// SPDX-License-Identifier: GPL-2.0

  /*

   * Key setup facility for FS encryption support.

   *
   * Copyright (C) 2015, Google, Inc.
   *

   * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
   * Heavily modified since then.

   */

  #include <crypto/skcipher.h>

  #include <linux/key.h>

  #include <linux/random.h>

  #include "fscrypt_private.h"

  struct fscrypt_mode fscrypt_modes[] = {

  	[FSCRYPT_MODE_AES_256_XTS] = {

  		.friendly_name = "AES-256-XTS",
  		.cipher_str = "xts(aes)",
  		.keysize = 64,

  		.ivsize = 16,

  		.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_256_XTS,

  	},

  	[FSCRYPT_MODE_AES_256_CTS] = {

  		.friendly_name = "AES-256-CTS-CBC",
  		.cipher_str = "cts(cbc(aes))",
  		.keysize = 32,

  		.ivsize = 16,

  	},

  	[FSCRYPT_MODE_AES_128_CBC] = {

  		.friendly_name = "AES-128-CBC-ESSIV",
  		.cipher_str = "essiv(cbc(aes),sha256)",

  		.keysize = 16,

  		.ivsize = 16,

  		.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_128_CBC_ESSIV,

  	},

  	[FSCRYPT_MODE_AES_128_CTS] = {

  		.friendly_name = "AES-128-CTS-CBC",
  		.cipher_str = "cts(cbc(aes))",
  		.keysize = 16,

  		.ivsize = 16,
  	},

  	[FSCRYPT_MODE_ADIANTUM] = {

  		.friendly_name = "Adiantum",
  		.cipher_str = "adiantum(xchacha12,aes)",
  		.keysize = 32,
  		.ivsize = 32,

  		.blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM,

  	},

  };

  static DEFINE_MUTEX(fscrypt_mode_key_setup_mutex);

  static struct fscrypt_mode *

  select_encryption_mode(const union fscrypt_policy *policy,
  		       const struct inode *inode)

  {

  	BUILD_BUG_ON(ARRAY_SIZE(fscrypt_modes) != FSCRYPT_MODE_MAX + 1);

  	if (S_ISREG(inode->i_mode))

  		return &fscrypt_modes[fscrypt_policy_contents_mode(policy)];

  
  	if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))

  		return &fscrypt_modes[fscrypt_policy_fnames_mode(policy)];

  	WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)
  ",
  		  inode->i_ino, (inode->i_mode & S_IFMT));
  	return ERR_PTR(-EINVAL);

  }

  /* Create a symmetric cipher object for the given encryption mode and key */

  static struct crypto_skcipher *
  fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
  			  const struct inode *inode)

  {
  	struct crypto_skcipher *tfm;
  	int err;
  
  	tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
  	if (IS_ERR(tfm)) {

  		if (PTR_ERR(tfm) == -ENOENT) {

  			fscrypt_warn(inode,
  				     "Missing crypto API support for %s (API name: \"%s\")",
  				     mode->friendly_name, mode->cipher_str);

  			return ERR_PTR(-ENOPKG);
  		}
  		fscrypt_err(inode, "Error allocating '%s' transform: %ld",
  			    mode->cipher_str, PTR_ERR(tfm));

  		return tfm;
  	}

  	if (!xchg(&mode->logged_impl_name, 1)) {

  		/*
  		 * fscrypt performance can vary greatly depending on which
  		 * crypto algorithm implementation is used.  Help people debug
  		 * performance problems by logging the ->cra_driver_name the

  		 * first time a mode is used.

  		 */

  		pr_info("fscrypt: %s using implementation \"%s\"
  ",

  			mode->friendly_name, crypto_skcipher_driver_name(tfm));

  	}

  	if (WARN_ON(crypto_skcipher_ivsize(tfm) != mode->ivsize)) {
  		err = -EINVAL;
  		goto err_free_tfm;

  	}

  	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);

  	err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
  	if (err)
  		goto err_free_tfm;
  
  	return tfm;
  
  err_free_tfm:
  	crypto_free_skcipher(tfm);
  	return ERR_PTR(err);
  }

  /*
   * Prepare the crypto transform object or blk-crypto key in @prep_key, given the
   * raw key, encryption mode, and flag indicating which encryption implementation
   * (fs-layer or blk-crypto) will be used.
   */
  int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key,

  			const u8 *raw_key, unsigned int raw_key_size,

  			bool is_hw_wrapped, const struct fscrypt_info *ci)

  {

  	struct crypto_skcipher *tfm;

  	if (fscrypt_using_inline_encryption(ci))

  		return fscrypt_prepare_inline_crypt_key(prep_key,

  				raw_key, raw_key_size, is_hw_wrapped, ci);

  	if (WARN_ON(is_hw_wrapped || raw_key_size != ci->ci_mode->keysize))

  		return -EINVAL;

  	tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode);

  	if (IS_ERR(tfm))
  		return PTR_ERR(tfm);

  	/*

  	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
  	 * I.e., here we publish ->tfm with a RELEASE barrier so that
  	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
  	 * possible for per-mode keys, not for per-file keys.

  	 */
  	smp_store_release(&prep_key->tfm, tfm);
  	return 0;
  }
  
  /* Destroy a crypto transform object and/or blk-crypto key. */
  void fscrypt_destroy_prepared_key(struct fscrypt_prepared_key *prep_key)
  {
  	crypto_free_skcipher(prep_key->tfm);
  	fscrypt_destroy_inline_crypt_key(prep_key);
  }

  /* Given a per-file encryption key, set up the file's crypto transform object */
  int fscrypt_set_per_file_enc_key(struct fscrypt_info *ci, const u8 *raw_key)

  {

  	ci->ci_owns_key = true;

  	return fscrypt_prepare_key(&ci->ci_enc_key, raw_key,
  				   ci->ci_mode->keysize,

  				   false /*is_hw_wrapped*/, ci);

  }

  static int setup_per_mode_enc_key(struct fscrypt_info *ci,
  				  struct fscrypt_master_key *mk,

  				  struct fscrypt_prepared_key *keys,

  				  u8 hkdf_context, bool include_fs_uuid)

  {

  	const struct inode *inode = ci->ci_inode;
  	const struct super_block *sb = inode->i_sb;

  	struct fscrypt_mode *mode = ci->ci_mode;

  	const u8 mode_num = mode - fscrypt_modes;

  	struct fscrypt_prepared_key *prep_key;

  	u8 mode_key[FSCRYPT_MAX_KEY_SIZE];

  	u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
  	unsigned int hkdf_infolen = 0;

  	int err;

  	if (WARN_ON(mode_num > FSCRYPT_MODE_MAX))

  		return -EINVAL;

  	prep_key = &keys[mode_num];
  	if (fscrypt_is_key_prepared(prep_key, ci)) {

  		ci->ci_enc_key = *prep_key;

  		return 0;
  	}

  	mutex_lock(&fscrypt_mode_key_setup_mutex);

  
  	if (fscrypt_is_key_prepared(prep_key, ci))
  		goto done_unlock;

  	if (mk->mk_secret.is_hw_wrapped && S_ISREG(inode->i_mode)) {
  		int i;
  
  		if (!fscrypt_using_inline_encryption(ci)) {
  			fscrypt_warn(ci->ci_inode,
  				     "Hardware-wrapped keys require inline encryption (-o inlinecrypt)");
  			err = -EINVAL;
  			goto out_unlock;
  		}

  		for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {

  			if (fscrypt_is_key_prepared(&keys[i], ci)) {
  				fscrypt_warn(ci->ci_inode,
  					     "Each hardware-wrapped key can only be used with one encryption mode");
  				err = -EINVAL;
  				goto out_unlock;
  			}
  		}
  		err = fscrypt_prepare_key(prep_key, mk->mk_secret.raw,

  					  mk->mk_secret.size, true, ci);

  		if (err)
  			goto out_unlock;
  	} else {
  		BUILD_BUG_ON(sizeof(mode_num) != 1);
  		BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
  		BUILD_BUG_ON(sizeof(hkdf_info) != 17);
  		hkdf_info[hkdf_infolen++] = mode_num;
  		if (include_fs_uuid) {
  			memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
  				   sizeof(sb->s_uuid));
  			hkdf_infolen += sizeof(sb->s_uuid);
  		}
  		err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
  					  hkdf_context, hkdf_info, hkdf_infolen,
  					  mode_key, mode->keysize);
  		if (err)
  			goto out_unlock;
  		err = fscrypt_prepare_key(prep_key, mode_key, mode->keysize,

  					  false /*is_hw_wrapped*/, ci);

  		memzero_explicit(mode_key, mode->keysize);
  		if (err)
  			goto out_unlock;

  	}

  done_unlock:

  	ci->ci_enc_key = *prep_key;

  	err = 0;
  out_unlock:

  	mutex_unlock(&fscrypt_mode_key_setup_mutex);

  	return err;

  }

  int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
  			       const struct fscrypt_master_key *mk)
  {
  	int err;
  
  	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, HKDF_CONTEXT_DIRHASH_KEY,

  				  ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,

  				  (u8 *)&ci->ci_dirhash_key,
  				  sizeof(ci->ci_dirhash_key));
  	if (err)
  		return err;
  	ci->ci_dirhash_key_initialized = true;
  	return 0;
  }

  void fscrypt_hash_inode_number(struct fscrypt_info *ci,
  			       const struct fscrypt_master_key *mk)
  {
  	WARN_ON(ci->ci_inode->i_ino == 0);
  	WARN_ON(!mk->mk_ino_hash_key_initialized);
  
  	ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino,
  					      &mk->mk_ino_hash_key);
  }

  static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_info *ci,
  					    struct fscrypt_master_key *mk)
  {
  	int err;
  
  	err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_32_keys,
  				     HKDF_CONTEXT_IV_INO_LBLK_32_KEY, true);
  	if (err)
  		return err;
  
  	/* pairs with smp_store_release() below */
  	if (!smp_load_acquire(&mk->mk_ino_hash_key_initialized)) {
  
  		mutex_lock(&fscrypt_mode_key_setup_mutex);
  
  		if (mk->mk_ino_hash_key_initialized)
  			goto unlock;
  
  		err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
  					  HKDF_CONTEXT_INODE_HASH_KEY, NULL, 0,
  					  (u8 *)&mk->mk_ino_hash_key,
  					  sizeof(mk->mk_ino_hash_key));
  		if (err)
  			goto unlock;
  		/* pairs with smp_load_acquire() above */
  		smp_store_release(&mk->mk_ino_hash_key_initialized, true);
  unlock:
  		mutex_unlock(&fscrypt_mode_key_setup_mutex);
  		if (err)
  			return err;
  	}

  	/*
  	 * New inodes may not have an inode number assigned yet.
  	 * Hashing their inode number is delayed until later.
  	 */

  	if (ci->ci_inode->i_ino)

  		fscrypt_hash_inode_number(ci, mk);

  	return 0;
  }

  static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,

  				     struct fscrypt_master_key *mk,
  				     bool need_dirhash_key)

  {

  	int err;

  	if (mk->mk_secret.is_hw_wrapped &&

  	    !(ci->ci_policy.v2.flags & (FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 |
  					FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))) {

  		fscrypt_warn(ci->ci_inode,

  			     "Hardware-wrapped keys are only supported with IV_INO_LBLK policies");

  		return -EINVAL;
  	}

  	if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
  		/*

  		 * DIRECT_KEY: instead of deriving per-file encryption keys, the
  		 * per-file nonce will be included in all the IVs.  But unlike
  		 * v1 policies, for v2 policies in this case we don't encrypt
  		 * with the master key directly but rather derive a per-mode
  		 * encryption key.  This ensures that the master key is
  		 * consistently used only for HKDF, avoiding key reuse issues.

  		 */

  		err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_keys,

  					     HKDF_CONTEXT_DIRECT_KEY, false);

  	} else if (ci->ci_policy.v2.flags &
  		   FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
  		/*
  		 * IV_INO_LBLK_64: encryption keys are derived from (master_key,
  		 * mode_num, filesystem_uuid), and inode number is included in
  		 * the IVs.  This format is optimized for use with inline

  		 * encryption hardware compliant with the UFS standard.

  		 */

  		err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_keys,

  					     HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
  					     true);

  	} else if (ci->ci_policy.v2.flags &
  		   FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
  		err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk);

  	} else {
  		u8 derived_key[FSCRYPT_MAX_KEY_SIZE];

  		err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,

  					  HKDF_CONTEXT_PER_FILE_ENC_KEY,

  					  ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,

  					  derived_key, ci->ci_mode->keysize);
  		if (err)
  			return err;

  		err = fscrypt_set_per_file_enc_key(ci, derived_key);

  		memzero_explicit(derived_key, ci->ci_mode->keysize);
  	}

  	if (err)
  		return err;

  	/* Derive a secret dirhash key for directories that need it. */

  	if (need_dirhash_key) {

  		err = fscrypt_derive_dirhash_key(ci, mk);
  		if (err)
  			return err;
  	}
  
  	return 0;

  }

  /*
   * Find the master key, then set up the inode's actual encryption key.

   *
   * If the master key is found in the filesystem-level keyring, then the

   * corresponding 'struct key' is returned in *master_key_ret with its semaphore
   * read-locked.  This is needed to ensure that only one task links the
   * fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race to create
   * an fscrypt_info for the same inode), and to synchronize the master key being
   * removed with a new inode starting to use it.

   */

  static int setup_file_encryption_key(struct fscrypt_info *ci,

  				     bool need_dirhash_key,

  				     struct key **master_key_ret)

  {

  	struct key *key;
  	struct fscrypt_master_key *mk = NULL;
  	struct fscrypt_key_specifier mk_spec;
  	int err;

  	switch (ci->ci_policy.version) {
  	case FSCRYPT_POLICY_V1:
  		mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
  		memcpy(mk_spec.u.descriptor,
  		       ci->ci_policy.v1.master_key_descriptor,
  		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
  		break;
  	case FSCRYPT_POLICY_V2:
  		mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
  		memcpy(mk_spec.u.identifier,
  		       ci->ci_policy.v2.master_key_identifier,
  		       FSCRYPT_KEY_IDENTIFIER_SIZE);
  		break;
  	default:
  		WARN_ON(1);
  		return -EINVAL;
  	}

  
  	key = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);
  	if (IS_ERR(key)) {

  		if (key != ERR_PTR(-ENOKEY) ||
  		    ci->ci_policy.version != FSCRYPT_POLICY_V1)

  			return PTR_ERR(key);

  		err = fscrypt_select_encryption_impl(ci, false);
  		if (err)
  			return err;

  		/*
  		 * As a legacy fallback for v1 policies, search for the key in
  		 * the current task's subscribed keyrings too.  Don't move this
  		 * to before the search of ->s_master_keys, since users
  		 * shouldn't be able to override filesystem-level keys.
  		 */

  		return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
  	}
  
  	mk = key->payload.data[0];

  	down_read(&key->sem);

  
  	/* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */
  	if (!is_master_key_secret_present(&mk->mk_secret)) {
  		err = -ENOKEY;
  		goto out_release_key;
  	}

  	/*
  	 * Require that the master key be at least as long as the derived key.
  	 * Otherwise, the derived key cannot possibly contain as much entropy as
  	 * that required by the encryption mode it will be used for.  For v1
  	 * policies it's also required for the KDF to work at all.
  	 */

  	if (mk->mk_secret.size < ci->ci_mode->keysize) {
  		fscrypt_warn(NULL,
  			     "key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
  			     master_key_spec_type(&mk_spec),
  			     master_key_spec_len(&mk_spec), (u8 *)&mk_spec.u,
  			     mk->mk_secret.size, ci->ci_mode->keysize);
  		err = -ENOKEY;
  		goto out_release_key;
  	}

  	err = fscrypt_select_encryption_impl(ci, mk->mk_secret.is_hw_wrapped);
  	if (err)
  		goto out_release_key;

  	switch (ci->ci_policy.version) {
  	case FSCRYPT_POLICY_V1:
  		err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
  		break;
  	case FSCRYPT_POLICY_V2:

  		err = fscrypt_setup_v2_file_key(ci, mk, need_dirhash_key);

  		break;
  	default:
  		WARN_ON(1);
  		err = -EINVAL;
  		break;
  	}

  	if (err)
  		goto out_release_key;
  
  	*master_key_ret = key;
  	return 0;

  
  out_release_key:

  	up_read(&key->sem);

  	key_put(key);
  	return err;

  }

  static void put_crypt_info(struct fscrypt_info *ci)
  {

  	struct key *key;

  	if (!ci)
  		return;

  	if (ci->ci_direct_key)

  		fscrypt_put_direct_key(ci->ci_direct_key);

  	else if (ci->ci_owns_key)

  		fscrypt_destroy_prepared_key(&ci->ci_enc_key);

  
  	key = ci->ci_master_key;
  	if (key) {
  		struct fscrypt_master_key *mk = key->payload.data[0];
  
  		/*
  		 * Remove this inode from the list of inodes that were unlocked
  		 * with the master key.
  		 *
  		 * In addition, if we're removing the last inode from a key that
  		 * already had its secret removed, invalidate the key so that it
  		 * gets removed from ->s_master_keys.
  		 */
  		spin_lock(&mk->mk_decrypted_inodes_lock);
  		list_del(&ci->ci_master_key_link);
  		spin_unlock(&mk->mk_decrypted_inodes_lock);
  		if (refcount_dec_and_test(&mk->mk_refcount))
  			key_invalidate(key);
  		key_put(key);
  	}

  	memzero_explicit(ci, sizeof(*ci));

  	kmem_cache_free(fscrypt_info_cachep, ci);
  }

  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)

  {

  	struct fscrypt_info *crypt_info;

  	struct fscrypt_mode *mode;

  	struct key *master_key = NULL;

  	int res;

  	res = fscrypt_initialize(inode->i_sb->s_cop->flags);

  	if (res)
  		return res;

  	crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_KERNEL);

  	if (!crypt_info)
  		return -ENOMEM;

  	crypt_info->ci_inode = inode;

  	crypt_info->ci_policy = *policy;
  	memcpy(crypt_info->ci_nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);

  	mode = select_encryption_mode(&crypt_info->ci_policy, inode);

  	if (IS_ERR(mode)) {
  		res = PTR_ERR(mode);

  		goto out;

  	}

  	WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
  	crypt_info->ci_mode = mode;

  	res = setup_file_encryption_key(crypt_info, need_dirhash_key,
  					&master_key);

  	if (res)
  		goto out;

  	/*

  	 * For existing inodes, multiple tasks may race to set ->i_crypt_info.
  	 * So use cmpxchg_release().  This pairs with the smp_load_acquire() in

  	 * fscrypt_get_info().  I.e., here we publish ->i_crypt_info with a
  	 * RELEASE barrier so that other tasks can ACQUIRE it.
  	 */

  	if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) {

  		/*
  		 * We won the race and set ->i_crypt_info to our crypt_info.
  		 * Now link it into the master key's inode list.
  		 */

  		if (master_key) {
  			struct fscrypt_master_key *mk =
  				master_key->payload.data[0];
  
  			refcount_inc(&mk->mk_refcount);
  			crypt_info->ci_master_key = key_get(master_key);
  			spin_lock(&mk->mk_decrypted_inodes_lock);
  			list_add(&crypt_info->ci_master_key_link,
  				 &mk->mk_decrypted_inodes);
  			spin_unlock(&mk->mk_decrypted_inodes_lock);
  		}

  		crypt_info = NULL;

  	}
  	res = 0;

  out:

  	if (master_key) {

  		up_read(&master_key->sem);

  		key_put(master_key);
  	}

  	put_crypt_info(crypt_info);
  	return res;
  }
  
  /**
   * fscrypt_get_encryption_info() - set up an inode's encryption key

   * @inode: the inode to set up the key for.  Must be encrypted.

   * @allow_unsupported: if %true, treat an unsupported encryption policy (or
   *		       unrecognized encryption context) the same way as the key
   *		       being unavailable, instead of returning an error.  Use
   *		       %false unless the operation being performed is needed in
   *		       order for files (or directories) to be deleted.

   *
   * Set up ->i_crypt_info, if it hasn't already been done.
   *
   * Note: unless ->i_crypt_info is already set, this isn't %GFP_NOFS-safe.  So
   * generally this shouldn't be called from within a filesystem transaction.
   *
   * Return: 0 if ->i_crypt_info was set or was already set, *or* if the
   *	   encryption key is unavailable.  (Use fscrypt_has_encryption_key() to
   *	   distinguish these cases.)  Also can return another -errno code.
   */

  int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)

  {
  	int res;
  	union fscrypt_context ctx;
  	union fscrypt_policy policy;
  
  	if (fscrypt_has_encryption_key(inode))
  		return 0;
  
  	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
  	if (res < 0) {

  		if (res == -ERANGE && allow_unsupported)
  			return 0;

  		fscrypt_warn(inode, "Error %d getting encryption context", res);
  		return res;

  	}
  
  	res = fscrypt_policy_from_context(&policy, &ctx, res);
  	if (res) {

  		if (allow_unsupported)
  			return 0;

  		fscrypt_warn(inode,
  			     "Unrecognized or corrupt encryption context");
  		return res;
  	}

  	if (!fscrypt_supported_policy(&policy, inode)) {
  		if (allow_unsupported)
  			return 0;

  		return -EINVAL;

  	}

  
  	res = fscrypt_setup_encryption_info(inode, &policy,
  					    fscrypt_context_nonce(&ctx),
  					    IS_CASEFOLDED(inode) &&
  					    S_ISDIR(inode->i_mode));

  
  	if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */
  		res = 0;

  	if (res == -ENOKEY)

  		res = 0;

  	return res;
  }

  /**

   * fscrypt_prepare_new_inode() - prepare to create a new inode in a directory
   * @dir: a possibly-encrypted directory
   * @inode: the new inode.  ->i_mode must be set already.
   *	   ->i_ino doesn't need to be set yet.
   * @encrypt_ret: (output) set to %true if the new inode will be encrypted
   *
   * If the directory is encrypted, set up its ->i_crypt_info in preparation for
   * encrypting the name of the new file.  Also, if the new inode will be
   * encrypted, set up its ->i_crypt_info and set *encrypt_ret=true.
   *
   * This isn't %GFP_NOFS-safe, and therefore it should be called before starting
   * any filesystem transaction to create the inode.  For this reason, ->i_ino
   * isn't required to be set yet, as the filesystem may not have set it yet.
   *
   * This doesn't persist the new inode's encryption context.  That still needs to
   * be done later by calling fscrypt_set_context().
   *
   * Return: 0 on success, -ENOKEY if the encryption key is missing, or another
   *	   -errno code
   */
  int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
  			      bool *encrypt_ret)
  {

  	const union fscrypt_policy *policy;

  	u8 nonce[FSCRYPT_FILE_NONCE_SIZE];

  	policy = fscrypt_policy_to_inherit(dir);
  	if (policy == NULL)

  		return 0;

  	if (IS_ERR(policy))
  		return PTR_ERR(policy);

  
  	if (WARN_ON_ONCE(inode->i_mode == 0))
  		return -EINVAL;
  
  	/*
  	 * Only regular files, directories, and symlinks are encrypted.
  	 * Special files like device nodes and named pipes aren't.
  	 */
  	if (!S_ISREG(inode->i_mode) &&
  	    !S_ISDIR(inode->i_mode) &&
  	    !S_ISLNK(inode->i_mode))
  		return 0;
  
  	*encrypt_ret = true;
  
  	get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);

  	return fscrypt_setup_encryption_info(inode, policy, nonce,

  					     IS_CASEFOLDED(dir) &&
  					     S_ISDIR(inode->i_mode));
  }
  EXPORT_SYMBOL_GPL(fscrypt_prepare_new_inode);
  
  /**

   * fscrypt_put_encryption_info() - free most of an inode's fscrypt data
   * @inode: an inode being evicted

   *
   * Free the inode's fscrypt_info.  Filesystems must call this when the inode is
   * being evicted.  An RCU grace period need not have elapsed yet.
   */

  void fscrypt_put_encryption_info(struct inode *inode)

  {

  	put_crypt_info(inode->i_crypt_info);
  	inode->i_crypt_info = NULL;

  }
  EXPORT_SYMBOL(fscrypt_put_encryption_info);

  
  /**

   * fscrypt_free_inode() - free an inode's fscrypt data requiring RCU delay
   * @inode: an inode being freed

   *
   * Free the inode's cached decrypted symlink target, if any.  Filesystems must
   * call this after an RCU grace period, just before they free the inode.
   */
  void fscrypt_free_inode(struct inode *inode)
  {
  	if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
  		kfree(inode->i_link);
  		inode->i_link = NULL;
  	}
  }
  EXPORT_SYMBOL(fscrypt_free_inode);

  
  /**

   * fscrypt_drop_inode() - check whether the inode's master key has been removed
   * @inode: an inode being considered for eviction

   *
   * Filesystems supporting fscrypt must call this from their ->drop_inode()
   * method so that encrypted inodes are evicted as soon as they're no longer in
   * use and their master key has been removed.
   *
   * Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
   */
  int fscrypt_drop_inode(struct inode *inode)
  {

  	const struct fscrypt_info *ci = fscrypt_get_info(inode);

  	const struct fscrypt_master_key *mk;
  
  	/*
  	 * If ci is NULL, then the inode doesn't have an encryption key set up
  	 * so it's irrelevant.  If ci_master_key is NULL, then the master key
  	 * was provided via the legacy mechanism of the process-subscribed
  	 * keyrings, so we don't know whether it's been removed or not.
  	 */
  	if (!ci || !ci->ci_master_key)
  		return 0;
  	mk = ci->ci_master_key->payload.data[0];
  
  	/*

  	 * With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
  	 * protected by the key were cleaned by sync_filesystem().  But if
  	 * userspace is still using the files, inodes can be dirtied between
  	 * then and now.  We mustn't lose any writes, so skip dirty inodes here.
  	 */
  	if (inode->i_state & I_DIRTY_ALL)
  		return 0;
  
  	/*

  	 * Note: since we aren't holding the key semaphore, the result here can

  	 * immediately become outdated.  But there's no correctness problem with
  	 * unnecessarily evicting.  Nor is there a correctness problem with not
  	 * evicting while iput() is racing with the key being removed, since
  	 * then the thread removing the key will either evict the inode itself
  	 * or will correctly detect that it wasn't evicted due to the race.
  	 */
  	return !is_master_key_secret_present(&mk->mk_secret);
  }
  EXPORT_SYMBOL_GPL(fscrypt_drop_inode);