root/fs/crypto/fscrypt_private.h

INCLUDED FROM

DEFINITIONS

1. fscrypt_context_size
2. fscrypt_policy_size
3. fscrypt_policy_contents_mode
4. fscrypt_policy_fnames_mode
5. fscrypt_policy_flags
6. fscrypt_is_direct_key_policy
7. fscrypt_valid_enc_modes
8. is_master_key_secret_present
9. master_key_spec_type
10. master_key_spec_len
11. fscrypt_mode_supports_direct_key

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * fscrypt_private.h
   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 #ifndef _FSCRYPT_PRIVATE_H
  12 #define _FSCRYPT_PRIVATE_H
  13 
  14 #include <linux/fscrypt.h>
  15 #include <crypto/hash.h>
  16 
  17 #define CONST_STRLEN(str)       (sizeof(str) - 1)
  18 
  19 #define FS_KEY_DERIVATION_NONCE_SIZE    16
  20 
  21 #define FSCRYPT_MIN_KEY_SIZE            16
  22 
  23 #define FSCRYPT_CONTEXT_V1      1
  24 #define FSCRYPT_CONTEXT_V2      2
  25 
  26 struct fscrypt_context_v1 {
  27         u8 version; /* FSCRYPT_CONTEXT_V1 */
  28         u8 contents_encryption_mode;
  29         u8 filenames_encryption_mode;
  30         u8 flags;
  31         u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
  32         u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
  33 };
  34 
  35 struct fscrypt_context_v2 {
  36         u8 version; /* FSCRYPT_CONTEXT_V2 */
  37         u8 contents_encryption_mode;
  38         u8 filenames_encryption_mode;
  39         u8 flags;
  40         u8 __reserved[4];
  41         u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
  42         u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
  43 };
  44 
  45 /**
  46  * fscrypt_context - the encryption context of an inode
  47  *
  48  * This is the on-disk equivalent of an fscrypt_policy, stored alongside each
  49  * encrypted file usually in a hidden extended attribute.  It contains the
  50  * fields from the fscrypt_policy, in order to identify the encryption algorithm
  51  * and key with which the file is encrypted.  It also contains a nonce that was
  52  * randomly generated by fscrypt itself; this is used as KDF input or as a tweak
  53  * to cause different files to be encrypted differently.
  54  */
  55 union fscrypt_context {
  56         u8 version;
  57         struct fscrypt_context_v1 v1;
  58         struct fscrypt_context_v2 v2;
  59 };
  60 
  61 /*
  62  * Return the size expected for the given fscrypt_context based on its version
  63  * number, or 0 if the context version is unrecognized.
  64  */
  65 static inline int fscrypt_context_size(const union fscrypt_context *ctx)
  66 {
  67         switch (ctx->version) {
  68         case FSCRYPT_CONTEXT_V1:
  69                 BUILD_BUG_ON(sizeof(ctx->v1) != 28);
  70                 return sizeof(ctx->v1);
  71         case FSCRYPT_CONTEXT_V2:
  72                 BUILD_BUG_ON(sizeof(ctx->v2) != 40);
  73                 return sizeof(ctx->v2);
  74         }
  75         return 0;
  76 }
  77 
  78 #undef fscrypt_policy
  79 union fscrypt_policy {
  80         u8 version;
  81         struct fscrypt_policy_v1 v1;
  82         struct fscrypt_policy_v2 v2;
  83 };
  84 
  85 /*
  86  * Return the size expected for the given fscrypt_policy based on its version
  87  * number, or 0 if the policy version is unrecognized.
  88  */
  89 static inline int fscrypt_policy_size(const union fscrypt_policy *policy)
  90 {
  91         switch (policy->version) {
  92         case FSCRYPT_POLICY_V1:
  93                 return sizeof(policy->v1);
  94         case FSCRYPT_POLICY_V2:
  95                 return sizeof(policy->v2);
  96         }
  97         return 0;
  98 }
  99 
 100 /* Return the contents encryption mode of a valid encryption policy */
 101 static inline u8
 102 fscrypt_policy_contents_mode(const union fscrypt_policy *policy)
 103 {
 104         switch (policy->version) {
 105         case FSCRYPT_POLICY_V1:
 106                 return policy->v1.contents_encryption_mode;
 107         case FSCRYPT_POLICY_V2:
 108                 return policy->v2.contents_encryption_mode;
 109         }
 110         BUG();
 111 }
 112 
 113 /* Return the filenames encryption mode of a valid encryption policy */
 114 static inline u8
 115 fscrypt_policy_fnames_mode(const union fscrypt_policy *policy)
 116 {
 117         switch (policy->version) {
 118         case FSCRYPT_POLICY_V1:
 119                 return policy->v1.filenames_encryption_mode;
 120         case FSCRYPT_POLICY_V2:
 121                 return policy->v2.filenames_encryption_mode;
 122         }
 123         BUG();
 124 }
 125 
 126 /* Return the flags (FSCRYPT_POLICY_FLAG*) of a valid encryption policy */
 127 static inline u8
 128 fscrypt_policy_flags(const union fscrypt_policy *policy)
 129 {
 130         switch (policy->version) {
 131         case FSCRYPT_POLICY_V1:
 132                 return policy->v1.flags;
 133         case FSCRYPT_POLICY_V2:
 134                 return policy->v2.flags;
 135         }
 136         BUG();
 137 }
 138 
 139 static inline bool
 140 fscrypt_is_direct_key_policy(const union fscrypt_policy *policy)
 141 {
 142         return fscrypt_policy_flags(policy) & FSCRYPT_POLICY_FLAG_DIRECT_KEY;
 143 }
 144 
 145 /**
 146  * For encrypted symlinks, the ciphertext length is stored at the beginning
 147  * of the string in little-endian format.
 148  */
 149 struct fscrypt_symlink_data {
 150         __le16 len;
 151         char encrypted_path[1];
 152 } __packed;
 153 
 154 /*
 155  * fscrypt_info - the "encryption key" for an inode
 156  *
 157  * When an encrypted file's key is made available, an instance of this struct is
 158  * allocated and stored in ->i_crypt_info.  Once created, it remains until the
 159  * inode is evicted.
 160  */
 161 struct fscrypt_info {
 162 
 163         /* The actual crypto transform used for encryption and decryption */
 164         struct crypto_skcipher *ci_ctfm;
 165 
 166         /*
 167          * Cipher for ESSIV IV generation.  Only set for CBC contents
 168          * encryption, otherwise is NULL.
 169          */
 170         struct crypto_cipher *ci_essiv_tfm;
 171 
 172         /*
 173          * Encryption mode used for this inode.  It corresponds to either the
 174          * contents or filenames encryption mode, depending on the inode type.
 175          */
 176         struct fscrypt_mode *ci_mode;
 177 
 178         /* Back-pointer to the inode */
 179         struct inode *ci_inode;
 180 
 181         /*
 182          * The master key with which this inode was unlocked (decrypted).  This
 183          * will be NULL if the master key was found in a process-subscribed
 184          * keyring rather than in the filesystem-level keyring.
 185          */
 186         struct key *ci_master_key;
 187 
 188         /*
 189          * Link in list of inodes that were unlocked with the master key.
 190          * Only used when ->ci_master_key is set.
 191          */
 192         struct list_head ci_master_key_link;
 193 
 194         /*
 195          * If non-NULL, then encryption is done using the master key directly
 196          * and ci_ctfm will equal ci_direct_key->dk_ctfm.
 197          */
 198         struct fscrypt_direct_key *ci_direct_key;
 199 
 200         /* The encryption policy used by this inode */
 201         union fscrypt_policy ci_policy;
 202 
 203         /* This inode's nonce, copied from the fscrypt_context */
 204         u8 ci_nonce[FS_KEY_DERIVATION_NONCE_SIZE];
 205 };
 206 
 207 typedef enum {
 208         FS_DECRYPT = 0,
 209         FS_ENCRYPT,
 210 } fscrypt_direction_t;
 211 
 212 #define FS_CTX_REQUIRES_FREE_ENCRYPT_FL         0x00000001
 213 
 214 static inline bool fscrypt_valid_enc_modes(u32 contents_mode,
 215                                            u32 filenames_mode)
 216 {
 217         if (contents_mode == FSCRYPT_MODE_AES_128_CBC &&
 218             filenames_mode == FSCRYPT_MODE_AES_128_CTS)
 219                 return true;
 220 
 221         if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
 222             filenames_mode == FSCRYPT_MODE_AES_256_CTS)
 223                 return true;
 224 
 225         if (contents_mode == FSCRYPT_MODE_ADIANTUM &&
 226             filenames_mode == FSCRYPT_MODE_ADIANTUM)
 227                 return true;
 228 
 229         return false;
 230 }
 231 
 232 /* crypto.c */
 233 extern struct kmem_cache *fscrypt_info_cachep;
 234 extern int fscrypt_initialize(unsigned int cop_flags);
 235 extern int fscrypt_crypt_block(const struct inode *inode,
 236                                fscrypt_direction_t rw, u64 lblk_num,
 237                                struct page *src_page, struct page *dest_page,
 238                                unsigned int len, unsigned int offs,
 239                                gfp_t gfp_flags);
 240 extern struct page *fscrypt_alloc_bounce_page(gfp_t gfp_flags);
 241 extern const struct dentry_operations fscrypt_d_ops;
 242 
 243 extern void __printf(3, 4) __cold
 244 fscrypt_msg(const struct inode *inode, const char *level, const char *fmt, ...);
 245 
 246 #define fscrypt_warn(inode, fmt, ...)           \
 247         fscrypt_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
 248 #define fscrypt_err(inode, fmt, ...)            \
 249         fscrypt_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
 250 
 251 #define FSCRYPT_MAX_IV_SIZE     32
 252 
 253 union fscrypt_iv {
 254         struct {
 255                 /* logical block number within the file */
 256                 __le64 lblk_num;
 257 
 258                 /* per-file nonce; only set in DIRECT_KEY mode */
 259                 u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
 260         };
 261         u8 raw[FSCRYPT_MAX_IV_SIZE];
 262 };
 263 
 264 void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 265                          const struct fscrypt_info *ci);
 266 
 267 /* fname.c */
 268 extern int fname_encrypt(struct inode *inode, const struct qstr *iname,
 269                          u8 *out, unsigned int olen);
 270 extern bool fscrypt_fname_encrypted_size(const struct inode *inode,
 271                                          u32 orig_len, u32 max_len,
 272                                          u32 *encrypted_len_ret);
 273 
 274 /* hkdf.c */
 275 
 276 struct fscrypt_hkdf {
 277         struct crypto_shash *hmac_tfm;
 278 };
 279 
 280 extern int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
 281                              unsigned int master_key_size);
 282 
 283 /*
 284  * The list of contexts in which fscrypt uses HKDF.  These values are used as
 285  * the first byte of the HKDF application-specific info string to guarantee that
 286  * info strings are never repeated between contexts.  This ensures that all HKDF
 287  * outputs are unique and cryptographically isolated, i.e. knowledge of one
 288  * output doesn't reveal another.
 289  */
 290 #define HKDF_CONTEXT_KEY_IDENTIFIER     1
 291 #define HKDF_CONTEXT_PER_FILE_KEY       2
 292 #define HKDF_CONTEXT_PER_MODE_KEY       3
 293 
 294 extern int fscrypt_hkdf_expand(struct fscrypt_hkdf *hkdf, u8 context,
 295                                const u8 *info, unsigned int infolen,
 296                                u8 *okm, unsigned int okmlen);
 297 
 298 extern void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);
 299 
 300 /* keyring.c */
 301 
 302 /*
 303  * fscrypt_master_key_secret - secret key material of an in-use master key
 304  */
 305 struct fscrypt_master_key_secret {
 306 
 307         /*
 308          * For v2 policy keys: HKDF context keyed by this master key.
 309          * For v1 policy keys: not set (hkdf.hmac_tfm == NULL).
 310          */
 311         struct fscrypt_hkdf     hkdf;
 312 
 313         /* Size of the raw key in bytes.  Set even if ->raw isn't set. */
 314         u32                     size;
 315 
 316         /* For v1 policy keys: the raw key.  Wiped for v2 policy keys. */
 317         u8                      raw[FSCRYPT_MAX_KEY_SIZE];
 318 
 319 } __randomize_layout;
 320 
 321 /*
 322  * fscrypt_master_key - an in-use master key
 323  *
 324  * This represents a master encryption key which has been added to the
 325  * filesystem and can be used to "unlock" the encrypted files which were
 326  * encrypted with it.
 327  */
 328 struct fscrypt_master_key {
 329 
 330         /*
 331          * The secret key material.  After FS_IOC_REMOVE_ENCRYPTION_KEY is
 332          * executed, this is wiped and no new inodes can be unlocked with this
 333          * key; however, there may still be inodes in ->mk_decrypted_inodes
 334          * which could not be evicted.  As long as some inodes still remain,
 335          * FS_IOC_REMOVE_ENCRYPTION_KEY can be retried, or
 336          * FS_IOC_ADD_ENCRYPTION_KEY can add the secret again.
 337          *
 338          * Locking: protected by key->sem (outer) and mk_secret_sem (inner).
 339          * The reason for two locks is that key->sem also protects modifying
 340          * mk_users, which ranks it above the semaphore for the keyring key
 341          * type, which is in turn above page faults (via keyring_read).  But
 342          * sometimes filesystems call fscrypt_get_encryption_info() from within
 343          * a transaction, which ranks it below page faults.  So we need a
 344          * separate lock which protects mk_secret but not also mk_users.
 345          */
 346         struct fscrypt_master_key_secret        mk_secret;
 347         struct rw_semaphore                     mk_secret_sem;
 348 
 349         /*
 350          * For v1 policy keys: an arbitrary key descriptor which was assigned by
 351          * userspace (->descriptor).
 352          *
 353          * For v2 policy keys: a cryptographic hash of this key (->identifier).
 354          */
 355         struct fscrypt_key_specifier            mk_spec;
 356 
 357         /*
 358          * Keyring which contains a key of type 'key_type_fscrypt_user' for each
 359          * user who has added this key.  Normally each key will be added by just
 360          * one user, but it's possible that multiple users share a key, and in
 361          * that case we need to keep track of those users so that one user can't
 362          * remove the key before the others want it removed too.
 363          *
 364          * This is NULL for v1 policy keys; those can only be added by root.
 365          *
 366          * Locking: in addition to this keyrings own semaphore, this is
 367          * protected by the master key's key->sem, so we can do atomic
 368          * search+insert.  It can also be searched without taking any locks, but
 369          * in that case the returned key may have already been removed.
 370          */
 371         struct key              *mk_users;
 372 
 373         /*
 374          * Length of ->mk_decrypted_inodes, plus one if mk_secret is present.
 375          * Once this goes to 0, the master key is removed from ->s_master_keys.
 376          * The 'struct fscrypt_master_key' will continue to live as long as the
 377          * 'struct key' whose payload it is, but we won't let this reference
 378          * count rise again.
 379          */
 380         refcount_t              mk_refcount;
 381 
 382         /*
 383          * List of inodes that were unlocked using this key.  This allows the
 384          * inodes to be evicted efficiently if the key is removed.
 385          */
 386         struct list_head        mk_decrypted_inodes;
 387         spinlock_t              mk_decrypted_inodes_lock;
 388 
 389         /* Per-mode tfms for DIRECT_KEY policies, allocated on-demand */
 390         struct crypto_skcipher  *mk_mode_keys[__FSCRYPT_MODE_MAX + 1];
 391 
 392 } __randomize_layout;
 393 
 394 static inline bool
 395 is_master_key_secret_present(const struct fscrypt_master_key_secret *secret)
 396 {
 397         /*
 398          * The READ_ONCE() is only necessary for fscrypt_drop_inode() and
 399          * fscrypt_key_describe().  These run in atomic context, so they can't
 400          * take ->mk_secret_sem and thus 'secret' can change concurrently which
 401          * would be a data race.  But they only need to know whether the secret
 402          * *was* present at the time of check, so READ_ONCE() suffices.
 403          */
 404         return READ_ONCE(secret->size) != 0;
 405 }
 406 
 407 static inline const char *master_key_spec_type(
 408                                 const struct fscrypt_key_specifier *spec)
 409 {
 410         switch (spec->type) {
 411         case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
 412                 return "descriptor";
 413         case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
 414                 return "identifier";
 415         }
 416         return "[unknown]";
 417 }
 418 
 419 static inline int master_key_spec_len(const struct fscrypt_key_specifier *spec)
 420 {
 421         switch (spec->type) {
 422         case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
 423                 return FSCRYPT_KEY_DESCRIPTOR_SIZE;
 424         case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
 425                 return FSCRYPT_KEY_IDENTIFIER_SIZE;
 426         }
 427         return 0;
 428 }
 429 
 430 extern struct key *
 431 fscrypt_find_master_key(struct super_block *sb,
 432                         const struct fscrypt_key_specifier *mk_spec);
 433 
 434 extern int fscrypt_verify_key_added(struct super_block *sb,
 435                                     const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
 436 
 437 extern int __init fscrypt_init_keyring(void);
 438 
 439 /* keysetup.c */
 440 
 441 struct fscrypt_mode {
 442         const char *friendly_name;
 443         const char *cipher_str;
 444         int keysize;
 445         int ivsize;
 446         bool logged_impl_name;
 447         bool needs_essiv;
 448 };
 449 
 450 static inline bool
 451 fscrypt_mode_supports_direct_key(const struct fscrypt_mode *mode)
 452 {
 453         return mode->ivsize >= offsetofend(union fscrypt_iv, nonce);
 454 }
 455 
 456 extern struct crypto_skcipher *
 457 fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
 458                           const struct inode *inode);
 459 
 460 extern int fscrypt_set_derived_key(struct fscrypt_info *ci,
 461                                    const u8 *derived_key);
 462 
 463 /* keysetup_v1.c */
 464 
 465 extern void fscrypt_put_direct_key(struct fscrypt_direct_key *dk);
 466 
 467 extern int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
 468                                      const u8 *raw_master_key);
 469 
 470 extern int fscrypt_setup_v1_file_key_via_subscribed_keyrings(
 471                                         struct fscrypt_info *ci);
 472 /* policy.c */
 473 
 474 extern bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
 475                                    const union fscrypt_policy *policy2);
 476 extern bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
 477                                      const struct inode *inode);
 478 extern int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
 479                                        const union fscrypt_context *ctx_u,
 480                                        int ctx_size);
 481 
 482 #endif /* _FSCRYPT_PRIVATE_H */