linux/security/keys/keyring.c
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   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 <linux/uaccess.h>
  21#include "internal.h"
  22
  23#define rcu_dereference_locked_keyring(keyring)                         \
  24        (rcu_dereference_protected(                                     \
  25                (keyring)->payload.subscriptions,                       \
  26                rwsem_is_locked((struct rw_semaphore *)&(keyring)->sem)))
  27
  28#define rcu_deref_link_locked(klist, index, keyring)                    \
  29        (rcu_dereference_protected(                                     \
  30                (klist)->keys[index],                                   \
  31                rwsem_is_locked((struct rw_semaphore *)&(keyring)->sem)))
  32
  33#define MAX_KEYRING_LINKS                                               \
  34        min_t(size_t, USHRT_MAX - 1,                                    \
  35              ((PAGE_SIZE - sizeof(struct keyring_list)) / sizeof(struct key *)))
  36
  37#define KEY_LINK_FIXQUOTA 1UL
  38
  39/*
  40 * When plumbing the depths of the key tree, this sets a hard limit
  41 * set on how deep we're willing to go.
  42 */
  43#define KEYRING_SEARCH_MAX_DEPTH 6
  44
  45/*
  46 * We keep all named keyrings in a hash to speed looking them up.
  47 */
  48#define KEYRING_NAME_HASH_SIZE  (1 << 5)
  49
  50static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
  51static DEFINE_RWLOCK(keyring_name_lock);
  52
  53static inline unsigned keyring_hash(const char *desc)
  54{
  55        unsigned bucket = 0;
  56
  57        for (; *desc; desc++)
  58                bucket += (unsigned char)*desc;
  59
  60        return bucket & (KEYRING_NAME_HASH_SIZE - 1);
  61}
  62
  63/*
  64 * The keyring key type definition.  Keyrings are simply keys of this type and
  65 * can be treated as ordinary keys in addition to having their own special
  66 * operations.
  67 */
  68static int keyring_instantiate(struct key *keyring,
  69                               const void *data, size_t datalen);
  70static int keyring_match(const struct key *keyring, const void *criterion);
  71static void keyring_revoke(struct key *keyring);
  72static void keyring_destroy(struct key *keyring);
  73static void keyring_describe(const struct key *keyring, struct seq_file *m);
  74static long keyring_read(const struct key *keyring,
  75                         char __user *buffer, size_t buflen);
  76
  77struct key_type key_type_keyring = {
  78        .name           = "keyring",
  79        .def_datalen    = sizeof(struct keyring_list),
  80        .instantiate    = keyring_instantiate,
  81        .match          = keyring_match,
  82        .revoke         = keyring_revoke,
  83        .destroy        = keyring_destroy,
  84        .describe       = keyring_describe,
  85        .read           = keyring_read,
  86};
  87EXPORT_SYMBOL(key_type_keyring);
  88
  89/*
  90 * Semaphore to serialise link/link calls to prevent two link calls in parallel
  91 * introducing a cycle.
  92 */
  93static DECLARE_RWSEM(keyring_serialise_link_sem);
  94
  95/*
  96 * Publish the name of a keyring so that it can be found by name (if it has
  97 * one).
  98 */
  99static void keyring_publish_name(struct key *keyring)
 100{
 101        int bucket;
 102
 103        if (keyring->description) {
 104                bucket = keyring_hash(keyring->description);
 105
 106                write_lock(&keyring_name_lock);
 107
 108                if (!keyring_name_hash[bucket].next)
 109                        INIT_LIST_HEAD(&keyring_name_hash[bucket]);
 110
 111                list_add_tail(&keyring->type_data.link,
 112                              &keyring_name_hash[bucket]);
 113
 114                write_unlock(&keyring_name_lock);
 115        }
 116}
 117
 118/*
 119 * Initialise a keyring.
 120 *
 121 * Returns 0 on success, -EINVAL if given any data.
 122 */
 123static int keyring_instantiate(struct key *keyring,
 124                               const void *data, size_t datalen)
 125{
 126        int ret;
 127
 128        ret = -EINVAL;
 129        if (datalen == 0) {
 130                /* make the keyring available by name if it has one */
 131                keyring_publish_name(keyring);
 132                ret = 0;
 133        }
 134
 135        return ret;
 136}
 137
 138/*
 139 * Match keyrings on their name
 140 */
 141static int keyring_match(const struct key *keyring, const void *description)
 142{
 143        return keyring->description &&
 144                strcmp(keyring->description, description) == 0;
 145}
 146
 147/*
 148 * Clean up a keyring when it is destroyed.  Unpublish its name if it had one
 149 * and dispose of its data.
 150 *
 151 * The garbage collector detects the final key_put(), removes the keyring from
 152 * the serial number tree and then does RCU synchronisation before coming here,
 153 * so we shouldn't need to worry about code poking around here with the RCU
 154 * readlock held by this time.
 155 */
 156static void keyring_destroy(struct key *keyring)
 157{
 158        struct keyring_list *klist;
 159        int loop;
 160
 161        if (keyring->description) {
 162                write_lock(&keyring_name_lock);
 163
 164                if (keyring->type_data.link.next != NULL &&
 165                    !list_empty(&keyring->type_data.link))
 166                        list_del(&keyring->type_data.link);
 167
 168                write_unlock(&keyring_name_lock);
 169        }
 170
 171        klist = rcu_access_pointer(keyring->payload.subscriptions);
 172        if (klist) {
 173                for (loop = klist->nkeys - 1; loop >= 0; loop--)
 174                        key_put(rcu_access_pointer(klist->keys[loop]));
 175                kfree(klist);
 176        }
 177}
 178
 179/*
 180 * Describe a keyring for /proc.
 181 */
 182static void keyring_describe(const struct key *keyring, struct seq_file *m)
 183{
 184        struct keyring_list *klist;
 185
 186        if (keyring->description)
 187                seq_puts(m, keyring->description);
 188        else
 189                seq_puts(m, "[anon]");
 190
 191        if (key_is_instantiated(keyring)) {
 192                rcu_read_lock();
 193                klist = rcu_dereference(keyring->payload.subscriptions);
 194                if (klist)
 195                        seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
 196                else
 197                        seq_puts(m, ": empty");
 198                rcu_read_unlock();
 199        }
 200}
 201
 202/*
 203 * Read a list of key IDs from the keyring's contents in binary form
 204 *
 205 * The keyring's semaphore is read-locked by the caller.
 206 */
 207static long keyring_read(const struct key *keyring,
 208                         char __user *buffer, size_t buflen)
 209{
 210        struct keyring_list *klist;
 211        struct key *key;
 212        size_t qty, tmp;
 213        int loop, ret;
 214
 215        ret = 0;
 216        klist = rcu_dereference_locked_keyring(keyring);
 217        if (klist) {
 218                /* calculate how much data we could return */
 219                qty = klist->nkeys * sizeof(key_serial_t);
 220
 221                if (buffer && buflen > 0) {
 222                        if (buflen > qty)
 223                                buflen = qty;
 224
 225                        /* copy the IDs of the subscribed keys into the
 226                         * buffer */
 227                        ret = -EFAULT;
 228
 229                        for (loop = 0; loop < klist->nkeys; loop++) {
 230                                key = rcu_deref_link_locked(klist, loop,
 231                                                            keyring);
 232
 233                                tmp = sizeof(key_serial_t);
 234                                if (tmp > buflen)
 235                                        tmp = buflen;
 236
 237                                if (copy_to_user(buffer,
 238                                                 &key->serial,
 239                                                 tmp) != 0)
 240                                        goto error;
 241
 242                                buflen -= tmp;
 243                                if (buflen == 0)
 244                                        break;
 245                                buffer += tmp;
 246                        }
 247                }
 248
 249                ret = qty;
 250        }
 251
 252error:
 253        return ret;
 254}
 255
 256/*
 257 * Allocate a keyring and link into the destination keyring.
 258 */
 259struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
 260                          const struct cred *cred, unsigned long flags,
 261                          struct key *dest)
 262{
 263        struct key *keyring;
 264        int ret;
 265
 266        keyring = key_alloc(&key_type_keyring, description,
 267                            uid, gid, cred,
 268                            (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
 269                            flags);
 270
 271        if (!IS_ERR(keyring)) {
 272                ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
 273                if (ret < 0) {
 274                        key_put(keyring);
 275                        keyring = ERR_PTR(ret);
 276                }
 277        }
 278
 279        return keyring;
 280}
 281
 282/**
 283 * keyring_search_aux - Search a keyring tree for a key matching some criteria
 284 * @keyring_ref: A pointer to the keyring with possession indicator.
 285 * @cred: The credentials to use for permissions checks.
 286 * @type: The type of key to search for.
 287 * @description: Parameter for @match.
 288 * @match: Function to rule on whether or not a key is the one required.
 289 * @no_state_check: Don't check if a matching key is bad
 290 *
 291 * Search the supplied keyring tree for a key that matches the criteria given.
 292 * The root keyring and any linked keyrings must grant Search permission to the
 293 * caller to be searchable and keys can only be found if they too grant Search
 294 * to the caller. The possession flag on the root keyring pointer controls use
 295 * of the possessor bits in permissions checking of the entire tree.  In
 296 * addition, the LSM gets to forbid keyring searches and key matches.
 297 *
 298 * The search is performed as a breadth-then-depth search up to the prescribed
 299 * limit (KEYRING_SEARCH_MAX_DEPTH).
 300 *
 301 * Keys are matched to the type provided and are then filtered by the match
 302 * function, which is given the description to use in any way it sees fit.  The
 303 * match function may use any attributes of a key that it wishes to to
 304 * determine the match.  Normally the match function from the key type would be
 305 * used.
 306 *
 307 * RCU is used to prevent the keyring key lists from disappearing without the
 308 * need to take lots of locks.
 309 *
 310 * Returns a pointer to the found key and increments the key usage count if
 311 * successful; -EAGAIN if no matching keys were found, or if expired or revoked
 312 * keys were found; -ENOKEY if only negative keys were found; -ENOTDIR if the
 313 * specified keyring wasn't a keyring.
 314 *
 315 * In the case of a successful return, the possession attribute from
 316 * @keyring_ref is propagated to the returned key reference.
 317 */
 318key_ref_t keyring_search_aux(key_ref_t keyring_ref,
 319                             const struct cred *cred,
 320                             struct key_type *type,
 321                             const void *description,
 322                             key_match_func_t match,
 323                             bool no_state_check)
 324{
 325        struct {
 326                /* Need a separate keylist pointer for RCU purposes */
 327                struct key *keyring;
 328                struct keyring_list *keylist;
 329                int kix;
 330        } stack[KEYRING_SEARCH_MAX_DEPTH];
 331
 332        struct keyring_list *keylist;
 333        struct timespec now;
 334        unsigned long possessed, kflags;
 335        struct key *keyring, *key;
 336        key_ref_t key_ref;
 337        long err;
 338        int sp, nkeys, kix;
 339
 340        keyring = key_ref_to_ptr(keyring_ref);
 341        possessed = is_key_possessed(keyring_ref);
 342        key_check(keyring);
 343
 344        /* top keyring must have search permission to begin the search */
 345        err = key_task_permission(keyring_ref, cred, KEY_SEARCH);
 346        if (err < 0) {
 347                key_ref = ERR_PTR(err);
 348                goto error;
 349        }
 350
 351        key_ref = ERR_PTR(-ENOTDIR);
 352        if (keyring->type != &key_type_keyring)
 353                goto error;
 354
 355        rcu_read_lock();
 356
 357        now = current_kernel_time();
 358        err = -EAGAIN;
 359        sp = 0;
 360
 361        /* firstly we should check to see if this top-level keyring is what we
 362         * are looking for */
 363        key_ref = ERR_PTR(-EAGAIN);
 364        kflags = keyring->flags;
 365        if (keyring->type == type && match(keyring, description)) {
 366                key = keyring;
 367                if (no_state_check)
 368                        goto found;
 369
 370                /* check it isn't negative and hasn't expired or been
 371                 * revoked */
 372                if (kflags & (1 << KEY_FLAG_REVOKED))
 373                        goto error_2;
 374                if (key->expiry && now.tv_sec >= key->expiry)
 375                        goto error_2;
 376                key_ref = ERR_PTR(key->type_data.reject_error);
 377                if (kflags & (1 << KEY_FLAG_NEGATIVE))
 378                        goto error_2;
 379                goto found;
 380        }
 381
 382        /* otherwise, the top keyring must not be revoked, expired, or
 383         * negatively instantiated if we are to search it */
 384        key_ref = ERR_PTR(-EAGAIN);
 385        if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
 386                      (1 << KEY_FLAG_REVOKED) |
 387                      (1 << KEY_FLAG_NEGATIVE)) ||
 388            (keyring->expiry && now.tv_sec >= keyring->expiry))
 389                goto error_2;
 390
 391        /* start processing a new keyring */
 392descend:
 393        kflags = keyring->flags;
 394        if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
 395                      (1 << KEY_FLAG_REVOKED)))
 396                goto not_this_keyring;
 397
 398        keylist = rcu_dereference(keyring->payload.subscriptions);
 399        if (!keylist)
 400                goto not_this_keyring;
 401
 402        /* iterate through the keys in this keyring first */
 403        nkeys = keylist->nkeys;
 404        smp_rmb();
 405        for (kix = 0; kix < nkeys; kix++) {
 406                key = rcu_dereference(keylist->keys[kix]);
 407                kflags = key->flags;
 408
 409                /* ignore keys not of this type */
 410                if (key->type != type)
 411                        continue;
 412
 413                /* skip invalidated, revoked and expired keys */
 414                if (!no_state_check) {
 415                        if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
 416                                      (1 << KEY_FLAG_REVOKED)))
 417                                continue;
 418
 419                        if (key->expiry && now.tv_sec >= key->expiry)
 420                                continue;
 421                }
 422
 423                /* keys that don't match */
 424                if (!match(key, description))
 425                        continue;
 426
 427                /* key must have search permissions */
 428                if (key_task_permission(make_key_ref(key, possessed),
 429                                        cred, KEY_SEARCH) < 0)
 430                        continue;
 431
 432                if (no_state_check)
 433                        goto found;
 434
 435                /* we set a different error code if we pass a negative key */
 436                if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
 437                        err = key->type_data.reject_error;
 438                        continue;
 439                }
 440
 441                goto found;
 442        }
 443
 444        /* search through the keyrings nested in this one */
 445        kix = 0;
 446ascend:
 447        nkeys = keylist->nkeys;
 448        smp_rmb();
 449        for (; kix < nkeys; kix++) {
 450                key = rcu_dereference(keylist->keys[kix]);
 451                if (key->type != &key_type_keyring)
 452                        continue;
 453
 454                /* recursively search nested keyrings
 455                 * - only search keyrings for which we have search permission
 456                 */
 457                if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 458                        continue;
 459
 460                if (key_task_permission(make_key_ref(key, possessed),
 461                                        cred, KEY_SEARCH) < 0)
 462                        continue;
 463
 464                /* stack the current position */
 465                stack[sp].keyring = keyring;
 466                stack[sp].keylist = keylist;
 467                stack[sp].kix = kix;
 468                sp++;
 469
 470                /* begin again with the new keyring */
 471                keyring = key;
 472                goto descend;
 473        }
 474
 475        /* the keyring we're looking at was disqualified or didn't contain a
 476         * matching key */
 477not_this_keyring:
 478        if (sp > 0) {
 479                /* resume the processing of a keyring higher up in the tree */
 480                sp--;
 481                keyring = stack[sp].keyring;
 482                keylist = stack[sp].keylist;
 483                kix = stack[sp].kix + 1;
 484                goto ascend;
 485        }
 486
 487        key_ref = ERR_PTR(err);
 488        goto error_2;
 489
 490        /* we found a viable match */
 491found:
 492        atomic_inc(&key->usage);
 493        key->last_used_at = now.tv_sec;
 494        keyring->last_used_at = now.tv_sec;
 495        while (sp > 0)
 496                stack[--sp].keyring->last_used_at = now.tv_sec;
 497        key_check(key);
 498        key_ref = make_key_ref(key, possessed);
 499error_2:
 500        rcu_read_unlock();
 501error:
 502        return key_ref;
 503}
 504
 505/**
 506 * keyring_search - Search the supplied keyring tree for a matching key
 507 * @keyring: The root of the keyring tree to be searched.
 508 * @type: The type of keyring we want to find.
 509 * @description: The name of the keyring we want to find.
 510 *
 511 * As keyring_search_aux() above, but using the current task's credentials and
 512 * type's default matching function.
 513 */
 514key_ref_t keyring_search(key_ref_t keyring,
 515                         struct key_type *type,
 516                         const char *description)
 517{
 518        if (!type->match)
 519                return ERR_PTR(-ENOKEY);
 520
 521        return keyring_search_aux(keyring, current->cred,
 522                                  type, description, type->match, false);
 523}
 524EXPORT_SYMBOL(keyring_search);
 525
 526/*
 527 * Search the given keyring only (no recursion).
 528 *
 529 * The caller must guarantee that the keyring is a keyring and that the
 530 * permission is granted to search the keyring as no check is made here.
 531 *
 532 * RCU is used to make it unnecessary to lock the keyring key list here.
 533 *
 534 * Returns a pointer to the found key with usage count incremented if
 535 * successful and returns -ENOKEY if not found.  Revoked keys and keys not
 536 * providing the requested permission are skipped over.
 537 *
 538 * If successful, the possession indicator is propagated from the keyring ref
 539 * to the returned key reference.
 540 */
 541key_ref_t __keyring_search_one(key_ref_t keyring_ref,
 542                               const struct key_type *ktype,
 543                               const char *description,
 544                               key_perm_t perm)
 545{
 546        struct keyring_list *klist;
 547        unsigned long possessed;
 548        struct key *keyring, *key;
 549        int nkeys, loop;
 550
 551        keyring = key_ref_to_ptr(keyring_ref);
 552        possessed = is_key_possessed(keyring_ref);
 553
 554        rcu_read_lock();
 555
 556        klist = rcu_dereference(keyring->payload.subscriptions);
 557        if (klist) {
 558                nkeys = klist->nkeys;
 559                smp_rmb();
 560                for (loop = 0; loop < nkeys ; loop++) {
 561                        key = rcu_dereference(klist->keys[loop]);
 562                        if (key->type == ktype &&
 563                            (!key->type->match ||
 564                             key->type->match(key, description)) &&
 565                            key_permission(make_key_ref(key, possessed),
 566                                           perm) == 0 &&
 567                            !(key->flags & ((1 << KEY_FLAG_INVALIDATED) |
 568                                            (1 << KEY_FLAG_REVOKED)))
 569                            )
 570                                goto found;
 571                }
 572        }
 573
 574        rcu_read_unlock();
 575        return ERR_PTR(-ENOKEY);
 576
 577found:
 578        atomic_inc(&key->usage);
 579        keyring->last_used_at = key->last_used_at =
 580                current_kernel_time().tv_sec;
 581        rcu_read_unlock();
 582        return make_key_ref(key, possessed);
 583}
 584
 585/*
 586 * Find a keyring with the specified name.
 587 *
 588 * All named keyrings in the current user namespace are searched, provided they
 589 * grant Search permission directly to the caller (unless this check is
 590 * skipped).  Keyrings whose usage points have reached zero or who have been
 591 * revoked are skipped.
 592 *
 593 * Returns a pointer to the keyring with the keyring's refcount having being
 594 * incremented on success.  -ENOKEY is returned if a key could not be found.
 595 */
 596struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
 597{
 598        struct key *keyring;
 599        int bucket;
 600
 601        if (!name)
 602                return ERR_PTR(-EINVAL);
 603
 604        bucket = keyring_hash(name);
 605
 606        read_lock(&keyring_name_lock);
 607
 608        if (keyring_name_hash[bucket].next) {
 609                /* search this hash bucket for a keyring with a matching name
 610                 * that's readable and that hasn't been revoked */
 611                list_for_each_entry(keyring,
 612                                    &keyring_name_hash[bucket],
 613                                    type_data.link
 614                                    ) {
 615                        if (keyring->user->user_ns != current_user_ns())
 616                                continue;
 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 (!skip_perm_check &&
 625                            key_permission(make_key_ref(keyring, 0),
 626                                           KEY_SEARCH) < 0)
 627                                continue;
 628
 629                        /* we've got a match but we might end up racing with
 630                         * key_cleanup() if the keyring is currently 'dead'
 631                         * (ie. it has a zero usage count) */
 632                        if (!atomic_inc_not_zero(&keyring->usage))
 633                                continue;
 634                        keyring->last_used_at = current_kernel_time().tv_sec;
 635                        goto out;
 636                }
 637        }
 638
 639        keyring = ERR_PTR(-ENOKEY);
 640out:
 641        read_unlock(&keyring_name_lock);
 642        return keyring;
 643}
 644
 645/*
 646 * See if a cycle will will be created by inserting acyclic tree B in acyclic
 647 * tree A at the topmost level (ie: as a direct child of A).
 648 *
 649 * Since we are adding B to A at the top level, checking for cycles should just
 650 * be a matter of seeing if node A is somewhere in tree B.
 651 */
 652static int keyring_detect_cycle(struct key *A, struct key *B)
 653{
 654        struct {
 655                struct keyring_list *keylist;
 656                int kix;
 657        } stack[KEYRING_SEARCH_MAX_DEPTH];
 658
 659        struct keyring_list *keylist;
 660        struct key *subtree, *key;
 661        int sp, nkeys, kix, ret;
 662
 663        rcu_read_lock();
 664
 665        ret = -EDEADLK;
 666        if (A == B)
 667                goto cycle_detected;
 668
 669        subtree = B;
 670        sp = 0;
 671
 672        /* start processing a new keyring */
 673descend:
 674        if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
 675                goto not_this_keyring;
 676
 677        keylist = rcu_dereference(subtree->payload.subscriptions);
 678        if (!keylist)
 679                goto not_this_keyring;
 680        kix = 0;
 681
 682ascend:
 683        /* iterate through the remaining keys in this keyring */
 684        nkeys = keylist->nkeys;
 685        smp_rmb();
 686        for (; kix < nkeys; kix++) {
 687                key = rcu_dereference(keylist->keys[kix]);
 688
 689                if (key == A)
 690                        goto cycle_detected;
 691
 692                /* recursively check nested keyrings */
 693                if (key->type == &key_type_keyring) {
 694                        if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 695                                goto too_deep;
 696
 697                        /* stack the current position */
 698                        stack[sp].keylist = keylist;
 699                        stack[sp].kix = kix;
 700                        sp++;
 701
 702                        /* begin again with the new keyring */
 703                        subtree = key;
 704                        goto descend;
 705                }
 706        }
 707
 708        /* the keyring we're looking at was disqualified or didn't contain a
 709         * matching key */
 710not_this_keyring:
 711        if (sp > 0) {
 712                /* resume the checking of a keyring higher up in the tree */
 713                sp--;
 714                keylist = stack[sp].keylist;
 715                kix = stack[sp].kix + 1;
 716                goto ascend;
 717        }
 718
 719        ret = 0; /* no cycles detected */
 720
 721error:
 722        rcu_read_unlock();
 723        return ret;
 724
 725too_deep:
 726        ret = -ELOOP;
 727        goto error;
 728
 729cycle_detected:
 730        ret = -EDEADLK;
 731        goto error;
 732}
 733
 734/*
 735 * Dispose of a keyring list after the RCU grace period, freeing the unlinked
 736 * key
 737 */
 738static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
 739{
 740        struct keyring_list *klist =
 741                container_of(rcu, struct keyring_list, rcu);
 742
 743        if (klist->delkey != USHRT_MAX)
 744                key_put(rcu_access_pointer(klist->keys[klist->delkey]));
 745        kfree(klist);
 746}
 747
 748/*
 749 * Preallocate memory so that a key can be linked into to a keyring.
 750 */
 751int __key_link_begin(struct key *keyring, const struct key_type *type,
 752                     const char *description, unsigned long *_prealloc)
 753        __acquires(&keyring->sem)
 754        __acquires(&keyring_serialise_link_sem)
 755{
 756        struct keyring_list *klist, *nklist;
 757        unsigned long prealloc;
 758        unsigned max;
 759        time_t lowest_lru;
 760        size_t size;
 761        int loop, lru, ret;
 762
 763        kenter("%d,%s,%s,", key_serial(keyring), type->name, description);
 764
 765        if (keyring->type != &key_type_keyring)
 766                return -ENOTDIR;
 767
 768        down_write(&keyring->sem);
 769
 770        ret = -EKEYREVOKED;
 771        if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 772                goto error_krsem;
 773
 774        /* serialise link/link calls to prevent parallel calls causing a cycle
 775         * when linking two keyring in opposite orders */
 776        if (type == &key_type_keyring)
 777                down_write(&keyring_serialise_link_sem);
 778
 779        klist = rcu_dereference_locked_keyring(keyring);
 780
 781        /* see if there's a matching key we can displace */
 782        lru = -1;
 783        if (klist && klist->nkeys > 0) {
 784                lowest_lru = TIME_T_MAX;
 785                for (loop = klist->nkeys - 1; loop >= 0; loop--) {
 786                        struct key *key = rcu_deref_link_locked(klist, loop,
 787                                                                keyring);
 788                        if (key->type == type &&
 789                            strcmp(key->description, description) == 0) {
 790                                /* Found a match - we'll replace the link with
 791                                 * one to the new key.  We record the slot
 792                                 * position.
 793                                 */
 794                                klist->delkey = loop;
 795                                prealloc = 0;
 796                                goto done;
 797                        }
 798                        if (key->last_used_at < lowest_lru) {
 799                                lowest_lru = key->last_used_at;
 800                                lru = loop;
 801                        }
 802                }
 803        }
 804
 805        /* If the keyring is full then do an LRU discard */
 806        if (klist &&
 807            klist->nkeys == klist->maxkeys &&
 808            klist->maxkeys >= MAX_KEYRING_LINKS) {
 809                kdebug("LRU discard %d\n", lru);
 810                klist->delkey = lru;
 811                prealloc = 0;
 812                goto done;
 813        }
 814
 815        /* check that we aren't going to overrun the user's quota */
 816        ret = key_payload_reserve(keyring,
 817                                  keyring->datalen + KEYQUOTA_LINK_BYTES);
 818        if (ret < 0)
 819                goto error_sem;
 820
 821        if (klist && klist->nkeys < klist->maxkeys) {
 822                /* there's sufficient slack space to append directly */
 823                klist->delkey = klist->nkeys;
 824                prealloc = KEY_LINK_FIXQUOTA;
 825        } else {
 826                /* grow the key list */
 827                max = 4;
 828                if (klist) {
 829                        max += klist->maxkeys;
 830                        if (max > MAX_KEYRING_LINKS)
 831                                max = MAX_KEYRING_LINKS;
 832                        BUG_ON(max <= klist->maxkeys);
 833                }
 834
 835                size = sizeof(*klist) + sizeof(struct key *) * max;
 836
 837                ret = -ENOMEM;
 838                nklist = kmalloc(size, GFP_KERNEL);
 839                if (!nklist)
 840                        goto error_quota;
 841
 842                nklist->maxkeys = max;
 843                if (klist) {
 844                        memcpy(nklist->keys, klist->keys,
 845                               sizeof(struct key *) * klist->nkeys);
 846                        nklist->delkey = klist->nkeys;
 847                        nklist->nkeys = klist->nkeys + 1;
 848                        klist->delkey = USHRT_MAX;
 849                } else {
 850                        nklist->nkeys = 1;
 851                        nklist->delkey = 0;
 852                }
 853
 854                /* add the key into the new space */
 855                RCU_INIT_POINTER(nklist->keys[nklist->delkey], NULL);
 856                prealloc = (unsigned long)nklist | KEY_LINK_FIXQUOTA;
 857        }
 858
 859done:
 860        *_prealloc = prealloc;
 861        kleave(" = 0");
 862        return 0;
 863
 864error_quota:
 865        /* undo the quota changes */
 866        key_payload_reserve(keyring,
 867                            keyring->datalen - KEYQUOTA_LINK_BYTES);
 868error_sem:
 869        if (type == &key_type_keyring)
 870                up_write(&keyring_serialise_link_sem);
 871error_krsem:
 872        up_write(&keyring->sem);
 873        kleave(" = %d", ret);
 874        return ret;
 875}
 876
 877/*
 878 * Check already instantiated keys aren't going to be a problem.
 879 *
 880 * The caller must have called __key_link_begin(). Don't need to call this for
 881 * keys that were created since __key_link_begin() was called.
 882 */
 883int __key_link_check_live_key(struct key *keyring, struct key *key)
 884{
 885        if (key->type == &key_type_keyring)
 886                /* check that we aren't going to create a cycle by linking one
 887                 * keyring to another */
 888                return keyring_detect_cycle(keyring, key);
 889        return 0;
 890}
 891
 892/*
 893 * Link a key into to a keyring.
 894 *
 895 * Must be called with __key_link_begin() having being called.  Discards any
 896 * already extant link to matching key if there is one, so that each keyring
 897 * holds at most one link to any given key of a particular type+description
 898 * combination.
 899 */
 900void __key_link(struct key *keyring, struct key *key,
 901                unsigned long *_prealloc)
 902{
 903        struct keyring_list *klist, *nklist;
 904        struct key *discard;
 905
 906        nklist = (struct keyring_list *)(*_prealloc & ~KEY_LINK_FIXQUOTA);
 907        *_prealloc = 0;
 908
 909        kenter("%d,%d,%p", keyring->serial, key->serial, nklist);
 910
 911        klist = rcu_dereference_locked_keyring(keyring);
 912
 913        atomic_inc(&key->usage);
 914        keyring->last_used_at = key->last_used_at =
 915                current_kernel_time().tv_sec;
 916
 917        /* there's a matching key we can displace or an empty slot in a newly
 918         * allocated list we can fill */
 919        if (nklist) {
 920                kdebug("reissue %hu/%hu/%hu",
 921                       nklist->delkey, nklist->nkeys, nklist->maxkeys);
 922
 923                RCU_INIT_POINTER(nklist->keys[nklist->delkey], key);
 924
 925                rcu_assign_pointer(keyring->payload.subscriptions, nklist);
 926
 927                /* dispose of the old keyring list and, if there was one, the
 928                 * displaced key */
 929                if (klist) {
 930                        kdebug("dispose %hu/%hu/%hu",
 931                               klist->delkey, klist->nkeys, klist->maxkeys);
 932                        call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
 933                }
 934        } else if (klist->delkey < klist->nkeys) {
 935                kdebug("replace %hu/%hu/%hu",
 936                       klist->delkey, klist->nkeys, klist->maxkeys);
 937
 938                discard = rcu_dereference_protected(
 939                        klist->keys[klist->delkey],
 940                        rwsem_is_locked(&keyring->sem));
 941                rcu_assign_pointer(klist->keys[klist->delkey], key);
 942                /* The garbage collector will take care of RCU
 943                 * synchronisation */
 944                key_put(discard);
 945        } else {
 946                /* there's sufficient slack space to append directly */
 947                kdebug("append %hu/%hu/%hu",
 948                       klist->delkey, klist->nkeys, klist->maxkeys);
 949
 950                RCU_INIT_POINTER(klist->keys[klist->delkey], key);
 951                smp_wmb();
 952                klist->nkeys++;
 953        }
 954}
 955
 956/*
 957 * Finish linking a key into to a keyring.
 958 *
 959 * Must be called with __key_link_begin() having being called.
 960 */
 961void __key_link_end(struct key *keyring, struct key_type *type,
 962                    unsigned long prealloc)
 963        __releases(&keyring->sem)
 964        __releases(&keyring_serialise_link_sem)
 965{
 966        BUG_ON(type == NULL);
 967        BUG_ON(type->name == NULL);
 968        kenter("%d,%s,%lx", keyring->serial, type->name, prealloc);
 969
 970        if (type == &key_type_keyring)
 971                up_write(&keyring_serialise_link_sem);
 972
 973        if (prealloc) {
 974                if (prealloc & KEY_LINK_FIXQUOTA)
 975                        key_payload_reserve(keyring,
 976                                            keyring->datalen -
 977                                            KEYQUOTA_LINK_BYTES);
 978                kfree((struct keyring_list *)(prealloc & ~KEY_LINK_FIXQUOTA));
 979        }
 980        up_write(&keyring->sem);
 981}
 982
 983/**
 984 * key_link - Link a key to a keyring
 985 * @keyring: The keyring to make the link in.
 986 * @key: The key to link to.
 987 *
 988 * Make a link in a keyring to a key, such that the keyring holds a reference
 989 * on that key and the key can potentially be found by searching that keyring.
 990 *
 991 * This function will write-lock the keyring's semaphore and will consume some
 992 * of the user's key data quota to hold the link.
 993 *
 994 * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring,
 995 * -EKEYREVOKED if the keyring has been revoked, -ENFILE if the keyring is
 996 * full, -EDQUOT if there is insufficient key data quota remaining to add
 997 * another link or -ENOMEM if there's insufficient memory.
 998 *
 999 * It is assumed that the caller has checked that it is permitted for a link to
1000 * be made (the keyring should have Write permission and the key Link
1001 * permission).
1002 */
1003int key_link(struct key *keyring, struct key *key)
1004{
1005        unsigned long prealloc;
1006        int ret;
1007
1008        key_check(keyring);
1009        key_check(key);
1010
1011        ret = __key_link_begin(keyring, key->type, key->description, &prealloc);
1012        if (ret == 0) {
1013                ret = __key_link_check_live_key(keyring, key);
1014                if (ret == 0)
1015                        __key_link(keyring, key, &prealloc);
1016                __key_link_end(keyring, key->type, prealloc);
1017        }
1018
1019        return ret;
1020}
1021EXPORT_SYMBOL(key_link);
1022
1023/**
1024 * key_unlink - Unlink the first link to a key from a keyring.
1025 * @keyring: The keyring to remove the link from.
1026 * @key: The key the link is to.
1027 *
1028 * Remove a link from a keyring to a key.
1029 *
1030 * This function will write-lock the keyring's semaphore.
1031 *
1032 * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring, -ENOENT if
1033 * the key isn't linked to by the keyring or -ENOMEM if there's insufficient
1034 * memory.
1035 *
1036 * It is assumed that the caller has checked that it is permitted for a link to
1037 * be removed (the keyring should have Write permission; no permissions are
1038 * required on the key).
1039 */
1040int key_unlink(struct key *keyring, struct key *key)
1041{
1042        struct keyring_list *klist, *nklist;
1043        int loop, ret;
1044
1045        key_check(keyring);
1046        key_check(key);
1047
1048        ret = -ENOTDIR;
1049        if (keyring->type != &key_type_keyring)
1050                goto error;
1051
1052        down_write(&keyring->sem);
1053
1054        klist = rcu_dereference_locked_keyring(keyring);
1055        if (klist) {
1056                /* search the keyring for the key */
1057                for (loop = 0; loop < klist->nkeys; loop++)
1058                        if (rcu_access_pointer(klist->keys[loop]) == key)
1059                                goto key_is_present;
1060        }
1061
1062        up_write(&keyring->sem);
1063        ret = -ENOENT;
1064        goto error;
1065
1066key_is_present:
1067        /* we need to copy the key list for RCU purposes */
1068        nklist = kmalloc(sizeof(*klist) +
1069                         sizeof(struct key *) * klist->maxkeys,
1070                         GFP_KERNEL);
1071        if (!nklist)
1072                goto nomem;
1073        nklist->maxkeys = klist->maxkeys;
1074        nklist->nkeys = klist->nkeys - 1;
1075
1076        if (loop > 0)
1077                memcpy(&nklist->keys[0],
1078                       &klist->keys[0],
1079                       loop * sizeof(struct key *));
1080
1081        if (loop < nklist->nkeys)
1082                memcpy(&nklist->keys[loop],
1083                       &klist->keys[loop + 1],
1084                       (nklist->nkeys - loop) * sizeof(struct key *));
1085
1086        /* adjust the user's quota */
1087        key_payload_reserve(keyring,
1088                            keyring->datalen - KEYQUOTA_LINK_BYTES);
1089
1090        rcu_assign_pointer(keyring->payload.subscriptions, nklist);
1091
1092        up_write(&keyring->sem);
1093
1094        /* schedule for later cleanup */
1095        klist->delkey = loop;
1096        call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
1097
1098        ret = 0;
1099
1100error:
1101        return ret;
1102nomem:
1103        ret = -ENOMEM;
1104        up_write(&keyring->sem);
1105        goto error;
1106}
1107EXPORT_SYMBOL(key_unlink);
1108
1109/*
1110 * Dispose of a keyring list after the RCU grace period, releasing the keys it
1111 * links to.
1112 */
1113static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
1114{
1115        struct keyring_list *klist;
1116        int loop;
1117
1118        klist = container_of(rcu, struct keyring_list, rcu);
1119
1120        for (loop = klist->nkeys - 1; loop >= 0; loop--)
1121                key_put(rcu_access_pointer(klist->keys[loop]));
1122
1123        kfree(klist);
1124}
1125
1126/**
1127 * keyring_clear - Clear a keyring
1128 * @keyring: The keyring to clear.
1129 *
1130 * Clear the contents of the specified keyring.
1131 *
1132 * Returns 0 if successful or -ENOTDIR if the keyring isn't a keyring.
1133 */
1134int keyring_clear(struct key *keyring)
1135{
1136        struct keyring_list *klist;
1137        int ret;
1138
1139        ret = -ENOTDIR;
1140        if (keyring->type == &key_type_keyring) {
1141                /* detach the pointer block with the locks held */
1142                down_write(&keyring->sem);
1143
1144                klist = rcu_dereference_locked_keyring(keyring);
1145                if (klist) {
1146                        /* adjust the quota */
1147                        key_payload_reserve(keyring,
1148                                            sizeof(struct keyring_list));
1149
1150                        rcu_assign_pointer(keyring->payload.subscriptions,
1151                                           NULL);
1152                }
1153
1154                up_write(&keyring->sem);
1155
1156                /* free the keys after the locks have been dropped */
1157                if (klist)
1158                        call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1159
1160                ret = 0;
1161        }
1162
1163        return ret;
1164}
1165EXPORT_SYMBOL(keyring_clear);
1166
1167/*
1168 * Dispose of the links from a revoked keyring.
1169 *
1170 * This is called with the key sem write-locked.
1171 */
1172static void keyring_revoke(struct key *keyring)
1173{
1174        struct keyring_list *klist;
1175
1176        klist = rcu_dereference_locked_keyring(keyring);
1177
1178        /* adjust the quota */
1179        key_payload_reserve(keyring, 0);
1180
1181        if (klist) {
1182                rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1183                call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1184        }
1185}
1186
1187/*
1188 * Collect garbage from the contents of a keyring, replacing the old list with
1189 * a new one with the pointers all shuffled down.
1190 *
1191 * Dead keys are classed as oned that are flagged as being dead or are revoked,
1192 * expired or negative keys that were revoked or expired before the specified
1193 * limit.
1194 */
1195void keyring_gc(struct key *keyring, time_t limit)
1196{
1197        struct keyring_list *klist, *new;
1198        struct key *key;
1199        int loop, keep, max;
1200
1201        kenter("{%x,%s}", key_serial(keyring), keyring->description);
1202
1203        down_write(&keyring->sem);
1204
1205        klist = rcu_dereference_locked_keyring(keyring);
1206        if (!klist)
1207                goto no_klist;
1208
1209        /* work out how many subscriptions we're keeping */
1210        keep = 0;
1211        for (loop = klist->nkeys - 1; loop >= 0; loop--)
1212                if (!key_is_dead(rcu_deref_link_locked(klist, loop, keyring),
1213                                 limit))
1214                        keep++;
1215
1216        if (keep == klist->nkeys)
1217                goto just_return;
1218
1219        /* allocate a new keyring payload */
1220        max = roundup(keep, 4);
1221        new = kmalloc(sizeof(struct keyring_list) + max * sizeof(struct key *),
1222                      GFP_KERNEL);
1223        if (!new)
1224                goto nomem;
1225        new->maxkeys = max;
1226        new->nkeys = 0;
1227        new->delkey = 0;
1228
1229        /* install the live keys
1230         * - must take care as expired keys may be updated back to life
1231         */
1232        keep = 0;
1233        for (loop = klist->nkeys - 1; loop >= 0; loop--) {
1234                key = rcu_deref_link_locked(klist, loop, keyring);
1235                if (!key_is_dead(key, limit)) {
1236                        if (keep >= max)
1237                                goto discard_new;
1238                        RCU_INIT_POINTER(new->keys[keep++], key_get(key));
1239                }
1240        }
1241        new->nkeys = keep;
1242
1243        /* adjust the quota */
1244        key_payload_reserve(keyring,
1245                            sizeof(struct keyring_list) +
1246                            KEYQUOTA_LINK_BYTES * keep);
1247
1248        if (keep == 0) {
1249                rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1250                kfree(new);
1251        } else {
1252                rcu_assign_pointer(keyring->payload.subscriptions, new);
1253        }
1254
1255        up_write(&keyring->sem);
1256
1257        call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1258        kleave(" [yes]");
1259        return;
1260
1261discard_new:
1262        new->nkeys = keep;
1263        keyring_clear_rcu_disposal(&new->rcu);
1264        up_write(&keyring->sem);
1265        kleave(" [discard]");
1266        return;
1267
1268just_return:
1269        up_write(&keyring->sem);
1270        kleave(" [no dead]");
1271        return;
1272
1273no_klist:
1274        up_write(&keyring->sem);
1275        kleave(" [no_klist]");
1276        return;
1277
1278nomem:
1279        up_write(&keyring->sem);
1280        kleave(" [oom]");
1281}
1282
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