crypto.c

/**
 * eCryptfs: Linux filesystem encryption layer
 *
 * Copyright (C) 1997-2004 Erez Zadok
 * Copyright (C) 2001-2004 Stony Brook University
 * Copyright (C) 2004-2007 International Business Machines Corp.
 *   Author(s): Michael A. Halcrow <mahalcro@us.ibm.com>
 *   		Michael C. Thompson <mcthomps@us.ibm.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
 * 02111-1307, USA.
 */

#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/random.h>
#include <linux/compiler.h>
#include <linux/key.h>
#include <linux/namei.h>
#include <linux/crypto.h>
#include <linux/file.h>
#include <linux/scatterlist.h>
#include "ecryptfs_kernel.h"

static int
ecryptfs_decrypt_page_offset(struct ecryptfs_crypt_stat *crypt_stat,
			     struct page *dst_page, int dst_offset,
			     struct page *src_page, int src_offset, int size,
			     unsigned char *iv);
static int
ecryptfs_encrypt_page_offset(struct ecryptfs_crypt_stat *crypt_stat,
			     struct page *dst_page, int dst_offset,
			     struct page *src_page, int src_offset, int size,
			     unsigned char *iv);

/**
 * ecryptfs_to_hex
 * @dst: Buffer to take hex character representation of contents of
 *       src; must be at least of size (src_size * 2)
 * @src: Buffer to be converted to a hex string respresentation
 * @src_size: number of bytes to convert
 */
void ecryptfs_to_hex(char *dst, char *src, size_t src_size)
{
	int x;

	for (x = 0; x < src_size; x++)
		sprintf(&dst[x * 2], "%.2x", (unsigned char)src[x]);
}

/**
 * ecryptfs_from_hex
 * @dst: Buffer to take the bytes from src hex; must be at least of
 *       size (src_size / 2)
 * @src: Buffer to be converted from a hex string respresentation to raw value
 * @dst_size: size of dst buffer, or number of hex characters pairs to convert
 */
void ecryptfs_from_hex(char *dst, char *src, int dst_size)
{
	int x;
	char tmp[3] = { 0, };

	for (x = 0; x < dst_size; x++) {
		tmp[0] = src[x * 2];
		tmp[1] = src[x * 2 + 1];
		dst[x] = (unsigned char)simple_strtol(tmp, NULL, 16);
	}
}

/**
 * ecryptfs_calculate_md5 - calculates the md5 of @src
 * @dst: Pointer to 16 bytes of allocated memory
 * @crypt_stat: Pointer to crypt_stat struct for the current inode
 * @src: Data to be md5'd
 * @len: Length of @src
 *
 * Uses the allocated crypto context that crypt_stat references to
 * generate the MD5 sum of the contents of src.
 */
static int ecryptfs_calculate_md5(char *dst,
				  struct ecryptfs_crypt_stat *crypt_stat,
				  char *src, int len)
{
	struct scatterlist sg;
	struct hash_desc desc = {
		.tfm = crypt_stat->hash_tfm,
		.flags = CRYPTO_TFM_REQ_MAY_SLEEP
	};
	int rc = 0;

	mutex_lock(&crypt_stat->cs_hash_tfm_mutex);
	sg_init_one(&sg, (u8 *)src, len);
	if (!desc.tfm) {
		desc.tfm = crypto_alloc_hash(ECRYPTFS_DEFAULT_HASH, 0,
					     CRYPTO_ALG_ASYNC);
		if (IS_ERR(desc.tfm)) {
			rc = PTR_ERR(desc.tfm);
			ecryptfs_printk(KERN_ERR, "Error attempting to "
					"allocate crypto context; rc = [%d]\n",
					rc);
			goto out;
		}
		crypt_stat->hash_tfm = desc.tfm;
	}
	crypto_hash_init(&desc);
	crypto_hash_update(&desc, &sg, len);
	crypto_hash_final(&desc, dst);
	mutex_unlock(&crypt_stat->cs_hash_tfm_mutex);
out:
	return rc;
}

int ecryptfs_crypto_api_algify_cipher_name(char **algified_name,
					   char *cipher_name,
					   char *chaining_modifier)
{
	int cipher_name_len = strlen(cipher_name);
	int chaining_modifier_len = strlen(chaining_modifier);
	int algified_name_len;
	int rc;

	algified_name_len = (chaining_modifier_len + cipher_name_len + 3);
	(*algified_name) = kmalloc(algified_name_len, GFP_KERNEL);
	if (!(*algified_name)) {
		rc = -ENOMEM;
		goto out;
	}
	snprintf((*algified_name), algified_name_len, "%s(%s)",
		 chaining_modifier, cipher_name);
	rc = 0;
out:
	return rc;
}

/**
 * ecryptfs_derive_iv
 * @iv: destination for the derived iv vale
 * @crypt_stat: Pointer to crypt_stat struct for the current inode
 * @offset: Offset of the page whose's iv we are to derive
 *
 * Generate the initialization vector from the given root IV and page
 * offset.
 *
 * Returns zero on success; non-zero on error.
 */
static int ecryptfs_derive_iv(char *iv, struct ecryptfs_crypt_stat *crypt_stat,
			      pgoff_t offset)
{
	int rc = 0;
	char dst[MD5_DIGEST_SIZE];
	char src[ECRYPTFS_MAX_IV_BYTES + 16];

	if (unlikely(ecryptfs_verbosity > 0)) {
		ecryptfs_printk(KERN_DEBUG, "root iv:\n");
		ecryptfs_dump_hex(crypt_stat->root_iv, crypt_stat->iv_bytes);
	}
	/* TODO: It is probably secure to just cast the least
	 * significant bits of the root IV into an unsigned long and
	 * add the offset to that rather than go through all this
	 * hashing business. -Halcrow */
	memcpy(src, crypt_stat->root_iv, crypt_stat->iv_bytes);
	memset((src + crypt_stat->iv_bytes), 0, 16);
	snprintf((src + crypt_stat->iv_bytes), 16, "%ld", offset);
	if (unlikely(ecryptfs_verbosity > 0)) {
		ecryptfs_printk(KERN_DEBUG, "source:\n");
		ecryptfs_dump_hex(src, (crypt_stat->iv_bytes + 16));
	}
	rc = ecryptfs_calculate_md5(dst, crypt_stat, src,
				    (crypt_stat->iv_bytes + 16));
	if (rc) {
		ecryptfs_printk(KERN_WARNING, "Error attempting to compute "
				"MD5 while generating IV for a page\n");
		goto out;
	}
	memcpy(iv, dst, crypt_stat->iv_bytes);
	if (unlikely(ecryptfs_verbosity > 0)) {
		ecryptfs_printk(KERN_DEBUG, "derived iv:\n");
		ecryptfs_dump_hex(iv, crypt_stat->iv_bytes);
	}
out:
	return rc;
}

/**
 * ecryptfs_init_crypt_stat
 * @crypt_stat: Pointer to the crypt_stat struct to initialize.
 *