git.oblomov.eu Git - linux-2.6/blob - security/keys/keyring.c

   1 /* Keyring handling
   2  *
   3  * Copyright (C) 2004-2005, 2008 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 <keys/keyring-type.h>
  20 #include <asm/uaccess.h>
  21 #include "internal.h"
  22
  23 /*
  24  * when plumbing the depths of the key tree, this sets a hard limit set on how
  25  * deep we're willing to go
  26  */
  27 #define KEYRING_SEARCH_MAX_DEPTH 6
  28
  29 /*
  30  * we keep all named keyrings in a hash to speed looking them up
  31  */
  32 #define KEYRING_NAME_HASH_SIZE  (1 << 5)
  33
  34 static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
  35 static DEFINE_RWLOCK(keyring_name_lock);
  36
  37 static inline unsigned keyring_hash(const char *desc)
  38 {
  39         unsigned bucket = 0;
  40
  41         for (; *desc; desc++)
  42                 bucket += (unsigned char) *desc;
  43
  44         return bucket & (KEYRING_NAME_HASH_SIZE - 1);
  45 }
  46
  47 /*
  48  * the keyring type definition
  49  */
  50 static int keyring_instantiate(struct key *keyring,
  51                                const void *data, size_t datalen);
  52 static int keyring_match(const struct key *keyring, const void *criterion);
  53 static void keyring_revoke(struct key *keyring);
  54 static void keyring_destroy(struct key *keyring);
  55 static void keyring_describe(const struct key *keyring, struct seq_file *m);
  56 static long keyring_read(const struct key *keyring,
  57                          char __user *buffer, size_t buflen);
  58
  59 struct key_type key_type_keyring = {
  60         .name           = "keyring",
  61         .def_datalen    = sizeof(struct keyring_list),
  62         .instantiate    = keyring_instantiate,
  63         .match          = keyring_match,
  64         .revoke         = keyring_revoke,
  65         .destroy        = keyring_destroy,
  66         .describe       = keyring_describe,
  67         .read           = keyring_read,
  68 };
  69
  70 EXPORT_SYMBOL(key_type_keyring);
  71
  72 /*
  73  * semaphore to serialise link/link calls to prevent two link calls in parallel
  74  * introducing a cycle
  75  */
  76 static DECLARE_RWSEM(keyring_serialise_link_sem);
  77
  78 /*****************************************************************************/
  79 /*
  80  * publish the name of a keyring so that it can be found by name (if it has
  81  * one)
  82  */
  83 static void keyring_publish_name(struct key *keyring)
  84 {
  85         int bucket;
  86
  87         if (keyring->description) {
  88                 bucket = keyring_hash(keyring->description);
  89
  90                 write_lock(&keyring_name_lock);
  91
  92                 if (!keyring_name_hash[bucket].next)
  93                         INIT_LIST_HEAD(&keyring_name_hash[bucket]);
  94
  95                 list_add_tail(&keyring->type_data.link,
  96                               &keyring_name_hash[bucket]);
  97
  98                 write_unlock(&keyring_name_lock);
  99         }
 100
 101 } /* end keyring_publish_name() */
 102
 103 /*****************************************************************************/
 104 /*
 105  * initialise a keyring
 106  * - we object if we were given any data
 107  */
 108 static int keyring_instantiate(struct key *keyring,
 109                                const void *data, size_t datalen)
 110 {
 111         int ret;
 112
 113         ret = -EINVAL;
 114         if (datalen == 0) {
 115                 /* make the keyring available by name if it has one */
 116                 keyring_publish_name(keyring);
 117                 ret = 0;
 118         }
 119
 120         return ret;
 121
 122 } /* end keyring_instantiate() */
 123
 124 /*****************************************************************************/
 125 /*
 126  * match keyrings on their name
 127  */
 128 static int keyring_match(const struct key *keyring, const void *description)
 129 {
 130         return keyring->description &&
 131                 strcmp(keyring->description, description) == 0;
 132
 133 } /* end keyring_match() */
 134
 135 /*****************************************************************************/
 136 /*
 137  * dispose of the data dangling from the corpse of a keyring
 138  */
 139 static void keyring_destroy(struct key *keyring)
 140 {
 141         struct keyring_list *klist;
 142         int loop;
 143
 144         if (keyring->description) {
 145                 write_lock(&keyring_name_lock);
 146
 147                 if (keyring->type_data.link.next != NULL &&
 148                     !list_empty(&keyring->type_data.link))
 149                         list_del(&keyring->type_data.link);
 150
 151                 write_unlock(&keyring_name_lock);
 152         }
 153
 154         klist = rcu_dereference(keyring->payload.subscriptions);
 155         if (klist) {
 156                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
 157                         key_put(klist->keys[loop]);
 158                 kfree(klist);
 159         }
 160
 161 } /* end keyring_destroy() */
 162
 163 /*****************************************************************************/
 164 /*
 165  * describe the keyring
 166  */
 167 static void keyring_describe(const struct key *keyring, struct seq_file *m)
 168 {
 169         struct keyring_list *klist;
 170
 171         if (keyring->description) {
 172                 seq_puts(m, keyring->description);
 173         }
 174         else {
 175                 seq_puts(m, "[anon]");
 176         }
 177
 178         rcu_read_lock();
 179         klist = rcu_dereference(keyring->payload.subscriptions);
 180         if (klist)
 181                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
 182         else
 183                 seq_puts(m, ": empty");
 184         rcu_read_unlock();
 185
 186 } /* end keyring_describe() */
 187
 188 /*****************************************************************************/
 189 /*
 190  * read a list of key IDs from the keyring's contents
 191  * - the keyring's semaphore is read-locked
 192  */
 193 static long keyring_read(const struct key *keyring,
 194                          char __user *buffer, size_t buflen)
 195 {
 196         struct keyring_list *klist;
 197         struct key *key;
 198         size_t qty, tmp;
 199         int loop, ret;
 200
 201         ret = 0;
 202         klist = rcu_dereference(keyring->payload.subscriptions);
 203
 204         if (klist) {
 205                 /* calculate how much data we could return */
 206                 qty = klist->nkeys * sizeof(key_serial_t);
 207
 208                 if (buffer && buflen > 0) {
 209                         if (buflen > qty)
 210                                 buflen = qty;
 211
 212                         /* copy the IDs of the subscribed keys into the
 213                          * buffer */
 214                         ret = -EFAULT;
 215
 216                         for (loop = 0; loop < klist->nkeys; loop++) {
 217                                 key = klist->keys[loop];
 218
 219                                 tmp = sizeof(key_serial_t);
 220                                 if (tmp > buflen)
 221                                         tmp = buflen;
 222
 223                                 if (copy_to_user(buffer,
 224                                                  &key->serial,
 225                                                  tmp) != 0)
 226                                         goto error;
 227
 228                                 buflen -= tmp;
 229                                 if (buflen == 0)
 230                                         break;
 231                                 buffer += tmp;
 232                         }
 233                 }
 234
 235                 ret = qty;
 236         }
 237
 238  error:
 239         return ret;
 240
 241 } /* end keyring_read() */
 242
 243 /*****************************************************************************/
 244 /*
 245  * allocate a keyring and link into the destination keyring
 246  */
 247 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
 248                           const struct cred *cred, unsigned long flags,
 249                           struct key *dest)
 250 {
 251         struct key *keyring;
 252         int ret;
 253
 254         keyring = key_alloc(&key_type_keyring, description,
 255                             uid, gid, cred,
 256                             (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
 257                             flags);
 258
 259         if (!IS_ERR(keyring)) {
 260                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
 261                 if (ret < 0) {
 262                         key_put(keyring);
 263                         keyring = ERR_PTR(ret);
 264                 }
 265         }
 266
 267         return keyring;
 268
 269 } /* end keyring_alloc() */
 270
 271 /*****************************************************************************/
 272 /*
 273  * search the supplied keyring tree for a key that matches the criterion
 274  * - perform a breadth-then-depth search up to the prescribed limit
 275  * - we only find keys on which we have search permission
 276  * - we use the supplied match function to see if the description (or other
 277  *   feature of interest) matches
 278  * - we rely on RCU to prevent the keyring lists from disappearing on us
 279  * - we return -EAGAIN if we didn't find any matching key
 280  * - we return -ENOKEY if we only found negative matching keys
 281  * - we propagate the possession attribute from the keyring ref to the key ref
 282  */
 283 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
 284                              const struct cred *cred,
 285                              struct key_type *type,
 286                              const void *description,
 287                              key_match_func_t match)
 288 {
 289         struct {
 290                 struct keyring_list *keylist;
 291                 int kix;
 292         } stack[KEYRING_SEARCH_MAX_DEPTH];
 293
 294         struct keyring_list *keylist;
 295         struct timespec now;
 296         unsigned long possessed, kflags;
 297         struct key *keyring, *key;
 298         key_ref_t key_ref;
 299         long err;
 300         int sp, kix;
 301
 302         keyring = key_ref_to_ptr(keyring_ref);
 303         possessed = is_key_possessed(keyring_ref);
 304         key_check(keyring);
 305
 306         /* top keyring must have search permission to begin the search */
 307         err = key_task_permission(keyring_ref, cred, KEY_SEARCH);
 308         if (err < 0) {
 309                 key_ref = ERR_PTR(err);
 310                 goto error;
 311         }
 312
 313         key_ref = ERR_PTR(-ENOTDIR);
 314         if (keyring->type != &key_type_keyring)
 315                 goto error;
 316
 317         rcu_read_lock();
 318
 319         now = current_kernel_time();
 320         err = -EAGAIN;
 321         sp = 0;
 322
 323         /* firstly we should check to see if this top-level keyring is what we
 324          * are looking for */
 325         key_ref = ERR_PTR(-EAGAIN);
 326         kflags = keyring->flags;
 327         if (keyring->type == type && match(keyring, description)) {
 328                 key = keyring;
 329
 330                 /* check it isn't negative and hasn't expired or been
 331                  * revoked */
 332                 if (kflags & (1 << KEY_FLAG_REVOKED))
 333                         goto error_2;
 334                 if (key->expiry && now.tv_sec >= key->expiry)
 335                         goto error_2;
 336                 key_ref = ERR_PTR(-ENOKEY);
 337                 if (kflags & (1 << KEY_FLAG_NEGATIVE))
 338                         goto error_2;
 339                 goto found;
 340         }
 341
 342         /* otherwise, the top keyring must not be revoked, expired, or
 343          * negatively instantiated if we are to search it */
 344         key_ref = ERR_PTR(-EAGAIN);
 345         if (kflags & ((1 << KEY_FLAG_REVOKED) | (1 << KEY_FLAG_NEGATIVE)) ||
 346             (keyring->expiry && now.tv_sec >= keyring->expiry))
 347                 goto error_2;
 348
 349         /* start processing a new keyring */
 350 descend:
 351         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 352                 goto not_this_keyring;
 353
 354         keylist = rcu_dereference(keyring->payload.subscriptions);
 355         if (!keylist)
 356                 goto not_this_keyring;
 357
 358         /* iterate through the keys in this keyring first */
 359         for (kix = 0; kix < keylist->nkeys; kix++) {
 360                 key = keylist->keys[kix];
 361                 kflags = key->flags;
 362
 363                 /* ignore keys not of this type */
 364                 if (key->type != type)
 365                         continue;
 366
 367                 /* skip revoked keys and expired keys */
 368                 if (kflags & (1 << KEY_FLAG_REVOKED))
 369                         continue;
 370
 371                 if (key->expiry && now.tv_sec >= key->expiry)
 372                         continue;
 373
 374                 /* keys that don't match */
 375                 if (!match(key, description))
 376                         continue;
 377
 378                 /* key must have search permissions */
 379                 if (key_task_permission(make_key_ref(key, possessed),
 380                                         cred, KEY_SEARCH) < 0)
 381                         continue;
 382
 383                 /* we set a different error code if we pass a negative key */
 384                 if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
 385                         err = -ENOKEY;
 386                         continue;
 387                 }
 388
 389                 goto found;
 390         }
 391
 392         /* search through the keyrings nested in this one */
 393         kix = 0;
 394 ascend:
 395         for (; kix < keylist->nkeys; kix++) {
 396                 key = keylist->keys[kix];
 397                 if (key->type != &key_type_keyring)
 398                         continue;
 399
 400                 /* recursively search nested keyrings
 401                  * - only search keyrings for which we have search permission
 402                  */
 403                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 404                         continue;
 405
 406                 if (key_task_permission(make_key_ref(key, possessed),
 407                                         cred, KEY_SEARCH) < 0)
 408                         continue;
 409
 410                 /* stack the current position */
 411                 stack[sp].keylist = keylist;
 412                 stack[sp].kix = kix;
 413                 sp++;
 414
 415                 /* begin again with the new keyring */
 416                 keyring = key;
 417                 goto descend;
 418         }
 419
 420         /* the keyring we're looking at was disqualified or didn't contain a
 421          * matching key */
 422 not_this_keyring:
 423         if (sp > 0) {
 424                 /* resume the processing of a keyring higher up in the tree */
 425                 sp--;
 426                 keylist = stack[sp].keylist;
 427                 kix = stack[sp].kix + 1;
 428                 goto ascend;
 429         }
 430
 431         key_ref = ERR_PTR(err);
 432         goto error_2;
 433
 434         /* we found a viable match */
 435 found:
 436         atomic_inc(&key->usage);
 437         key_check(key);
 438         key_ref = make_key_ref(key, possessed);
 439 error_2:
 440         rcu_read_unlock();
 441 error:
 442         return key_ref;
 443
 444 } /* end keyring_search_aux() */
 445
 446 /*****************************************************************************/
 447 /*
 448  * search the supplied keyring tree for a key that matches the criterion
 449  * - perform a breadth-then-depth search up to the prescribed limit
 450  * - we only find keys on which we have search permission
 451  * - we readlock the keyrings as we search down the tree
 452  * - we return -EAGAIN if we didn't find any matching key
 453  * - we return -ENOKEY if we only found negative matching keys
 454  */
 455 key_ref_t keyring_search(key_ref_t keyring,
 456                          struct key_type *type,
 457                          const char *description)
 458 {
 459         if (!type->match)
 460                 return ERR_PTR(-ENOKEY);
 461
 462         return keyring_search_aux(keyring, current->cred,
 463                                   type, description, type->match);
 464
 465 } /* end keyring_search() */
 466
 467 EXPORT_SYMBOL(keyring_search);
 468
 469 /*****************************************************************************/
 470 /*
 471  * search the given keyring only (no recursion)
 472  * - keyring must be locked by caller
 473  * - caller must guarantee that the keyring is a keyring
 474  */
 475 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
 476                                const struct key_type *ktype,
 477                                const char *description,
 478                                key_perm_t perm)
 479 {
 480         struct keyring_list *klist;
 481         unsigned long possessed;
 482         struct key *keyring, *key;
 483         int loop;
 484
 485         keyring = key_ref_to_ptr(keyring_ref);
 486         possessed = is_key_possessed(keyring_ref);
 487
 488         rcu_read_lock();
 489
 490         klist = rcu_dereference(keyring->payload.subscriptions);
 491         if (klist) {
 492                 for (loop = 0; loop < klist->nkeys; loop++) {
 493                         key = klist->keys[loop];
 494
 495                         if (key->type == ktype &&
 496                             (!key->type->match ||
 497                              key->type->match(key, description)) &&
 498                             key_permission(make_key_ref(key, possessed),
 499                                            perm) == 0 &&
 500                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
 501                             )
 502                                 goto found;
 503                 }
 504         }
 505
 506         rcu_read_unlock();
 507         return ERR_PTR(-ENOKEY);
 508
 509  found:
 510         atomic_inc(&key->usage);
 511         rcu_read_unlock();
 512         return make_key_ref(key, possessed);
 513
 514 } /* end __keyring_search_one() */
 515
 516 /*****************************************************************************/
 517 /*
 518  * find a keyring with the specified name
 519  * - all named keyrings are searched
 520  * - normally only finds keyrings with search permission for the current process
 521  */
 522 struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
 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 (keyring->user->user_ns != current_user_ns())
 543                                 continue;
 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 (!skip_perm_check &&
 552                             key_permission(make_key_ref(keyring, 0),
 553                                            KEY_SEARCH) < 0)
 554                                 continue;
 555
 556                         /* we've got a match */
 557                         atomic_inc(&keyring->usage);
 558                         read_unlock(&keyring_name_lock);
 559                         goto error;
 560                 }
 561         }
 562
 563         read_unlock(&keyring_name_lock);
 564         keyring = ERR_PTR(-ENOKEY);
 565
 566  error:
 567         return keyring;
 568
 569 } /* end find_keyring_by_name() */
 570
 571 /*****************************************************************************/
 572 /*
 573  * see if a cycle will will be created by inserting acyclic tree B in acyclic
 574  * tree A at the topmost level (ie: as a direct child of A)
 575  * - since we are adding B to A at the top level, checking for cycles should
 576  *   just be a matter of seeing if node A is somewhere in tree B
 577  */
 578 static int keyring_detect_cycle(struct key *A, struct key *B)
 579 {
 580         struct {
 581                 struct keyring_list *keylist;
 582                 int kix;
 583         } stack[KEYRING_SEARCH_MAX_DEPTH];
 584
 585         struct keyring_list *keylist;
 586         struct key *subtree, *key;
 587         int sp, kix, ret;
 588
 589         rcu_read_lock();
 590
 591         ret = -EDEADLK;
 592         if (A == B)
 593                 goto cycle_detected;
 594
 595         subtree = B;
 596         sp = 0;
 597
 598         /* start processing a new keyring */
 599  descend:
 600         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
 601                 goto not_this_keyring;
 602
 603         keylist = rcu_dereference(subtree->payload.subscriptions);
 604         if (!keylist)
 605                 goto not_this_keyring;
 606         kix = 0;
 607
 608  ascend:
 609         /* iterate through the remaining keys in this keyring */
 610         for (; kix < keylist->nkeys; kix++) {
 611                 key = keylist->keys[kix];
 612
 613                 if (key == A)
 614                         goto cycle_detected;
 615
 616                 /* recursively check nested keyrings */
 617                 if (key->type == &key_type_keyring) {
 618                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 619                                 goto too_deep;
 620
 621                         /* stack the current position */
 622                         stack[sp].keylist = keylist;
 623                         stack[sp].kix = kix;
 624                         sp++;
 625
 626                         /* begin again with the new keyring */
 627                         subtree = key;
 628                         goto descend;
 629                 }
 630         }
 631
 632         /* the keyring we're looking at was disqualified or didn't contain a
 633          * matching key */
 634  not_this_keyring:
 635         if (sp > 0) {
 636                 /* resume the checking of a keyring higher up in the tree */
 637                 sp--;
 638                 keylist = stack[sp].keylist;
 639                 kix = stack[sp].kix + 1;
 640                 goto ascend;
 641         }
 642
 643         ret = 0; /* no cycles detected */
 644
 645  error:
 646         rcu_read_unlock();
 647         return ret;
 648
 649  too_deep:
 650         ret = -ELOOP;
 651         goto error;
 652
 653  cycle_detected:
 654         ret = -EDEADLK;
 655         goto error;
 656
 657 } /* end keyring_detect_cycle() */
 658
 659 /*****************************************************************************/
 660 /*
 661  * dispose of a keyring list after the RCU grace period
 662  */
 663 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
 664 {
 665         struct keyring_list *klist =
 666                 container_of(rcu, struct keyring_list, rcu);
 667
 668         kfree(klist);
 669
 670 } /* end keyring_link_rcu_disposal() */
 671
 672 /*****************************************************************************/
 673 /*
 674  * dispose of a keyring list after the RCU grace period, freeing the unlinked
 675  * key
 676  */
 677 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
 678 {
 679         struct keyring_list *klist =
 680                 container_of(rcu, struct keyring_list, rcu);
 681
 682         key_put(klist->keys[klist->delkey]);
 683         kfree(klist);
 684
 685 } /* end keyring_unlink_rcu_disposal() */
 686
 687 /*****************************************************************************/
 688 /*
 689  * link a key into to a keyring
 690  * - must be called with the keyring's semaphore write-locked
 691  * - discard already extant link to matching key if there is one
 692  */
 693 int __key_link(struct key *keyring, struct key *key)
 694 {
 695         struct keyring_list *klist, *nklist;
 696         unsigned max;
 697         size_t size;
 698         int loop, ret;
 699
 700         ret = -EKEYREVOKED;
 701         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 702                 goto error;
 703
 704         ret = -ENOTDIR;
 705         if (keyring->type != &key_type_keyring)
 706                 goto error;
 707
 708         /* serialise link/link calls to prevent parallel calls causing a
 709          * cycle when applied to two keyring in opposite orders */
 710         down_write(&keyring_serialise_link_sem);
 711
 712         /* check that we aren't going to create a cycle adding one keyring to
 713          * another */
 714         if (key->type == &key_type_keyring) {
 715                 ret = keyring_detect_cycle(keyring, key);
 716                 if (ret < 0)
 717                         goto error2;
 718         }
 719
 720         /* see if there's a matching key we can displace */
 721         klist = keyring->payload.subscriptions;
 722
 723         if (klist && klist->nkeys > 0) {
 724                 struct key_type *type = key->type;
 725
 726                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
 727                         if (klist->keys[loop]->type == type &&
 728                             strcmp(klist->keys[loop]->description,
 729                                    key->description) == 0
 730                             ) {
 731                                 /* found a match - replace with new key */
 732                                 size = sizeof(struct key *) * klist->maxkeys;
 733                                 size += sizeof(*klist);
 734                                 BUG_ON(size > PAGE_SIZE);
 735
 736                                 ret = -ENOMEM;
 737                                 nklist = kmemdup(klist, size, GFP_KERNEL);
 738                                 if (!nklist)
 739                                         goto error2;
 740
 741                                 /* replace matched key */
 742                                 atomic_inc(&key->usage);
 743                                 nklist->keys[loop] = key;
 744
 745                                 rcu_assign_pointer(
 746                                         keyring->payload.subscriptions,
 747                                         nklist);
 748
 749                                 /* dispose of the old keyring list and the
 750                                  * displaced key */
 751                                 klist->delkey = loop;
 752                                 call_rcu(&klist->rcu,
 753                                          keyring_unlink_rcu_disposal);
 754
 755                                 goto done;
 756                         }
 757                 }
 758         }
 759
 760         /* check that we aren't going to overrun the user's quota */
 761         ret = key_payload_reserve(keyring,
 762                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
 763         if (ret < 0)
 764                 goto error2;
 765
 766         klist = keyring->payload.subscriptions;
 767
 768         if (klist && klist->nkeys < klist->maxkeys) {
 769                 /* there's sufficient slack space to add directly */
 770                 atomic_inc(&key->usage);
 771
 772                 klist->keys[klist->nkeys] = key;
 773                 smp_wmb();
 774                 klist->nkeys++;
 775                 smp_wmb();
 776         }
 777         else {
 778                 /* grow the key list */
 779                 max = 4;
 780                 if (klist)
 781                         max += klist->maxkeys;
 782
 783                 ret = -ENFILE;
 784                 if (max > 65535)
 785                         goto error3;
 786                 size = sizeof(*klist) + sizeof(struct key *) * max;
 787                 if (size > PAGE_SIZE)
 788                         goto error3;
 789
 790                 ret = -ENOMEM;
 791                 nklist = kmalloc(size, GFP_KERNEL);
 792                 if (!nklist)
 793                         goto error3;
 794                 nklist->maxkeys = max;
 795                 nklist->nkeys = 0;
 796
 797                 if (klist) {
 798                         nklist->nkeys = klist->nkeys;
 799                         memcpy(nklist->keys,
 800                                klist->keys,
 801                                sizeof(struct key *) * klist->nkeys);
 802                 }
 803
 804                 /* add the key into the new space */
 805                 atomic_inc(&key->usage);
 806                 nklist->keys[nklist->nkeys++] = key;
 807
 808                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 809
 810                 /* dispose of the old keyring list */
 811                 if (klist)
 812                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
 813         }
 814
 815 done:
 816         ret = 0;
 817 error2:
 818         up_write(&keyring_serialise_link_sem);
 819 error:
 820         return ret;
 821
 822 error3:
 823         /* undo the quota changes */
 824         key_payload_reserve(keyring,
 825                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 826         goto error2;
 827
 828 } /* end __key_link() */
 829
 830 /*****************************************************************************/
 831 /*
 832  * link a key to a keyring
 833  */
 834 int key_link(struct key *keyring, struct key *key)
 835 {
 836         int ret;
 837
 838         key_check(keyring);
 839         key_check(key);
 840
 841         down_write(&keyring->sem);
 842         ret = __key_link(keyring, key);
 843         up_write(&keyring->sem);
 844
 845         return ret;
 846
 847 } /* end key_link() */
 848
 849 EXPORT_SYMBOL(key_link);
 850
 851 /*****************************************************************************/
 852 /*
 853  * unlink the first link to a key from a keyring
 854  */
 855 int key_unlink(struct key *keyring, struct key *key)
 856 {
 857         struct keyring_list *klist, *nklist;
 858         int loop, ret;
 859
 860         key_check(keyring);
 861         key_check(key);
 862
 863         ret = -ENOTDIR;
 864         if (keyring->type != &key_type_keyring)
 865                 goto error;
 866
 867         down_write(&keyring->sem);
 868
 869         klist = keyring->payload.subscriptions;
 870         if (klist) {
 871                 /* search the keyring for the key */
 872                 for (loop = 0; loop < klist->nkeys; loop++)
 873                         if (klist->keys[loop] == key)
 874                                 goto key_is_present;
 875         }
 876
 877         up_write(&keyring->sem);
 878         ret = -ENOENT;
 879         goto error;
 880
 881 key_is_present:
 882         /* we need to copy the key list for RCU purposes */
 883         nklist = kmalloc(sizeof(*klist) +
 884                          sizeof(struct key *) * klist->maxkeys,
 885                          GFP_KERNEL);
 886         if (!nklist)
 887                 goto nomem;
 888         nklist->maxkeys = klist->maxkeys;
 889         nklist->nkeys = klist->nkeys - 1;
 890
 891         if (loop > 0)
 892                 memcpy(&nklist->keys[0],
 893                        &klist->keys[0],
 894                        loop * sizeof(struct key *));
 895
 896         if (loop < nklist->nkeys)
 897                 memcpy(&nklist->keys[loop],
 898                        &klist->keys[loop + 1],
 899                        (nklist->nkeys - loop) * sizeof(struct key *));
 900
 901         /* adjust the user's quota */
 902         key_payload_reserve(keyring,
 903                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 904
 905         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 906
 907         up_write(&keyring->sem);
 908
 909         /* schedule for later cleanup */
 910         klist->delkey = loop;
 911         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
 912
 913         ret = 0;
 914
 915 error:
 916         return ret;
 917 nomem:
 918         ret = -ENOMEM;
 919         up_write(&keyring->sem);
 920         goto error;
 921
 922 } /* end key_unlink() */
 923
 924 EXPORT_SYMBOL(key_unlink);
 925
 926 /*****************************************************************************/
 927 /*
 928  * dispose of a keyring list after the RCU grace period, releasing the keys it
 929  * links to
 930  */
 931 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
 932 {
 933         struct keyring_list *klist;
 934         int loop;
 935
 936         klist = container_of(rcu, struct keyring_list, rcu);
 937
 938         for (loop = klist->nkeys - 1; loop >= 0; loop--)
 939                 key_put(klist->keys[loop]);
 940
 941         kfree(klist);
 942
 943 } /* end keyring_clear_rcu_disposal() */
 944
 945 /*****************************************************************************/
 946 /*
 947  * clear the specified process keyring
 948  * - implements keyctl(KEYCTL_CLEAR)
 949  */
 950 int keyring_clear(struct key *keyring)
 951 {
 952         struct keyring_list *klist;
 953         int ret;
 954
 955         ret = -ENOTDIR;
 956         if (keyring->type == &key_type_keyring) {
 957                 /* detach the pointer block with the locks held */
 958                 down_write(&keyring->sem);
 959
 960                 klist = keyring->payload.subscriptions;
 961                 if (klist) {
 962                         /* adjust the quota */
 963                         key_payload_reserve(keyring,
 964                                             sizeof(struct keyring_list));
 965
 966                         rcu_assign_pointer(keyring->payload.subscriptions,
 967                                            NULL);
 968                 }
 969
 970                 up_write(&keyring->sem);
 971
 972                 /* free the keys after the locks have been dropped */
 973                 if (klist)
 974                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
 975
 976                 ret = 0;
 977         }
 978
 979         return ret;
 980
 981 } /* end keyring_clear() */
 982
 983 EXPORT_SYMBOL(keyring_clear);
 984
 985 /*****************************************************************************/
 986 /*
 987  * dispose of the links from a revoked keyring
 988  * - called with the key sem write-locked
 989  */
 990 static void keyring_revoke(struct key *keyring)
 991 {
 992         struct keyring_list *klist = keyring->payload.subscriptions;
 993
 994         /* adjust the quota */
 995         key_payload_reserve(keyring, 0);
 996
 997         if (klist) {
 998                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
 999                 call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1000         }
1001
1002 } /* end keyring_revoke() */