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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
26struct 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
35struct 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 */
55union 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 */
65static 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
79union 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 */
89static 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 */
101static inline u8
102fscrypt_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 */
114static inline u8
115fscrypt_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 */
127static inline u8
128fscrypt_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
139static inline bool
140fscrypt_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 */
149struct 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 */
161struct 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
207typedef enum {
208 FS_DECRYPT = 0,
209 FS_ENCRYPT,
210} fscrypt_direction_t;
211
212#define FS_CTX_REQUIRES_FREE_ENCRYPT_FL 0x00000001
213
214static 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 */
233extern struct kmem_cache *fscrypt_info_cachep;
234extern int fscrypt_initialize(unsigned int cop_flags);
235extern 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);
240extern struct page *fscrypt_alloc_bounce_page(gfp_t gfp_flags);
241extern const struct dentry_operations fscrypt_d_ops;
242
243extern void __printf(3, 4) __cold
244fscrypt_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
253union 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
264void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
265 const struct fscrypt_info *ci);
266
267/* fname.c */
268extern int fname_encrypt(struct inode *inode, const struct qstr *iname,
269 u8 *out, unsigned int olen);
270extern 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
276struct fscrypt_hkdf {
277 struct crypto_shash *hmac_tfm;
278};
279
280extern 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
294extern int fscrypt_hkdf_expand(struct fscrypt_hkdf *hkdf, u8 context,
295 const u8 *info, unsigned int infolen,
296 u8 *okm, unsigned int okmlen);
297
298extern 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 */
305struct 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 */
328struct 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
394static inline bool
395is_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
407static 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
419static 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
430extern struct key *
431fscrypt_find_master_key(struct super_block *sb,
432 const struct fscrypt_key_specifier *mk_spec);
433
434extern int fscrypt_verify_key_added(struct super_block *sb,
435 const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
436
437extern int __init fscrypt_init_keyring(void);
438
439/* keysetup.c */
440
441struct 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
450static inline bool
451fscrypt_mode_supports_direct_key(const struct fscrypt_mode *mode)
452{
453 return mode->ivsize >= offsetofend(union fscrypt_iv, nonce);
454}
455
456extern struct crypto_skcipher *
457fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
458 const struct inode *inode);
459
460extern int fscrypt_set_derived_key(struct fscrypt_info *ci,
461 const u8 *derived_key);
462
463/* keysetup_v1.c */
464
465extern void fscrypt_put_direct_key(struct fscrypt_direct_key *dk);
466
467extern int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
468 const u8 *raw_master_key);
469
470extern int fscrypt_setup_v1_file_key_via_subscribed_keyrings(
471 struct fscrypt_info *ci);
472/* policy.c */
473
474extern bool fscrypt_policies_equal(const union fscrypt_policy *policy1,
475 const union fscrypt_policy *policy2);
476extern bool fscrypt_supported_policy(const union fscrypt_policy *policy_u,
477 const struct inode *inode);
478extern 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 */