1 // SPDX-License-Identifier: GPL-2.0
3 * key management facility for FS encryption support.
5 * Copyright (C) 2015, Google, Inc.
7 * This contains encryption key functions.
9 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
12 #include <keys/user-type.h>
13 #include <linux/hashtable.h>
14 #include <linux/scatterlist.h>
15 #include <crypto/aes.h>
16 #include <crypto/algapi.h>
17 #include <crypto/sha.h>
18 #include <crypto/skcipher.h>
19 #include "fscrypt_private.h"
21 static struct crypto_shash *essiv_hash_tfm;
23 /* Table of keys referenced by FS_POLICY_FLAG_DIRECT_KEY policies */
24 static DEFINE_HASHTABLE(fscrypt_master_keys, 6); /* 6 bits = 64 buckets */
25 static DEFINE_SPINLOCK(fscrypt_master_keys_lock);
28 * Key derivation function. This generates the derived key by encrypting the
29 * master key with AES-128-ECB using the inode's nonce as the AES key.
31 * The master key must be at least as long as the derived key. If the master
32 * key is longer, then only the first 'derived_keysize' bytes are used.
34 static int derive_key_aes(const u8 *master_key,
35 const struct fscrypt_context *ctx,
36 u8 *derived_key, unsigned int derived_keysize)
39 struct skcipher_request *req = NULL;
40 DECLARE_CRYPTO_WAIT(wait);
41 struct scatterlist src_sg, dst_sg;
42 struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
49 crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
50 req = skcipher_request_alloc(tfm, GFP_NOFS);
55 skcipher_request_set_callback(req,
56 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
57 crypto_req_done, &wait);
58 res = crypto_skcipher_setkey(tfm, ctx->nonce, sizeof(ctx->nonce));
62 sg_init_one(&src_sg, master_key, derived_keysize);
63 sg_init_one(&dst_sg, derived_key, derived_keysize);
64 skcipher_request_set_crypt(req, &src_sg, &dst_sg, derived_keysize,
66 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
68 skcipher_request_free(req);
69 crypto_free_skcipher(tfm);
74 * Search the current task's subscribed keyrings for a "logon" key with
75 * description prefix:descriptor, and if found acquire a read lock on it and
76 * return a pointer to its validated payload in *payload_ret.
79 find_and_lock_process_key(const char *prefix,
80 const u8 descriptor[FS_KEY_DESCRIPTOR_SIZE],
81 unsigned int min_keysize,
82 const struct fscrypt_key **payload_ret)
86 const struct user_key_payload *ukp;
87 const struct fscrypt_key *payload;
89 description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
90 FS_KEY_DESCRIPTOR_SIZE, descriptor);
92 return ERR_PTR(-ENOMEM);
94 key = request_key(&key_type_logon, description, NULL);
100 ukp = user_key_payload_locked(key);
102 if (!ukp) /* was the key revoked before we acquired its semaphore? */
105 payload = (const struct fscrypt_key *)ukp->data;
107 if (ukp->datalen != sizeof(struct fscrypt_key) ||
108 payload->size < 1 || payload->size > FS_MAX_KEY_SIZE) {
110 "key with description '%s' has invalid payload",
115 if (payload->size < min_keysize) {
117 "key with description '%s' is too short (got %u bytes, need %u+ bytes)",
118 key->description, payload->size, min_keysize);
122 *payload_ret = payload;
128 return ERR_PTR(-ENOKEY);
131 static struct fscrypt_mode available_modes[] = {
132 [FS_ENCRYPTION_MODE_AES_256_XTS] = {
133 .friendly_name = "AES-256-XTS",
134 .cipher_str = "xts(aes)",
138 [FS_ENCRYPTION_MODE_AES_256_CTS] = {
139 .friendly_name = "AES-256-CTS-CBC",
140 .cipher_str = "cts(cbc(aes))",
144 [FS_ENCRYPTION_MODE_AES_128_CBC] = {
145 .friendly_name = "AES-128-CBC",
146 .cipher_str = "cbc(aes)",
151 [FS_ENCRYPTION_MODE_AES_128_CTS] = {
152 .friendly_name = "AES-128-CTS-CBC",
153 .cipher_str = "cts(cbc(aes))",
157 [FS_ENCRYPTION_MODE_ADIANTUM] = {
158 .friendly_name = "Adiantum",
159 .cipher_str = "adiantum(xchacha12,aes)",
165 static struct fscrypt_mode *
166 select_encryption_mode(const struct fscrypt_info *ci, const struct inode *inode)
168 if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
169 fscrypt_warn(inode->i_sb,
170 "inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)",
171 inode->i_ino, ci->ci_data_mode,
172 ci->ci_filename_mode);
173 return ERR_PTR(-EINVAL);
176 if (S_ISREG(inode->i_mode))
177 return &available_modes[ci->ci_data_mode];
179 if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
180 return &available_modes[ci->ci_filename_mode];
182 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
183 inode->i_ino, (inode->i_mode & S_IFMT));
184 return ERR_PTR(-EINVAL);
187 /* Find the master key, then derive the inode's actual encryption key */
188 static int find_and_derive_key(const struct inode *inode,
189 const struct fscrypt_context *ctx,
190 u8 *derived_key, const struct fscrypt_mode *mode)
193 const struct fscrypt_key *payload;
196 key = find_and_lock_process_key(FS_KEY_DESC_PREFIX,
197 ctx->master_key_descriptor,
198 mode->keysize, &payload);
199 if (key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) {
200 key = find_and_lock_process_key(inode->i_sb->s_cop->key_prefix,
201 ctx->master_key_descriptor,
202 mode->keysize, &payload);
207 if (ctx->flags & FS_POLICY_FLAG_DIRECT_KEY) {
208 if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
209 fscrypt_warn(inode->i_sb,
210 "direct key mode not allowed with %s",
211 mode->friendly_name);
213 } else if (ctx->contents_encryption_mode !=
214 ctx->filenames_encryption_mode) {
215 fscrypt_warn(inode->i_sb,
216 "direct key mode not allowed with different contents and filenames modes");
219 memcpy(derived_key, payload->raw, mode->keysize);
223 err = derive_key_aes(payload->raw, ctx, derived_key,
231 /* Allocate and key a symmetric cipher object for the given encryption mode */
232 static struct crypto_skcipher *
233 allocate_skcipher_for_mode(struct fscrypt_mode *mode, const u8 *raw_key,
234 const struct inode *inode)
236 struct crypto_skcipher *tfm;
239 tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
241 fscrypt_warn(inode->i_sb,
242 "error allocating '%s' transform for inode %lu: %ld",
243 mode->cipher_str, inode->i_ino, PTR_ERR(tfm));
246 if (unlikely(!mode->logged_impl_name)) {
248 * fscrypt performance can vary greatly depending on which
249 * crypto algorithm implementation is used. Help people debug
250 * performance problems by logging the ->cra_driver_name the
251 * first time a mode is used. Note that multiple threads can
252 * race here, but it doesn't really matter.
254 mode->logged_impl_name = true;
255 pr_info("fscrypt: %s using implementation \"%s\"\n",
257 crypto_skcipher_alg(tfm)->base.cra_driver_name);
259 crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
260 err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
267 crypto_free_skcipher(tfm);
271 /* Master key referenced by FS_POLICY_FLAG_DIRECT_KEY policy */
272 struct fscrypt_master_key {
273 struct hlist_node mk_node;
274 refcount_t mk_refcount;
275 const struct fscrypt_mode *mk_mode;
276 struct crypto_skcipher *mk_ctfm;
277 u8 mk_descriptor[FS_KEY_DESCRIPTOR_SIZE];
278 u8 mk_raw[FS_MAX_KEY_SIZE];
281 static void free_master_key(struct fscrypt_master_key *mk)
284 crypto_free_skcipher(mk->mk_ctfm);
289 static void put_master_key(struct fscrypt_master_key *mk)
291 if (!refcount_dec_and_lock(&mk->mk_refcount, &fscrypt_master_keys_lock))
293 hash_del(&mk->mk_node);
294 spin_unlock(&fscrypt_master_keys_lock);
300 * Find/insert the given master key into the fscrypt_master_keys table. If
301 * found, it is returned with elevated refcount, and 'to_insert' is freed if
302 * non-NULL. If not found, 'to_insert' is inserted and returned if it's
303 * non-NULL; otherwise NULL is returned.
305 static struct fscrypt_master_key *
306 find_or_insert_master_key(struct fscrypt_master_key *to_insert,
307 const u8 *raw_key, const struct fscrypt_mode *mode,
308 const struct fscrypt_info *ci)
310 unsigned long hash_key;
311 struct fscrypt_master_key *mk;
314 * Careful: to avoid potentially leaking secret key bytes via timing
315 * information, we must key the hash table by descriptor rather than by
316 * raw key, and use crypto_memneq() when comparing raw keys.
319 BUILD_BUG_ON(sizeof(hash_key) > FS_KEY_DESCRIPTOR_SIZE);
320 memcpy(&hash_key, ci->ci_master_key_descriptor, sizeof(hash_key));
322 spin_lock(&fscrypt_master_keys_lock);
323 hash_for_each_possible(fscrypt_master_keys, mk, mk_node, hash_key) {
324 if (memcmp(ci->ci_master_key_descriptor, mk->mk_descriptor,
325 FS_KEY_DESCRIPTOR_SIZE) != 0)
327 if (mode != mk->mk_mode)
329 if (crypto_memneq(raw_key, mk->mk_raw, mode->keysize))
331 /* using existing tfm with same (descriptor, mode, raw_key) */
332 refcount_inc(&mk->mk_refcount);
333 spin_unlock(&fscrypt_master_keys_lock);
334 free_master_key(to_insert);
338 hash_add(fscrypt_master_keys, &to_insert->mk_node, hash_key);
339 spin_unlock(&fscrypt_master_keys_lock);
343 /* Prepare to encrypt directly using the master key in the given mode */
344 static struct fscrypt_master_key *
345 fscrypt_get_master_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
346 const u8 *raw_key, const struct inode *inode)
348 struct fscrypt_master_key *mk;
351 /* Is there already a tfm for this key? */
352 mk = find_or_insert_master_key(NULL, raw_key, mode, ci);
356 /* Nope, allocate one. */
357 mk = kzalloc(sizeof(*mk), GFP_NOFS);
359 return ERR_PTR(-ENOMEM);
360 refcount_set(&mk->mk_refcount, 1);
362 mk->mk_ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
363 if (IS_ERR(mk->mk_ctfm)) {
364 err = PTR_ERR(mk->mk_ctfm);
368 memcpy(mk->mk_descriptor, ci->ci_master_key_descriptor,
369 FS_KEY_DESCRIPTOR_SIZE);
370 memcpy(mk->mk_raw, raw_key, mode->keysize);
372 return find_or_insert_master_key(mk, raw_key, mode, ci);
379 static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
381 struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
383 /* init hash transform on demand */
384 if (unlikely(!tfm)) {
385 struct crypto_shash *prev_tfm;
387 tfm = crypto_alloc_shash("sha256", 0, 0);
390 "error allocating SHA-256 transform: %ld",
394 prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
396 crypto_free_shash(tfm);
402 SHASH_DESC_ON_STACK(desc, tfm);
405 return crypto_shash_digest(desc, key, keysize, salt);
409 static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
413 struct crypto_cipher *essiv_tfm;
414 u8 salt[SHA256_DIGEST_SIZE];
416 essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
417 if (IS_ERR(essiv_tfm))
418 return PTR_ERR(essiv_tfm);
420 ci->ci_essiv_tfm = essiv_tfm;
422 err = derive_essiv_salt(raw_key, keysize, salt);
427 * Using SHA256 to derive the salt/key will result in AES-256 being
428 * used for IV generation. File contents encryption will still use the
429 * configured keysize (AES-128) nevertheless.
431 err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
436 memzero_explicit(salt, sizeof(salt));
440 void __exit fscrypt_essiv_cleanup(void)
442 crypto_free_shash(essiv_hash_tfm);
446 * Given the encryption mode and key (normally the derived key, but for
447 * FS_POLICY_FLAG_DIRECT_KEY mode it's the master key), set up the inode's
448 * symmetric cipher transform object(s).
450 static int setup_crypto_transform(struct fscrypt_info *ci,
451 struct fscrypt_mode *mode,
452 const u8 *raw_key, const struct inode *inode)
454 struct fscrypt_master_key *mk;
455 struct crypto_skcipher *ctfm;
458 if (ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY) {
459 mk = fscrypt_get_master_key(ci, mode, raw_key, inode);
465 ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
467 return PTR_ERR(ctfm);
469 ci->ci_master_key = mk;
472 if (mode->needs_essiv) {
473 /* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
474 WARN_ON(mode->ivsize != AES_BLOCK_SIZE);
475 WARN_ON(ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY);
477 err = init_essiv_generator(ci, raw_key, mode->keysize);
479 fscrypt_warn(inode->i_sb,
480 "error initializing ESSIV generator for inode %lu: %d",
488 static void put_crypt_info(struct fscrypt_info *ci)
493 if (ci->ci_master_key) {
494 put_master_key(ci->ci_master_key);
496 crypto_free_skcipher(ci->ci_ctfm);
497 crypto_free_cipher(ci->ci_essiv_tfm);
499 kmem_cache_free(fscrypt_info_cachep, ci);
502 int fscrypt_get_encryption_info(struct inode *inode)
504 struct fscrypt_info *crypt_info;
505 struct fscrypt_context ctx;
506 struct fscrypt_mode *mode;
510 if (fscrypt_has_encryption_key(inode))
513 res = fscrypt_initialize(inode->i_sb->s_cop->flags);
517 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
519 if (!fscrypt_dummy_context_enabled(inode) ||
522 /* Fake up a context for an unencrypted directory */
523 memset(&ctx, 0, sizeof(ctx));
524 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
525 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
526 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
527 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
528 } else if (res != sizeof(ctx)) {
532 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
535 if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
538 crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
542 crypt_info->ci_flags = ctx.flags;
543 crypt_info->ci_data_mode = ctx.contents_encryption_mode;
544 crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
545 memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor,
546 FS_KEY_DESCRIPTOR_SIZE);
547 memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
549 mode = select_encryption_mode(crypt_info, inode);
554 WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
555 crypt_info->ci_mode = mode;
558 * This cannot be a stack buffer because it may be passed to the
559 * scatterlist crypto API as part of key derivation.
562 raw_key = kmalloc(mode->keysize, GFP_NOFS);
566 res = find_and_derive_key(inode, &ctx, raw_key, mode);
570 res = setup_crypto_transform(crypt_info, mode, raw_key, inode);
574 if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL)
579 put_crypt_info(crypt_info);
583 EXPORT_SYMBOL(fscrypt_get_encryption_info);
586 * fscrypt_put_encryption_info - free most of an inode's fscrypt data
588 * Free the inode's fscrypt_info. Filesystems must call this when the inode is
589 * being evicted. An RCU grace period need not have elapsed yet.
591 void fscrypt_put_encryption_info(struct inode *inode)
593 put_crypt_info(inode->i_crypt_info);
594 inode->i_crypt_info = NULL;
596 EXPORT_SYMBOL(fscrypt_put_encryption_info);
599 * fscrypt_free_inode - free an inode's fscrypt data requiring RCU delay
601 * Free the inode's cached decrypted symlink target, if any. Filesystems must
602 * call this after an RCU grace period, just before they free the inode.
604 void fscrypt_free_inode(struct inode *inode)
606 if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
607 kfree(inode->i_link);
608 inode->i_link = NULL;
611 EXPORT_SYMBOL(fscrypt_free_inode);