cbc.c

// 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;

	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);
}

subsys_initcall(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");