cryptoloop.c

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/*
   Linux loop encryption enabling module

   Copyright (C)  2002 Herbert Valerio Riedel <[email protected]>
   Copyright (C)  2003 Fruhwirth Clemens <[email protected]>

   This module 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 module 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 module; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/module.h>

#include <linux/init.h>
#include <linux/string.h>
#include <linux/crypto.h>
#include <linux/blkdev.h>
#include <linux/loop.h>
#include <linux/scatterlist.h>
#include <asm/uaccess.h>

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("loop blockdevice transferfunction adaptor / CryptoAPI");
MODULE_AUTHOR("Herbert Valerio Riedel <[email protected]>");

#define LOOP_IV_SECTOR_BITS 9
#define LOOP_IV_SECTOR_SIZE (1 << LOOP_IV_SECTOR_BITS)

static int
cryptoloop_init(struct loop_device *lo, const struct loop_info64 *info)
{
    int err = -EINVAL;
    int cipher_len;
    int mode_len;
    char cms[LO_NAME_SIZE];         /* cipher-mode string */
    char *cipher;
    char *mode;
    char *cmsp = cms;           /* c-m string pointer */
    struct crypto_blkcipher *tfm;

    /* encryption breaks for non sector aligned offsets */

    if (info->lo_offset % LOOP_IV_SECTOR_SIZE)
        goto out;

    strncpy(cms, info->lo_crypt_name, LO_NAME_SIZE);
    cms[LO_NAME_SIZE - 1] = 0;

    cipher = cmsp;
    cipher_len = strcspn(cmsp, "-");

    mode = cmsp + cipher_len;
    mode_len = 0;
    if (*mode) {
        mode++;
        mode_len = strcspn(mode, "-");
    }

    if (!mode_len) {
        mode = "cbc";
        mode_len = 3;
    }

    if (cipher_len + mode_len + 3 > LO_NAME_SIZE)
        return -EINVAL;

    memmove(cms, mode, mode_len);
    cmsp = cms + mode_len;
    *cmsp++ = '(';
    memcpy(cmsp, info->lo_crypt_name, cipher_len);
    cmsp += cipher_len;
    *cmsp++ = ')';
    *cmsp = 0;

    tfm = crypto_alloc_blkcipher(cms, 0, CRYPTO_ALG_ASYNC);
    if (IS_ERR(tfm))
        return PTR_ERR(tfm);

    err = crypto_blkcipher_setkey(tfm, info->lo_encrypt_key,
                      info->lo_encrypt_key_size);
    
    if (err != 0)
        goto out_free_tfm;

    lo->key_data = tfm;
    return 0;

 out_free_tfm:
    crypto_free_blkcipher(tfm);

 out:
    return err;
}


typedef int (*encdec_cbc_t)(struct blkcipher_desc *desc,
            struct scatterlist *sg_out,
            struct scatterlist *sg_in,
            unsigned int nsg);

static int
cryptoloop_transfer(struct loop_device *lo, int cmd,
            struct page *raw_page, unsigned raw_off,
            struct page *loop_page, unsigned loop_off,
            int size, sector_t IV)
{
    struct crypto_blkcipher *tfm = lo->key_data;
    struct blkcipher_desc desc = {
        .tfm = tfm,
        .flags = CRYPTO_TFM_REQ_MAY_SLEEP,
    };
    struct scatterlist sg_out;
    struct scatterlist sg_in;

    encdec_cbc_t encdecfunc;
    struct page *in_page, *out_page;
    unsigned in_offs, out_offs;
    int err;

    sg_init_table(&sg_out, 1);
    sg_init_table(&sg_in, 1);

    if (cmd == READ) {
        in_page = raw_page;
        in_offs = raw_off;
        out_page = loop_page;
        out_offs = loop_off;
        encdecfunc = crypto_blkcipher_crt(tfm)->decrypt;
    } else {
        in_page = loop_page;
        in_offs = loop_off;
        out_page = raw_page;
        out_offs = raw_off;
        encdecfunc = crypto_blkcipher_crt(tfm)->encrypt;
    }

    while (size > 0) {
        const int sz = min(size, LOOP_IV_SECTOR_SIZE);
        u32 iv[4] = { 0, };
        iv[0] = cpu_to_le32(IV & 0xffffffff);

        sg_set_page(&sg_in, in_page, sz, in_offs);
        sg_set_page(&sg_out, out_page, sz, out_offs);

        desc.info = iv;
        err = encdecfunc(&desc, &sg_out, &sg_in, sz);
        if (err)
            return err;

        IV++;
        size -= sz;
        in_offs += sz;
        out_offs += sz;
    }

    return 0;
}

static int
cryptoloop_ioctl(struct loop_device *lo, int cmd, unsigned long arg)
{
    return -EINVAL;
}

static int
cryptoloop_release(struct loop_device *lo)
{
    struct crypto_blkcipher *tfm = lo->key_data;
    if (tfm != NULL) {
        crypto_free_blkcipher(tfm);
        lo->key_data = NULL;
        return 0;
    }
    printk(KERN_ERR "cryptoloop_release(): tfm == NULL?\n");
    return -EINVAL;
}

static struct loop_func_table cryptoloop_funcs = {
    .number = LO_CRYPT_CRYPTOAPI,
    .init = cryptoloop_init,
    .ioctl = cryptoloop_ioctl,
    .transfer = cryptoloop_transfer,
    .release = cryptoloop_release,
    .owner = THIS_MODULE
};

static int __init
init_cryptoloop(void)
{
    int rc = loop_register_transfer(&cryptoloop_funcs);

    if (rc)
        printk(KERN_ERR "cryptoloop: loop_register_transfer failed\n");
    return rc;
}

static void __exit
cleanup_cryptoloop(void)
{
    if (loop_unregister_transfer(LO_CRYPT_CRYPTOAPI))
        printk(KERN_ERR
            "cryptoloop: loop_unregister_transfer failed\n");
}

module_init(init_cryptoloop);
module_exit(cleanup_cryptoloop);