root/fs/crypto/keysetup.c

DEFINITIONS

1. select_encryption_mode
2. fscrypt_allocate_skcipher
3. derive_essiv_salt
4. init_essiv_generator
5. fscrypt_set_derived_key
6. setup_per_mode_key
7. fscrypt_setup_v2_file_key
8. setup_file_encryption_key
9. put_crypt_info
10. fscrypt_get_encryption_info
11. fscrypt_put_encryption_info
12. fscrypt_free_inode
13. fscrypt_drop_inode

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Key setup facility for FS encryption support.
   4  *
   5  * Copyright (C) 2015, Google, Inc.
   6  *
   7  * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
   8  * Heavily modified since then.
   9  */
  10 
  11 #include <crypto/aes.h>
  12 #include <crypto/sha.h>
  13 #include <crypto/skcipher.h>
  14 #include <linux/key.h>
  15 
  16 #include "fscrypt_private.h"
  17 
  18 static struct crypto_shash *essiv_hash_tfm;
  19 
  20 static struct fscrypt_mode available_modes[] = {
  21         [FSCRYPT_MODE_AES_256_XTS] = {
  22                 .friendly_name = "AES-256-XTS",
  23                 .cipher_str = "xts(aes)",
  24                 .keysize = 64,
  25                 .ivsize = 16,
  26         },
  27         [FSCRYPT_MODE_AES_256_CTS] = {
  28                 .friendly_name = "AES-256-CTS-CBC",
  29                 .cipher_str = "cts(cbc(aes))",
  30                 .keysize = 32,
  31                 .ivsize = 16,
  32         },
  33         [FSCRYPT_MODE_AES_128_CBC] = {
  34                 .friendly_name = "AES-128-CBC",
  35                 .cipher_str = "cbc(aes)",
  36                 .keysize = 16,
  37                 .ivsize = 16,
  38                 .needs_essiv = true,
  39         },
  40         [FSCRYPT_MODE_AES_128_CTS] = {
  41                 .friendly_name = "AES-128-CTS-CBC",
  42                 .cipher_str = "cts(cbc(aes))",
  43                 .keysize = 16,
  44                 .ivsize = 16,
  45         },
  46         [FSCRYPT_MODE_ADIANTUM] = {
  47                 .friendly_name = "Adiantum",
  48                 .cipher_str = "adiantum(xchacha12,aes)",
  49                 .keysize = 32,
  50                 .ivsize = 32,
  51         },
  52 };
  53 
  54 static struct fscrypt_mode *
  55 select_encryption_mode(const union fscrypt_policy *policy,
  56                        const struct inode *inode)
  57 {
  58         if (S_ISREG(inode->i_mode))
  59                 return &available_modes[fscrypt_policy_contents_mode(policy)];
  60 
  61         if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
  62                 return &available_modes[fscrypt_policy_fnames_mode(policy)];
  63 
  64         WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
  65                   inode->i_ino, (inode->i_mode & S_IFMT));
  66         return ERR_PTR(-EINVAL);
  67 }
  68 
  69 /* Create a symmetric cipher object for the given encryption mode and key */
  70 struct crypto_skcipher *fscrypt_allocate_skcipher(struct fscrypt_mode *mode,
  71                                                   const u8 *raw_key,
  72                                                   const struct inode *inode)
  73 {
  74         struct crypto_skcipher *tfm;
  75         int err;
  76 
  77         tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
  78         if (IS_ERR(tfm)) {
  79                 if (PTR_ERR(tfm) == -ENOENT) {
  80                         fscrypt_warn(inode,
  81                                      "Missing crypto API support for %s (API name: \"%s\")",
  82                                      mode->friendly_name, mode->cipher_str);
  83                         return ERR_PTR(-ENOPKG);
  84                 }
  85                 fscrypt_err(inode, "Error allocating '%s' transform: %ld",
  86                             mode->cipher_str, PTR_ERR(tfm));
  87                 return tfm;
  88         }
  89         if (unlikely(!mode->logged_impl_name)) {
  90                 /*
  91                  * fscrypt performance can vary greatly depending on which
  92                  * crypto algorithm implementation is used.  Help people debug
  93                  * performance problems by logging the ->cra_driver_name the
  94                  * first time a mode is used.  Note that multiple threads can
  95                  * race here, but it doesn't really matter.
  96                  */
  97                 mode->logged_impl_name = true;
  98                 pr_info("fscrypt: %s using implementation \"%s\"\n",
  99                         mode->friendly_name,
 100                         crypto_skcipher_alg(tfm)->base.cra_driver_name);
 101         }
 102         crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
 103         err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
 104         if (err)
 105                 goto err_free_tfm;
 106 
 107         return tfm;
 108 
 109 err_free_tfm:
 110         crypto_free_skcipher(tfm);
 111         return ERR_PTR(err);
 112 }
 113 
 114 static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
 115 {
 116         struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
 117 
 118         /* init hash transform on demand */
 119         if (unlikely(!tfm)) {
 120                 struct crypto_shash *prev_tfm;
 121 
 122                 tfm = crypto_alloc_shash("sha256", 0, 0);
 123                 if (IS_ERR(tfm)) {
 124                         if (PTR_ERR(tfm) == -ENOENT) {
 125                                 fscrypt_warn(NULL,
 126                                              "Missing crypto API support for SHA-256");
 127                                 return -ENOPKG;
 128                         }
 129                         fscrypt_err(NULL,
 130                                     "Error allocating SHA-256 transform: %ld",
 131                                     PTR_ERR(tfm));
 132                         return PTR_ERR(tfm);
 133                 }
 134                 prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
 135                 if (prev_tfm) {
 136                         crypto_free_shash(tfm);
 137                         tfm = prev_tfm;
 138                 }
 139         }
 140 
 141         {
 142                 SHASH_DESC_ON_STACK(desc, tfm);
 143                 desc->tfm = tfm;
 144 
 145                 return crypto_shash_digest(desc, key, keysize, salt);
 146         }
 147 }
 148 
 149 static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
 150                                 int keysize)
 151 {
 152         int err;
 153         struct crypto_cipher *essiv_tfm;
 154         u8 salt[SHA256_DIGEST_SIZE];
 155 
 156         if (WARN_ON(ci->ci_mode->ivsize != AES_BLOCK_SIZE))
 157                 return -EINVAL;
 158 
 159         essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
 160         if (IS_ERR(essiv_tfm))
 161                 return PTR_ERR(essiv_tfm);
 162 
 163         ci->ci_essiv_tfm = essiv_tfm;
 164 
 165         err = derive_essiv_salt(raw_key, keysize, salt);
 166         if (err)
 167                 goto out;
 168 
 169         /*
 170          * Using SHA256 to derive the salt/key will result in AES-256 being
 171          * used for IV generation. File contents encryption will still use the
 172          * configured keysize (AES-128) nevertheless.
 173          */
 174         err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
 175         if (err)
 176                 goto out;
 177 
 178 out:
 179         memzero_explicit(salt, sizeof(salt));
 180         return err;
 181 }
 182 
 183 /* Given the per-file key, set up the file's crypto transform object(s) */
 184 int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key)
 185 {
 186         struct fscrypt_mode *mode = ci->ci_mode;
 187         struct crypto_skcipher *ctfm;
 188         int err;
 189 
 190         ctfm = fscrypt_allocate_skcipher(mode, derived_key, ci->ci_inode);
 191         if (IS_ERR(ctfm))
 192                 return PTR_ERR(ctfm);
 193 
 194         ci->ci_ctfm = ctfm;
 195 
 196         if (mode->needs_essiv) {
 197                 err = init_essiv_generator(ci, derived_key, mode->keysize);
 198                 if (err) {
 199                         fscrypt_warn(ci->ci_inode,
 200                                      "Error initializing ESSIV generator: %d",
 201                                      err);
 202                         return err;
 203                 }
 204         }
 205         return 0;
 206 }
 207 
 208 static int setup_per_mode_key(struct fscrypt_info *ci,
 209                               struct fscrypt_master_key *mk)
 210 {
 211         struct fscrypt_mode *mode = ci->ci_mode;
 212         u8 mode_num = mode - available_modes;
 213         struct crypto_skcipher *tfm, *prev_tfm;
 214         u8 mode_key[FSCRYPT_MAX_KEY_SIZE];
 215         int err;
 216 
 217         if (WARN_ON(mode_num >= ARRAY_SIZE(mk->mk_mode_keys)))
 218                 return -EINVAL;
 219 
 220         /* pairs with cmpxchg() below */
 221         tfm = READ_ONCE(mk->mk_mode_keys[mode_num]);
 222         if (likely(tfm != NULL))
 223                 goto done;
 224 
 225         BUILD_BUG_ON(sizeof(mode_num) != 1);
 226         err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
 227                                   HKDF_CONTEXT_PER_MODE_KEY,
 228                                   &mode_num, sizeof(mode_num),
 229                                   mode_key, mode->keysize);
 230         if (err)
 231                 return err;
 232         tfm = fscrypt_allocate_skcipher(mode, mode_key, ci->ci_inode);
 233         memzero_explicit(mode_key, mode->keysize);
 234         if (IS_ERR(tfm))
 235                 return PTR_ERR(tfm);
 236 
 237         /* pairs with READ_ONCE() above */
 238         prev_tfm = cmpxchg(&mk->mk_mode_keys[mode_num], NULL, tfm);
 239         if (prev_tfm != NULL) {
 240                 crypto_free_skcipher(tfm);
 241                 tfm = prev_tfm;
 242         }
 243 done:
 244         ci->ci_ctfm = tfm;
 245         return 0;
 246 }
 247 
 248 static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
 249                                      struct fscrypt_master_key *mk)
 250 {
 251         u8 derived_key[FSCRYPT_MAX_KEY_SIZE];
 252         int err;
 253 
 254         if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
 255                 /*
 256                  * DIRECT_KEY: instead of deriving per-file keys, the per-file
 257                  * nonce will be included in all the IVs.  But unlike v1
 258                  * policies, for v2 policies in this case we don't encrypt with
 259                  * the master key directly but rather derive a per-mode key.
 260                  * This ensures that the master key is consistently used only
 261                  * for HKDF, avoiding key reuse issues.
 262                  */
 263                 if (!fscrypt_mode_supports_direct_key(ci->ci_mode)) {
 264                         fscrypt_warn(ci->ci_inode,
 265                                      "Direct key flag not allowed with %s",
 266                                      ci->ci_mode->friendly_name);
 267                         return -EINVAL;
 268                 }
 269                 return setup_per_mode_key(ci, mk);
 270         }
 271 
 272         err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
 273                                   HKDF_CONTEXT_PER_FILE_KEY,
 274                                   ci->ci_nonce, FS_KEY_DERIVATION_NONCE_SIZE,
 275                                   derived_key, ci->ci_mode->keysize);
 276         if (err)
 277                 return err;
 278 
 279         err = fscrypt_set_derived_key(ci, derived_key);
 280         memzero_explicit(derived_key, ci->ci_mode->keysize);
 281         return err;
 282 }
 283 
 284 /*
 285  * Find the master key, then set up the inode's actual encryption key.
 286  *
 287  * If the master key is found in the filesystem-level keyring, then the
 288  * corresponding 'struct key' is returned in *master_key_ret with
 289  * ->mk_secret_sem read-locked.  This is needed to ensure that only one task
 290  * links the fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race
 291  * to create an fscrypt_info for the same inode), and to synchronize the master
 292  * key being removed with a new inode starting to use it.
 293  */
 294 static int setup_file_encryption_key(struct fscrypt_info *ci,
 295                                      struct key **master_key_ret)
 296 {
 297         struct key *key;
 298         struct fscrypt_master_key *mk = NULL;
 299         struct fscrypt_key_specifier mk_spec;
 300         int err;
 301 
 302         switch (ci->ci_policy.version) {
 303         case FSCRYPT_POLICY_V1:
 304                 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
 305                 memcpy(mk_spec.u.descriptor,
 306                        ci->ci_policy.v1.master_key_descriptor,
 307                        FSCRYPT_KEY_DESCRIPTOR_SIZE);
 308                 break;
 309         case FSCRYPT_POLICY_V2:
 310                 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
 311                 memcpy(mk_spec.u.identifier,
 312                        ci->ci_policy.v2.master_key_identifier,
 313                        FSCRYPT_KEY_IDENTIFIER_SIZE);
 314                 break;
 315         default:
 316                 WARN_ON(1);
 317                 return -EINVAL;
 318         }
 319 
 320         key = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);
 321         if (IS_ERR(key)) {
 322                 if (key != ERR_PTR(-ENOKEY) ||
 323                     ci->ci_policy.version != FSCRYPT_POLICY_V1)
 324                         return PTR_ERR(key);
 325 
 326                 /*
 327                  * As a legacy fallback for v1 policies, search for the key in
 328                  * the current task's subscribed keyrings too.  Don't move this
 329                  * to before the search of ->s_master_keys, since users
 330                  * shouldn't be able to override filesystem-level keys.
 331                  */
 332                 return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
 333         }
 334 
 335         mk = key->payload.data[0];
 336         down_read(&mk->mk_secret_sem);
 337 
 338         /* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */
 339         if (!is_master_key_secret_present(&mk->mk_secret)) {
 340                 err = -ENOKEY;
 341                 goto out_release_key;
 342         }
 343 
 344         /*
 345          * Require that the master key be at least as long as the derived key.
 346          * Otherwise, the derived key cannot possibly contain as much entropy as
 347          * that required by the encryption mode it will be used for.  For v1
 348          * policies it's also required for the KDF to work at all.
 349          */
 350         if (mk->mk_secret.size < ci->ci_mode->keysize) {
 351                 fscrypt_warn(NULL,
 352                              "key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
 353                              master_key_spec_type(&mk_spec),
 354                              master_key_spec_len(&mk_spec), (u8 *)&mk_spec.u,
 355                              mk->mk_secret.size, ci->ci_mode->keysize);
 356                 err = -ENOKEY;
 357                 goto out_release_key;
 358         }
 359 
 360         switch (ci->ci_policy.version) {
 361         case FSCRYPT_POLICY_V1:
 362                 err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
 363                 break;
 364         case FSCRYPT_POLICY_V2:
 365                 err = fscrypt_setup_v2_file_key(ci, mk);
 366                 break;
 367         default:
 368                 WARN_ON(1);
 369                 err = -EINVAL;
 370                 break;
 371         }
 372         if (err)
 373                 goto out_release_key;
 374 
 375         *master_key_ret = key;
 376         return 0;
 377 
 378 out_release_key:
 379         up_read(&mk->mk_secret_sem);
 380         key_put(key);
 381         return err;
 382 }
 383 
 384 static void put_crypt_info(struct fscrypt_info *ci)
 385 {
 386         struct key *key;
 387 
 388         if (!ci)
 389                 return;
 390 
 391         if (ci->ci_direct_key) {
 392                 fscrypt_put_direct_key(ci->ci_direct_key);
 393         } else if ((ci->ci_ctfm != NULL || ci->ci_essiv_tfm != NULL) &&
 394                    !fscrypt_is_direct_key_policy(&ci->ci_policy)) {
 395                 crypto_free_skcipher(ci->ci_ctfm);
 396                 crypto_free_cipher(ci->ci_essiv_tfm);
 397         }
 398 
 399         key = ci->ci_master_key;
 400         if (key) {
 401                 struct fscrypt_master_key *mk = key->payload.data[0];
 402 
 403                 /*
 404                  * Remove this inode from the list of inodes that were unlocked
 405                  * with the master key.
 406                  *
 407                  * In addition, if we're removing the last inode from a key that
 408                  * already had its secret removed, invalidate the key so that it
 409                  * gets removed from ->s_master_keys.
 410                  */
 411                 spin_lock(&mk->mk_decrypted_inodes_lock);
 412                 list_del(&ci->ci_master_key_link);
 413                 spin_unlock(&mk->mk_decrypted_inodes_lock);
 414                 if (refcount_dec_and_test(&mk->mk_refcount))
 415                         key_invalidate(key);
 416                 key_put(key);
 417         }
 418         kmem_cache_free(fscrypt_info_cachep, ci);
 419 }
 420 
 421 int fscrypt_get_encryption_info(struct inode *inode)
 422 {
 423         struct fscrypt_info *crypt_info;
 424         union fscrypt_context ctx;
 425         struct fscrypt_mode *mode;
 426         struct key *master_key = NULL;
 427         int res;
 428 
 429         if (fscrypt_has_encryption_key(inode))
 430                 return 0;
 431 
 432         res = fscrypt_initialize(inode->i_sb->s_cop->flags);
 433         if (res)
 434                 return res;
 435 
 436         res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 437         if (res < 0) {
 438                 if (!fscrypt_dummy_context_enabled(inode) ||
 439                     IS_ENCRYPTED(inode)) {
 440                         fscrypt_warn(inode,
 441                                      "Error %d getting encryption context",
 442                                      res);
 443                         return res;
 444                 }
 445                 /* Fake up a context for an unencrypted directory */
 446                 memset(&ctx, 0, sizeof(ctx));
 447                 ctx.version = FSCRYPT_CONTEXT_V1;
 448                 ctx.v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
 449                 ctx.v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
 450                 memset(ctx.v1.master_key_descriptor, 0x42,
 451                        FSCRYPT_KEY_DESCRIPTOR_SIZE);
 452                 res = sizeof(ctx.v1);
 453         }
 454 
 455         crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
 456         if (!crypt_info)
 457                 return -ENOMEM;
 458 
 459         crypt_info->ci_inode = inode;
 460 
 461         res = fscrypt_policy_from_context(&crypt_info->ci_policy, &ctx, res);
 462         if (res) {
 463                 fscrypt_warn(inode,
 464                              "Unrecognized or corrupt encryption context");
 465                 goto out;
 466         }
 467 
 468         switch (ctx.version) {
 469         case FSCRYPT_CONTEXT_V1:
 470                 memcpy(crypt_info->ci_nonce, ctx.v1.nonce,
 471                        FS_KEY_DERIVATION_NONCE_SIZE);
 472                 break;
 473         case FSCRYPT_CONTEXT_V2:
 474                 memcpy(crypt_info->ci_nonce, ctx.v2.nonce,
 475                        FS_KEY_DERIVATION_NONCE_SIZE);
 476                 break;
 477         default:
 478                 WARN_ON(1);
 479                 res = -EINVAL;
 480                 goto out;
 481         }
 482 
 483         if (!fscrypt_supported_policy(&crypt_info->ci_policy, inode)) {
 484                 res = -EINVAL;
 485                 goto out;
 486         }
 487 
 488         mode = select_encryption_mode(&crypt_info->ci_policy, inode);
 489         if (IS_ERR(mode)) {
 490                 res = PTR_ERR(mode);
 491                 goto out;
 492         }
 493         WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
 494         crypt_info->ci_mode = mode;
 495 
 496         res = setup_file_encryption_key(crypt_info, &master_key);
 497         if (res)
 498                 goto out;
 499 
 500         if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) {
 501                 if (master_key) {
 502                         struct fscrypt_master_key *mk =
 503                                 master_key->payload.data[0];
 504 
 505                         refcount_inc(&mk->mk_refcount);
 506                         crypt_info->ci_master_key = key_get(master_key);
 507                         spin_lock(&mk->mk_decrypted_inodes_lock);
 508                         list_add(&crypt_info->ci_master_key_link,
 509                                  &mk->mk_decrypted_inodes);
 510                         spin_unlock(&mk->mk_decrypted_inodes_lock);
 511                 }
 512                 crypt_info = NULL;
 513         }
 514         res = 0;
 515 out:
 516         if (master_key) {
 517                 struct fscrypt_master_key *mk = master_key->payload.data[0];
 518 
 519                 up_read(&mk->mk_secret_sem);
 520                 key_put(master_key);
 521         }
 522         if (res == -ENOKEY)
 523                 res = 0;
 524         put_crypt_info(crypt_info);
 525         return res;
 526 }
 527 EXPORT_SYMBOL(fscrypt_get_encryption_info);
 528 
 529 /**
 530  * fscrypt_put_encryption_info - free most of an inode's fscrypt data
 531  *
 532  * Free the inode's fscrypt_info.  Filesystems must call this when the inode is
 533  * being evicted.  An RCU grace period need not have elapsed yet.
 534  */
 535 void fscrypt_put_encryption_info(struct inode *inode)
 536 {
 537         put_crypt_info(inode->i_crypt_info);
 538         inode->i_crypt_info = NULL;
 539 }
 540 EXPORT_SYMBOL(fscrypt_put_encryption_info);
 541 
 542 /**
 543  * fscrypt_free_inode - free an inode's fscrypt data requiring RCU delay
 544  *
 545  * Free the inode's cached decrypted symlink target, if any.  Filesystems must
 546  * call this after an RCU grace period, just before they free the inode.
 547  */
 548 void fscrypt_free_inode(struct inode *inode)
 549 {
 550         if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
 551                 kfree(inode->i_link);
 552                 inode->i_link = NULL;
 553         }
 554 }
 555 EXPORT_SYMBOL(fscrypt_free_inode);
 556 
 557 /**
 558  * fscrypt_drop_inode - check whether the inode's master key has been removed
 559  *
 560  * Filesystems supporting fscrypt must call this from their ->drop_inode()
 561  * method so that encrypted inodes are evicted as soon as they're no longer in
 562  * use and their master key has been removed.
 563  *
 564  * Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
 565  */
 566 int fscrypt_drop_inode(struct inode *inode)
 567 {
 568         const struct fscrypt_info *ci = READ_ONCE(inode->i_crypt_info);
 569         const struct fscrypt_master_key *mk;
 570 
 571         /*
 572          * If ci is NULL, then the inode doesn't have an encryption key set up
 573          * so it's irrelevant.  If ci_master_key is NULL, then the master key
 574          * was provided via the legacy mechanism of the process-subscribed
 575          * keyrings, so we don't know whether it's been removed or not.
 576          */
 577         if (!ci || !ci->ci_master_key)
 578                 return 0;
 579         mk = ci->ci_master_key->payload.data[0];
 580 
 581         /*
 582          * With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
 583          * protected by the key were cleaned by sync_filesystem().  But if
 584          * userspace is still using the files, inodes can be dirtied between
 585          * then and now.  We mustn't lose any writes, so skip dirty inodes here.
 586          */
 587         if (inode->i_state & I_DIRTY_ALL)
 588                 return 0;
 589 
 590         /*
 591          * Note: since we aren't holding ->mk_secret_sem, the result here can
 592          * immediately become outdated.  But there's no correctness problem with
 593          * unnecessarily evicting.  Nor is there a correctness problem with not
 594          * evicting while iput() is racing with the key being removed, since
 595          * then the thread removing the key will either evict the inode itself
 596          * or will correctly detect that it wasn't evicted due to the race.
 597          */
 598         return !is_master_key_secret_present(&mk->mk_secret);
 599 }
 600 EXPORT_SYMBOL_GPL(fscrypt_drop_inode);