keysetup.c

  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/export.h>
 13#include <linux/random.h>
 14
 15#include "fscrypt_private.h"
 16
 17struct fscrypt_mode fscrypt_modes[] = {
 18	[FSCRYPT_MODE_AES_256_XTS] = {
 19		.friendly_name = "AES-256-XTS",
 20		.cipher_str = "xts(aes)",
 21		.keysize = 64,
 22		.security_strength = 32,
 23		.ivsize = 16,
 24		.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_256_XTS,
 25	},
 26	[FSCRYPT_MODE_AES_256_CTS] = {
 27		.friendly_name = "AES-256-CBC-CTS",
 28		.cipher_str = "cts(cbc(aes))",
 29		.keysize = 32,
 30		.security_strength = 32,
 31		.ivsize = 16,
 32	},
 33	[FSCRYPT_MODE_AES_128_CBC] = {
 34		.friendly_name = "AES-128-CBC-ESSIV",
 35		.cipher_str = "essiv(cbc(aes),sha256)",
 36		.keysize = 16,
 37		.security_strength = 16,
 38		.ivsize = 16,
 39		.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_128_CBC_ESSIV,
 40	},
 41	[FSCRYPT_MODE_AES_128_CTS] = {
 42		.friendly_name = "AES-128-CBC-CTS",
 43		.cipher_str = "cts(cbc(aes))",
 44		.keysize = 16,
 45		.security_strength = 16,
 46		.ivsize = 16,
 47	},
 48	[FSCRYPT_MODE_SM4_XTS] = {
 49		.friendly_name = "SM4-XTS",
 50		.cipher_str = "xts(sm4)",
 51		.keysize = 32,
 52		.security_strength = 16,
 53		.ivsize = 16,
 54		.blk_crypto_mode = BLK_ENCRYPTION_MODE_SM4_XTS,
 55	},
 56	[FSCRYPT_MODE_SM4_CTS] = {
 57		.friendly_name = "SM4-CBC-CTS",
 58		.cipher_str = "cts(cbc(sm4))",
 59		.keysize = 16,
 60		.security_strength = 16,
 61		.ivsize = 16,
 62	},
 63	[FSCRYPT_MODE_ADIANTUM] = {
 64		.friendly_name = "Adiantum",
 65		.cipher_str = "adiantum(xchacha12,aes)",
 66		.keysize = 32,
 67		.security_strength = 32,
 68		.ivsize = 32,
 69		.blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM,
 70	},
 71	[FSCRYPT_MODE_AES_256_HCTR2] = {
 72		.friendly_name = "AES-256-HCTR2",
 73		.cipher_str = "hctr2(aes)",
 74		.keysize = 32,
 75		.security_strength = 32,
 76		.ivsize = 32,
 77	},
 78};
 79
 80static DEFINE_MUTEX(fscrypt_mode_key_setup_mutex);
 81
 82static struct fscrypt_mode *
 83select_encryption_mode(const union fscrypt_policy *policy,
 84		       const struct inode *inode)
 85{
 86	BUILD_BUG_ON(ARRAY_SIZE(fscrypt_modes) != FSCRYPT_MODE_MAX + 1);
 87
 88	if (S_ISREG(inode->i_mode))
 89		return &fscrypt_modes[fscrypt_policy_contents_mode(policy)];
 90
 91	if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
 92		return &fscrypt_modes[fscrypt_policy_fnames_mode(policy)];
 93
 94	WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
 95		  inode->i_ino, (inode->i_mode & S_IFMT));
 96	return ERR_PTR(-EINVAL);
 97}
 98
 99/* Create a symmetric cipher object for the given encryption mode and key */
100static struct crypto_sync_skcipher *
101fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
102			  const struct inode *inode)
103{
104	struct crypto_sync_skcipher *tfm;
105	int err;
106
107	tfm = crypto_alloc_sync_skcipher(mode->cipher_str, 0,
108					 FSCRYPT_CRYPTOAPI_MASK);
109	if (IS_ERR(tfm)) {
110		if (PTR_ERR(tfm) == -ENOENT) {
111			fscrypt_warn(inode,
112				     "Missing crypto API support for %s (API name: \"%s\")",
113				     mode->friendly_name, mode->cipher_str);
114			return ERR_PTR(-ENOPKG);
115		}
116		fscrypt_err(inode, "Error allocating '%s' transform: %ld",
117			    mode->cipher_str, PTR_ERR(tfm));
118		return tfm;
119	}
120	if (!xchg(&mode->logged_cryptoapi_impl, 1)) {
121		/*
122		 * fscrypt performance can vary greatly depending on which
123		 * crypto algorithm implementation is used.  Help people debug
124		 * performance problems by logging the ->cra_driver_name the
125		 * first time a mode is used.
126		 */
127		pr_info("fscrypt: %s using implementation \"%s\"\n",
128			mode->friendly_name,
129			crypto_skcipher_driver_name(&tfm->base));
130	}
131	if (WARN_ON_ONCE(crypto_sync_skcipher_ivsize(tfm) != mode->ivsize)) {
132		err = -EINVAL;
133		goto err_free_tfm;
134	}
135	crypto_sync_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
136	err = crypto_sync_skcipher_setkey(tfm, raw_key, mode->keysize);
137	if (err)
138		goto err_free_tfm;
139
140	return tfm;
141
142err_free_tfm:
143	crypto_free_sync_skcipher(tfm);
144	return ERR_PTR(err);
145}
146
147/*
148 * Prepare the crypto transform object or blk-crypto key in @prep_key, given the
149 * raw key, encryption mode (@ci->ci_mode), flag indicating which encryption
150 * implementation (fs-layer or blk-crypto) will be used (@ci->ci_inlinecrypt),
151 * and IV generation method (@ci->ci_policy.flags).
152 */
153int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key,
154			const u8 *raw_key, const struct fscrypt_inode_info *ci)
155{
156	struct crypto_sync_skcipher *tfm;
157
158	if (fscrypt_using_inline_encryption(ci))
159		return fscrypt_prepare_inline_crypt_key(prep_key, raw_key,
160							ci->ci_mode->keysize,
161							false, ci);
162
163	tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode);
164	if (IS_ERR(tfm))
165		return PTR_ERR(tfm);
166	/*
167	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
168	 * I.e., here we publish ->tfm with a RELEASE barrier so that
169	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
170	 * possible for per-mode keys, not for per-file keys.
171	 */
172	smp_store_release(&prep_key->tfm, tfm);
173	return 0;
174}
175
176/* Destroy a crypto transform object and/or blk-crypto key. */
177void fscrypt_destroy_prepared_key(struct super_block *sb,
178				  struct fscrypt_prepared_key *prep_key)
179{
180	crypto_free_sync_skcipher(prep_key->tfm);
181	fscrypt_destroy_inline_crypt_key(sb, prep_key);
182	memzero_explicit(prep_key, sizeof(*prep_key));
183}
184
185/* Given a per-file encryption key, set up the file's crypto transform object */
186int fscrypt_set_per_file_enc_key(struct fscrypt_inode_info *ci,
187				 const u8 *raw_key)
188{
189	ci->ci_owns_key = true;
190	return fscrypt_prepare_key(&ci->ci_enc_key, raw_key, ci);
191}
192
193static int setup_per_mode_enc_key(struct fscrypt_inode_info *ci,
194				  struct fscrypt_master_key *mk,
195				  struct fscrypt_prepared_key *keys,
196				  u8 hkdf_context, bool include_fs_uuid)
197{
198	const struct inode *inode = ci->ci_inode;
199	const struct super_block *sb = inode->i_sb;
200	struct fscrypt_mode *mode = ci->ci_mode;
201	const u8 mode_num = mode - fscrypt_modes;
202	struct fscrypt_prepared_key *prep_key;
203	u8 mode_key[FSCRYPT_MAX_RAW_KEY_SIZE];
204	u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
205	unsigned int hkdf_infolen = 0;
206	bool use_hw_wrapped_key = false;
207	int err;
208
209	if (WARN_ON_ONCE(mode_num > FSCRYPT_MODE_MAX))
210		return -EINVAL;
211
212	if (mk->mk_secret.is_hw_wrapped && S_ISREG(inode->i_mode)) {
213		/* Using a hardware-wrapped key for file contents encryption */
214		if (!fscrypt_using_inline_encryption(ci)) {
215			if (sb->s_flags & SB_INLINECRYPT)
216				fscrypt_warn(ci->ci_inode,
217					     "Hardware-wrapped key required, but no suitable inline encryption capabilities are available");
218			else
219				fscrypt_warn(ci->ci_inode,
220					     "Hardware-wrapped keys require inline encryption (-o inlinecrypt)");
221			return -EINVAL;
222		}
223		use_hw_wrapped_key = true;
224	}
225
226	prep_key = &keys[mode_num];
227	if (fscrypt_is_key_prepared(prep_key, ci)) {
228		ci->ci_enc_key = *prep_key;
229		return 0;
230	}
231
232	mutex_lock(&fscrypt_mode_key_setup_mutex);
233
234	if (fscrypt_is_key_prepared(prep_key, ci))
235		goto done_unlock;
236
237	if (use_hw_wrapped_key) {
238		err = fscrypt_prepare_inline_crypt_key(prep_key,
239						       mk->mk_secret.bytes,
240						       mk->mk_secret.size, true,
241						       ci);
242		if (err)
243			goto out_unlock;
244		goto done_unlock;
245	}
246
247	BUILD_BUG_ON(sizeof(mode_num) != 1);
248	BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
249	BUILD_BUG_ON(sizeof(hkdf_info) != 17);
250	hkdf_info[hkdf_infolen++] = mode_num;
251	if (include_fs_uuid) {
252		memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
253		       sizeof(sb->s_uuid));
254		hkdf_infolen += sizeof(sb->s_uuid);
255	}
256	fscrypt_hkdf_expand(&mk->mk_secret.hkdf, hkdf_context, hkdf_info,
257			    hkdf_infolen, mode_key, mode->keysize);
258	err = fscrypt_prepare_key(prep_key, mode_key, ci);
259	memzero_explicit(mode_key, mode->keysize);
260	if (err)
261		goto out_unlock;
262done_unlock:
263	ci->ci_enc_key = *prep_key;
264	err = 0;
265out_unlock:
266	mutex_unlock(&fscrypt_mode_key_setup_mutex);
267	return err;
268}
269
270/*
271 * Derive a SipHash key from the given fscrypt master key and the given
272 * application-specific information string.
273 *
274 * Note that the KDF produces a byte array, but the SipHash APIs expect the key
275 * as a pair of 64-bit words.  Therefore, on big endian CPUs we have to do an
276 * endianness swap in order to get the same results as on little endian CPUs.
277 */
278static void fscrypt_derive_siphash_key(const struct fscrypt_master_key *mk,
279				       u8 context, const u8 *info,
280				       unsigned int infolen, siphash_key_t *key)
281{
282	fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen,
283			    (u8 *)key, sizeof(*key));
284	BUILD_BUG_ON(sizeof(*key) != 16);
285	BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2);
286	le64_to_cpus(&key->key[0]);
287	le64_to_cpus(&key->key[1]);
288}
289
290void fscrypt_derive_dirhash_key(struct fscrypt_inode_info *ci,
291				const struct fscrypt_master_key *mk)
292{
293	fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,
294				   ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
295				   &ci->ci_dirhash_key);
296	ci->ci_dirhash_key_initialized = true;
297}
298
299void fscrypt_hash_inode_number(struct fscrypt_inode_info *ci,
300			       const struct fscrypt_master_key *mk)
301{
302	WARN_ON_ONCE(ci->ci_inode->i_ino == 0);
303	WARN_ON_ONCE(!mk->mk_ino_hash_key_initialized);
304
305	ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino,
306					      &mk->mk_ino_hash_key);
307}
308
309static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info *ci,
310					    struct fscrypt_master_key *mk)
311{
312	int err;
313
314	err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_32_keys,
315				     HKDF_CONTEXT_IV_INO_LBLK_32_KEY, true);
316	if (err)
317		return err;
318
319	/* pairs with smp_store_release() below */
320	if (!smp_load_acquire(&mk->mk_ino_hash_key_initialized)) {
321
322		mutex_lock(&fscrypt_mode_key_setup_mutex);
323
324		if (mk->mk_ino_hash_key_initialized)
325			goto unlock;
326
327		fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_INODE_HASH_KEY,
328					   NULL, 0, &mk->mk_ino_hash_key);
329		/* pairs with smp_load_acquire() above */
330		smp_store_release(&mk->mk_ino_hash_key_initialized, true);
331unlock:
332		mutex_unlock(&fscrypt_mode_key_setup_mutex);
333	}
334
335	/*
336	 * New inodes may not have an inode number assigned yet.
337	 * Hashing their inode number is delayed until later.
338	 */
339	if (ci->ci_inode->i_ino)
340		fscrypt_hash_inode_number(ci, mk);
341	return 0;
342}
343
344static int fscrypt_setup_v2_file_key(struct fscrypt_inode_info *ci,
345				     struct fscrypt_master_key *mk,
346				     bool need_dirhash_key)
347{
348	int err;
349
350	if (mk->mk_secret.is_hw_wrapped &&
351	    !(ci->ci_policy.v2.flags & (FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 |
352					FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))) {
353		fscrypt_warn(ci->ci_inode,
354			     "Hardware-wrapped keys are only supported with IV_INO_LBLK policies");
355		return -EINVAL;
356	}
357
358	if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
359		/*
360		 * DIRECT_KEY: instead of deriving per-file encryption keys, the
361		 * per-file nonce will be included in all the IVs.  But unlike
362		 * v1 policies, for v2 policies in this case we don't encrypt
363		 * with the master key directly but rather derive a per-mode
364		 * encryption key.  This ensures that the master key is
365		 * consistently used only for HKDF, avoiding key reuse issues.
366		 */
367		err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_keys,
368					     HKDF_CONTEXT_DIRECT_KEY, false);
369	} else if (ci->ci_policy.v2.flags &
370		   FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
371		/*
372		 * IV_INO_LBLK_64: encryption keys are derived from (master_key,
373		 * mode_num, filesystem_uuid), and inode number is included in
374		 * the IVs.  This format is optimized for use with inline
375		 * encryption hardware compliant with the UFS standard.
376		 */
377		err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_keys,
378					     HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
379					     true);
380	} else if (ci->ci_policy.v2.flags &
381		   FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
382		err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk);
383	} else {
384		u8 derived_key[FSCRYPT_MAX_RAW_KEY_SIZE];
385
386		fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
387				    HKDF_CONTEXT_PER_FILE_ENC_KEY,
388				    ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
389				    derived_key, ci->ci_mode->keysize);
390		err = fscrypt_set_per_file_enc_key(ci, derived_key);
391		memzero_explicit(derived_key, ci->ci_mode->keysize);
392	}
393	if (err)
394		return err;
395
396	/* Derive a secret dirhash key for directories that need it. */
397	if (need_dirhash_key)
398		fscrypt_derive_dirhash_key(ci, mk);
399
400	return 0;
401}
402
403/*
404 * Check whether the size of the given master key (@mk) is appropriate for the
405 * encryption settings which a particular file will use (@ci).
406 *
407 * If the file uses a v1 encryption policy, then the master key must be at least
408 * as long as the derived key, as this is a requirement of the v1 KDF.
409 *
410 * Otherwise, the KDF can accept any size key, so we enforce a slightly looser
411 * requirement: we require that the size of the master key be at least the
412 * maximum security strength of any algorithm whose key will be derived from it
413 * (but in practice we only need to consider @ci->ci_mode, since any other
414 * possible subkeys such as DIRHASH and INODE_HASH will never increase the
415 * required key size over @ci->ci_mode).  This allows AES-256-XTS keys to be
416 * derived from a 256-bit master key, which is cryptographically sufficient,
417 * rather than requiring a 512-bit master key which is unnecessarily long.  (We
418 * still allow 512-bit master keys if the user chooses to use them, though.)
419 */
420static bool fscrypt_valid_master_key_size(const struct fscrypt_master_key *mk,
421					  const struct fscrypt_inode_info *ci)
422{
423	unsigned int min_keysize;
424
425	if (ci->ci_policy.version == FSCRYPT_POLICY_V1)
426		min_keysize = ci->ci_mode->keysize;
427	else
428		min_keysize = ci->ci_mode->security_strength;
429
430	if (mk->mk_secret.size < min_keysize) {
431		fscrypt_warn(NULL,
432			     "key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
433			     master_key_spec_type(&mk->mk_spec),
434			     master_key_spec_len(&mk->mk_spec),
435			     (u8 *)&mk->mk_spec.u,
436			     mk->mk_secret.size, min_keysize);
437		return false;
438	}
439	return true;
440}
441
442/*
443 * Find the master key, then set up the inode's actual encryption key.
444 *
445 * If the master key is found in the filesystem-level keyring, then it is
446 * returned in *mk_ret with its semaphore read-locked.  This is needed to ensure
447 * that only one task links the fscrypt_inode_info into ->mk_decrypted_inodes
448 * (as multiple tasks may race to create an fscrypt_inode_info for the same
449 * inode), and to synchronize the master key being removed with a new inode
450 * starting to use it.
451 */
452static int setup_file_encryption_key(struct fscrypt_inode_info *ci,
453				     bool need_dirhash_key,
454				     struct fscrypt_master_key **mk_ret)
455{
456	struct super_block *sb = ci->ci_inode->i_sb;
457	struct fscrypt_key_specifier mk_spec;
458	struct fscrypt_master_key *mk;
459	int err;
460
461	err = fscrypt_policy_to_key_spec(&ci->ci_policy, &mk_spec);
462	if (err)
463		return err;
464
465	mk = fscrypt_find_master_key(sb, &mk_spec);
466	if (unlikely(!mk)) {
467		const union fscrypt_policy *dummy_policy =
468			fscrypt_get_dummy_policy(sb);
469
470		/*
471		 * Add the test_dummy_encryption key on-demand.  In principle,
472		 * it should be added at mount time.  Do it here instead so that
473		 * the individual filesystems don't need to worry about adding
474		 * this key at mount time and cleaning up on mount failure.
475		 */
476		if (dummy_policy &&
477		    fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {
478			err = fscrypt_add_test_dummy_key(sb, &mk_spec);
479			if (err)
480				return err;
481			mk = fscrypt_find_master_key(sb, &mk_spec);
482		}
483	}
484	if (unlikely(!mk)) {
485		if (ci->ci_policy.version != FSCRYPT_POLICY_V1)
486			return -ENOKEY;
487
488		err = fscrypt_select_encryption_impl(ci, false);
489		if (err)
490			return err;
491
492		/*
493		 * As a legacy fallback for v1 policies, search for the key in
494		 * the current task's subscribed keyrings too.  Don't move this
495		 * to before the search of ->s_master_keys, since users
496		 * shouldn't be able to override filesystem-level keys.
497		 */
498		return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
499	}
500	down_read(&mk->mk_sem);
501
502	if (!mk->mk_present) {
503		/* FS_IOC_REMOVE_ENCRYPTION_KEY has been executed on this key */
504		err = -ENOKEY;
505		goto out_release_key;
506	}
507
508	if (!fscrypt_valid_master_key_size(mk, ci)) {
509		err = -ENOKEY;
510		goto out_release_key;
511	}
512
513	err = fscrypt_select_encryption_impl(ci, mk->mk_secret.is_hw_wrapped);
514	if (err)
515		goto out_release_key;
516
517	switch (ci->ci_policy.version) {
518	case FSCRYPT_POLICY_V1:
519		if (WARN_ON_ONCE(mk->mk_secret.is_hw_wrapped)) {
520			/*
521			 * This should never happen, as adding a v1 policy key
522			 * that is hardware-wrapped isn't allowed.
523			 */
524			err = -EINVAL;
525			goto out_release_key;
526		}
527		err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.bytes);
528		break;
529	case FSCRYPT_POLICY_V2:
530		err = fscrypt_setup_v2_file_key(ci, mk, need_dirhash_key);
531		break;
532	default:
533		WARN_ON_ONCE(1);
534		err = -EINVAL;
535		break;
536	}
537	if (err)
538		goto out_release_key;
539
540	*mk_ret = mk;
541	return 0;
542
543out_release_key:
544	up_read(&mk->mk_sem);
545	fscrypt_put_master_key(mk);
546	return err;
547}
548
549static void put_crypt_info(struct fscrypt_inode_info *ci)
550{
551	struct fscrypt_master_key *mk;
552
553	if (!ci)
554		return;
555
556	if (ci->ci_direct_key)
557		fscrypt_put_direct_key(ci->ci_direct_key);
558	else if (ci->ci_owns_key)
559		fscrypt_destroy_prepared_key(ci->ci_inode->i_sb,
560					     &ci->ci_enc_key);
561
562	mk = ci->ci_master_key;
563	if (mk) {
564		/*
565		 * Remove this inode from the list of inodes that were unlocked
566		 * with the master key.  In addition, if we're removing the last
567		 * inode from an incompletely removed key, then complete the
568		 * full removal of the key.
569		 */
570		spin_lock(&mk->mk_decrypted_inodes_lock);
571		list_del(&ci->ci_master_key_link);
572		spin_unlock(&mk->mk_decrypted_inodes_lock);
573		fscrypt_put_master_key_activeref(ci->ci_inode->i_sb, mk);
574	}
575	memzero_explicit(ci, sizeof(*ci));
576	kmem_cache_free(fscrypt_inode_info_cachep, ci);
577}
578
579static int
580fscrypt_setup_encryption_info(struct inode *inode,
581			      const union fscrypt_policy *policy,
582			      const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],
583			      bool need_dirhash_key)
584{
585	struct fscrypt_inode_info *crypt_info;
586	struct fscrypt_mode *mode;
587	struct fscrypt_master_key *mk = NULL;
588	int res;
589
590	res = fscrypt_initialize(inode->i_sb);
591	if (res)
592		return res;
593
594	crypt_info = kmem_cache_zalloc(fscrypt_inode_info_cachep, GFP_KERNEL);
595	if (!crypt_info)
596		return -ENOMEM;
597
598	crypt_info->ci_inode = inode;
599	crypt_info->ci_policy = *policy;
600	memcpy(crypt_info->ci_nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
601
602	mode = select_encryption_mode(&crypt_info->ci_policy, inode);
603	if (IS_ERR(mode)) {
604		res = PTR_ERR(mode);
605		goto out;
606	}
607	WARN_ON_ONCE(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
608	crypt_info->ci_mode = mode;
609
610	crypt_info->ci_data_unit_bits =
611		fscrypt_policy_du_bits(&crypt_info->ci_policy, inode);
612	crypt_info->ci_data_units_per_block_bits =
613		inode->i_blkbits - crypt_info->ci_data_unit_bits;
614
615	res = setup_file_encryption_key(crypt_info, need_dirhash_key, &mk);
616	if (res)
617		goto out;
618
619	/*
620	 * For existing inodes, multiple tasks may race to set the inode's
621	 * fscrypt info pointer.  So use cmpxchg_release().  This pairs with the
622	 * smp_load_acquire() in fscrypt_get_inode_info().  I.e., publish the
623	 * pointer with a RELEASE barrier so that other tasks can ACQUIRE it.
624	 */
625	if (cmpxchg_release(fscrypt_inode_info_addr(inode), NULL, crypt_info) ==
626	    NULL) {
627		/*
628		 * We won the race and set the inode's fscrypt info to our
629		 * crypt_info.  Now link it into the master key's inode list.
630		 */
631		if (mk) {
632			crypt_info->ci_master_key = mk;
633			refcount_inc(&mk->mk_active_refs);
634			spin_lock(&mk->mk_decrypted_inodes_lock);
635			list_add(&crypt_info->ci_master_key_link,
636				 &mk->mk_decrypted_inodes);
637			spin_unlock(&mk->mk_decrypted_inodes_lock);
638		}
639		crypt_info = NULL;
640	}
641	res = 0;
642out:
643	if (mk) {
644		up_read(&mk->mk_sem);
645		fscrypt_put_master_key(mk);
646	}
647	put_crypt_info(crypt_info);
648	return res;
649}
650
651/**
652 * fscrypt_get_encryption_info() - set up an inode's encryption key
653 * @inode: the inode to set up the key for.  Must be encrypted.
654 * @allow_unsupported: if %true, treat an unsupported encryption policy (or
655 *		       unrecognized encryption context) the same way as the key
656 *		       being unavailable, instead of returning an error.  Use
657 *		       %false unless the operation being performed is needed in
658 *		       order for files (or directories) to be deleted.
659 *
660 * Set up the inode's encryption key, if it hasn't already been done.
661 *
662 * Note: unless the key setup was already done, this isn't %GFP_NOFS-safe.  So
663 * generally this shouldn't be called from within a filesystem transaction.
664 *
665 * Return: 0 if the key is now set up, *or* if it couldn't be set up because the
666 *	   needed master key is absent.  (Use fscrypt_has_encryption_key() to
667 *	   distinguish these cases.)  Also can return another -errno code.
668 */
669int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)
670{
671	int res;
672	union fscrypt_context ctx;
673	union fscrypt_policy policy;
674
675	if (fscrypt_has_encryption_key(inode))
676		return 0;
677
678	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
679	if (res < 0) {
680		if (res == -ERANGE && allow_unsupported)
681			return 0;
682		fscrypt_warn(inode, "Error %d getting encryption context", res);
683		return res;
684	}
685
686	res = fscrypt_policy_from_context(&policy, &ctx, res);
687	if (res) {
688		if (allow_unsupported)
689			return 0;
690		fscrypt_warn(inode,
691			     "Unrecognized or corrupt encryption context");
692		return res;
693	}
694
695	if (!fscrypt_supported_policy(&policy, inode)) {
696		if (allow_unsupported)
697			return 0;
698		return -EINVAL;
699	}
700
701	res = fscrypt_setup_encryption_info(inode, &policy,
702					    fscrypt_context_nonce(&ctx),
703					    IS_CASEFOLDED(inode) &&
704					    S_ISDIR(inode->i_mode));
705
706	if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */
707		res = 0;
708	if (res == -ENOKEY)
709		res = 0;
710	return res;
711}
712
713/**
714 * fscrypt_prepare_new_inode() - prepare to create a new inode in a directory
715 * @dir: a possibly-encrypted directory
716 * @inode: the new inode.  ->i_mode and ->i_blkbits must be set already.
717 *	   ->i_ino doesn't need to be set yet.
718 * @encrypt_ret: (output) set to %true if the new inode will be encrypted
719 *
720 * If the directory is encrypted, set up its encryption key in preparation for
721 * encrypting the name of the new file.  Also, if the new inode will be
722 * encrypted, set up its encryption key too and set *encrypt_ret=true.
723 *
724 * This isn't %GFP_NOFS-safe, and therefore it should be called before starting
725 * any filesystem transaction to create the inode.  For this reason, ->i_ino
726 * isn't required to be set yet, as the filesystem may not have set it yet.
727 *
728 * This doesn't persist the new inode's encryption context.  That still needs to
729 * be done later by calling fscrypt_set_context().
730 *
731 * Return: 0 on success, -ENOKEY if a key needs to be set up for @dir or @inode
732 *	   but the needed master key is absent, or another -errno code
733 */
734int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
735			      bool *encrypt_ret)
736{
737	const union fscrypt_policy *policy;
738	u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
739
740	policy = fscrypt_policy_to_inherit(dir);
741	if (policy == NULL)
742		return 0;
743	if (IS_ERR(policy))
744		return PTR_ERR(policy);
745
746	if (WARN_ON_ONCE(inode->i_blkbits == 0))
747		return -EINVAL;
748
749	if (WARN_ON_ONCE(inode->i_mode == 0))
750		return -EINVAL;
751
752	/*
753	 * Only regular files, directories, and symlinks are encrypted.
754	 * Special files like device nodes and named pipes aren't.
755	 */
756	if (!S_ISREG(inode->i_mode) &&
757	    !S_ISDIR(inode->i_mode) &&
758	    !S_ISLNK(inode->i_mode))
759		return 0;
760
761	*encrypt_ret = true;
762
763	get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);
764	return fscrypt_setup_encryption_info(inode, policy, nonce,
765					     IS_CASEFOLDED(dir) &&
766					     S_ISDIR(inode->i_mode));
767}
768EXPORT_SYMBOL_GPL(fscrypt_prepare_new_inode);
769
770/**
771 * fscrypt_put_encryption_info() - free most of an inode's fscrypt data
772 * @inode: an inode being evicted
773 *
774 * Free the inode's fscrypt_inode_info.  Filesystems must call this when the
775 * inode is being evicted.  An RCU grace period need not have elapsed yet.
776 */
777void fscrypt_put_encryption_info(struct inode *inode)
778{
779	/*
780	 * Ideally we'd start with a lightweight IS_ENCRYPTED() check here
781	 * before proceeding to retrieve and check the pointer.  However, during
782	 * inode creation, the fscrypt_inode_info is set before S_ENCRYPTED.  If
783	 * an error occurs, it needs to be cleaned up regardless.
784	 */
785	struct fscrypt_inode_info **ci_addr = fscrypt_inode_info_addr(inode);
786
787	put_crypt_info(*ci_addr);
788	*ci_addr = NULL;
789}
790EXPORT_SYMBOL(fscrypt_put_encryption_info);
791
792/**
793 * fscrypt_free_inode() - free an inode's fscrypt data requiring RCU delay
794 * @inode: an inode being freed
795 *
796 * Free the inode's cached decrypted symlink target, if any.  Filesystems must
797 * call this after an RCU grace period, just before they free the inode.
798 */
799void fscrypt_free_inode(struct inode *inode)
800{
801	if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
802		kfree(inode->i_link);
803		inode->i_link = NULL;
804	}
805}
806EXPORT_SYMBOL(fscrypt_free_inode);
807
808/**
809 * fscrypt_drop_inode() - check whether the inode's master key has been removed
810 * @inode: an inode being considered for eviction
811 *
812 * Filesystems supporting fscrypt must call this from their ->drop_inode()
813 * method so that encrypted inodes are evicted as soon as they're no longer in
814 * use and their master key has been removed.
815 *
816 * Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
817 */
818int fscrypt_drop_inode(struct inode *inode)
819{
820	const struct fscrypt_inode_info *ci = fscrypt_get_inode_info(inode);
821
822	/*
823	 * If ci is NULL, then the inode doesn't have an encryption key set up
824	 * so it's irrelevant.  If ci_master_key is NULL, then the master key
825	 * was provided via the legacy mechanism of the process-subscribed
826	 * keyrings, so we don't know whether it's been removed or not.
827	 */
828	if (!ci || !ci->ci_master_key)
829		return 0;
830
831	/*
832	 * With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
833	 * protected by the key were cleaned by sync_filesystem().  But if
834	 * userspace is still using the files, inodes can be dirtied between
835	 * then and now.  We mustn't lose any writes, so skip dirty inodes here.
836	 */
837	if (inode_state_read(inode) & I_DIRTY_ALL)
838		return 0;
839
840	/*
841	 * We can't take ->mk_sem here, since this runs in atomic context.
842	 * Therefore, ->mk_present can change concurrently, and our result may
843	 * immediately become outdated.  But there's no correctness problem with
844	 * unnecessarily evicting.  Nor is there a correctness problem with not
845	 * evicting while iput() is racing with the key being removed, since
846	 * then the thread removing the key will either evict the inode itself
847	 * or will correctly detect that it wasn't evicted due to the race.
848	 */
849	return !READ_ONCE(ci->ci_master_key->mk_present);
850}
851EXPORT_SYMBOL_GPL(fscrypt_drop_inode);