2 * key management facility for FS encryption support.
4 * Copyright (C) 2015, Google, Inc.
6 * This contains encryption key functions.
8 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
11 #include <keys/user-type.h>
12 #include <linux/scatterlist.h>
13 #include <linux/ratelimit.h>
14 #include <crypto/aes.h>
15 #include <crypto/sha.h>
16 #include "fscrypt_private.h"
18 static struct crypto_shash *essiv_hash_tfm;
20 static void derive_crypt_complete(struct crypto_async_request *req, int rc)
22 struct fscrypt_completion_result *ecr = req->data;
24 if (rc == -EINPROGRESS)
28 complete(&ecr->completion);
32 * derive_key_aes() - Derive a key using AES-128-ECB
33 * @deriving_key: Encryption key used for derivation.
34 * @source_key: Source key to which to apply derivation.
35 * @derived_raw_key: Derived raw key.
37 * Return: Zero on success; non-zero otherwise.
39 static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
40 const struct fscrypt_key *source_key,
41 u8 derived_raw_key[FS_MAX_KEY_SIZE])
44 struct skcipher_request *req = NULL;
45 DECLARE_FS_COMPLETION_RESULT(ecr);
46 struct scatterlist src_sg, dst_sg;
47 struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
54 crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
55 req = skcipher_request_alloc(tfm, GFP_NOFS);
60 skcipher_request_set_callback(req,
61 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
62 derive_crypt_complete, &ecr);
63 res = crypto_skcipher_setkey(tfm, deriving_key,
64 FS_AES_128_ECB_KEY_SIZE);
68 sg_init_one(&src_sg, source_key->raw, source_key->size);
69 sg_init_one(&dst_sg, derived_raw_key, source_key->size);
70 skcipher_request_set_crypt(req, &src_sg, &dst_sg, source_key->size,
72 res = crypto_skcipher_encrypt(req);
73 if (res == -EINPROGRESS || res == -EBUSY) {
74 wait_for_completion(&ecr.completion);
78 skcipher_request_free(req);
79 crypto_free_skcipher(tfm);
83 static int validate_user_key(struct fscrypt_info *crypt_info,
84 struct fscrypt_context *ctx, u8 *raw_key,
85 const char *prefix, int min_keysize)
88 struct key *keyring_key;
89 struct fscrypt_key *master_key;
90 const struct user_key_payload *ukp;
93 description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
94 FS_KEY_DESCRIPTOR_SIZE,
95 ctx->master_key_descriptor);
99 keyring_key = request_key(&key_type_logon, description, NULL);
101 if (IS_ERR(keyring_key))
102 return PTR_ERR(keyring_key);
103 down_read(&keyring_key->sem);
105 if (keyring_key->type != &key_type_logon) {
106 printk_once(KERN_WARNING
107 "%s: key type must be logon\n", __func__);
111 ukp = user_key_payload_locked(keyring_key);
113 /* key was revoked before we acquired its semaphore */
117 if (ukp->datalen != sizeof(struct fscrypt_key)) {
121 master_key = (struct fscrypt_key *)ukp->data;
122 BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
124 if (master_key->size < min_keysize || master_key->size > FS_MAX_KEY_SIZE
125 || master_key->size % AES_BLOCK_SIZE != 0) {
126 printk_once(KERN_WARNING
127 "%s: key size incorrect: %d\n",
128 __func__, master_key->size);
132 res = derive_key_aes(ctx->nonce, master_key, raw_key);
134 up_read(&keyring_key->sem);
135 key_put(keyring_key);
139 static const struct {
140 const char *cipher_str;
142 } available_modes[] = {
143 [FS_ENCRYPTION_MODE_AES_256_XTS] = { "xts(aes)",
144 FS_AES_256_XTS_KEY_SIZE },
145 [FS_ENCRYPTION_MODE_AES_256_CTS] = { "cts(cbc(aes))",
146 FS_AES_256_CTS_KEY_SIZE },
147 [FS_ENCRYPTION_MODE_AES_128_CBC] = { "cbc(aes)",
148 FS_AES_128_CBC_KEY_SIZE },
149 [FS_ENCRYPTION_MODE_AES_128_CTS] = { "cts(cbc(aes))",
150 FS_AES_128_CTS_KEY_SIZE },
153 static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
154 const char **cipher_str_ret, int *keysize_ret)
158 if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
159 pr_warn_ratelimited("fscrypt: inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)\n",
161 ci->ci_data_mode, ci->ci_filename_mode);
165 if (S_ISREG(inode->i_mode)) {
166 mode = ci->ci_data_mode;
167 } else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
168 mode = ci->ci_filename_mode;
170 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
171 inode->i_ino, (inode->i_mode & S_IFMT));
175 *cipher_str_ret = available_modes[mode].cipher_str;
176 *keysize_ret = available_modes[mode].keysize;
180 static void put_crypt_info(struct fscrypt_info *ci)
185 crypto_free_skcipher(ci->ci_ctfm);
186 crypto_free_cipher(ci->ci_essiv_tfm);
187 kmem_cache_free(fscrypt_info_cachep, ci);
190 static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
192 struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
194 /* init hash transform on demand */
195 if (unlikely(!tfm)) {
196 struct crypto_shash *prev_tfm;
198 tfm = crypto_alloc_shash("sha256", 0, 0);
200 pr_warn_ratelimited("fscrypt: error allocating SHA-256 transform: %ld\n",
204 prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
206 crypto_free_shash(tfm);
212 SHASH_DESC_ON_STACK(desc, tfm);
216 return crypto_shash_digest(desc, key, keysize, salt);
220 static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
224 struct crypto_cipher *essiv_tfm;
225 u8 salt[SHA256_DIGEST_SIZE];
227 essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
228 if (IS_ERR(essiv_tfm))
229 return PTR_ERR(essiv_tfm);
231 ci->ci_essiv_tfm = essiv_tfm;
233 err = derive_essiv_salt(raw_key, keysize, salt);
238 * Using SHA256 to derive the salt/key will result in AES-256 being
239 * used for IV generation. File contents encryption will still use the
240 * configured keysize (AES-128) nevertheless.
242 err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
247 memzero_explicit(salt, sizeof(salt));
251 void __exit fscrypt_essiv_cleanup(void)
253 crypto_free_shash(essiv_hash_tfm);
256 int fscrypt_get_encryption_info(struct inode *inode)
258 struct fscrypt_info *crypt_info;
259 struct fscrypt_context ctx;
260 struct crypto_skcipher *ctfm;
261 const char *cipher_str;
266 if (inode->i_crypt_info)
269 res = fscrypt_initialize(inode->i_sb->s_cop->flags);
273 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
275 if (!fscrypt_dummy_context_enabled(inode) ||
276 inode->i_sb->s_cop->is_encrypted(inode))
278 /* Fake up a context for an unencrypted directory */
279 memset(&ctx, 0, sizeof(ctx));
280 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
281 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
282 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
283 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
284 } else if (res != sizeof(ctx)) {
288 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
291 if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
294 crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
298 crypt_info->ci_flags = ctx.flags;
299 crypt_info->ci_data_mode = ctx.contents_encryption_mode;
300 crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
301 crypt_info->ci_ctfm = NULL;
302 crypt_info->ci_essiv_tfm = NULL;
303 memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
304 sizeof(crypt_info->ci_master_key));
306 res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
311 * This cannot be a stack buffer because it is passed to the scatterlist
312 * crypto API as part of key derivation.
315 raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);
319 res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX,
321 if (res && inode->i_sb->s_cop->key_prefix) {
322 int res2 = validate_user_key(crypt_info, &ctx, raw_key,
323 inode->i_sb->s_cop->key_prefix,
333 ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
334 if (!ctfm || IS_ERR(ctfm)) {
335 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
336 pr_debug("%s: error %d (inode %lu) allocating crypto tfm\n",
337 __func__, res, inode->i_ino);
340 crypt_info->ci_ctfm = ctfm;
341 crypto_skcipher_clear_flags(ctfm, ~0);
342 crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
344 * if the provided key is longer than keysize, we use the first
345 * keysize bytes of the derived key only
347 res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
351 if (S_ISREG(inode->i_mode) &&
352 crypt_info->ci_data_mode == FS_ENCRYPTION_MODE_AES_128_CBC) {
353 res = init_essiv_generator(crypt_info, raw_key, keysize);
355 pr_debug("%s: error %d (inode %lu) allocating essiv tfm\n",
356 __func__, res, inode->i_ino);
360 if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL)
365 put_crypt_info(crypt_info);
369 EXPORT_SYMBOL(fscrypt_get_encryption_info);
371 void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci)
373 struct fscrypt_info *prev;
376 ci = ACCESS_ONCE(inode->i_crypt_info);
380 prev = cmpxchg(&inode->i_crypt_info, ci, NULL);
386 EXPORT_SYMBOL(fscrypt_put_encryption_info);