eseqiv.c

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/*
 * eseqiv: Encrypted Sequence Number IV Generator
 *
 * This generator generates an IV based on a sequence number by xoring it
 * with a salt and then encrypting it with the same key as used to encrypt
 * the plain text.  This algorithm requires that the block size be equal
 * to the IV size.  It is mainly useful for CBC.
 *
 * Copyright (c) 2007 Herbert Xu <[email protected]>
 *
 * 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.
 *
 */

#include <crypto/internal/skcipher.h>
#include <crypto/rng.h>
#include <crypto/scatterwalk.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/spinlock.h>
#include <linux/string.h>

struct eseqiv_request_ctx {
    struct scatterlist src[2];
    struct scatterlist dst[2];
    char tail[];
};

struct eseqiv_ctx {
    spinlock_t lock;
    unsigned int reqoff;
    char salt[];
};

static void eseqiv_complete2(struct skcipher_givcrypt_request *req)
{
    struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
    struct eseqiv_request_ctx *reqctx = skcipher_givcrypt_reqctx(req);

    memcpy(req->giv, PTR_ALIGN((u8 *)reqctx->tail,
             crypto_ablkcipher_alignmask(geniv) + 1),
           crypto_ablkcipher_ivsize(geniv));
}

static void eseqiv_complete(struct crypto_async_request *base, int err)
{
    struct skcipher_givcrypt_request *req = base->data;

    if (err)
        goto out;

    eseqiv_complete2(req);

out:
    skcipher_givcrypt_complete(req, err);
}

static int eseqiv_givencrypt(struct skcipher_givcrypt_request *req)
{
    struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
    struct eseqiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
    struct eseqiv_request_ctx *reqctx = skcipher_givcrypt_reqctx(req);
    struct ablkcipher_request *subreq;
    crypto_completion_t complete;
    void *data;
    struct scatterlist *osrc, *odst;
    struct scatterlist *dst;
    struct page *srcp;
    struct page *dstp;
    u8 *giv;
    u8 *vsrc;
    u8 *vdst;
    __be64 seq;
    unsigned int ivsize;
    unsigned int len;
    int err;

    subreq = (void *)(reqctx->tail + ctx->reqoff);
    ablkcipher_request_set_tfm(subreq, skcipher_geniv_cipher(geniv));

    giv = req->giv;
    complete = req->creq.base.complete;
    data = req->creq.base.data;

    osrc = req->creq.src;
    odst = req->creq.dst;
    srcp = sg_page(osrc);
    dstp = sg_page(odst);
    vsrc = PageHighMem(srcp) ? NULL : page_address(srcp) + osrc->offset;
    vdst = PageHighMem(dstp) ? NULL : page_address(dstp) + odst->offset;

    ivsize = crypto_ablkcipher_ivsize(geniv);

    if (vsrc != giv + ivsize && vdst != giv + ivsize) {
        giv = PTR_ALIGN((u8 *)reqctx->tail,
                crypto_ablkcipher_alignmask(geniv) + 1);
        complete = eseqiv_complete;
        data = req;
    }

    ablkcipher_request_set_callback(subreq, req->creq.base.flags, complete,
                    data);

    sg_init_table(reqctx->src, 2);
    sg_set_buf(reqctx->src, giv, ivsize);
    scatterwalk_crypto_chain(reqctx->src, osrc, vsrc == giv + ivsize, 2);

    dst = reqctx->src;
    if (osrc != odst) {
        sg_init_table(reqctx->dst, 2);
        sg_set_buf(reqctx->dst, giv, ivsize);
        scatterwalk_crypto_chain(reqctx->dst, odst, vdst == giv + ivsize, 2);

        dst = reqctx->dst;
    }

    ablkcipher_request_set_crypt(subreq, reqctx->src, dst,
                     req->creq.nbytes + ivsize,
                     req->creq.info);

    memcpy(req->creq.info, ctx->salt, ivsize);

    len = ivsize;
    if (ivsize > sizeof(u64)) {
        memset(req->giv, 0, ivsize - sizeof(u64));
        len = sizeof(u64);
    }
    seq = cpu_to_be64(req->seq);
    memcpy(req->giv + ivsize - len, &seq, len);

    err = crypto_ablkcipher_encrypt(subreq);
    if (err)
        goto out;

    if (giv != req->giv)
        eseqiv_complete2(req);

out:
    return err;
}

static int eseqiv_givencrypt_first(struct skcipher_givcrypt_request *req)
{
    struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
    struct eseqiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
    int err = 0;

    spin_lock_bh(&ctx->lock);
    if (crypto_ablkcipher_crt(geniv)->givencrypt != eseqiv_givencrypt_first)
        goto unlock;

    crypto_ablkcipher_crt(geniv)->givencrypt = eseqiv_givencrypt;
    err = crypto_rng_get_bytes(crypto_default_rng, ctx->salt,
                   crypto_ablkcipher_ivsize(geniv));

unlock:
    spin_unlock_bh(&ctx->lock);

    if (err)
        return err;

    return eseqiv_givencrypt(req);
}

static int eseqiv_init(struct crypto_tfm *tfm)
{
    struct crypto_ablkcipher *geniv = __crypto_ablkcipher_cast(tfm);
    struct eseqiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
    unsigned long alignmask;
    unsigned int reqsize;

    spin_lock_init(&ctx->lock);

    alignmask = crypto_tfm_ctx_alignment() - 1;
    reqsize = sizeof(struct eseqiv_request_ctx);

    if (alignmask & reqsize) {
        alignmask &= reqsize;
        alignmask--;
    }

    alignmask = ~alignmask;
    alignmask &= crypto_ablkcipher_alignmask(geniv);

    reqsize += alignmask;
    reqsize += crypto_ablkcipher_ivsize(geniv);
    reqsize = ALIGN(reqsize, crypto_tfm_ctx_alignment());

    ctx->reqoff = reqsize - sizeof(struct eseqiv_request_ctx);

    tfm->crt_ablkcipher.reqsize = reqsize +
                      sizeof(struct ablkcipher_request);

    return skcipher_geniv_init(tfm);
}

static struct crypto_template eseqiv_tmpl;

static struct crypto_instance *eseqiv_alloc(struct rtattr **tb)
{
    struct crypto_instance *inst;
    int err;

    err = crypto_get_default_rng();
    if (err)
        return ERR_PTR(err);

    inst = skcipher_geniv_alloc(&eseqiv_tmpl, tb, 0, 0);
    if (IS_ERR(inst))
        goto put_rng;

    err = -EINVAL;
    if (inst->alg.cra_ablkcipher.ivsize != inst->alg.cra_blocksize)
        goto free_inst;

    inst->alg.cra_ablkcipher.givencrypt = eseqiv_givencrypt_first;

    inst->alg.cra_init = eseqiv_init;
    inst->alg.cra_exit = skcipher_geniv_exit;

    inst->alg.cra_ctxsize = sizeof(struct eseqiv_ctx);
    inst->alg.cra_ctxsize += inst->alg.cra_ablkcipher.ivsize;

out:
    return inst;

free_inst:
    skcipher_geniv_free(inst);
    inst = ERR_PTR(err);
put_rng:
    crypto_put_default_rng();
    goto out;
}

static void eseqiv_free(struct crypto_instance *inst)
{
    skcipher_geniv_free(inst);
    crypto_put_default_rng();
}

static struct crypto_template eseqiv_tmpl = {
    .name = "eseqiv",
    .alloc = eseqiv_alloc,
    .free = eseqiv_free,
    .module = THIS_MODULE,
};

static int __init eseqiv_module_init(void)
{
    return crypto_register_template(&eseqiv_tmpl);
}

static void __exit eseqiv_module_exit(void)
{
    crypto_unregister_template(&eseqiv_tmpl);
}

module_init(eseqiv_module_init);
module_exit(eseqiv_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Encrypted Sequence Number IV Generator");