linux/fs/crypto/keyring.c
<<
>>
Prefs
   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Filesystem-level keyring for fscrypt
   4 *
   5 * Copyright 2019 Google LLC
   6 */
   7
   8/*
   9 * This file implements management of fscrypt master keys in the
  10 * filesystem-level keyring, including the ioctls:
  11 *
  12 * - FS_IOC_ADD_ENCRYPTION_KEY
  13 * - FS_IOC_REMOVE_ENCRYPTION_KEY
  14 * - FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS
  15 * - FS_IOC_GET_ENCRYPTION_KEY_STATUS
  16 *
  17 * See the "User API" section of Documentation/filesystems/fscrypt.rst for more
  18 * information about these ioctls.
  19 */
  20
  21#include <crypto/skcipher.h>
  22#include <linux/key-type.h>
  23#include <linux/random.h>
  24#include <linux/seq_file.h>
  25
  26#include "fscrypt_private.h"
  27
  28static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
  29{
  30        fscrypt_destroy_hkdf(&secret->hkdf);
  31        memzero_explicit(secret, sizeof(*secret));
  32}
  33
  34static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
  35                                   struct fscrypt_master_key_secret *src)
  36{
  37        memcpy(dst, src, sizeof(*dst));
  38        memzero_explicit(src, sizeof(*src));
  39}
  40
  41static void free_master_key(struct fscrypt_master_key *mk)
  42{
  43        size_t i;
  44
  45        wipe_master_key_secret(&mk->mk_secret);
  46
  47        for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {
  48                fscrypt_destroy_prepared_key(&mk->mk_direct_keys[i]);
  49                fscrypt_destroy_prepared_key(&mk->mk_iv_ino_lblk_64_keys[i]);
  50                fscrypt_destroy_prepared_key(&mk->mk_iv_ino_lblk_32_keys[i]);
  51        }
  52
  53        key_put(mk->mk_users);
  54        kfree_sensitive(mk);
  55}
  56
  57static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
  58{
  59        if (spec->__reserved)
  60                return false;
  61        return master_key_spec_len(spec) != 0;
  62}
  63
  64static int fscrypt_key_instantiate(struct key *key,
  65                                   struct key_preparsed_payload *prep)
  66{
  67        key->payload.data[0] = (struct fscrypt_master_key *)prep->data;
  68        return 0;
  69}
  70
  71static void fscrypt_key_destroy(struct key *key)
  72{
  73        free_master_key(key->payload.data[0]);
  74}
  75
  76static void fscrypt_key_describe(const struct key *key, struct seq_file *m)
  77{
  78        seq_puts(m, key->description);
  79
  80        if (key_is_positive(key)) {
  81                const struct fscrypt_master_key *mk = key->payload.data[0];
  82
  83                if (!is_master_key_secret_present(&mk->mk_secret))
  84                        seq_puts(m, ": secret removed");
  85        }
  86}
  87
  88/*
  89 * Type of key in ->s_master_keys.  Each key of this type represents a master
  90 * key which has been added to the filesystem.  Its payload is a
  91 * 'struct fscrypt_master_key'.  The "." prefix in the key type name prevents
  92 * users from adding keys of this type via the keyrings syscalls rather than via
  93 * the intended method of FS_IOC_ADD_ENCRYPTION_KEY.
  94 */
  95static struct key_type key_type_fscrypt = {
  96        .name                   = "._fscrypt",
  97        .instantiate            = fscrypt_key_instantiate,
  98        .destroy                = fscrypt_key_destroy,
  99        .describe               = fscrypt_key_describe,
 100};
 101
 102static int fscrypt_user_key_instantiate(struct key *key,
 103                                        struct key_preparsed_payload *prep)
 104{
 105        /*
 106         * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
 107         * each key, regardless of the exact key size.  The amount of memory
 108         * actually used is greater than the size of the raw key anyway.
 109         */
 110        return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
 111}
 112
 113static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
 114{
 115        seq_puts(m, key->description);
 116}
 117
 118/*
 119 * Type of key in ->mk_users.  Each key of this type represents a particular
 120 * user who has added a particular master key.
 121 *
 122 * Note that the name of this key type really should be something like
 123 * ".fscrypt-user" instead of simply ".fscrypt".  But the shorter name is chosen
 124 * mainly for simplicity of presentation in /proc/keys when read by a non-root
 125 * user.  And it is expected to be rare that a key is actually added by multiple
 126 * users, since users should keep their encryption keys confidential.
 127 */
 128static struct key_type key_type_fscrypt_user = {
 129        .name                   = ".fscrypt",
 130        .instantiate            = fscrypt_user_key_instantiate,
 131        .describe               = fscrypt_user_key_describe,
 132};
 133
 134/* Search ->s_master_keys or ->mk_users */
 135static struct key *search_fscrypt_keyring(struct key *keyring,
 136                                          struct key_type *type,
 137                                          const char *description)
 138{
 139        /*
 140         * We need to mark the keyring reference as "possessed" so that we
 141         * acquire permission to search it, via the KEY_POS_SEARCH permission.
 142         */
 143        key_ref_t keyref = make_key_ref(keyring, true /* possessed */);
 144
 145        keyref = keyring_search(keyref, type, description, false);
 146        if (IS_ERR(keyref)) {
 147                if (PTR_ERR(keyref) == -EAGAIN || /* not found */
 148                    PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
 149                        keyref = ERR_PTR(-ENOKEY);
 150                return ERR_CAST(keyref);
 151        }
 152        return key_ref_to_ptr(keyref);
 153}
 154
 155#define FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE     \
 156        (CONST_STRLEN("fscrypt-") + sizeof_field(struct super_block, s_id))
 157
 158#define FSCRYPT_MK_DESCRIPTION_SIZE     (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + 1)
 159
 160#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE       \
 161        (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
 162         CONST_STRLEN("-users") + 1)
 163
 164#define FSCRYPT_MK_USER_DESCRIPTION_SIZE        \
 165        (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
 166
 167static void format_fs_keyring_description(
 168                        char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE],
 169                        const struct super_block *sb)
 170{
 171        sprintf(description, "fscrypt-%s", sb->s_id);
 172}
 173
 174static void format_mk_description(
 175                        char description[FSCRYPT_MK_DESCRIPTION_SIZE],
 176                        const struct fscrypt_key_specifier *mk_spec)
 177{
 178        sprintf(description, "%*phN",
 179                master_key_spec_len(mk_spec), (u8 *)&mk_spec->u);
 180}
 181
 182static void format_mk_users_keyring_description(
 183                        char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
 184                        const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
 185{
 186        sprintf(description, "fscrypt-%*phN-users",
 187                FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
 188}
 189
 190static void format_mk_user_description(
 191                        char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
 192                        const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
 193{
 194
 195        sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
 196                mk_identifier, __kuid_val(current_fsuid()));
 197}
 198
 199/* Create ->s_master_keys if needed.  Synchronized by fscrypt_add_key_mutex. */
 200static int allocate_filesystem_keyring(struct super_block *sb)
 201{
 202        char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE];
 203        struct key *keyring;
 204
 205        if (sb->s_master_keys)
 206                return 0;
 207
 208        format_fs_keyring_description(description, sb);
 209        keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
 210                                current_cred(), KEY_POS_SEARCH |
 211                                  KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
 212                                KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
 213        if (IS_ERR(keyring))
 214                return PTR_ERR(keyring);
 215
 216        /*
 217         * Pairs with the smp_load_acquire() in fscrypt_find_master_key().
 218         * I.e., here we publish ->s_master_keys with a RELEASE barrier so that
 219         * concurrent tasks can ACQUIRE it.
 220         */
 221        smp_store_release(&sb->s_master_keys, keyring);
 222        return 0;
 223}
 224
 225void fscrypt_sb_free(struct super_block *sb)
 226{
 227        key_put(sb->s_master_keys);
 228        sb->s_master_keys = NULL;
 229}
 230
 231/*
 232 * Find the specified master key in ->s_master_keys.
 233 * Returns ERR_PTR(-ENOKEY) if not found.
 234 */
 235struct key *fscrypt_find_master_key(struct super_block *sb,
 236                                    const struct fscrypt_key_specifier *mk_spec)
 237{
 238        struct key *keyring;
 239        char description[FSCRYPT_MK_DESCRIPTION_SIZE];
 240
 241        /*
 242         * Pairs with the smp_store_release() in allocate_filesystem_keyring().
 243         * I.e., another task can publish ->s_master_keys concurrently,
 244         * executing a RELEASE barrier.  We need to use smp_load_acquire() here
 245         * to safely ACQUIRE the memory the other task published.
 246         */
 247        keyring = smp_load_acquire(&sb->s_master_keys);
 248        if (keyring == NULL)
 249                return ERR_PTR(-ENOKEY); /* No keyring yet, so no keys yet. */
 250
 251        format_mk_description(description, mk_spec);
 252        return search_fscrypt_keyring(keyring, &key_type_fscrypt, description);
 253}
 254
 255static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
 256{
 257        char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
 258        struct key *keyring;
 259
 260        format_mk_users_keyring_description(description,
 261                                            mk->mk_spec.u.identifier);
 262        keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
 263                                current_cred(), KEY_POS_SEARCH |
 264                                  KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
 265                                KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
 266        if (IS_ERR(keyring))
 267                return PTR_ERR(keyring);
 268
 269        mk->mk_users = keyring;
 270        return 0;
 271}
 272
 273/*
 274 * Find the current user's "key" in the master key's ->mk_users.
 275 * Returns ERR_PTR(-ENOKEY) if not found.
 276 */
 277static struct key *find_master_key_user(struct fscrypt_master_key *mk)
 278{
 279        char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
 280
 281        format_mk_user_description(description, mk->mk_spec.u.identifier);
 282        return search_fscrypt_keyring(mk->mk_users, &key_type_fscrypt_user,
 283                                      description);
 284}
 285
 286/*
 287 * Give the current user a "key" in ->mk_users.  This charges the user's quota
 288 * and marks the master key as added by the current user, so that it cannot be
 289 * removed by another user with the key.  Either the master key's key->sem must
 290 * be held for write, or the master key must be still undergoing initialization.
 291 */
 292static int add_master_key_user(struct fscrypt_master_key *mk)
 293{
 294        char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
 295        struct key *mk_user;
 296        int err;
 297
 298        format_mk_user_description(description, mk->mk_spec.u.identifier);
 299        mk_user = key_alloc(&key_type_fscrypt_user, description,
 300                            current_fsuid(), current_gid(), current_cred(),
 301                            KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
 302        if (IS_ERR(mk_user))
 303                return PTR_ERR(mk_user);
 304
 305        err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
 306        key_put(mk_user);
 307        return err;
 308}
 309
 310/*
 311 * Remove the current user's "key" from ->mk_users.
 312 * The master key's key->sem must be held for write.
 313 *
 314 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
 315 */
 316static int remove_master_key_user(struct fscrypt_master_key *mk)
 317{
 318        struct key *mk_user;
 319        int err;
 320
 321        mk_user = find_master_key_user(mk);
 322        if (IS_ERR(mk_user))
 323                return PTR_ERR(mk_user);
 324        err = key_unlink(mk->mk_users, mk_user);
 325        key_put(mk_user);
 326        return err;
 327}
 328
 329/*
 330 * Allocate a new fscrypt_master_key which contains the given secret, set it as
 331 * the payload of a new 'struct key' of type fscrypt, and link the 'struct key'
 332 * into the given keyring.  Synchronized by fscrypt_add_key_mutex.
 333 */
 334static int add_new_master_key(struct fscrypt_master_key_secret *secret,
 335                              const struct fscrypt_key_specifier *mk_spec,
 336                              struct key *keyring)
 337{
 338        struct fscrypt_master_key *mk;
 339        char description[FSCRYPT_MK_DESCRIPTION_SIZE];
 340        struct key *key;
 341        int err;
 342
 343        mk = kzalloc(sizeof(*mk), GFP_KERNEL);
 344        if (!mk)
 345                return -ENOMEM;
 346
 347        mk->mk_spec = *mk_spec;
 348
 349        move_master_key_secret(&mk->mk_secret, secret);
 350
 351        refcount_set(&mk->mk_refcount, 1); /* secret is present */
 352        INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
 353        spin_lock_init(&mk->mk_decrypted_inodes_lock);
 354
 355        if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
 356                err = allocate_master_key_users_keyring(mk);
 357                if (err)
 358                        goto out_free_mk;
 359                err = add_master_key_user(mk);
 360                if (err)
 361                        goto out_free_mk;
 362        }
 363
 364        /*
 365         * Note that we don't charge this key to anyone's quota, since when
 366         * ->mk_users is in use those keys are charged instead, and otherwise
 367         * (when ->mk_users isn't in use) only root can add these keys.
 368         */
 369        format_mk_description(description, mk_spec);
 370        key = key_alloc(&key_type_fscrypt, description,
 371                        GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
 372                        KEY_POS_SEARCH | KEY_USR_SEARCH | KEY_USR_VIEW,
 373                        KEY_ALLOC_NOT_IN_QUOTA, NULL);
 374        if (IS_ERR(key)) {
 375                err = PTR_ERR(key);
 376                goto out_free_mk;
 377        }
 378        err = key_instantiate_and_link(key, mk, sizeof(*mk), keyring, NULL);
 379        key_put(key);
 380        if (err)
 381                goto out_free_mk;
 382
 383        return 0;
 384
 385out_free_mk:
 386        free_master_key(mk);
 387        return err;
 388}
 389
 390#define KEY_DEAD        1
 391
 392static int add_existing_master_key(struct fscrypt_master_key *mk,
 393                                   struct fscrypt_master_key_secret *secret)
 394{
 395        struct key *mk_user;
 396        bool rekey;
 397        int err;
 398
 399        /*
 400         * If the current user is already in ->mk_users, then there's nothing to
 401         * do.  (Not applicable for v1 policy keys, which have NULL ->mk_users.)
 402         */
 403        if (mk->mk_users) {
 404                mk_user = find_master_key_user(mk);
 405                if (mk_user != ERR_PTR(-ENOKEY)) {
 406                        if (IS_ERR(mk_user))
 407                                return PTR_ERR(mk_user);
 408                        key_put(mk_user);
 409                        return 0;
 410                }
 411        }
 412
 413        /* If we'll be re-adding ->mk_secret, try to take the reference. */
 414        rekey = !is_master_key_secret_present(&mk->mk_secret);
 415        if (rekey && !refcount_inc_not_zero(&mk->mk_refcount))
 416                return KEY_DEAD;
 417
 418        /* Add the current user to ->mk_users, if applicable. */
 419        if (mk->mk_users) {
 420                err = add_master_key_user(mk);
 421                if (err) {
 422                        if (rekey && refcount_dec_and_test(&mk->mk_refcount))
 423                                return KEY_DEAD;
 424                        return err;
 425                }
 426        }
 427
 428        /* Re-add the secret if needed. */
 429        if (rekey)
 430                move_master_key_secret(&mk->mk_secret, secret);
 431        return 0;
 432}
 433
 434static int do_add_master_key(struct super_block *sb,
 435                             struct fscrypt_master_key_secret *secret,
 436                             const struct fscrypt_key_specifier *mk_spec)
 437{
 438        static DEFINE_MUTEX(fscrypt_add_key_mutex);
 439        struct key *key;
 440        int err;
 441
 442        mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
 443retry:
 444        key = fscrypt_find_master_key(sb, mk_spec);
 445        if (IS_ERR(key)) {
 446                err = PTR_ERR(key);
 447                if (err != -ENOKEY)
 448                        goto out_unlock;
 449                /* Didn't find the key in ->s_master_keys.  Add it. */
 450                err = allocate_filesystem_keyring(sb);
 451                if (err)
 452                        goto out_unlock;
 453                err = add_new_master_key(secret, mk_spec, sb->s_master_keys);
 454        } else {
 455                /*
 456                 * Found the key in ->s_master_keys.  Re-add the secret if
 457                 * needed, and add the user to ->mk_users if needed.
 458                 */
 459                down_write(&key->sem);
 460                err = add_existing_master_key(key->payload.data[0], secret);
 461                up_write(&key->sem);
 462                if (err == KEY_DEAD) {
 463                        /* Key being removed or needs to be removed */
 464                        key_invalidate(key);
 465                        key_put(key);
 466                        goto retry;
 467                }
 468                key_put(key);
 469        }
 470out_unlock:
 471        mutex_unlock(&fscrypt_add_key_mutex);
 472        return err;
 473}
 474
 475static int add_master_key(struct super_block *sb,
 476                          struct fscrypt_master_key_secret *secret,
 477                          struct fscrypt_key_specifier *key_spec)
 478{
 479        int err;
 480
 481        if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
 482                err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,
 483                                        secret->size);
 484                if (err)
 485                        return err;
 486
 487                /*
 488                 * Now that the HKDF context is initialized, the raw key is no
 489                 * longer needed.
 490                 */
 491                memzero_explicit(secret->raw, secret->size);
 492
 493                /* Calculate the key identifier */
 494                err = fscrypt_hkdf_expand(&secret->hkdf,
 495                                          HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,
 496                                          key_spec->u.identifier,
 497                                          FSCRYPT_KEY_IDENTIFIER_SIZE);
 498                if (err)
 499                        return err;
 500        }
 501        return do_add_master_key(sb, secret, key_spec);
 502}
 503
 504static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
 505{
 506        const struct fscrypt_provisioning_key_payload *payload = prep->data;
 507
 508        if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
 509            prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
 510                return -EINVAL;
 511
 512        if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
 513            payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
 514                return -EINVAL;
 515
 516        if (payload->__reserved)
 517                return -EINVAL;
 518
 519        prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
 520        if (!prep->payload.data[0])
 521                return -ENOMEM;
 522
 523        prep->quotalen = prep->datalen;
 524        return 0;
 525}
 526
 527static void fscrypt_provisioning_key_free_preparse(
 528                                        struct key_preparsed_payload *prep)
 529{
 530        kfree_sensitive(prep->payload.data[0]);
 531}
 532
 533static void fscrypt_provisioning_key_describe(const struct key *key,
 534                                              struct seq_file *m)
 535{
 536        seq_puts(m, key->description);
 537        if (key_is_positive(key)) {
 538                const struct fscrypt_provisioning_key_payload *payload =
 539                        key->payload.data[0];
 540
 541                seq_printf(m, ": %u [%u]", key->datalen, payload->type);
 542        }
 543}
 544
 545static void fscrypt_provisioning_key_destroy(struct key *key)
 546{
 547        kfree_sensitive(key->payload.data[0]);
 548}
 549
 550static struct key_type key_type_fscrypt_provisioning = {
 551        .name                   = "fscrypt-provisioning",
 552        .preparse               = fscrypt_provisioning_key_preparse,
 553        .free_preparse          = fscrypt_provisioning_key_free_preparse,
 554        .instantiate            = generic_key_instantiate,
 555        .describe               = fscrypt_provisioning_key_describe,
 556        .destroy                = fscrypt_provisioning_key_destroy,
 557};
 558
 559/*
 560 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
 561 * store it into 'secret'.
 562 *
 563 * The key must be of type "fscrypt-provisioning" and must have the field
 564 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
 565 * only usable with fscrypt with the particular KDF version identified by
 566 * 'type'.  We don't use the "logon" key type because there's no way to
 567 * completely restrict the use of such keys; they can be used by any kernel API
 568 * that accepts "logon" keys and doesn't require a specific service prefix.
 569 *
 570 * The ability to specify the key via Linux keyring key is intended for cases
 571 * where userspace needs to re-add keys after the filesystem is unmounted and
 572 * re-mounted.  Most users should just provide the raw key directly instead.
 573 */
 574static int get_keyring_key(u32 key_id, u32 type,
 575                           struct fscrypt_master_key_secret *secret)
 576{
 577        key_ref_t ref;
 578        struct key *key;
 579        const struct fscrypt_provisioning_key_payload *payload;
 580        int err;
 581
 582        ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
 583        if (IS_ERR(ref))
 584                return PTR_ERR(ref);
 585        key = key_ref_to_ptr(ref);
 586
 587        if (key->type != &key_type_fscrypt_provisioning)
 588                goto bad_key;
 589        payload = key->payload.data[0];
 590
 591        /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
 592        if (payload->type != type)
 593                goto bad_key;
 594
 595        secret->size = key->datalen - sizeof(*payload);
 596        memcpy(secret->raw, payload->raw, secret->size);
 597        err = 0;
 598        goto out_put;
 599
 600bad_key:
 601        err = -EKEYREJECTED;
 602out_put:
 603        key_ref_put(ref);
 604        return err;
 605}
 606
 607/*
 608 * Add a master encryption key to the filesystem, causing all files which were
 609 * encrypted with it to appear "unlocked" (decrypted) when accessed.
 610 *
 611 * When adding a key for use by v1 encryption policies, this ioctl is
 612 * privileged, and userspace must provide the 'key_descriptor'.
 613 *
 614 * When adding a key for use by v2+ encryption policies, this ioctl is
 615 * unprivileged.  This is needed, in general, to allow non-root users to use
 616 * encryption without encountering the visibility problems of process-subscribed
 617 * keyrings and the inability to properly remove keys.  This works by having
 618 * each key identified by its cryptographically secure hash --- the
 619 * 'key_identifier'.  The cryptographic hash ensures that a malicious user
 620 * cannot add the wrong key for a given identifier.  Furthermore, each added key
 621 * is charged to the appropriate user's quota for the keyrings service, which
 622 * prevents a malicious user from adding too many keys.  Finally, we forbid a
 623 * user from removing a key while other users have added it too, which prevents
 624 * a user who knows another user's key from causing a denial-of-service by
 625 * removing it at an inopportune time.  (We tolerate that a user who knows a key
 626 * can prevent other users from removing it.)
 627 *
 628 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
 629 * Documentation/filesystems/fscrypt.rst.
 630 */
 631int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
 632{
 633        struct super_block *sb = file_inode(filp)->i_sb;
 634        struct fscrypt_add_key_arg __user *uarg = _uarg;
 635        struct fscrypt_add_key_arg arg;
 636        struct fscrypt_master_key_secret secret;
 637        int err;
 638
 639        if (copy_from_user(&arg, uarg, sizeof(arg)))
 640                return -EFAULT;
 641
 642        if (!valid_key_spec(&arg.key_spec))
 643                return -EINVAL;
 644
 645        if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
 646                return -EINVAL;
 647
 648        /*
 649         * Only root can add keys that are identified by an arbitrary descriptor
 650         * rather than by a cryptographic hash --- since otherwise a malicious
 651         * user could add the wrong key.
 652         */
 653        if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
 654            !capable(CAP_SYS_ADMIN))
 655                return -EACCES;
 656
 657        memset(&secret, 0, sizeof(secret));
 658        if (arg.key_id) {
 659                if (arg.raw_size != 0)
 660                        return -EINVAL;
 661                err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
 662                if (err)
 663                        goto out_wipe_secret;
 664        } else {
 665                if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
 666                    arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
 667                        return -EINVAL;
 668                secret.size = arg.raw_size;
 669                err = -EFAULT;
 670                if (copy_from_user(secret.raw, uarg->raw, secret.size))
 671                        goto out_wipe_secret;
 672        }
 673
 674        err = add_master_key(sb, &secret, &arg.key_spec);
 675        if (err)
 676                goto out_wipe_secret;
 677
 678        /* Return the key identifier to userspace, if applicable */
 679        err = -EFAULT;
 680        if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
 681            copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,
 682                         FSCRYPT_KEY_IDENTIFIER_SIZE))
 683                goto out_wipe_secret;
 684        err = 0;
 685out_wipe_secret:
 686        wipe_master_key_secret(&secret);
 687        return err;
 688}
 689EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
 690
 691/*
 692 * Add the key for '-o test_dummy_encryption' to the filesystem keyring.
 693 *
 694 * Use a per-boot random key to prevent people from misusing this option.
 695 */
 696int fscrypt_add_test_dummy_key(struct super_block *sb,
 697                               struct fscrypt_key_specifier *key_spec)
 698{
 699        static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
 700        struct fscrypt_master_key_secret secret;
 701        int err;
 702
 703        get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
 704
 705        memset(&secret, 0, sizeof(secret));
 706        secret.size = FSCRYPT_MAX_KEY_SIZE;
 707        memcpy(secret.raw, test_key, FSCRYPT_MAX_KEY_SIZE);
 708
 709        err = add_master_key(sb, &secret, key_spec);
 710        wipe_master_key_secret(&secret);
 711        return err;
 712}
 713
 714/*
 715 * Verify that the current user has added a master key with the given identifier
 716 * (returns -ENOKEY if not).  This is needed to prevent a user from encrypting
 717 * their files using some other user's key which they don't actually know.
 718 * Cryptographically this isn't much of a problem, but the semantics of this
 719 * would be a bit weird, so it's best to just forbid it.
 720 *
 721 * The system administrator (CAP_FOWNER) can override this, which should be
 722 * enough for any use cases where encryption policies are being set using keys
 723 * that were chosen ahead of time but aren't available at the moment.
 724 *
 725 * Note that the key may have already removed by the time this returns, but
 726 * that's okay; we just care whether the key was there at some point.
 727 *
 728 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
 729 */
 730int fscrypt_verify_key_added(struct super_block *sb,
 731                             const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
 732{
 733        struct fscrypt_key_specifier mk_spec;
 734        struct key *key, *mk_user;
 735        struct fscrypt_master_key *mk;
 736        int err;
 737
 738        mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
 739        memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
 740
 741        key = fscrypt_find_master_key(sb, &mk_spec);
 742        if (IS_ERR(key)) {
 743                err = PTR_ERR(key);
 744                goto out;
 745        }
 746        mk = key->payload.data[0];
 747        mk_user = find_master_key_user(mk);
 748        if (IS_ERR(mk_user)) {
 749                err = PTR_ERR(mk_user);
 750        } else {
 751                key_put(mk_user);
 752                err = 0;
 753        }
 754        key_put(key);
 755out:
 756        if (err == -ENOKEY && capable(CAP_FOWNER))
 757                err = 0;
 758        return err;
 759}
 760
 761/*
 762 * Try to evict the inode's dentries from the dentry cache.  If the inode is a
 763 * directory, then it can have at most one dentry; however, that dentry may be
 764 * pinned by child dentries, so first try to evict the children too.
 765 */
 766static void shrink_dcache_inode(struct inode *inode)
 767{
 768        struct dentry *dentry;
 769
 770        if (S_ISDIR(inode->i_mode)) {
 771                dentry = d_find_any_alias(inode);
 772                if (dentry) {
 773                        shrink_dcache_parent(dentry);
 774                        dput(dentry);
 775                }
 776        }
 777        d_prune_aliases(inode);
 778}
 779
 780static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
 781{
 782        struct fscrypt_info *ci;
 783        struct inode *inode;
 784        struct inode *toput_inode = NULL;
 785
 786        spin_lock(&mk->mk_decrypted_inodes_lock);
 787
 788        list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
 789                inode = ci->ci_inode;
 790                spin_lock(&inode->i_lock);
 791                if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
 792                        spin_unlock(&inode->i_lock);
 793                        continue;
 794                }
 795                __iget(inode);
 796                spin_unlock(&inode->i_lock);
 797                spin_unlock(&mk->mk_decrypted_inodes_lock);
 798
 799                shrink_dcache_inode(inode);
 800                iput(toput_inode);
 801                toput_inode = inode;
 802
 803                spin_lock(&mk->mk_decrypted_inodes_lock);
 804        }
 805
 806        spin_unlock(&mk->mk_decrypted_inodes_lock);
 807        iput(toput_inode);
 808}
 809
 810static int check_for_busy_inodes(struct super_block *sb,
 811                                 struct fscrypt_master_key *mk)
 812{
 813        struct list_head *pos;
 814        size_t busy_count = 0;
 815        unsigned long ino;
 816        char ino_str[50] = "";
 817
 818        spin_lock(&mk->mk_decrypted_inodes_lock);
 819
 820        list_for_each(pos, &mk->mk_decrypted_inodes)
 821                busy_count++;
 822
 823        if (busy_count == 0) {
 824                spin_unlock(&mk->mk_decrypted_inodes_lock);
 825                return 0;
 826        }
 827
 828        {
 829                /* select an example file to show for debugging purposes */
 830                struct inode *inode =
 831                        list_first_entry(&mk->mk_decrypted_inodes,
 832                                         struct fscrypt_info,
 833                                         ci_master_key_link)->ci_inode;
 834                ino = inode->i_ino;
 835        }
 836        spin_unlock(&mk->mk_decrypted_inodes_lock);
 837
 838        /* If the inode is currently being created, ino may still be 0. */
 839        if (ino)
 840                snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino);
 841
 842        fscrypt_warn(NULL,
 843                     "%s: %zu inode(s) still busy after removing key with %s %*phN%s",
 844                     sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
 845                     master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
 846                     ino_str);
 847        return -EBUSY;
 848}
 849
 850static int try_to_lock_encrypted_files(struct super_block *sb,
 851                                       struct fscrypt_master_key *mk)
 852{
 853        int err1;
 854        int err2;
 855
 856        /*
 857         * An inode can't be evicted while it is dirty or has dirty pages.
 858         * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
 859         *
 860         * Just do it the easy way: call sync_filesystem().  It's overkill, but
 861         * it works, and it's more important to minimize the amount of caches we
 862         * drop than the amount of data we sync.  Also, unprivileged users can
 863         * already call sync_filesystem() via sys_syncfs() or sys_sync().
 864         */
 865        down_read(&sb->s_umount);
 866        err1 = sync_filesystem(sb);
 867        up_read(&sb->s_umount);
 868        /* If a sync error occurs, still try to evict as much as possible. */
 869
 870        /*
 871         * Inodes are pinned by their dentries, so we have to evict their
 872         * dentries.  shrink_dcache_sb() would suffice, but would be overkill
 873         * and inappropriate for use by unprivileged users.  So instead go
 874         * through the inodes' alias lists and try to evict each dentry.
 875         */
 876        evict_dentries_for_decrypted_inodes(mk);
 877
 878        /*
 879         * evict_dentries_for_decrypted_inodes() already iput() each inode in
 880         * the list; any inodes for which that dropped the last reference will
 881         * have been evicted due to fscrypt_drop_inode() detecting the key
 882         * removal and telling the VFS to evict the inode.  So to finish, we
 883         * just need to check whether any inodes couldn't be evicted.
 884         */
 885        err2 = check_for_busy_inodes(sb, mk);
 886
 887        return err1 ?: err2;
 888}
 889
 890/*
 891 * Try to remove an fscrypt master encryption key.
 892 *
 893 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
 894 * claim to the key, then removes the key itself if no other users have claims.
 895 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
 896 * key itself.
 897 *
 898 * To "remove the key itself", first we wipe the actual master key secret, so
 899 * that no more inodes can be unlocked with it.  Then we try to evict all cached
 900 * inodes that had been unlocked with the key.
 901 *
 902 * If all inodes were evicted, then we unlink the fscrypt_master_key from the
 903 * keyring.  Otherwise it remains in the keyring in the "incompletely removed"
 904 * state (without the actual secret key) where it tracks the list of remaining
 905 * inodes.  Userspace can execute the ioctl again later to retry eviction, or
 906 * alternatively can re-add the secret key again.
 907 *
 908 * For more details, see the "Removing keys" section of
 909 * Documentation/filesystems/fscrypt.rst.
 910 */
 911static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
 912{
 913        struct super_block *sb = file_inode(filp)->i_sb;
 914        struct fscrypt_remove_key_arg __user *uarg = _uarg;
 915        struct fscrypt_remove_key_arg arg;
 916        struct key *key;
 917        struct fscrypt_master_key *mk;
 918        u32 status_flags = 0;
 919        int err;
 920        bool dead;
 921
 922        if (copy_from_user(&arg, uarg, sizeof(arg)))
 923                return -EFAULT;
 924
 925        if (!valid_key_spec(&arg.key_spec))
 926                return -EINVAL;
 927
 928        if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
 929                return -EINVAL;
 930
 931        /*
 932         * Only root can add and remove keys that are identified by an arbitrary
 933         * descriptor rather than by a cryptographic hash.
 934         */
 935        if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
 936            !capable(CAP_SYS_ADMIN))
 937                return -EACCES;
 938
 939        /* Find the key being removed. */
 940        key = fscrypt_find_master_key(sb, &arg.key_spec);
 941        if (IS_ERR(key))
 942                return PTR_ERR(key);
 943        mk = key->payload.data[0];
 944
 945        down_write(&key->sem);
 946
 947        /* If relevant, remove current user's (or all users) claim to the key */
 948        if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
 949                if (all_users)
 950                        err = keyring_clear(mk->mk_users);
 951                else
 952                        err = remove_master_key_user(mk);
 953                if (err) {
 954                        up_write(&key->sem);
 955                        goto out_put_key;
 956                }
 957                if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
 958                        /*
 959                         * Other users have still added the key too.  We removed
 960                         * the current user's claim to the key, but we still
 961                         * can't remove the key itself.
 962                         */
 963                        status_flags |=
 964                                FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
 965                        err = 0;
 966                        up_write(&key->sem);
 967                        goto out_put_key;
 968                }
 969        }
 970
 971        /* No user claims remaining.  Go ahead and wipe the secret. */
 972        dead = false;
 973        if (is_master_key_secret_present(&mk->mk_secret)) {
 974                wipe_master_key_secret(&mk->mk_secret);
 975                dead = refcount_dec_and_test(&mk->mk_refcount);
 976        }
 977        up_write(&key->sem);
 978        if (dead) {
 979                /*
 980                 * No inodes reference the key, and we wiped the secret, so the
 981                 * key object is free to be removed from the keyring.
 982                 */
 983                key_invalidate(key);
 984                err = 0;
 985        } else {
 986                /* Some inodes still reference this key; try to evict them. */
 987                err = try_to_lock_encrypted_files(sb, mk);
 988                if (err == -EBUSY) {
 989                        status_flags |=
 990                                FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
 991                        err = 0;
 992                }
 993        }
 994        /*
 995         * We return 0 if we successfully did something: removed a claim to the
 996         * key, wiped the secret, or tried locking the files again.  Users need
 997         * to check the informational status flags if they care whether the key
 998         * has been fully removed including all files locked.
 999         */
1000out_put_key:
1001        key_put(key);
1002        if (err == 0)
1003                err = put_user(status_flags, &uarg->removal_status_flags);
1004        return err;
1005}
1006
1007int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
1008{
1009        return do_remove_key(filp, uarg, false);
1010}
1011EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
1012
1013int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
1014{
1015        if (!capable(CAP_SYS_ADMIN))
1016                return -EACCES;
1017        return do_remove_key(filp, uarg, true);
1018}
1019EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);
1020
1021/*
1022 * Retrieve the status of an fscrypt master encryption key.
1023 *
1024 * We set ->status to indicate whether the key is absent, present, or
1025 * incompletely removed.  "Incompletely removed" means that the master key
1026 * secret has been removed, but some files which had been unlocked with it are
1027 * still in use.  This field allows applications to easily determine the state
1028 * of an encrypted directory without using a hack such as trying to open a
1029 * regular file in it (which can confuse the "incompletely removed" state with
1030 * absent or present).
1031 *
1032 * In addition, for v2 policy keys we allow applications to determine, via
1033 * ->status_flags and ->user_count, whether the key has been added by the
1034 * current user, by other users, or by both.  Most applications should not need
1035 * this, since ordinarily only one user should know a given key.  However, if a
1036 * secret key is shared by multiple users, applications may wish to add an
1037 * already-present key to prevent other users from removing it.  This ioctl can
1038 * be used to check whether that really is the case before the work is done to
1039 * add the key --- which might e.g. require prompting the user for a passphrase.
1040 *
1041 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
1042 * Documentation/filesystems/fscrypt.rst.
1043 */
1044int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
1045{
1046        struct super_block *sb = file_inode(filp)->i_sb;
1047        struct fscrypt_get_key_status_arg arg;
1048        struct key *key;
1049        struct fscrypt_master_key *mk;
1050        int err;
1051
1052        if (copy_from_user(&arg, uarg, sizeof(arg)))
1053                return -EFAULT;
1054
1055        if (!valid_key_spec(&arg.key_spec))
1056                return -EINVAL;
1057
1058        if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1059                return -EINVAL;
1060
1061        arg.status_flags = 0;
1062        arg.user_count = 0;
1063        memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
1064
1065        key = fscrypt_find_master_key(sb, &arg.key_spec);
1066        if (IS_ERR(key)) {
1067                if (key != ERR_PTR(-ENOKEY))
1068                        return PTR_ERR(key);
1069                arg.status = FSCRYPT_KEY_STATUS_ABSENT;
1070                err = 0;
1071                goto out;
1072        }
1073        mk = key->payload.data[0];
1074        down_read(&key->sem);
1075
1076        if (!is_master_key_secret_present(&mk->mk_secret)) {
1077                arg.status = FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED;
1078                err = 0;
1079                goto out_release_key;
1080        }
1081
1082        arg.status = FSCRYPT_KEY_STATUS_PRESENT;
1083        if (mk->mk_users) {
1084                struct key *mk_user;
1085
1086                arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
1087                mk_user = find_master_key_user(mk);
1088                if (!IS_ERR(mk_user)) {
1089                        arg.status_flags |=
1090                                FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
1091                        key_put(mk_user);
1092                } else if (mk_user != ERR_PTR(-ENOKEY)) {
1093                        err = PTR_ERR(mk_user);
1094                        goto out_release_key;
1095                }
1096        }
1097        err = 0;
1098out_release_key:
1099        up_read(&key->sem);
1100        key_put(key);
1101out:
1102        if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
1103                err = -EFAULT;
1104        return err;
1105}
1106EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
1107
1108int __init fscrypt_init_keyring(void)
1109{
1110        int err;
1111
1112        err = register_key_type(&key_type_fscrypt);
1113        if (err)
1114                return err;
1115
1116        err = register_key_type(&key_type_fscrypt_user);
1117        if (err)
1118                goto err_unregister_fscrypt;
1119
1120        err = register_key_type(&key_type_fscrypt_provisioning);
1121        if (err)
1122                goto err_unregister_fscrypt_user;
1123
1124        return 0;
1125
1126err_unregister_fscrypt_user:
1127        unregister_key_type(&key_type_fscrypt_user);
1128err_unregister_fscrypt:
1129        unregister_key_type(&key_type_fscrypt);
1130        return err;
1131}
1132
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.