root/fs/crypto/keyring.c

DEFINITIONS

1. wipe_master_key_secret
2. move_master_key_secret
3. free_master_key
4. valid_key_spec
5. fscrypt_key_instantiate
6. fscrypt_key_destroy
7. fscrypt_key_describe
8. fscrypt_user_key_instantiate
9. fscrypt_user_key_describe
10. search_fscrypt_keyring
11. format_fs_keyring_description
12. format_mk_description
13. format_mk_users_keyring_description
14. format_mk_user_description
15. allocate_filesystem_keyring
16. fscrypt_sb_free
17. fscrypt_find_master_key
18. allocate_master_key_users_keyring
19. find_master_key_user
20. add_master_key_user
21. remove_master_key_user
22. add_new_master_key
23. add_existing_master_key
24. add_master_key
25. fscrypt_ioctl_add_key
26. fscrypt_verify_key_added
27. shrink_dcache_inode
28. evict_dentries_for_decrypted_inodes
29. check_for_busy_inodes
30. try_to_lock_encrypted_files
31. do_remove_key
32. fscrypt_ioctl_remove_key
33. fscrypt_ioctl_remove_key_all_users
34. fscrypt_ioctl_get_key_status
35. fscrypt_init_keyring

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