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)) {
170 "Unsupported encryption modes (contents mode %d, filenames mode %d)",
171 ci->ci_data_mode, ci->ci_filename_mode);
172 return ERR_PTR(-EINVAL);
175 if (S_ISREG(inode->i_mode))
176 return &available_modes[ci->ci_data_mode];
178 if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
179 return &available_modes[ci->ci_filename_mode];
181 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
182 inode->i_ino, (inode->i_mode & S_IFMT));
183 return ERR_PTR(-EINVAL);
186 /* Find the master key, then derive the inode's actual encryption key */
187 static int find_and_derive_key(const struct inode *inode,
188 const struct fscrypt_context *ctx,
189 u8 *derived_key, const struct fscrypt_mode *mode)
192 const struct fscrypt_key *payload;
195 key = find_and_lock_process_key(FS_KEY_DESC_PREFIX,
196 ctx->master_key_descriptor,
197 mode->keysize, &payload);
198 if (key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) {
199 key = find_and_lock_process_key(inode->i_sb->s_cop->key_prefix,
200 ctx->master_key_descriptor,
201 mode->keysize, &payload);
206 if (ctx->flags & FS_POLICY_FLAG_DIRECT_KEY) {
207 if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
209 "Direct key mode not allowed with %s",
210 mode->friendly_name);
212 } else if (ctx->contents_encryption_mode !=
213 ctx->filenames_encryption_mode) {
215 "Direct key mode not allowed with different contents and filenames modes");
218 memcpy(derived_key, payload->raw, mode->keysize);
222 err = derive_key_aes(payload->raw, ctx, derived_key,
230 /* Allocate and key a symmetric cipher object for the given encryption mode */
231 static struct crypto_skcipher *
232 allocate_skcipher_for_mode(struct fscrypt_mode *mode, const u8 *raw_key,
233 const struct inode *inode)
235 struct crypto_skcipher *tfm;
238 tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
240 fscrypt_warn(inode, "Error allocating '%s' transform: %ld",
241 mode->cipher_str, PTR_ERR(tfm));
244 if (unlikely(!mode->logged_impl_name)) {
246 * fscrypt performance can vary greatly depending on which
247 * crypto algorithm implementation is used. Help people debug
248 * performance problems by logging the ->cra_driver_name the
249 * first time a mode is used. Note that multiple threads can
250 * race here, but it doesn't really matter.
252 mode->logged_impl_name = true;
253 pr_info("fscrypt: %s using implementation \"%s\"\n",
255 crypto_skcipher_alg(tfm)->base.cra_driver_name);
257 crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
258 err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
265 crypto_free_skcipher(tfm);
269 /* Master key referenced by FS_POLICY_FLAG_DIRECT_KEY policy */
270 struct fscrypt_master_key {
271 struct hlist_node mk_node;
272 refcount_t mk_refcount;
273 const struct fscrypt_mode *mk_mode;
274 struct crypto_skcipher *mk_ctfm;
275 u8 mk_descriptor[FS_KEY_DESCRIPTOR_SIZE];
276 u8 mk_raw[FS_MAX_KEY_SIZE];
279 static void free_master_key(struct fscrypt_master_key *mk)
282 crypto_free_skcipher(mk->mk_ctfm);
287 static void put_master_key(struct fscrypt_master_key *mk)
289 if (!refcount_dec_and_lock(&mk->mk_refcount, &fscrypt_master_keys_lock))
291 hash_del(&mk->mk_node);
292 spin_unlock(&fscrypt_master_keys_lock);
298 * Find/insert the given master key into the fscrypt_master_keys table. If
299 * found, it is returned with elevated refcount, and 'to_insert' is freed if
300 * non-NULL. If not found, 'to_insert' is inserted and returned if it's
301 * non-NULL; otherwise NULL is returned.
303 static struct fscrypt_master_key *
304 find_or_insert_master_key(struct fscrypt_master_key *to_insert,
305 const u8 *raw_key, const struct fscrypt_mode *mode,
306 const struct fscrypt_info *ci)
308 unsigned long hash_key;
309 struct fscrypt_master_key *mk;
312 * Careful: to avoid potentially leaking secret key bytes via timing
313 * information, we must key the hash table by descriptor rather than by
314 * raw key, and use crypto_memneq() when comparing raw keys.
317 BUILD_BUG_ON(sizeof(hash_key) > FS_KEY_DESCRIPTOR_SIZE);
318 memcpy(&hash_key, ci->ci_master_key_descriptor, sizeof(hash_key));
320 spin_lock(&fscrypt_master_keys_lock);
321 hash_for_each_possible(fscrypt_master_keys, mk, mk_node, hash_key) {
322 if (memcmp(ci->ci_master_key_descriptor, mk->mk_descriptor,
323 FS_KEY_DESCRIPTOR_SIZE) != 0)
325 if (mode != mk->mk_mode)
327 if (crypto_memneq(raw_key, mk->mk_raw, mode->keysize))
329 /* using existing tfm with same (descriptor, mode, raw_key) */
330 refcount_inc(&mk->mk_refcount);
331 spin_unlock(&fscrypt_master_keys_lock);
332 free_master_key(to_insert);
336 hash_add(fscrypt_master_keys, &to_insert->mk_node, hash_key);
337 spin_unlock(&fscrypt_master_keys_lock);
341 /* Prepare to encrypt directly using the master key in the given mode */
342 static struct fscrypt_master_key *
343 fscrypt_get_master_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
344 const u8 *raw_key, const struct inode *inode)
346 struct fscrypt_master_key *mk;
349 /* Is there already a tfm for this key? */
350 mk = find_or_insert_master_key(NULL, raw_key, mode, ci);
354 /* Nope, allocate one. */
355 mk = kzalloc(sizeof(*mk), GFP_NOFS);
357 return ERR_PTR(-ENOMEM);
358 refcount_set(&mk->mk_refcount, 1);
360 mk->mk_ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
361 if (IS_ERR(mk->mk_ctfm)) {
362 err = PTR_ERR(mk->mk_ctfm);
366 memcpy(mk->mk_descriptor, ci->ci_master_key_descriptor,
367 FS_KEY_DESCRIPTOR_SIZE);
368 memcpy(mk->mk_raw, raw_key, mode->keysize);
370 return find_or_insert_master_key(mk, raw_key, mode, ci);
377 static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
379 struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
381 /* init hash transform on demand */
382 if (unlikely(!tfm)) {
383 struct crypto_shash *prev_tfm;
385 tfm = crypto_alloc_shash("sha256", 0, 0);
388 "error allocating SHA-256 transform: %ld",
392 prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
394 crypto_free_shash(tfm);
400 SHASH_DESC_ON_STACK(desc, tfm);
403 return crypto_shash_digest(desc, key, keysize, salt);
407 static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
411 struct crypto_cipher *essiv_tfm;
412 u8 salt[SHA256_DIGEST_SIZE];
414 essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
415 if (IS_ERR(essiv_tfm))
416 return PTR_ERR(essiv_tfm);
418 ci->ci_essiv_tfm = essiv_tfm;
420 err = derive_essiv_salt(raw_key, keysize, salt);
425 * Using SHA256 to derive the salt/key will result in AES-256 being
426 * used for IV generation. File contents encryption will still use the
427 * configured keysize (AES-128) nevertheless.
429 err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
434 memzero_explicit(salt, sizeof(salt));
439 * Given the encryption mode and key (normally the derived key, but for
440 * FS_POLICY_FLAG_DIRECT_KEY mode it's the master key), set up the inode's
441 * symmetric cipher transform object(s).
443 static int setup_crypto_transform(struct fscrypt_info *ci,
444 struct fscrypt_mode *mode,
445 const u8 *raw_key, const struct inode *inode)
447 struct fscrypt_master_key *mk;
448 struct crypto_skcipher *ctfm;
451 if (ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY) {
452 mk = fscrypt_get_master_key(ci, mode, raw_key, inode);
458 ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
460 return PTR_ERR(ctfm);
462 ci->ci_master_key = mk;
465 if (mode->needs_essiv) {
466 /* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
467 WARN_ON(mode->ivsize != AES_BLOCK_SIZE);
468 WARN_ON(ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY);
470 err = init_essiv_generator(ci, raw_key, mode->keysize);
473 "Error initializing ESSIV generator: %d",
481 static void put_crypt_info(struct fscrypt_info *ci)
486 if (ci->ci_master_key) {
487 put_master_key(ci->ci_master_key);
489 crypto_free_skcipher(ci->ci_ctfm);
490 crypto_free_cipher(ci->ci_essiv_tfm);
492 kmem_cache_free(fscrypt_info_cachep, ci);
495 int fscrypt_get_encryption_info(struct inode *inode)
497 struct fscrypt_info *crypt_info;
498 struct fscrypt_context ctx;
499 struct fscrypt_mode *mode;
503 if (fscrypt_has_encryption_key(inode))
506 res = fscrypt_initialize(inode->i_sb->s_cop->flags);
510 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
512 if (!fscrypt_dummy_context_enabled(inode) ||
513 IS_ENCRYPTED(inode)) {
515 "Error %d getting encryption context",
519 /* Fake up a context for an unencrypted directory */
520 memset(&ctx, 0, sizeof(ctx));
521 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
522 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
523 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
524 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
525 } else if (res != sizeof(ctx)) {
527 "Unknown encryption context size (%d bytes)", res);
531 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1) {
532 fscrypt_warn(inode, "Unknown encryption context version (%d)",
537 if (ctx.flags & ~FS_POLICY_FLAGS_VALID) {
538 fscrypt_warn(inode, "Unknown encryption context flags (0x%02x)",
543 crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
547 crypt_info->ci_flags = ctx.flags;
548 crypt_info->ci_data_mode = ctx.contents_encryption_mode;
549 crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
550 memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor,
551 FS_KEY_DESCRIPTOR_SIZE);
552 memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE);
554 mode = select_encryption_mode(crypt_info, inode);
559 WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
560 crypt_info->ci_mode = mode;
563 * This cannot be a stack buffer because it may be passed to the
564 * scatterlist crypto API as part of key derivation.
567 raw_key = kmalloc(mode->keysize, GFP_NOFS);
571 res = find_and_derive_key(inode, &ctx, raw_key, mode);
575 res = setup_crypto_transform(crypt_info, mode, raw_key, inode);
579 if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL)
584 put_crypt_info(crypt_info);
588 EXPORT_SYMBOL(fscrypt_get_encryption_info);
591 * fscrypt_put_encryption_info - free most of an inode's fscrypt data
593 * Free the inode's fscrypt_info. Filesystems must call this when the inode is
594 * being evicted. An RCU grace period need not have elapsed yet.
596 void fscrypt_put_encryption_info(struct inode *inode)
598 put_crypt_info(inode->i_crypt_info);
599 inode->i_crypt_info = NULL;
601 EXPORT_SYMBOL(fscrypt_put_encryption_info);
604 * fscrypt_free_inode - free an inode's fscrypt data requiring RCU delay
606 * Free the inode's cached decrypted symlink target, if any. Filesystems must
607 * call this after an RCU grace period, just before they free the inode.
609 void fscrypt_free_inode(struct inode *inode)
611 if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
612 kfree(inode->i_link);
613 inode->i_link = NULL;
616 EXPORT_SYMBOL(fscrypt_free_inode);