fs/crypto/fscrypt_private.h

   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         /* True if the key should be freed when this fscrypt_info is freed */
 167         bool ci_owns_key;
 168
 169         /*
 170          * Encryption mode used for this inode.  It corresponds to either the
 171          * contents or filenames encryption mode, depending on the inode type.
 172          */
 173         struct fscrypt_mode *ci_mode;
 174
 175         /* Back-pointer to the inode */
 176         struct inode *ci_inode;
 177
 178         /*
 179          * The master key with which this inode was unlocked (decrypted).  This
 180          * will be NULL if the master key was found in a process-subscribed
 181          * keyring rather than in the filesystem-level keyring.
 182          */
 183         struct key *ci_master_key;
 184
 185         /*
 186          * Link in list of inodes that were unlocked with the master key.
 187          * Only used when ->ci_master_key is set.
 188          */
 189         struct list_head ci_master_key_link;
 190
 191         /*
 192          * If non-NULL, then encryption is done using the master key directly
 193          * and ci_ctfm will equal ci_direct_key->dk_ctfm.
 194          */
 195         struct fscrypt_direct_key *ci_direct_key;
 196
 197         /* The encryption policy used by this inode */
 198         union fscrypt_policy ci_policy;
 199
 200         /* This inode's nonce, copied from the fscrypt_context */
 201         u8 ci_nonce[FS_KEY_DERIVATION_NONCE_SIZE];
 202 };
 203
 204 typedef enum {
 205         FS_DECRYPT = 0,
 206         FS_ENCRYPT,
 207 } fscrypt_direction_t;
 208
 209 static inline bool fscrypt_valid_enc_modes(u32 contents_mode,
 210                                            u32 filenames_mode)
 211 {
 212         if (contents_mode == FSCRYPT_MODE_AES_128_CBC &&
 213             filenames_mode == FSCRYPT_MODE_AES_128_CTS)
 214                 return true;
 215
 216         if (contents_mode == FSCRYPT_MODE_AES_256_XTS &&
 217             filenames_mode == FSCRYPT_MODE_AES_256_CTS)
 218                 return true;
 219
 220         if (contents_mode == FSCRYPT_MODE_ADIANTUM &&
 221             filenames_mode == FSCRYPT_MODE_ADIANTUM)
 222                 return true;
 223
 224         return false;
 225 }
 226
 227 /* crypto.c */
 228 extern struct kmem_cache *fscrypt_info_cachep;
 229 extern int fscrypt_initialize(unsigned int cop_flags);
 230 extern int fscrypt_crypt_block(const struct inode *inode,
 231                                fscrypt_direction_t rw, u64 lblk_num,
 232                                struct page *src_page, struct page *dest_page,
 233                                unsigned int len, unsigned int offs,
 234                                gfp_t gfp_flags);
 235 extern struct page *fscrypt_alloc_bounce_page(gfp_t gfp_flags);
 236 extern const struct dentry_operations fscrypt_d_ops;
 237
 238 extern void __printf(3, 4) __cold
 239 fscrypt_msg(const struct inode *inode, const char *level, const char *fmt, ...);
 240
 241 #define fscrypt_warn(inode, fmt, ...)           \
 242         fscrypt_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
 243 #define fscrypt_err(inode, fmt, ...)            \
 244         fscrypt_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
 245
 246 #define FSCRYPT_MAX_IV_SIZE     32
 247
 248 union fscrypt_iv {
 249         struct {
 250                 /* logical block number within the file */
 251                 __le64 lblk_num;
 252
 253                 /* per-file nonce; only set in DIRECT_KEY mode */
 254                 u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
 255         };
 256         u8 raw[FSCRYPT_MAX_IV_SIZE];
 257 };
 258
 259 void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 260                          const struct fscrypt_info *ci);
 261
 262 /* fname.c */
 263 extern int fname_encrypt(struct inode *inode, const struct qstr *iname,
 264                          u8 *out, unsigned int olen);
 265 extern bool fscrypt_fname_encrypted_size(const struct inode *inode,
 266                                          u32 orig_len, u32 max_len,
 267                                          u32 *encrypted_len_ret);
 268
 269 /* hkdf.c */
 270
 271 struct fscrypt_hkdf {
 272         struct crypto_shash *hmac_tfm;
 273 };
 274
 275 extern int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
 276                              unsigned int master_key_size);
 277
 278 /*
 279  * The list of contexts in which fscrypt uses HKDF.  These values are used as
 280  * the first byte of the HKDF application-specific info string to guarantee that
 281  * info strings are never repeated between contexts.  This ensures that all HKDF
 282  * outputs are unique and cryptographically isolated, i.e. knowledge of one
 283  * output doesn't reveal another.
 284  */
 285 #define HKDF_CONTEXT_KEY_IDENTIFIER     1
 286 #define HKDF_CONTEXT_PER_FILE_KEY       2
 287 #define HKDF_CONTEXT_DIRECT_KEY         3
 288 #define HKDF_CONTEXT_IV_INO_LBLK_64_KEY 4
 289
 290 extern int fscrypt_hkdf_expand(struct fscrypt_hkdf *hkdf, u8 context,
 291                                const u8 *info, unsigned int infolen,
 292                                u8 *okm, unsigned int okmlen);
 293
 294 extern void fscrypt_destroy_hkdf(struct fscrypt_hkdf *hkdf);
 295
 296 /* keyring.c */
 297
 298 /*
 299  * fscrypt_master_key_secret - secret key material of an in-use master key
 300  */
 301 struct fscrypt_master_key_secret {
 302
 303         /*
 304          * For v2 policy keys: HKDF context keyed by this master key.
 305          * For v1 policy keys: not set (hkdf.hmac_tfm == NULL).
 306          */
 307         struct fscrypt_hkdf     hkdf;
 308
 309         /* Size of the raw key in bytes.  Set even if ->raw isn't set. */
 310         u32                     size;
 311
 312         /* For v1 policy keys: the raw key.  Wiped for v2 policy keys. */
 313         u8                      raw[FSCRYPT_MAX_KEY_SIZE];
 314
 315 } __randomize_layout;
 316
 317 /*
 318  * fscrypt_master_key - an in-use master key
 319  *
 320  * This represents a master encryption key which has been added to the
 321  * filesystem and can be used to "unlock" the encrypted files which were
 322  * encrypted with it.
 323  */
 324 struct fscrypt_master_key {
 325
 326         /*
 327          * The secret key material.  After FS_IOC_REMOVE_ENCRYPTION_KEY is
 328          * executed, this is wiped and no new inodes can be unlocked with this
 329          * key; however, there may still be inodes in ->mk_decrypted_inodes
 330          * which could not be evicted.  As long as some inodes still remain,
 331          * FS_IOC_REMOVE_ENCRYPTION_KEY can be retried, or
 332          * FS_IOC_ADD_ENCRYPTION_KEY can add the secret again.
 333          *
 334          * Locking: protected by key->sem (outer) and mk_secret_sem (inner).
 335          * The reason for two locks is that key->sem also protects modifying
 336          * mk_users, which ranks it above the semaphore for the keyring key
 337          * type, which is in turn above page faults (via keyring_read).  But
 338          * sometimes filesystems call fscrypt_get_encryption_info() from within
 339          * a transaction, which ranks it below page faults.  So we need a
 340          * separate lock which protects mk_secret but not also mk_users.
 341          */
 342         struct fscrypt_master_key_secret        mk_secret;
 343         struct rw_semaphore                     mk_secret_sem;
 344
 345         /*
 346          * For v1 policy keys: an arbitrary key descriptor which was assigned by
 347          * userspace (->descriptor).
 348          *
 349          * For v2 policy keys: a cryptographic hash of this key (->identifier).
 350          */
 351         struct fscrypt_key_specifier            mk_spec;
 352
 353         /*
 354          * Keyring which contains a key of type 'key_type_fscrypt_user' for each
 355          * user who has added this key.  Normally each key will be added by just
 356          * one user, but it's possible that multiple users share a key, and in
 357          * that case we need to keep track of those users so that one user can't
 358          * remove the key before the others want it removed too.
 359          *
 360          * This is NULL for v1 policy keys; those can only be added by root.
 361          *
 362          * Locking: in addition to this keyrings own semaphore, this is
 363          * protected by the master key's key->sem, so we can do atomic
 364          * search+insert.  It can also be searched without taking any locks, but
 365          * in that case the returned key may have already been removed.
 366          */
 367         struct key              *mk_users;
 368
 369         /*
 370          * Length of ->mk_decrypted_inodes, plus one if mk_secret is present.
 371          * Once this goes to 0, the master key is removed from ->s_master_keys.
 372          * The 'struct fscrypt_master_key' will continue to live as long as the
 373          * 'struct key' whose payload it is, but we won't let this reference
 374          * count rise again.
 375          */
 376         refcount_t              mk_refcount;
 377
 378         /*
 379          * List of inodes that were unlocked using this key.  This allows the
 380          * inodes to be evicted efficiently if the key is removed.
 381          */
 382         struct list_head        mk_decrypted_inodes;
 383         spinlock_t              mk_decrypted_inodes_lock;
 384
 385         /* Crypto API transforms for DIRECT_KEY policies, allocated on-demand */
 386         struct crypto_skcipher  *mk_direct_tfms[__FSCRYPT_MODE_MAX + 1];
 387
 388         /*
 389          * Crypto API transforms for filesystem-layer implementation of
 390          * IV_INO_LBLK_64 policies, allocated on-demand.
 391          */
 392         struct crypto_skcipher  *mk_iv_ino_lblk_64_tfms[__FSCRYPT_MODE_MAX + 1];
 393
 394 } __randomize_layout;
 395
 396 static inline bool
 397 is_master_key_secret_present(const struct fscrypt_master_key_secret *secret)
 398 {
 399         /*
 400          * The READ_ONCE() is only necessary for fscrypt_drop_inode() and
 401          * fscrypt_key_describe().  These run in atomic context, so they can't
 402          * take ->mk_secret_sem and thus 'secret' can change concurrently which
 403          * would be a data race.  But they only need to know whether the secret
 404          * *was* present at the time of check, so READ_ONCE() suffices.
 405          */
 406         return READ_ONCE(secret->size) != 0;
 407 }
 408
 409 static inline const char *master_key_spec_type(
 410                                 const struct fscrypt_key_specifier *spec)
 411 {
 412         switch (spec->type) {
 413         case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
 414                 return "descriptor";
 415         case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
 416                 return "identifier";
 417         }
 418         return "[unknown]";
 419 }
 420
 421 static inline int master_key_spec_len(const struct fscrypt_key_specifier *spec)
 422 {
 423         switch (spec->type) {
 424         case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
 425                 return FSCRYPT_KEY_DESCRIPTOR_SIZE;
 426         case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
 427                 return FSCRYPT_KEY_IDENTIFIER_SIZE;
 428         }
 429         return 0;
 430 }
 431
 432 extern struct key *
 433 fscrypt_find_master_key(struct super_block *sb,
 434                         const struct fscrypt_key_specifier *mk_spec);
 435
 436 extern int fscrypt_verify_key_added(struct super_block *sb,
 437                                     const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
 438
 439 extern int __init fscrypt_init_keyring(void);
 440
 441 /* keysetup.c */
 442
 443 struct fscrypt_mode {
 444         const char *friendly_name;
 445         const char *cipher_str;
 446         int keysize;
 447         int ivsize;
 448         int logged_impl_name;
 449 };
 450
 451 static inline bool
 452 fscrypt_mode_supports_direct_key(const struct fscrypt_mode *mode)
 453 {
 454         return mode->ivsize >= offsetofend(union fscrypt_iv, nonce);
 455 }
 456
 457 extern struct crypto_skcipher *
 458 fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
 459                           const struct inode *inode);
 460
 461 extern int fscrypt_set_derived_key(struct fscrypt_info *ci,
 462                                    const u8 *derived_key);
 463
 464 /* keysetup_v1.c */
 465
 466 extern void fscrypt_put_direct_key(struct fscrypt_direct_key *dk);
 467
 468 extern int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
 469                                      const u8 *raw_master_key);
 470
 471 extern int fscrypt_setup_v1_file_key_via_subscribed_keyrings(
 472                                         struct fscrypt_info *ci);
 473 /* policy.c */
 474
 475 extern bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
 476                                    const union fscrypt_policy *policy2);
 477 extern bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
 478                                      const struct inode *inode);
 479 extern int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
 480                                        const union fscrypt_context *ctx_u,
 481                                        int ctx_size);
 482
 483 #endif /* _FSCRYPT_PRIVATE_H */