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_check(keyring->payload.subscriptions,
 155                                       rcu_read_lock_held() ||
 156                                       atomic_read(&keyring->usage) == 0);
 157         if (klist) {
 158                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
 159                         key_put(klist->keys[loop]);
 160                 kfree(klist);
 161         }
 162
 163 } /* end keyring_destroy() */
 164
 165 /*****************************************************************************/
 166 /*
 167  * describe the keyring
 168  */
 169 static void keyring_describe(const struct key *keyring, struct seq_file *m)
 170 {
 171         struct keyring_list *klist;
 172
 173         if (keyring->description) {
 174                 seq_puts(m, keyring->description);
 175         }
 176         else {
 177                 seq_puts(m, "[anon]");
 178         }
 179
 180         rcu_read_lock();
 181         klist = rcu_dereference(keyring->payload.subscriptions);
 182         if (klist)
 183                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
 184         else
 185                 seq_puts(m, ": empty");
 186         rcu_read_unlock();
 187
 188 } /* end keyring_describe() */
 189
 190 /*****************************************************************************/
 191 /*
 192  * read a list of key IDs from the keyring's contents
 193  * - the keyring's semaphore is read-locked
 194  */
 195 static long keyring_read(const struct key *keyring,
 196                          char __user *buffer, size_t buflen)
 197 {
 198         struct keyring_list *klist;
 199         struct key *key;
 200         size_t qty, tmp;
 201         int loop, ret;
 202
 203         ret = 0;
 204         klist = rcu_dereference(keyring->payload.subscriptions);
 205
 206         if (klist) {
 207                 /* calculate how much data we could return */
 208                 qty = klist->nkeys * sizeof(key_serial_t);
 209
 210                 if (buffer && buflen > 0) {
 211                         if (buflen > qty)
 212                                 buflen = qty;
 213
 214                         /* copy the IDs of the subscribed keys into the
 215                          * buffer */
 216                         ret = -EFAULT;
 217
 218                         for (loop = 0; loop < klist->nkeys; loop++) {
 219                                 key = klist->keys[loop];
 220
 221                                 tmp = sizeof(key_serial_t);
 222                                 if (tmp > buflen)
 223                                         tmp = buflen;
 224
 225                                 if (copy_to_user(buffer,
 226                                                  &key->serial,
 227                                                  tmp) != 0)
 228                                         goto error;
 229
 230                                 buflen -= tmp;
 231                                 if (buflen == 0)
 232                                         break;
 233                                 buffer += tmp;
 234                         }
 235                 }
 236
 237                 ret = qty;
 238         }
 239
 240  error:
 241         return ret;
 242
 243 } /* end keyring_read() */
 244
 245 /*****************************************************************************/
 246 /*
 247  * allocate a keyring and link into the destination keyring
 248  */
 249 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
 250                           const struct cred *cred, unsigned long flags,
 251                           struct key *dest)
 252 {
 253         struct key *keyring;
 254         int ret;
 255
 256         keyring = key_alloc(&key_type_keyring, description,
 257                             uid, gid, cred,
 258                             (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
 259                             flags);
 260
 261         if (!IS_ERR(keyring)) {
 262                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
 263                 if (ret < 0) {
 264                         key_put(keyring);
 265                         keyring = ERR_PTR(ret);
 266                 }
 267         }
 268
 269         return keyring;
 270
 271 } /* end keyring_alloc() */
 272
 273 /*****************************************************************************/
 274 /*
 275  * search the supplied keyring tree for a key that matches the criterion
 276  * - perform a breadth-then-depth search up to the prescribed limit
 277  * - we only find keys on which we have search permission
 278  * - we use the supplied match function to see if the description (or other
 279  *   feature of interest) matches
 280  * - we rely on RCU to prevent the keyring lists from disappearing on us
 281  * - we return -EAGAIN if we didn't find any matching key
 282  * - we return -ENOKEY if we only found negative matching keys
 283  * - we propagate the possession attribute from the keyring ref to the key ref
 284  */
 285 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
 286                              const struct cred *cred,
 287                              struct key_type *type,
 288                              const void *description,
 289                              key_match_func_t match)
 290 {
 291         struct {
 292                 struct keyring_list *keylist;
 293                 int kix;
 294         } stack[KEYRING_SEARCH_MAX_DEPTH];
 295
 296         struct keyring_list *keylist;
 297         struct timespec now;
 298         unsigned long possessed, kflags;
 299         struct key *keyring, *key;
 300         key_ref_t key_ref;
 301         long err;
 302         int sp, kix;
 303
 304         keyring = key_ref_to_ptr(keyring_ref);
 305         possessed = is_key_possessed(keyring_ref);
 306         key_check(keyring);
 307
 308         /* top keyring must have search permission to begin the search */
 309         err = key_task_permission(keyring_ref, cred, KEY_SEARCH);
 310         if (err < 0) {
 311                 key_ref = ERR_PTR(err);
 312                 goto error;
 313         }
 314
 315         key_ref = ERR_PTR(-ENOTDIR);
 316         if (keyring->type != &key_type_keyring)
 317                 goto error;
 318
 319         rcu_read_lock();
 320
 321         now = current_kernel_time();
 322         err = -EAGAIN;
 323         sp = 0;
 324
 325         /* firstly we should check to see if this top-level keyring is what we
 326          * are looking for */
 327         key_ref = ERR_PTR(-EAGAIN);
 328         kflags = keyring->flags;
 329         if (keyring->type == type && match(keyring, description)) {
 330                 key = keyring;
 331
 332                 /* check it isn't negative and hasn't expired or been
 333                  * revoked */
 334                 if (kflags & (1 << KEY_FLAG_REVOKED))
 335                         goto error_2;
 336                 if (key->expiry && now.tv_sec >= key->expiry)
 337                         goto error_2;
 338                 key_ref = ERR_PTR(-ENOKEY);
 339                 if (kflags & (1 << KEY_FLAG_NEGATIVE))
 340                         goto error_2;
 341                 goto found;
 342         }
 343
 344         /* otherwise, the top keyring must not be revoked, expired, or
 345          * negatively instantiated if we are to search it */
 346         key_ref = ERR_PTR(-EAGAIN);
 347         if (kflags & ((1 << KEY_FLAG_REVOKED) | (1 << KEY_FLAG_NEGATIVE)) ||
 348             (keyring->expiry && now.tv_sec >= keyring->expiry))
 349                 goto error_2;
 350
 351         /* start processing a new keyring */
 352 descend:
 353         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 354                 goto not_this_keyring;
 355
 356         keylist = rcu_dereference(keyring->payload.subscriptions);
 357         if (!keylist)
 358                 goto not_this_keyring;
 359
 360         /* iterate through the keys in this keyring first */
 361         for (kix = 0; kix < keylist->nkeys; kix++) {
 362                 key = keylist->keys[kix];
 363                 kflags = key->flags;
 364
 365                 /* ignore keys not of this type */
 366                 if (key->type != type)
 367                         continue;
 368
 369                 /* skip revoked keys and expired keys */
 370                 if (kflags & (1 << KEY_FLAG_REVOKED))
 371                         continue;
 372
 373                 if (key->expiry && now.tv_sec >= key->expiry)
 374                         continue;
 375
 376                 /* keys that don't match */
 377                 if (!match(key, description))
 378                         continue;
 379
 380                 /* key must have search permissions */
 381                 if (key_task_permission(make_key_ref(key, possessed),
 382                                         cred, KEY_SEARCH) < 0)
 383                         continue;
 384
 385                 /* we set a different error code if we pass a negative key */
 386                 if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
 387                         err = -ENOKEY;
 388                         continue;
 389                 }
 390
 391                 goto found;
 392         }
 393
 394         /* search through the keyrings nested in this one */
 395         kix = 0;
 396 ascend:
 397         for (; kix < keylist->nkeys; kix++) {
 398                 key = keylist->keys[kix];
 399                 if (key->type != &key_type_keyring)
 400                         continue;
 401
 402                 /* recursively search nested keyrings
 403                  * - only search keyrings for which we have search permission
 404                  */
 405                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 406                         continue;
 407
 408                 if (key_task_permission(make_key_ref(key, possessed),
 409                                         cred, KEY_SEARCH) < 0)
 410                         continue;
 411
 412                 /* stack the current position */
 413                 stack[sp].keylist = keylist;
 414                 stack[sp].kix = kix;
 415                 sp++;
 416
 417                 /* begin again with the new keyring */
 418                 keyring = key;
 419                 goto descend;
 420         }
 421
 422         /* the keyring we're looking at was disqualified or didn't contain a
 423          * matching key */
 424 not_this_keyring:
 425         if (sp > 0) {
 426                 /* resume the processing of a keyring higher up in the tree */
 427                 sp--;
 428                 keylist = stack[sp].keylist;
 429                 kix = stack[sp].kix + 1;
 430                 goto ascend;
 431         }
 432
 433         key_ref = ERR_PTR(err);
 434         goto error_2;
 435
 436         /* we found a viable match */
 437 found:
 438         atomic_inc(&key->usage);
 439         key_check(key);
 440         key_ref = make_key_ref(key, possessed);
 441 error_2:
 442         rcu_read_unlock();
 443 error:
 444         return key_ref;
 445
 446 } /* end keyring_search_aux() */
 447
 448 /*****************************************************************************/
 449 /*
 450  * search the supplied keyring tree for a key that matches the criterion
 451  * - perform a breadth-then-depth search up to the prescribed limit
 452  * - we only find keys on which we have search permission
 453  * - we readlock the keyrings as we search down the tree
 454  * - we return -EAGAIN if we didn't find any matching key
 455  * - we return -ENOKEY if we only found negative matching keys
 456  */
 457 key_ref_t keyring_search(key_ref_t keyring,
 458                          struct key_type *type,
 459                          const char *description)
 460 {
 461         if (!type->match)
 462                 return ERR_PTR(-ENOKEY);
 463
 464         return keyring_search_aux(keyring, current->cred,
 465                                   type, description, type->match);
 466
 467 } /* end keyring_search() */
 468
 469 EXPORT_SYMBOL(keyring_search);
 470
 471 /*****************************************************************************/
 472 /*
 473  * search the given keyring only (no recursion)
 474  * - keyring must be locked by caller
 475  * - caller must guarantee that the keyring is a keyring
 476  */
 477 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
 478                                const struct key_type *ktype,
 479                                const char *description,
 480                                key_perm_t perm)
 481 {
 482         struct keyring_list *klist;
 483         unsigned long possessed;
 484         struct key *keyring, *key;
 485         int loop;
 486
 487         keyring = key_ref_to_ptr(keyring_ref);
 488         possessed = is_key_possessed(keyring_ref);
 489
 490         rcu_read_lock();
 491
 492         klist = rcu_dereference(keyring->payload.subscriptions);
 493         if (klist) {
 494                 for (loop = 0; loop < klist->nkeys; loop++) {
 495                         key = klist->keys[loop];
 496
 497                         if (key->type == ktype &&
 498                             (!key->type->match ||
 499                              key->type->match(key, description)) &&
 500                             key_permission(make_key_ref(key, possessed),
 501                                            perm) == 0 &&
 502                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
 503                             )
 504                                 goto found;
 505                 }
 506         }
 507
 508         rcu_read_unlock();
 509         return ERR_PTR(-ENOKEY);
 510
 511  found:
 512         atomic_inc(&key->usage);
 513         rcu_read_unlock();
 514         return make_key_ref(key, possessed);
 515
 516 } /* end __keyring_search_one() */
 517
 518 /*****************************************************************************/
 519 /*
 520  * find a keyring with the specified name
 521  * - all named keyrings are searched
 522  * - normally only finds keyrings with search permission for the current process
 523  */
 524 struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
 525 {
 526         struct key *keyring;
 527         int bucket;
 528
 529         keyring = ERR_PTR(-EINVAL);
 530         if (!name)
 531                 goto error;
 532
 533         bucket = keyring_hash(name);
 534
 535         read_lock(&keyring_name_lock);
 536
 537         if (keyring_name_hash[bucket].next) {
 538                 /* search this hash bucket for a keyring with a matching name
 539                  * that's readable and that hasn't been revoked */
 540                 list_for_each_entry(keyring,
 541                                     &keyring_name_hash[bucket],
 542                                     type_data.link
 543                                     ) {
 544                         if (keyring->user->user_ns != current_user_ns())
 545                                 continue;
 546
 547                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 548                                 continue;
 549
 550                         if (strcmp(keyring->description, name) != 0)
 551                                 continue;
 552
 553                         if (!skip_perm_check &&
 554                             key_permission(make_key_ref(keyring, 0),
 555                                            KEY_SEARCH) < 0)
 556                                 continue;
 557
 558                         /* we've got a match */
 559                         atomic_inc(&keyring->usage);
 560                         read_unlock(&keyring_name_lock);
 561                         goto error;
 562                 }
 563         }
 564
 565         read_unlock(&keyring_name_lock);
 566         keyring = ERR_PTR(-ENOKEY);
 567
 568  error:
 569         return keyring;
 570
 571 } /* end find_keyring_by_name() */
 572
 573 /*****************************************************************************/
 574 /*
 575  * see if a cycle will will be created by inserting acyclic tree B in acyclic
 576  * tree A at the topmost level (ie: as a direct child of A)
 577  * - since we are adding B to A at the top level, checking for cycles should
 578  *   just be a matter of seeing if node A is somewhere in tree B
 579  */
 580 static int keyring_detect_cycle(struct key *A, struct key *B)
 581 {
 582         struct {
 583                 struct keyring_list *keylist;
 584                 int kix;
 585         } stack[KEYRING_SEARCH_MAX_DEPTH];
 586
 587         struct keyring_list *keylist;
 588         struct key *subtree, *key;
 589         int sp, kix, ret;
 590
 591         rcu_read_lock();
 592
 593         ret = -EDEADLK;
 594         if (A == B)
 595                 goto cycle_detected;
 596
 597         subtree = B;
 598         sp = 0;
 599
 600         /* start processing a new keyring */
 601  descend:
 602         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
 603                 goto not_this_keyring;
 604
 605         keylist = rcu_dereference(subtree->payload.subscriptions);
 606         if (!keylist)
 607                 goto not_this_keyring;
 608         kix = 0;
 609
 610  ascend:
 611         /* iterate through the remaining keys in this keyring */
 612         for (; kix < keylist->nkeys; kix++) {
 613                 key = keylist->keys[kix];
 614
 615                 if (key == A)
 616                         goto cycle_detected;
 617
 618                 /* recursively check nested keyrings */
 619                 if (key->type == &key_type_keyring) {
 620                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 621                                 goto too_deep;
 622
 623                         /* stack the current position */
 624                         stack[sp].keylist = keylist;
 625                         stack[sp].kix = kix;
 626                         sp++;
 627
 628                         /* begin again with the new keyring */
 629                         subtree = key;
 630                         goto descend;
 631                 }
 632         }
 633
 634         /* the keyring we're looking at was disqualified or didn't contain a
 635          * matching key */
 636  not_this_keyring:
 637         if (sp > 0) {
 638                 /* resume the checking of a keyring higher up in the tree */
 639                 sp--;
 640                 keylist = stack[sp].keylist;
 641                 kix = stack[sp].kix + 1;
 642                 goto ascend;
 643         }
 644
 645         ret = 0; /* no cycles detected */
 646
 647  error:
 648         rcu_read_unlock();
 649         return ret;
 650
 651  too_deep:
 652         ret = -ELOOP;
 653         goto error;
 654
 655  cycle_detected:
 656         ret = -EDEADLK;
 657         goto error;
 658
 659 } /* end keyring_detect_cycle() */
 660
 661 /*****************************************************************************/
 662 /*
 663  * dispose of a keyring list after the RCU grace period
 664  */
 665 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
 666 {
 667         struct keyring_list *klist =
 668                 container_of(rcu, struct keyring_list, rcu);
 669
 670         kfree(klist);
 671
 672 } /* end keyring_link_rcu_disposal() */
 673
 674 /*****************************************************************************/
 675 /*
 676  * dispose of a keyring list after the RCU grace period, freeing the unlinked
 677  * key
 678  */
 679 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
 680 {
 681         struct keyring_list *klist =
 682                 container_of(rcu, struct keyring_list, rcu);
 683
 684         key_put(klist->keys[klist->delkey]);
 685         kfree(klist);
 686
 687 } /* end keyring_unlink_rcu_disposal() */
 688
 689 /*****************************************************************************/
 690 /*
 691  * link a key into to a keyring
 692  * - must be called with the keyring's semaphore write-locked
 693  * - discard already extant link to matching key if there is one
 694  */
 695 int __key_link(struct key *keyring, struct key *key)
 696 {
 697         struct keyring_list *klist, *nklist;
 698         unsigned max;
 699         size_t size;
 700         int loop, ret;
 701
 702         ret = -EKEYREVOKED;
 703         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 704                 goto error;
 705
 706         ret = -ENOTDIR;
 707         if (keyring->type != &key_type_keyring)
 708                 goto error;
 709
 710         /* serialise link/link calls to prevent parallel calls causing a
 711          * cycle when applied to two keyring in opposite orders */
 712         down_write(&keyring_serialise_link_sem);
 713
 714         /* check that we aren't going to create a cycle adding one keyring to
 715          * another */
 716         if (key->type == &key_type_keyring) {
 717                 ret = keyring_detect_cycle(keyring, key);
 718                 if (ret < 0)
 719                         goto error2;
 720         }
 721
 722         /* see if there's a matching key we can displace */
 723         klist = keyring->payload.subscriptions;
 724
 725         if (klist && klist->nkeys > 0) {
 726                 struct key_type *type = key->type;
 727
 728                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
 729                         if (klist->keys[loop]->type == type &&
 730                             strcmp(klist->keys[loop]->description,
 731                                    key->description) == 0
 732                             ) {
 733                                 /* found a match - replace with new key */
 734                                 size = sizeof(struct key *) * klist->maxkeys;
 735                                 size += sizeof(*klist);
 736                                 BUG_ON(size > PAGE_SIZE);
 737
 738                                 ret = -ENOMEM;
 739                                 nklist = kmemdup(klist, size, GFP_KERNEL);
 740                                 if (!nklist)
 741                                         goto error2;
 742
 743                                 /* replace matched key */
 744                                 atomic_inc(&key->usage);
 745                                 nklist->keys[loop] = key;
 746
 747                                 rcu_assign_pointer(
 748                                         keyring->payload.subscriptions,
 749                                         nklist);
 750
 751                                 /* dispose of the old keyring list and the
 752                                  * displaced key */
 753                                 klist->delkey = loop;
 754                                 call_rcu(&klist->rcu,
 755                                          keyring_unlink_rcu_disposal);
 756
 757                                 goto done;
 758                         }
 759                 }
 760         }
 761
 762         /* check that we aren't going to overrun the user's quota */
 763         ret = key_payload_reserve(keyring,
 764                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
 765         if (ret < 0)
 766                 goto error2;
 767
 768         klist = keyring->payload.subscriptions;
 769
 770         if (klist && klist->nkeys < klist->maxkeys) {
 771                 /* there's sufficient slack space to add directly */
 772                 atomic_inc(&key->usage);
 773
 774                 klist->keys[klist->nkeys] = key;
 775                 smp_wmb();
 776                 klist->nkeys++;
 777                 smp_wmb();
 778         }
 779         else {
 780                 /* grow the key list */
 781                 max = 4;
 782                 if (klist)
 783                         max += klist->maxkeys;
 784
 785                 ret = -ENFILE;
 786                 if (max > 65535)
 787                         goto error3;
 788                 size = sizeof(*klist) + sizeof(struct key *) * max;
 789                 if (size > PAGE_SIZE)
 790                         goto error3;
 791
 792                 ret = -ENOMEM;
 793                 nklist = kmalloc(size, GFP_KERNEL);
 794                 if (!nklist)
 795                         goto error3;
 796                 nklist->maxkeys = max;
 797                 nklist->nkeys = 0;
 798
 799                 if (klist) {
 800                         nklist->nkeys = klist->nkeys;
 801                         memcpy(nklist->keys,
 802                                klist->keys,
 803                                sizeof(struct key *) * klist->nkeys);
 804                 }
 805
 806                 /* add the key into the new space */
 807                 atomic_inc(&key->usage);
 808                 nklist->keys[nklist->nkeys++] = key;
 809
 810                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 811
 812                 /* dispose of the old keyring list */
 813                 if (klist)
 814                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
 815         }
 816
 817 done:
 818         ret = 0;
 819 error2:
 820         up_write(&keyring_serialise_link_sem);
 821 error:
 822         return ret;
 823
 824 error3:
 825         /* undo the quota changes */
 826         key_payload_reserve(keyring,
 827                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 828         goto error2;
 829
 830 } /* end __key_link() */
 831
 832 /*****************************************************************************/
 833 /*
 834  * link a key to a keyring
 835  */
 836 int key_link(struct key *keyring, struct key *key)
 837 {
 838         int ret;
 839
 840         key_check(keyring);
 841         key_check(key);
 842
 843         down_write(&keyring->sem);
 844         ret = __key_link(keyring, key);
 845         up_write(&keyring->sem);
 846
 847         return ret;
 848
 849 } /* end key_link() */
 850
 851 EXPORT_SYMBOL(key_link);
 852
 853 /*****************************************************************************/
 854 /*
 855  * unlink the first link to a key from a keyring
 856  */
 857 int key_unlink(struct key *keyring, struct key *key)
 858 {
 859         struct keyring_list *klist, *nklist;
 860         int loop, ret;
 861
 862         key_check(keyring);
 863         key_check(key);
 864
 865         ret = -ENOTDIR;
 866         if (keyring->type != &key_type_keyring)
 867                 goto error;
 868
 869         down_write(&keyring->sem);
 870
 871         klist = keyring->payload.subscriptions;
 872         if (klist) {
 873                 /* search the keyring for the key */
 874                 for (loop = 0; loop < klist->nkeys; loop++)
 875                         if (klist->keys[loop] == key)
 876                                 goto key_is_present;
 877         }
 878
 879         up_write(&keyring->sem);
 880         ret = -ENOENT;
 881         goto error;
 882
 883 key_is_present:
 884         /* we need to copy the key list for RCU purposes */
 885         nklist = kmalloc(sizeof(*klist) +
 886                          sizeof(struct key *) * klist->maxkeys,
 887                          GFP_KERNEL);
 888         if (!nklist)
 889                 goto nomem;
 890         nklist->maxkeys = klist->maxkeys;
 891         nklist->nkeys = klist->nkeys - 1;
 892
 893         if (loop > 0)
 894                 memcpy(&nklist->keys[0],
 895                        &klist->keys[0],
 896                        loop * sizeof(struct key *));
 897
 898         if (loop < nklist->nkeys)
 899                 memcpy(&nklist->keys[loop],
 900                        &klist->keys[loop + 1],
 901                        (nklist->nkeys - loop) * sizeof(struct key *));
 902
 903         /* adjust the user's quota */
 904         key_payload_reserve(keyring,
 905                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 906
 907         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 908
 909         up_write(&keyring->sem);
 910
 911         /* schedule for later cleanup */
 912         klist->delkey = loop;
 913         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
 914
 915         ret = 0;
 916
 917 error:
 918         return ret;
 919 nomem:
 920         ret = -ENOMEM;
 921         up_write(&keyring->sem);
 922         goto error;
 923
 924 } /* end key_unlink() */
 925
 926 EXPORT_SYMBOL(key_unlink);
 927
 928 /*****************************************************************************/
 929 /*
 930  * dispose of a keyring list after the RCU grace period, releasing the keys it
 931  * links to
 932  */
 933 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
 934 {
 935         struct keyring_list *klist;
 936         int loop;
 937
 938         klist = container_of(rcu, struct keyring_list, rcu);
 939
 940         for (loop = klist->nkeys - 1; loop >= 0; loop--)
 941                 key_put(klist->keys[loop]);
 942
 943         kfree(klist);
 944
 945 } /* end keyring_clear_rcu_disposal() */
 946
 947 /*****************************************************************************/
 948 /*
 949  * clear the specified process keyring
 950  * - implements keyctl(KEYCTL_CLEAR)
 951  */
 952 int keyring_clear(struct key *keyring)
 953 {
 954         struct keyring_list *klist;
 955         int ret;
 956
 957         ret = -ENOTDIR;
 958         if (keyring->type == &key_type_keyring) {
 959                 /* detach the pointer block with the locks held */
 960                 down_write(&keyring->sem);
 961
 962                 klist = keyring->payload.subscriptions;
 963                 if (klist) {
 964                         /* adjust the quota */
 965                         key_payload_reserve(keyring,
 966                                             sizeof(struct keyring_list));
 967
 968                         rcu_assign_pointer(keyring->payload.subscriptions,
 969                                            NULL);
 970                 }
 971
 972                 up_write(&keyring->sem);
 973
 974                 /* free the keys after the locks have been dropped */
 975                 if (klist)
 976                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
 977
 978                 ret = 0;
 979         }
 980
 981         return ret;
 982
 983 } /* end keyring_clear() */
 984
 985 EXPORT_SYMBOL(keyring_clear);
 986
 987 /*****************************************************************************/
 988 /*
 989  * dispose of the links from a revoked keyring
 990  * - called with the key sem write-locked
 991  */
 992 static void keyring_revoke(struct key *keyring)
 993 {
 994         struct keyring_list *klist = keyring->payload.subscriptions;
 995
 996         /* adjust the quota */
 997         key_payload_reserve(keyring, 0);
 998
 999         if (klist) {
1000                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1001                 call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1002         }
1003
1004 } /* end keyring_revoke() */
1005
1006 /*
1007  * Determine whether a key is dead
1008  */
1009 static bool key_is_dead(struct key *key, time_t limit)
1010 {
1011         return test_bit(KEY_FLAG_DEAD, &key->flags) ||
1012                 (key->expiry > 0 && key->expiry <= limit);
1013 }
1014
1015 /*
1016  * Collect garbage from the contents of a keyring
1017  */
1018 void keyring_gc(struct key *keyring, time_t limit)
1019 {
1020         struct keyring_list *klist, *new;
1021         struct key *key;
1022         int loop, keep, max;
1023
1024         kenter("{%x,%s}", key_serial(keyring), keyring->description);
1025
1026         down_write(&keyring->sem);
1027
1028         klist = keyring->payload.subscriptions;
1029         if (!klist)
1030                 goto no_klist;
1031
1032         /* work out how many subscriptions we're keeping */
1033         keep = 0;
1034         for (loop = klist->nkeys - 1; loop >= 0; loop--)
1035                 if (!key_is_dead(klist->keys[loop], limit))
1036                         keep++;
1037
1038         if (keep == klist->nkeys)
1039                 goto just_return;
1040
1041         /* allocate a new keyring payload */
1042         max = roundup(keep, 4);
1043         new = kmalloc(sizeof(struct keyring_list) + max * sizeof(struct key *),
1044                       GFP_KERNEL);
1045         if (!new)
1046                 goto nomem;
1047         new->maxkeys = max;
1048         new->nkeys = 0;
1049         new->delkey = 0;
1050
1051         /* install the live keys
1052          * - must take care as expired keys may be updated back to life
1053          */
1054         keep = 0;
1055         for (loop = klist->nkeys - 1; loop >= 0; loop--) {
1056                 key = klist->keys[loop];
1057                 if (!key_is_dead(key, limit)) {
1058                         if (keep >= max)
1059                                 goto discard_new;
1060                         new->keys[keep++] = key_get(key);
1061                 }
1062         }
1063         new->nkeys = keep;
1064
1065         /* adjust the quota */
1066         key_payload_reserve(keyring,
1067                             sizeof(struct keyring_list) +
1068                             KEYQUOTA_LINK_BYTES * keep);
1069
1070         if (keep == 0) {
1071                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1072                 kfree(new);
1073         } else {
1074                 rcu_assign_pointer(keyring->payload.subscriptions, new);
1075         }
1076
1077         up_write(&keyring->sem);
1078
1079         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1080         kleave(" [yes]");
1081         return;
1082
1083 discard_new:
1084         new->nkeys = keep;
1085         keyring_clear_rcu_disposal(&new->rcu);
1086         up_write(&keyring->sem);
1087         kleave(" [discard]");
1088         return;
1089
1090 just_return:
1091         up_write(&keyring->sem);
1092         kleave(" [no dead]");
1093         return;
1094
1095 no_klist:
1096         up_write(&keyring->sem);
1097         kleave(" [no_klist]");
1098         return;
1099
1100 nomem:
1101         up_write(&keyring->sem);
1102         kleave(" [oom]");
1103 }