xref: /linux/fs/crypto/keysetup.c (revision 79790b6818e96c58fe2bffee1b418c16e64e7b80)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Key setup facility for FS encryption support.
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 #include <crypto/skcipher.h>
12 #include <linux/random.h>
13 
14 #include "fscrypt_private.h"
15 
16 struct fscrypt_mode fscrypt_modes[] = {
17 	[FSCRYPT_MODE_AES_256_XTS] = {
18 		.friendly_name = "AES-256-XTS",
19 		.cipher_str = "xts(aes)",
20 		.keysize = 64,
21 		.security_strength = 32,
22 		.ivsize = 16,
23 		.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_256_XTS,
24 	},
25 	[FSCRYPT_MODE_AES_256_CTS] = {
26 		.friendly_name = "AES-256-CBC-CTS",
27 		.cipher_str = "cts(cbc(aes))",
28 		.keysize = 32,
29 		.security_strength = 32,
30 		.ivsize = 16,
31 	},
32 	[FSCRYPT_MODE_AES_128_CBC] = {
33 		.friendly_name = "AES-128-CBC-ESSIV",
34 		.cipher_str = "essiv(cbc(aes),sha256)",
35 		.keysize = 16,
36 		.security_strength = 16,
37 		.ivsize = 16,
38 		.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_128_CBC_ESSIV,
39 	},
40 	[FSCRYPT_MODE_AES_128_CTS] = {
41 		.friendly_name = "AES-128-CBC-CTS",
42 		.cipher_str = "cts(cbc(aes))",
43 		.keysize = 16,
44 		.security_strength = 16,
45 		.ivsize = 16,
46 	},
47 	[FSCRYPT_MODE_SM4_XTS] = {
48 		.friendly_name = "SM4-XTS",
49 		.cipher_str = "xts(sm4)",
50 		.keysize = 32,
51 		.security_strength = 16,
52 		.ivsize = 16,
53 		.blk_crypto_mode = BLK_ENCRYPTION_MODE_SM4_XTS,
54 	},
55 	[FSCRYPT_MODE_SM4_CTS] = {
56 		.friendly_name = "SM4-CBC-CTS",
57 		.cipher_str = "cts(cbc(sm4))",
58 		.keysize = 16,
59 		.security_strength = 16,
60 		.ivsize = 16,
61 	},
62 	[FSCRYPT_MODE_ADIANTUM] = {
63 		.friendly_name = "Adiantum",
64 		.cipher_str = "adiantum(xchacha12,aes)",
65 		.keysize = 32,
66 		.security_strength = 32,
67 		.ivsize = 32,
68 		.blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM,
69 	},
70 	[FSCRYPT_MODE_AES_256_HCTR2] = {
71 		.friendly_name = "AES-256-HCTR2",
72 		.cipher_str = "hctr2(aes)",
73 		.keysize = 32,
74 		.security_strength = 32,
75 		.ivsize = 32,
76 	},
77 };
78 
79 static DEFINE_MUTEX(fscrypt_mode_key_setup_mutex);
80 
81 static struct fscrypt_mode *
select_encryption_mode(const union fscrypt_policy * policy,const struct inode * inode)82 select_encryption_mode(const union fscrypt_policy *policy,
83 		       const struct inode *inode)
84 {
85 	BUILD_BUG_ON(ARRAY_SIZE(fscrypt_modes) != FSCRYPT_MODE_MAX + 1);
86 
87 	if (S_ISREG(inode->i_mode))
88 		return &fscrypt_modes[fscrypt_policy_contents_mode(policy)];
89 
90 	if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
91 		return &fscrypt_modes[fscrypt_policy_fnames_mode(policy)];
92 
93 	WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
94 		  inode->i_ino, (inode->i_mode & S_IFMT));
95 	return ERR_PTR(-EINVAL);
96 }
97 
98 /* Create a symmetric cipher object for the given encryption mode and key */
99 static struct crypto_skcipher *
fscrypt_allocate_skcipher(struct fscrypt_mode * mode,const u8 * raw_key,const struct inode * inode)100 fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
101 			  const struct inode *inode)
102 {
103 	struct crypto_skcipher *tfm;
104 	int err;
105 
106 	tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
107 	if (IS_ERR(tfm)) {
108 		if (PTR_ERR(tfm) == -ENOENT) {
109 			fscrypt_warn(inode,
110 				     "Missing crypto API support for %s (API name: \"%s\")",
111 				     mode->friendly_name, mode->cipher_str);
112 			return ERR_PTR(-ENOPKG);
113 		}
114 		fscrypt_err(inode, "Error allocating '%s' transform: %ld",
115 			    mode->cipher_str, PTR_ERR(tfm));
116 		return tfm;
117 	}
118 	if (!xchg(&mode->logged_cryptoapi_impl, 1)) {
119 		/*
120 		 * fscrypt performance can vary greatly depending on which
121 		 * crypto algorithm implementation is used.  Help people debug
122 		 * performance problems by logging the ->cra_driver_name the
123 		 * first time a mode is used.
124 		 */
125 		pr_info("fscrypt: %s using implementation \"%s\"\n",
126 			mode->friendly_name, crypto_skcipher_driver_name(tfm));
127 	}
128 	if (WARN_ON_ONCE(crypto_skcipher_ivsize(tfm) != mode->ivsize)) {
129 		err = -EINVAL;
130 		goto err_free_tfm;
131 	}
132 	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
133 	err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
134 	if (err)
135 		goto err_free_tfm;
136 
137 	return tfm;
138 
139 err_free_tfm:
140 	crypto_free_skcipher(tfm);
141 	return ERR_PTR(err);
142 }
143 
144 /*
145  * Prepare the crypto transform object or blk-crypto key in @prep_key, given the
146  * raw key, encryption mode (@ci->ci_mode), flag indicating which encryption
147  * implementation (fs-layer or blk-crypto) will be used (@ci->ci_inlinecrypt),
148  * and IV generation method (@ci->ci_policy.flags).
149  */
fscrypt_prepare_key(struct fscrypt_prepared_key * prep_key,const u8 * raw_key,const struct fscrypt_inode_info * ci)150 int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key,
151 			const u8 *raw_key, const struct fscrypt_inode_info *ci)
152 {
153 	struct crypto_skcipher *tfm;
154 
155 	if (fscrypt_using_inline_encryption(ci))
156 		return fscrypt_prepare_inline_crypt_key(prep_key, raw_key, ci);
157 
158 	tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode);
159 	if (IS_ERR(tfm))
160 		return PTR_ERR(tfm);
161 	/*
162 	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
163 	 * I.e., here we publish ->tfm with a RELEASE barrier so that
164 	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
165 	 * possible for per-mode keys, not for per-file keys.
166 	 */
167 	smp_store_release(&prep_key->tfm, tfm);
168 	return 0;
169 }
170 
171 /* Destroy a crypto transform object and/or blk-crypto key. */
fscrypt_destroy_prepared_key(struct super_block * sb,struct fscrypt_prepared_key * prep_key)172 void fscrypt_destroy_prepared_key(struct super_block *sb,
173 				  struct fscrypt_prepared_key *prep_key)
174 {
175 	crypto_free_skcipher(prep_key->tfm);
176 	fscrypt_destroy_inline_crypt_key(sb, prep_key);
177 	memzero_explicit(prep_key, sizeof(*prep_key));
178 }
179 
180 /* Given a per-file encryption key, set up the file's crypto transform object */
fscrypt_set_per_file_enc_key(struct fscrypt_inode_info * ci,const u8 * raw_key)181 int fscrypt_set_per_file_enc_key(struct fscrypt_inode_info *ci,
182 				 const u8 *raw_key)
183 {
184 	ci->ci_owns_key = true;
185 	return fscrypt_prepare_key(&ci->ci_enc_key, raw_key, ci);
186 }
187 
setup_per_mode_enc_key(struct fscrypt_inode_info * ci,struct fscrypt_master_key * mk,struct fscrypt_prepared_key * keys,u8 hkdf_context,bool include_fs_uuid)188 static int setup_per_mode_enc_key(struct fscrypt_inode_info *ci,
189 				  struct fscrypt_master_key *mk,
190 				  struct fscrypt_prepared_key *keys,
191 				  u8 hkdf_context, bool include_fs_uuid)
192 {
193 	const struct inode *inode = ci->ci_inode;
194 	const struct super_block *sb = inode->i_sb;
195 	struct fscrypt_mode *mode = ci->ci_mode;
196 	const u8 mode_num = mode - fscrypt_modes;
197 	struct fscrypt_prepared_key *prep_key;
198 	u8 mode_key[FSCRYPT_MAX_KEY_SIZE];
199 	u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
200 	unsigned int hkdf_infolen = 0;
201 	int err;
202 
203 	if (WARN_ON_ONCE(mode_num > FSCRYPT_MODE_MAX))
204 		return -EINVAL;
205 
206 	prep_key = &keys[mode_num];
207 	if (fscrypt_is_key_prepared(prep_key, ci)) {
208 		ci->ci_enc_key = *prep_key;
209 		return 0;
210 	}
211 
212 	mutex_lock(&fscrypt_mode_key_setup_mutex);
213 
214 	if (fscrypt_is_key_prepared(prep_key, ci))
215 		goto done_unlock;
216 
217 	BUILD_BUG_ON(sizeof(mode_num) != 1);
218 	BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
219 	BUILD_BUG_ON(sizeof(hkdf_info) != 17);
220 	hkdf_info[hkdf_infolen++] = mode_num;
221 	if (include_fs_uuid) {
222 		memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
223 		       sizeof(sb->s_uuid));
224 		hkdf_infolen += sizeof(sb->s_uuid);
225 	}
226 	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
227 				  hkdf_context, hkdf_info, hkdf_infolen,
228 				  mode_key, mode->keysize);
229 	if (err)
230 		goto out_unlock;
231 	err = fscrypt_prepare_key(prep_key, mode_key, ci);
232 	memzero_explicit(mode_key, mode->keysize);
233 	if (err)
234 		goto out_unlock;
235 done_unlock:
236 	ci->ci_enc_key = *prep_key;
237 	err = 0;
238 out_unlock:
239 	mutex_unlock(&fscrypt_mode_key_setup_mutex);
240 	return err;
241 }
242 
243 /*
244  * Derive a SipHash key from the given fscrypt master key and the given
245  * application-specific information string.
246  *
247  * Note that the KDF produces a byte array, but the SipHash APIs expect the key
248  * as a pair of 64-bit words.  Therefore, on big endian CPUs we have to do an
249  * endianness swap in order to get the same results as on little endian CPUs.
250  */
fscrypt_derive_siphash_key(const struct fscrypt_master_key * mk,u8 context,const u8 * info,unsigned int infolen,siphash_key_t * key)251 static int fscrypt_derive_siphash_key(const struct fscrypt_master_key *mk,
252 				      u8 context, const u8 *info,
253 				      unsigned int infolen, siphash_key_t *key)
254 {
255 	int err;
256 
257 	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen,
258 				  (u8 *)key, sizeof(*key));
259 	if (err)
260 		return err;
261 
262 	BUILD_BUG_ON(sizeof(*key) != 16);
263 	BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2);
264 	le64_to_cpus(&key->key[0]);
265 	le64_to_cpus(&key->key[1]);
266 	return 0;
267 }
268 
fscrypt_derive_dirhash_key(struct fscrypt_inode_info * ci,const struct fscrypt_master_key * mk)269 int fscrypt_derive_dirhash_key(struct fscrypt_inode_info *ci,
270 			       const struct fscrypt_master_key *mk)
271 {
272 	int err;
273 
274 	err = fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,
275 					 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
276 					 &ci->ci_dirhash_key);
277 	if (err)
278 		return err;
279 	ci->ci_dirhash_key_initialized = true;
280 	return 0;
281 }
282 
fscrypt_hash_inode_number(struct fscrypt_inode_info * ci,const struct fscrypt_master_key * mk)283 void fscrypt_hash_inode_number(struct fscrypt_inode_info *ci,
284 			       const struct fscrypt_master_key *mk)
285 {
286 	WARN_ON_ONCE(ci->ci_inode->i_ino == 0);
287 	WARN_ON_ONCE(!mk->mk_ino_hash_key_initialized);
288 
289 	ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino,
290 					      &mk->mk_ino_hash_key);
291 }
292 
fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info * ci,struct fscrypt_master_key * mk)293 static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info *ci,
294 					    struct fscrypt_master_key *mk)
295 {
296 	int err;
297 
298 	err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_32_keys,
299 				     HKDF_CONTEXT_IV_INO_LBLK_32_KEY, true);
300 	if (err)
301 		return err;
302 
303 	/* pairs with smp_store_release() below */
304 	if (!smp_load_acquire(&mk->mk_ino_hash_key_initialized)) {
305 
306 		mutex_lock(&fscrypt_mode_key_setup_mutex);
307 
308 		if (mk->mk_ino_hash_key_initialized)
309 			goto unlock;
310 
311 		err = fscrypt_derive_siphash_key(mk,
312 						 HKDF_CONTEXT_INODE_HASH_KEY,
313 						 NULL, 0, &mk->mk_ino_hash_key);
314 		if (err)
315 			goto unlock;
316 		/* pairs with smp_load_acquire() above */
317 		smp_store_release(&mk->mk_ino_hash_key_initialized, true);
318 unlock:
319 		mutex_unlock(&fscrypt_mode_key_setup_mutex);
320 		if (err)
321 			return err;
322 	}
323 
324 	/*
325 	 * New inodes may not have an inode number assigned yet.
326 	 * Hashing their inode number is delayed until later.
327 	 */
328 	if (ci->ci_inode->i_ino)
329 		fscrypt_hash_inode_number(ci, mk);
330 	return 0;
331 }
332 
fscrypt_setup_v2_file_key(struct fscrypt_inode_info * ci,struct fscrypt_master_key * mk,bool need_dirhash_key)333 static int fscrypt_setup_v2_file_key(struct fscrypt_inode_info *ci,
334 				     struct fscrypt_master_key *mk,
335 				     bool need_dirhash_key)
336 {
337 	int err;
338 
339 	if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
340 		/*
341 		 * DIRECT_KEY: instead of deriving per-file encryption keys, the
342 		 * per-file nonce will be included in all the IVs.  But unlike
343 		 * v1 policies, for v2 policies in this case we don't encrypt
344 		 * with the master key directly but rather derive a per-mode
345 		 * encryption key.  This ensures that the master key is
346 		 * consistently used only for HKDF, avoiding key reuse issues.
347 		 */
348 		err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_keys,
349 					     HKDF_CONTEXT_DIRECT_KEY, false);
350 	} else if (ci->ci_policy.v2.flags &
351 		   FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
352 		/*
353 		 * IV_INO_LBLK_64: encryption keys are derived from (master_key,
354 		 * mode_num, filesystem_uuid), and inode number is included in
355 		 * the IVs.  This format is optimized for use with inline
356 		 * encryption hardware compliant with the UFS standard.
357 		 */
358 		err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_keys,
359 					     HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
360 					     true);
361 	} else if (ci->ci_policy.v2.flags &
362 		   FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
363 		err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk);
364 	} else {
365 		u8 derived_key[FSCRYPT_MAX_KEY_SIZE];
366 
367 		err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
368 					  HKDF_CONTEXT_PER_FILE_ENC_KEY,
369 					  ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
370 					  derived_key, ci->ci_mode->keysize);
371 		if (err)
372 			return err;
373 
374 		err = fscrypt_set_per_file_enc_key(ci, derived_key);
375 		memzero_explicit(derived_key, ci->ci_mode->keysize);
376 	}
377 	if (err)
378 		return err;
379 
380 	/* Derive a secret dirhash key for directories that need it. */
381 	if (need_dirhash_key) {
382 		err = fscrypt_derive_dirhash_key(ci, mk);
383 		if (err)
384 			return err;
385 	}
386 
387 	return 0;
388 }
389 
390 /*
391  * Check whether the size of the given master key (@mk) is appropriate for the
392  * encryption settings which a particular file will use (@ci).
393  *
394  * If the file uses a v1 encryption policy, then the master key must be at least
395  * as long as the derived key, as this is a requirement of the v1 KDF.
396  *
397  * Otherwise, the KDF can accept any size key, so we enforce a slightly looser
398  * requirement: we require that the size of the master key be at least the
399  * maximum security strength of any algorithm whose key will be derived from it
400  * (but in practice we only need to consider @ci->ci_mode, since any other
401  * possible subkeys such as DIRHASH and INODE_HASH will never increase the
402  * required key size over @ci->ci_mode).  This allows AES-256-XTS keys to be
403  * derived from a 256-bit master key, which is cryptographically sufficient,
404  * rather than requiring a 512-bit master key which is unnecessarily long.  (We
405  * still allow 512-bit master keys if the user chooses to use them, though.)
406  */
fscrypt_valid_master_key_size(const struct fscrypt_master_key * mk,const struct fscrypt_inode_info * ci)407 static bool fscrypt_valid_master_key_size(const struct fscrypt_master_key *mk,
408 					  const struct fscrypt_inode_info *ci)
409 {
410 	unsigned int min_keysize;
411 
412 	if (ci->ci_policy.version == FSCRYPT_POLICY_V1)
413 		min_keysize = ci->ci_mode->keysize;
414 	else
415 		min_keysize = ci->ci_mode->security_strength;
416 
417 	if (mk->mk_secret.size < min_keysize) {
418 		fscrypt_warn(NULL,
419 			     "key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
420 			     master_key_spec_type(&mk->mk_spec),
421 			     master_key_spec_len(&mk->mk_spec),
422 			     (u8 *)&mk->mk_spec.u,
423 			     mk->mk_secret.size, min_keysize);
424 		return false;
425 	}
426 	return true;
427 }
428 
429 /*
430  * Find the master key, then set up the inode's actual encryption key.
431  *
432  * If the master key is found in the filesystem-level keyring, then it is
433  * returned in *mk_ret with its semaphore read-locked.  This is needed to ensure
434  * that only one task links the fscrypt_inode_info into ->mk_decrypted_inodes
435  * (as multiple tasks may race to create an fscrypt_inode_info for the same
436  * inode), and to synchronize the master key being removed with a new inode
437  * starting to use it.
438  */
setup_file_encryption_key(struct fscrypt_inode_info * ci,bool need_dirhash_key,struct fscrypt_master_key ** mk_ret)439 static int setup_file_encryption_key(struct fscrypt_inode_info *ci,
440 				     bool need_dirhash_key,
441 				     struct fscrypt_master_key **mk_ret)
442 {
443 	struct super_block *sb = ci->ci_inode->i_sb;
444 	struct fscrypt_key_specifier mk_spec;
445 	struct fscrypt_master_key *mk;
446 	int err;
447 
448 	err = fscrypt_select_encryption_impl(ci);
449 	if (err)
450 		return err;
451 
452 	err = fscrypt_policy_to_key_spec(&ci->ci_policy, &mk_spec);
453 	if (err)
454 		return err;
455 
456 	mk = fscrypt_find_master_key(sb, &mk_spec);
457 	if (unlikely(!mk)) {
458 		const union fscrypt_policy *dummy_policy =
459 			fscrypt_get_dummy_policy(sb);
460 
461 		/*
462 		 * Add the test_dummy_encryption key on-demand.  In principle,
463 		 * it should be added at mount time.  Do it here instead so that
464 		 * the individual filesystems don't need to worry about adding
465 		 * this key at mount time and cleaning up on mount failure.
466 		 */
467 		if (dummy_policy &&
468 		    fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {
469 			err = fscrypt_add_test_dummy_key(sb, &mk_spec);
470 			if (err)
471 				return err;
472 			mk = fscrypt_find_master_key(sb, &mk_spec);
473 		}
474 	}
475 	if (unlikely(!mk)) {
476 		if (ci->ci_policy.version != FSCRYPT_POLICY_V1)
477 			return -ENOKEY;
478 
479 		/*
480 		 * As a legacy fallback for v1 policies, search for the key in
481 		 * the current task's subscribed keyrings too.  Don't move this
482 		 * to before the search of ->s_master_keys, since users
483 		 * shouldn't be able to override filesystem-level keys.
484 		 */
485 		return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
486 	}
487 	down_read(&mk->mk_sem);
488 
489 	if (!mk->mk_present) {
490 		/* FS_IOC_REMOVE_ENCRYPTION_KEY has been executed on this key */
491 		err = -ENOKEY;
492 		goto out_release_key;
493 	}
494 
495 	if (!fscrypt_valid_master_key_size(mk, ci)) {
496 		err = -ENOKEY;
497 		goto out_release_key;
498 	}
499 
500 	switch (ci->ci_policy.version) {
501 	case FSCRYPT_POLICY_V1:
502 		err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
503 		break;
504 	case FSCRYPT_POLICY_V2:
505 		err = fscrypt_setup_v2_file_key(ci, mk, need_dirhash_key);
506 		break;
507 	default:
508 		WARN_ON_ONCE(1);
509 		err = -EINVAL;
510 		break;
511 	}
512 	if (err)
513 		goto out_release_key;
514 
515 	*mk_ret = mk;
516 	return 0;
517 
518 out_release_key:
519 	up_read(&mk->mk_sem);
520 	fscrypt_put_master_key(mk);
521 	return err;
522 }
523 
put_crypt_info(struct fscrypt_inode_info * ci)524 static void put_crypt_info(struct fscrypt_inode_info *ci)
525 {
526 	struct fscrypt_master_key *mk;
527 
528 	if (!ci)
529 		return;
530 
531 	if (ci->ci_direct_key)
532 		fscrypt_put_direct_key(ci->ci_direct_key);
533 	else if (ci->ci_owns_key)
534 		fscrypt_destroy_prepared_key(ci->ci_inode->i_sb,
535 					     &ci->ci_enc_key);
536 
537 	mk = ci->ci_master_key;
538 	if (mk) {
539 		/*
540 		 * Remove this inode from the list of inodes that were unlocked
541 		 * with the master key.  In addition, if we're removing the last
542 		 * inode from an incompletely removed key, then complete the
543 		 * full removal of the key.
544 		 */
545 		spin_lock(&mk->mk_decrypted_inodes_lock);
546 		list_del(&ci->ci_master_key_link);
547 		spin_unlock(&mk->mk_decrypted_inodes_lock);
548 		fscrypt_put_master_key_activeref(ci->ci_inode->i_sb, mk);
549 	}
550 	memzero_explicit(ci, sizeof(*ci));
551 	kmem_cache_free(fscrypt_inode_info_cachep, ci);
552 }
553 
554 static int
fscrypt_setup_encryption_info(struct inode * inode,const union fscrypt_policy * policy,const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],bool need_dirhash_key)555 fscrypt_setup_encryption_info(struct inode *inode,
556 			      const union fscrypt_policy *policy,
557 			      const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],
558 			      bool need_dirhash_key)
559 {
560 	struct fscrypt_inode_info *crypt_info;
561 	struct fscrypt_mode *mode;
562 	struct fscrypt_master_key *mk = NULL;
563 	int res;
564 
565 	res = fscrypt_initialize(inode->i_sb);
566 	if (res)
567 		return res;
568 
569 	crypt_info = kmem_cache_zalloc(fscrypt_inode_info_cachep, GFP_KERNEL);
570 	if (!crypt_info)
571 		return -ENOMEM;
572 
573 	crypt_info->ci_inode = inode;
574 	crypt_info->ci_policy = *policy;
575 	memcpy(crypt_info->ci_nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
576 
577 	mode = select_encryption_mode(&crypt_info->ci_policy, inode);
578 	if (IS_ERR(mode)) {
579 		res = PTR_ERR(mode);
580 		goto out;
581 	}
582 	WARN_ON_ONCE(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
583 	crypt_info->ci_mode = mode;
584 
585 	crypt_info->ci_data_unit_bits =
586 		fscrypt_policy_du_bits(&crypt_info->ci_policy, inode);
587 	crypt_info->ci_data_units_per_block_bits =
588 		inode->i_blkbits - crypt_info->ci_data_unit_bits;
589 
590 	res = setup_file_encryption_key(crypt_info, need_dirhash_key, &mk);
591 	if (res)
592 		goto out;
593 
594 	/*
595 	 * For existing inodes, multiple tasks may race to set ->i_crypt_info.
596 	 * So use cmpxchg_release().  This pairs with the smp_load_acquire() in
597 	 * fscrypt_get_inode_info().  I.e., here we publish ->i_crypt_info with
598 	 * a RELEASE barrier so that other tasks can ACQUIRE it.
599 	 */
600 	if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) {
601 		/*
602 		 * We won the race and set ->i_crypt_info to our crypt_info.
603 		 * Now link it into the master key's inode list.
604 		 */
605 		if (mk) {
606 			crypt_info->ci_master_key = mk;
607 			refcount_inc(&mk->mk_active_refs);
608 			spin_lock(&mk->mk_decrypted_inodes_lock);
609 			list_add(&crypt_info->ci_master_key_link,
610 				 &mk->mk_decrypted_inodes);
611 			spin_unlock(&mk->mk_decrypted_inodes_lock);
612 		}
613 		crypt_info = NULL;
614 	}
615 	res = 0;
616 out:
617 	if (mk) {
618 		up_read(&mk->mk_sem);
619 		fscrypt_put_master_key(mk);
620 	}
621 	put_crypt_info(crypt_info);
622 	return res;
623 }
624 
625 /**
626  * fscrypt_get_encryption_info() - set up an inode's encryption key
627  * @inode: the inode to set up the key for.  Must be encrypted.
628  * @allow_unsupported: if %true, treat an unsupported encryption policy (or
629  *		       unrecognized encryption context) the same way as the key
630  *		       being unavailable, instead of returning an error.  Use
631  *		       %false unless the operation being performed is needed in
632  *		       order for files (or directories) to be deleted.
633  *
634  * Set up ->i_crypt_info, if it hasn't already been done.
635  *
636  * Note: unless ->i_crypt_info is already set, this isn't %GFP_NOFS-safe.  So
637  * generally this shouldn't be called from within a filesystem transaction.
638  *
639  * Return: 0 if ->i_crypt_info was set or was already set, *or* if the
640  *	   encryption key is unavailable.  (Use fscrypt_has_encryption_key() to
641  *	   distinguish these cases.)  Also can return another -errno code.
642  */
fscrypt_get_encryption_info(struct inode * inode,bool allow_unsupported)643 int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)
644 {
645 	int res;
646 	union fscrypt_context ctx;
647 	union fscrypt_policy policy;
648 
649 	if (fscrypt_has_encryption_key(inode))
650 		return 0;
651 
652 	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
653 	if (res < 0) {
654 		if (res == -ERANGE && allow_unsupported)
655 			return 0;
656 		fscrypt_warn(inode, "Error %d getting encryption context", res);
657 		return res;
658 	}
659 
660 	res = fscrypt_policy_from_context(&policy, &ctx, res);
661 	if (res) {
662 		if (allow_unsupported)
663 			return 0;
664 		fscrypt_warn(inode,
665 			     "Unrecognized or corrupt encryption context");
666 		return res;
667 	}
668 
669 	if (!fscrypt_supported_policy(&policy, inode)) {
670 		if (allow_unsupported)
671 			return 0;
672 		return -EINVAL;
673 	}
674 
675 	res = fscrypt_setup_encryption_info(inode, &policy,
676 					    fscrypt_context_nonce(&ctx),
677 					    IS_CASEFOLDED(inode) &&
678 					    S_ISDIR(inode->i_mode));
679 
680 	if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */
681 		res = 0;
682 	if (res == -ENOKEY)
683 		res = 0;
684 	return res;
685 }
686 
687 /**
688  * fscrypt_prepare_new_inode() - prepare to create a new inode in a directory
689  * @dir: a possibly-encrypted directory
690  * @inode: the new inode.  ->i_mode and ->i_blkbits must be set already.
691  *	   ->i_ino doesn't need to be set yet.
692  * @encrypt_ret: (output) set to %true if the new inode will be encrypted
693  *
694  * If the directory is encrypted, set up its ->i_crypt_info in preparation for
695  * encrypting the name of the new file.  Also, if the new inode will be
696  * encrypted, set up its ->i_crypt_info and set *encrypt_ret=true.
697  *
698  * This isn't %GFP_NOFS-safe, and therefore it should be called before starting
699  * any filesystem transaction to create the inode.  For this reason, ->i_ino
700  * isn't required to be set yet, as the filesystem may not have set it yet.
701  *
702  * This doesn't persist the new inode's encryption context.  That still needs to
703  * be done later by calling fscrypt_set_context().
704  *
705  * Return: 0 on success, -ENOKEY if the encryption key is missing, or another
706  *	   -errno code
707  */
fscrypt_prepare_new_inode(struct inode * dir,struct inode * inode,bool * encrypt_ret)708 int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
709 			      bool *encrypt_ret)
710 {
711 	const union fscrypt_policy *policy;
712 	u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
713 
714 	policy = fscrypt_policy_to_inherit(dir);
715 	if (policy == NULL)
716 		return 0;
717 	if (IS_ERR(policy))
718 		return PTR_ERR(policy);
719 
720 	if (WARN_ON_ONCE(inode->i_blkbits == 0))
721 		return -EINVAL;
722 
723 	if (WARN_ON_ONCE(inode->i_mode == 0))
724 		return -EINVAL;
725 
726 	/*
727 	 * Only regular files, directories, and symlinks are encrypted.
728 	 * Special files like device nodes and named pipes aren't.
729 	 */
730 	if (!S_ISREG(inode->i_mode) &&
731 	    !S_ISDIR(inode->i_mode) &&
732 	    !S_ISLNK(inode->i_mode))
733 		return 0;
734 
735 	*encrypt_ret = true;
736 
737 	get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);
738 	return fscrypt_setup_encryption_info(inode, policy, nonce,
739 					     IS_CASEFOLDED(dir) &&
740 					     S_ISDIR(inode->i_mode));
741 }
742 EXPORT_SYMBOL_GPL(fscrypt_prepare_new_inode);
743 
744 /**
745  * fscrypt_put_encryption_info() - free most of an inode's fscrypt data
746  * @inode: an inode being evicted
747  *
748  * Free the inode's fscrypt_inode_info.  Filesystems must call this when the
749  * inode is being evicted.  An RCU grace period need not have elapsed yet.
750  */
fscrypt_put_encryption_info(struct inode * inode)751 void fscrypt_put_encryption_info(struct inode *inode)
752 {
753 	put_crypt_info(inode->i_crypt_info);
754 	inode->i_crypt_info = NULL;
755 }
756 EXPORT_SYMBOL(fscrypt_put_encryption_info);
757 
758 /**
759  * fscrypt_free_inode() - free an inode's fscrypt data requiring RCU delay
760  * @inode: an inode being freed
761  *
762  * Free the inode's cached decrypted symlink target, if any.  Filesystems must
763  * call this after an RCU grace period, just before they free the inode.
764  */
fscrypt_free_inode(struct inode * inode)765 void fscrypt_free_inode(struct inode *inode)
766 {
767 	if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
768 		kfree(inode->i_link);
769 		inode->i_link = NULL;
770 	}
771 }
772 EXPORT_SYMBOL(fscrypt_free_inode);
773 
774 /**
775  * fscrypt_drop_inode() - check whether the inode's master key has been removed
776  * @inode: an inode being considered for eviction
777  *
778  * Filesystems supporting fscrypt must call this from their ->drop_inode()
779  * method so that encrypted inodes are evicted as soon as they're no longer in
780  * use and their master key has been removed.
781  *
782  * Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
783  */
fscrypt_drop_inode(struct inode * inode)784 int fscrypt_drop_inode(struct inode *inode)
785 {
786 	const struct fscrypt_inode_info *ci = fscrypt_get_inode_info(inode);
787 
788 	/*
789 	 * If ci is NULL, then the inode doesn't have an encryption key set up
790 	 * so it's irrelevant.  If ci_master_key is NULL, then the master key
791 	 * was provided via the legacy mechanism of the process-subscribed
792 	 * keyrings, so we don't know whether it's been removed or not.
793 	 */
794 	if (!ci || !ci->ci_master_key)
795 		return 0;
796 
797 	/*
798 	 * With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
799 	 * protected by the key were cleaned by sync_filesystem().  But if
800 	 * userspace is still using the files, inodes can be dirtied between
801 	 * then and now.  We mustn't lose any writes, so skip dirty inodes here.
802 	 */
803 	if (inode->i_state & I_DIRTY_ALL)
804 		return 0;
805 
806 	/*
807 	 * We can't take ->mk_sem here, since this runs in atomic context.
808 	 * Therefore, ->mk_present can change concurrently, and our result may
809 	 * immediately become outdated.  But there's no correctness problem with
810 	 * unnecessarily evicting.  Nor is there a correctness problem with not
811 	 * evicting while iput() is racing with the key being removed, since
812 	 * then the thread removing the key will either evict the inode itself
813 	 * or will correctly detect that it wasn't evicted due to the race.
814 	 */
815 	return !READ_ONCE(ci->ci_master_key->mk_present);
816 }
817 EXPORT_SYMBOL_GPL(fscrypt_drop_inode);
818