crypto_cipher_kernel.c

// SPDX-License-Identifier: LGPL-2.1-or-later
/*
 * Linux kernel userspace API crypto backend implementation (skcipher)
 *
 * Copyright (C) 2012-2024 Red Hat, Inc. All rights reserved.
 * Copyright (C) 2012-2024 Milan Broz
 */

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include "crypto_backend_internal.h"

#ifdef ENABLE_AF_ALG

#include <linux/if_alg.h>

#ifndef AF_ALG
#define AF_ALG 38
#endif
#ifndef SOL_ALG
#define SOL_ALG 279
#endif

#ifndef ALG_SET_AEAD_AUTHSIZE
#define ALG_SET_AEAD_AUTHSIZE 5
#endif

/*
 * ciphers
 *
 * ENOENT - algorithm not available
 * ENOTSUP - AF_ALG family not available
 * (but cannot check specifically for skcipher API)
 */
static int _crypt_cipher_init(struct crypt_cipher_kernel *ctx,
			      const void *key, size_t key_length,
			      size_t tag_length, struct sockaddr_alg *sa)
{
	if (!ctx)
		return -EINVAL;

	ctx->opfd = -1;
	ctx->tfmfd = socket(AF_ALG, SOCK_SEQPACKET, 0);
	if (ctx->tfmfd < 0) {
		crypt_cipher_destroy_kernel(ctx);
		return -ENOTSUP;
	}

	if (bind(ctx->tfmfd, (struct sockaddr *)sa, sizeof(*sa)) < 0) {
		crypt_cipher_destroy_kernel(ctx);
		return -ENOENT;
	}

	if (setsockopt(ctx->tfmfd, SOL_ALG, ALG_SET_KEY, key, key_length) < 0) {
		crypt_cipher_destroy_kernel(ctx);
		return -EINVAL;
	}

	if (tag_length && setsockopt(ctx->tfmfd, SOL_ALG, ALG_SET_AEAD_AUTHSIZE, NULL, tag_length) < 0) {
		crypt_cipher_destroy_kernel(ctx);
		return -EINVAL;
	}

	ctx->opfd = accept(ctx->tfmfd, NULL, 0);
	if (ctx->opfd < 0) {
		crypt_cipher_destroy_kernel(ctx);
		return -EINVAL;
	}

	return 0;
}

int crypt_cipher_init_kernel(struct crypt_cipher_kernel *ctx, const char *name,
			     const char *mode, const void *key, size_t key_length)
{
	struct sockaddr_alg sa = {
		.salg_family = AF_ALG,
		.salg_type = "skcipher",
	};
	int r;

	if (!strcmp(name, "cipher_null"))
		key_length = 0;

	if (!strncmp(name, "capi:", 5))
		strncpy((char *)sa.salg_name, &name[5], sizeof(sa.salg_name) - 1);
	else {
		r = snprintf((char *)sa.salg_name, sizeof(sa.salg_name), "%s(%s)", mode, name);
		if (r < 0 || (size_t)r >= sizeof(sa.salg_name))
			return -EINVAL;
	}

	return _crypt_cipher_init(ctx, key, key_length, 0, &sa);
}

/* The in/out should be aligned to page boundary */
/* coverity[ -taint_source : arg-3 ] */
static int _crypt_cipher_crypt(struct crypt_cipher_kernel *ctx,
			       const char *in, size_t in_length,
			       char *out, size_t out_length,
			       const char *iv, size_t iv_length,
			       uint32_t direction)
{
	int r = 0;
	ssize_t len;
	struct af_alg_iv *alg_iv;
	struct cmsghdr *header;
	uint32_t *type;
	struct iovec iov = {
		.iov_base = (void*)(uintptr_t)in,
		.iov_len = in_length,
	};
	int iv_msg_size = iv ? CMSG_SPACE(sizeof(*alg_iv) + iv_length) : 0;
	char buffer[CMSG_SPACE(sizeof(*type)) + iv_msg_size];
	struct msghdr msg = {
		.msg_control = buffer,
		.msg_controllen = sizeof(buffer),
		.msg_iov = &iov,
		.msg_iovlen = 1,
	};

	if (!in || !out || !in_length)
		return -EINVAL;

	if ((!iv && iv_length) || (iv && !iv_length))
		return -EINVAL;

	memset(buffer, 0, sizeof(buffer));

	/* Set encrypt/decrypt operation */
	header = CMSG_FIRSTHDR(&msg);
	if (!header)
		return -EINVAL;

	header->cmsg_level = SOL_ALG;
	header->cmsg_type = ALG_SET_OP;
	header->cmsg_len = CMSG_LEN(sizeof(*type));
	type = (void*)CMSG_DATA(header);
	*type = direction;

	/* Set IV */
	if (iv) {
		header = CMSG_NXTHDR(&msg, header);
		if (!header)
			return -EINVAL;

		header->cmsg_level = SOL_ALG;
		header->cmsg_type = ALG_SET_IV;
		header->cmsg_len = iv_msg_size;
		alg_iv = (void*)CMSG_DATA(header);
		alg_iv->ivlen = iv_length;
		crypt_backend_memcpy(alg_iv->iv, iv, iv_length);
	}

	len = sendmsg(ctx->opfd, &msg, 0);
	if (len != (ssize_t)(in_length))
		r = -EIO;
	else {
		len = read(ctx->opfd, out, out_length);
		if (len != (ssize_t)out_length)
			r = -EIO;
	}

	crypt_backend_memzero(buffer, sizeof(buffer));
	return r;
}

int crypt_cipher_encrypt_kernel(struct crypt_cipher_kernel *ctx,
				const char *in, char *out, size_t length,
				const char *iv, size_t iv_length)
{
	return _crypt_cipher_crypt(ctx, in, length, out, length,
				   iv, iv_length, ALG_OP_ENCRYPT);
}

int crypt_cipher_decrypt_kernel(struct crypt_cipher_kernel *ctx,
				const char *in, char *out, size_t length,
				const char *iv, size_t iv_length)
{
	return _crypt_cipher_crypt(ctx, in, length, out, length,
				   iv, iv_length, ALG_OP_DECRYPT);
}

void crypt_cipher_destroy_kernel(struct crypt_cipher_kernel *ctx)
{
	if (ctx->tfmfd >= 0)
		close(ctx->tfmfd);
	if (ctx->opfd >= 0)
		close(ctx->opfd);

	ctx->tfmfd = -1;
	ctx->opfd = -1;
}

int crypt_cipher_check_kernel(const char *name, const char *mode,
			      const char *integrity, size_t key_length)
{
	struct crypt_cipher_kernel c;
	char mode_name[64], tmp_salg_name[180], *cipher_iv = NULL, *key;
	const char *salg_type, *real_mode;
	bool aead;
	int r;
	struct sockaddr_alg sa = {
		.salg_family = AF_ALG,
	};

	aead = integrity && strcmp(integrity, "none");
	real_mode = NULL;

	/* Remove IV if present */
	if (mode) {
		strncpy(mode_name, mode, sizeof(mode_name));
		mode_name[sizeof(mode_name) - 1] = 0;
		cipher_iv = strchr(mode_name, '-');
		if (cipher_iv) {
			*cipher_iv = '\0';
			real_mode = mode_name;
		}
	}

	salg_type = aead ? "aead" : "skcipher";
	r = snprintf((char *)sa.salg_type, sizeof(sa.salg_type), "%s", salg_type);
	if (r < 0 || (size_t)r >= sizeof(sa.salg_name))
		return -EINVAL;

	memset(tmp_salg_name, 0, sizeof(tmp_salg_name));

	/* FIXME: this is duplicating a part of devmapper backend */
	if (aead) {
		/* In AEAD, mode parameter can be just IV like "random" */
		if (!strcmp(integrity, "poly1305"))
			r = snprintf(tmp_salg_name, sizeof(tmp_salg_name), "rfc7539(%s,%s)", name, integrity);
		else if (!real_mode)
			r = snprintf(tmp_salg_name, sizeof(tmp_salg_name), "%s", name);
		else if (!strcmp(real_mode, "ccm"))
			r = snprintf(tmp_salg_name, sizeof(tmp_salg_name), "rfc4309(%s(%s))", real_mode, name);
		else
			r = snprintf(tmp_salg_name, sizeof(tmp_salg_name), "%s(%s)", real_mode, name);
	} else {
		if (!mode)
			r = snprintf(tmp_salg_name, sizeof(tmp_salg_name), "%s", name);
		else
			r = snprintf(tmp_salg_name, sizeof(tmp_salg_name), "%s(%s)", real_mode ?: mode_name, name);
	}

	if (r < 0 || (size_t)r >= sizeof(tmp_salg_name))
		return -EINVAL;

	memcpy(sa.salg_name, tmp_salg_name, sizeof(sa.salg_name));

	key = malloc(key_length);
	if (!key)
		return -ENOMEM;

	/* We cannot use RNG yet, any key works here, tweak the first part if it is split key (XTS). */
	memset(key, 0xab, key_length);
	*key = 0xef;

	r = _crypt_cipher_init(&c, key, key_length, 0, &sa);
	crypt_cipher_destroy_kernel(&c);
	free(key);

	return r;
}

int crypt_bitlk_decrypt_key_kernel(const void *key, size_t key_length,
				   const char *in, char *out, size_t length,
				   const char *iv, size_t iv_length,
				   const char *tag, size_t tag_length)
{
	struct crypt_cipher_kernel c;
	struct sockaddr_alg sa = {
		.salg_family = AF_ALG,
		.salg_type = "aead",
		.salg_name = "ccm(aes)",
	};
	int r;
	char buffer[128], ccm_iv[16];

	if (length + tag_length > sizeof(buffer))
		return -EINVAL;

	if (iv_length > sizeof(ccm_iv) - 2)
		return -EINVAL;

	r = _crypt_cipher_init(&c, key, key_length, tag_length, &sa);
	if (r < 0)
		return r;

	memcpy(buffer, in, length);
	memcpy(buffer + length, tag, tag_length);

	/* CCM IV - RFC3610 */
	memset(ccm_iv, 0, sizeof(ccm_iv));
	ccm_iv[0] = 15 - iv_length - 1;
	memcpy(ccm_iv + 1, iv, iv_length);
	memset(ccm_iv + 1 + iv_length, 0, ccm_iv[0] + 1);
	iv_length = sizeof(ccm_iv);

	r =  _crypt_cipher_crypt(&c, buffer, length + tag_length, out, length,
				 ccm_iv, iv_length, ALG_OP_DECRYPT);

	crypt_cipher_destroy_kernel(&c);
	crypt_backend_memzero(buffer, sizeof(buffer));

	return r;
}

#else /* ENABLE_AF_ALG */
#pragma GCC diagnostic ignored "-Wunused-parameter"

int crypt_cipher_init_kernel(struct crypt_cipher_kernel *ctx, const char *name,
			     const char *mode, const void *key, size_t key_length)
{
	return -ENOTSUP;
}

void crypt_cipher_destroy_kernel(struct crypt_cipher_kernel *ctx)
{
	return;
}

int crypt_cipher_encrypt_kernel(struct crypt_cipher_kernel *ctx,
				const char *in, char *out, size_t length,
				const char *iv, size_t iv_length)
{
	return -EINVAL;
}
int crypt_cipher_decrypt_kernel(struct crypt_cipher_kernel *ctx,
				const char *in, char *out, size_t length,
				const char *iv, size_t iv_length)
{
	return -EINVAL;
}
int crypt_cipher_check_kernel(const char *name, const char *mode,
			      const char *integrity, size_t key_length)
{
	/* Cannot check, expect success. */
	return 0;
}
int crypt_bitlk_decrypt_key_kernel(const void *key, size_t key_length,
				   const char *in, char *out, size_t length,
				   const char *iv, size_t iv_length,
				   const char *tag, size_t tag_length)
{
	return -ENOTSUP;
}
#endif