// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2010 IBM Corporation
 * Copyright (C) 2010 Politecnico di Torino, Italy
 *                    TORSEC group -- https://security.polito.it
 *
 * Authors:
 * Mimi Zohar <zohar@us.ibm.com>
 * Roberto Sassu <roberto.sassu@polito.it>
 *
 * See Documentation/security/keys/trusted-encrypted.rst
 */

#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/parser.h>
#include <linux/string.h>
#include <linux/err.h>
#include <keys/user-type.h>
#include <keys/trusted-type.h>
#include <keys/encrypted-type.h>
#include <linux/key-type.h>
#include <linux/random.h>
#include <linux/rcupdate.h>
#include <linux/scatterlist.h>
#include <linux/ctype.h>
#include <crypto/aes.h>
#include <crypto/algapi.h>
#include <crypto/hash.h>
#include <crypto/sha2.h>
#include <crypto/skcipher.h>

#include "encrypted.h"
#include "ecryptfs_format.h"

static const char KEY_TRUSTED_PREFIX[] = "trusted:";
static const char KEY_USER_PREFIX[] = "user:";
static const char hash_alg[] = "sha256";
static const char hmac_alg[] = "hmac(sha256)";
static const char blkcipher_alg[] = "cbc(aes)";
static const char key_format_default[] = "default";
static const char key_format_ecryptfs[] = "ecryptfs";
static const char key_format_enc32[] = "enc32";
static unsigned int ivsize;
static int blksize;

#define KEY_TRUSTED_PREFIX_LEN (sizeof (KEY_TRUSTED_PREFIX) - 1)
#define KEY_USER_PREFIX_LEN (sizeof (KEY_USER_PREFIX) - 1)
#define KEY_ECRYPTFS_DESC_LEN 16
#define HASH_SIZE SHA256_DIGEST_SIZE
#define MAX_DATA_SIZE 4096
#define MIN_DATA_SIZE  20
#define KEY_ENC32_PAYLOAD_LEN 32

static struct crypto_shash *hash_tfm;

enum {
        Opt_new, Opt_load, Opt_update, Opt_err
};

enum {
        Opt_default, Opt_ecryptfs, Opt_enc32, Opt_error
};

static const match_table_t key_format_tokens = {
        {Opt_default, "default"},
        {Opt_ecryptfs, "ecryptfs"},
        {Opt_enc32, "enc32"},
        {Opt_error, NULL}
};

static const match_table_t key_tokens = {
        {Opt_new, "new"},
        {Opt_load, "load"},
        {Opt_update, "update"},
        {Opt_err, NULL}
};

static int aes_get_sizes(void)
{
        struct crypto_skcipher *tfm;

        tfm = crypto_alloc_skcipher(blkcipher_alg, 0, CRYPTO_ALG_ASYNC);
        if (IS_ERR(tfm)) {
                pr_err("encrypted_key: failed to alloc_cipher (%ld)\n",
                       PTR_ERR(tfm));
                return PTR_ERR(tfm);
        }
        ivsize = crypto_skcipher_ivsize(tfm);
        blksize = crypto_skcipher_blocksize(tfm);
        crypto_free_skcipher(tfm);
        return 0;
}

/*
 * valid_ecryptfs_desc - verify the description of a new/loaded encrypted key
 *
 * The description of a encrypted key with format 'ecryptfs' must contain
 * exactly 16 hexadecimal characters.
 *
 */
static int valid_ecryptfs_desc(const char *ecryptfs_desc)
{
        int i;

        if (strlen(ecryptfs_desc) != KEY_ECRYPTFS_DESC_LEN) {
                pr_err("encrypted_key: key description must be %d hexadecimal "
                       "characters long\n", KEY_ECRYPTFS_DESC_LEN);
                return -EINVAL;
        }

        for (i = 0; i < KEY_ECRYPTFS_DESC_LEN; i++) {
                if (!isxdigit(ecryptfs_desc[i])) {
                        pr_err("encrypted_key: key description must contain "
                               "only hexadecimal characters\n");
                        return -EINVAL;
                }
        }

        return 0;
}

/*
 * valid_master_desc - verify the 'key-type:desc' of a new/updated master-key
 *
 * key-type:= "trusted:" | "user:"
 * desc:= master-key description
 *
 * Verify that 'key-type' is valid and that 'desc' exists. On key update,
 * only the master key description is permitted to change, not the key-type.
 * The key-type remains constant.
 *
 * On success returns 0, otherwise -EINVAL.
 */
static int valid_master_desc(const char *new_desc, const char *orig_desc)
{
        int prefix_len;

        if (!strncmp(new_desc, KEY_TRUSTED_PREFIX, KEY_TRUSTED_PREFIX_LEN))
                prefix_len = KEY_TRUSTED_PREFIX_LEN;
        else if (!strncmp(new_desc, KEY_USER_PREFIX, KEY_USER_PREFIX_LEN))
                prefix_len = KEY_USER_PREFIX_LEN;
        else
                return -EINVAL;

        if (!new_desc[prefix_len])
                return -EINVAL;

        if (orig_desc && strncmp(new_desc, orig_desc, prefix_len))
                return -EINVAL;

        return 0;
}

/*
 * datablob_parse - parse the keyctl data
 *
 * datablob format:
 * new [<format>] <master-key name> <decrypted data length>
 * load [<format>] <master-key name> <decrypted data length>
 *     <encrypted iv + data>
 * update <new-master-key name>
 *
 * Tokenizes a copy of the keyctl data, returning a pointer to each token,
 * which is null terminated.
 *
 * On success returns 0, otherwise -EINVAL.
 */
static int datablob_parse(char *datablob, const char **format,
                          char **master_desc, char **decrypted_datalen,
                          char **hex_encoded_iv)
{
        substring_t args[MAX_OPT_ARGS];
        int ret = -EINVAL;
        int key_cmd;
        int key_format;
        char *p, *keyword;

        keyword = strsep(&datablob, " \t");
        if (!keyword) {
                pr_info("encrypted_key: insufficient parameters specified\n");
                return ret;
        }
        key_cmd = match_token(keyword, key_tokens, args);

        /* Get optional format: default | ecryptfs */
        p = strsep(&datablob, " \t");
        if (!p) {
                pr_err("encrypted_key: insufficient parameters specified\n");
                return ret;
        }

        key_format = match_token(p, key_format_tokens, args);
        switch (key_format) {
        case Opt_ecryptfs:
        case Opt_enc32:
        case Opt_default:
                *format = p;
                *master_desc = strsep(&datablob, " \t");
                break;
        case Opt_error:
                *master_desc = p;
                break;
        }

        if (!*master_desc) {
                pr_info("encrypted_key: master key parameter is missing\n");
                goto out;
        }

        if (valid_master_desc(*master_desc, NULL) < 0) {
                pr_info("encrypted_key: master key parameter \'%s\' "
                        "is invalid\n", *master_desc);
                goto out;
        }

        if (decrypted_datalen) {
                *decrypted_datalen = strsep(&datablob, " \t");
                if (!*decrypted_datalen) {
                        pr_info("encrypted_key: keylen parameter is missing\n");
                        goto out;
                }
        }

        switch (key_cmd) {
        case Opt_new:
                if (!decrypted_datalen) {
                        pr_info("encrypted_key: keyword \'%s\' not allowed "
                                "when called from .update method\n", keyword);
                        break;
                }
                ret = 0;
                break;
        case Opt_load:
                if (!decrypted_datalen) {
                        pr_info("encrypted_key: keyword \'%s\' not allowed "
                                "when called from .update method\n", keyword);
                        break;
                }
                *hex_encoded_iv = strsep(&datablob, " \t");
                if (!*hex_encoded_iv) {
                        pr_info("encrypted_key: hex blob is missing\n");
                        break;
                }
                ret = 0;
                break;
        case Opt_update:
                if (decrypted_datalen) {
                        pr_info("encrypted_key: keyword \'%s\' not allowed "
                                "when called from .instantiate method\n",
                                keyword);
                        break;
                }
                ret = 0;
                break;
        case Opt_err:
                pr_info("encrypted_key: keyword \'%s\' not recognized\n",
                        keyword);
                break;
        }
out:
        return ret;
}

/*
 * datablob_format - format as an ascii string, before copying to userspace
 */
static char *datablob_format(struct encrypted_key_payload *epayload,
                             size_t asciiblob_len)
{
        char *ascii_buf, *bufp;
        u8 *iv = epayload->iv;
        int len;
        int i;

        ascii_buf = kmalloc(asciiblob_len + 1, GFP_KERNEL);
        if (!ascii_buf)
                goto out;

        ascii_buf[asciiblob_len] = '\0';

        /* copy datablob master_desc and datalen strings */
        len = sprintf(ascii_buf, "%s %s %s ", epayload->format,
                      epayload->master_desc, epayload->datalen);

        /* convert the hex encoded iv, encrypted-data and HMAC to ascii */
        bufp = &ascii_buf[len];
        for (i = 0; i < (asciiblob_len - len) / 2; i++)
                bufp = hex_byte_pack(bufp, iv[i]);
out:
        return ascii_buf;
}

/*
 * request_user_key - request the user key
 *
 * Use a user provided key to encrypt/decrypt an encrypted-key.
 */
static struct key *request_user_key(const char *master_desc, const u8 **master_key,
                                    size_t *master_keylen)
{
        const struct user_key_payload *upayload;
        struct key *ukey;

        ukey = request_key(&key_type_user, master_desc, NULL);
        if (IS_ERR(ukey))
                goto error;

        down_read(&ukey->sem);
        upayload = user_key_payload_locked(ukey);
        if (!upayload) {
                /* key was revoked before we acquired its semaphore */
                up_read(&ukey->sem);
                key_put(ukey);
                ukey = ERR_PTR(-EKEYREVOKED);
                goto error;
        }
        *master_key = upayload->data;
        *master_keylen = upayload->datalen;
error:
        return ukey;
}

static int calc_hmac(u8 *digest, const u8 *key, unsigned int keylen,
                     const u8 *buf, unsigned int buflen)
{
        struct crypto_shash *tfm;
        int err;

        tfm = crypto_alloc_shash(hmac_alg, 0, 0);
        if (IS_ERR(tfm)) {
                pr_err("encrypted_key: can't alloc %s transform: %ld\n",
                       hmac_alg, PTR_ERR(tfm));
                return PTR_ERR(tfm);
        }

        err = crypto_shash_setkey(tfm, key, keylen);
        if (!err)
                err = crypto_shash_tfm_digest(tfm, buf, buflen, digest);
        crypto_free_shash(tfm);
        return err;
}

enum derived_key_type { ENC_KEY, AUTH_KEY };

/* Derive authentication/encryption key from trusted key */
static int get_derived_key(u8 *derived_key, enum derived_key_type key_type,
                           const u8 *master_key, size_t master_keylen)
{
        u8 *derived_buf;
        unsigned int derived_buf_len;
        int ret;

        derived_buf_len = strlen("AUTH_KEY") + 1 + master_keylen;
        if (derived_buf_len < HASH_SIZE)
                derived_buf_len = HASH_SIZE;

        derived_buf = kzalloc(derived_buf_len, GFP_KERNEL);
        if (!derived_buf)
                return -ENOMEM;

        if (key_type)
                strcpy(derived_buf, "AUTH_KEY");
        else
                strcpy(derived_buf, "ENC_KEY");

        memcpy(derived_buf + strlen(derived_buf) + 1, master_key,
               master_keylen);
        ret = crypto_shash_tfm_digest(hash_tfm, derived_buf, derived_buf_len,
                                      derived_key);
        kfree_sensitive(derived_buf);
        return ret;
}

static struct skcipher_request *init_skcipher_req(const u8 *key,
                                                  unsigned int key_len)
{
        struct skcipher_request *req;
        struct crypto_skcipher *tfm;
        int ret;

        tfm = crypto_alloc_skcipher(blkcipher_alg, 0, CRYPTO_ALG_ASYNC);
        if (IS_ERR(tfm)) {
                pr_err("encrypted_key: failed to load %s transform (%ld)\n",
                       blkcipher_alg, PTR_ERR(tfm));
                return ERR_CAST(tfm);
        }

        ret = crypto_skcipher_setkey(tfm, key, key_len);
        if (ret < 0) {
                pr_err("encrypted_key: failed to setkey (%d)\n", ret);
                crypto_free_skcipher(tfm);
                return ERR_PTR(ret);
        }

        req = skcipher_request_alloc(tfm, GFP_KERNEL);
        if (!req) {
                pr_err("encrypted_key: failed to allocate request for %s\n",
                       blkcipher_alg);
                crypto_free_skcipher(tfm);
                return ERR_PTR(-ENOMEM);
        }

        skcipher_request_set_callback(req, 0, NULL, NULL);
        return req;
}

static struct key *request_master_key(struct encrypted_key_payload *epayload,
                                      const u8 **master_key, size_t *master_keylen)
{
        struct key *mkey = ERR_PTR(-EINVAL);

        if (!strncmp(epayload->master_desc, KEY_TRUSTED_PREFIX,
                     KEY_TRUSTED_PREFIX_LEN)) {
                mkey = request_trusted_key(epayload->master_desc +
                                           KEY_TRUSTED_PREFIX_LEN,
                                           master_key, master_keylen);
        } else if (!strncmp(epayload->master_desc, KEY_USER_PREFIX,
                            KEY_USER_PREFIX_LEN)) {
                mkey = request_user_key(epayload->master_desc +
                                        KEY_USER_PREFIX_LEN,
                                        master_key, master_keylen);
        } else
                goto out;

        if (IS_ERR(mkey)) {
                int ret = PTR_ERR(mkey);

                if (ret == -ENOTSUPP)
                        pr_info("encrypted_key: key %s not supported",
                                epayload->master_desc);
                else
                        pr_info("encrypted_key: key %s not found",
                                epayload->master_desc);
                goto out;
        }

        dump_master_key(*master_key, *master_keylen);
out:
        return mkey;
}

/* Before returning data to userspace, encrypt decrypted data. */
static int derived_key_encrypt(struct encrypted_key_payload *epayload,
                               const u8 *derived_key,
                               unsigned int derived_keylen)
{
        struct scatterlist sg_in[2];
        struct scatterlist sg_out[1];
        struct crypto_skcipher *tfm;
        struct skcipher_request *req;
        unsigned int encrypted_datalen;
        u8 iv[AES_BLOCK_SIZE];
        int ret;

        encrypted_datalen = roundup(epayload->decrypted_datalen, blksize);

        req = init_skcipher_req(derived_key, derived_keylen);
        ret = PTR_ERR(req);
        if (IS_ERR(req))
                goto out;
        dump_decrypted_data(epayload);

        sg_init_table(sg_in, 2);
        sg_set_buf(&sg_in[0], epayload->decrypted_data,
                   epayload->decrypted_datalen);
        sg_set_page(&sg_in[1], ZERO_PAGE(0), AES_BLOCK_SIZE, 0);

        sg_init_table(sg_out, 1);
        sg_set_buf(sg_out, epayload->encrypted_data, encrypted_datalen);

        memcpy(iv, epayload->iv, sizeof(iv));
        skcipher_request_set_crypt(req, sg_in, sg_out, encrypted_datalen, iv);
        ret = crypto_skcipher_encrypt(req);
        tfm = crypto_skcipher_reqtfm(req);
        skcipher_request_free(req);
        crypto_free_skcipher(tfm);
        if (ret < 0)
                pr_err("encrypted_key: failed to encrypt (%d)\n", ret);
        else
                dump_encrypted_data(epayload, encrypted_datalen);
out:
        return ret;
}

static int datablob_hmac_append(struct encrypted_key_payload *epayload,
                                const u8 *master_key, size_t master_keylen)
{
        u8 derived_key[HASH_SIZE];
        u8 *digest;
        int ret;

        ret = get_derived_key(derived_key, AUTH_KEY, master_key, master_keylen);
        if (ret < 0)
                goto out;

        digest = epayload->format + epayload->datablob_len;
        ret = calc_hmac(digest, derived_key, sizeof derived_key,
                        epayload->format, epayload->datablob_len);
        if (!ret)
                dump_hmac(NULL, digest, HASH_SIZE);
out:
        memzero_explicit(derived_key, sizeof(derived_key));
        return ret;
}

/* verify HMAC before decrypting encrypted key */
static int datablob_hmac_verify(struct encrypted_key_payload *epayload,
                                const u8 *format, const u8 *master_key,
                                size_t master_keylen)
{
        u8 derived_key[HASH_SIZE];
        u8 digest[HASH_SIZE];
        int ret;
        char *p;
        unsigned short len;

        ret = get_derived_key(derived_key, AUTH_KEY, master_key, master_keylen);
        if (ret < 0)
                goto out;

        len = epayload->datablob_len;
        if (!format) {
                p = epayload->master_desc;
                len -= strlen(epayload->format) + 1;
        } else
                p = epayload->format;

        ret = calc_hmac(digest, derived_key, sizeof derived_key, p, len);
        if (ret < 0)
                goto out;
        ret = crypto_memneq(digest, epayload->format + epayload->datablob_len,
                            sizeof(digest));
        if (ret) {
                ret = -EINVAL;
                dump_hmac("datablob",
                          epayload->format + epayload->datablob_len,
                          HASH_SIZE);
                dump_hmac("calc", digest, HASH_SIZE);
        }
out:
        memzero_explicit(derived_key, sizeof(derived_key));
        return ret;
}

static int derived_key_decrypt(struct encrypted_key_payload *epayload,
                               const u8 *derived_key,
                               unsigned int derived_keylen)
{
        struct scatterlist sg_in[1];
        struct scatterlist sg_out[2];
        struct crypto_skcipher *tfm;
        struct skcipher_request *req;
        unsigned int encrypted_datalen;
        u8 iv[AES_BLOCK_SIZE];
        u8 *pad;
        int ret;

        /* Throwaway buffer to hold the unused zero padding at the end */
        pad = kmalloc(AES_BLOCK_SIZE, GFP_KERNEL);
        if (!pad)
                return -ENOMEM;

        encrypted_datalen = roundup(epayload->decrypted_datalen, blksize);
        req = init_skcipher_req(derived_key, derived_keylen);
        ret = PTR_ERR(req);
        if (IS_ERR(req))
                goto out;
        dump_encrypted_data(epayload, encrypted_datalen);

        sg_init_table(sg_in, 1);
        sg_init_table(sg_out, 2);
        sg_set_buf(sg_in, epayload->encrypted_data, encrypted_datalen);
        sg_set_buf(&sg_out[0], epayload->decrypted_data,
                   epayload->decrypted_datalen);
        sg_set_buf(&sg_out[1], pad, AES_BLOCK_SIZE);

        memcpy(iv, epayload->iv, sizeof(iv));
        skcipher_request_set_crypt(req, sg_in, sg_out, encrypted_datalen, iv);
        ret = crypto_skcipher_decrypt(req);
        tfm = crypto_skcipher_reqtfm(req);
        skcipher_request_free(req);
        crypto_free_skcipher(tfm);
        if (ret < 0)
                goto out;
        dump_decrypted_data(epayload);
out:
        kfree(pad);
        return ret;
}

/* Allocate memory for decrypted key and datablob. */
static struct encrypted_key_payload *encrypted_key_alloc(struct key *key,
                                                         const char *format,
                                                         const char *master_desc,
                                                         const char *datalen)
{
        struct encrypted_key_payload *epayload = NULL;
        unsigned short datablob_len;
        unsigned short decrypted_datalen;
        unsigned short payload_datalen;
        unsigned int encrypted_datalen;
        unsigned int format_len;
        long dlen;
        int ret;

        ret = kstrtol(datalen, 10, &dlen);
        if (ret < 0 || dlen < MIN_DATA_SIZE || dlen > MAX_DATA_SIZE)
                return ERR_PTR(-EINVAL);

        format_len = (!format) ? strlen(key_format_default) : strlen(format);
        decrypted_datalen = dlen;
        payload_datalen = decrypted_datalen;
        if (format) {
                if (!strcmp(format, key_format_ecryptfs)) {
                        if (dlen != ECRYPTFS_MAX_KEY_BYTES) {
                                pr_err("encrypted_key: keylen for the ecryptfs format must be equal to %d bytes\n",
                                        ECRYPTFS_MAX_KEY_BYTES);
                                return ERR_PTR(-EINVAL);
                        }
                        decrypted_datalen = ECRYPTFS_MAX_KEY_BYTES;
                        payload_datalen = sizeof(struct ecryptfs_auth_tok);
                } else if (!strcmp(format, key_format_enc32)) {
                        if (decrypted_datalen != KEY_ENC32_PAYLOAD_LEN) {
                                pr_err("encrypted_key: enc32 key payload incorrect length: %d\n",
                                                decrypted_datalen);
                                return ERR_PTR(-EINVAL);
                        }
                }
        }

        encrypted_datalen = roundup(decrypted_datalen, blksize);

        datablob_len = format_len + 1 + strlen(master_desc) + 1
            + strlen(datalen) + 1 + ivsize + 1 + encrypted_datalen;

        ret = key_payload_reserve(key, payload_datalen + datablob_len
                                  + HASH_SIZE + 1);
        if (ret < 0)
                return ERR_PTR(ret);

        epayload = kzalloc(sizeof(*epayload) + payload_datalen +
                           datablob_len + HASH_SIZE + 1, GFP_KERNEL);
        if (!epayload)
                return ERR_PTR(-ENOMEM);

        epayload->payload_datalen = payload_datalen;
        epayload->decrypted_datalen = decrypted_datalen;
        epayload->datablob_len = datablob_len;
        return epayload;
}

static int encrypted_key_decrypt(struct encrypted_key_payload *epayload,
                                 const char *format, const char *hex_encoded_iv)
{
        struct key *mkey;
        u8 derived_key[HASH_SIZE];
        const u8 *master_key;
        u8 *hmac;
        const char *hex_encoded_data;
        unsigned int encrypted_datalen;
        size_t master_keylen;
        size_t asciilen;
        int ret;

        encrypted_datalen = roundup(epayload->decrypted_datalen, blksize);
        asciilen = (ivsize + 1 + encrypted_datalen + HASH_SIZE) * 2;
        if (strlen(hex_encoded_iv) != asciilen)
                return -EINVAL;

        hex_encoded_data = hex_encoded_iv + (2 * ivsize) + 2;
        ret = hex2bin(epayload->iv, hex_encoded_iv, ivsize);
        if (ret < 0)
                return -EINVAL;
        ret = hex2bin(epayload->encrypted_data, hex_encoded_data,
                      encrypted_datalen);
        if (ret < 0)
                return -EINVAL;

        hmac = epayload->format + epayload->datablob_len;
        ret = hex2bin(hmac, hex_encoded_data + (encrypted_datalen * 2),
                      HASH_SIZE);
        if (ret < 0)
                return -EINVAL;

        mkey = request_master_key(epayload, &master_key, &master_keylen);
        if (IS_ERR(mkey))
                return PTR_ERR(mkey);

        ret = datablob_hmac_verify(epayload, format, master_key, master_keylen);
        if (ret < 0) {
                pr_err("encrypted_key: bad hmac (%d)\n", ret);
                goto out;
        }

        ret = get_derived_key(derived_key, ENC_KEY, master_key, master_keylen);
        if (ret < 0)
                goto out;

        ret = derived_key_decrypt(epayload, derived_key, sizeof derived_key);
        if (ret < 0)
                pr_err("encrypted_key: failed to decrypt key (%d)\n", ret);
out:
        up_read(&mkey->sem);
        key_put(mkey);
        memzero_explicit(derived_key, sizeof(derived_key));
        return ret;
}

static void __ekey_init(struct encrypted_key_payload *epayload,
                        const char *format, const char *master_desc,
                        const char *datalen)
{
        unsigned int format_len;

        format_len = (!format) ? strlen(key_format_default) : strlen(format);
        epayload->format = epayload->payload_data + epayload->payload_datalen;
        epayload->master_desc = epayload->format + format_len + 1;
        epayload->datalen = epayload->master_desc + strlen(master_desc) + 1;
        epayload->iv = epayload->datalen + strlen(datalen) + 1;
        epayload->encrypted_data = epayload->iv + ivsize + 1;
        epayload->decrypted_data = epayload->payload_data;

        if (!format)
                memcpy(epayload->format, key_format_default, format_len);
        else {
                if (!strcmp(format, key_format_ecryptfs))
                        epayload->decrypted_data =
                                ecryptfs_get_auth_tok_key((struct ecryptfs_auth_tok *)epayload->payload_data);

                memcpy(epayload->format, format, format_len);
        }

        memcpy(epayload->master_desc, master_desc, strlen(master_desc));
        memcpy(epayload->datalen, datalen, strlen(datalen));
}

/*
 * encrypted_init - initialize an encrypted key
 *
 * For a new key, use a random number for both the iv and data
 * itself.  For an old key, decrypt the hex encoded data.
 */
static int encrypted_init(struct encrypted_key_payload *epayload,
                          const char *key_desc, const char *format,
                          const char *master_desc, const char *datalen,
                          const char *hex_encoded_iv)
{
        int ret = 0;

        if (format && !strcmp(format, key_format_ecryptfs)) {
                ret = valid_ecryptfs_desc(key_desc);
                if (ret < 0)
                        return ret;

                ecryptfs_fill_auth_tok((struct ecryptfs_auth_tok *)epayload->payload_data,
                                       key_desc);
        }

        __ekey_init(epayload, format, master_desc, datalen);
        if (!hex_encoded_iv) {
                get_random_bytes(epayload->iv, ivsize);

                get_random_bytes(epayload->decrypted_data,
                                 epayload->decrypted_datalen);
        } else
                ret = encrypted_key_decrypt(epayload, format, hex_encoded_iv);
        return ret;
}

/*
 * encrypted_instantiate - instantiate an encrypted key
 *
 * Decrypt an existing encrypted datablob or create a new encrypted key
 * based on a kernel random number.
 *
 * On success, return 0. Otherwise return errno.
 */
static int encrypted_instantiate(struct key *key,
                                 struct key_preparsed_payload *prep)
{
        struct encrypted_key_payload *epayload = NULL;
        char *datablob = NULL;
        const char *format = NULL;
        char *master_desc = NULL;
        char *decrypted_datalen = NULL;
        char *hex_encoded_iv = NULL;
        size_t datalen = prep->datalen;
        int ret;

        if (datalen <= 0 || datalen > 32767 || !prep->data)
                return -EINVAL;

        datablob = kmalloc(datalen + 1, GFP_KERNEL);
        if (!datablob)
                return -ENOMEM;
        datablob[datalen] = 0;
        memcpy(datablob, prep->data, datalen);
        ret = datablob_parse(datablob, &format, &master_desc,
                             &decrypted_datalen, &hex_encoded_iv);
        if (ret < 0)
                goto out;

        epayload = encrypted_key_alloc(key, format, master_desc,
                                       decrypted_datalen);
        if (IS_ERR(epayload)) {
                ret = PTR_ERR(epayload);
                goto out;
        }
        ret = encrypted_init(epayload, key->description, format, master_desc,
                             decrypted_datalen, hex_encoded_iv);
        if (ret < 0) {
                kfree_sensitive(epayload);
                goto out;
        }

        rcu_assign_keypointer(key, epayload);
out:
        kfree_sensitive(datablob);
        return ret;
}

static void encrypted_rcu_free(struct rcu_head *rcu)
{
        struct encrypted_key_payload *epayload;

        epayload = container_of(rcu, struct encrypted_key_payload, rcu);
        kfree_sensitive(epayload);
}

/*
 * encrypted_update - update the master key description
 *
 * Change the master key description for an existing encrypted key.
 * The next read will return an encrypted datablob using the new
 * master key description.
 *
 * On success, return 0. Otherwise return errno.
 */
static int encrypted_update(struct key *key, struct key_preparsed_payload *prep)
{
        struct encrypted_key_payload *epayload = key->payload.data[0];
        struct encrypted_key_payload *new_epayload;
        char *buf;
        char *new_master_desc = NULL;
        const char *format = NULL;
        size_t datalen = prep->datalen;
        int ret = 0;

        if (key_is_negative(key))
                return -ENOKEY;
        if (datalen <= 0 || datalen > 32767 || !prep->data)
                return -EINVAL;

        buf = kmalloc(datalen + 1, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        buf[datalen] = 0;
        memcpy(buf, prep->data, datalen);
        ret = datablob_parse(buf, &format, &new_master_desc, NULL, NULL);
        if (ret < 0)
                goto out;

        ret = valid_master_desc(new_master_desc, epayload->master_desc);
        if (ret < 0)
                goto out;

        new_epayload = encrypted_key_alloc(key, epayload->format,
                                           new_master_desc, epayload->datalen);
        if (IS_ERR(new_epayload)) {
                ret = PTR_ERR(new_epayload);
                goto out;
        }

        __ekey_init(new_epayload, epayload->format, new_master_desc,
                    epayload->datalen);

        memcpy(new_epayload->iv, epayload->iv, ivsize);
        memcpy(new_epayload->payload_data, epayload->payload_data,
               epayload->payload_datalen);

        rcu_assign_keypointer(key, new_epayload);
        call_rcu(&epayload->rcu, encrypted_rcu_free);
out:
        kfree_sensitive(buf);
        return ret;
}

/*
 * encrypted_read - format and copy out the encrypted data
 *
 * The resulting datablob format is:
 * <master-key name> <decrypted data length> <encrypted iv> <encrypted data>
 *
 * On success, return to userspace the encrypted key datablob size.
 */
static long encrypted_read(const struct key *key, char *buffer,
                           size_t buflen)
{
        struct encrypted_key_payload *epayload;
        struct key *mkey;
        const u8 *master_key;
        size_t master_keylen;
        char derived_key[HASH_SIZE];
        char *ascii_buf;
        size_t asciiblob_len;
        int ret;

        epayload = dereference_key_locked(key);

        /* returns the hex encoded iv, encrypted-data, and hmac as ascii */
        asciiblob_len = epayload->datablob_len + ivsize + 1
            + roundup(epayload->decrypted_datalen, blksize)
            + (HASH_SIZE * 2);

        if (!buffer || buflen < asciiblob_len)
                return asciiblob_len;

        mkey = request_master_key(epayload, &master_key, &master_keylen);
        if (IS_ERR(mkey))
                return PTR_ERR(mkey);

        ret = get_derived_key(derived_key, ENC_KEY, master_key, master_keylen);
        if (ret < 0)
                goto out;

        ret = derived_key_encrypt(epayload, derived_key, sizeof derived_key);
        if (ret < 0)
                goto out;

        ret = datablob_hmac_append(epayload, master_key, master_keylen);
        if (ret < 0)
                goto out;

        ascii_buf = datablob_format(epayload, asciiblob_len);
        if (!ascii_buf) {
                ret = -ENOMEM;
                goto out;
        }

        up_read(&mkey->sem);
        key_put(mkey);
        memzero_explicit(derived_key, sizeof(derived_key));

        memcpy(buffer, ascii_buf, asciiblob_len);
        kfree_sensitive(ascii_buf);

        return asciiblob_len;
out:
        up_read(&mkey->sem);
        key_put(mkey);
        memzero_explicit(derived_key, sizeof(derived_key));
        return ret;
}

/*
 * encrypted_destroy - clear and free the key's payload
 */
static void encrypted_destroy(struct key *key)
{
        kfree_sensitive(key->payload.data[0]);
}

struct key_type key_type_encrypted = {
        .name = "encrypted",
        .instantiate = encrypted_instantiate,
        .update = encrypted_update,
        .destroy = encrypted_destroy,
        .describe = user_describe,
        .read = encrypted_read,
};
EXPORT_SYMBOL_GPL(key_type_encrypted);

static int __init init_encrypted(void)
{
        int ret;

        hash_tfm = crypto_alloc_shash(hash_alg, 0, 0);
        if (IS_ERR(hash_tfm)) {
                pr_err("encrypted_key: can't allocate %s transform: %ld\n",
                       hash_alg, PTR_ERR(hash_tfm));
                return PTR_ERR(hash_tfm);
        }

        ret = aes_get_sizes();
        if (ret < 0)
                goto out;
        ret = register_key_type(&key_type_encrypted);
        if (ret < 0)
                goto out;
        return 0;
out:
        crypto_free_shash(hash_tfm);
        return ret;

}

static void __exit cleanup_encrypted(void)
{
        crypto_free_shash(hash_tfm);
        unregister_key_type(&key_type_encrypted);
}

late_initcall(init_encrypted);
module_exit(cleanup_encrypted);

MODULE_LICENSE("GPL");