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   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_duplicate(struct key *keyring, const struct key *source);
  52 static int keyring_match(const struct key *keyring, const void *criterion);
  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         .duplicate      = keyring_duplicate,
  63         .match          = keyring_match,
  64         .destroy        = keyring_destroy,
  65         .describe       = keyring_describe,
  66         .read           = keyring_read,
  67 };
  68
  69 /*
  70  * semaphore to serialise link/link calls to prevent two link calls in parallel
  71  * introducing a cycle
  72  */
  73 DECLARE_RWSEM(keyring_serialise_link_sem);
  74
  75 /*****************************************************************************/
  76 /*
  77  * publish the name of a keyring so that it can be found by name (if it has
  78  * one)
  79  */
  80 void keyring_publish_name(struct key *keyring)
  81 {
  82         int bucket;
  83
  84         if (keyring->description) {
  85                 bucket = keyring_hash(keyring->description);
  86
  87                 write_lock(&keyring_name_lock);
  88
  89                 if (!keyring_name_hash[bucket].next)
  90                         INIT_LIST_HEAD(&keyring_name_hash[bucket]);
  91
  92                 list_add_tail(&keyring->type_data.link,
  93                               &keyring_name_hash[bucket]);
  94
  95                 write_unlock(&keyring_name_lock);
  96         }
  97
  98 } /* end keyring_publish_name() */
  99
 100 /*****************************************************************************/
 101 /*
 102  * initialise a keyring
 103  * - we object if we were given any data
 104  */
 105 static int keyring_instantiate(struct key *keyring,
 106                                const void *data, size_t datalen)
 107 {
 108         int ret;
 109
 110         ret = -EINVAL;
 111         if (datalen == 0) {
 112                 /* make the keyring available by name if it has one */
 113                 keyring_publish_name(keyring);
 114                 ret = 0;
 115         }
 116
 117         return ret;
 118
 119 } /* end keyring_instantiate() */
 120
 121 /*****************************************************************************/
 122 /*
 123  * duplicate the list of subscribed keys from a source keyring into this one
 124  */
 125 static int keyring_duplicate(struct key *keyring, const struct key *source)
 126 {
 127         struct keyring_list *sklist, *klist;
 128         unsigned max;
 129         size_t size;
 130         int loop, ret;
 131
 132         const unsigned limit =
 133                 (PAGE_SIZE - sizeof(*klist)) / sizeof(struct key *);
 134
 135         ret = 0;
 136
 137         /* find out how many keys are currently linked */
 138         rcu_read_lock();
 139         sklist = rcu_dereference(source->payload.subscriptions);
 140         max = 0;
 141         if (sklist)
 142                 max = sklist->nkeys;
 143         rcu_read_unlock();
 144
 145         /* allocate a new payload and stuff load with key links */
 146         if (max > 0) {
 147                 BUG_ON(max > limit);
 148
 149                 max = (max + 3) & ~3;
 150                 if (max > limit)
 151                         max = limit;
 152
 153                 ret = -ENOMEM;
 154                 size = sizeof(*klist) + sizeof(struct key *) * max;
 155                 klist = kmalloc(size, GFP_KERNEL);
 156                 if (!klist)
 157                         goto error;
 158
 159                 /* set links */
 160                 rcu_read_lock();
 161                 sklist = rcu_dereference(source->payload.subscriptions);
 162
 163                 klist->maxkeys = max;
 164                 klist->nkeys = sklist->nkeys;
 165                 memcpy(klist->keys,
 166                        sklist->keys,
 167                        sklist->nkeys * sizeof(struct key *));
 168
 169                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
 170                         atomic_inc(&klist->keys[loop]->usage);
 171
 172                 rcu_read_unlock();
 173
 174                 rcu_assign_pointer(keyring->payload.subscriptions, klist);
 175                 ret = 0;
 176         }
 177
 178  error:
 179         return ret;
 180
 181 } /* end keyring_duplicate() */
 182
 183 /*****************************************************************************/
 184 /*
 185  * match keyrings on their name
 186  */
 187 static int keyring_match(const struct key *keyring, const void *description)
 188 {
 189         return keyring->description &&
 190                 strcmp(keyring->description, description) == 0;
 191
 192 } /* end keyring_match() */
 193
 194 /*****************************************************************************/
 195 /*
 196  * dispose of the data dangling from the corpse of a keyring
 197  */
 198 static void keyring_destroy(struct key *keyring)
 199 {
 200         struct keyring_list *klist;
 201         int loop;
 202
 203         if (keyring->description) {
 204                 write_lock(&keyring_name_lock);
 205
 206                 if (keyring->type_data.link.next != NULL &&
 207                     !list_empty(&keyring->type_data.link))
 208                         list_del(&keyring->type_data.link);
 209
 210                 write_unlock(&keyring_name_lock);
 211         }
 212
 213         klist = rcu_dereference(keyring->payload.subscriptions);
 214         if (klist) {
 215                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
 216                         key_put(klist->keys[loop]);
 217                 kfree(klist);
 218         }
 219
 220 } /* end keyring_destroy() */
 221
 222 /*****************************************************************************/
 223 /*
 224  * describe the keyring
 225  */
 226 static void keyring_describe(const struct key *keyring, struct seq_file *m)
 227 {
 228         struct keyring_list *klist;
 229
 230         if (keyring->description) {
 231                 seq_puts(m, keyring->description);
 232         }
 233         else {
 234                 seq_puts(m, "[anon]");
 235         }
 236
 237         rcu_read_lock();
 238         klist = rcu_dereference(keyring->payload.subscriptions);
 239         if (klist)
 240                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
 241         else
 242                 seq_puts(m, ": empty");
 243         rcu_read_unlock();
 244
 245 } /* end keyring_describe() */
 246
 247 /*****************************************************************************/
 248 /*
 249  * read a list of key IDs from the keyring's contents
 250  * - the keyring's semaphore is read-locked
 251  */
 252 static long keyring_read(const struct key *keyring,
 253                          char __user *buffer, size_t buflen)
 254 {
 255         struct keyring_list *klist;
 256         struct key *key;
 257         size_t qty, tmp;
 258         int loop, ret;
 259
 260         ret = 0;
 261         klist = rcu_dereference(keyring->payload.subscriptions);
 262
 263         if (klist) {
 264                 /* calculate how much data we could return */
 265                 qty = klist->nkeys * sizeof(key_serial_t);
 266
 267                 if (buffer && buflen > 0) {
 268                         if (buflen > qty)
 269                                 buflen = qty;
 270
 271                         /* copy the IDs of the subscribed keys into the
 272                          * buffer */
 273                         ret = -EFAULT;
 274
 275                         for (loop = 0; loop < klist->nkeys; loop++) {
 276                                 key = klist->keys[loop];
 277
 278                                 tmp = sizeof(key_serial_t);
 279                                 if (tmp > buflen)
 280                                         tmp = buflen;
 281
 282                                 if (copy_to_user(buffer,
 283                                                  &key->serial,
 284                                                  tmp) != 0)
 285                                         goto error;
 286
 287                                 buflen -= tmp;
 288                                 if (buflen == 0)
 289                                         break;
 290                                 buffer += tmp;
 291                         }
 292                 }
 293
 294                 ret = qty;
 295         }
 296
 297  error:
 298         return ret;
 299
 300 } /* end keyring_read() */
 301
 302 /*****************************************************************************/
 303 /*
 304  * allocate a keyring and link into the destination keyring
 305  */
 306 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
 307                           int not_in_quota, struct key *dest)
 308 {
 309         struct key *keyring;
 310         int ret;
 311
 312         keyring = key_alloc(&key_type_keyring, description,
 313                             uid, gid,
 314                             (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
 315                             not_in_quota);
 316
 317         if (!IS_ERR(keyring)) {
 318                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
 319                 if (ret < 0) {
 320                         key_put(keyring);
 321                         keyring = ERR_PTR(ret);
 322                 }
 323         }
 324
 325         return keyring;
 326
 327 } /* end keyring_alloc() */
 328
 329 /*****************************************************************************/
 330 /*
 331  * search the supplied keyring tree for a key that matches the criterion
 332  * - perform a breadth-then-depth search up to the prescribed limit
 333  * - we only find keys on which we have search permission
 334  * - we use the supplied match function to see if the description (or other
 335  *   feature of interest) matches
 336  * - we rely on RCU to prevent the keyring lists from disappearing on us
 337  * - we return -EAGAIN if we didn't find any matching key
 338  * - we return -ENOKEY if we only found negative matching keys
 339  * - we propagate the possession attribute from the keyring ref to the key ref
 340  */
 341 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
 342                              struct task_struct *context,
 343                              struct key_type *type,
 344                              const void *description,
 345                              key_match_func_t match)
 346 {
 347         struct {
 348                 struct keyring_list *keylist;
 349                 int kix;
 350         } stack[KEYRING_SEARCH_MAX_DEPTH];
 351
 352         struct keyring_list *keylist;
 353         struct timespec now;
 354         unsigned long possessed;
 355         struct key *keyring, *key;
 356         key_ref_t key_ref;
 357         long err;
 358         int sp, kix;
 359
 360         keyring = key_ref_to_ptr(keyring_ref);
 361         possessed = is_key_possessed(keyring_ref);
 362         key_check(keyring);
 363
 364         /* top keyring must have search permission to begin the search */
 365         err = key_task_permission(keyring_ref, context, KEY_SEARCH);
 366         if (err < 0) {
 367                 key_ref = ERR_PTR(err);
 368                 goto error;
 369         }
 370
 371         key_ref = ERR_PTR(-ENOTDIR);
 372         if (keyring->type != &key_type_keyring)
 373                 goto error;
 374
 375         rcu_read_lock();
 376
 377         now = current_kernel_time();
 378         err = -EAGAIN;
 379         sp = 0;
 380
 381         /* start processing a new keyring */
 382 descend:
 383         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 384                 goto not_this_keyring;
 385
 386         keylist = rcu_dereference(keyring->payload.subscriptions);
 387         if (!keylist)
 388                 goto not_this_keyring;
 389
 390         /* iterate through the keys in this keyring first */
 391         for (kix = 0; kix < keylist->nkeys; kix++) {
 392                 key = keylist->keys[kix];
 393
 394                 /* ignore keys not of this type */
 395                 if (key->type != type)
 396                         continue;
 397
 398                 /* skip revoked keys and expired keys */
 399                 if (test_bit(KEY_FLAG_REVOKED, &key->flags))
 400                         continue;
 401
 402                 if (key->expiry && now.tv_sec >= key->expiry)
 403                         continue;
 404
 405                 /* keys that don't match */
 406                 if (!match(key, description))
 407                         continue;
 408
 409                 /* key must have search permissions */
 410                 if (key_task_permission(make_key_ref(key, possessed),
 411                                         context, KEY_SEARCH) < 0)
 412                         continue;
 413
 414                 /* we set a different error code if we find a negative key */
 415                 if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
 416                         err = -ENOKEY;
 417                         continue;
 418                 }
 419
 420                 goto found;
 421         }
 422
 423         /* search through the keyrings nested in this one */
 424         kix = 0;
 425 ascend:
 426         for (; kix < keylist->nkeys; kix++) {
 427                 key = keylist->keys[kix];
 428                 if (key->type != &key_type_keyring)
 429                         continue;
 430
 431                 /* recursively search nested keyrings
 432                  * - only search keyrings for which we have search permission
 433                  */
 434                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 435                         continue;
 436
 437                 if (key_task_permission(make_key_ref(key, possessed),
 438                                         context, KEY_SEARCH) < 0)
 439                         continue;
 440
 441                 /* stack the current position */
 442                 stack[sp].keylist = keylist;
 443                 stack[sp].kix = kix;
 444                 sp++;
 445
 446                 /* begin again with the new keyring */
 447                 keyring = key;
 448                 goto descend;
 449         }
 450
 451         /* the keyring we're looking at was disqualified or didn't contain a
 452          * matching key */
 453 not_this_keyring:
 454         if (sp > 0) {
 455                 /* resume the processing of a keyring higher up in the tree */
 456                 sp--;
 457                 keylist = stack[sp].keylist;
 458                 kix = stack[sp].kix + 1;
 459                 goto ascend;
 460         }
 461
 462         key_ref = ERR_PTR(err);
 463         goto error_2;
 464
 465         /* we found a viable match */
 466 found:
 467         atomic_inc(&key->usage);
 468         key_check(key);
 469         key_ref = make_key_ref(key, possessed);
 470 error_2:
 471         rcu_read_unlock();
 472 error:
 473         return key_ref;
 474
 475 } /* end keyring_search_aux() */
 476
 477 /*****************************************************************************/
 478 /*
 479  * search the supplied keyring tree for a key that matches the criterion
 480  * - perform a breadth-then-depth search up to the prescribed limit
 481  * - we only find keys on which we have search permission
 482  * - we readlock the keyrings as we search down the tree
 483  * - we return -EAGAIN if we didn't find any matching key
 484  * - we return -ENOKEY if we only found negative matching keys
 485  */
 486 key_ref_t keyring_search(key_ref_t keyring,
 487                          struct key_type *type,
 488                          const char *description)
 489 {
 490         if (!type->match)
 491                 return ERR_PTR(-ENOKEY);
 492
 493         return keyring_search_aux(keyring, current,
 494                                   type, description, type->match);
 495
 496 } /* end keyring_search() */
 497
 498 EXPORT_SYMBOL(keyring_search);
 499
 500 /*****************************************************************************/
 501 /*
 502  * search the given keyring only (no recursion)
 503  * - keyring must be locked by caller
 504  */
 505 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
 506                                const struct key_type *ktype,
 507                                const char *description,
 508                                key_perm_t perm)
 509 {
 510         struct keyring_list *klist;
 511         unsigned long possessed;
 512         struct key *keyring, *key;
 513         int loop;
 514
 515         keyring = key_ref_to_ptr(keyring_ref);
 516         possessed = is_key_possessed(keyring_ref);
 517
 518         rcu_read_lock();
 519
 520         klist = rcu_dereference(keyring->payload.subscriptions);
 521         if (klist) {
 522                 for (loop = 0; loop < klist->nkeys; loop++) {
 523                         key = klist->keys[loop];
 524
 525                         if (key->type == ktype &&
 526                             (!key->type->match ||
 527                              key->type->match(key, description)) &&
 528                             key_permission(make_key_ref(key, possessed),
 529                                            perm) < 0 &&
 530                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
 531                             )
 532                                 goto found;
 533                 }
 534         }
 535
 536         rcu_read_unlock();
 537         return ERR_PTR(-ENOKEY);
 538
 539  found:
 540         atomic_inc(&key->usage);
 541         rcu_read_unlock();
 542         return make_key_ref(key, possessed);
 543
 544 } /* end __keyring_search_one() */
 545
 546 /*****************************************************************************/
 547 /*
 548  * search for an instantiation authorisation key matching a target key
 549  * - the RCU read lock must be held by the caller
 550  * - a target_id of zero specifies any valid token
 551  */
 552 struct key *keyring_search_instkey(struct key *keyring,
 553                                    key_serial_t target_id)
 554 {
 555         struct request_key_auth *rka;
 556         struct keyring_list *klist;
 557         struct key *instkey;
 558         int loop;
 559
 560         klist = rcu_dereference(keyring->payload.subscriptions);
 561         if (klist) {
 562                 for (loop = 0; loop < klist->nkeys; loop++) {
 563                         instkey = klist->keys[loop];
 564
 565                         if (instkey->type != &key_type_request_key_auth)
 566                                 continue;
 567
 568                         rka = instkey->payload.data;
 569                         if (target_id && rka->target_key->serial != target_id)
 570                                 continue;
 571
 572                         /* the auth key is revoked during instantiation */
 573                         if (!test_bit(KEY_FLAG_REVOKED, &instkey->flags))
 574                                 goto found;
 575
 576                         instkey = ERR_PTR(-EKEYREVOKED);
 577                         goto error;
 578                 }
 579         }
 580
 581         instkey = ERR_PTR(-EACCES);
 582         goto error;
 583
 584 found:
 585         atomic_inc(&instkey->usage);
 586 error:
 587         return instkey;
 588
 589 } /* end keyring_search_instkey() */
 590
 591 /*****************************************************************************/
 592 /*
 593  * find a keyring with the specified name
 594  * - all named keyrings are searched
 595  * - only find keyrings with search permission for the process
 596  * - only find keyrings with a serial number greater than the one specified
 597  */
 598 struct key *find_keyring_by_name(const char *name, key_serial_t bound)
 599 {
 600         struct key *keyring;
 601         int bucket;
 602
 603         keyring = ERR_PTR(-EINVAL);
 604         if (!name)
 605                 goto error;
 606
 607         bucket = keyring_hash(name);
 608
 609         read_lock(&keyring_name_lock);
 610
 611         if (keyring_name_hash[bucket].next) {
 612                 /* search this hash bucket for a keyring with a matching name
 613                  * that's readable and that hasn't been revoked */
 614                 list_for_each_entry(keyring,
 615                                     &keyring_name_hash[bucket],
 616                                     type_data.link
 617                                     ) {
 618                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 619                                 continue;
 620
 621                         if (strcmp(keyring->description, name) != 0)
 622                                 continue;
 623
 624                         if (key_permission(make_key_ref(keyring, 0),
 625                                            KEY_SEARCH) < 0)
 626                                 continue;
 627
 628                         /* found a potential candidate, but we still need to
 629                          * check the serial number */
 630                         if (keyring->serial <= bound)
 631                                 continue;
 632
 633                         /* we've got a match */
 634                         atomic_inc(&keyring->usage);
 635                         read_unlock(&keyring_name_lock);
 636                         goto error;
 637                 }
 638         }
 639
 640         read_unlock(&keyring_name_lock);
 641         keyring = ERR_PTR(-ENOKEY);
 642
 643  error:
 644         return keyring;
 645
 646 } /* end find_keyring_by_name() */
 647
 648 /*****************************************************************************/
 649 /*
 650  * see if a cycle will will be created by inserting acyclic tree B in acyclic
 651  * tree A at the topmost level (ie: as a direct child of A)
 652  * - since we are adding B to A at the top level, checking for cycles should
 653  *   just be a matter of seeing if node A is somewhere in tree B
 654  */
 655 static int keyring_detect_cycle(struct key *A, struct key *B)
 656 {
 657         struct {
 658                 struct keyring_list *keylist;
 659                 int kix;
 660         } stack[KEYRING_SEARCH_MAX_DEPTH];
 661
 662         struct keyring_list *keylist;
 663         struct key *subtree, *key;
 664         int sp, kix, ret;
 665
 666         rcu_read_lock();
 667
 668         ret = -EDEADLK;
 669         if (A == B)
 670                 goto cycle_detected;
 671
 672         subtree = B;
 673         sp = 0;
 674
 675         /* start processing a new keyring */
 676  descend:
 677         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
 678                 goto not_this_keyring;
 679
 680         keylist = rcu_dereference(subtree->payload.subscriptions);
 681         if (!keylist)
 682                 goto not_this_keyring;
 683         kix = 0;
 684
 685  ascend:
 686         /* iterate through the remaining keys in this keyring */
 687         for (; kix < keylist->nkeys; kix++) {
 688                 key = keylist->keys[kix];
 689
 690                 if (key == A)
 691                         goto cycle_detected;
 692
 693                 /* recursively check nested keyrings */
 694                 if (key->type == &key_type_keyring) {
 695                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 696                                 goto too_deep;
 697
 698                         /* stack the current position */
 699                         stack[sp].keylist = keylist;
 700                         stack[sp].kix = kix;
 701                         sp++;
 702
 703                         /* begin again with the new keyring */
 704                         subtree = key;
 705                         goto descend;
 706                 }
 707         }
 708
 709         /* the keyring we're looking at was disqualified or didn't contain a
 710          * matching key */
 711  not_this_keyring:
 712         if (sp > 0) {
 713                 /* resume the checking of a keyring higher up in the tree */
 714                 sp--;
 715                 keylist = stack[sp].keylist;
 716                 kix = stack[sp].kix + 1;
 717                 goto ascend;
 718         }
 719
 720         ret = 0; /* no cycles detected */
 721
 722  error:
 723         rcu_read_unlock();
 724         return ret;
 725
 726  too_deep:
 727         ret = -ELOOP;
 728         goto error;
 729
 730  cycle_detected:
 731         ret = -EDEADLK;
 732         goto error;
 733
 734 } /* end keyring_detect_cycle() */
 735
 736 /*****************************************************************************/
 737 /*
 738  * dispose of a keyring list after the RCU grace period
 739  */
 740 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
 741 {
 742         struct keyring_list *klist =
 743                 container_of(rcu, struct keyring_list, rcu);
 744
 745         kfree(klist);
 746
 747 } /* end keyring_link_rcu_disposal() */
 748
 749 /*****************************************************************************/
 750 /*
 751  * link a key into to a keyring
 752  * - must be called with the keyring's semaphore write-locked
 753  */
 754 int __key_link(struct key *keyring, struct key *key)
 755 {
 756         struct keyring_list *klist, *nklist;
 757         unsigned max;
 758         size_t size;
 759         int ret;
 760
 761         ret = -EKEYREVOKED;
 762         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 763                 goto error;
 764
 765         ret = -ENOTDIR;
 766         if (keyring->type != &key_type_keyring)
 767                 goto error;
 768
 769         /* serialise link/link calls to prevent parallel calls causing a
 770          * cycle when applied to two keyring in opposite orders */
 771         down_write(&keyring_serialise_link_sem);
 772
 773         /* check that we aren't going to create a cycle adding one keyring to
 774          * another */
 775         if (key->type == &key_type_keyring) {
 776                 ret = keyring_detect_cycle(keyring, key);
 777                 if (ret < 0)
 778                         goto error2;
 779         }
 780
 781         /* check that we aren't going to overrun the user's quota */
 782         ret = key_payload_reserve(keyring,
 783                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
 784         if (ret < 0)
 785                 goto error2;
 786
 787         klist = keyring->payload.subscriptions;
 788
 789         if (klist && klist->nkeys < klist->maxkeys) {
 790                 /* there's sufficient slack space to add directly */
 791                 atomic_inc(&key->usage);
 792
 793                 klist->keys[klist->nkeys] = key;
 794                 smp_wmb();
 795                 klist->nkeys++;
 796                 smp_wmb();
 797
 798                 ret = 0;
 799         }
 800         else {
 801                 /* grow the key list */
 802                 max = 4;
 803                 if (klist)
 804                         max += klist->maxkeys;
 805
 806                 ret = -ENFILE;
 807                 if (max > 65535)
 808                         goto error3;
 809                 size = sizeof(*klist) + sizeof(struct key *) * max;
 810                 if (size > PAGE_SIZE)
 811                         goto error3;
 812
 813                 ret = -ENOMEM;
 814                 nklist = kmalloc(size, GFP_KERNEL);
 815                 if (!nklist)
 816                         goto error3;
 817                 nklist->maxkeys = max;
 818                 nklist->nkeys = 0;
 819
 820                 if (klist) {
 821                         nklist->nkeys = klist->nkeys;
 822                         memcpy(nklist->keys,
 823                                klist->keys,
 824                                sizeof(struct key *) * klist->nkeys);
 825                 }
 826
 827                 /* add the key into the new space */
 828                 atomic_inc(&key->usage);
 829                 nklist->keys[nklist->nkeys++] = key;
 830
 831                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 832
 833                 /* dispose of the old keyring list */
 834                 if (klist)
 835                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
 836
 837                 ret = 0;
 838         }
 839
 840  error2:
 841         up_write(&keyring_serialise_link_sem);
 842  error:
 843         return ret;
 844
 845  error3:
 846         /* undo the quota changes */
 847         key_payload_reserve(keyring,
 848                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 849         goto error2;
 850
 851 } /* end __key_link() */
 852
 853 /*****************************************************************************/
 854 /*
 855  * link a key to a keyring
 856  */
 857 int key_link(struct key *keyring, struct key *key)
 858 {
 859         int ret;
 860
 861         key_check(keyring);
 862         key_check(key);
 863
 864         down_write(&keyring->sem);
 865         ret = __key_link(keyring, key);
 866         up_write(&keyring->sem);
 867
 868         return ret;
 869
 870 } /* end key_link() */
 871
 872 EXPORT_SYMBOL(key_link);
 873
 874 /*****************************************************************************/
 875 /*
 876  * dispose of a keyring list after the RCU grace period, freeing the unlinked
 877  * key
 878  */
 879 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
 880 {
 881         struct keyring_list *klist =
 882                 container_of(rcu, struct keyring_list, rcu);
 883
 884         key_put(klist->keys[klist->delkey]);
 885         kfree(klist);
 886
 887 } /* end keyring_unlink_rcu_disposal() */
 888
 889 /*****************************************************************************/
 890 /*
 891  * unlink the first link to a key from a keyring
 892  */
 893 int key_unlink(struct key *keyring, struct key *key)
 894 {
 895         struct keyring_list *klist, *nklist;
 896         int loop, ret;
 897
 898         key_check(keyring);
 899         key_check(key);
 900
 901         ret = -ENOTDIR;
 902         if (keyring->type != &key_type_keyring)
 903                 goto error;
 904
 905         down_write(&keyring->sem);
 906
 907         klist = keyring->payload.subscriptions;
 908         if (klist) {
 909                 /* search the keyring for the key */
 910                 for (loop = 0; loop < klist->nkeys; loop++)
 911                         if (klist->keys[loop] == key)
 912                                 goto key_is_present;
 913         }
 914
 915         up_write(&keyring->sem);
 916         ret = -ENOENT;
 917         goto error;
 918
 919 key_is_present:
 920         /* we need to copy the key list for RCU purposes */
 921         nklist = kmalloc(sizeof(*klist) +
 922                          sizeof(struct key *) * klist->maxkeys,
 923                          GFP_KERNEL);
 924         if (!nklist)
 925                 goto nomem;
 926         nklist->maxkeys = klist->maxkeys;
 927         nklist->nkeys = klist->nkeys - 1;
 928
 929         if (loop > 0)
 930                 memcpy(&nklist->keys[0],
 931                        &klist->keys[0],
 932                        loop * sizeof(struct key *));
 933
 934         if (loop < nklist->nkeys)
 935                 memcpy(&nklist->keys[loop],
 936                        &klist->keys[loop + 1],
 937                        (nklist->nkeys - loop) * sizeof(struct key *));
 938
 939         /* adjust the user's quota */
 940         key_payload_reserve(keyring,
 941                             keyring->datalen - KEYQUOTA_LINK_BYTES);
 942
 943         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 944
 945         up_write(&keyring->sem);
 946
 947         /* schedule for later cleanup */
 948         klist->delkey = loop;
 949         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
 950
 951         ret = 0;
 952
 953 error:
 954         return ret;
 955 nomem:
 956         ret = -ENOMEM;
 957         up_write(&keyring->sem);
 958         goto error;
 959
 960 } /* end key_unlink() */
 961
 962 EXPORT_SYMBOL(key_unlink);
 963
 964 /*****************************************************************************/
 965 /*
 966  * dispose of a keyring list after the RCU grace period, releasing the keys it
 967  * links to
 968  */
 969 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
 970 {
 971         struct keyring_list *klist;
 972         int loop;
 973
 974         klist = container_of(rcu, struct keyring_list, rcu);
 975
 976         for (loop = klist->nkeys - 1; loop >= 0; loop--)
 977                 key_put(klist->keys[loop]);
 978
 979         kfree(klist);
 980
 981 } /* end keyring_clear_rcu_disposal() */
 982
 983 /*****************************************************************************/
 984 /*
 985  * clear the specified process keyring
 986  * - implements keyctl(KEYCTL_CLEAR)
 987  */
 988 int keyring_clear(struct key *keyring)
 989 {
 990         struct keyring_list *klist;
 991         int ret;
 992
 993         ret = -ENOTDIR;
 994         if (keyring->type == &key_type_keyring) {
 995                 /* detach the pointer block with the locks held */
 996                 down_write(&keyring->sem);
 997
 998                 klist = keyring->payload.subscriptions;
 999                 if (klist) {
1000                         /* adjust the quota */
1001                         key_payload_reserve(keyring,
1002                                             sizeof(struct keyring_list));
1003
1004                         rcu_assign_pointer(keyring->payload.subscriptions,
1005                                            NULL);
1006                 }
1007
1008                 up_write(&keyring->sem);
1009
1010                 /* free the keys after the locks have been dropped */
1011                 if (klist)
1012                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1013
1014                 ret = 0;
1015         }
1016
1017         return ret;
1018
1019 } /* end keyring_clear() */
1020
1021 EXPORT_SYMBOL(keyring_clear);