crypto/essiv.c

root/crypto/essiv.c
// SPDX-License-Identifier: GPL-2.0
/*
 * ESSIV skcipher and aead template for block encryption
 *
 * This template encapsulates the ESSIV IV generation algorithm used by
 * dm-crypt and fscrypt, which converts the initial vector for the skcipher
 * used for block encryption, by encrypting it using the hash of the
 * skcipher key as encryption key. Usually, the input IV is a 64-bit sector
 * number in LE representation zero-padded to the size of the IV, but this
 * is not assumed by this driver.
 *
 * The typical use of this template is to instantiate the skcipher
 * 'essiv(cbc(aes),sha256)', which is the only instantiation used by
 * fscrypt, and the most relevant one for dm-crypt. However, dm-crypt
 * also permits ESSIV to be used in combination with the authenc template,
 * e.g., 'essiv(authenc(hmac(sha256),cbc(aes)),sha256)', in which case
 * we need to instantiate an aead that accepts the same special key format
 * as the authenc template, and deals with the way the encrypted IV is
 * embedded into the AAD area of the aead request. This means the AEAD
 * flavor produced by this template is tightly coupled to the way dm-crypt
 * happens to use it.
 *
 * Copyright (c) 2019 Linaro, Ltd. <ard.biesheuvel@linaro.org>
 *
 * Heavily based on:
 * adiantum length-preserving encryption mode
 *
 * Copyright 2018 Google LLC
 */

#include <crypto/authenc.h>
#include <crypto/internal/aead.h>
#include <crypto/internal/cipher.h>
#include <crypto/internal/hash.h>
#include <crypto/internal/skcipher.h>
#include <crypto/scatterwalk.h>
#include <linux/module.h>

#include "internal.h"

struct essiv_instance_ctx {
        union {
                struct crypto_skcipher_spawn    skcipher_spawn;
                struct crypto_aead_spawn        aead_spawn;
        } u;
        char    essiv_cipher_name[CRYPTO_MAX_ALG_NAME];
        char    shash_driver_name[CRYPTO_MAX_ALG_NAME];
};

struct essiv_tfm_ctx {
        union {
                struct crypto_skcipher  *skcipher;
                struct crypto_aead      *aead;
        } u;
        struct crypto_cipher            *essiv_cipher;
        struct crypto_shash             *hash;
        int                             ivoffset;
};

struct essiv_aead_request_ctx {
        struct scatterlist              sg[4];
        u8                              *assoc;
        struct aead_request             aead_req;
};

static int essiv_skcipher_setkey(struct crypto_skcipher *tfm,
                                 const u8 *key, unsigned int keylen)
{
        struct essiv_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
        u8 salt[HASH_MAX_DIGESTSIZE];
        int err;

        crypto_skcipher_clear_flags(tctx->u.skcipher, CRYPTO_TFM_REQ_MASK);
        crypto_skcipher_set_flags(tctx->u.skcipher,
                                  crypto_skcipher_get_flags(tfm) &
                                  CRYPTO_TFM_REQ_MASK);
        err = crypto_skcipher_setkey(tctx->u.skcipher, key, keylen);
        if (err)
                return err;

        err = crypto_shash_tfm_digest(tctx->hash, key, keylen, salt);
        if (err)
                return err;

        crypto_cipher_clear_flags(tctx->essiv_cipher, CRYPTO_TFM_REQ_MASK);
        crypto_cipher_set_flags(tctx->essiv_cipher,
                                crypto_skcipher_get_flags(tfm) &
                                CRYPTO_TFM_REQ_MASK);
        return crypto_cipher_setkey(tctx->essiv_cipher, salt,
                                    crypto_shash_digestsize(tctx->hash));
}

static int essiv_aead_setkey(struct crypto_aead *tfm, const u8 *key,
                             unsigned int keylen)
{
        struct essiv_tfm_ctx *tctx = crypto_aead_ctx(tfm);
        SHASH_DESC_ON_STACK(desc, tctx->hash);
        struct crypto_authenc_keys keys;
        u8 salt[HASH_MAX_DIGESTSIZE];
        int err;

        crypto_aead_clear_flags(tctx->u.aead, CRYPTO_TFM_REQ_MASK);
        crypto_aead_set_flags(tctx->u.aead, crypto_aead_get_flags(tfm) &
                                            CRYPTO_TFM_REQ_MASK);
        err = crypto_aead_setkey(tctx->u.aead, key, keylen);
        if (err)
                return err;

        if (crypto_authenc_extractkeys(&keys, key, keylen) != 0)
                return -EINVAL;

        desc->tfm = tctx->hash;
        err = crypto_shash_init(desc) ?:
              crypto_shash_update(desc, keys.enckey, keys.enckeylen) ?:
              crypto_shash_finup(desc, keys.authkey, keys.authkeylen, salt);
        if (err)
                return err;

        crypto_cipher_clear_flags(tctx->essiv_cipher, CRYPTO_TFM_REQ_MASK);
        crypto_cipher_set_flags(tctx->essiv_cipher, crypto_aead_get_flags(tfm) &
                                                    CRYPTO_TFM_REQ_MASK);
        return crypto_cipher_setkey(tctx->essiv_cipher, salt,
                                    crypto_shash_digestsize(tctx->hash));
}

static int essiv_aead_setauthsize(struct crypto_aead *tfm,
                                  unsigned int authsize)
{
        struct essiv_tfm_ctx *tctx = crypto_aead_ctx(tfm);

        return crypto_aead_setauthsize(tctx->u.aead, authsize);
}

static void essiv_skcipher_done(void *data, int err)
{
        struct skcipher_request *req = data;

        skcipher_request_complete(req, err);
}

static int essiv_skcipher_crypt(struct skcipher_request *req, bool enc)
{
        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
        const struct essiv_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
        struct skcipher_request *subreq = skcipher_request_ctx(req);

        crypto_cipher_encrypt_one(tctx->essiv_cipher, req->iv, req->iv);

        skcipher_request_set_tfm(subreq, tctx->u.skcipher);
        skcipher_request_set_crypt(subreq, req->src, req->dst, req->cryptlen,
                                   req->iv);
        skcipher_request_set_callback(subreq, skcipher_request_flags(req),
                                      essiv_skcipher_done, req);

        return enc ? crypto_skcipher_encrypt(subreq) :
                     crypto_skcipher_decrypt(subreq);
}

static int essiv_skcipher_encrypt(struct skcipher_request *req)
{
        return essiv_skcipher_crypt(req, true);
}

static int essiv_skcipher_decrypt(struct skcipher_request *req)
{
        return essiv_skcipher_crypt(req, false);
}

static void essiv_aead_done(void *data, int err)
{
        struct aead_request *req = data;
        struct essiv_aead_request_ctx *rctx = aead_request_ctx(req);

        if (err == -EINPROGRESS)
                goto out;

        kfree(rctx->assoc);

out:
        aead_request_complete(req, err);
}

static int essiv_aead_crypt(struct aead_request *req, bool enc)
{
        struct crypto_aead *tfm = crypto_aead_reqtfm(req);
        const struct essiv_tfm_ctx *tctx = crypto_aead_ctx(tfm);
        struct essiv_aead_request_ctx *rctx = aead_request_ctx(req);
        struct aead_request *subreq = &rctx->aead_req;
        int ivsize = crypto_aead_ivsize(tfm);
        int ssize = req->assoclen - ivsize;
        struct scatterlist *src = req->src;
        int err;

        if (ssize < 0)
                return -EINVAL;

        crypto_cipher_encrypt_one(tctx->essiv_cipher, req->iv, req->iv);

        /*
         * dm-crypt embeds the sector number and the IV in the AAD region, so
         * we have to copy the converted IV into the right scatterlist before
         * we pass it on.
         */
        rctx->assoc = NULL;
        if (req->src == req->dst || !enc) {
                scatterwalk_map_and_copy(req->iv, req->dst, ssize, ivsize, 1);
        } else {
                u8 *iv = (u8 *)aead_request_ctx(req) + tctx->ivoffset;
                struct scatterlist *sg;
                int nents;

                nents = sg_nents_for_len(req->src, ssize);
                if (nents < 0)
                        return -EINVAL;

                memcpy(iv, req->iv, ivsize);
                sg_init_table(rctx->sg, 4);

                if (unlikely(nents > 1)) {
                        /*
                         * This is a case that rarely occurs in practice, but
                         * for correctness, we have to deal with it nonetheless.
                         */
                        rctx->assoc = kmalloc(ssize, GFP_ATOMIC);
                        if (!rctx->assoc)
                                return -ENOMEM;

                        scatterwalk_map_and_copy(rctx->assoc, req->src, 0,
                                                 ssize, 0);
                        sg_set_buf(rctx->sg, rctx->assoc, ssize);
                } else {
                        sg_set_page(rctx->sg, sg_page(req->src), ssize,
                                    req->src->offset);
                }

                sg_set_buf(rctx->sg + 1, iv, ivsize);
                sg = scatterwalk_ffwd(rctx->sg + 2, req->src, req->assoclen);
                if (sg != rctx->sg + 2)
                        sg_chain(rctx->sg, 3, sg);

                src = rctx->sg;
        }

        aead_request_set_tfm(subreq, tctx->u.aead);
        aead_request_set_ad(subreq, req->assoclen);
        aead_request_set_callback(subreq, aead_request_flags(req),
                                  essiv_aead_done, req);
        aead_request_set_crypt(subreq, src, req->dst, req->cryptlen, req->iv);

        err = enc ? crypto_aead_encrypt(subreq) :
                    crypto_aead_decrypt(subreq);

        if (rctx->assoc && err != -EINPROGRESS && err != -EBUSY)
                kfree(rctx->assoc);
        return err;
}

static int essiv_aead_encrypt(struct aead_request *req)
{
        return essiv_aead_crypt(req, true);
}

static int essiv_aead_decrypt(struct aead_request *req)
{
        return essiv_aead_crypt(req, false);
}

static int essiv_init_tfm(struct essiv_instance_ctx *ictx,
                          struct essiv_tfm_ctx *tctx)
{
        struct crypto_cipher *essiv_cipher;
        struct crypto_shash *hash;
        int err;

        essiv_cipher = crypto_alloc_cipher(ictx->essiv_cipher_name, 0, 0);
        if (IS_ERR(essiv_cipher))
                return PTR_ERR(essiv_cipher);

        hash = crypto_alloc_shash(ictx->shash_driver_name, 0, 0);
        if (IS_ERR(hash)) {
                err = PTR_ERR(hash);
                goto err_free_essiv_cipher;
        }

        tctx->essiv_cipher = essiv_cipher;
        tctx->hash = hash;

        return 0;

err_free_essiv_cipher:
        crypto_free_cipher(essiv_cipher);
        return err;
}

static int essiv_skcipher_init_tfm(struct crypto_skcipher *tfm)
{
        struct skcipher_instance *inst = skcipher_alg_instance(tfm);
        struct essiv_instance_ctx *ictx = skcipher_instance_ctx(inst);
        struct essiv_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
        struct crypto_skcipher *skcipher;
        int err;

        skcipher = crypto_spawn_skcipher(&ictx->u.skcipher_spawn);
        if (IS_ERR(skcipher))
                return PTR_ERR(skcipher);

        crypto_skcipher_set_reqsize(tfm, sizeof(struct skcipher_request) +
                                         crypto_skcipher_reqsize(skcipher));

        err = essiv_init_tfm(ictx, tctx);
        if (err) {
                crypto_free_skcipher(skcipher);
                return err;
        }

        tctx->u.skcipher = skcipher;
        return 0;
}

static int essiv_aead_init_tfm(struct crypto_aead *tfm)
{
        struct aead_instance *inst = aead_alg_instance(tfm);
        struct essiv_instance_ctx *ictx = aead_instance_ctx(inst);
        struct essiv_tfm_ctx *tctx = crypto_aead_ctx(tfm);
        struct crypto_aead *aead;
        unsigned int subreq_size;
        int err;

        BUILD_BUG_ON(offsetofend(struct essiv_aead_request_ctx, aead_req) !=
                     sizeof(struct essiv_aead_request_ctx));

        aead = crypto_spawn_aead(&ictx->u.aead_spawn);
        if (IS_ERR(aead))
                return PTR_ERR(aead);

        subreq_size = sizeof_field(struct essiv_aead_request_ctx, aead_req) +
                      crypto_aead_reqsize(aead);

        tctx->ivoffset = offsetof(struct essiv_aead_request_ctx, aead_req) +
                         subreq_size;
        crypto_aead_set_reqsize(tfm, tctx->ivoffset + crypto_aead_ivsize(aead));

        err = essiv_init_tfm(ictx, tctx);
        if (err) {
                crypto_free_aead(aead);
                return err;
        }

        tctx->u.aead = aead;
        return 0;
}

static void essiv_skcipher_exit_tfm(struct crypto_skcipher *tfm)
{
        struct essiv_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);

        crypto_free_skcipher(tctx->u.skcipher);
        crypto_free_cipher(tctx->essiv_cipher);
        crypto_free_shash(tctx->hash);
}

static void essiv_aead_exit_tfm(struct crypto_aead *tfm)
{
        struct essiv_tfm_ctx *tctx = crypto_aead_ctx(tfm);

        crypto_free_aead(tctx->u.aead);
        crypto_free_cipher(tctx->essiv_cipher);
        crypto_free_shash(tctx->hash);
}

static void essiv_skcipher_free_instance(struct skcipher_instance *inst)
{
        struct essiv_instance_ctx *ictx = skcipher_instance_ctx(inst);

        crypto_drop_skcipher(&ictx->u.skcipher_spawn);
        kfree(inst);
}

static void essiv_aead_free_instance(struct aead_instance *inst)
{
        struct essiv_instance_ctx *ictx = aead_instance_ctx(inst);

        crypto_drop_aead(&ictx->u.aead_spawn);
        kfree(inst);
}

static bool parse_cipher_name(char *essiv_cipher_name, const char *cra_name)
{
        const char *p, *q;
        int len;

        /* find the last opening parens */
        p = strrchr(cra_name, '(');
        if (!p++)
                return false;

        /* find the first closing parens in the tail of the string */
        q = strchr(p, ')');
        if (!q)
                return false;

        len = q - p;
        if (len >= CRYPTO_MAX_ALG_NAME)
                return false;

        strscpy(essiv_cipher_name, p, len + 1);
        return true;
}

static bool essiv_supported_algorithms(const char *essiv_cipher_name,
                                       struct shash_alg *hash_alg,
                                       int ivsize)
{
        struct crypto_alg *alg;
        bool ret = false;

        alg = crypto_alg_mod_lookup(essiv_cipher_name,
                                    CRYPTO_ALG_TYPE_CIPHER,
                                    CRYPTO_ALG_TYPE_MASK);
        if (IS_ERR(alg))
                return false;

        if (hash_alg->digestsize < alg->cra_cipher.cia_min_keysize ||
            hash_alg->digestsize > alg->cra_cipher.cia_max_keysize)
                goto out;

        if (ivsize != alg->cra_blocksize)
                goto out;

        if (crypto_shash_alg_needs_key(hash_alg))
                goto out;

        ret = true;

out:
        crypto_mod_put(alg);
        return ret;
}

static int essiv_create(struct crypto_template *tmpl, struct rtattr **tb)
{
        struct skcipher_alg_common *skcipher_alg = NULL;
        struct crypto_attr_type *algt;
        const char *inner_cipher_name;
        const char *shash_name;
        struct skcipher_instance *skcipher_inst = NULL;
        struct aead_instance *aead_inst = NULL;
        struct crypto_instance *inst;
        struct crypto_alg *base, *block_base;
        struct essiv_instance_ctx *ictx;
        struct aead_alg *aead_alg = NULL;
        struct crypto_alg *_hash_alg;
        struct shash_alg *hash_alg;
        int ivsize;
        u32 type;
        u32 mask;
        int err;

        algt = crypto_get_attr_type(tb);
        if (IS_ERR(algt))
                return PTR_ERR(algt);

        inner_cipher_name = crypto_attr_alg_name(tb[1]);
        if (IS_ERR(inner_cipher_name))
                return PTR_ERR(inner_cipher_name);

        shash_name = crypto_attr_alg_name(tb[2]);
        if (IS_ERR(shash_name))
                return PTR_ERR(shash_name);

        type = algt->type & algt->mask;
        mask = crypto_algt_inherited_mask(algt);

        switch (type) {
        case CRYPTO_ALG_TYPE_LSKCIPHER:
                skcipher_inst = kzalloc(sizeof(*skcipher_inst) +
                                        sizeof(*ictx), GFP_KERNEL);
                if (!skcipher_inst)
                        return -ENOMEM;
                inst = skcipher_crypto_instance(skcipher_inst);
                base = &skcipher_inst->alg.base;
                ictx = crypto_instance_ctx(inst);

                /* Symmetric cipher, e.g., "cbc(aes)" */
                err = crypto_grab_skcipher(&ictx->u.skcipher_spawn, inst,
                                           inner_cipher_name, 0, mask);
                if (err)
                        goto out_free_inst;
                skcipher_alg = crypto_spawn_skcipher_alg_common(
                        &ictx->u.skcipher_spawn);
                block_base = &skcipher_alg->base;
                ivsize = skcipher_alg->ivsize;
                break;

        case CRYPTO_ALG_TYPE_AEAD:
                aead_inst = kzalloc(sizeof(*aead_inst) +
                                    sizeof(*ictx), GFP_KERNEL);
                if (!aead_inst)
                        return -ENOMEM;
                inst = aead_crypto_instance(aead_inst);
                base = &aead_inst->alg.base;
                ictx = crypto_instance_ctx(inst);

                /* AEAD cipher, e.g., "authenc(hmac(sha256),cbc(aes))" */
                err = crypto_grab_aead(&ictx->u.aead_spawn, inst,
                                       inner_cipher_name, 0, mask);
                if (err)
                        goto out_free_inst;
                aead_alg = crypto_spawn_aead_alg(&ictx->u.aead_spawn);
                block_base = &aead_alg->base;
                if (!strstarts(block_base->cra_name, "authenc(")) {
                        pr_warn("Only authenc() type AEADs are supported by ESSIV\n");
                        err = -EINVAL;
                        goto out_drop_skcipher;
                }
                ivsize = aead_alg->ivsize;
                break;

        default:
                return -EINVAL;
        }

        if (!parse_cipher_name(ictx->essiv_cipher_name, block_base->cra_name)) {
                pr_warn("Failed to parse ESSIV cipher name from skcipher cra_name\n");
                err = -EINVAL;
                goto out_drop_skcipher;
        }

        /* Synchronous hash, e.g., "sha256" */
        _hash_alg = crypto_alg_mod_lookup(shash_name,
                                          CRYPTO_ALG_TYPE_SHASH,
                                          CRYPTO_ALG_TYPE_MASK | mask);
        if (IS_ERR(_hash_alg)) {
                err = PTR_ERR(_hash_alg);
                goto out_drop_skcipher;
        }
        hash_alg = __crypto_shash_alg(_hash_alg);

        /* Check the set of algorithms */
        if (!essiv_supported_algorithms(ictx->essiv_cipher_name, hash_alg,
                                        ivsize)) {
                pr_warn("Unsupported essiv instantiation: essiv(%s,%s)\n",
                        block_base->cra_name, hash_alg->base.cra_name);
                err = -EINVAL;
                goto out_free_hash;
        }

        /* record the driver name so we can instantiate this exact algo later */
        strscpy(ictx->shash_driver_name, hash_alg->base.cra_driver_name);

        /* Instance fields */

        err = -ENAMETOOLONG;
        if (snprintf(base->cra_name, CRYPTO_MAX_ALG_NAME,
                     "essiv(%s,%s)", block_base->cra_name,
                     hash_alg->base.cra_name) >= CRYPTO_MAX_ALG_NAME)
                goto out_free_hash;
        if (snprintf(base->cra_driver_name, CRYPTO_MAX_ALG_NAME,
                     "essiv(%s,%s)", block_base->cra_driver_name,
                     hash_alg->base.cra_driver_name) >= CRYPTO_MAX_ALG_NAME)
                goto out_free_hash;

        /*
         * hash_alg wasn't gotten via crypto_grab*(), so we need to inherit its
         * flags manually.
         */
        base->cra_flags        |= (hash_alg->base.cra_flags &
                                   CRYPTO_ALG_INHERITED_FLAGS);
        base->cra_blocksize     = block_base->cra_blocksize;
        base->cra_ctxsize       = sizeof(struct essiv_tfm_ctx);
        base->cra_alignmask     = block_base->cra_alignmask;
        base->cra_priority      = block_base->cra_priority;

        if (type == CRYPTO_ALG_TYPE_LSKCIPHER) {
                skcipher_inst->alg.setkey       = essiv_skcipher_setkey;
                skcipher_inst->alg.encrypt      = essiv_skcipher_encrypt;
                skcipher_inst->alg.decrypt      = essiv_skcipher_decrypt;
                skcipher_inst->alg.init         = essiv_skcipher_init_tfm;
                skcipher_inst->alg.exit         = essiv_skcipher_exit_tfm;

                skcipher_inst->alg.min_keysize  = skcipher_alg->min_keysize;
                skcipher_inst->alg.max_keysize  = skcipher_alg->max_keysize;
                skcipher_inst->alg.ivsize       = ivsize;
                skcipher_inst->alg.chunksize    = skcipher_alg->chunksize;

                skcipher_inst->free             = essiv_skcipher_free_instance;

                err = skcipher_register_instance(tmpl, skcipher_inst);
        } else {
                aead_inst->alg.setkey           = essiv_aead_setkey;
                aead_inst->alg.setauthsize      = essiv_aead_setauthsize;
                aead_inst->alg.encrypt          = essiv_aead_encrypt;
                aead_inst->alg.decrypt          = essiv_aead_decrypt;
                aead_inst->alg.init             = essiv_aead_init_tfm;
                aead_inst->alg.exit             = essiv_aead_exit_tfm;

                aead_inst->alg.ivsize           = ivsize;
                aead_inst->alg.maxauthsize      = crypto_aead_alg_maxauthsize(aead_alg);
                aead_inst->alg.chunksize        = crypto_aead_alg_chunksize(aead_alg);

                aead_inst->free                 = essiv_aead_free_instance;

                err = aead_register_instance(tmpl, aead_inst);
        }

        if (err)
                goto out_free_hash;

        crypto_mod_put(_hash_alg);
        return 0;

out_free_hash:
        crypto_mod_put(_hash_alg);
out_drop_skcipher:
        if (type == CRYPTO_ALG_TYPE_LSKCIPHER)
                crypto_drop_skcipher(&ictx->u.skcipher_spawn);
        else
                crypto_drop_aead(&ictx->u.aead_spawn);
out_free_inst:
        kfree(skcipher_inst);
        kfree(aead_inst);
        return err;
}

/* essiv(cipher_name, shash_name) */
static struct crypto_template essiv_tmpl = {
        .name   = "essiv",
        .create = essiv_create,
        .module = THIS_MODULE,
};

static int __init essiv_module_init(void)
{
        return crypto_register_template(&essiv_tmpl);
}

static void __exit essiv_module_exit(void)
{
        crypto_unregister_template(&essiv_tmpl);
}

module_init(essiv_module_init);
module_exit(essiv_module_exit);

MODULE_DESCRIPTION("ESSIV skcipher/aead wrapper for block encryption");
MODULE_LICENSE("GPL v2");
MODULE_ALIAS_CRYPTO("essiv");
MODULE_IMPORT_NS("CRYPTO_INTERNAL");
Linux
