// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * CBC: Cipher Block Chaining mode
 *
 * Copyright (c) 2006-2016 Herbert Xu <herbert@gondor.apana.org.au>
 */

#include <crypto/internal/skcipher.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/log2.h>
#include <linux/module.h>

static int crypto_cbc_encrypt_segment(struct crypto_lskcipher *tfm,
                                      const u8 *src, u8 *dst, unsigned nbytes,
                                      u8 *iv)
{
        unsigned int bsize = crypto_lskcipher_blocksize(tfm);

        for (; nbytes >= bsize; src += bsize, dst += bsize, nbytes -= bsize) {
                crypto_xor(iv, src, bsize);
                crypto_lskcipher_encrypt(tfm, iv, dst, bsize, NULL);
                memcpy(iv, dst, bsize);
        }

        return nbytes;
}

static int crypto_cbc_encrypt_inplace(struct crypto_lskcipher *tfm,
                                      u8 *src, unsigned nbytes, u8 *oiv)
{
        unsigned int bsize = crypto_lskcipher_blocksize(tfm);
        u8 *iv = oiv;

        if (nbytes < bsize)
                goto out;

        do {
                crypto_xor(src, iv, bsize);
                crypto_lskcipher_encrypt(tfm, src, src, bsize, NULL);
                iv = src;

                src += bsize;
        } while ((nbytes -= bsize) >= bsize);

        memcpy(oiv, iv, bsize);

out:
        return nbytes;
}

static int crypto_cbc_encrypt(struct crypto_lskcipher *tfm, const u8 *src,
                              u8 *dst, unsigned len, u8 *iv, u32 flags)
{
        struct crypto_lskcipher **ctx = crypto_lskcipher_ctx(tfm);
        bool final = flags & CRYPTO_LSKCIPHER_FLAG_FINAL;
        struct crypto_lskcipher *cipher = *ctx;
        int rem;

        if (src == dst)
                rem = crypto_cbc_encrypt_inplace(cipher, dst, len, iv);
        else
                rem = crypto_cbc_encrypt_segment(cipher, src, dst, len, iv);

        return rem && final ? -EINVAL : rem;
}

static int crypto_cbc_decrypt_segment(struct crypto_lskcipher *tfm,
                                      const u8 *src, u8 *dst, unsigned nbytes,
                                      u8 *oiv)
{
        unsigned int bsize = crypto_lskcipher_blocksize(tfm);
        const u8 *iv = oiv;

        if (nbytes < bsize)
                goto out;

        do {
                crypto_lskcipher_decrypt(tfm, src, dst, bsize, NULL);
                crypto_xor(dst, iv, bsize);
                iv = src;

                src += bsize;
                dst += bsize;
        } while ((nbytes -= bsize) >= bsize);

        memcpy(oiv, iv, bsize);

out:
        return nbytes;
}

static int crypto_cbc_decrypt_inplace(struct crypto_lskcipher *tfm,
                                      u8 *src, unsigned nbytes, u8 *iv)
{
        unsigned int bsize = crypto_lskcipher_blocksize(tfm);
        u8 last_iv[MAX_CIPHER_BLOCKSIZE];

        if (nbytes < bsize)
                goto out;

        /* Start of the last block. */
        src += nbytes - (nbytes & (bsize - 1)) - bsize;
        memcpy(last_iv, src, bsize);

        for (;;) {
                crypto_lskcipher_decrypt(tfm, src, src, bsize, NULL);
                if ((nbytes -= bsize) < bsize)
                        break;
                crypto_xor(src, src - bsize, bsize);
                src -= bsize;
        }

        crypto_xor(src, iv, bsize);
        memcpy(iv, last_iv, bsize);

out:
        return nbytes;
}

static int crypto_cbc_decrypt(struct crypto_lskcipher *tfm, const u8 *src,
                              u8 *dst, unsigned len, u8 *iv, u32 flags)
{
        struct crypto_lskcipher **ctx = crypto_lskcipher_ctx(tfm);
        bool final = flags & CRYPTO_LSKCIPHER_FLAG_FINAL;
        struct crypto_lskcipher *cipher = *ctx;
        int rem;

        if (src == dst)
                rem = crypto_cbc_decrypt_inplace(cipher, dst, len, iv);
        else
                rem = crypto_cbc_decrypt_segment(cipher, src, dst, len, iv);

        return rem && final ? -EINVAL : rem;
}

static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb)
{
        struct lskcipher_instance *inst;
        int err;

        inst = lskcipher_alloc_instance_simple(tmpl, tb);
        if (IS_ERR(inst))
                return PTR_ERR(inst);

        err = -EINVAL;
        if (!is_power_of_2(inst->alg.co.base.cra_blocksize))
                goto out_free_inst;

        if (inst->alg.co.statesize)
                goto out_free_inst;

        inst->alg.encrypt = crypto_cbc_encrypt;
        inst->alg.decrypt = crypto_cbc_decrypt;

        err = lskcipher_register_instance(tmpl, inst);
        if (err) {
out_free_inst:
                inst->free(inst);
        }

        return err;
}

static struct crypto_template crypto_cbc_tmpl = {
        .name = "cbc",
        .create = crypto_cbc_create,
        .module = THIS_MODULE,
};

static int __init crypto_cbc_module_init(void)
{
        return crypto_register_template(&crypto_cbc_tmpl);
}

static void __exit crypto_cbc_module_exit(void)
{
        crypto_unregister_template(&crypto_cbc_tmpl);
}

module_init(crypto_cbc_module_init);
module_exit(crypto_cbc_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("CBC block cipher mode of operation");
MODULE_ALIAS_CRYPTO("cbc");