Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 772 insertions, 0 deletions

diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
new file mode 100644
index 000000000..f7407071a
--- /dev/null
+++ b/fs/crypto/keysetup.c
@@ -0,0 +1,772 @@
+// 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/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,
+		.security_strength = 32,
+		.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,
+		.security_strength = 32,
+		.ivsize = 16,
+	},
+	[FSCRYPT_MODE_AES_128_CBC] = {
+		.friendly_name = "AES-128-CBC-ESSIV",
+		.cipher_str = "essiv(cbc(aes),sha256)",
+		.keysize = 16,
+		.security_strength = 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,
+		.security_strength = 16,
+		.ivsize = 16,
+	},
+	[FSCRYPT_MODE_ADIANTUM] = {
+		.friendly_name = "Adiantum",
+		.cipher_str = "adiantum(xchacha12,aes)",
+		.keysize = 32,
+		.security_strength = 32,
+		.ivsize = 32,
+		.blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM,
+	},
+	[FSCRYPT_MODE_AES_256_HCTR2] = {
+		.friendly_name = "AES-256-HCTR2",
+		.cipher_str = "hctr2(aes)",
+		.keysize = 32,
+		.security_strength = 32,
+		.ivsize = 32,
+	},
+};
+
+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)\n",
+		  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_cryptoapi_impl, 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\"\n",
+			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 (@ci->ci_mode), flag indicating which encryption
+ * implementation (fs-layer or blk-crypto) will be used (@ci->ci_inlinecrypt),
+ * and IV generation method (@ci->ci_policy.flags).
+ */
+int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key,
+			const u8 *raw_key, 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, ci);
+
+	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 super_block *sb,
+				  struct fscrypt_prepared_key *prep_key)
+{
+	crypto_free_skcipher(prep_key->tfm);
+	fscrypt_destroy_inline_crypt_key(sb, prep_key);
+	memzero_explicit(prep_key, sizeof(*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);
+}
+
+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;
+
+	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, 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;
+}
+
+/*
+ * Derive a SipHash key from the given fscrypt master key and the given
+ * application-specific information string.
+ *
+ * Note that the KDF produces a byte array, but the SipHash APIs expect the key
+ * as a pair of 64-bit words.  Therefore, on big endian CPUs we have to do an
+ * endianness swap in order to get the same results as on little endian CPUs.
+ */
+static int fscrypt_derive_siphash_key(const struct fscrypt_master_key *mk,
+				      u8 context, const u8 *info,
+				      unsigned int infolen, siphash_key_t *key)
+{
+	int err;
+
+	err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen,
+				  (u8 *)key, sizeof(*key));
+	if (err)
+		return err;
+
+	BUILD_BUG_ON(sizeof(*key) != 16);
+	BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2);
+	le64_to_cpus(&key->key[0]);
+	le64_to_cpus(&key->key[1]);
+	return 0;
+}
+
+int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
+			       const struct fscrypt_master_key *mk)
+{
+	int err;
+
+	err = fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,
+					 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
+					 &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_derive_siphash_key(mk,
+						 HKDF_CONTEXT_INODE_HASH_KEY,
+						 NULL, 0, &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 (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;
+}
+
+/*
+ * Check whether the size of the given master key (@mk) is appropriate for the
+ * encryption settings which a particular file will use (@ci).
+ *
+ * If the file uses a v1 encryption policy, then the master key must be at least
+ * as long as the derived key, as this is a requirement of the v1 KDF.
+ *
+ * Otherwise, the KDF can accept any size key, so we enforce a slightly looser
+ * requirement: we require that the size of the master key be at least the
+ * maximum security strength of any algorithm whose key will be derived from it
+ * (but in practice we only need to consider @ci->ci_mode, since any other
+ * possible subkeys such as DIRHASH and INODE_HASH will never increase the
+ * required key size over @ci->ci_mode).  This allows AES-256-XTS keys to be
+ * derived from a 256-bit master key, which is cryptographically sufficient,
+ * rather than requiring a 512-bit master key which is unnecessarily long.  (We
+ * still allow 512-bit master keys if the user chooses to use them, though.)
+ */
+static bool fscrypt_valid_master_key_size(const struct fscrypt_master_key *mk,
+					  const struct fscrypt_info *ci)
+{
+	unsigned int min_keysize;
+
+	if (ci->ci_policy.version == FSCRYPT_POLICY_V1)
+		min_keysize = ci->ci_mode->keysize;
+	else
+		min_keysize = ci->ci_mode->security_strength;
+
+	if (mk->mk_secret.size < min_keysize) {
+		fscrypt_warn(NULL,
+			     "key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
+			     master_key_spec_type(&mk->mk_spec),
+			     master_key_spec_len(&mk->mk_spec),
+			     (u8 *)&mk->mk_spec.u,
+			     mk->mk_secret.size, min_keysize);
+		return false;
+	}
+	return true;
+}
+
+/*
+ * 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 it is
+ * returned in *mk_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 fscrypt_master_key **mk_ret)
+{
+	struct fscrypt_key_specifier mk_spec;
+	struct fscrypt_master_key *mk;
+	int err;
+
+	err = fscrypt_select_encryption_impl(ci);
+	if (err)
+		return err;
+
+	err = fscrypt_policy_to_key_spec(&ci->ci_policy, &mk_spec);
+	if (err)
+		return err;
+
+	mk = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);
+	if (!mk) {
+		if (ci->ci_policy.version != FSCRYPT_POLICY_V1)
+			return -ENOKEY;
+
+		/*
+		 * 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);
+	}
+	down_read(&mk->mk_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;
+	}
+
+	if (!fscrypt_valid_master_key_size(mk, ci)) {
+		err = -ENOKEY;
+		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;
+
+	*mk_ret = mk;
+	return 0;
+
+out_release_key:
+	up_read(&mk->mk_sem);
+	fscrypt_put_master_key(mk);
+	return err;
+}
+
+static void put_crypt_info(struct fscrypt_info *ci)
+{
+	struct fscrypt_master_key *mk;
+
+	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_inode->i_sb,
+					     &ci->ci_enc_key);
+
+	mk = ci->ci_master_key;
+	if (mk) {
+		/*
+		 * 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 master key struct that already had its secret
+		 * removed, then complete the full removal of the struct.
+		 */
+		spin_lock(&mk->mk_decrypted_inodes_lock);
+		list_del(&ci->ci_master_key_link);
+		spin_unlock(&mk->mk_decrypted_inodes_lock);
+		fscrypt_put_master_key_activeref(mk);
+	}
+	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 fscrypt_master_key *mk = 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, &mk);
+	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 (mk) {
+			crypt_info->ci_master_key = mk;
+			refcount_inc(&mk->mk_active_refs);
+			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 (mk) {
+		up_read(&mk->mk_sem);
+		fscrypt_put_master_key(mk);
+	}
+	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);
+
+	/*
+	 * 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;
+
+	/*
+	 * 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(&ci->ci_master_key->mk_secret);
+}
+EXPORT_SYMBOL_GPL(fscrypt_drop_inode);