613
 614                 if (key == A)
 615                         goto cycle_detected;
 616
 617                 /* recursively check nested keyrings */
 618                 if (key->type == &key_type_keyring) {
 619                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 620                                 goto too_deep;
 621
 622                         /* stack the current position */
 623                         stack[sp].keylist = keylist;
 624                         stack[sp].kix = kix;
 625                         sp++;
 626
 627                         /* begin again with the new keyring */
 628                         subtree = key;
 629                         goto descend;
 630                 }
 631         }
 632
 633         /* the keyring we're looking at was disqualified or didn't contain a
 634          * matching key */
 635  not_this_keyring:
 636         if (sp > 0) {
 637                 /* resume the checking of a keyring higher up in the tree */
 638                 sp--;
 639                 keylist = stack[sp].keylist;
 640                 kix = stack[sp].kix + 1;
 641                 goto ascend;
 642         }
 643
 644         ret = 0; /* no cycles detected */
 645
 646  error:
 647         rcu_read_unlock();
 648         return ret;
 649
 650  too_deep:
 651         ret = -ELOOP;
 652         goto error;
 653
 654  cycle_detected:
 655         ret = -EDEADLK;
 656         goto error;
 657
 658 } /* end keyring_detect_cycle() */
 659
 660 /*****************************************************************************/
 661 /*
 662  * dispose of a keyring list after the RCU grace period
 663  */
 664 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
 665 {
 666         struct keyring_list *klist =
 667                 container_of(rcu, struct keyring_list, rcu);
 668
 669         kfree(klist);
 670
 671 } /* end keyring_link_rcu_disposal() */
 672
 673 /*****************************************************************************/
 674 /*
 675  * dispose of a keyring list after the RCU grace period, freeing the unlinked
 676  * key
 677  */
 678 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
 679 {
 680         struct keyring_list *klist =
 681                 container_of(rcu, struct keyring_list, rcu);
 682
 683         key_put(klist->keys[klist->delkey]);
 684         kfree(klist);
 685
 686 } /* end keyring_unlink_rcu_disposal() */
 687
 688 /*****************************************************************************/
 689 /*
 690  * link a key into to a keyring
 691  * - must be called with the keyring's semaphore write-locked
 692  * - discard already extant link to matching key if there is one
 693  */
 694 int __key_link(struct key *keyring, struct key *key)
 695 {
 696         struct keyring_list *klist, *nklist;
 697         unsigned max;
 698         size_t size;
 699         int loop, ret;
 700
 701         ret = -EKEYREVOKED;
 702         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 703                 goto error;
 704
 705         ret = -ENOTDIR;
 706         if (keyring->type != &key_type_keyring)
 707                 goto error;
 708
 709         /* serialise link/link calls to prevent parallel calls causing a
 710          * cycle when applied to two keyring in opposite orders */
 711         down_write(&keyring_serialise_link_sem);
 712
 713         /* check that we aren't going to create a cycle adding one keyring to
 714          * another */
 715         if (key->type == &key_type_keyring) {
 716                 ret = keyring_detect_cycle(keyring, key);
 717                 if (ret < 0)
 718                         goto error2;
 719         }
 720
 721         /* see if there's a matching key we can displace */
 722         klist = keyring->payload.subscriptions;
 723
 724         if (klist && klist->nkeys > 0) {
 725                 struct key_type *type = key->type;
 726
 727                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
 728                         if (klist->keys[loop]->type == type &&
 729                             strcmp(klist->keys[loop]->description,
 730                                    key->description) == 0
 731                             ) {
 732                                 /* found a match - replace with new key */
 733                                 size = sizeof(struct key *) * klist->maxkeys;
 734                                 size += sizeof(*klist);
 735                                 BUG_ON(size > PAGE_SIZE);
 736
 737                                 ret = -ENOMEM;
 738                                 nklist = kmemdup(klist, size, GFP_KERNEL);
 739                                 if (!nklist)
 740                                         goto error2;
 741
 742                                 /* replace matched key */
 743                                 atomic_inc(&key->usage);
 744                                 nklist->keys[loop] = key;
 745
 746                                 rcu_assign_pointer(
 747                                         keyring->payload.subscriptions,
 748                                         nklist);
 749
 750                                 /* dispose of the old keyring list and the
 751                                  * displaced key */
 752                                 klist->delkey = loop;
 753                                 call_rcu(&klist->rcu,
 754                                          keyring_unlink_rcu_disposal);
 755
 756                                 goto done;
 757                         }
 758                 }
 759         }
 760
 761         /* check that we aren't going to overrun the user's quota */
 762         ret = key_payload_reserve(keyring,
 763                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
 764         if (ret < 0)
 765                 goto error2;
 766
 767         klist = keyring->payload.subscriptions;
 768
 769         if (klist && klist->nkeys < klist->maxkeys) {
 770                 /* there's sufficient slack space to add directly */
 771                 atomic_inc(&key->usage);
 772
 773                 klist->keys[klist->nkeys] = key;
 774                 smp_wmb();
 775                 klist->nkeys++;
 776                 smp_wmb();
 777         }
 778         else {
 779                 /* grow the key list */
 780                 max = 4;
 781                 if (klist)
 782                         max += klist->maxkeys;
 783
 784                 ret = -ENFILE;
 785                 if (max > 65535)
 786                         goto error3;
 787                 size = sizeof(*klist) + sizeof(struct key *) * max;
 788                 if (size > PAGE_SIZE)
 789                         goto error3;
 790
 791                 ret = -ENOMEM;
 792                 nklist = kmalloc(size, GFP_KERNEL);
 793                 if (!nklist)
 794                         goto error3;
 795                 nklist->maxkeys = max;
 796                 nklist->nkeys = 0;
 797
 798                 if (klist) {
 799                         nklist->nkeys = klist->nkeys;
 800                         memcpy(nklist->keys,
 801                                klist->keys,
 802                                sizeof(struct key *) * klist->nkeys);
 803                 }
 804
 805                 /* add the key into the new space */
 806                 atomic_inc(&key->usage);
 807                 nklist->keys[nklist->nkeys++] = key;
 808
 809                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 810
 811                 /* dispose of the old keyring list */
 812                 if (klist)
 813                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
 814         }
 815
 816 done:
 817         ret = 0;
 818 error2:
 819         up_write(&keyring_serialise_link_sem);
 820 error:
 821         return ret;
 822
 823 error3:
 824         /* undo the quota changes */
 825         key_payload_reserve(keyring,
 826                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 827         goto error2;
 828
 829 } /* end __key_link() */
 830
 831 /*****************************************************************************/
 832 /*
 833  * link a key to a keyring
 834  */
 835 int key_link(struct key *keyring, struct key *key)
 836 {
 837         int ret;
 838
 839         key_check(keyring);
 840         key_check(key);
 841
 842         down_write(&keyring->sem);
 843         ret = __key_link(keyring, key);
 844         up_write(&keyring->sem);
 845
 846         return ret;
 847
 848 } /* end key_link() */
 849
 850 EXPORT_SYMBOL(key_link);
 851
 852 /*****************************************************************************/
 853 /*
 854  * unlink the first link to a key from a keyring
 855  */
 856 int key_unlink(struct key *keyring, struct key *key)
 857 {
 858         struct keyring_list *klist, *nklist;
 859         int loop, ret;
 860
 861         key_check(keyring);
 862         key_check(key);
 863
 864         ret = -ENOTDIR;
 865         if (keyring->type != &key_type_keyring)
 866                 goto error;
 867
 868         down_write(&keyring->sem);
 869
 870         klist = keyring->payload.subscriptions;
 871         if (klist) {
 872                 /* search the keyring for the key */
 873                 for (loop = 0; loop < klist->nkeys; loop++)
 874                         if (klist->keys[loop] == key)
 875                                 goto key_is_present;
 876         }
 877
 878         up_write(&keyring->sem);
 879         ret = -ENOENT;
 880         goto error;
 881
 882 key_is_present:
 883         /* we need to copy the key list for RCU purposes */
 884         nklist = kmalloc(sizeof(*klist) +
 885                          sizeof(struct key *) * klist->maxkeys,
 886                          GFP_KERNEL);
 887         if (!nklist)
 888                 goto nomem;
 889         nklist->maxkeys = klist->maxkeys;
 890         nklist->nkeys = klist->nkeys - 1;
 891
 892         if (loop > 0)
 893                 memcpy(&nklist->keys[0],
 894                        &klist->keys[0],
 895                        loop * sizeof(struct key *));
 896
 897         if (loop < nklist->nkeys)
 898                 memcpy(&nklist->keys[loop],
 899                        &klist->keys[loop + 1],
 900                        (nklist->nkeys - loop) * sizeof(struct key *));
 901
 902         /* adjust the user's quota */
 903         key_payload_reserve(keyring,
 904                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 905
 906         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 907
 908         up_write(&keyring->sem);
 909
 910         /* schedule for later cleanup */
 911         klist->delkey = loop;
 912         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
 913
 914         ret = 0;
 915
 916 error:
 917         return ret;
 918 nomem:
 919         ret = -ENOMEM;
 920         up_write(&keyring->sem);
 921         goto error;
 922
 923 } /* end key_unlink() */
 924
 925 EXPORT_SYMBOL(key_unlink);
 926
 927 /*****************************************************************************/
 928 /*
 929  * dispose of a keyring list after the RCU grace period, releasing the keys it
 930  * links to
 931  */
 932 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
 933 {
 934         struct keyring_list *klist;
 935         int loop;
 936
 937         klist = container_of(rcu, struct keyring_list, rcu);
 938
 939         for (loop = klist->nkeys - 1; loop >= 0; loop--)
 940                 key_put(klist->keys[loop]);
 941
 942         kfree(klist);
 943
 944 } /* end keyring_clear_rcu_disposal() */
 945
 946 /*****************************************************************************/
 947 /*
 948  * clear the specified process keyring
 949  * - implements keyctl(KEYCTL_CLEAR)
 950  */
 951 int keyring_clear(struct key *keyring)
 952 {
 953         struct keyring_list *klist;
 954         int ret;
 955
 956         ret = -ENOTDIR;
 957         if (keyring->type == &key_type_keyring) {
 958                 /* detach the pointer block with the locks held */
 959                 down_write(&keyring->sem);
 960
 961                 klist = keyring->payload.subscriptions;
 962                 if (klist) {
 963                         /* adjust the quota */
 964                         key_payload_reserve(keyring,
 965                                             sizeof(struct keyring_list));
 966
 967                         rcu_assign_pointer(keyring->payload.subscriptions,
 968                                            NULL);
 969                 }
 970
 971                 up_write(&keyring->sem);
 972
 973                 /* free the keys after the locks have been dropped */
 974                 if (klist)
 975                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
 976
 977                 ret = 0;
 978         }
 979
 980         return ret;
 981
 982 } /* end keyring_clear() */
 983
 984 EXPORT_SYMBOL(keyring_clear);
 985
 986 /*****************************************************************************/
 987 /*
 988  * dispose of the links from a revoked keyring
 989  * - called with the key sem write-locked
 990  */
 991 static void keyring_revoke(struct key *keyring)
 992 {
 993         struct keyring_list *klist = keyring->payload.subscriptions;
 994
 995         /* adjust the quota */
 996         key_payload_reserve(keyring, 0);
 997
 998         if (klist) {
 999                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1000                 call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1001         }
1002
1003 } /* end keyring_revoke() */