drm/modes: Fix drm_mode_vrefres() docs

[drm/drm-misc.git] / fs / crypto / keysetup.c

// 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-CBC-CTS",
                .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-CBC-CTS",
                .cipher_str = "cts(cbc(aes))",
                .keysize = 16,
                .security_strength = 16,
                .ivsize = 16,
        },
        [FSCRYPT_MODE_SM4_XTS] = {
                .friendly_name = "SM4-XTS",
                .cipher_str = "xts(sm4)",
                .keysize = 32,
                .security_strength = 16,
                .ivsize = 16,
                .blk_crypto_mode = BLK_ENCRYPTION_MODE_SM4_XTS,
        },
        [FSCRYPT_MODE_SM4_CTS] = {
                .friendly_name = "SM4-CBC-CTS",
                .cipher_str = "cts(cbc(sm4))",
                .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_ONCE(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_inode_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_inode_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_inode_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_ONCE(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_inode_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_inode_info *ci,
                               const struct fscrypt_master_key *mk)
{
        WARN_ON_ONCE(ci->ci_inode->i_ino == 0);
        WARN_ON_ONCE(!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_inode_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_inode_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_inode_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_inode_info into ->mk_decrypted_inodes
 * (as multiple tasks may race to create an fscrypt_inode_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_inode_info *ci,
                                     bool need_dirhash_key,
                                     struct fscrypt_master_key **mk_ret)
{
        struct super_block *sb = ci->ci_inode->i_sb;
        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(sb, &mk_spec);
        if (unlikely(!mk)) {
                const union fscrypt_policy *dummy_policy =
                        fscrypt_get_dummy_policy(sb);

                /*
                 * Add the test_dummy_encryption key on-demand.  In principle,
                 * it should be added at mount time.  Do it here instead so that
                 * the individual filesystems don't need to worry about adding
                 * this key at mount time and cleaning up on mount failure.
                 */
                if (dummy_policy &&
                    fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {
                        err = fscrypt_add_test_dummy_key(sb, &mk_spec);
                        if (err)
                                return err;
                        mk = fscrypt_find_master_key(sb, &mk_spec);
                }
        }
        if (unlikely(!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);

        if (!mk->mk_present) {
                /* FS_IOC_REMOVE_ENCRYPTION_KEY has been executed on this key */
                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_ONCE(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_inode_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 an incompletely removed key, then complete the
                 * full removal of the key.
                 */
                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(ci->ci_inode->i_sb, mk);
        }
        memzero_explicit(ci, sizeof(*ci));
        kmem_cache_free(fscrypt_inode_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_inode_info *crypt_info;
        struct fscrypt_mode *mode;
        struct fscrypt_master_key *mk = NULL;
        int res;

        res = fscrypt_initialize(inode->i_sb);
        if (res)
                return res;

        crypt_info = kmem_cache_zalloc(fscrypt_inode_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_ONCE(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
        crypt_info->ci_mode = mode;

        crypt_info->ci_data_unit_bits =
                fscrypt_policy_du_bits(&crypt_info->ci_policy, inode);
        crypt_info->ci_data_units_per_block_bits =
                inode->i_blkbits - crypt_info->ci_data_unit_bits;

        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_inode_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 and ->i_blkbits 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_blkbits == 0))
                return -EINVAL;

        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_inode_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_inode_info *ci = fscrypt_get_inode_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;

        /*
         * We can't take ->mk_sem here, since this runs in atomic context.
         * Therefore, ->mk_present can change concurrently, and our result may
         * 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 !READ_ONCE(ci->ci_master_key->mk_present);
}
EXPORT_SYMBOL_GPL(fscrypt_drop_inode);