1 /*
2 * key management facility for FS encryption support.
3 *
4 * Copyright (C) 2015, Google, Inc.
5 *
6 * This contains encryption key functions.
7 *
8 * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
9 */
10
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 <crypto/skcipher.h>
17 #include "fscrypt_private.h"
18
19 static struct crypto_shash *essiv_hash_tfm;
20
21 /**
22 * derive_key_aes() - Derive a key using AES-128-ECB
23 * @deriving_key: Encryption key used for derivation.
24 * @source_key: Source key to which to apply derivation.
25 * @derived_raw_key: Derived raw key.
26 *
27 * Return: Zero on success; non-zero otherwise.
28 */
derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],const struct fscrypt_key * source_key,u8 derived_raw_key[FS_MAX_KEY_SIZE])29 static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
30 const struct fscrypt_key *source_key,
31 u8 derived_raw_key[FS_MAX_KEY_SIZE])
32 {
33 int res = 0;
34 struct skcipher_request *req = NULL;
35 DECLARE_CRYPTO_WAIT(wait);
36 struct scatterlist src_sg, dst_sg;
37 struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
38
39 if (IS_ERR(tfm)) {
40 res = PTR_ERR(tfm);
41 tfm = NULL;
42 goto out;
43 }
44 crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
45 req = skcipher_request_alloc(tfm, GFP_NOFS);
46 if (!req) {
47 res = -ENOMEM;
48 goto out;
49 }
50 skcipher_request_set_callback(req,
51 CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
52 crypto_req_done, &wait);
53 res = crypto_skcipher_setkey(tfm, deriving_key,
54 FS_AES_128_ECB_KEY_SIZE);
55 if (res < 0)
56 goto out;
57
58 sg_init_one(&src_sg, source_key->raw, source_key->size);
59 sg_init_one(&dst_sg, derived_raw_key, source_key->size);
60 skcipher_request_set_crypt(req, &src_sg, &dst_sg, source_key->size,
61 NULL);
62 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
63 out:
64 skcipher_request_free(req);
65 crypto_free_skcipher(tfm);
66 return res;
67 }
68
validate_user_key(struct fscrypt_info * crypt_info,struct fscrypt_context * ctx,u8 * raw_key,const char * prefix,int min_keysize)69 static int validate_user_key(struct fscrypt_info *crypt_info,
70 struct fscrypt_context *ctx, u8 *raw_key,
71 const char *prefix, int min_keysize)
72 {
73 char *description;
74 struct key *keyring_key;
75 struct fscrypt_key *master_key;
76 const struct user_key_payload *ukp;
77 int res;
78
79 description = kasprintf(GFP_NOFS, "%s%*phN", prefix,
80 FS_KEY_DESCRIPTOR_SIZE,
81 ctx->master_key_descriptor);
82 if (!description)
83 return -ENOMEM;
84
85 keyring_key = request_key(&key_type_logon, description, NULL);
86 kfree(description);
87 if (IS_ERR(keyring_key))
88 return PTR_ERR(keyring_key);
89 down_read(&keyring_key->sem);
90
91 if (keyring_key->type != &key_type_logon) {
92 printk_once(KERN_WARNING
93 "%s: key type must be logon\n", __func__);
94 res = -ENOKEY;
95 goto out;
96 }
97 ukp = user_key_payload_locked(keyring_key);
98 if (!ukp) {
99 /* key was revoked before we acquired its semaphore */
100 res = -EKEYREVOKED;
101 goto out;
102 }
103 if (ukp->datalen != sizeof(struct fscrypt_key)) {
104 res = -EINVAL;
105 goto out;
106 }
107 master_key = (struct fscrypt_key *)ukp->data;
108 BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
109
110 if (master_key->size < min_keysize || master_key->size > FS_MAX_KEY_SIZE
111 || master_key->size % AES_BLOCK_SIZE != 0) {
112 printk_once(KERN_WARNING
113 "%s: key size incorrect: %d\n",
114 __func__, master_key->size);
115 res = -ENOKEY;
116 goto out;
117 }
118 res = derive_key_aes(ctx->nonce, master_key, raw_key);
119 out:
120 up_read(&keyring_key->sem);
121 key_put(keyring_key);
122 return res;
123 }
124
125 static const struct {
126 const char *cipher_str;
127 int keysize;
128 } available_modes[] = {
129 [FS_ENCRYPTION_MODE_AES_256_XTS] = { "xts(aes)",
130 FS_AES_256_XTS_KEY_SIZE },
131 [FS_ENCRYPTION_MODE_AES_256_CTS] = { "cts(cbc(aes))",
132 FS_AES_256_CTS_KEY_SIZE },
133 [FS_ENCRYPTION_MODE_AES_128_CBC] = { "cbc(aes)",
134 FS_AES_128_CBC_KEY_SIZE },
135 [FS_ENCRYPTION_MODE_AES_128_CTS] = { "cts(cbc(aes))",
136 FS_AES_128_CTS_KEY_SIZE },
137 };
138
determine_cipher_type(struct fscrypt_info * ci,struct inode * inode,const char ** cipher_str_ret,int * keysize_ret)139 static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,
140 const char **cipher_str_ret, int *keysize_ret)
141 {
142 u32 mode;
143
144 if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) {
145 pr_warn_ratelimited("fscrypt: inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)\n",
146 inode->i_ino,
147 ci->ci_data_mode, ci->ci_filename_mode);
148 return -EINVAL;
149 }
150
151 if (S_ISREG(inode->i_mode)) {
152 mode = ci->ci_data_mode;
153 } else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) {
154 mode = ci->ci_filename_mode;
155 } else {
156 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
157 inode->i_ino, (inode->i_mode & S_IFMT));
158 return -EINVAL;
159 }
160
161 *cipher_str_ret = available_modes[mode].cipher_str;
162 *keysize_ret = available_modes[mode].keysize;
163 return 0;
164 }
165
put_crypt_info(struct fscrypt_info * ci)166 static void put_crypt_info(struct fscrypt_info *ci)
167 {
168 if (!ci)
169 return;
170
171 crypto_free_skcipher(ci->ci_ctfm);
172 crypto_free_cipher(ci->ci_essiv_tfm);
173 kmem_cache_free(fscrypt_info_cachep, ci);
174 }
175
derive_essiv_salt(const u8 * key,int keysize,u8 * salt)176 static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
177 {
178 struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
179
180 /* init hash transform on demand */
181 if (unlikely(!tfm)) {
182 struct crypto_shash *prev_tfm;
183
184 tfm = crypto_alloc_shash("sha256", 0, 0);
185 if (IS_ERR(tfm)) {
186 pr_warn_ratelimited("fscrypt: error allocating SHA-256 transform: %ld\n",
187 PTR_ERR(tfm));
188 return PTR_ERR(tfm);
189 }
190 prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
191 if (prev_tfm) {
192 crypto_free_shash(tfm);
193 tfm = prev_tfm;
194 }
195 }
196
197 {
198 SHASH_DESC_ON_STACK(desc, tfm);
199 desc->tfm = tfm;
200 desc->flags = 0;
201
202 return crypto_shash_digest(desc, key, keysize, salt);
203 }
204 }
205
init_essiv_generator(struct fscrypt_info * ci,const u8 * raw_key,int keysize)206 static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
207 int keysize)
208 {
209 int err;
210 struct crypto_cipher *essiv_tfm;
211 u8 salt[SHA256_DIGEST_SIZE];
212
213 essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
214 if (IS_ERR(essiv_tfm))
215 return PTR_ERR(essiv_tfm);
216
217 ci->ci_essiv_tfm = essiv_tfm;
218
219 err = derive_essiv_salt(raw_key, keysize, salt);
220 if (err)
221 goto out;
222
223 /*
224 * Using SHA256 to derive the salt/key will result in AES-256 being
225 * used for IV generation. File contents encryption will still use the
226 * configured keysize (AES-128) nevertheless.
227 */
228 err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
229 if (err)
230 goto out;
231
232 out:
233 memzero_explicit(salt, sizeof(salt));
234 return err;
235 }
236
fscrypt_essiv_cleanup(void)237 void __exit fscrypt_essiv_cleanup(void)
238 {
239 crypto_free_shash(essiv_hash_tfm);
240 }
241
fscrypt_get_encryption_info(struct inode * inode)242 int fscrypt_get_encryption_info(struct inode *inode)
243 {
244 struct fscrypt_info *crypt_info;
245 struct fscrypt_context ctx;
246 struct crypto_skcipher *ctfm;
247 const char *cipher_str;
248 int keysize;
249 u8 *raw_key = NULL;
250 int res;
251
252 if (inode->i_crypt_info)
253 return 0;
254
255 res = fscrypt_initialize(inode->i_sb->s_cop->flags);
256 if (res)
257 return res;
258
259 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
260 if (res < 0) {
261 if (!fscrypt_dummy_context_enabled(inode) ||
262 IS_ENCRYPTED(inode))
263 return res;
264 /* Fake up a context for an unencrypted directory */
265 memset(&ctx, 0, sizeof(ctx));
266 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
267 ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS;
268 ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
269 memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
270 } else if (res != sizeof(ctx)) {
271 return -EINVAL;
272 }
273
274 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
275 return -EINVAL;
276
277 if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
278 return -EINVAL;
279
280 crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS);
281 if (!crypt_info)
282 return -ENOMEM;
283
284 crypt_info->ci_flags = ctx.flags;
285 crypt_info->ci_data_mode = ctx.contents_encryption_mode;
286 crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
287 crypt_info->ci_ctfm = NULL;
288 crypt_info->ci_essiv_tfm = NULL;
289 memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
290 sizeof(crypt_info->ci_master_key));
291
292 res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize);
293 if (res)
294 goto out;
295
296 /*
297 * This cannot be a stack buffer because it is passed to the scatterlist
298 * crypto API as part of key derivation.
299 */
300 res = -ENOMEM;
301 raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);
302 if (!raw_key)
303 goto out;
304
305 res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX,
306 keysize);
307 if (res && inode->i_sb->s_cop->key_prefix) {
308 int res2 = validate_user_key(crypt_info, &ctx, raw_key,
309 inode->i_sb->s_cop->key_prefix,
310 keysize);
311 if (res2) {
312 if (res2 == -ENOKEY)
313 res = -ENOKEY;
314 goto out;
315 }
316 } else if (res) {
317 goto out;
318 }
319 ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
320 if (!ctfm || IS_ERR(ctfm)) {
321 res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
322 pr_debug("%s: error %d (inode %lu) allocating crypto tfm\n",
323 __func__, res, inode->i_ino);
324 goto out;
325 }
326 crypt_info->ci_ctfm = ctfm;
327 crypto_skcipher_clear_flags(ctfm, ~0);
328 crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY);
329 /*
330 * if the provided key is longer than keysize, we use the first
331 * keysize bytes of the derived key only
332 */
333 res = crypto_skcipher_setkey(ctfm, raw_key, keysize);
334 if (res)
335 goto out;
336
337 if (S_ISREG(inode->i_mode) &&
338 crypt_info->ci_data_mode == FS_ENCRYPTION_MODE_AES_128_CBC) {
339 res = init_essiv_generator(crypt_info, raw_key, keysize);
340 if (res) {
341 pr_debug("%s: error %d (inode %lu) allocating essiv tfm\n",
342 __func__, res, inode->i_ino);
343 goto out;
344 }
345 }
346 if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL)
347 crypt_info = NULL;
348 out:
349 if (res == -ENOKEY)
350 res = 0;
351 put_crypt_info(crypt_info);
352 kzfree(raw_key);
353 return res;
354 }
355 EXPORT_SYMBOL(fscrypt_get_encryption_info);
356
fscrypt_put_encryption_info(struct inode * inode)357 void fscrypt_put_encryption_info(struct inode *inode)
358 {
359 put_crypt_info(inode->i_crypt_info);
360 inode->i_crypt_info = NULL;
361 }
362 EXPORT_SYMBOL(fscrypt_put_encryption_info);
363